SBD Dauntless

Before I start a new model, I collect its photos — as many as I can find, everywhere: in the books, magazines, on the Internet. Some of these photos are high-quality, detailed photos of restored airplanes. One of them is this a high-resolution photo from the web page of Chino Planes of Fame Air Museum:

This is a special photo: it was made from a long distance using a “telescope” lens, which minimized the perspective barrel distortion. The airplane on this picture lowered its right wing, so its bottom parts are slightly shifted downward, but except this area it is a perfect reference!

I placed this photo in Inkscape (a free, Open Source image editor), and set it horizontally (along the canopy frames). Then I mirrored it, for the comparison with the left side view:

In Dauntless there are two long parallel lines that were perpendicular to the fuselage centerline: the trailing edge of the wing center section, and elevator leading edge. On this photo they are also parallel (more or less). This is the proof that we can neglect the perspective (barrel) distortion.
Now let’s compare the BuAer drawing (see the post above) with the reference photo:

In the first post I mentioned that this BuAer side view is too short. To make a fair comparison, I marked on this drawing the proper fuselage length (as on the BuAer top view). As you can see, the drawing matches the reference photo quite well!

It fits the photo even better when you correct the tail contour (so it matches the fuselage length in the BuAer top view):

It seems that the BuAer drawing from 1944 matches the contour of the real aircraft quite well. In fact, it is much better than the contours of the detailed KAGERO drawings from 2007 (see previous post), which most probably are based on the drawings made by previous authors:

I think that these KAGERO plans “accumulated” many decades of various errors. Do not be surprised: before the 1990 it was practically impossible to make such a “photo verification” like this one. Even today authors are used to redrawing earlier plans. They seldom compare their work with the real photos in the manner shown above.

Concluding: there is no good reference among the existing Dauntless drawings: the BuAer lacks details, while the KAGERO plans contain too many deviations. The plans from other authors have similar errors (I will not elaborate about it here).

It seems that I have to crate my own drawings!

In the next post I will refer the progress of this work (I hope that I will show you the corrected side view).

As I wrote a week ago, I am working on a better drawing of the SBD-5. It is based on more than 1000 various photos. Below you can see the first version of the side view:

(click here to see the high-resolution version)

This is not an ultimate drawing: I suppose that it will be updated during my work, following the new findings about the airframe shape and/or details. The dotted lines mark the rivet seams, but size and spacing of these dots does not match the real rivets. I prepare these plans to build a model: that’s why I removed the outer wing section and horizontal tailplane. For these parts the most important drawing is the top view. To build them, on the side view I need the precise contours of their key sections (i.e. their airfoils as well as the incidence angles and spar locations). I draw three profiles: first of the wing root, then the root of the outer wing section, and then the wing tip. Two different sources specifies different wing tip profiles: NACA-2409 (Performance Test Report, 1942) or NACA-2407 (BuAer drawing, 1944). However, the bottom contour of the NACA-2407 seems to be a little concave. Because I did not observe such an effect on the photos, I decided to use the thicker airfoil of NACA-2409. I still have to verify this detail when I build the wing. The airfoils of the tailplane were specified nowhere. I copied its root airfoil from a photo.

While drawing the side view you still have to think “in 3D”. That’s why you can see around this silhouette some auxiliary sketches: the front view of the engine cowling, and the contours of the center wing section. I draw the latter element just to mark the exact position of the first rib of the wing. It was hidden inside the fuselage. Note that this airfoil was a specific modification of the NACA-2415 shape: the part of the wing that houses the main landing gear was reshaped. In the effect, the leading edge of the center wing section has a small downward inclination.

On the next week I will present side views of two earlier Dauntless versions: the SBD-2 and SBD-3. I will discuss where are the differences in the length of the SBD-5 and SBD-3, 4, as well as the mystery of the “missing 7 inches” of the SBD-2.

Within two weeks I will present the corrected/verified top view.

In this post I will show you how do I create Dauntless side views. First I used the “semi-orthogonal” photo of the SBD-5 as the reference to draw the side view of this version. This is the most important picture, because it provides reliable “general reference”:

Then I used many other photos and sketched fragments of the other views to complete the side view details (note the multiple guide lines on these pictures):

Note the large B/W photo that I used to verify the shape of the propeller hub and engine cowling. I could not compare it with other areas — the cockpit canopy, for example — because its perspective (barrel) distortion was too intense.
However, when the barrel distortion is moderate, we can revert it! See for example this side photo of another Dauntless version: the SBD-3:

First I identified the undeformed fragment of the fuselage (in this case — around the firewall and the windscreen) then fitted this part of the photo into the drawing. Then, comparing the lengths of this photo and the side view, I concluded that it has a moderate barrel distortion. From the history of this design I know that the SBD-3 and SBD-5 had different engine cowlings. The other parts of their airframes had the same shape. This means that I could use the existing SBD-5 drawing from the firewall to the fin as the reference for the unwrapping process of this SBD-3. Then I unwrapped this photo using the GIMP. (Speaking more precisely – its “Lens Distortion” image filter. You can find all the details of this process in this book).

Note that this operation “flattens” only the airplane contour that lies on the symmetry plane of the fuselage. All protruding elements, like wing and horizontal tailplane remain deformed. But it’s OK, I need this just this contour. While drawing, I will compensate the small remaining deformation of the bulkhead lines. (For example, the leading edge of the NACA cowling from this photo should be a straight line, but it is a very flat ellipse).

Of course, it is always better to prepare more than one of such “flattened” pictures, to minimize inevitable errors:

NOTE: these two SBD-3 photos depict training aircraft, without the telescope gunsight. Such a gunsight was protruding through the windscreen in the combat airplanes.

On both SBD-3 photos you can see that the engine cowling is somewhat shorter than in the SBD-5. In fact, in the specifications you can find that these versions had different overall length:

• SBD-5: 33’  ¹/₈”;
• SBD-3: 32’ 8 ” (in some sources I also saw 32’ 8 ⁴/₅”)

However, on the scale plans authors attribute this difference to the longer propeller hub of the SBD-5 (It used different propeller: Hamilton standard hydromatic). Others did not bother about the different lengths of the SBD variants, and draw the profiles of all Dauntless versions alike.

Following the findings on the unwrapped photos I analyzed many other archival pictures. Below you can see the conclusion:

It seems that in the SBD-5 the engine, together with the NACA cowling, was moved slightly forward. All other bulkheads remain in the same places. This modification shifted forward the center of gravity. I suppose that this correction improved some handling characteristics that changed after the doubling of the rear guns. (The second gun in the rear was introduced in 1942 to the SBD-3 as the “field” modification. It shifted the cg backward).

In my next post I will finish the side view matter, delivering you the complete side views of the SBD-3, SBD-2 and SBD-1 variants. I will also write about other non-existent length difference, which you can find in the books about the SBD Dauntless.

In addition to the side view of the SBD-5 presented in one of my previous posts, I have prepared side views of the earlier Dauntless versions: SBD-2 and SBD-3:

(Here are the links to the high-resolution profile images of: SBD-2, SBD-3).

When you look into Dauntless specifications, you will find that all its models have the same span, but they often differ from each other in the length. This is a typical case, because the wing geometry determines the aircraft behavior. Thus, once “debugged” in the prototype (the stall characteristics etc.) it remains unaltered between subsequent versions. The fuselage shape is not so important, so it is often modified. In the effect, the length of the airplane often vary between subsequent versions.

In the previous post I described how the photos confirmed the different length of the SBD-5 (33’ ¹/₈”) and the SBD-3 (32’ 8”), listed in their specifications. The reason was the different engine mount, modified in the SBD-5. The same sources specify the length of the SBD-2 as 32’ 2”. This is something strange, because I cannot find any evidence of this significant, 6 inch difference between SBD-3 and SBD-2 on the photos!

The SBD-3 was a “quick and dirty” adaptation of the SBD-2 to the recognized requirements of the modern war. Douglas added armor plates to the pilot and gunner seats, self-sealing fuel tanks (reducing their capacity), doubled the rear guns. All the key elements of the design: the airframe and the engine, remained the same. Where is there the modification that changed the overall of length of the SBD-3 by 6”!?

I started to look for the sources of this information (the subsequent publications copy their specification data from the earlier ones, up to an ultimate source document). Ultimately it seems that it comes from the BuAer Performance Data Reports. There are two of such documents, created in 1942: one for the SBD-2 and one for the SBD-3. On their last pages you can find the measured airplane dimensions. The difference is there: LENGTH, LEVEL: 32’-8” in the SBD-3 report, and LENGTH, LEVEL: 32’-2” in the SBD-2 report. (Unfortunately, they did not specified the length on wheels for the SBD-2, so there is no double-check). Note that all other dimensions are the same. I speculated that the reason of these differences lies in the propeller spinner: it was often removed. If the tested SBD-3 had this spinner, and the SBD-2 didn’t — what was the eventual difference? I tried to check this option, but it shortens the fuselage length by less than 4”.

What’s more interesting: the only survived SBD-2 is owned by the National Navy Aviation Museum in Pensacola. On their web page the owner specifies the length of this airplane as 32’ 8” — the same as the SBD-3! Thinking further about it, I noticed the manual corrections of typing errors in other SBD performance data reports. So I have following hypothesis:

-          The SBD-2 and SBD-3 had the same length: 32’ 8”, as specified by the owner of the restored SBD-2 (NAM in Pensacola);

-          The typist of the BuAer Performance Data Report made a mistake (most probably —deciphering the handwritten measure results he/she read “2” instead “8”). The authors of the first publications about SBD Dauntless used this source, and the others used their publications. So the initial error was multiplied;

Thus I assumed that the SBD-2 length specified in Performance Data report is wrong. Basically it was the same as the SBD-3. It also applies to the SBD-1:

(Here is the link to high resolution profile image of the SBD-1). The only external difference between the SBD-1 and SBD-2 is the larger air scoop on the top of the engine cowling.

Conclusion from this little investigation (in fact, it took me a few days): do not trust blindly the specified width and wing span of a historical airplane! When you compare the different sources you will find that sometimes these figures are different. Always try to verify available data. The wing span is less error-prone because it usually does not vary between subsequent versions. Remember that the photos are always the ultimate evidence.

In the next post I will present the updated/verified Dauntless top view.

This Monday I finally got the “Instructions for the Erection and Maintenance of the Model SBD-6 Airplane” book – more than 600 pages about the Dauntless, published by Douglas in March 1944. Because of the lengthy title, I will refer to this book as the “SBD Maintenance Manual” or the “Douglas manual”. In spite that it describes the last produced version, it is also usable for the earlier models: as I mentioned in one of the previous posts, the SBD-1 airframe behind the firewall differs only in a few details (the double gun mount, gunsight type, lack of the YAGI antennas) from the SBD-6.

Inside you can find the SBD-6 general arrangement drawings, as well as the stations diagram:

Here are the links to the high-resolution versions: side view (cropped from the page), top and front view, stations diagram. As you can see these Douglas diagrams contain more dimensions than the BuAer drawings. Their chains on the side view allows for verification of the wing location, as well as the wing and tailplane incidence angles. They also allow you to determine the basic “trapeze” around the rudder and the fin. From the front view you can also read the dihedral angle of the outer wing panels (9⁰ 19’).

The dimensions from the top view allowed me to draw the basic trapezes around the wing and tailplane, as well as to determine locations of the aileron and elevator hinge axes. This information, combined with dimensions from the side view, allows for determining the precise location of the firewall, wings and empennage. I used them to verify my scale plans. Sometimes they just confirmed what I determined before (for example — locations of the wing or the last bulkhead). Sometimes they revealed the errors I made. I will write more about it in the next post. So here is the current, updated version of my drawing:

Because of the formatting issues I had to split this image into two parts:

(Click here to get these drawings as a single, high-resolution image). Note that I draw the outer wing panel without its dihedral (it is much easier to build its model using such a “flat” reference). Thus when you check proportions of this top view, its span/length ratio is somewhat greater than the expected value of 41’ 6” / 33’. What is interesting, the dimensions on the general arrangement drawing indicate that the “official” wing span does not include the size of the running lights:

To obtain the “physical” wing span value you have to add 1.5” to each wing. I used similar convention when I matched the fuselage contour against its dimension (33’ ¹/₈”). These dimension lines are more obscured on the side view, but for the matching purposes I skipped the length of the running light cover protruding from the tip of the tail (1”).

In general, after all these updates I feel more confidence in my drawings.  I know which elements come from the explicit dimensions of the general arrangement diagram, which from the photos, and which are based on other drawings or just on an assumption. The only larger element that I was not able to verify is the fuselage width (i.e. its contour in the top view). It is copied from the Douglas drawing. I was able just to verify it at the 9^th bulkhead (station 140). I have a photo of this bulkhead from one of the Dauntless restorations, so I am sure that it fits properly into the fuselage contour on both views: the side view and the top view. However, I did not verify in any way the curved contour of the tail on the top view.

Frankly speaking, after this experience I am really glad that I am doing such a “slow start” to the modeling by preparing these drawings. It forced me to think twice (or even more times than twice) about every part of this airplane, resulting in better understanding of various nuances of its geometry. Sometimes I had to deliberate over a single line (like the gap between the elevator and stabilizer) for a whole day, watching and comparing hundreds of photos. In the effect I had to move a few lines around it on the plans. It was not a big deal. However, if I already started to build the model, adaptation of such findings would require a lot of work!

In the next post I will tell you more on how I used the explicit dimensions from the Douglas drawings. They allowed me to find some flaws in my plans. Description of this case will give you an insight into the errors that you can make using the photos.

In my previous post you can find the updated scale plans of the SBD-5 Dauntless, consisting the side and top views. The ultimate shape of depicted airplane resulted from matching my initial drawings against the Douglas general arrangement diagram. I couldn’t do it before, because this diagram comes from the Dauntless maintenance manual, which I received in previous week.

In this post I will show you how I do such a matching using the diagram shown below:

When you use such a drawing, you can follow the general rules of the technical drawings. In particular:

• The ultimate contour of the depicted object is on the outer side of the drawing lines;
• When the shape on the drawing differs from the result of its explicit dimensions, the result of these dimensions prevails

So, starting from the thrust line (i.e. the propeller axis) and from the firewall (the base of all dimensions), we can use the dimensions from this diagram to determine the wing chord position (points A and B in the picture below):

We can read from the side view dimensions that A (the rib tip) is located 20.38” from the thrust line and 9” from the firewall. The end of this rib is located 2.5⁰ lower, and the chord length of this rib is 115.12” (this dimension you can read from the top view). This determines location of point B.

I used the scale of my drawing (3.02 px/in) to convert the dimensions listed above into drawing units. Then I used guide lines to find these points of the wing chord on my plans:

Fortunately points A, B on my plans occurred very close to wing leading and trailing edges.

You can use dimensions from the general arrangement drawings to sketch the basic trapeze around the wing (in the top view) as well as around the fin, rudder, and horizontal tailplane. These trapezes allow you to determine the basic shape and proportions of the airplane. I will show this method on the example of the fin and the rudder. Figure above shows their dimensions on the original drawing:

Using these dimensions you can draw the basic trapezoid around the rudder and fin. You can also locate the chord of the horizontal tailplane as we did for the wing.

When I mapped these elements onto my plans, they revealed a serious flaw in my drawings:

The whole tailplane seems to be shifted downward, and the rudder hinge is moved left! However, if the wing chord fits to the dimensions, then most probably this is the result of a random rotation. I have quickly verified this hypothesis using the reference photo:

When I set the pivot point of this transformation above the wing (see picture below), it was enough to rotate this photo by 0.27⁰ to fit the rudder and fin into given contour:

It seems that I made mistake at the very beginning, trying to set this photo horizontally (in the second post of this thread). I estimated it using cockpit edge (see previous picture), because the better candidate for such a reference — the seam running on the side view along the reference line — is not visible on this picture. It seems that this fragment was too short for precise estimation of the horizontal direction. What’s more, I did not know at the beginning that in the top view this edge is not parallel to the fuselage centerline. Because the depicted airplane is slightly inclined toward the photo, I had to estimate location of this edge as the line lying between two cockpit edges visible on this picture. The BuAer drawing (copied from the Douglas general Arrangement Diagram) would help, if its draftsman did not made additional errors around the tail and empennage (see the second post).

Of course, the drawings that I published in the previous post did not contain any of the flaws that I have found here. I fixed all of them before. I just wanted to show you in this post what kind of errors you can do using a photo reference.

Conclusion: always try to find a general arrangement diagram of the airplane and use its explicit dimensions to verify your drawings. They often allow you to fix severe flaws in the geometry of the depicted aircraft!

Holy cow! I cannot wait to see this come together.

Chris

Thank you, Compressorman! Within two weeks I should start modeling.

However, before I do this, I will shortly describe how did I create the top view. Drawing such vertical views (from the top or bottom) of the SBD Dauntless is more difficult than the side views, because there are no “vertical” photos which you can use to verify and enhance the available plans. The methods presented below can be useful when you want to draw or verify blueprints of an aircraft.

Anyway, I started using everything I could, for example some photos from the restoration done by the Pacific Aviation Museum:

The photo on the picture above has a strong barrel distortion. We cannot effectively “revert” it as we did for the side view. Why? Because the photo of the side view all contours of the aircraft lie on a single plane (the symmetry plane). This one contains are at least three important planes: the edges of the cockpit, the center of the fuselage (along its maximum width) and the wing contour. Each of them is located at a different distance from the camera, and each requires different distortion (fixing one of them you would spoil the others).

Nevertheless, taking all of this into account, this high-resolution photo is still useful to determine the rivets pattern of the center wing section, as well as the width of the cockpit frame. The edge of the Dauntless cockpit is formed by an important longeron: it determines the fuselage shape in this area. To precisely estimate the width of the cockpit canopies I draw auxiliary contours of their cross sections (you can see them on the picture above as the blue lines). Positions of the bulkheads are copied from the side view. On this top view I roughly approximated positons of the longerons below the cockpit edge. This is just a “workshop drawing”, not a regular scale plan: I will form the fuselage following its contour on the side view and a few key cross sections which I will draw later. Because of the barrel distortion of the reference photo I was not able to check the contour of the fuselage in the top view. This is the only element I had to redraw without any verification from the Douglas general arrangement drawing.

In next step I used dimensions from the Douglas diagram to draw the trapezes of the outer wing panels and horizontal tailplane:

Picture above shows all the lines which you can deduce from the general dimensions provided by the manufacturer. We can further enrich it using the information from the stations diagram:

The station diagram provides precise position of all wing ribs. Most of them are just a row of rivets, but along some of them you can find the panel seams.

All right, but this wing drawing is still missing its “vertical” elements: rivet and panel seams along the spars and stringers. How to determine their locations?

I had to review all the collected photos. Ultimately I chose one of the pictures from the  web page of Chino Planes of Fame Air Museum:

I rotated this photo, aligning the wings of this airplane to the vertical guides. As you can see, it is made with a telescopic camera, so that it is very close to a perfectly orthographic projection. (The guides of the tailplane are not ideally parallel to corresponding guides on the wings, but this difference is minimal). The left wing is depicted at a relatively high angle, so you can see clearly the rivet seams along the spars and stringers. I decided that I can use this picture to map these lines onto my drawing.

I flipped this image from right to left, and stretched it, fitting its wing into the basic trapeze:

It allowed me to recreate the wingtip curve. In such a highly-deformed image the rib lines are bent. They match their “true” positions only on the wing edges. However, we can easily map from this image the spar and stringer lines. All of them continue from the center wing section. Combined with the ribs these lines form a kind of the “reference grid”, which cells allowed me to draw all the remaining details: the circular holes in the flaps, fixed slats openings, etc.

I used similar method to map the tip of the horizontal tailplane as well as its two spars. In the effect I obtained a detailed top view of the SBD Dauntless.

In the next post I will publish the bottom view.

Dzień dobry, Witold, lots of good info here!

By the way, are you planning to build a Dauntless from scratch? What scale?

Thanks for sharing, good luck with your project and have a nice day

Paweł

Witam !

Yes, I will build this model - at this moment I am just preparing the "workshop blueprints" I need to do it. If you are asking about its scale: Well, I practice a new branch of scale modeling which emerged during the previous decade: see my models. In the models built this way you can properly recreate all the details you can see on the reference photos - the only limit is your patience and experience in interpretation of such "raw information". I plan to recreate not only the exterior, but also the interior of the SBD Dauntless: all the ribs, cables, details behind the engine, hydraulic actuators. All control surfaces, flaps, and landing gear will be animated (so you will be able to open and close the flaps, or retract the landing gear). Thus, if you wish, you can assume that this model will be in "1:1 scale", but of course it is just a perfectly scalable thing, like a vector drawing.

I expect that this model will take me a year.  I will share it on a CC license, like my other models. (If you would like to learn more about this new branch of scale modeling - see this book).

During previous weeks I was working on the bottom view and other details of the SBD Dauntless. For example — I added a modified side view that reveals the engine and the cowling hidden under the NACA ring:

Because of the formatting issues of this post I had to split the original square drawing into two parts:

(Click here to get these drawings as a single, high-resolution image). As in the case of the top view I draw the outer wing panel without its dihedral.

Detailing of the bottom view resulted in minor updates of the side view:

(See its high-resolution version).

I have already started working on the front view. One of the elements I need for the model are the key cross sections, thus I identified their shapes, and incorporated them into this drawing:

I did not draw the first sections of the NACA cowling here, because they will be visible on the front view. As you can see there are large gaps between sections 2 and 3 and between 8 and 9. Why I did not add these intermediate contours? Because nothing special “happens” between these bulkheads: the resulting shape will be automatically interpolated during modeling.

I sketched the engine and the inner cowling, because I am going to model these parts. Analyzing this area I discovered many differences between the earlier versions (SBD-2, -3, -4) and the later versions (SBD-5, -6) than were not mentioned in any previous publications about the SBD:

• Different cross section B (in the SBD-1…SBD-4 it had wider, elliptic shape);
• Different widths of the oil radiator scoop;
• Yet another carburetor air scoop: you can find in the books that in the SBD-5 it was removed from the NACA cowling and replaced by two intakes located between upper cylinders of the radial engine. However, they did not mention that they were just additional intakes for the filtered air (for the takeoff/landing from provisional ground airstrips). The main air scoop was still at the top of the fuselage, but since SBD-5 it was hidden behind the NACA cowling!

In the next post I will elaborate about these unpublished differences between the SBD versions, showing them on drawings. I will also prepare a simplified front view (for my model I do not need to redraw all the minor details there).

The drawings of this aircraft will be complete soon. I think that I will start building the first part of the model within two weeks.

To recapitulate my work on the Dauntless plans, I decided to draw all the external differences between its subsequent Navy versions. Because of the numerous changes that occurred in the SBD-5, I decided to split this description into two posts. This is the part one describing changes from the SBD-1 to the SBD-4. The part two (about the SBD-5 and the SBD-6) will be ready in the next week.

NOTE: All airplanes on the drawings below are equipped with the small tailwheel with solid rubber tire for the carrier operations. However, for ground airfields Douglas provided alternate, pneumatic, two times larger wheel. These tail wheels could be easily replaced in workshops.

Starting from the beginning: here is the SBD-1, the first of the Douglas Dauntless series:

(See the high-resolution SBD-1 left & top view).

US Navy originally ordered 144 SBD-1s in March 1939. The first of these aircraft took off from Douglas airfield in May 1939. However, the Navy was not satisfied with their relatively short combat radius. Probably the outbreak of the war in Europe (September 1939) forced the Navy to accept first 57 SBD-1s “as they were”, assigning them to the Marines squadrons. For the 87 remaining airplanes from the original contract, the Navy requested longer range. To improve Dauntless combat radius, Douglas installed additional fuel tanks in the external wing panels. They also equipped these airplanes with the Sperry autopilots. This new variant was named SBD-2. It was delivered in 1940 to carrier squadrons of the US Navy. Externally, the SBD-2 had lower carburetor air scoop than the SBD-1:

(See the high-resolution SBD-2 left & top view).

The next Dauntless version — the SBD-3 — was originally ordered in 1940 by French Aeronavale. SBD-3 was updated for the identified requirements of contemporary battlefield. It had armor plates protecting pilot and gunner seats, armor glass plate inside the windshield (I did not draw this and other cockpit internal details). Douglas installed also the self-sealing fuel tanks. After June 1940 all 174 ordered aircraft were taken over by the US Navy, which then ordered additional 411 airplanes. The Navy workshops doubled in these machines their rear guns. This modification was adopted by Douglas in the later series of this aircraft. Externally — the boxes containing flotation gear (“balloons”) were removed from the engine compartment:

(See the high-resolution SBD-3 left & top view).

The side slots of the SBD-3 cowling were slightly larger than those in the SBD-1 and SBD-2:

The next version — SBD-4 — received new, 24V electric installation, which allowed for installment of the radar and broader range of other electronic equipment. However, in the 1942 the Navy was short of these devices, and the factory-fresh aircraft did not have any of them. (The Navy workshops installed radars on some SBD-4s later). Externally you can recognize this version by the new Hamilton Standard Hydromatic propeller:

(See the high-resolution SBD-4 left & top view).

The previous SBD versions (-1, -2, -3) used the Hamilton Standard Automatic propeller. As you can see in the drawing below, the blades of these propellers had different shapes:

(See the high-resolution SBD-4 front view, SBD-3 front view).

Below you can see another drawing of the SBD-4, consisting the bottom view as well as the side view without the NACA cowling:

(See the high-resolution SBD-4 bottom view).

Comparing it to similar drawing of the SBD-5 published in the previous post, note the different profile of the internal cowling (the cowling behind the engine cylinders). For this version I had no photo of its upper part! The shape of this element is deduced from the shape of similar part in the SBD-5 and from the size and location of the Stromberg-Bendix injection carburetor, located just behind this cowling.

Next week I will describe the external differences between SBD-4 and SBD-5. It will be the last post about the “general” reference drawings. Then I will report my progress on the first element of this model: the wing.

In this last post about scale plans I will write about the modifications introduced in the SBD-5 Dauntless version.

For the reference, I placed below the drawing of the previous version: the SBD-4:

(See the high-resolution SBD-4 left & top view).

In February 1943 Douglas started to produce another Dauntless version: the SBD-5. It used more powerful Wright R-1820-60 engine (performing 1200 HP on takeoff: 20% more than the R-1820-52 used in the SBD-4). The engine was moved a few inches forward, and the whole area in the front of the firewall was redesigned:

The old telescopic sight was replaced by modern reflector sight. The SBD-5 had heated windscreen (because it sometimes misted over in dives). (See the high-resolution SBD-5 left & top view).

The engine in the SBD-5 was moved forward by 4 inches, together with its NACA cowling. The overall shape of the NACA ring was the same as in the previous versions, except the removed carburetor air scoop. (The cross sections A in the figure below are the same in both versions):

The shape of the firewall (section C in the figure above) remains unaltered. However, there is a difference in the width of the gap behind the NACA ring. In the SBD-1 … 4 this gap was relatively narrow, and the cross section of the fuselage below (section b in the figure above) forms a regular ellipse. Thus in the previous versions the upper part of the NACA ring had six flaps that controlled the flow of the cooling air through the engine. In the SBD-5 the fuselage was a little bit “thinner” here, and the bottom part of its cross section (section B in the figure above) had slightly different shape. The larger gap between the NACA cowling and the fuselage increased the constant amount of the incoming air that cooled the engine. It allowed Dauntless designers to reduce the number of cowling flaps from 6 to just 2.

Figure below reveals more differences between the SBD-4 and SBD5 engine cowling:

(See the high-resolution SBD-5 bottom view).

Some of these changes are well known, like the removal of carburetor air scoop from the top of the NACA cowling or the different shape of the side ventilation slots. However, while studying the photos, I have found two minor differences that were not yet mentioned in any source:

• The oil radiator air scoop was in the SBD-5 was wider than in previous versions (as well as its panel);
• The bottom seam of the NACA cowling was in the SBD-5 shifted left, while in the previous versions it was running along the symmetry plane;

Finally, I would also like to share with you my findings about the carburetor air intake in the SBD-5. As I mentioned earlier, it disappeared from the cowling, as you can see it on the front views:

(See the larger SBD-5 front view).

But where did they place this air scoop in the SBD-5? Studying the photos and descriptions in the books you can find two air intakes located between engine cylinders (as in the figure below). However, in the original SBD Dauntless maintenance manual I discovered that the central air intake remained — just hidden under the NACA cowling!

The side air scoops were filtered, while the central air scoop was not. I used the Pilot’s Manual to find that there was a switch to flip the carburetor air intake between the filtered and non-filtered air. The filters were auxiliary devices, intended for takeoff and landing on dusty ground airstrips. (You can see similar solutions in contemporary designs from 1943: P-40L and P-51C). In the Pilot’s Manual you can read that you should switch into the non-filtered (i.e. central) air scoop to get the full power from the engine.

I must say that I was used to more streamlined carburetor air ducts. Such a location of the main air scoop is quite strange. It seems that the designers of the SBD-5 concluded that there is enough air behind the single-row radial engine to feed its supercharger. (In an airplane flying 100mph or more the amount of the air passing around the engine is several times larger than during takeoff. Thus such a solution could work if we assume that for the takeoff pilots used the less obscured side air scoops).

I did not prepare drawings of the last Dauntless version — the SBD-6. It had even more powerful engine (R-1820-66, rated 1350 HP on takeoff). Douglass built 450 of these airplanes between April and July 1944. Their radars were fitted in the factory. However, there is no external difference between the SBD-5 and the SBD-6!

In the next post I will report my progress in building the first part of this airplane — the wing.

I started building this model by setting up the initial scene in Blender:

Although Blender allows for arranging the reference drawings on the three perpendicular planes like in the 3D Max, I prefer the alternate way: the Background images feature. Using them, I can assign appropriate image to the corresponding view, and simultaneously use all the six views (bottom, top, left, right, front, rear). They appear just when I set appropriate projection.

This is also the moment to determine the “scale” of this model. Because on the SBD drawings that I have all the dimensions are in inches, I decided to assume that 1 unit in this Blender scene = 1 inch on the real airplane. However, I have no experience with the Blender Units setting, so I left them set to None. If you want to check details of this setup, here is the original *.blend file.

I started modeling the wing by forming the contour of its root rib. (For this purpose I draw the shape NACA2415 airfoil on the reference drawing). I smooth most of the model meshes with Subdivision Surface modifier (it uses the classic Catmull-Clark scheme). The shape of a single edge loop smoothed by this scheme is a piecewise Bezier curve (or, if you wish, a NURBS curve – this is just an alternate math representation). The edge vertices are its control points, so I can easily shape this contour. You can see the result in teh figure below. (In this image you can see that the vertices lie on the rib contour, because the mesh drawing mode there was switched to draw the resulting surface):

The theoretical shape of the NACA-2415 airfoil has a thin, sharp trailing edge. However, in the real airplane it was rounded because of the technological reasons. I tried to determine its radius from the photos. As you can see in the enlarged fragment of the picture above, it forms a small wedge with rounded corner. It is shaped using five vertices. (Their number corresponds the number of the leading edge vertices — I will explain the reason further in this text). The Dauntless inherited many solutions from its Northrop Delta lineage. For example — its wing spars are not perpendicular to the wing airfoil chord. Instead, they are perpendicular to the fuselage centerline. (In the SBD, like in the earlier Northrop designs, the center wing panel and the fuselage form a single unit.  I suppose that it was easier to put together the wing spars and fuselage bulkheads when they shared the same technological bases).

To provide as many “technological bases” for my model as possible, the X axis of the wing object is parallel to the wing chord. I can set it “in the Northrop way” by setting the object incidence angle to 2.5⁰. In this position I can work with the wing mesh, moving vertices along the global coordinate axes (i.e. the axes of the fuselage), and then switch to the local wing object axes when needed.

In the next step I formed the basic wing trapeze. I did it by extruding the wing root edge, and shrinking the airfoil located at the wing ti:

Now you can see why I draw this wing section on the plans without dihedral. This drawing would be useless if it depicted the wing “properly”! From the reference images and descriptions it seems that the wing tip had the NACA-2409 airfoil. In the first approximation I scaled down the rib of the tip, fitting it to the reference drawing. (To fit this mesh to the front view I temporarily rotated the wing by its dihedral angle — 10⁰ 8’ — as in the picture below). However, although scaling down the original NACA-2415 coordinates produces the NACA-2409, it does not work precisely for the airfoil shape recreated with the Bezier curves. To fix these small differences I prepared an auxiliary “guide” rib of the NACA-2409 airfoil and placed it in the tip. (see the picture above). Then I modified the wing tip airfoil, fitting the wing surface to the contour of this guide rib (you can see on the picture that it minimally protrudes from the wing – as a very thin line).

Then I rotated the root airfoil, adjusting it to the wing dihedral:

In the SBD Dauntless all the wing ribs were perpendicular to the wing chord plane, except the root rib of the outer panel. To easily insert properly oriented ribs in the middle of this wing, I inserted another rib after the skewed wing root rib. It is perpendicular to the chord plane. I marked this rib edge as “sharp” (by increasing its Crease weight to 100% —you can recognize it on the picture by different edge color). In this way I ensured that the skewed root rib has no influence on the new edges I will add in the middle of this mesh.

In the Catmull-Clark subdivision surfaces, you can use the Crease weights to obtain a local sharp edge or to separate a mesh fragment from the influence of the outer mesh vertices. I learned this method from a Pixar paper, presented on SIGGRAPH 2000 by Tony DeRose. (Before I started my first model, I studied the subdivision surfaces math, to know better properties of the basic “material” used in the digital modeling).

I had an occasion to learn that it works as expected in the next step: forming of the rounded wing tip. First I inserted into the tip area a few new ribs (using the Loop Cut command). Then I started bending their trailing and leading edges, to finally join them into an arch:

As you can see in this picture, I also removed some of the internal mesh faces. I did it because I had to alter the topology of this area. (It is easier for me to determine the new faces when the old ones are removed).

Note that it was a good idea to have the same number of vertices on the trailing and leading edge. Now I can easily join them at the wing tip.

Figure below shows the resulting surface:

Note that the wing tip edge lies on the wing chord plane. As we can see from the reference drawing, in the real airplane the wing tips were slightly bent upward. We can easily obtain such an effect by moving upward (and slightly rotating) last vertices of the tip:

In the figure below you can see the control (i.e. not subdivided) mesh of this wing:

Note that I tried to align as many “longitudinal” mesh edges as possible to the stringers and spars visible on the reference drawing. This will be extremely useful when I draw skin details on the wing surface unwrapped in the UV space (for texturing).

In this source *.blend file you can check any detail of the mesh presented in this post. The next post will describe further steps of the wing modeling: separation of the aileron and forming of its bay in the wing.

This blog provides just an overall picture of the process. If you want to learn more about Blender, digital aircraft modeling and subdivision surfaces, see this guide: “Virtual Airplane” (vol. II).

Jaworski, this is incredible!  And incredible timing as well.  I've just begun working on a Dauntless myself and I've been pooling together sources to up the detail in my build.  What a wealth of knowledge right here. =]  One thing I haven't found with any ease are pictures of the -3 engine and the parts within the mounts.  Would you have any references on that or know where to find them?

I'm really enjoying this thread.  I'll be watching.  =D

You are welcome! :)

I can see no special differences in the R-1820 engine between subsequent SBD versions. Here are:

R-1820 engine manual (contains photos and drawings):

Some photos of the Bendix-Stromberg carburetor (not covered by the R-1820 manual)
Hamilton Standard Propeller governor details (not covered by the R-1820 manual):

So far I have not found too many pictures of the elements inside engine mounts of the SBD-3:

The details from the later version (SBD-5) can be also useful: the SBD-3 was simpler: if you remove the filtered carburetor air ducts it will be still usable:

Let me know if you will find more photos of this area...

This will definitely be of some help.  Many thanks! =]

I hate to break up the continuity of this thread... but I just can't help myself.  

I am in awe of your attention to detail.  You are amazing.

Mark, thank you very much!

(Do not worry about the thread continuity - your feedback is as important as my posts that report the progress of the work )

In the previous post I have formed the general shape of the Dauntless wing. Now I will work on its trailing edge, separating the aileron and flaps. They were attached to the internal wing reinforcements. These reinforcements were distributed in parallel to the trailing edge:

In the first step I will split the wing mesh along this line. However, before I do this, let me mention a certain geometrical effect which can be surprising for many modelers. (Frankly speaking: it was also surprising for me — I knew that such an effect exists, but I thought that its results can be neglected for this wing area).

When you place on the wing a plane shaped like the "cutting line" shown on the picture above (see below, left), you will discover that the resulting intersection edge on the wing surface forms a curved contour (see below, right):

The curve on the wing tip is not a surprise, but why the intersection of the flat plane and the wing trapeze (i.e. the line between point 1 and 2) is also curved? The answer is: because this wing is like a section of an elliptic cone. The only straight line on the cone surface connects its base and apex. Any other direction (like our cutting plane) produces a curve. When the curvature of the wing airfoil on this area is low, the deviation from the straight line can be neglected. However, in this wing it produces a 0.23” deviation at the aileron root rib. You had to adapt contours of the spars and stringers used there.

Obtaining such a gently curved shape on a relatively long element is difficult from the technological point of view (i.e. costly). It can be applied if the high performance is on the stake (as in the Spitfire case). However, even the Spitfire designers had to make a compromise with the workshop and made the bottom of their wing flat. (In this way they provided a technological base).

What could do a pragmatic Northrop (then Douglas) designer in such a case? I have no direct photographic proof, but it seems that they approximated this shape with two straight segments. They are split at the aileron root section:

In the next post I will show you that in this wing each of these two segments was made in a different way. The flaps were attached to a reinforced vertical wall (a kind of a partial spar), while in the front of the aileron there was a lighter structure matching the shape of the aileron leading edge.

After these deliberations we can cut off the trailing edge from the win:

(I did it in two steps. In the first step I created a new edge along the intended split line, using the Knife tool. In the next step I separated the rear part of this mesh into a new object).

We will deal with the red elements in the next post. In this post let’s recreate wing details along the flaps and aileron bay:

The ultimate edges of aileron bay are located a little bit further than the “reinforcement line”. I extruded them from the original mesh.

When a part of the original control mesh is removed, the shape of the resulting object can have small deviations from the original shape of the complete wing. Thus before I separated the trailing edge I copied the complete wing into an auxiliary, “reference” object. Now I am using it to ensure that all these newly extruded vertices lie on the appropriate height:

On the picture above you can see solid red areas around the modified vertex. This is the result of the approximation of the curve section (the flap hinges have to be straight lines).

To determine exact shape of the aileron bay edges I placed an auxiliary “stick” along the aileron axis, as well as some circles around it. The radii of these circles match the shape of the aileron leading edge (+ the width of the eventual gap — see picture below, bottom left). Then I set the view perpendicularly to this aileron axis object, and used auxiliary circles to determine the shape of the aileron bay edge:

Finally I closed the aileron bay with a curved wall that matches the shape of aileron leading edge:

In this source *.blend file you can check all details of the mesh presented in this post. The next post will report further progress on the wing trailing edge details (I will form and fit the aileron).

In the previous post I have modeled the aileron bay in the SBD Dauntless wing. However, it was one of the cases when I followed my intuition and the mathematical precision of the computer models instead checking how this detail looks in the real airplane. So let’s do it now. I have reviewed many photos. The figure below shows the one which is the most useful (made by my friend in 2014 in one of the air museums):

We can see here that the flaps are attached (via a very long hinge) to a reinforced structure which resembles a spar. It ends at the first aileron hinge. On the other hand, the aileron is mounted on three “point” hinges which protrude from the ribs. Thus the curved sheet metal that closes the aileron bay has much lighter structure, because it is merely a cover. It is riveted to the ribs and other wing skin panels. The “sharp corner” at the upper edge of the aileron bay is obtained by a fragment of the upper wing skin that overlaps (by about half of inch) the bent, rounded edge of the internal wall.

I recreated in my mesh the auxiliary spar along the flaps and the fragment of the wing skin that overlaps the upper edge of the aileron bay:

I will model the bent upper edge of the internal wall later, during the detailing phase. The lightening holes in the spar will not be modeled. For such less important openings I will use transparency textures.

At the beginning of the previous post I cut off the wing trailing edge. Now I split it into two objects: the aileron and the flaps. Then I started to work on adapting the aileron mesh. First I simplified its topology: I slid its upper longitudinal edge forward, where the curved leading edge begins (Figure a), below). I do not need its bottom counterpart, so it will disappear. In the effect the aileron cross section resembles a triangle, as in the real airplane. (Such simplifications of the theoretical trailing edge geometry were common in this aircraft generation).

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To form the curved shape of the aileron leading edge I extruded vertically from its bottom edge two face rows (Figure b), above). Then I closed the remaining gap with another row of faces.

After small adjustments of their vertices at the wing tip I obtained the rounded shape of the aileron leading edge:

Then I did some further adjustments, checking if the gap between the aileron and the wing is wide enough (0.2”) for the whole aileron rotation range (from -10⁰ to +17⁰). You can see the result in the figure below:

However, comparing this result with the photos, I discovered that I fitted it too tightly! What’s more, I also noticed differences in the shapes of the aileron tip and its bay between various restored aircraft:

The outer wing panels were the same in all the SBD versions (at least their external details — see this post) — so I cannot explain these differences as the differences between various aircraft versions. Well, it seems that one of these restored aircraft was modified afterward. But which one?

Restored aircrafts are great resource of information for all modelers. However, some of them contain various modifications. Most of such differences you can find in the airplanes restored before 1990. Since that time the average level of restorations has significantly improved.

To determine which case is wrong, you have to look at the archival photos:

In the picture of a factory-fresh SBD-1 you can see that the tip of the aileron was curved. Nevertheless, I had to widen the gap between the aileron and the wing tip, reproducing the case I can see on the archival photo:

In this source *.blend file you can check all details of the model presented in this post.

In the next post I will recreate the flaps.

Summer break: I am leaving on vacation (away from the computer for two weeks). I will describe further progress of my work on the SBD Daunless on August 29th.

Perforated split wing flaps were the hallmark of the SBD Dauntless. Their inner side was reinforced by the “grid” made of stringers and ribs. Because these flaps were often wide open — during landing or in dives — I have to recreate their internal structure. In this and the next post I will describe how I did it.

All the SBD flaps had fixed chord (they were made from perforated sheet metal of rhomboidal shape). After studying many photos I assume that all their ribs have the same size and shape — also the parts attached to the trapezoidal, outer wing section. It seems that Douglas factories built all five flaps of the SBD in the same way, using unified components. The flaps for the external wing panels had to be twisted a little during riveting — most probably on appropriate mounting pads. The trailing edge of the upper flap is the trailing edge of the whole wing. It was a thin wedge, profiled from a sheet metal and riveted to the flap skin:

(Similar wedge is riveted to the upper skin of the center wing — see the picture above). The chordwise contour of these flaps looks flat on the photos. In fact there is only a small difference (less than 0.2 inches) between the theoretical contours of the wing airfoil and a straight line on the area around the trailing edge. I think that for the designers such a technological simplification was not a big deal — they had already made a more serious modification by perforating the flaps.

I started building the SBD flaps by creating their upper and lower planes. (I created them by simplification of the mesh fragment that I previously cut off from the wing). I used the Solidify modifier to give them thickness of a sheet metal. (I used this modifier for all parts which I will create in this post). Then I added the wedge (another object) along their trailing edge:

I started this wedge as a single contour, which I extruded along the whole span of the flap. Because of the trapezoidal shape of this wing, I had to twist a little the outer end of this wedge, fitting it better to the upper flap. Then I shortened the trailing edge of the bottom flap, fitting it into the wedge when it is closed.

When it was done, I added the main “spar” of the flap (in fact it was a U-shaped stringer). I did it in the same way as I created the trailing edge: shaping the profile, then extruding it lengthwise:

Once extruded, I had to rotate this object and twist its end, lying its outer edges on the inner surface of the flap skin. To facilitate this process I assigned this object a contrast, red color.

While fitting this spar, I discovered that the twisted, four-vertex face of the flap skin has small elevation along its diagonal (as in picture above). It is not something “real” — just an effect of the internal decomposition of all quads into triangles made by Blender.

To eliminate this artificial effect I had to divide this sigle, large face into several smaller pieces:

It minimized the influence of Blender internal “triangulation” and allowed me to properly fit the stringer to the flap. As you can see in the picture above, the end profile of this spar is twisted, following the twist of the flap skin.

After the first stringer I created in a similar way two other reinforcements on the flap edges:

As you can see, I used two clones of the rib contour. (I needed them to determine slopes of the front and rear reinforcements in the side view — as in picture above).

When the flap lengthwise reinforcements are in place, I can add the ribs:

All the internal ribs are clones of a single mesh. The external ribs have the same contour, but each of them has its own mesh (because they do not have the cutout for the central spar, as the internal ribs). These flap ribs have quite complex shape, but I managed to keep their mesh quite simple. It was possible, because a part of this complexity (the sheet metal thickness, rounded edges) is created by the Solidify and Bevel modifiers.

When the ribs were in place, I added the last stringer. It was a “L”-shaped beam:

Modeling internal structures of the flap forced me to carefully measure anew all of its details, especially the width and location of its spars. In the effect you can see that my wing drawings are not as precise as you could expect:

In this source *.blend file you can check all details of the model presented in this post. In the next post I will continue my work — this time on the upper flap.

Man....this aint model building. This is freekin' engineering!!! Nice job!! And that's putting it mildly bud!

Thank you!

I simply cannot resist temptation to recreate most of the details I can see on the photos! For the first time you can have a "material" which allows you to recreate all these sheet metal elements as thick as they were in the reality... In this work your patience is the only limit :).

In this post I will create internal structure of the upper split flap. Structures of both flaps are similar, thus I started this job by copying stringers from the bottom flap, finished in the previous post:

Every copied stringer is a duplicate of its counterpart from the bottom flap (I just used the negative scale: -1). I had to rotate these objects, placing them on the internal side of the upper flap skin. I copied the internal ribs in the same way (see picture below). (All of them are clones, which use the same mesh):

As you can see in the side view (see in the picture above, upper left), there is just a small vertical distance between the last ribs of the upper and lower flap (i.e. at the aileron). This is the thinnest place of this structure.

At the trailing edge of the upper flap there is the profiled wedge (I described it in the previous post). The upper flap is little bit wider (it has longer chord length than the bottom flap). Because of this the ribs of the unified size used in these flaps are too short to reach the closing wedge (see picture above).

We can observe this effect on the photos. To make these ribs longer, designers added at their ends small “U”-shaped profiles (see picture below):

I recreated these elements in my model (see in the picture above, right).

The upper flap has a cutout in its inner edge. Thus there is “one and half” of the external rib here:

I recreated this structure in my model and modified the mesh of the upper skin:

These flaps were attached to the wing by two long hinges. I recreated them as two very long cylinders and placed between the flaps and the wing:

Now, when I rotate the hinge along its local Z axis, the whole flap rotates, like in the real aircraft:

This is a preparation for the future animation of this movement (during the detailing phase).

In this and the previous post I built the split flaps and their basic skeleton. I recreated these ribs and stringers because they are visible when the flaps are extended. The additional benefit of this work was the verification of my reference drawings. (Now I know that I have to shift a little the perforation and rivet seams on both flaps. I will do it when I prepare their textures). However, on this stage it is too early to finish all remaining details of these flaps. It still may happen that I will discover something which will force me to modify the geometry of this wing and its flaps. Thus in the picture below I marked what I prefer to postpone until the detailing phase:

As you can see in this picture, I will create the openings in the flap skin later. At this moment I am going to recreate them using the same technique as for the lightening holes: textures (the bump map and transparency map). However, if this idea fails, I will model these openings in the flap skin mesh. (This method requires much more time than the textures).

In addition to these openings I will also recreate all the minor details of the flap structure. For example — I will split the “L”-shaped auxiliary stringer between the ribs. I have also to split the flap forward reinforcements into separate segments.

The complex system of the flap actuators will be also a challenge for the detailing phase (however, I already analyzed how it works).

In this source *.blend file you can check all details of the model presented in this post. In the next post I will create the fixed slats and finish this outer wing panel for this “general modeling” stage of work. Of course, I will work on it again later, during texturing and detailing.

In the next post I will add fixed slats, completing this outer wing section.

In one of the previous posts I showed the details of the aileron bay. Now I separated the corresponding wing mesh fragment into a new object. I bent its upper edge like it was depicted on the photo:

On some photos I could see that this wall was built of two pieces of sheet metal. Their seam was located below the aileron pushrod.

The reason for such split became obvious after the comment I received from one of the readers (thank you, Brian!). It happened that a few weeks ago he visited the Yanks Air Museum in Chino, and had an occasion to examine wings of their SBD-4. He reported that while the bottom edge of the aileron bay is a straight line, the upper edge has a break at the pushrod. The difference from the straight line at this point is about 0.1-0.2 inches. Checking this tip, I examined photos of this particular SBD-4, then I verified photos of the other SBD version:

This nuance of the aileron edge is hardly visible in a perspective view. It explains why I missed it studying the photos!

Finally I recreated this detail in my model:

(Doing it, I had to modify shapes of three objects: the wing, the rear wall of the aileron bay, and the aileron).

I could not resist the temptation to recreate the rounded corner of the wing skin at the aileron root:

Frankly speaking, I should model such a thing during the detailing phase. I allowed myself to use some n-gons (faces that have more than 4 vertices) here, because this surface is flat so these n-gons will not deform the smoothed result.

However, looking on the photo above I noticed that the aileron bay edge seems to lie on the same line as one of the rivet seams on the flap. (The seam that runs along the rear edge of the hinge reinforcements). So it was on the reference drawing. However, do you remember that I had to modify these flap reinforcements, shifting them forward (in this post)? So now I know that this rivet seam is in another place on this flap, different from the place where you can see it on my drawing. Now I have to update accordingly the location of the aileron edge!

To preserve its vertical shape, I did it by two rotations: first I rotated it along Z axis:

Then I had to make a small rotation along Y axis (along the same pivot point), elevating these faces back onto the wing surface.

The updated layout of the flap ribs and struts means that I will have to move forward not only the rivet seams, but also the rows of the circular openings placed on the flaps (I mentioned it in one of the previous posts). What’s interesting, the auxiliary “L”-shaped stringers on the upper and lower flap have different chordwise locations. In the result, the last row of the holes in the upper flap does not match its counterpart on the bottom flap (see picture above).

The last detail I will recreate during this stage of work is the fixed slat. It requires six openings in the wing skin: three on the upper surface and three on the bottom surface. I did not modify the wing mesh for this purpose, because additional edges around these openings would seriously complicate its topology. I decided to create them in another way: it may happen that ultimately I will make these holes using transparency textures, but for now I will do it using the Boolean modifier. First I prepared an auxiliary object — the “cutting tool”

I set the wing as its parent, and placed on a hidden layer. Then I used a Boolean modifier to dynamically cut out these openings in the wing:

Note that I placed the Boolean modifier after the Subdivision Surface modifier, to cut these holes in the resulting, smooth wing surface. As an additional bonus, this modifier also creates their internal walls (they come from the auxiliary object).

Although the “rib” walls obtained in this way are OK, I decided to create the front and rear walls of this slat as a separate object. Why? Because it is easier to modify its shape when it is not split into three “boxes”, as the “cutting tool” object is:

I will join all these internal faces of the slats during the detailing phase. Currently I am leaving them in the current state, just in case I will have to modify the wingtip geometry.

This was the last element of the outer wing panel I wanted to create during the “general modeling” phase. I will recreate all of remaining parts (landing light, approaching light, Pitot tube, aileron axis arms, etc.) later, during the detailing phase.

In this source *.blend file you can check all details of the wing presented in this post.

In the next post I will start working on the centerwing. It will be occasion to find another parent for the “cutting tool” object, resolving the issue of disappearing slats.

On the first glance the SBD center wing section seems to be a simple rectangular (i.e. constant chord) wing, with modified leading edge:



However, the landing gear openings visible on the photo can be difficult to recreate in a mesh smoothed by the subdivision surface modifier.

Additional photos from one of the SBD restorations made by Vulture Aviation in 2012-2013 reveal that the fuselage was mounted on the top of the wing (see the a) picture below):



A part of the upper wing surface was simultaneously the cockpit floor. Note the rectangular cutout in the middle of the leading edge. The SBD had a small window on the bottom of the fuselage, in the space between the two root ribs.

On the photo of the bottom of this wing (as in the b) picture, above) you can see that these root ribs had a modified airfoil shape: it bottom contour has a straight edge from the leading edge to the main spar.

I started to form the center wing section by preparing the single curve of its external rib. (I copied it from the root rib of the wing reference object, which I used during modeling of the outer wing panel):



I think that creation of these large landing gear bays (as the first picture in this post) will require a lot of modification in the wing mesh. Thus I decided to separate the mesh fragment that contains these openings (from the leading edge to the main spar) into a separate object. (It is always easier to modify topology of such a medium-size mesh part, than the whole wing). To ensure a smooth, invisible seam between this forward and the rear part of the wing, I had to accordingly prepare the control polygon of the initial airfoil. I added an additional point on each side of the vertices located above and below the spar line:



What’s important, such three points have to be collinear. The resulting subdivision surface “touches” the middle point of such a fragment of the control polygon, and it is tangent in this point to these two adjacent control polygon segments. (This is just one of the mathematical properties of the Catmull-Clark subdivision surfaces, which are implemented in Blender).

However, these four new control points altered the shape of the airfoil curve. Now I have to fit this shape to the original NACA-2415 airfoil of the outer wing panel:


Fortunately, the Catmull-Clark curves/surfaces have another property similar to the NURBS: so-called local change. Their formula ensures that influence of a single control point does not exceeds two subsequent segments of the control polygon (two segments in both directions — see picture above, right). It is easier to focus on the modified mesh fragment, when you know this rule.

Once the initial rib shape fits the outer panel, I can extrude it forming the center wing section:



To shape the leading edge I had to stretch a little bit the forward part of this mesh. As you can see (in the picture above), I placed this new edge loop in the place of the wing root rib.

However, comparing the resulting object with the photos I discovered that the leading edge of the center wing section should have constant radius (at least approximately):



In this way I have found another error in my reference drawing: the wrong shape of the root airfoil:



The tangent direction at the wing spar differs from the direction estimated on the drawing, thus the bottom, straight segment of the root airfoil has a slightly different slope. The leading edge is much thicker than I draw on these plans.

Adapting the well-known von Moltke’s sentence: “no plan survives contact with the enemy” to this situation, we can say that “no scale plans survive contact with their 3D model”.

I created a first approximation of the main wheel (it lacks the details) to check if it fits into the space between the leading edge and the main spar:



When I was sure that the shape of the wing is OK, I separated the forward part of this mesh (by splitting it along the main spar). As you can see (in picture above, right) these two parts join in a seamless way. It was quite simple to prepare such an effect in the initial curve by adding additional control points (as I described in the beginning of this post). It would be much more difficult to introduce similar modifications into the extruded mesh.

If you want to learn more about properties of the Catmull-Clark subdivision surfaces, as well as the details of the modeling workflow, see Vol. II of the “Virtual Airplane” guide.

In this source *.blend file you can check all details of the wing presented in this post.

In the next post I will create the opening for the landing gear.

In this post I will cut out the opening of the landing gear bay in the wing. In the SBD Dauntless its shape consists a rectangle and a circle:

However, when you look closer, you will notice that the contour of the main wheel bay is not perfectly circular. There is a small deformation of its shape on the leading edge (see picture above). I think that it looks in this way because of the technological reasons. Another feature of this opening is the fragment “cut out” in the bottom part of the fuselage, below the wing. (We will make it when we will form the fuselage).

I started by applying all the information that was confirmed by the general arrangement drawing and various technical descriptions: the main wheel used 30”x7” tire. Its center was placed 18.5” from the firewall (measured along the global Y axis):

The X coordinate of the wheel center can be determined by the location of the root rib (10”) + small gap + tire radius (30”/2) ≈ 26”.

Then I tried to put around the main wheel a test contour of the opening in the wing:

Initially I thought that I will recreate this opening by embedding a subdivided octagonal hole in the wing mesh, as I did in my P-40 model (see Vol. II of the “Virtual Airplane” guide).

However, when I created an appropriate octagon around the wheel, I discovered that one of its vertices lies outside the wing mesh (see figure a), above). You cannot compose such a contour into the wing. Therefore I decided to create this opening using another Boolean modifier, as I did in the case of the fixed slats (described in one of the previous posts). I prepared the basic contour of the “cutting tool” — a smooth circle based on a 16-vertex polygon (as in figure b), above).

The fragment of the main wheel opening that “touches” the wing leading edge seems to be flatten a little (see the first picture in this post). To obtain such an effect I rotated the “cutting tool” object (the ring) by a few degrees so its Y axis was perpendicular to the leading edge. Then I shifted a little the single edge of this ring along the Y axis, fitting it into the wing:

By small movement of these two vertices I was able to precisely recreate the shape of this opening visible on the photos:

If I do not want to get the inner part of the “cutting ring” inside the resulting opening, I have to assign to this wing mesh a sheet metal thickness (using the Solidify modifier – as in picture below):

Because the forward and rear part of the wing are separated, I can use this Solidify modifier only in the front part. In this way I do not increase the polygon count of this model with unnecessary faces.

As you can see in the picture above, I also created a second “cutting object” — a box. I will use it to recreate the rectangular opening around the landing gear leg. Both of these tool objects are located on a single layer (9) which will be hidden during rendering. Their parent is the rear part of the center wing section (to avoid dependency conflict with the front part of the wing).

Finally I assigned both of these “cutting” objects to the Boolean (Difference) modifiers of the wing skin (The same method as used for the fixed slats). You can see the result in picture below:

It would be quite difficult to recreate such an opening by altering the control mesh of the wing skin. It also would make its shape more complex, and difficult to unwrap in the UV space (for the textures).

The openings created by Boolean modifiers have another advantage: it is very easy to modify their contours. I had to do this just after I created these holes. I discovered that I made minor error in the reference drawing: the landing gear leg opening should lie a little bit back. (Its centerline should pass through the landing gear wheel center

All what I had to do was to shift back the auxiliary box object, which creates this opening. So easy!

On the other hand, I observed small shadows caused by triangular faces created by the Boolean modifiers along edges of this opening. It was impossible to remove them in the typical way — using the Auto Smooth option or the Edge Split modifier. The only solution was to increase (from 2 to 4) the level of the Subdivision Surface modifier assigned to the wing surface object. It increased 16 times the number of resulting smooth faces created from this mesh. Fortunately, I split the wing into two parts, so I could set keep such a dense mesh only around the area where it is needed.

In this source *.blend file you can check all details of the wing presented in this post.

In the next post I will create main spars and ribs, visible inside this opening.

AI aircraft are the top of the modeling world. as you can fly them forever. Wish There was a FS for Win10..... intresting insight Jaworski!!!!

Thank you!

Last time I played FS Combat Simulator on an old Windows XP in 2005 . Frankly speaking, such a computer model like mine lives as long as there is a program that you can use to handle its format.

On the other hand, I can see many advantages of this new branch of scale modeling: you can recreate any model you want, in any painting scheme you want! You can always modify them when you find a better reference materials. The only limit of detailing is your own patience...

The only thing I am missing in these digital models is that I cannot touch them. However, it can be possible using a 3D printer! I suppose, that it is possible to "print" the details you are missing in your plastic kit... Or to publish a file that contains all parts of a completely new model kit, "ready to glue" - you would print such a kit on a 3D printer. (It would create a similar situation to the paper models, where authors share some of their models as images that you can print for yourself). A lot of new, interesting  possibilities!

Inside the Dauntless landing gear bay (which I cut out in the previous post) you can see fragment of the wing internal structure. Because I plan to create this model with retractable landing gear, I have to recreate these details. During this “general modeling” phase I will create here just the few key ribs and spars. I will show it in this post. The remaining details have to wait for the detailing phase.

Examining the photos I identified two auxiliary spars and three ribs as the key elements of this structure:



The spar is relatively simple to recreate. Initially I created a rectangle. Then I split it into six faces. Then I removed one of these faces, creating the space for the wheel bay:



Then I added flanges, rounded corners, and the sheet metal thickness, to give this spar a more realistic look, as you can see in picture "a", below:



However, when you examine this object, you will discover that the mesh of this spar is very simple (as you can see in picture "b", above). I obtained all these effects using a Solidify and two Bevel modifiers. It even did not require any special smoothing (I did not use the Subdivision Surface modifier here).

In the same way I created the second spar:



While working on these spars I also decided to recreate the wing skin that covered the gap between the main spar and Spar 1:



It would be possible to shape such a hole by altering the wing mesh. However, if I already used the Boolean modifier in this object to cut the opening for the landing gear, it was much simpler to extend it for this purpose. Thus I extruded the whole leading edge section, up to the centerline. Then I cut out a part of this newly created surface using the modified “cutting tool” object that I used to form the landing gear bay (as you can see in the picture above).

The mesh of the wing skin already contains a “rib” edge loop in place of the root rib (see picture "a", below). Thus it was easy to duplicate this edge into a new object, and extrude it by an inch into a flange. I offset this flange by a metal sheet thickness, placing it below the wing skin. (I did it by applying a temporary Solidify modifier — in Blender it produces better results than the Offset command). Finally I created faces between the vertices of the upper and lower rib edges (as in picture "b", below):



As in the spar, the rib object uses a Solidify modifier to recreate the sheet metal thickness and a Bevel modifier to round flange edge. It also uses Subdivision Surface modifier to fit it tightly into the wing.

A new rib that fits a trapezoidal wing segment requires somewhat more work. To create it, I prepared auxiliary “cutting tool”: two parallel planes (as in picture "a", below):



I used this helpful Intersection Blender add on (I created it for similar purposes) to find the intersection of these two planes and the wing mesh. I separated the result of this operation — two edge loops (see picture "b", above) into new object. Then I continued as in the case of the previous rib: created the flange (see picture "a", below) and offset it from the wing skin. In this case I had to modify the bottom part of the rib, creating space for the wheel bay. Finally I created the vertical walls (see picture "b", below):



In similar way I created another rib. You can see the result in the picture below:



At this moment I am not recreating in this structure the lightening holes — I will obtain this effect using bump and transparency textures.

I mentioned the “textured holes” many times in the previous posts. However, I will apply it much later, during the texturing phase. Thus, if you want to find more about this particular method, you can find its detailed description in Vol III of the “Virtual Aircraft” guide. (It is an introduction to materials and textures).

In this source *.blend file you can check all details of the wing presented in this post.

In the next post I will create the remaining elements of the wing.

In this post I will finish the “general modeling” phase of the wing, recreating the last missing elements. Of course, the result presented in this section is not the “final product”. It is just detailed enough for the next phase — applying textures and materials. (I will do it when I form the whole model). After applying the textures I will come back to this wing during the detailing phase, and recreate all its small details (like various small openings, aileron hinges, running lights, landing light, etc.).

Finishing the wheel bay, I decided to add the rounded flange around its edges:



I just did it because I do not like to see a non-realistic, “suspended in the air” edge of an opening. A part of this flange has to fit into the bottom of the fuselage. At this moment I left on that flange an “informal”, elevated fragment. I will fit it to the fuselage when it will be ready.

There is another detail which is too subtle to be found on any scale plans. It is the shape of the landing gear leg bay, speaking more precisely —of its front edge:



In the top view the front edge of this opening is a straight line, perpendicular to the aircraft centerline. Such an edge goes across several theoretical straight lines that you could draw on the bottom wing surface (see picture "a", above). This means that in the front view this edge forms a gentle curve.

Initially I did not know if the Dauntless designers reproduced such a geometrically correct, but technologically more difficult shape. (Such a curved shape is more expensive because it requires additional formers for the wing skin panels and landing gear cover). I could imagine the situation when they decide to simplify this edge to a straight line. Fortunately, I have many high-resolution pictures of various restored SBDs. Photos of the landing gear confirm that this edge was curved (see picture "b", above).

Another element I added was the solid rib that closes the center wing section. It is a standard Northrop solution for joining multicellular stressed-skin wing, designed in 1930 for their Alpha aircraft. Both wings were joined by multiple bolts evenly distributed around the airfoil circumference. The forces from the bolts were transferred to the wing skin via “L”-shaped flanges. You need to place a stiff rib between such flanges, because otherwise the whole structure would collapse. That’s why the rib closing the wing section is a solid, thick aluminum plate:



I am not sure if I estimated properly the thickness of this rib. Anyway, I did it using a Solidify modifier, so it will be easy to alter this setting later. Because of this unusual thickness I am not sure if I will recreate the openings in this element (you can see them on the photo) using textures. The alternative method is to modify this mesh (it should be not very complicated, because it is a flat plate). During the detailing phase I will also recreate the vertical reinforcements visible on the photo.

I started the bottom flap of the center wing section by preparing the auxiliary spar running along the flap hinges:



As you can see, I also created the symmetric, right side of this wing section, using a Mirror modifier.

The flap is created in the same way as the flaps of the outer wing panel. I separated the bottom part of the wing trailing edge into the flap skin. I added a very long, thin cylinder as the flap hinges. I copied the trailing wedge from the outer wing panel and placed it on the trailing edge:



Then I copied the flap stringers from the outer flaps. In fact, I used just the cross sections of these original objects, extruding them into new stringers. I used Mirror modifiers to create the opposite sides of all of these spanwise flap reinforcements.

In the next step I copied from the outer flaps the “standard” flap ribs (they all are clones that share the same mesh - see picture "a", below):



Finally I modified the upper part of the center wing mesh, integrating it with the trailing wedge (see picture "b", above).

When you open the split flap, you can see the internal structure of the wing:



I studied the available photos of the flap bay in the center wing, then recreated the key ribs and spars:



Finally I organized the whole wing into the appropriate hierarchy. At this moment the root element is the wing center — more precisely, its rear part:



I placed all external wing elements on layer 1, while all internal parts are on layer 11. The auxiliary “cutting tools” used in the Boolean modifiers are in layer 9. To avoid “circular reference” conflicts I assigned the outer wing panel and the object that cuts its fixed slats to the common parent — the ”stiff” root rib.

In this source *.blend file you can check all details of the wing presented in this post.

In the next post I will start working on a more difficult part: the fuselage.

Before I start forming the mesh of the SBD fuselage, I will prepare an auxiliary object: the simplified version that will help me to grasp the general concept of its shape. I will describe it in this post.

In the first step, I created the three key bulkheads:



First one — the firewall — seems to have an elliptical shape:



The contour of the station 140 on my plans is copied from one of the photos which I have found on the Vultures Row Aviation web site:



For this conceptual shape I replaced the bottom part (after the trailing edge) with the curve extrapolated from the further tail cross sections.

Finally, in station 271, which closes the main fuselage structure, I had to extrapolate its upper part:



Then I extended between stations 140 and 271 a mesh, forming in this way the simplified tail (without the wing root fairing):



I put another edgeloop in the middle of this tail to fit its contour in the side and top views.

In the next step I recreated the mid-fuselage:



In this concept object I entirely skipped the wing root fairing — because it requires a lot of work. I will recreate it directly in the final fuselage object. Note that the fuselage contours along the cockpit are straight lines. This detail is visible on many photos.

I added in the middle of the cockpit another “bulkhead” edgeloop, and used it to determine shape of the bottom part of this fuselage:



I fitted the contours of the fuselage that protrudes from the wing bottom surface into the contours in my reference drawings. It took some iterations to fit them. (The contour you can see in the bottom view was copied from original Douglas photo, so it is an important reference. The side view is not based on such a confirmed information). To preserve the straight edges on the cockpit sides, I had to move this central bulkhead along the fuselage centerline using the Edge Slide command. I was able to move or scale this edge only along the Z direction.

Finally, when I finished this element, I checked if the cockpit sides are still straight, like before. They were not:



As you can see in the picture above, I used an auxiliary horizontal plane set in the contrast color to see the effective shape of the fuselage mesh. I placed it just above the “longeron” edge that runs along the maximum width. The fuselage contour you can see on this plane is bent in the front of station 140. I think that such a shape is the effect of the “saddle”-like shape of the fuselage in this area. I am glad that I identified this issue on this simplified model. I will try to avoid such an effect in the final fuselage by directing all the lengthwise (“longeron”) edges along their real-life counterparts (upper-left to bottom-right on the side view).

In this source *.blend file you can check all details of the model presented in this post.

In the next post I will continue working on the fuselage. (I will use the object crated in this post as the reference).

In the previous post I created a simplified model of the SBD fuselage that helped me to identify the eventual troubles in the modeling process. In this post I will create the mid-fuselage (more precisely: its upper part).

I always try to think ahead about the mesh topology required for a given shape. In the case of the subdivision surfaces that are used here, this approach is extremely useful. When you place vertices of the initial bulkhead in the proper places, it greatly simplifies further modeling. To mark some “longeron” edges as “sharp” (Crease = 1), I started with a thin mesh “strip” instead of a single contour:



As you can see in the picture above, it is built around the cockpit sides. Looking on the photos you can notice that one pair of the main longerons forms the side edges of the cockpit. It will be the upper edge of my fuselage. (The part below the windscreen seems to be a separate assembly, riveted over the longerons (see picture "a" below). I will create it later:



I recreated the small fillet around the cockpit edge using two parallel edges placed close to each other (see figure "b" above). I could obtain similar effect using a single, partially sharp edge. However, in such a case the contour of this fillet on the fuselage cross section would have a shape that significantly differs from the circular profile in the real aircraft. What’s more, I will split these double edges at the rear edge of the cockpit opening. I expect that in this way they will help me to shape its rear, rounded corner.

I extended the initial mesh strip from the firewall to station 140 (station locations — see previous post). After fitting vertices of this “bulkhead” edgeloop around station 140, I inserted in the middle of this mesh a new edge, just at the end of the skewed station 54. Then I removed the bottom fragment from the rear part of the resulting mesh:



To avoid the curved contours of this mesh in the top view, I directed the lengthwise edges little downward in the second segment of this fuselage (see picture "a" below):



To verify if the cockpit sides are really straight in the top view, I placed (on the tools layer – 10) many straight “stringer” probes (see picture "b" above). All of them are horizontal, arranged like the real longerons in the airplane (see picture "a" below):



For the properly shaped surface, these probe objects should minimally protrude from the fuselage skin (as in picture "b" above). I used them to apply small adjustments to this mesh.

When the cockpit sides are ready, I recreated the upper part of the station 140, and extruded it toward the cockpit. In this way I obtained the initial strip of the tail upper surface (see picture "a" below):



It is relatively easy to prepare in this mesh a rectangular opening for the gun doors. The general rule of the subdivision surfaces is that their sharp edges (i.e. edges which Crease = 1) have the same shape as the free edges (for example — opening borders). Thus, if I incorporate into a smooth surface an area encompassed by sharp edges, I can later remove its inner faces without altering the shape of the outer mesh faces.

But how to obtain a smooth surface around a sharp edge? It is simple: place it in the middle of a flat face of the control mesh. I did so. As you can see in picture "b" above, it is enough to make the three vertices on every bulkhead collinear. (In practice, small deviations from the theoretical line still produce acceptable results).

In the next step I cut in this mesh strip the skewed rear edge of the cockpit opening:



After removing the unnecessary vertices, I created a few new faces that finally joined this fragment with the rest of the fuselage mesh. As you can see in picture below, I also inserted another edgeloop just after the cockpit rear edge:



This additional edgeloop and the few vertices in the corner control the surface curvature around of the cockpit opening. As you can see in the picture above, one of the resulting mesh faces has five vertices (so-called n-gon). In general, it is possible to decompose it into a triangle and a quad. However, I carefully examined the resulting surface and decided that this additional vertex does not deform in any way its smooth shape. Thus I decided to leave it “as it is”.

Note that there is a single vertex in this mesh that controls the shape of the fuselage skin in the corner of the cockpit opening:



I modeled it to resemble the original shape as I can see it on the photos. However, I will return to this fragment during the detailing phase of the modeling. With the cockpit canopy in place, I will then re-examine my photos and decide about the further details (for example — cutting the smaller openings for the ammunition feeders on the gun doors sides, which were introduced in the SBD-3).

In this source *.blend file you can check all details of the model presented in this post.

In the next post I will continue working on the fuselage.

In this post I will begin the wing root fairing and recreate the tail of this SBD fuselage.

To be able to fit the fuselage to the wing, I started by creating a new set of the “bulkhead” edges. I placed them at the stations of the original bulkheads:



In most airplanes the wing root fairing and tailplane fairing are created from additional sheet metal elements, fastened to the fuselage with multiple bolts. In the case of the SBD lineage — Northrop Alpha, Gamma and BT-1 — the wing root fairing was the integral part of the fuselage structure. (However, the SBD tailplane fairing had the conventional, “fastened” design).

At the beginning I decided to form the rear part of the wing fairing as a separate object. In this way I will avoid the messing with the topology of the existing mesh. I will merge these two meshes later. Thus I copied into this new object a part of the fuselage mesh, and combined it with the initial part of the fairing cone:



It is always worth to analyze how the modeled element was built in the real aircraft. Let’s look on the photos:



On the picture above I marked straight lines in white, circular cross-sections in red and other curves in yellow. Note that the stringers connecting the circular sections are straight or gently curved. If you would think how this part was built in a workshop, it makes sense. It is not too difficult to recreate the circular cross sections of the fairing in the subsequent bulkheads. Then you have to set these bulkheads at the corresponding stations and connect them with the thin stringers. In this process you can always bent (a little) the initially straight stringer. That’s why all the lengthwise lines on the photo are straight or form a gentle curve.

To ensure that I will recreate this shape properly, I placed three auxiliary stringers as they were located in the real airframe:



Ideally, the outer edges of these test stringers should protrude a little from the wing root fairing surface. Using such them as indicators, I added new edgeloops in the middle of this mesh, and adjusted its bottom shape, fitting it to the wing:



For the further work on the wing root fairing I need the tail. I extruded it from the station 140 up to station 271. Then I put one of the middle bulkheads at station 195 as a reference. Finally I adjusted the shape of this surface to the contours drawn in the side and top views. I did it using three new “bulkhead” edge loops, inserted in the middle of the tail:



Evaluating the shape of this newly created part I examined not only the resulting surface, but also the control mesh. In the case of a fuselage, some geometrical problems are more evident when you check the flow of the lengthwise (“longeron”) edges. In this case I noticed that something is wrong with the last segment of the tail.

The edge marked in yellow in the picture above corresponds to a real longeron on the fuselage. On the photos this longeron seems to be nearly straight. However, in the last segment of my tail its direction is altered:



I re-examined my photos and concluded that I made mistake in the shape of the bulkhead at the end of the tail (station 271). The top contour of this bulkhead had larger radius than in my model. (However, I have an excuse: this part of the last bulkhead is an extrapolated shape, because its upper part is inside the tailplane — see the bulkhead pictures in the post where I started working on the fuselage. On these pictures you can see that I proportionally decreased width of the whole bulkhead contour. This deformation was the direct reason of this mistake). I corrected the tail shape, increasing the corresponding radii in the two rear bulkheads:



Finally I modified edges around the gun door opening:



I prepared horizontal edges of this opening earlier, while shaping the upper part of the station 140 bulkhead (see my previous post). Now I added another sharp edge that closes this opening. Note that for such a rectangular border I avoid crossing two sharp edges — because the resulting corner would create additional elevation above the smooth fuselage surface.

In this source *.blend file you can check all details of the model presented in this post.

In this file you can delete the vertices inside the gun door opening (as in figure above), and check that the shape of the fuselage around the gun bay remains unaltered. I “programmed” such a result into this mesh from the beginning. (I did it by appropriate adjustment of the few vertices in the first tail bulkhead).

In the next post I will form the difficult, rear part of the wing root fairing.

I find this thread literally awe-inspiring. I know so little about computer graphics that I can't understand at least 75% of what Mr. Jaworski has written, but I think I can recognize the work of a true master when I see it - and that is what I certainly see here. I've rarely derived so much pleasure and wonder from something that's so far beyond my comprehension.

JTilley, thank you very much! However, I am merely an average craftsman - I know at least dozen other guys who are much better on this field than me. I just want to popularize this new branch of scale modeling. Thus I share my models (here) as well as the guides that teach how to begin (they start from the very basics - for those who know nothing about the CG). The software that I use is free (Open Source).

I noticed that on this forum you are most interested in the tall ships, and that these plastic kits slowly disappear from the shelves. I think that it is possible to recreate at least the hull and eventually some more "bulky" parts (like the guns) of these models on the 3D printer. (You can already find some interesting models, however they are created for visualizations). I am not sure about the rigging and the sails, but I suppose that there are several ways to recreate them. I can even imagine a community of the modelers who share such digital definitions, ready for 3D printing, available for everyone who would like to build a classic model of a historical ship...

In this post I will finish the rear part (the most difficult in this aircraft!) of the wing root fairing. I started this fairing in the previous post.

I previously formed the basic cone, up to the trailing edge. I created it as a separated object, to easier modify its topology. Now I copied into this mesh the further fragment of the fuselage, above the fairing (see figure "a" below):



I also created a small rounded edge along the trailing edge of the wing (figure "b" above) (more precisely — along its closing wedge, as in figure "c").

This inconspicuous part plays the key role in forming of wing root fairing. First, I extruded it up to the station 140, then I inserted in the middle additional edgeloop. Then I could bent this fragment at will, by moving and sliding this middle edgeloop. I aligned this mesh patch to the wing fairing contour in the top view. Then modified its vertical shape, bending this mesh patch around the fairing cone:



In the next step I extruded this patch from station 140 to station 195. I fitted its end to the bottom part of the bulkhead at station 195. Then I inserted in the middle two edgeloops (at stations 158 and 177). I shifted them on the planes of the corresponding bulkheads, fitting this wing root fairing to the reference cross-sections:



When it was done, I extruded the bottom edge horizontally, to the centerline. I created in this way the bottom surface of the wing root fairing:



While evaluating the bottom contour of the fairing in the side view, I realized that its shape depends on two factors. First of them is the fairing contour in the top view (because the trailing edge “slides” on the cone of the fairing upper surface). The second factor is the rounding radius of this trailing edge. To keep the bottom contour in accordance to the side view I had to decrease this radius a little (as in figure "a" below):



After these adjustments, I cut out the corner of the fairing cone, adjusting it roughly to the shape of the trailing edge (as in figure "b", above). Then I slided this last edge of the fairing cone, fitting it to the upper contour of the trailing edge. Finally I joined these two surfaces by adding a few new faces:



As you can see on the picture some of these faces have more than four edges. I left them in this state, because they do not disturb the smooth shape of the resulting mesh. (If I split them into a triangle and a quad faces, the triangles would disturb it a little).

As I mentioned before, I copied into this wing fairing object large fragments of the fuselage mesh. I did it to better prepare this element for merging with the fuselage. Finally I did it: I removed all unnecessary faces and created the new ones between the fairing and the fuselage. Figure "a" below shows this new fragment of the fuselage mesh in yellow:



Figure "b" above shows the resulting surface.

In this source *.blend file you can evaluate yourself the model presented in the picture above.

In the next post I will form the forward part of the wing root fairing.

Such a great tutorial!  Thank you for posting this, and thank you for making available your finished models.  They are great for studying. 

GAF - you are welcome !

In this post I will recreate the forward part of the wing root fairing. Basically, it is a variable radius fillet. It starts just at the wing leading edge and transforms smoothly into the cone of the rear wing fairing:



I extruded subsequent mesh segments of this fillet from the edge of the rear part of the wing fairing (from the point where I left it in the previous post). After each of these extrusions I decreased slightly the size of the last segment before extruding another one, obtaining in this way the variable-radius fillet:



Initially these new segments are disconnected from the fuselage mesh, although I fit them to both: the fuselage and the wing surface.

In fact the first two of these newly extruded fairing segments technologically belong to the rear part of the fairing. Thus I had to fit their surface to the three straight longerons that are there in the real airplane (I described details of this issue in the previous post):



The panel that connects the rear and forward parts of the fairing had a straight upper edge. Of course, I recreated it in the mesh (you can see it in figure above).

In the next step I merged these next three segments of the fairing with the fuselage:



Note that I added another section (edgeloop) in the middle segment of the fairing (as in figure above) — just to fit it better to the wing surface. I did not want to extend it across whole fuselage, thus I terminated it in a triangle at the upper edge of this fairing. Surprisingly, such a triangle does not disturb the resulting smooth, concave surface.

In figure above you can also see the auxiliary reference longerons, which helped me to ensure that this surface forms a straight line along their edges.

To merge the most forward part of this fairing with the rest of this mesh, I had to add more edges to the fuselage:



Each of these lengthwise fuselage edges “touches” the end vertex of corresponding fillet section. Once I placed them in this way, I removed the original fuselage faces and replaced them with the new ones. The right edge in each of these faces belong to the fairing:



When I did it, I used an auxiliary plane to evaluate the resulting cross-sections of this fairing along the fuselage centerline. It seems that the presence of the adjacent fuselage faces in the control mesh deformed the circular sections of the fairing around wing leading edge. I decided to fix this minor deformation by sliding the last edge of this fairing outside:



Finishing the wing fairing, I finished the main part of the fuselage:



In this source *.blend file you can evaluate yourself the model presented in the picture above.

In the next post I will form the bottom part of the fuselage (i.e. the part below the wing). I decided to build it as a separate object.

For this week I prepared the bottom of the SBD fuselage:

The designers extended the SBD Dauntless fuselage below the wing, creating there a kind of the bomb bay. However, it was too shallow to house even a 500lb bomb (see figure "a" below). (The ceiling of this bay was formed by the skin of the center wing). There was a single mounting point inside, and the bombs were always partially hidden in the fuselage. When the airplane was not carrying any payload, the bomb bay was closed by covers (see figure "b" below). They were bolted to the flanges punched in the fuselage skin along edges of this opening:



I suppose that in the future I will have to make some close shots of this area, thus I decided to recreate this detail “in the mesh”. This decision means that I cannot use the Boolean modifier to recreate this opening. In the effect, it will require much more work than similar details (like the landing gear bays) which I made in the wings. I will start working on the bottom fuselage in this post, and will finish it in the next one.

In one of the previous posts I created a reference shape that fits the contours of this bottom fuselage in the side and bottom views. Now I have turned its layer on, to see this reference object again (in figure "a" below it is in red):




I decided to create this part as a separate object — as it was in the real SBD. To begin, I copied the bottom part of the firewall into a new edge, and extruded it, forming in this way the first segment of the bottom fuselage (figure "b" above). Preparing for “cutting out” the bomb bay opening, I placed two sharp (Crease = 1) lengthwise edges in this mesh. They run along the opening borders (figure "c" above). To preserve the smooth circular cross-section of this body, these sharp edges are accompanied by adjacent, coplanar faces. (This is the same solution that I used for the rear gun bay opening in another post). These sharp edges will allow me to remove the faces from inside of this opening without altering the outer part of the resulting surface.

After extrusion of these initial two segments I extruded four more, up to the flap hinge:



I consequently marked as sharp the edges that follow the opening borders (as in figure "b" above).

When it was done, I created the bomb bay opening by removing its inner faces. I also removed most of the faces from the rear segment, because I have to modify the mesh in this area (as in figure "a" below):



In the view from bottom the rear edge of this opening had a circular contour. To recreate this effect I placed a quarter of 16-gon there (the symmetric side of this object on the picture is mirrored). Note the additional vertex at the external end of this “arc” — it helps to obtain a regular arc on the resulting curve. Then I projected (manually) the all six vertices of this polygon onto the reference body (see figure "b" above). Note also that the radius of this arc is a little bit bigger than in the bottom view on the reference drawing. After studying some photos I decided that it was slightly larger than on the reference drawing.

In the next step I extruded the inner segments of this edgeloop into a new surface strip:



Immediately after this extrusion I “flattened” this edge (by scaling it along the Y direction to 0), then adjusted its vertices on the XZ plane, fitting them to the reference contour. I also extruded forward the last vertex of this edgeloop, forming in this way the last straight segment of this opening border.

Finally I created new faces, filling the gap between these new edges and the remaining mesh:



Finally I created new faces, filling the gap between these new edges and the remaining mesh:
When the central opening was formed, I extruded the tip of this body (the part below the flap — as in figure below):



I will have to separate this tip later, because it was attached to the flap. To ensure that this separation will not deform the resulting meshes, I marked the future split edge as sharp (Crease = 1). Then I adjusted shape of this tip to its contours on the side and bottom views. Finally I created the rounded tip, by rotating its last “bulkhead” edge around Z axis. (Frankly speaking, I can see no special reason for the existence of such a tip. I can only guess that, beside the aesthetic reasons, its presence allowed to preserve a little more height in the rear area of the bomb bay space.

I created the circular cut-outs for the wheel bays as in the wing — using the same auxiliary objects and additional Boolean modifiers (as in figure "a" below):



Strangely enough, for this object the Boolean modifier works “in reverse”, and I obtained the proper effect using the “Union” (!) instead of the “Difference” mode. Once I did it, I adjusted the shape of the wheel bay flanges, fitting them to the bottom fuselage (as in figure "b" above).

In figure below you can see the final object I created in this section:



In this source *.blend file you can evaluate yourself the model presented in the picture above.

In the next post I will continue my work on this assembly. I will recreate the covers for this opening, as well as their mounting flanges.

Sometimes the relatively simple shapes may require some substantial amount of work. In my previous post I created the basic shape of the bottom fuselage. It occurred quite complicated, because I decided to recreate the opening of the bomb bay “in the mesh”, instead of using the Boolean modifier. In this post I will complete the remaining details, enlisted in the illustration below:



I started by forming the bottom part of the fairing along the wing leading edge. It is not as difficult as the upper fairing. To show you the basic idea I just added a new edge loop near the firewall, then I moved down the corner vertex downward. As you can see below, the resulting surface starts to wrap around the wing:



Then I added another edge loop, adjusted locations of some vertices, and extruded fragment of this mesh in the spanwise direction:



As you can see in the figure above (left) I hid the upper edge of this fairing below the lower edge of the upper fuselage panel. (You can see these overlapping panels on the close-up photos of the real aircraft).

When I finished the wing root fairing, I recreated the bottom covers. I started each cover by copying the border edges from the adjacent meshes (as in picture "a", below):



Then I adjusted these edges, matching the number of corresponding vertices. Once they were ready, I connected them with the strip of new faces as in figure "b", above).

However, this cover was not completely flat! To fit it to the side view contour (and the reference shape) I inserted a new edgeloop in the middle of this mesh. Then I adjusted its height, fitting it to the contour of the fuselage:



These removable covers were bolted to the flanges that extrude from the bomb bay edges. To obtain a better fit, these mounting flanges were stamped by the sheet metal thickness (as in figure "a", below):



How do I form such a “depressed” flange? I started by extruding its borders (see figure "b", above). Then I connected these faces into a single strip (as in figure "a", below). Finally I extruded these faces (not edges!) along their individual normals (I shifted the extruded faces using the Shrink/Fatten command) as in figure "b" below:



Finally I marked the outer edge in the control mesh as partially sharp (as in figure "c", above) to improve the profile of this flange.

Figure "a" below shows the layout of the newly created cover panels. After all these modifications it is good idea to match this result against the available photos. As it often happens, I discovered that I should do it more often: there were some errors in this initial arrangement:



Well, in fact I had to rebuild anew the side doors and the rear cover (repeating all the tasks depicted earlier in this post). You can see the final result in figure "b" above.

Note that I slightly reduced the width (i.e. radius) of the rear cover. I decided that I was wrong estimating its size in my previous post. This time my reference drawing was right:



Figure above shows the completed bottom part of the fuselage (I hid the removable covers). As you can see, there still are many small details that I have to recreate during the detailing stage.

In this source *.blend file you can evaluate yourself the model presented in the picture above.

The issue that I had with the bottom covers shows that I should do such a verification from time to time! In the next post I will “step back” a little and match the overall shape of this model against the photos. I will do it using a new method.

Once again, beautiful work and attention to detail.  While you cannot touch these models, I have seen some incredible artworks produced with virtual aircraft, so there is that.

I do wonder about using photos for reference, and how you know this image is from the SBD version you are attempting to model?

Gary

Gary, thank you! I will do my best :)

GAF

I do wonder about using photos for reference, and how you know this image is from the SBD version you are attempting to model?

Some months ago I analyzed the differences between Dauntless versions. (You can find description of the identified differences in the previous page of this thread, in my posts from 11th ad 18th July 2015). One of the conclusions was that behind the firewall the geometry of this airplane remains constant from the first to the last version. The differences were in minor details: additional cutouts behind the gunner cockpit for the doubled ammunition feeder in the SBD-3,  the reflector sight in the SBD-5 instead of the old-fashioned telescope. Thus I can use use every Dauntless photo.

_{P.S. As you have already noticed, I recently found the Britmodeller forum. Despite that I already have run this project for six months, I decided to start publishing the archival post there, because I think that it is another opportunity for interesting discussion. Initially I am going to publish these archival posts on that forum twice a week, so within a few months they will become up to date with this thread. Then I will continue tehse threads in parallel.}

During the previous weeks I formed two main elements of my model: the wing and the main part of fuselage. As you saw, I could not resist myself for adding some details to the wing (like the ribs and spars of the flaps).

Now I think that this is a proper time to stop modeling for a moment and compare the shape of the newly modeled parts to the real airplane. If I find and fix an error in the fuselage shape now, it will save me from much more troubles in the future! If I find an error in the wing shape – well, I will have more work, because I already fit it with some details which will also require reworking… You will see.

The idea of using photos as a precise references emerged from the job that I did two years ago. One of my colleagues asked me if I can recreate the precise shape of the stencils painted on an airplane. He wanted to determine details of the numbers painted on the P-40s stationed in 1941 around Oahu. He sent me the photo. I started by fitting the 3D model to this historical picture, finding by trial-and-error the location and focus of the camera (as in figure below):



Then I made the model surface completely transparent. I placed the opaque drawing (texture) of the large white tactical numbers on its fuselage, and the black, smaller, radio call numbers on the fin. I rendered the result over the underlying photo, finding all the differences. Then I adjusted the drawing and made another check. After several approximations I recreated precisely shapes and sizes of these “decals”.

The key point in this process was to recreate the location and focus of the camera that was used to make the particular photo. Now I realized that it is possible to use the photos in the same way as precise references for my model. All I needed was a high-resolution picture.

I decided to begin with one of the archival photos of the SBD-5 from VMSB 231, made in spring 1944 (the original photo below is 2127px wide):



To find the camera projection that fits the model into airplane contours on the photo, you have to coordinate the location of the camera and its direction (I used for this purpose an auxiliary “Target” object). Yet another parameter to be adjusted is the camera lens length:



The whole process is an iteration: I started from a rough first approximation (as in figure above). Then I enhanced it, gradually determining the ultimate camera and target location, as well as the focal length.

In this process I based mostly on the elements which dimensions were determined by the “hard” evidence. It pays off that I placed most of the the fuselage mesh edges along the original bulkheads and longerons. (I will also benefit from this during further stages of my work). I was quite sure of the bulkhead stations because they were set according the original diagram. Thus I started by fitting to the photo the fuselage between the firewall (station 0) and the last bulkhead (station 271). Then I tried to find the proper camera focus that fits the middle bulkheads to the rivet seams and panel lines which are visible on the photo:



I was also able to fit to this photo the root rib of the outer wing panels. However, I could not match the position of the wing tip! When I fit this tip to the photo, the fuselage deflection was wrong. Otherwise, as you can see (in the figure above) the wing tip of the model was a few inches below the tip on the photo. I started to wonder why I have such a problem…

Figure below shows the best projection I was able to find. The fuselage bulkheads fit well the seam lines from the photo. It seems that the bottom contour of the tail was somewhat lower than in my model:



The only weak point is the different elevation of the wing tip. I cannot say that it had a greater dihedral, because it was dimensioned on the original general arrangement diagram (7⁰ 30’ along the upper wing contour, in the front view).

Finally I came to conclusion that what I can see on this photo is the elastic deformation (bending) of the loaded wing! This aircraft here is depicted in the flight, right? This means that these wings are carrying the load of about 4 tons of its weight. Their structure was stiff, but not absolutely rigid: every beam deforms (more or less) under the load. The airplane wings are not the exception: while flying in an airliner (like Boeing or Airbus) you can observe how their wing tips bend in the air. Of course, the relatively short, wide wings of the SBD Dauntless were much more resistant to such deformations. Nevertheless I think that we can trace the slight bending of this wing leading edge on the other shots of this airplane. For example, the white sun reflection on the photo in figure below allows me to reveal this dynamic deformation:



We can see here the bending of the outer wing panel. However, there was another deformation: in its joint with the center wing. The root rib under loads slightly rotates around the wing chord, which elevates the wing tip even further (in figure "b", above). I suppose that the center wing was much stiffer (it had thicker airfoil and shorter span than the outer panels).

Frankly speaking, this conclusion was a little surprise. I have not noticed such a deformation before — maybe because I was mainly focused on the WW II fighters? Fighter wings are the stiffest ones…

In the airplane standing on the ground the wing deformation is minimal, thus such a picture suits better the reference purposes. Ultimately I decided to use some of the photos published by the Pacific Aviation Museum on flickr.com. Figure below shows the result (I had to flip this photo from left to right because I modeled the left wing):



As you can see, the wing perfectly fits its contour in this photo. I have found that the left aileron airplane was rotated upward by about 4⁰. I can see some differences in the hinge location of the upper wing flap (on the photo it seems to be placed at somewhat different angle, and shifted to the rear). The contour of the aileron bay also seems to be a little bit lower. On the fuselage you can see that the bottom contour of the tail is placed lower than in my model — confirming the observation form the previous photo.

When you find deviations as these that I have found in the aileron and flap hinges, it is always a good idea to check them on another photo. Thus I fitted my model into a different picture from the same PAM photo stream on flickr:



In this case I opened the wing flaps, because their straight contours helped me in precise positioning of my camera. It was possible to fit the bottom flaps to this photo (I just discovered that in this photo their deflection angle is 40⁰, while according to the specs it should be 42⁰). I was able to verify locations of their ribs and spars. (It occurs that these ribs, set according the stations diagram, are in the proper places). However, the upper flap did not fit properly into its contour in the photo. It was only possible when I shifted its hinge to the rear, placing it as in figure above. In this way I confirmed that these wing elements require corrections.

After these initial findings I decided to verify both: the wing and the fuselage, to fix all the differences I would find. Of course, it required more photos. Matching the model projection to a single picture takes me several hours of work (usually — one evening). I assigned to each of these pictures a separate camera (as well as the camera target object). Their names are three-letter shortcuts of the source photo followed by the ordinal number: thus PAM-1 means “Pacific Aviation Museum – 1.jpg”, UND-1 is “Unidentified – 1.jpg” and so on. I think that these reference pictures will be also useful in the future stages of this work. Switching between these cameras requires several steps: you have to type the path to the corresponding photo, as well as to alter the scene renderer aspect ratio. To facilitate this operation I created a dedicated add-on, which allows me to switch between these pictures with one click:



The ability to immediately switch between various reference photos definitely makes the difference! It encourages to study the same fragment from all possible sides.

In this source *.blend file you can evaluate yourself the model matched to the first picture from the Pacific Aviation Museum.

In the next two posts I will write about the results of this verification. In the first one I will describe the errors that I found in the shape of my fuselage. In the second post I will describe the differences that I found in the wing. Sometimes fixing these minor errors require several hours of work… But this is why we are the modelers (“a slightly different human being” ).

Currently I am using the method discussed in previous post to verify teh geometry of my model. It is a good idea to do it when there are no additional details. All the differences that I will find now will save me a lot of troubles in the future. For example — what if I would find that the base of the cockpit canopy in my model should be somewhat wider, when this canopy was ready? I would have to fix both shapes: the canopy and the fuselage. And what if I would already recreate the inner fuselage structure — the longerons and bulkheads — before such a finding? I would also have to fix them all. This is a general rule: the later modifications require much more work than the earlier ones! Thus I have to check everything when the model is relatively simple. You can compare the differences I will find in this post with the plans I published earlier in this thread: they contain various minor errors! Just as every drawing.

Last week (see my post from 2015-12-06) I discovered that the bottom contour of the tail was somewhat lower than in my model:



The main problem with mapping the tail shape was that its bottom part behind the wing was wide and completely flat. On every photo that I have the airplane is more or less deflected toward the camera, so the precise bottom contour of the SBD tail in the side view is an average of multiple estimations. That’s why it can be wrong on my scale plans! I also found a minor difference in the forward part of the fuselage below the wing. However, its forward part on the photo above is obscured by the truck. Nevertheless, I guess that the forward part of this cover it had a straight side contour, located minimally below than this contour in my model. To check this I mapped another photo of the firewall:



This photo confirms my observations from the side view picture. Although the bottom of the fuselage here is lacking the bottom covers, the corner of their mounting flange “touches” the bottom contour of my model. It means that the real contour was somewhat lower, more or less along the yellow line that I sketched on this picture. However, you can see here another difference: the upper part of the firewall is little wider than the elliptic contour that I assumed (It seems that the shape of the firewall was not an ellipse, as I assumed in one of the previous posts).

To make sure that this is not a mistake in the matching the model and the photo (or the effect of a barrel distortion), I also used another picture, from other restoration:



The photo above confirms that the fuselage was little bit wider at the cockpit edges than it is in my model. The trace of the bolt seams on the wing reveals another difference: the wing root fairing was also wider (at least its forward part).

To make sure that this difference is true, I have to find it on every photo that I map onto my model. Thus I mapped two other photos. They come from Pacific Air Museum. I can use them to verify the width of the mid-fuselage and the span of the rear part of the wing root fairing:



The good news is that the maximum width of my fuselage perfectly matches the photo (a good luck!). I found that the width difference at the cockpit edges found at the firewall is (approximately) constant along the whole length of the cockpit (figure "b", above). It disappears behind the cockpit (i.e. in the front of station 140). The wing root fairing was somewhat wider at the trailing edge (figure "a", above).

As usual, I used another photo to confirm these findings:



Because this photo depicts the whole fuselage, I had to check these details using higher zoom factors. This photo confirmed what I have found in the previous one. In addition, it seems that the width of the fuselage in my model matches the real contour of the tail up to station 271.

Once I confirmed all these differences, I had to fix my model.

The wider wing root fairing behind the trailing edge can create impression of lower tail contour on the photos taken from the side (in the first photo in this post). This is because none of these photos is an ideal side view shot. In each of them the camera was located above or below the fuselage centerline. That’s why I decided to begin by fixing these differences in the fuselage width:



Once they were corrected, I could fit the side contour, matching it to the horizontal photo of the tail:



As you can see in this picture, I also minimally modified the upper contour of the fuselage. (Because the upper arc of its cross sections was looking like a part of a flat ellipse, while it should be a regular arc).

Figure below shows the ultimate differences between the reference drawings I created several month ago and the contour obtaining from matching the 3D model to the photo:



As you can see, nobody is perfect, so I also did some mistakes. However, I was aware that the bottom contour of the fuselage was a guess: I did not have any photo where it was directly visible. All the pictures were taken from below or above, leaving some space for various assumptions (which often results in some errors).

Finally I fit the covers on the bottom fuselage (below the wing) to their contours in the photo:



I moved slightly downward the forward part of these covers. As you can see in figure "a", above it was a relatively small difference. Initially I assumed that the cross sections of this bottom fuselage were elliptic arcs. However, in such a case, for the given width and height (from the side and bottom views), the edges of the wheel bays would appear a little bit lower than those visible in the photos. Thus I think that the contour of the middle cover in the front view had a slightly different shape (as depicted in figure "b", above).

In this source *.blend file you can evaluate yourself the model from this post.

While matching the model to the photo (PAM-3) taken from left side, I noticed slight differences in the wing rib shape: it seems to be a little bit thicker than on the picture. I will analyze this and other differences of the wing in the next post.

In this post I will continue verification of my model by matching it against the photos. This time I will check the wing geometry.

In the first photo from the Pacific Aviation Museum (in my model it is marked as PAM-1) I identified several differences:



First I noticed that the hinge of the upper flap in my model is in the wrong location (I had to shift it forward by 0.7 inch). The upper edge of the aileron bay had slightly different shape on this photo. In this picture the tip of the aileron (the point lying on the wing tip outer edge) is located in the front of the corresponding point in my model. (The difference is less than 1 inch). Surprisingly, the inner (root) rib of the aileron seems to be a little bit higher in my model than on the photo. I can see also similar difference in the root rib of the outer wing panel. Location of the aileron bay upper edge on this photo can also be interpreted as located below the corresponding edge in my model. Does it mean that I made an error in forming this wing? The last visible difference are the outlets of the fixed slats. According the photo they were smaller and set at slightly different angle.

To check the differences in the wing thickness and the details around its trailing edge, I matched my model to another photo:



I opened the wing flaps to better match the projection of my model to this photo. I used the shorter edges of the flaps to precisely determine their deflection. The bottom flaps fits well into this photo (if you take into account that in the depicted airplane the outer flap is bent). To fit the upper flap I had to shift it by 0.8 inch, as shown in the previous photo (as in the first figure in this post). This confirms that there is a difference! What is interesting, the wing on this photo is also slightly thinner than in my model — which confirms that I made a mistake in recreating the shape of its ribs.

As I wrote, I was convinced that I properly recreated the airfoil shape. I used the original coordinates of the NACA-2415 (and NACA-2409) airfoils (as you can see in figure "a", below)! Thus I used another, side photo (PAM-3) to check this finding:



The overall chord of the wing rib in figure above seems to be OK (luckily, on this photo you can see the fragment of the leading edge between the truck forks). The chord of its bottom flaps in my model also fits corresponding chord on the photo. However, the upper edge of the root rib in my model seems to be too high (by about 0.3 inch). I can see clearly that it occurs in the middle of the upper flange of this rib. On the scale plans this difference corresponds to just half of the contour line width! That’s why we have to use photos: the drawing conventions alone make the scale plans not as precise as we wish… The PAM-2 photo reveals that this difference (maybe somewhat smaller than at the root) extends over the whole wing span.

Well, so I had to fix it. While lowering the upper part of the center wing was relatively easy (figure "a", below), I had also to modify all the adjacent objects — ribs, spars, and the fuselage



The more difficult was to make similar modification in the outer panels. The difference was smaller at the wing tip. To preserve the straight lines of the spanwise mesh edges I moved the whole selected area down by 0.3 inch, then compensated the difference at the wing tip by small rotation around the wing root chord. (I had to separately rotate each of these “longeron edges”). Of course, then I had to make a lot of minor compensations in the upper flap and the aileron contours.

However, I had to modify these trailing edge details anyway, following the other findings from the photos:



In this modification I had to revert the changes I made three months ago to the aileron bay edge (in my post from 2015-09-12 about details of the outer wing panel). It was the wrong location of the flap hinge, while the aileron bay edge should be in the place depicted on the reference drawings! In fact, drawing these scale plans I assumed that the hinge of the upper flap was directly above the hinge of the bottom flap. (You cannot see the difference on the most common, horizontal photos). Now I know that it is shifted away from the auxiliary rear spar by about 0.8 inch. After this modification I had to shorten the chord of the upper flap and rotate its ribs and spars, adjusting them to the altered directions of the flap skin. It required a few additional hours...

Once I finished with the trailing edge, fixing of the outlets of the fixed slats was easier. I just had to modify the shape of the “cutting tool” auxiliary object, used in their Boolean modifier:



Then I adjusted the slat internal surfaces, fitting their upper edges to these modified openings (as in figure "b", above).

If I encountered such surprises on the upper wing surface, what do I find on the bottom of the wing? I started by examining the outer wing panel:



It was surprisingly difficult to find an appropriate projection for this wing — I badly missed the fuselage here! (It would allow me to better determine the proper direction of the camera). The barrel distortion of this photo could also have some influences on this matching. Fortunately, it seems that my model fits better this area of the real wing. The first difference I found was in the fixed slats: minor adjustment of their direction and sizes. I fixed them in the same way as their outlets on the wing upper surface (I will not bother you by describing the details). Another difference is more subtle: it seems that the real wing tip has slightly different shape than in my model!

Of course, I had to check it on another photo, taken from another direction:



This photo confirms my finding: it seems that I made another wrong assumption about the shape of the wing tip. (I assumed that the rear part was a single arc, while it is at least a smaller arc and an unidentified curve — maybe short piece of another arc of larger radius?). Of course I accordingly modified the wing tip (by adjusting location of a few of its vertices — in fact it was not as complicated as it sounds).

For the complete verification of the wing, I used the picture from the SBD manual. I checked the bottom surfaces of the center wing:



To speed up narration in this post, the picture above is showing the updated mesh. I just enlisted the modifications that I made. As you can see I had to adjust the outer edge of the wheel bay (because it was not a simple circle). There were some minor differences in the split lines of the bottom covers (I had to adjust the bottom fuselage! Again!). Ultimately, I discovered that I placed the fixed ribs above the flaps in wrong locations (I really do not know why I not followed the stations diagram— now I corrected this mistake).

In this source *.blend file you can evaluate yourself the model from this post.

This is the last post about this “great verification”. Now I am coming back to modeling. In next two posts I will recreate the empennage of this aircraft.

In this post I start to work on the tail assembly. The horizontal tailplane has similar structure to the wing — but it is simpler. Thus I started it in the same way as the wing, by forming its root airfoil:



In the most of the aircraft the tailplane has a symmetric airfoil. So it was in the Dauntless. I did not find its signature (family) in any of the reference materials, thus I carefully copied its contour from the photos (its rear part — the elevator — seems to have modified shape, anyway). It has incidence angle of 2⁰, so I rotated the rib object and used a Mirror modifier to generate its bottom part.

During this work I decided that I will use this rib as an auxiliary reference object for shaping the horizontal stabilizer. To precisely match the contour copied from the photos, I rotated part of this curve in the top view. Now it runs along the outer edge of the tailplane fairing:



However, because I am going to copy this rib into the initial edge of the horizontal stabilizer, I already prepared three vertices for the leading edge of the elevator (as in the figure above).

During this work I was struck by the idea that it is stupid thing to model the whole empennage, and then to verify it against the photos. The much better approach is first to “draw” in the 3D space their contours and match them to the photos, then to model their surfaces. In this way I can identify errors in my reference drawings before I start the modeling! The parts formed in this “verified” way and continuously matched to the references will have better quality!

Thus I interrupted forming the horizontal tailplane, and quickly shaped another auxiliary object — the contour of the rudder and fin:



What’s more, I decided to recreate in the model the basic reference “trapezes” of the fin and rudder. They are determined by the explicit dimensions in the general arrangement drawing, which I already used some months ago to draw the 2D reference drawings:



While in the model space the 1 unit corresponds to 1 inch, I did not need to multiply every dimension by the scale coefficient. It was a big surprise when the trapeze drawn according these re-applied dimensions occurred shifted left by 0.7”!:



I immediately did the same test for the horizontal tailplane. It also was shifted by 0.7”!:



Well, such a coincidence suggest that I made a kind of systematic error in calculating locations of the elevator and rudder axis for my scale plans. Most probably there was something in their extremely long position, measured from the wing leading edge (see the general arrangement diagram in the fourth figure from this post). For example, it could be a rounding error of the scale coefficient!

If I was wrong in this case, I could made other errors. I decided that it is proper time to re-use the original photos from the web page of Chino Planes of Fame Air Museum. Their resolution is only half of the resolution of the photos from Pacific Aviation Museum Pearl Harbor. However, they were made using a long-lens camera. (You can read that the standard length from the EXIF section of the Chino photos — it was 400 mm. The photos from Pacific Aviation Museum Pearl Harbor were made with the standard lens length: 36 mm).

Using this focus length, it is easier to fit the model and the photo:



As you can see, this is a flying airplane — and there is no visible dynamic deformation of the wingtip! This means that the whole “theory” about the wing deformation that I described in my post from 5th December was wrong! The wing is much stiffer than I thought. The deformation of the historical photo can have other reason. It could be significant barrel distortion of its lens, or the deformation of the negative. I do not know.

I verified contours of the horizontal tailplane by matching the model to another photo:



Note, that this is another photo that I used to draw my scale plans. However, this time I left it unaltered, to avoid eventual errors that I could made by setting it horizontally and scaling.

In general, the model fits this photo pretty well. However, there are small differences at tailplane and wing tips. I started to suspect that such a photo can still have a small barrel distortion.

Finally, I used the third Chino photo to further verify the side view:



The dimensioned contours of the empennage helped me to match better the other photos. For example, I slightly updated the projection parameters of the SBD-5 pictures from Pacific Aviation Museum Pearl Harbor:



The contours of the tail and fuselage fits the photo pretty well. There is just a visible difference in the wing tip spans — I think that this is the effect of the barrel distortion.

In this source *.blend file you can evaluate yourself the model from this post.

Well, I started to build the tailplane in this post, but this process ended in another verification. However, it spared me from similar check that I would have to perform on the finished empennage. Now I can quickly build this assembly — in the next post I will finish the horizontal tailplane.

I think your supposition about wing "deformation" in flight is correct, except it is not uniform throughout the flight.  Wing "wobble" is present in most aircraft to a greater or lesser extent, so using an image of aircraft in flight by over-laying your model for wing positioning and dimensions is only approximate.

http://www.ondair.net/the-science-behind-why-airplane-wings-wobble-in-turbulence/

If you can get your tolerances down to only around 1/8 inch, then you've done extremely well.

Thanks for posting this great tutorial!

Gary

Thank you, Gary!

GAF

I think your supposition about wing "deformation" in flight is correct, except it is not uniform throughout the flight.  Wing "wobble" is present in most aircraft to a greater or lesser extent, so using an image of aircraft in flight by over-laying your model for wing positioning and dimensions is only approximate.

You are right - I think that the truth "lies in the middle", as usual: sometimes there can be a small influence of the dynamic wing deformation (even more or less "wobbling"), in other cases the picture on a photo can be deformed because of different reasons...

After some verification of the reference contours that I described in the previous week, I am coming back to modeling of the horizontal tailplane.

In the previous post I created the reference airfoil of its root rib. Now I copied it into a new object, straighten along the fuselage centerline, and finally extruded spanwise:

I checked the resulting shape, ensuring that the thickness of the tip ribs matches their counterparts on the photos:

When this base shape was verified, I started to form the curved contour of the tip. Basically, it was an arc, thus I shaped it by extruding and rotating subsequent mesh segments:

Preparing the horizontal tailplane for such a mesh topology, I used the same number of rib vertices to form the leading and trailing edges of its root airfoil.

In the next step I created an additional gap in this mesh, at the point where it will be split between the stabilizer and the elevator (as in figure "a" below):

Such a gap deforms the original circular contour of the tip. To restore its shape, I had to move a little two nearest vertices on each side of the gap. Facilitating this task, I used an auxiliary circle as the reference shape.

To fill the empty space inside the tip, I extruded the internal edges of the last rib (as in figure "b", above).

I slid the last vertex of the edge that runs along the elevator leading edge, forming in this way the angle visible on the reference drawings (as in figure "a", below). In fact, its location was re-checked on the reference photos, thus it lies in a slightly different place than you can see on the underlying scale plans.

Of course, I also scaled the thickness of this newly formed “rib” (as in figure "b", above), aligning it to the slope of the previous, trapezoidal segment of this tailplane.

In the next step I started to build different topologies in each part of this tip mesh. In the “stabilizer” part I joined the “tab” of the internal faces and the leading edge (as in figure "a", below). In the “elevator” part, I removed the first and the last face of this tab, and shifted the vertices of the middle face, forming a thinner trapeze. Then I extruded the outer edge of this face several times, rotating them around the “corner” of the elevator leading edge. Note that each of these faces corresponds to a single mesh segment on the tip external contour:

I also joined the “gap” in the tip contour into a single, “sharp” (Crease = 1) edge. (In fact, I should create it as a single sharp edge in the beginning). Such an arrangement allows me to quickly create an array of new faces that closed the tip of the elevator (as in figure "b", above). Note that I filled the gap in the “corner” using two quad faces.

To match the topology of the elevator tip, I had to add additional “rib” to the stabilizer mesh. I did it in three steps. First, I created edges that joined the corresponding vertices of the tip external contour and the internal faces (as in figure "a", below). Then I split them by half (using the Subdivide command). Finally I used all these vertices to create new faces (as in figure "b", below):

Note that I had to create a single triangular face near the leading edge (see figure "b", above). Fortunately, the mesh curvature in this place is low enough that it does not disturb the resulting, smooth shape of the tip.

When the overall shape of the tailplane was ready, I split it into the stabilizer and elevator objects. I did it by copying the original object and then removing the “elevator” part of its mesh faces (figure "a", below):

Similarly, I removed the “stabilizer” faces from the elevator object (see figure "b", above). Ultimately I also simplified this mesh by removing one of its “longeron” edges. (It seems that the tip contour in the front view requires just a three-point curve).

The elevator of the SBD Dauntless had an oval leading edge (it was the aerodynamic compensation, an area shifted in the front of the hinge line). I started to form this element by inserting on the symmetry plane a circle (consisting 12 vertices):

Then I extruded it spanwise, adapting its radius to the local airfoil thickness (as in figure "a", below):

In the next step I removed the rear faces from the leading edge cone, and joined it with the rest of the elevator mesh (see figure "b", above).

The presence of a single middle edge in the elevator tip allowed me to remove similar edge from the stabilizer tip (as in figure "a", below):

Of course, it would be even easier to not create this edge at all — but this is typical situation, when I modify the initial concept of the mesh topology during the progress of the work. Figure "b" (above) displays the resulting tailplane assembly.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will describe my work on tailplane fairing.

In the previous post I formed horizontal tailplane of the SBD Dauntless. In this part I will describe how I created the fairing between this tailplane and the fuselage. It is an easier part than the wing root fairing, because it is smaller and most of its cross sections are not circular.

At the beginning I cut out from the stabilizer its middle segment, along the root rib:



Then I “draw” the outer contour of this fairing in the side view. I also checked it in the reference photo (as you can see in the figure above).

Then I projected this “sketched” outer contour onto the fuselage. I did it by extruding its polyline into a face strip that crosses fuselage surface (figure "a", below), then finding the intersection edge of this mesh with the fuselage (figure "b", below):



The intersection edge was calculated by one of my Blender add-ons (named Intersection — you can download it from here). In general, it would be easier to extrude this edge horizontally (because I sketched this contour in the side view). However, I was afraid that the add-on will lost the track of the upper rear part of this mesh (the part that crosses just the upper tip of the fuselage surface). That’s why I initially shifted this contour close to the fuselage, and extruded it in a more-or-less perpendicular direction to the fuselage surface.

All in all, after this operation I have the three edges, which is enough to create the first version of a smooth fairing:



Figure below shows the initial smooth, subdivided mesh based on these three edges:



It starts to resemble the original element. I created here the new row of faces, from the middle edge to the outer contour. Then, before creating this screenshot, I switched the display mode to the resulting subdivision surface.

To have better control over the shape of this fairing, I inserted two additional edge loops into this mesh



These additional vertices were extremely useful in shaping the bottom edge of this fairing, which had a semi-circular cross section:



In the most of the aircraft designs the fairing is just a piece of sheet metal bolted over the fuselage skin. In the SBD Dauntless it was an integral part of the fuselage skin (except the area around the stabilizer leading edge). Thus I had to extend the bottom part of this mesh, copying the fragment of the fuselage surface (as you can see in the figure above).

Figure below shows the finished fairing. As you can see, it smoothly fits the fuselage:



It was not necessary, but I also created the rear spar of this tailplane — just because I do not like to see a large empty space in a finished element (the fuselage is not finished, yet!).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will create the fin and the rudder.

This week I have worked on the SBD vertical tailplane. I started by forming its root airfoil (see the figure below). I had no description nor a direct photo of the airfoil used here. However, the reference photos reveal that it could have similar shape to the airfoil of the horizontal tailplane. Thus I copied that curve into this mesh.



Note that I used here a thin strip of the faces instead of a single curve (which I used in the case of the horizontal tailplane or the wing). The reason is simple: on the single subdivision curve I cannot mark a “sharp corner” at a control point (original mesh vertex). On the face “strip” I can mark the corresponding edge as sharp (increasing its Crease coefficient to 1). I marked in this way the edge at the split between the rudder and fin. Simultaneously I can form such a face strip in the top view as easily as a single curve. (I just have to remember to select its vertices using the group select commands (Border-select or Circle-select), instead of the simple mouse click). Why didn’t I use this method in the previous cases? Well, good ideas require some time to emerge…

Once the root airfoil was ready, I extruded it into the basic trapeze:



Then I split this mesh into the rudder and fin (i.e. into separate objects, as in figure below):



Note that I added additional “rib” edges to the mesh of the fin. They will be useful in forming the forward fragment of this part.

Initially, I extruded the first approximation of the dorsal fin from the bottom edges of the lower ribs:



However, I decided that the resulting topology of this mesh differs too much from the original layout of the panel seams (and the original ribs and spars). To make a better approximation, I used the fin shaped in the previous step as the reference object (in the figure below it is in red):



I cut out the forward part of the original fin, forming in this mesh the first vertical edge. Then I extruded it into next segment:



The next segments were extruded in similar way:



In each new segment the vertical cross section is significantly smaller than in the previous one. I had to compensate it by cutting out its bottom fragment (using the Knife tool — as in figure above) and reducing the number of remaining faces.

Figure below shows the resulting dorsal fin:



The tip of this fin was formed in an unusual way — it was stamped in the cover of a fuselage hatch (as you can see on the photo). I will form this cover later.

Figure below shows the objects created in this posts:



You can examine them in this source *.blend file.

In the next post I will describe my work on the fairing of this fin (it seems quite simple, but occurred more difficult than I expected!).

In the SBD Dauntless the fillet along the fin and the fuselage was formed from the bent bottom edges of the fin panels. I am showing it in the figure below:



(To make some of these panel seams more visible on thee photos, I sketched along them thin lines). You can observe that each fin panel overlaps the next one, starting from the tip stamped as the part of one of the fuselage doors (see the second-last figure in the previous post). The outer contours of these panes are not perfectly aligned: you can see small overlaps on the photos (see the figure above). Surprisingly, such a detail makes the modeling more difficult. However, the most difficult part will be the seam between the fin and the horizontal tailplane fairings (as in the figure above). It runs along the fuselage longeron, across the fillet between the stabilizers and fuselage.

Well, I started this fillet by extruding some faces from the bottom edges of the fin mesh:



As you can see, I already recreated the sharp panel corners in these extruded faces. Then I lowered their outer edges and aligned them to their contours on the top view:



This is the first, rough approximation that fits these panels to the fuselage surface. In this process I discovered that I had to make some modifications to the upper part of the tailplane fairing. However, I was not entirely satisfied with the result: comparing to the photos, something was wrong at station 242 (see the figure above). The outer seam of the fin fillet should be a little bit wider here!

After some additional deliberations I decided that the fuselage under the fin was somewhat higher (by about 0.5”) than on my reference drawings, and the upper arc of these bulkheads had larger radius. Thus I had to modify this part of the fuselage:



I rotated a little this mesh fragment, then scaled up the upper part of each of its three bulkheads.

Basing on the corrected fuselage, I was able to fit better the outer edges of this fin to the fuselage and the tailplane fairing:



However, I was not satisfied with the forward part of the seam between these two fairings: despite all my efforts, it looked a little bit sharp!

Ultimately, I had to reshape a little bit the tailplane fairing and cut out the excess of its surface along this seam using a Boolean modifier:



This method produced results that resemble the smooth shape that I can see on the photos:



However, I do not like such a “Boolean – based” solution. It seems too complicated. In the next post I will try to eliminate such a “hard” seam between these two panels. I think that much better solution here will be a continuous, smooth surface. The seam can be recreated later, using textures.

Anyway, in this source *.blend file you can evaluate yourself the model from this post.

After the previous post I decided to simplify the empennage fairing. Originally I created it from two separate objects: the fin fairing and the tailplane fairing, split across their fillet. Now I decided to eliminate this troublesome seam by joining these two meshes into single object:



I will split it later, along the bottom rib of the fin (there was another panel seam in the real airplane). To simplify creation of the original overlapped panels, I simultaneously split the fin into the forward and the rear part, along one of the original seams.

As you can see in figure above, there are the same number of spanwise edges on both fairing meshes. It is a matter of sheer luck, but it makes the process of joining these two parts much easier.

First, I modified these edges, bringing them closer to each other. (I did it by sliding their vertices along perpendicular edges — as you can see in figure "a", below):



Then I removed the unnecessary faces (as in figure "b", above).

Finally I filled this gap with new faces, effectively merging these two meshes (figure "a", below):



In the side view (as in figure "b", above) you can see that the forward part of the fin extends a little the panel line visible on the reference drawing. It will be overlapped by the forward part, which will end precisely along the original seam. (Such an overlap is visible on the photos). Note also that the seam along the fuselage upper panel (marked on the drawing by the dotted line) is somewhat higher than on my scale plans. This is the effect of the modification that I made in the upper part of the fuselage (described in my previous post). My reference drawings are simply wrong about its location in the side view.

I think that the empennage fairing looks much better after this modification:



It fits well all the three elements it joins: the fuselage, the fin and the tailplane. The fillets looks smooth and natural. As you can see, I split the fin and the fairing along the bottom rib edge, as I planned. (There was original panel seam). I think that this new arrangement of the model objects will facilitate further detailing of this assembly (for example, now the forward fin panel overlaps the other elements, as in the real airplane).

The last element of this assembly is the fin tip: in the real airplane it was stamped in one of the fuselage inspection doors. I started to form this part by creating a plain, rectangular cover placed over the fuselage, and separating the corresponding fragment of the fin tip (figure "a", below):



Then I joined these two object into a single mesh (figure "b", above).

In the next step I adjusted corresponding edges of both elements, and removed the unnecessary faces (figure "a", below):



Finally I filled this gap with new faces. Finally, after some rearrangements of the mesh topology, the resulting elements looks like in figure "b", above).

Figure below shows the final object, fitted to the fin and the fuselage:



The last element that I need to finish in this empennage is the rudder leading edge. I created it in the same way as the leading edge of the elevator: from a single circle (see my post from January 9th). I extruded it into a cone (figure "a", below), then removed the unnecessary faces and created new ones (figure "b", below):



Figure below shows the completed empennage (note that I also created the fin spar):



The last missing element is the tail tip. It has a rather complex shape, so I started modeling this part by copying its outer edges from the fuselage, fairing, rudder and elevator. You can see them in the picture above. I do so when I have no clear idea how to start. In the next post I will describe what I did next.

In this source *.blend file you can evaluate yourself the model from this post.

The tip of the SBD tail was a light fairing, attached to the last bulkhead (at station 271 — see figure "b" below). That’s why you can see “NO PUSH” label on the photo in figure "a". The tail wheel was attached to the bulkhead 271, which transferred the resulting loads forward, via the tail structure. The tail tip fairing was always free of any significant loads. However, the shape of this part is a combination of the empennage fairing and the last fuselage segment. What’s worse, there is a large opening at the bottom — for the eventual tail wheel deflection:



I had no initial idea about the mesh topology that I should use for such a part. Thus I started by copying all of its external edges from the adjacent objects (see figure "a" below):



Then I worked out an idea of its topology by sketching possible mesh edges on a scrap of paper. (I often do that before I start modeling a complex mesh). You can see the scan of my sketch of this tip in figure "b", above. I “think by drawing”, so this method helps me to better realize the shape that I have to create. These working sketches object do not have to perfect. The more important thing is the order of the individual edges and vertices (identified by the numerical IDs).

When the mesh topology on the sketch looked simple enough, I started building this mesh by extruding the trailing edges of the elevator fairing (see figure "a" below):



Then I extruded the upper edge of the elevator fairing into another rectangular “patch” (see figure "b", above). In the next step I extruded similar “patch” from the rudder contour (see figure "a", below):



Finally I filled the gaps between these three mesh “patches” by creating two rows of new faces (as in figure "b", above).

The resulting subdivision surface required some minor adjustments of the control mesh vertices. They formed the proper shape of the mesh behind the elevator trailing edge (figure "a", below):



While sketching this tip, I decided that it will be better to close it with a separate object — the “closing strip”. Such a strip reproduces the original piece of the sheet metal that contained the frame of the running light. (I thought that the side-view contour of this tail tip might require different edge distribution than the mesh of its sides). At this moment I created the initial segment of the “closing strip”: the part around the running light frame. Then I used it as the reference object for shaping the mesh of the tip sides (see figure "b", above)

When the upper part of the tip was ready, I started forming its bottom part. As you can see in figure below, I did it in the same way as the upper fairing. First I extruded a part of the bulkhead contour (figure "a"), then I created new faces to incorporate this patch into the main mesh (figure "b"):



I extruded the side faces of this tip from the bulkhead edge (figure "a", below), then filled the gap in the resulting mesh by creating a row of new faces (figure "b", below):



(Note that I had to create more “bulkhead” edges in this mesh than I originally sketched (see the second figure in this post). Some of these edges came from the original vertices of the elevator edge, while the other were required by the shape of the bottom edge (around the tailwheel opening).

Finally I extruded and merged the last part of this tip:



As you can see in figure "b" above, I added an additional, diagonal edge below the trailing edge. I did it to obtain a better shape of the elevator fairing

Figure below shows the smooth resulting shape:



I had no photo taken from the top or the bottom that would precisely reveal the vertical contours of this part. Thus I assumed that this tip is a smooth continuation of the tail cone (as I marked with the dashed line in Figure 38‑9). In the next post I will verify this assumption using available photos.

In this source *.blend file you can evaluate yourself the model from this post.

In the previous post I formed the shape of the SBD Dauntless tail tip. In this post I will finish its “closing strip” that contains the running light frame. I will also verify the overall shape of the tail tip using the available photos.

There is one thing I didn’t mention in the previous post, just to keep the narration focused on the pure modeling. Before the modeling I carefully studied the reference photos. In the result I found differences in the shape of the curved trailing edges of the fairing behind the elevator. On the photos you can see a straight fragment of this edge (figure "a", below). Its presence means that the curve of the trailing edge was smaller, and the fuselage was somewhat thinner here. You can see the differences between the real shape and my reference drawing in figure "b", below:



I did not notice these detail before. As you can see, I applied this modification when I started to model this part.
When the mesh of the tail tip was formed, I worked on the “closing” strip. I created a part of it as a separate object in my post from 2016-02-13. Now I extruded it along the side contour (see figure "a", below), then extruded the side faces of this strip (figure "b", below):



I rounded the sharp edges of this element with a fillet. It is dynamically generated by a multiple-segment Bevel modifier — you can see the result in figure "a", below:



However, when I compared the bottom part of this tip to the photos, I saw that there are significant differences! Jut compare it in figure "a" and "b" above. The side edges of the tailwheel opening are less curved, and its rear edge is wider.

What is the reason of these differences? So far I tried to shape the bottom part of this tip as the smooth continuation of the previous tail segment (see figures "b" and "c", below). It seems that I was wrong: these lines were broken at station 271, where the tip fairing was attached to the last bulkhead of the tail (see figure "a", below):



To correct this shape, I first made the tailwheel opening wider by rotating the bottom part of the mesh:



Finally I adjusted the shape of the “closing” strip to this new opening (figure "b", above). Now it resembles the original in the photo.

When I fixed the shape of this opening, I noticed another difference, this time in the shape of the tip cross-section. It is revealed by the vertical panel seam behind the tailplane:



This vertical seam seems to be flat, especially in the restored SBD from figure "b", above. In my model this line is much more convex (figure "c", above).

Well, to make this section more “rectangular”, I have to make the fuselage even thinner in this area:



Yet the photos reveal another small difference, this time between the two different restorations of the SBD Dauntless: compare the photos "a" and "b" in the second-last figure above. The aircraft from photo "a" has the edges of the tailwheel opening bent inside, while in the SBD from photo "b" the tip cross-section contour is straight to the end. Which one is true? At this moment I do not know! However, it will be better to modify the mesh of this tip in a way that makes such a rounding possible. (You can always straighten a curved surface. However, bending a flat mesh requires additional edges). That’s why I modified the mesh topology around this opening, adding another “longeron” edge (figure "a", below):



Then I shifted two bottom edges a little (figure "b", above), forming such a cross section as you can see in photo "a" (compare it with the shape in figure "c", above).

Below you can see tip, finished for now:



I will recreate its internal reinforcements (bulkheads, stringers) later, during the detailing phase. At this moment I do not know whether I have to modify this part in the future. (It may happen when I find a better reference materials). Such a modification would require adjusting these internal structures, so it is better to postpone their creation as long as possible.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will start to work on the engine cowling.

You're pretty good at pushing verts, Witold!  I'm envious. :D

Watchmann

You're pretty good at pushing verts, Witold!  I'm envious. :D

Thank you! :)

Anyway, I published all my know-how in this guide, so you can easily adapt my methods!

SBD Dauntless had a radial engine hidden under typical NACA cowling. The Douglas designers placed its carburetor air intake on the top of this cowling, and the two Browning M2 guns behind it. In the result, the upper part of the SBD fuselage, up to the pilot’s windscreen, had a quite complex shape:



I am sure that I will tweak this shape multiple times before I reach the most probable compromise between all the reference photos I have. It will be much easier to do it by modifying a simple mesh instead of the complex topologies of the final cowling. Thus I decided to create first a simpler version of this fuselage section and adjust it to the all of the available photos. I will describe this process in this and the next post. Once this shape “stabilizes”, I will use it as the 3D reference in forming the ultimate cowling. Because I am going to recreate all the internal details of the engine compartment, I will create each cowling panel as a separate object.

I started by creating the three key contours of the NACA cowling:



Section 1 (see figure "b", above) was a perfect circle, while section 2 was a little bit higher than wider (see figure "a", above). Ultimately section 3 was a regular ellipse. Note that all these sections have the same number of the vertices (32).

Once I created these three edges, I connected them using three arrays of faces. Them I added in between (using the Loop Cut command) three additional edge loops. I needed them to form the curved forward part of this cowling:



As you can see above, I fit the silhouette of this NACA cowling to the reference photos. This is a photo of the SBD-5, so I moved this cowling forward by 3.5” (see in this post about differences between SBD-3 and SBD-5 cowlings Figure 4-6, for the explanation).

When I finished the NACA cowling, I formed the basic shape of the next fuselage section:



I created this part in the same way as the previous one. First I copied and shrunk the last NACA cowling edge, creating the gap for the outgoing air. Then I copied the firewall edge, and joined these two edges by an array of new faces.

In the next step I extruded the upper part of this surface, creating the section below the windscreen:



It is a “linear” continuation of the previous fuselage segment. I fitted its sides to the mid-fuselage, which I formed some months ago.
The next elements are the “bulges” that covered breeches of the Browning M2 guns. In this ‘quick and dirty’ approximation I formed them from a separate mesh patch (see figure "c", below):



Of course, I verified their shape on the available photos, as you can see in figure "c", above.

This comparison revealed, that the intersection lines between these “bulges” and the main fuselage require some improvements: they have to resemble straight lines:



To obtain such an effect, I had to decrease the upper radius of the last bulkhead (figure "b", above). In such a simple mesh it required just to move a few vertices. If I had to perform such an operation on the final panels, it would be much more difficult!

In the front of the gun barrels there were long recesses in the NACA cowling. The outer edges of such a feature are always a tough test for the model, because they depend on the proper shape of the both intersecting elements. First of these objects is the NACA cowling, the second is the shape of this recess — a cylinder in this case:



I cut these openings using a Boolean modifier. Figure below shows the result:



In figures "b" and "c", above, you can see the evaluation of the obtained contours. They seem to fit the borders of the recesses on the reference photos. (There are minor differences, but I suppose that they are results of the rounded edges of these features.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will continue shaping this first approximation of the engine cowling.

I don't want to interrupt your thread, but I was thinking about how earlier on you said that there were others who are better at this than you.

I have my own little corner of my base website where I show off my plastic models. Everybody there tells me how brilliant I am and wonderful my models are. I reply that not one of them could even compete in a contest, let alone win. All I see is the warts.

What I'm trying to say is, you say there are others better than you. Maybe, but I don't see it. I think your work is brilliant, and I've read this entire thread at least once through, and I keep coming back to see what's next. Keep up the good work.

Sailor Steve, thank you very much!

Just one thought about this fragment:

Sailor Steve

(...) you say there are others better than you. Maybe, but I don't see it.  (...)

 

In this post I will continue my work on the engine cowling. I started it in the previous week by forming a “first approximation” of the forward part of the SBD Dauntless fuselage. Now I will create the last elements of this auxiliary object.

First of them are the covers around the M2 gun barrels. They were hinged around their inner edges, and their cross-section varies from a semi-circle at the NACA cowling to a flat line at the firewall:



I started forming this cover from a conic cylinder, created around the gun barrel:



Then I cut out its bottom part and flattened its end section along the side “bulge”:



I formed it to resemble the gun barrel covers as they were in the SBD-1..-4s. Studying the photos I identified that this detail looks a little bit different in the SBD-5 and -6:



As the last element of this auxiliary object I will form the windscreen. I need it for determining the ultimate slope of the “bulges” around the breeches of the M2 guns, and for checking the shape of its intersection with the fuselage. (If I did it later, it could reveal some unexpected surprises about the fuselage geometry, resulting in additional work).

I used the reference photos to determine the basic radii of the canopy hood and the windscreen cross sections:



(In this aircraft canopy hood slide under the windscreen, thus the radius of the windscreen cross-section was a little bit larger). As you can see in Figure "b", abve, the obtained contours differs a little to my reference drawings. (It seems that on these drawings the top of the cockpit canopy is a little bit lower than I have ultimately found it now on the photos).

In the next step I determined the radii of the cylindrical fragment of the windscreen:



It seems that it was not a regular cylinder — its radius at the top of the windscreen seems to be larger than the radius at the bottom (figure "a", above).

I created this cylinder as the first part of the windscreen surface (figure "a", below). I verified its shape using another reference photo (figure "b", below):



In the next step I removed the rear part of this cylinder and formed the flat, triangular side plates of the windscreen. As you can see in figure "b" above), they were hinged, providing the maintenance access to the M2 guns on the cockpit sides.

Then I extruded two additional rows of faces, forming the upper part of the windscreen (figure "a", below):



When the shape of the intersection between the windscreen and fuselage matched the reference photos, I also verified its side contour (figure "b", above).

Figure "a" below shows the complete object that approximates the shape of the SBD engine cowling. I set its color to red, as I do for all the reference objects in this model:



In figure "b" above you can see that it fits pretty well the reference photos. This is a picture of the SBD-5 from Chino Air Museum. The SBD-5 and -6 had their engines and the NACA cowlings shifted forward by about 4”, so did I in this model (see in this post Figure 4-6 for details).

In this source *.blend file you can evaluate yourself the model from this post.

I've been following this since it started last year and think the world of this venture that you are on. You point out there are others into this and that's great. I , for one, appreciate that you are taking the time to post this here for all who are interested here to see. It may at times feel that you are posting to yourself as I don't see many responses, but I can tell you that I'm watching all this closely.

Joe

mustang1989

I've been following this since it started last year and think the world of this venture that you are on. You point out there are others into this and that's great. I , for one, appreciate that you are taking the time to post this here for all who are interested here to see. It may at times feel that you are posting to yourself as I don't see many responses, but I can tell you that I'm watching all this closely.

Joe

Thank you very much! Indeed, I want to popularize this new branch of our hobby. Posting in this thread is just a weekly reporting of the progress. Even when there are no answers, I can see the growing visit counter - and the 5-"star" rating, so it is not bad :).

In this post I describe a break in the modeling that I made this week, because I had to fix my reference photos before the further work. The reason for this fixing was simple: the NACA cowling of my model did fit only the long-lens photos. For the further work I needed more information. This information was available in the high-resolution photos made by the Pacific Aviation Museum Pearl Harbor. However, they are slightly distorted.

In the ‘mathematically ideal perspective’ calculated for the computer cameras all of the straight lines remains straight. Unfortunately, the real-world camera lens can slightly deform (bend) the straight contours. This is so-called ‘barrel’ (or ‘cushion’) distortion of a photo. Unless you are using a panoramic lens, this deformation is hardly noticeable for the naked eye. Unfortunately, these differences become evident when you place a photo behind a 3D model, projected by a computer camera.

In case of reference photos that I used to verify my SBD Dauntless, the differences caused by the barrel distortion are visible around the forward part of the engine cowling:



It is really difficult to find the precise shape of this airplane on such a deformed photo. Thus I started searching the Internet for a method that would allow me to revert this deformation. First I encountered some advanced tools, like Hugin software. However, it seems to require series of similar photos to make a really improved picture. None of my single photos met this criteria.

On the Internet I also found some general scientific/engineering papers about the barrel distortion, as well as the tutorials how to fix it (for the architectural visualizations). They advised to use some originally straight contours/lines visible on the photo to estimate the image distortion. Indeed, for the photos as above, I can use the splits between airstrip slabs as such a reference:



I marked these lines on the photo above using dashed line. To see better their deformation, I draw along them straight lines, in blue. Note that these straight lines are tangent to the dashed lines on the left side of this picture. On the right side of this picture you can see maximum deformation of these split lines. This is the evidence of the barrel distortion.

I tried to reverse barrel deformation of this image using these split lines as indicators. I used a simple Lens Distortion filter from GIMP 2-D graphic program. The idea was that when I apply a deformation that makes these lines straight. Maybe such an operation will reverse the whole barrel distortion in this photo?

Figure below shows the Lens Distortion filter dialog window (GIMP), which I used to find the proper “reverse deformation” for this photo:



As you can see I used only the first (Main) parameter of this filter. I decreased its value until the split between the airstrip slabs on the preview became straight.

Then I matched the projection of my 3D model to this photo:



This is really a rough, approximate method, but the obtained results look really promising! Now the whole cowling fits the modified photo!

If it worked well for this picture, I tried it on another one:



The SBD fuselage spans over the whole length of this photo, thus the barrel distortion is more visible here. You can see it in the fin and the last bulkhead (see figure "a", above), as well as in the engine cowling (see figure "b", above). However, the contour of the hangar roof was a great reference for the reverse deformation. What’s more, the GIMP dialog windows preserves the last used parameters. Thus I even did not have to adjust again the Lens Deformation filter! The same value of Main = -6.8 (as set in the filter dialog window - see the third figure in this post) made this hangar roof ideally straight. Both photos come from the same source, and their EXIF data reveal that they were made by the same camera. Thus I think that this deformation value is the “constant” property of this particular camera, which is repeated in each photo it made.

As you can see in figure above, after reverting the deformation, this picture perfectly matches the 3D model over the whole length, from the cowling to the fin.

During careful examination of all the nook and crannies of the fuselage, I encountered the difference at the root of the tailplane. In my model this rib seemed little bit shorter than in the photo (figure "a", below):



When all other element of this section fits the photo, such a gap means a real difference between my model and the original airplane. After some tweaks I decided that this rib was less deflected from the fuselage centerline (figure "b", above). (It seems that I made wrong estimation of its angle when I sketched these drawings). In fact, this rib run in parallel to the fuselage surface. Figure "c", above, shows that such a modified rib fits the reference photo pretty well.

I quickly converted most of the other photos from the same air museum. Unfortunately, I encountered the limits of this simplified method, when I tried it on the photos taken from a ¾ view:



I could not fit the model to the modified version of this photo! I had to revert to the original picture and its matching (using a slightly different lens length co compensate most of the barrel deformation).

For the consolation, I scanned again the Google image search (I have not done it for over four months). It was a fruitful idea, because I found two new reference photos, made by a long-lens (600 mm) camera. (They were published in this post from General Aviation News blog). The first of these pictures is even more banked aircraft than I have found before:



In spite of the same Navy blue camouflage, this is a different SBD-5 from Commemorative Air Force (note its '5' side number). It allows me to verify the important details of the vertical view: the width of the fuselage or the shape of the engine cowling. As you can see, the model fits this photo pretty well. In particular, I found here the confirmation of the new deflection angle of the tailplane root rib.

Another photo is an extremely high resolution (5400 x 3600 px) picture of the same aircraft, taken during landing. It allows me to check better the side view details:



Ultimately, on such a detailed picture I was able to find the dynamic deformation of the wing: it is slightly bent upward, so its tip is no more than an inch above its non-loaded location. The Dauntless wings were as stiff as in the fighters!

In this source *.blend file you can find one of these updated photos.

In the next post I will start to work on the NACA cowling details, using the reference objects formed in the two previous posts.

In this post I will shape panels of the Dauntless NACA cowling. Working on the scale plans a couple months ago I came to the conclusion that the basic shape of this cowling was the same in all the SBD versions (see Figure 4.6 in this post). You can find the differences in their ‘ornaments’, like the sizes and locations of the carburetor air intake, or the number of their cowling flaps. Thus I used the high-resolution, long-lens photo of the SBD-5 (described in the previous week), to determine the ultimate shape of this cowling, and the split lines of its panels (figure "a", below):



Basically, the SBD Dauntless NACA cowling was split into a single upper panel and two symmetric side panels. I started by copying corresponding part of the reference shape (created in this post) into the single side panel (figure "b", above). The subdivision surface of such a 120⁰ mesh ‘arc’ is somewhat flat at both ends. Thus I had to tweak a little mesh edges in these areas, fitting them to the reference contour.

In the next step I extruded the ‘strip’ that overlapped the upper panel (figure "a", below):



I also marked the bottom edge of this panel as sharp (figure "b", above). In fact, the right panel overlapped the left panel along this line (they were similar, but not identical).

What’s more, in the SBD-5 and -6 the split line between these panels was shifted left by about one inch. Nevertheless I decided that I will split these two panels later, during the detailing phase. At this moment I just dynamically mirrored the left panel using modifiers. It will be easier to unwrap in the UV space this single element, then copy its unwrapped mesh and form the right panel during the detailing phase.

To keep the topology of this mesh as simple as possible, I decided to cut out the exhaust stacks openings using a Boolean modifier:



The high-resolution photo was a very useful reference for the ultimate check of the shape of this opening. (Its contour contains two arches connected by short straight lines).

In a similar way I cut out the space for the cowling flaps:



Actually, I am preparing the three-flaps sections, as used in the SBD-1.. -4. Note that I used the same auxiliary object to cut the upper cowling panel.

The overlapping ‘strip’ along the upper edges of the side panels was chamfered just on the cowling leading edge (figure "a", below):



It would be very difficult to shape such an effect ‘in the mesh’ here, because of the two-dimensional curvature of this area. That’s why I created it using two auxiliary objects and another Boolean modifier (as in figure "b", above). This was the last detail of this panel, for the modeling phase.

The next element are the cowling flaps. Initially I created them as a three-segment ‘strip’ (one quad face per each flap). I marked all edges of this initial mesh as ‘sharp’ (Crease = 1). Once I determined the size and shape of these basic faces, I added new, internal edges and started to bend this ‘strip’ along the reference shape (red object in the figure below):



When this ‘strip’ was fitted to the reference cowling panel, I added temporary edges connecting their opposite vertices. These auxiliary lines helped me to determine direction of individual rotation axes of these flaps, as well as their origins (figure "a", below):



Then I separated appropriate fragments of this mesh into three cowling flaps (figure "b", above).

Finally I cloned and mirrored the three left cowling flaps into the three right cowling flaps (figure "a", below):



At this moment the right flaps objects have a negative scale, thus for the movement test I have to rotate these left and right flaps separately (along their local Z axes, using the Individual Centers pivot point mode — as in figure "b", above).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will form the gun recesses in the upper cowling panel. It will be a quite difficult detail!

Where did you learn this art?

SubarooMike

Where did you learn this art?

Well, I am a self-taught. I determined my methods using various available resources (books and tutorials). However, I paved the way for the others, describing everything in a comprehensive guide :).

The gun recesses in the aircraft usually are tricky elements. Their edges depends on the shape of two curved surfaces: the fuselage around the recess and the tubular inner surface. When you make mistake in any of these two shapes — you have to remodel the whole thing.

In the SBD there are two symmetric gun recesses in the upper part of the NACA cowling. Figure below shows the left one:



As you can see on the photo, these recesses were formed in a separate metal sheet. It was riveted afterwards to the main body of the NACA cowling. I will repeat such an arrangement in my model, because using a separate object for such a feature simplifies its mesh. (I can make this mesh denser than the NACA cowling around it, and still I do not have to worry about the topological implications). The sheet metal around these recesses seems to be relatively thick, which ultimately makes the fitting of this panel to the NACA cowling surface easier. To make some space for this dedicated panel, I created initial openings for the gun recesses in the upper panel of the NACA cowling. They are generated by a Boolean modifier, and are a little bit larger than the final recesses.

The most difficult part of the gun recess in this aircraft is the fillet around its edge. To obtain a high-quality shape, I decided to start this panel as two separate objects. The first of them is the tubular inner surface (copied from the “cutting” object used in the Boolean modifier). The second object is just a small cylinder, which radius is close to the fillet radius. I will deform it along a 3D curve, which follows the border of the gun recess opening:



When I started to extrude subsequent segments of the “fillet” cylinder, it automatically follows the assigned curve. (The curve allows me to do it without worrying about preserving the circular cross-section along the whole length of the opening border). Technically, this is the effect of a Curve Deform modifier that I assigned to the cylinder object. This is the first modifier in the stack, and it precedes the smoothing (Subdivision Surface) modifier. Such an arrangement allows me freely slide the circular cylinder sections around the opening border, finding the proper locations for these key vertices:



Then I shifted this resulting contour down, and adjusted its “spine” curve so that the “fillet” cylinder barely touches the opening edge.

When the basic cylinder was shaped, I removed (applied) the curve modifier, as well as the unnecessary ¾ of the cylinder surface. The result is a regular fillet, formed around the opening (figure "a", below):



Now I started prepare the inner part of this recess for joining with this fillet. I had to add some additional sections. They are placed at the corresponding sections in the fillet mesh (figure "b", above).

When all the edges of the inner recess mesh were verified and adjusted to match the filet, I joined these two objects and removed the unnecessary faces (figure "a", below):



Then I created new faces that join these two meshes (figure "b", above).

Once the inner part of the recess panel was completed, I started to form its outer part by extruding its outer edge (figure "a", below):



I placed its vertices on the outer edges of this panel (figure "b", above). Then I added another edge loop in the middle and started to elevate the ‘sunken’ part of this surface above the cowling panel (figure "c", above).

Figure "a" below shows the outer surface neatly fitted to the cowling. As you can see, it requires not one, but two inner edge loops outside the fillet, to reproduce circular cross section of the NACA cowling around this recess:



Finally I used the same auxiliary object as for the underlying panel to cut out the space for the topmost cowling flap (figure "b", above). (It is made using the Boolean modifier).

The gun recess in figure "b", above, looks good enough. However, when I looked onto another reference photo, and then onto another, I slowly started to discover that these recesses had different cross sections! I assumed that it was an arc, while the more I study the photos, the more I came to a conclusion that it had narrower, ‘U’-shape cross-section!

That’s why I still keep as much features as possible implemented as the modifiers applied to relatively simple meshes. Thanks to such an arrangement, the adjustment of the recess shape does not require a lot of work:



First I created a simple auxiliary object as the reference of the correct cross-section shape (white contour in figure "a", above). Then I placed the panel being modified over the reference shape of the NACA cowling (in red). Then I started to shift the complete fillet sections and the near lengthwise edges in the front view, placing them on the new contour. When it was done, I made minor adjustments along the recess edge, shifting the fillet sections until they fit the red surface of the NACA cowling

Figure below shows the final result: gun recesses in the upper panel of the NACA cowling:



For convenient “handling”, the gun recess panels are attached to their cowling panel by the “parent” relation in the internal hierarchy of this model.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will form another element of the upper cowling panel: the carburetor scoop.

This week I have worked on the carburetor air scoop. This scoop passed significant evolution in the subsequent Dauntless versions. In the SBD-1 there was a rather large air duct placed on the top of the NACA cowling (see figure "a", below):



However, it was quickly discovered that it obscures one of the most important spots in the pilot’s field of view: straight ahead and slightly below the flight path. That’s why it was somewhat corrected in the next version (SBD-2). In this aircraft the designers lowered the scoop, increasing the field of view from the cockpit (see figure "b", above). Such a solution persisted in the SBD-3 and -4. In the SBD-5 they completely redesigned it, placing the carburetor scoops inside the NACA cowling (more about this — see in this post the paragraphs around Figure 11-6).

Close examination of the various reference photos led me to the conclusion that in the SBD-1 the air duct ran between the inner surfaces of the scoop and the top of the NACA cowling (figure "a", below):



There was a rectangular opening in the rear part of the cowling, located just above the Bendix-Stromberg carburetor of the R-1820 engine. (There was a short, vertical duct inside the NACA cowling from this opening to the carburetor intake. I will model it later, together with the engine).

The later scoop version (from the SBD-2, through SBD-3, up to SBD-4) was a typical “quick and dirty” solution for the identified problem. The designers could not split the upper panel to place the lowered air duct there, because it would hinder the stiffness of the whole NACA cowling. Instead, they cut out another rectangular opening in its leading edge (figure "b", above). In this way a half of the incoming air went to the engine as before, over the NACA cowling. However, the bottom part of the air stream was directed below the cowling surface. Both streams were joining inside the rear opening, before they went into the carburetor.

I created both openings using Boolean modifiers:



Then I started by forming the lower part of the air intake. I started with a single strip fitted to the side edges of the frontal opening (figure "a", below):



Then I extruded this edge and flatten the subsequent segments, forming the characteristic shape of the inner inlet, as in the reference photos (figure 'b", above).

When this first part of the bottom air duct was ready, I extruded its subsequent segments, forming the rear part (figure "a", below):



Finally I reduced the roundings along the duct side edges by adding there a multi-segment Bevel modifier. It not only diminished their size, but also made its cross section more circular (figure "b", above).

When the bottom part of the scoop was ready, I started the upper part. It begins in the same way: from a single strip, fitted to the cowling surface (figure "a", below):



Then I extruded the vertical faces (figure "b", above).

In the next step I extruded their upper edge into the horizontal surface (figure "a", below):



Finally I extruded the subsequent segments of the rear part of this mesh (figure "b", above).

Initially I kept the lengthwise edges of this object sharp, because I intended to create their fillets using the Bevel modifiers. However, a careful study of the reference photos revealed that the radii of the upper and bottom edge vary along the length of the scoop. Thus I created them by adding two additional lengthwise edgeloops to this mesh:



Figure below shows the real scoop (on the left) and the final version of the same scoop my model (on the right):



Although I did not managed to set up the picture on the right precisely as in the left photo, the carburetor scoop looks quite similar on both images. I can leave it “as it is” and start the work on the next cowling element. I can always fix its shape during the next stages of this project.

In this source *.blend file you can evaluate yourself the model from this post.

In this post I will finish the engine cowling of the Dauntless (of course, for this stage of the project). In the previous posts I formed its outer panels. In the case of the air-cooled radial engines like the one used in the SBD, there is always another, inner panel: the central part of the cowling. It is located behind the cylinders and exhaust stacks. In the classic arrangement of the NACA cowling it is nearly invisible. In the SBD-1..-4 you could see only its outer rim. That’s why I had to use all available pictures of the Dauntless engine maintenance or the wrecks, to learn about its general shape:



This panel had two variants. The first one (let’s call it “flat”) is visible on the photo above. It was used in the SBD-1..-4. In the SBD-5 and -6 the engine was shifted forward by 4”, so the central panel became a little bit longer (“deeper”).

Frankly speaking, I still need more photos and drawings to better determine the shape of this part, especially the details of its earlier, “flat” version! Let me know if you have one — I am especially interested in the upper area, around the carburetor, in the SBD-1…-4. (The few photos that I have reveal that behind the upper cylinders of the R-1820 engine there was a vertical air duct from the air scoop to the carburetor. I still need to determine its shape, as well as the shape of the inner cowling around it).

That’s why I decided to determine the exact shape of this hidden panel later, when I fit the engine and its mounts. (I count on the indirect information coming from the geometry of the engine mount and the exhaust stack shape). At this moment I am leaving this area “as it is”, because too much of its geometry is based on my assumptions.

However, I can precisely shape the recesses around the gun barrels, because they are better visible on the photos. I have to make these details easily adaptable when I have to alter the shape of this panel. (I expect that in the future I will tweak the area around the carburetor multiple times, before it “stabilizes” in the most probable state).

The cross-section of these gun recesses have the same shape as their troughs in the NACA cowling. Thus I started by copying the control polygon of this “U”-like cross-section shape (five control vertices) and extruding it into an auxiliary “trough” (see figure "a", below):



I examined the interesection edge of this auxiliary object with the central panel. The goal was to place its vertices as close as possible to the existing mesh edges. I could easily check it in the front view, because the “trough” in this projection is reduced to a single contour (figure "b", above). While the both of its side vertices are very close to one of the elliptical edge loops, the middle vertex was too far from the nearest radial edge loop. I had to adjust the mesh of the central panel by rotating a little all of its upper radial edges.

After these preparations, I generated in the panel mesh the intersection edge with the auxiliary “trough” (I used my Interesct add-on for this purpose):



I removed the three vertices that were inside the contour of this intersection. It also deleted all the mesh faces around these points. Then I created new faces in this place, merging the intersection contour with the rest of the mesh of this panel (as in the figure above).

Figure below shows how I created the inner surface of this gun trough:



I started by creating a new face that “bridged” the opposite edges of the opening. Then I split it twice, obtaining three inner edges. I placed these edges directly behind the corresponding vertices of the opening contour. Then I closed this opening, creating the four remaining faces. (Now I can see that I could do the same in a simpler way, by extruding the bottom part of the opening contour. Never mind, both methods lead to the same result). At this moment the edges of this recess are too smooth. To reduce the radius of this rounding, and make it similar to a regular fillet, I assigned these edges the full Bevel Weight (=1.0). Then I added to this object a multi-segment Bevel modifier (before the smoothing Subdivision Surface modifier). The last picture from figure above shows the faces generated by this Bevel, before they were smoothed.

Finally I compared the shape of the resulting gun trough to the corresponding troughs in the upper cowling panel:



(I made it transparent, to better see the eventual differences in their shapes). Indeed, there were some deviations. I quickly fixed them, adjusting in the front view the whole edges of this recess. (In this view these edges are reduced to a single point).

Now I have to trim ends of the troughs in the NACA cowling, creating the space for the central cowling panel. I could do it by modifying their mesh. However, because the shape of this panel may be altered in the future, I decided to use another Boolean modifier for this purpose. I just created an appropriate auxiliary object, and applied it to the gun trough panel:



This was the last element of the NACA cowling. Figure "a", below, shows the recesses in the central panel that I formed in this post, while figure "b" shows details of the whole assembly:



As you have probably noticed in the course of the few previous posts, I had often to move the location of the NACA cowling, switching between the SBD-5 and the SBD-3 versions. To avoid such endless movements in the future, I decided to split the Bledner file of this project into several separate scenes for each Dauntless version that I need. For the beginning I created two additional scenes, for the SBD-1 and SBD-5. They are named after the Dauntless version they contain, thus I renamed the current scene to “SBD-3”.

Figure below shows the SBD-5 scene (and the scene selection menu):



When I created the scene for this Dauntless variant, I chose the option that created it as a copy of the original scene. Initially both scenes share the same objects (the same fuselage object or the wing objects are “linked” to SBD-3 and SBD-5 scenes). In the effect, I can edit these shared objects in any of these scenes. Every change I apply to their meshes, modifier stacks, or general positions/scales/rotations is visible everywhere.

Because the NACA cowling in the SBD-5 was shifted forward by 4”, I had to make in its scene local copies of the panel objects. However, they still share with the SBD-3 their meshes. In the effect, they became “clones” of their counterparts from the SBD-3 scene. Clones share the common meshes, thus they have the same basic shape, but they can have different general transformation (location/rotation/scale). Thanks to this, in the SBD-5 scene the bottom panels of the NACA cowling have the same shape as in the SBD-3, but their location is different. What’s more, the clones can have different modifier stacks. Thus in this SBD-5 model I was able to remove the carburetor scoop openings from the upper NACA panel, and modify the cutouts for the different cowling flaps (see figure above) because they were generated dynamically, by a Boolean modifier.

Ultimately — there are a few objects specific for the SBD-5, which exist only in this scene: the central cowling panel and the panels around the gun troughs. I copied their meshes from the SBD-3 and then modified them according the SBD-5 reference drawings. In the SBD-5 the central cowling panel, placed behind the engine cylinders, was longer by 3.5” than in the previous versions. I had to scale and reshape this mesh. Fortunately, its gun recesses (formed at beginning of this post) are easily adjustable, thanks to their simple topology.

In similar way I created a separate scene for the SBD-1:



At this moment the only difference between the SBD-1 and SBD-3 is the carburetor scoop on the top of the NACA cowling. However, there will be another minor differences in the next row of cowling panels.

In the future I will also create the SBD-2 scene (combining the NACA cowling from the SBD-3 and further cowling panels from the SBD-1), and the SBD-4 scene (basically – it is the SBD-3 with the SBD-5 Hamilton Standard Hydromatic propeller). As you can see, the SBD-2 and SBD-4 will be just combinations of various parts from the “key” versions (SBD-1, SBD-3, SBD-5), thus I will create them at the end of this build.

In this source *.blend file you can evaluate yourself these SBD-1, SBD-3 and SBD-5 scenes and their initial contents. In the next posts I will continue my work on the SBD-3, then update the SBD-1 and SBD-5.

This relatively short post contains a digression about the aircraft shape. It was sparked by a suggestion that I received. Some time ago Alan from SOARING Simulator.com pointed me that the SBD NACA cowling was not as smooth as in my model (thanks, Alan!). He suggested that its contour was created from a combination of two or three arcs and a straight segment:



I thought about it and decided that this is a highly probable hypothesis. For most of the 20th century aircraft engineers did not have CAD systems. During that “BC” (“Before Computers” ) era the typical problem in the ship, aircraft, or car industry was: “how to precisely recreate in the workshops the shapes sketched — usually in scale — on the designers’ drawing boards”. The most important shape — the wing airfoil — was recreated using a “cloud” of data points. However, it was a time-consuming (i.e. costly) method. That’s why for the less important areas, as the fuselage, designers used simpler solutions. The most obvious method to define a specific contour was a curve composed from two or three arc segments. It is relatively easy to recreate such a contour, because you need only to know the radii and the center point coordinates of the subsequent arcs. For example, there are many cases of such curves in the P-36 and P-40. There was also another drawing method for obtaining more “fancy” shapes (like the rudder contours) which was based on a general conic curves. To overcome this problem in a more advanced way the design team of the P-51 “Mustang” described all key contours of this aircraft using polynomial (2D) functions. Still the resulting points of the “Mustang” curves had to be calculated by hand!

The modern, computer-generated curves and surfaces (Bezier, NURBS, subdivision) have continuous curvature (as in figure "a", above). Thus it requires some effort to recreate in a computer model such a contour like the one sketched in figure "b", above), where the curvature continuity is broken between each segment. (BTW: the air flow “likes” the shapes that have continuous curvature. That’s why designers always tried to preserve it in the airfoil contours).

All in all, I turned to the reference photos, trying to identify a kind of the contour like the one depicted in figure "b", above). Ultimately I discovered a more severe break than the lack of the continuous curvature: a minor difference in the tangent directions along the panel seam (i.e. the contour of this NACA cowling does not preserve even the tangent continuity!):



I marked the tangent directions along the panel seam in blue. This is a modern, high-resolution picture of a restored SBD-5. To exclude the possibility that this is an accidental inaccuracy made during restoration, I started to search for this break in all other photos. Surprisingly, I think that I was able to identify this “bulge” in the others SBD-5s. In the previous versions (SBD-1 to -4) it was hidden under the carburetor air scoop. But even there I think that I can trace it in the lines of the nearby panel seams (the gun troughs panels, side edges of the air scoop). Such a small deviations are usually a “side effects” of the technology applied to the particular element. Finally I used the reference photo to recreate this “bulge” in the side view:



What’s interesting: previously the contour of this NACA cowling had a small convex break in the top view. (When I shaped it for the first time, without the additional section, I was not able to eliminate such a break in the tangent directions. It had to occur somewhere along this panel seam. I had only the choice where to place it, and I decided to leave it on the vertical contour). Now this contour is smooth, and there is a concave break in the side view.

I suppose that initially the forward ring of this NACA cowling was formed as a perfect solid of revolution. Then it was slightly deformed while fitting to the rear, “flat” part of the cowling. The cross section along the seam between these parts is not a perfect circle: it is somewhat higher than wider. Thus the rear edge of the forward cowling sheet had to follow this shape. It altered the tangent dimensions along this panel seam. In the top view it improved the fitting between these two panels of the NACA cowling. In the side view it only decreased the initial difference in the tangent directions.

Well, I hope that this post gives you a better insight, how we can deliberate on each small detail of the recreated airplane. In the overall picture of this aircraft the differences between the shapes before and after modification described above are hardly noticeable. However, I am a hobbyist, and sometimes we are the only ones who have the time to care about such minor things.

In this source *.blend file you can find this modified NACA cowling. (The change in its shape required some adjustments in the other panels).

In this post I will create the next section of the engine cowling. I copied its forward edge from the rear edge of the inner cowling panel. Then I extruded it toward the firewall:



I am going to split this object into individual panels, thus I already marked their future edges as “sharp” (as you can see in the figure above). It allowed me to preserve continuity of the tangent directions around these future panel borders from the very beginning.

In the next step I created the space necessary for the covers of the gun barrels:



Then I split this object into separate cowling panels:



I also used auxiliary “boxes” and the Boolean modifiers to cut out various openings in the side and bottom panel.

To keep the mesh topologies as simple as possible, I decided to model the inner part of the air outlet in the side cowling as a separate object:



(In the real SBD-3 it was also a separate piece of sheet metal). Its vertical contour was rounded to fit the fuselage behind the firewall (as you can see in Figure 48‑4), thus to shape it in this way I added three additional edge loops in the middle of this mesh.

The initial version of the gun cover was copied from the reference object, then I adjusted its shape fitting it to the adjacent panels (at least to their contours — see figure below):



Note that it is possible to have a corner in the middle of the border of a 3D surface that was carefully fit at its front and the rear contour (see the figure above)! In this case this is an intended effect, recreating the effect visible on the reference photos.

The last element of this cowling is the adjustable scoop (see the figure below), directing the air into the oil radiator (hidden inside engine compartment). It seems to have thick walls, but I suppose that they were empty inside (however, I am not sure — I cannot see any seams there):



I started forming this element by fitting its bottom surface into the fuselage contour:



Then I formed the side walls of this object. As the reference I used an auxiliary circle, centered at the scoop pivot point (as in figure "a", below):



Then I created the thick walls of this scoop using a Solidify modifier (see figure "b", above)

Initially I was going to round the edges of this object using a multi-segment Bevel modifier, placed after the Solid modifier. However it occurred that the Solid modifier created in some corners of this mesh dynamic faces that cause problems in the result generated by the Bevel modifier. Thus I had to “fix” the results of the Solid modifier before using the Bevel tool. You can see the rounded, thick edges of this scoop in figure "a", below, while figure "b" demonstrates the complete cowling panels:



Figure below shows the complete engine cowling, compared to an original aircraft:



Note that the model in the picture above uses different lighting than in the photo. It results in different shadows and reflections from the curved surfaces of the fuselage.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will create the last panel of this fuselage: the hinged doors in the front of the windscreen.

In this post I will form the fuselage panels in the front of the windscreen. In the SBD there were two hinged cowlings, split in the middle. They allowed for quick and easy access to the M2 gun breeches and the internal cabling behind the instrument panels:



The parts of the fuselage around the cockpit are always tricky to model. It especially applies to the panel around the windscreen. When you obtain the intersection edge of these two objects, it can reveal every error in the windscreen or the fuselage shape. To be better prepared for this task, I created an auxiliary, simplified model of this fuselage section (see this post and the next one). Now I copied a part of it as the initial mesh of this panel:



In the next step I used my Intersection add-on to obtain the intersection edge between this mesh and the windscreen object (see figure "a", below):



Initially this edge is not connected to any of the mesh faces. To fit this panel to the windscreen I removed some of the original faces and created in their place the new ones. They incorporated the intersection edge into this mesh (see figure "b", above).

The resulting curve that I obtained in this way required just a few minor adjustments (see figure "a", below):



It is always good idea to check this shape in the reference photo (see figure "b", above). Fortunately, it seems that my edge between the windscreen and the fuselage fits its real counterpart.

When I verified the basic shape of this panel, I extruded it into the “frame” strip that spans around the windscreen:



To obtain a shape that resembles the real part, I assigned to the intersection edge a multi-segment Bevel modifier. It produces a fillet that forces the Subdivision Surface modifier (applied later) to generate a more regular rounding along this windscreen bottom frame.

Finally I created the armor plates that were attached to this hinged cowling. It was an easy part: I copied corresponding fragment of the cowling mesh, then I used a Solidify modifier to make it thick enough (on the photos it seems to have just a few millimeters):



I think that in this armor I will use textures (bump texture, ref texture) to recreate the bolts and the circular recesses around their heads (as visible in the photos). However, I will do it during the next stage of this project.

The last element that I modeled in this mesh was the seam along the bottom border of this panel. It was stamped in the sheet metal to overlap the upper longeron of the fuselage (see figure "a", below):



I also thought about recreating this detail in the textures, but ultimately I decided that it needs a more pronounced appearance. It is an easy effect (see figure "b", above) that required just a few additional edges (as in figure "c", above).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will form the multiple segments of the SBD “greenhouse” cockpit canopy.

Like many contemporary designs, the SBD had a long, segmented (“greenhouse”) cockpit canopy. In this post I will show you how I recreated it in my model. I will begin with pilot’s canopy, then continue by creating the three next transparent segments.

I formed the pilot’s canopy by extruding the windscreen rear edge (see figure below). (I formed this windscreen earlier, it is described in this post). The high-resolution reference photo was a significant help in precise determining its size and shape:



Generally, the canopy shape in the SBD is quite simple. The tricky part was that each of its segments slides into the previous one. (Oh, well, the pilot’s canopy slides to the rear, but it does not matter in this case). This means that there were clearances between each pair of neighbor canopies that permitted such movements. If I made them too small or too wide, the last (fourth) canopy segment would not fit into cockpit rear border (i.e. the first tail bulkhead)! In such a case I would have to adjust back all the canopy segments. Well, I will do my best to avoid such error.

After the pilot’s cockpit canopy I created the next, fixed segment:



It was a fixed part of the cockpit canopy, bolted to the fuselage. I used the available reference photos to precisely recreate its shape. Of course, I also had to determine the distance between the sliding pilot’s canopy and this segment. It was a key moment: making it too narrow or too wide would spoil all further segments.

The photo references can be useful even when the modeled object is not visible: you can see such a case in figure below:



Although in the reference photo the gunner’s canopy is hidden under the fixed segment, the last canopy element is in place. Thus I used its forward edge as the reference shape for the rear edge of the previous canopy. The front edge of this element is deduced from the cross section of the previous canopy segment, offset inside by the clearance distance.

Initially I created the last canopy segment by extruding such an “offset” rear edge of gunner’s canopy:



The initial evaluation of the cockpit rear edge revealed that I had to extend a little the last edge of this object, to match the shape visible in the photos:



Of course, I also had to take care about the clearance between this and the previous canopy segment (see figure "a", below):



In the next step I cut out the unnecessary part of this mesh (see figure "b", above).

Finally I recreated the rounded corner of this segment. I did it using an additional vertex, located on the bottom edge of the last mesh face. (See figure below. In this way that face becomes an n-gon). When I slide this vertex forward along the bottom edge, it reduces the radius of this corner. A movement into opposite direction enlarges it:



Figure below shows the complete cockpit canopy:



Fortunately, its last segment fits well into the cockpit rear edge, so I do not have to adjust all these canopy segments! (I mentioned such a possibility at the beginning of this post).

In this source *.blend file you can evaluate yourself the model from the figure above.

The shapes you can see in red in figure above will become the transparent plexiglass surface. I still have to place the sheet metal frames on these elements (I will do it in the next post). There were also internal tubular structures that supported these canopies from inside. I will recreate them during the last, detailing phase of this project

Today I will add the basic details of the cockpit canopy: its outer frames. However, before I started this work, I had to conduct yet another verification of the canopy shape. I placed the canopy rails on the cockpit sides, and verified if they fit the corresponding canopy segments. First I tested the rails of the pilot’s canopy (see figure "a", below):



They were formed from open-profile beams (see figure "b", above). Why these rails are such an important test tool? Because they always have to be parallel to the fuselage centerline! It sounds obvious, but it can reveal various unexpected errors in the canopy shapes. In this case I discovered that the fixed segment of the cockpit canopy was mounted on the pilot’s canopy rails. (In the previous post I assumed that this rail was placed between the pilot’s canopy and this fixed canopy). If I did not find this error now, it would cost me much more work during the later stages of this project! Now I could quickly fix it (see figure "b", below).

In the rear part of the SBD cockpit you can find a double (two-beam) rail see figure "a", below). The forward segment of the gunner’s canopy slides along the outer rail, while the rear (i.e. the last) segment — along the inner rail:



In figure "b", above, you can see that this rail protrudes from the last segment of the canopy. It’s OK — in the real aircraft they cut out a half of its bottom edge, to make room for it (see figure "a", below):



Frankly speaking, these rails forced a lot of small modifications along this “canopy sequence”. Their presence allowed me to fix various small differences between the reference photos and this model. In particular, now the roundings on the canopy rear edges match the photos, as well as the clearance between these canopies.

The typical cockpit canopy frame of a WW II airplane was a structure made from duralumin (or steel) tubes. In the SBD these tubes had rectangular cross sections, and were riveted to each other. They formed frames, which were covered with relatively thin (2-3mm) transparent organic glass plates. These plates were attached to the tubular “skeleton” by rows of small bolts:



The heads of these bolts had flat (conic) heads, which were “sunken” in the thin sheet metal strips placed over the organic glass plates. (There was also a seal layer under these thin duralumin strips). In this post I will recreate these external sheet metal elements. The internal tubular frame of the canopies will appear during the last, detailing stage.

As the first I created the windscreen frame (figure "a", below). The general method is always the same: I copied the mesh from the “glass” object, then cut out the frame stripes (figure "b", below):



Of course, the subdivision surface generated by these strips in some places does not lie on the reference “glass”. Thus I had to adjust this mesh a little (as in figure "a", below):



Finally I obtained the result as in figure "b", above. Note that I created the frame of the hinged windscreen part as a separate object (just in case).

I formed the further canopy segments in a similar way. First I copied the mesh of the corresponding “glass” object. If it was required, I shifted it along its rails to match it against the reference photo (figure "a", below):



Then I inserted into this mesh additional, sharp (Crease = 1) edges along the borders of the frame strips that are visible on the reference photo. Finally I removed the unnecessary faces from the areas between these strips (figure "b", above).

When the frame shape matched the reference, I shifted it back onto the corresponding “glass object” (figure "a", below):



Finally I made this frame thick (by the “sheet-metal thickness” — about 0.02 or 0.03”). I did it using a Solidify modifier. It is directed outside, so it creates an illusion of thin stripes lying on the “glass” surface (figure "b", above).

In a similar way I created frames of the all other segments of this cockpit canopy:



In this source *.blend file you can evaluate yourself the model from this post.

As you can see, this Dauntless model starts to resemble the original aircraft. However, it still misses the propeller. I will work on it in the next post.

The SBD Dauntless used two types of the Hamilton Standard propellers:

• Hamilton Standard Constant Speed (counterweight propeller) used in the earlier Dauntless versions (SBD-1 … SBD-3). The blades of this propeller had smaller tips (see figure "a", below);
• Hamilton Standard Hydromatic used in the later Dauntless versions (SBD-4 … SBD-6). The blades of this propeller had larger tips (see figure "b", below):

These two blades had different shapes. In this post I will recreate the earlier version, which was used in the SBD-1 .. -3 (figure "a", above). Several posts later I will modify its copy to obtain the later model of the blade, as used in the SBD-4 .. -6 (figure "b", below).

The main problem with recreating propeller blades of various historical aircraft is the lack of their precise drawings. In fact, I saw such a thing once, in the detailed plans of the Soviet WWII fighters. (Such a drawing contains the contour of the blade in the front and side view, as well as the set of subsequent airfoil sections, from the rotation axis to the tip). Nothing like this you can find for the typical Hamilton Standard blades! I looked for any trace of such drawings in the Internet. All what I found was a thread in one of the aviation forums. One of the participants of this discussion showed letters that he exchanged several years ago with the Hamilton Standard company. He asked for drawings of a blade that was designed in 1936. HS declined to reveal it, explaining that this design still remains their “business secret”.

In such a situation, all what we have are the photos of the real blades. (Until somebody makes a 3D scan of such a blade, and will publish it in the Internet — I hope that such a reverse engineering is legal). I used these references to draw the most possible blade contour in my scale plans. However, I had to rely on the photos for best estimation of the size and thickness of the airfoil sections of this blade, as well as the variation of their pitch along the span (i.e. propeller radius). Thus they may be less precise copies of the original than the rest of this model.

Now I see that I should draw the propeller blade vertically or horizontally on my reference drawings (see figure below). Well, I sketched them at the fancy angle of 120⁰, but never mind — it is still possible to use it. I will have to slide and scale the mesh vertices along the local axes of the blade object.

I started the work on the blade by creating a cylinder object. Then I rotated it by 120⁰, aligning to the reference drawing (as in figure "a", below):



Then I extruded its upper edge and flattened it at the tip (as in figure "b", above).

In the next step I inserted a few additional edges in the middle of this blade (figure "a", below), and shaped them so they resemble a flat-bottom airfoil (figure "b", below):

I do not know what was the airfoil used in the Hamilton Standard blades. In one of the aviation forums I have found that it was RAF-6. It is not confirmed information. If it would be true, the leading edge of this blade should be sharper (RAF-6 had smaller radius of the leading edge).

When the cross-section shape of the blade was set, I started to form its contour in the front view:



I stretched and shifted its airfoil edges until the blade contour fit the reference drawing. Figure "a", above, shows how the base (i.e. control) mesh of this contour looks like. In fact, I formed it directly, using the alternative display mode of the smooth resulting surface (as in figure "b", above).

Finally I closed this mesh along the circular tip. Comparing the reference drawing with the photos, I decided that the contour of this tip was a perfect arc. What’s more, I decided that it was a little bit larger than on my reference drawings. Thus I created a reference object — a circle (figure "a", below):



I modified the last edge of this mesh, shaping the resulting contour around the reference circle. Figure "b", above, shows the final shape of the mesh, while figure "c" — the resulting tip surface.

Because I missed the information about pitch distribution along this blade, I decided to deform it in a dynamic way, using a curve via a Curve Deform modifier assigned to the blade object. In this case the deforming curve is a straight line, placed along the local Z axis of the blade (figure "a", below):



In such an arrangement I can control the pitch of this blade by changing the tilt value in the curve control points. At the tip the tilt is 0⁰, while at the last point (which lies on the propeller axis) it reaches the maximum value (25⁰). These values are just an estimation. The tilts in the middle points of the curve lie within this range (figure "b", above). It dynamically deforms the control mesh of this blade (figure "c", above). After a few trials I obtained the twisted shape that resembles the photos.

Figure below shows the three clones of this blade, arranged as in the propeller:



Their mesh is a copy of the original, with the “applied” (i.e. fixed) result of the Curve Deform modifier. Just in case, I preserved the original (not twisted) mesh of this blade together with the deformation curve in the References scene, among other auxiliary objects. It will be useful later, for the Hamilton Standard Hydromatic propeller, used in the SBD-5.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will create the hub of this Hamilton Standard Constant Speed propeller.

In my post from the previous week I modeled the blade of Hamilton Standard Constant Speed propeller, which was used in the SBD-1, -2 and -3. The Douglas factory mounted on the hub of this propeller a small spinner (as in figure "a", below):



It seems that during the service of these aircraft, the ground crew often removed this spinner. It exposed the propeller pitch control mechanism (figure "b", above). There are many photos of the SBD-2 and SBD-3 without spinners, thus I decided that I had also to model this “bare” variant.

These constant speed propellers were in wide use during the 30’, but it was not easy to find any detailed photos or sketches of their counterweight pitch control mechanism. Finally I figured out that the counterweights were connected to the corresponding blades (figure "c", above). The central cylinder shifted along the propeller axis, controlling the angle of the counterweight arm (and, in the effect — the angle of the propeller blade pitch).

How to start forming such a complex shape like this variable pitch mechanism? I began by identifying its key axes and base planes:



The most difficult part of this process is not visible here: I had to realize the basic shape of these parts. I spent some hours studying the photos before I decided that the hub (referred also as “barrel”) of this propeller can be composed from several cylindrical elements. After this conclusion I could start forming this object. I began by shaping a cylinder around the blade base:



To facilitate my modeling, I used all of the symmetries that exist in this part. I formed just a quarter of the cylinder mesh, then mirrored it across the blade axis. In the next step I placed clones of this mesh around the two other blades. (When I modify the original mesh, it will also modify these clones).

I formed the side surfaces of this barrel from a half of an elliptic cylinder:



I started it as a classic cylinder of a circular base. Then I rotated this object by 60⁰ and scaled it along its local Z axis until I obtained the shape resembling the photos. Then I used my Interesction add-on to obtain the intersection edge between this surface and the neighbor cylinder.

Finally I joined these two meshes and removed all of their faces. I preserved just the three edges: around the blade base, the inner edge of the elliptic cylinder and the intersection edge. I joined them with the new faces (figure "a", below):



In this way I obtained a solid which looks like the original propeller hub. Note that the three segments “touch” each other without visible seams — it looks like a continuous surface (figure "b", above). I used a multi-segment Bevel modifier to generate regular fillets along the sharp edges of this mesh.

I could make the opening for the counterweight arms in the front of this barrel using a Boolean modifier. However, it was relatively easy to recreate this particular shape by small modifications in the control mesh (figure "a", below):



In a similar way I integrated the small fragment of the cylindrical rear axis with the rear faces of the barrel mesh (figure "b", above).

The next difficult element are the flanges for the bolts that in the real propeller joined the two halves of this barrel. If I tried to incorporate them into the barrel object, it would significantly complicate its mesh. In the effect I would spent some additional hours on various adjustments. Thus I decided to create this flange as a separate object, that joins with the main body of the barrel in a more-or-less seamless way.

Figure below shows how I shaped this element:



As in the case of the main body, I model here just a single segment of this flange — the rest is replicated by the Mirror modifier. I started from a cylinder created around the eventual bolt axis (figure "a", above). Then I modified this mesh, fitting it to the underlying surface of the central barrel (figure "b", above). In the next step I extruded additional “strips” of the faces that lie on the barrel surface (figure "c", above). I rounded the sharp edges around these faces with a fillet (generated by a multi-segment Bevel modifier). Finally I extruded the part of the small wall that accompanies these bolt flanges (figure "d", above), and shifted its origin point onto the propeller axis, to create similar flange on the opposite side of the blade base.

I created two additional clones of this object, placing them around the blade bases (figure "a", below):



I also made the walls of this barrel thick, using a Solid modifier. Looking at figure "b" (above) you can see that these bolt flanges look now like integral parts of the barrel. I will recreate the remaining elements of this hub during the detailing phase (for example — the bolts that kept halves of this hub together).

The last element I have to model now are the counterweight bearing shafts. They were attached to the control cylinder. I started this part by adding a small shaft bushing on the bottom side of the counterweight arm (figure "a", below):



Then I created the first row of vertical faces around this cylinder (figure "b", above). I also created two additional clones of this mesh and placed them around the control cylinder, below corresponding counterweight arms. When they fit each other, I modified the topology of these faces, preparing them for joining the mesh of the shaft bush (figure "c", above). Note that I placed these faces precisely below the second-last pair of the cylinder vertices. I also prepared additional faces, which will allow me to quickly join them with the octagonal cylinder of the shaft. Finally I duplicated these vertical faces, placing them on the opposite side of the shaft mesh. It allowed me to quickly create the last missing faces in this mesh, and obtaining the finished shaft bushing object (figure "d", above).

Figure "a" (below) shows the complete pitch control mechanism of the constant speed counterweight propeller:



I will add more of its details (the bolts, for example) during the last phase of this project. In the last step I also recreated the spinner (figure "b", above). It was an easy solid of revolution — I will not elaborate here how to create it. (If you want to learn more about shaping the spinners — see this guide). There is one missing thing: I do not know how this spinner was attached to the propeller hub. Do you have any hint on this subject?

In this source *.blend file you can evaluate yourself the model from this post.

I will create the R-1820 engine during the detailing phase. This was the last element of the SBD-3 that I created before the UV-mapping and texturing phase. (In fact, I am not going to unwrap the small elements of the variable pitch mechanism. I could just create the propeller blades and the spinner. I created it just because this propeller hub is a quite large part of the Dauntless silhouette). In next post I will recreate the few details which differ the SBD-1 from the SBD-3.

As I described it in one of my previous posts, in parallel to the SBD-3 I build a SBD-1 model and a SBD-5 model. They are in the same Blender file, but in separate scenes. Since I completed the SBD-3 model for this project stage, now it is time to take care of these other versions. These models share all the common objects with the SBD-3, so I have to recreate a few different details. I already modified their NACA cowlings. In this post I will update the SBD-1, because there is just a single remaining difference: the ventilation slot in the side panel of the engine cowling.

The SBD-3 had this slot much wider than the SBD-1 and SBD-2:



(I used here an archival photo of the SBD-2, because it had the same side cowling as the SBD-1. There were only 57 SBD-1s ever built, so the photos of this version are not as numerous as the later ones).

Figure below reveals the reason of this difference in the cowling shapes:



The SBD-1 and SBD-2 had special emergency device: pneumatic balloons, which automatically opened when the aircraft ditched on the water. They had to keep the airframe on the surface, giving the pilot and gunner more time to evacuate. These balloons and their trigger installations were stowed in boxes behind the ventilation slots (figure "a", above).

In the SBD-3 the designers removed these balloons, creating more room for the air coming out from the oil radiator (figure "b", above). In this version these ventilation slots are completely integrated into the side cowling panels.

Because of the frame around the balloon compartments (as in figure "a", above), the side cowling of the engine had a slightly different shape in the SBD-1 and SBD-2. I modeled it by copying the corresponding cowling panel from the SBD-3, and inserting an additional edge loop in the middle (figure "a", below):



I marked this edge as sharp and used it for the minor modifications of the panel shape (figure "b", above).

It seems that the shape of the cutouts in the side view is identical in the SBD-1,-2 and SBD-3, thus I used the same auxiliary objects for its Boolean modifiers (figure "a", below):



However, I had to create anew the inner panel, located inside this cutout. I started with the edge copied from the firewall. I extruded it forward (figure "a", above), then inserted some additional edges in the middle (figure "b", above).

I shaped this inner panel forming it as a smooth continuation of the fuselage shape (figure "a", below):



Then I concentrated all the inner edges of this mesh at the ventilation slot (figure "b", above), and bent the forward edge of this panel toward this outlet (figure "c", above).

In the effect I obtained the shape that closely resembles the original cowling:



You can compare this photo with the first illustration in this post.

It was the last element that I had to modify in this model. Figure below shows the complete airframe of the SBD-1:



It is ready for the next stage of this project (applying materials and textures).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will start updating the model of another Dauntless version: the SBD-5. (There will be more differences than between this SBD-1 and the SBD-3).

In this post I start finishing the SBD-5 model. It differs in more details from the SBD-3 than the SBD1. One of the most prominent differences is the propeller. I will create it in this post.

In the later Dauntless versions (starting from the SBD-4) Douglas used the new propeller: Hamilton Standard Hydromatic. The SBD-1,-2,-3 used the older constant speed propellers, which used counterweights to oppose the force generated by the oil pressure in the control cylinder. (I created the model of this propeller in this post). The Hydromatic propeller used the oil pressure on both sides of the piston that controlled the pitch. It eliminated the massive counterweights, creating a lighter, smaller, and more precise pitch control unit. Hamilton Standard Hydromatic propellers has been widely used since 40’ (you can still encounter them in the various modern aircraft).

In the Dauntless, these Hydromatic propellers came with slightly modified blades:



I used some photos to copy the contour of this new blade into the reference drawing. Then I copied the “old”, untwisted blade from the SBD-3 and modified its vertices so it fits the new shape (this is the view from the rear):



(It was quite similar to the las stages of shaping the SBD-3 propeller blade, described in this post. Thus I will not elaborate about it here).

The hub (Hamilton also refers this part as the “barrel”) of this propeller had a quite complex shape:



This barrel splits into the front and rear halves. Because there is an oil under pressure inside, there are three bolts on each of the three flanges that keep these barrel halves together.

Beware: it seems that these classic Hydromatic propellers are rare, and some of the restored SBDs use different, non-original models. As a quick indicator you can use the number of the bolts around the barrel. The original propellers had a single bolt in the middle of each flange (as the propeller from the figure above).

The propeller from the figure above was used in the flyable SBD-5 (“white 39”) from Chino Planes of Fame air museum. It seems OK, just misses a small detail: the cap on the tip of the dome. Another example: in the flyable “white 5” from the Commemorative Air Force you can find a larger hub with two bolts in the middle of each barrel flange. What’s more, the blades of this aircraft have non-original shape. To further increase the confusion, there is a non-flyable SBD at the Palm Springs Air Museum, (“white 25”) which combines a non-original, larger Hydromatic barrel and the propeller blades from an earlier SBD version (SBD-3?).

The halves of this hub barrel were forged (or casted?), thus all of its edges and corners are rounded. It makes modeling of this element much more difficult, at least in Blender (you will see it in a moment).

To better understand this shape, I started with its conceptual model, without all these fillets and flanges:



Studying the photos and available drawings of this control pitch mechanism, I decided that this “barrel” is a combination of three cylinders (the bases of the propeller blades) and a solid of revolution resembling a jug (as in the figure above). Using this conceptual model, I quickly determined the exact shape of this central “jug” that produces the same intersection edges as you can see in the photos.

In a CAD system the next steps would be easy: I would create the basic flange shape by adding some plates and small cylinders. Then I would rounded all their edges using various fillets, and the barrel would be ready.

Unfortunately, Blender has no such a powerful fillet feature: it only has a multi-segment Bevel command, which can create a fillet between two elementary faces. It is usually sufficient for architects. However, If I joined the conceptual model from the figure above into a single mesh (using Boolean union operator), I would to be able to create the appropriate fillet along its edges. (Boolean operation produces in Blender a lot of small elementary faces along the intersection edge. Their size determine the maximum radius of a fillet). I started to think about following pzzf7s’ suggestion about using the free AutoCAD 123D as an auxiliary tool for such parts. Ultimately I decided that before I do it, it is a good idea to create at least one of such difficult shapes using Blender tools. Later it will allow me to make a fair comparison between making complex mechanical parts in Blender and AutoCad 123D.

So I started modeling the propeller barrel in Blender. During this process I used the conceptual model as the reference object (I marked it in red):



I decided to take the advantage of the internal symmetries of this shape, and prepared the mesh for 1/6^th of the barrel — just half of a single blade base and one and half of the flange bolts. Thus I initially created two cylinders for these bolts (figure "a", above). Then I joined these two cylinders into a single object, which is rotated along Y axis by 60⁰ (to create the local symmetry axis along the flange). I removed the half of the inner cylinder, because it is dynamically recreated by the Mirror modifier. In the next step I created the basic flange that connects these two cylinders (figure "b", above). Then I added two inner edges, to bend the side faces of this mesh along the rounded sides of the reference surface (figure "c", above).

Once I formed this flange, I started to shape the remaining part of this mesh. I added an arc that lies on the surface of the central solid of the barrel (figure "a", below):



The number of the arc vertices is extremely important here. It had to be similar to the distance between vertices of the flange edges that connects the bolt cylinders. In similar way I added another arc around the blade base cylinder, then extruded both these edges into two intersecting surfaces (figure "b", above). Finally I generated in this mesh the intersection edge of these two surfaces (using my Intersection add-on). I used this edge as the base for forming two new rows of faces that replaced the original ones (figure 'c", above).

Now the shape of this object starts to resemble the barrel. I improved the shape of its fillet by adding additional edge (figure "a", below):



Finally I shaped the inner part of the blade base (figure "b", above) and filled the gap in the front of flange cylinders (figure "c", above).

The rear half of the barrel was easier, because I started it from a mirror copy of the forward part (figure "a", below):



Then I removed some of its faces and modified the shape of remaining key edges (figure "b", above). Finally I connected these edges with new faces, and added additional edges along the fillets (figure "c", above).

All in all, forming this element in Blender was not easy. On the next occasion I will try the AutoCAD 123. (I have to learn it).

In figure "a", below, you can see the finished hub barrel. I also added the cap on the dome tip:



Figure "b", above, shows the finished assembly. I suppose that I will reuse this hub in many other models. A lot of the various aircraft which used the Hamilton Standard Hydromatic propellers. (At least those, which used the tree-blade model with the single bolt in the middle of their barrel flanges. I know that such a specific conditions sound strange, but it is a quite common model).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will recreate other SBD-5 details that differ from the SBD-3.

I continue updating the Dauntless versions that I am building in parallel to the basic SBD-3. In the previous post I updated the one important element of the SBD-5 model: its propeller (SBD-3 used an older version of the Hamilton Standard propeller). In this post I will continue this update.

While I already recreated the SBD-5 NACA cowling (see Figure 46-8 in this post), now it is time to adapt the panels behind it. I started by copying the corresponding cowling from the SBD-3. When it appeared in the place, I discovered a 1” gap between this cowling and the SBD-5 inner cowling panel (see figure "a"), below:



I immediately verified these cowling panels in the reference photos (figure "b", above). It does not look like my mistake: the side panels perfectly fit the firewall and the upper and lower fuselage contour. It seems that this segment of the engine cowling really was in the SBD-5 and SBD-6 longer by 1”! (It seems quite probable: if the designers shifted the whole engine forward by about 3”, they could also modify this segment).

Following this finding, I modified all the panels of this cowling segment. I also modified the auxiliary “boxes” used by the Boolean modifier, to obtain thinner and higher air ventilation outlets. (This is another difference between the SBD-3 and SBD-5):



I shaped the inner surface of these outlets starting from a rectangular plane, as I did in the SBD-1 model:



When the side cowling panels were finished, I modified the oil radiator air scoop, located in the bottom panel:



The photos reveal that this panel was in the SBD-5 wider than it was in the SBD-3 by about 2”, because it housed a larger (wider) air scoop. (I suppose that they mounted in the SBD-5 a larger oil radiator, because it had a more powerful engine – 1200 HP instead of 1000 HP in the SBD-1…4).

When I finished the bottom panel, I started shaping the upper panels that cover the pilot’s gun barrels:



It seems that they have slightly different shape than in the SBD-3. What’s more, the protruding upper edge of the side panel (as in the figure above) indicates that the designers remodeled (simplified) this area altering both shapes: of the side panel and of the upper panel.

I compared these elements with all available photos, then remodeled both of them:



Note that in this SBD-5 the upper border of the side panel is not a straight line, like in the previous versions. The last mesh face that contains this edge has 5 edges, while all the other faces in this mesh have four edges. This is an intended effect — it seems that such a n-gon creates in this place the desired shape.

There is yet another difference, which you can hardly find on any scale plans: the windscreen frame:



In the older versions (from SBD-1 to SBD-4) it was built from the upper part and two rectangular plates on the sides. It seems that in the SBD-5 they simplified its technology, and created it from two metal stripes. The thinner, forward strip runs around the windshield, while the much wider rear strip forms its trailing edge. The pilot’s canopy hood slid under this rear strip — I suppose it better sealed this canopy edge.

I used a copy of the SBD-3 windscreen frame as the starting point. I modified most of its inner edges, recreating the “two-strip” shape:



Finally the whole front of this SBD-5 was ready (as in figure "a", below):



In the last minute I discovered that in the SBD-5 they also simplified the upper cowling panel. In the earlier versions it consisted two hinged covers above the gun barrels and a central panel (see this post). In the SBD-5 it was just a single panel (as in figure "b", above).

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will recreate the last remaining details for this project stage: the cutouts behind the gunner’s cockpit.

The last details that I create in this project stage are the gun doors behind the gunner’s cockpit. In the SBD-1 they covered a single Browning gun. Fortunately, they were wide enough for stowing the double guns, which were mounted in the SBD-2 and SBD-3 by the Navy workshops:



Note that stowing the ammunition belts of this double gun required additional cutouts in the cockpit rear border. They were covered by slide plates on both sides of the gun doors (see figure above). In this post I will recreate these details.

Before I do it, I have to fix a certain error that I have recently found: the shape of the tail cross-section, near the cockpit edge. When I formed it, I relied on the photos from a certain restoration project (as in figure "a", below):



The upper part of the first bulkhead behind the cockpit (at station 140) in figure "a", above was shaped along a single, gentle arc/curve. Looking on the other photos I assumed that in the front view the gun doors formed an arc, and this arc smoothly joins the curve of the bulkhead contour at the hinge line. Basing on these assumptions (marked in figure "a", above) in blue), I prepared appropriate mesh topology (as in figure "a". below). I created a “sharp” edge along the future gun doors hinge line, which enables me to cut out the inner area for the gun doors (as you can see in this post, Figure 24-9).

However, since that time I still had an impression that something is wrong with this tail shape. Finally, when I started to look at the sliding panels behind the gunner’s cockpit, I found that their cross-sections are different than I expected. I have found the ultimate confirmation in the picture from SBD-1 manual (figure "b", above). The top arc of this contour had larger radius, and its endpoints were outside the hinge lines. It was smoothly combined with a straight contour segment, spanning from the topmost longeron of the fuselage (the same that runs along the canopy side border).

Well, great! This means that I have to modify the concept of the mesh topology for this area in my model! Figure "a", below, shows the original layout, while figure "b" shows the modified mesh:



The enlarged arc of the tail cross-sections forced me to shift the mesh edges away from the gun door hinge line. In the effect, I had to switch to the “plan B” for this opening: I will create it using a Boolean modifier. (Never mind, I was going to use it anyway during the detailed phase, for the other openings in the fuselage).

To better fit the fuselage to the straight edges of the gun doors, I already placed their hinges on the tail upper surface (figure "a", below):



I tweaked the mesh edges around the cockpit rear border, obtaining the shape that closely resembles the original part in the reference photos (figure "b", above). However, I do not like their complex topology: such a thing can be an obstacle for eventual further modifications.

After this, I decided to verify how the last cockpit canopy slides under the previous segment. (This is another test before I start to work on the cutouts in the tail surface). In general, the gunner had to rotate it first into horizontal position, then slide it under the previous canopy (figure "a", below):



However, when I started sliding it, I had to stop: its rear edge was too wide (figure "b", above)! It seems that its radius is exaggerated: it was larger than the radius in the forward section of this canopy (figure "a", below):



Well, I adjusted the size of this last section, so that in the rotated position the last canopy segment fits the previous one (figure "b", above). Of course, then I also had to adjust the corresponding frame object to this new glass shape. I definitely should check it earlier! On the other hand, after this modification the gunner’s cockpit of my model better resembles the original photos.

The decision of using the Boolean operator for the gunner’s opening allows me to simplify the fuselage mesh (figure "a", below):



As I mentioned earlier in this post, I was not satisfied with the complex topology of the cockpit rear border. Now I decided to create it as a separate panel (i.e. separate object). It will differ between the SBD-1 and the later SBD versions, because in the SBD-1 (and SBD-2) the fuselage did not have the side cutouts (compare the first figure from this post and figure "a", below). That’s why the auxiliary “cutting object” for the Boolean operation has a shape that resembles the “T” letter (figure "b", above). In this way I created the main fuselage part that fits all the SBD versions. The topologies of both meshes — the fuselage and the rear panel around the gunner’s cockpit — became simpler. It means that it will be easier to introduce eventual further modifications.



There was an issue with the internal hierarchy of this model: the fuselage could not be the parent of the auxiliary “T”-like object, because it “cuts” its shape. (Such an arrangement causes problems with displaying the model — I already encountered it in the case of the wing fixed slats). The obvious solution was to assign both objects used by the Boolean modifier to a common parent. In the case of the wing it was its root rib. However, so far this main part of the fuselage was the root object of the whole model hierarchy. To resolve this problem I decided to create a new root: an Empty object. Because I will need it for posing the airplane in an eventual final scene, thus I placed it on layer 19, among other auxiliary handles (figure "b", above).

After these preparations I was finally able to make the sliding panels and their rails:



I used the reference photos to precisely recreate these elements. (The picture of a SBD-5 wreck in the figure above comes from Pacific Aviation Museum Pearl Harbor. I decided that when I work with the details, I can more trust the wrecks than the restored aircraft). The cutout for the ammunition belt was made between two fuselage stringers and the bulkhead at station 140 (see figure "a", above). Note that it creates a triangular hole between the sliding plate and the canopy rear frame (figure "c", above). Ultimately it was covered by a rubber band, attached to the canopy. (I will recreate it during the detailing stage of this project).

I created the sliding panel from a rectangle, which received the oblique forward edge. Initially I created the shapes embossed on its surface from separate cylinder halves. Then I recreated the faces around their edges, integrating these shapes with the base plate.

The “rails” of this sliding panel were made from simple duralumin stripes, folded inside. They were riveted to the fuselage stringers. Because these rails had to be parallel to each other, the axis of the fold in the bottom rail was deflected from the stringer axis (figure "b", above). That’s why this element had a wedge-like shape.

The archival photos revealed that there was also an alternate version of the sliding plates, which appeared in the SBD-3s. You can see it in the figure below:



I think that the photo in figure "a", above, was taken during operation “Torch” (November 1942), because the star on this picture has a wide light outline, most probably in yellow. Note that the gun has no armor plates there, and the sliding panel has no embossed stiffener along its rear edge. Figure "c", above, shows such a panel in a restored aircraft. (I have found it in the photos from the Kalamazoo Air Museum). We can see clearly here that the lower rail strip is not folded like in the previous figure, but just bent upward, and it is riveted to the stringer along its lower edge. This means that this sliding panel is somewhat narrower than the one from the SBD-5. (Why? Because the lower edge of this panel lies above the stringer axis, while in the SBD-5 it is slightly below the stringer axis). I suppose that it can be a field modification of an original SBD-3, adapting it for the double gun. However, I am not sure that all the SBD-3s had such sliding plates. Anyway, I recreated it in my SBD-3 model. The other version of the sliding panel, as in the previous figure, you can find in the SBD-5 model.

In this source *.blend file you can evaluate yourself the SBD-1, SBD-3 and SBD-5 models from this post.

While working on the cowling details, I discovered that the SBD-5 from the Commemorative Air Force (“white 5”) uses a non-original Hamilton Standard propeller. It has larger hub and a pair of bolts in the middle of the hub barrel edges. (As I wrote in this post, the original Hamilton Standard hubs used in the SBDs were smaller, thus they had a single bolt in the middle of each barrel edge). What’s more, I also noticed that the centerline of my model does not precisely pass through the tip of the propeller dome visible in this photo. When I corrected this mistake, I also noticed that the edges of certain cowling panels in my model are minimally below their counterparts on the photo. I examined this difference and decided that I should fix it by rotating the camera of this projection around the fuselage centerline. It was really a “cosmetic” adjustment — the rotation angle was about 0.7⁰. However, suddenly everything in this model matched better the reference photo — except the horizontal tailplane:

When I previously matched my model to this photo (see Figure 42-9 in this post), I aligned it along its horizontal stabilizer. (I assumed that it is not deformed by any significant load). It seems that I was wrong: the Dauntless on this picture is taking off (its wing flaps are retracted). What’s more, its elevator is slightly rotated upward, what means that this airplane has already gained enough speed and currently the pilot is lifting its nose to leave the ground. Thus there is an aerodynamic force which bends the tailplane downward, while the lift force tries to bend the wingtips upward:

I think that I would obtain a perfect match between the fuselages of my model and in the photo by placing the viewpoint of this projection between its previous and the current location. (In its previous location it matched the deformed tailplane, while in the current one — it matches the deformed wing).

However, both of these tailplane and wing deformations are small. Thus aligning the wing of my model to the wing in this photo delivers me much more useful information, than a “geometrically pure” match somewhere between these two points. The influence of viewport rotation of 0.7⁰/2 = 0.35⁰ on the fuselage can be neglected, and now the only part of my model that does not fit the photo is the tailplane. It’s OK, because in this projection I cannot see any special details on this element. On the other hand, now I can use this high-resolution photo to check various details on the bottom side of the wing.

Currently we are close to the end of the modeling stage of this project. All the elements of this model that I am going to ‘unwrap’ for the image textures are already in place. Now I will use this high-resolution reference photo to re-examine the model shape and fix all the remaining differences. I started from the empennage:

I fixed it working directly on this picture (I restricted the movement of the mesh vertices to the global YZ planes).

Then I shifted forward, fixing the dorsal fin:

There still was a difference in the tail bottom contour. This time I had to alternate the lower part of the tailplane bulkheads:

I did it by scaling these parts of the bulkheads downward. The most difficult part of this operation was the preservation of the straight lengthwise (“longeron”) edges in the rear part of the tail.

Of course, I also used other photos for this check. In the figure below you can see matching the wing against a “semi-vertical” shot of a Dauntless in a steep bank (most probably in a tight turn):

I can see here a difference in the wingtip shape. However, I already verified it against other photos, several months ago (see Figure 31-8 in this post). What’s more, I discovered that when I slightly rotate the wing tip around the wing span axis, it perfectly fits the photo (figure "b", above). Thus I again started to think about the forces — this time acting on these wings in such a turn. The lift force has to counter the centrifugal force here. For such a steep bank it can be several times greater than the weight of the aircraft. Thus the wing in this photo is under extremely heavy load, and it wing tips can be twisted as severely, as those in figure "b", above). Ultimately I assumed that this is an effect of dynamic deformation, and I should not modify the wingtip. (The photos of this wing in static conditions do not confirm this shape).

However, in figure "c" above you can see another difference that has haunted me for a long time: the gap between the wing flaps and the aileron. On the various photos, both static and in-flight, it seems that the trailing edge of the wing flap was a little bit shorter than in my model.

First I checked if in this photo the flap is not shifted nor rotated:

I placed auxiliary lines on the flap surface of my model. They go along the last row of holes in each of the 6 segments of this flap (figures "a", "b" above). These lines reveal the “natural” direction of the flap ribs. At the outer end of this flap I put a polyline, which upper edge matches the flap upper. (I wanted to check if this edge is parallel do the flap ribs).

Then I put the wing and these auxiliary lines flat on my reference drawings (i.e. I set the wing dihedral and incidence angles to 0). You can the result in figure "c", above). It seems that the middle sections match my reference drawings (and my model). However, the most inner section (containing the four rows of three holes in each row) should be slightly wider, while the most outer section was shorter (although it contains the same number of holes!). This result was a little surprise, because when I drew these scale plans, I assumed that the spacing between the flap holes was constant. (It would be easier to machine such a perforation). Now it seems that this distance varies in different segments of this flap! Finally, the polygon on the outer end of the flap clearly indicates that its outer edge is oblique (as in figure "c", above).

Of course, I verified these findings in other reference materials:

The close-up photos of various aircraft confirmed that the outer edge of the upper flap was slightly oblique (figure 'a", above). I can also see that the distances between the rows of holes in the last flap segment were shorter than in the segments in the middle. (It implies that the spacing between these rows in the most inner segment could be also a little bit wider). What’s more, I could see these differences in one of the original Douglas drawings (figure 'b", above). However, I neglected them before, because this is not a regular, orthogonal view. (Such a drawings can be often deformed in various ways).

Thus I modified the aileron and the flap according these findings (figure "a", below). When I attached wing to the centerplane (i.e. when I set its incidence and dihedral angles) I discovered that the corresponding aileron and flap edges became vertical in the rear view (figure "b", below):

An additional headache was the outer edge of the bottom flap, which was parallel to the last rib (figure "c", above). Ultimately I decided that most probably the outer corners of the upper and lower flaps overlaps as in figure "b", above).

Of course, I reviewed the whole model and made much more minor adjustments. I will not bother you describing them all. Fortunately, most of them did not require as much work as this small gap!

Figure below shows the resulting SBD-5 model:

In this source *.blend file you can evaluate yourself the current version, described in this post.

In the next post I will start the “painting” stage of this project. I begins with mapping of the texture coordinates (UV) onto the model surfaces (so-called UV-unwrapping).

In the previous post I promised that I will start the UV-unwrapping. However, last week I found a new edition of Bert Kinzey’s “SBD Dauntless” book. After ten years break, Bert started to continue his “Detail & Scale” series, this time in a different form: digital editions. This e-book is the “updated and revised” version of an earlier publication (from 1995). For me, the most important part of Kinzey’s books are the “walk around” photos. They differ from all other “walk arounds” by careful selection of the pictures and comprehensive comments that explain many technical details depicted on these images. Usually these comments are as important as the photos.



Take for example such a caption that you can find on page 102, below the picture of the forward firing guns (as in figure above):

All versions of the Dauntless had two fixed, forward-firing, .50-caliber machine guns which were fired by the pilot. This photograph was taken from the Pilot’s Manual for the SBD-2, and it shows both of the two fixed guns in place. However, the manual also states that the left side gun was usually removed from the SBD-2 in order to save weight. This was done only on the SBD-2 and usually only during peacetime. Once the war started, the additional firepower of the second gun was more important than the weight advantage gained from deleting one of these guns.

It is a great clarification that cites a reliable source: the original manual. In the other books on this subject you can find various, often contradictory versions about the SBD-1 and SBD-2 forward guns. For example:

This statement implies that the SBD-1 had a single 0.50 gun! (And it does not tell us about the source of this revelation).

Another one:

This statement implies that all SBD-2 had a single 0.50 gun because of the design reasons (aircraft balance). This is also an information without specified source.

You can find in the Web many other descriptions of the SBD-1 and SBD-2. I remember that I encountered somewhere yet another variation of this story. It stated that the pilot in the SBD-1 had two smaller, 0.30-caliber guns.

I am really happy that Bert gives us the ultimate answer on this issue. (In another place in his book he mentions that for this writing he used the six original manuals, one for every Dauntless version. That’s why I take for granted his statement that all SBDs had two 0.50 forward guns).

In the chapter about wings (page 85) I found the confirmation of my hypothesis about the overlapped flap edges:

Compare figure above with the second-last picture from my post from previous week. This was a result of the deduction, because when I wrote it, I had no such a vertical photo of the wing with closed flaps.

However, when I studied the photos of the cockpit canopy, I noticed a difference in the shape of the rear segments:



Figure "a", above, shows a fragment of the photo, taken from above. It reveals that the upper part of the last segment had a cylindrical surface, and the radius of the cross section between the third and the last canopy segment was larger than in my model (shown in figure "b", above).

It was further confirmed by all other photos: the side edges of all cockpit canopy segments were parallel, while in my model they are not:



I had to be blind that I did not noticed this mistake before! In fact, it happens when you stick too much to your assumptions about particular shape. In such a state of mind you can see only the details that confirm your hypothesis, and neglecting the others. I assumed that the top radius of the subsequent canopy segments decreased like in the telescope tube: each segment has smaller radius than the previous one. In the effect I received much smaller radius at the end of the third canopy segment than you can see on the Detail & Scale photo.

As the first approximation of this radius I placed inside the model an auxiliary circle (Figure "a", below):



I fitted this circle between the sides of the previous segment and decreased it by an appropriate clearance. Then I checked how it looks in another reference photo (Figure "b", above). In this way I have found that it should be slightly smaller. Thus I started to search for the reason of such a result.

Finally I think that I found the reason: the canopy sides should have a little less steep slope in the rear view. The error comes from the wrong assumption about the shape of the pilot’s canopy:



I assumed that the upper horizontal “sticks” of this canopy frame were nearly parallel to the fuselage centerline. In the effect the front and the rear edges of this segment were not parallel (figure "a", above). The photo from Detail & Scale book reveals that I was wrong (Figure "b", above). You can see on this shot from above that both horizontal elements of this canopy frame are parallel to the cockpit border edge. Thus I had to rotate a little the rear edge of the pilot’s canopy, making it parallel to the front edge. It forced me to decrease (by scaling) the radius of the arc that closes the upper part of this canopy. In the effect, I will have to decrease the corresponding arcs in all subsequent canopy segments, including the last segment. As I mentioned in one of the previous posts, I tried to avoid such things, but nevertheless I am prepared: the meshes of my model are relatively simple, so such a modification is not a great problem.

If you want to create a precise copy of any complex object, be prepared that from time to time you have to step back and alter the shape of some finished elements. The work on such a model more resembles a “spiral” than the classic “waterfall” process.

Well, I documented these small bur laborious modifications on the pictures below. Generally, in each canopy segment I had to rotate the side faces along their base (see it in the second segment, depicted in Figure "a", below). Then I scaled down (a little) the upper faces of such a mesh, decreasing in this way the cross-section radius of the resulting surface.



The third segment was more difficult, because the radius of the top arc in its cross sections increases toward the rear (Figure "b", above).

The most difficult part was the last, fourth canopy segment (see the picture below). First I formed its faces in the rotated position (figure "a", below), ensuring that it properly slides into the previous segment, and that its upper part forms a clean cylindrical surface:



Then I rotated it back into “closed” position, and verified all other details (figure "b", above). Fortunately, it seems that the radius of its rear edge did not significantly change, and it still fits the rear border of the cockpit. (It still looks like in the reference photos). The biggest change occurred in the frontal cross section of this canopy segment.

Figure "a", below, shows the modified shape of the cockpit canopy:



Figure "b", above, shows the same canopy with the updated frames. It is hard to notice any of my changes in this side view, isn’t it? In fact, fitting anew the frame meshes to the altered canopy segments required even more time than the adjusting of the canopy basic shapes! I am really happy that some posts ago I managed to tame the temptation to recreate the internal frames of these canopies. Now I would have much more work with them.

That’s why I am going to recreate all the internal details in the last, fourth phase of this project. In this way I am just creating “time buffer” for eventual new findings, like this one.

Of course I checked the updated canopy on the reference photos. This time I did not want to be blind on eventual differences — as you saw in this post, even slight distance between the model and the photo can indicate a significant error. I slid all the canopy segments into “open” position, to compare them to the CAF photo (this photo has the highest available resolution - see figure "a", below):



To better see the model on this picture, I assigned a red material to these frame objects. As you can see, most of the canopy frames match the photo. However, there are two exceptions, on the pilot’s cockpit canopy. The bottom ends of the middle and rear frames seem to be shifted (by about 0.2” and 0.3”). It could mean that the slope of these canopy sides had a slightly different angle. However, the front edge and the rear edge of this segment match the photo (figure "a", above). At this moment I will leave this difference unresolved — maybe in the future I will find something, which will help me to explain this difference.

There are also slight differences in the last canopy segment (figure "b", above). However, I think that I can explain them now. This part of the cockpit canopy has two degrees of freedom: you can slide it as well as rotate around its corner. The canopy in figure "b" seems to be rotated by about 0.5⁰. Such a small rotation can be within the tolerance of its lock mechanism. It can be caused by the gun doors, which seem to be slightly opened in this photo. There is also a thick rubber (or leather) strip around the rear edge of this canopy segment. It seals the rear border of the cockpit. (I will recreate it later). I think that the influence of the gun doors and this strip can rotate of this last canopy segment by such a small angle.

In this source *.blend file you can evaluate yourself the current version of the model, described in this post.

This post ends the “modeling” stage of this project. During this phase I formed the general shape of the model, and created all the surfaces which require the classic “image” textures. In the next post I will unwrap these surfaces in the UV space, preparing them for the “painting”. For all other details that I will create during the last, “detailing” phase, I will use procedural textures, which do not require UV-mapping. (The only exception are certain elements of the cockpit interiors, like the instrument panels, but they will have their own, separate texture images).

I have just begun the third stage of this project: “painting” the model. At this moment I am unwrapping its meshes in the UV space. I will deliver you a full post about this process next Sunday. Today I will just signalize how it looks like.

So I started by creating a new reference picture. It had to have a rectangular shape. Inside I placed my drawings of the fuselage, wings, and the tailplane:

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The most important thing: all elements of this drawing have exactly the same scale. As you can see, I used flipped left side silhouette in place of the right side view. In fact, I should prepare a 2D drawing of the right side view first, then place it here. On the right side of the Dauntless fuselage, the steps to the gunner’s and pilot’s cockpits were located in different places. There was also a rectangular hatch of the luggage compartment. However, I am a little bit lazy, and I prefer recreating these details directly on the final textures. I will describe what I mean in August, when I report how I drew it.

I use the reference images to keep the proportions between all unwrapped model parts. Sometimes it is also useful for hiding the seams, as in the case of these wings:

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I split the mesh into the upper and lower surfaces, and mapped it onto the corresponding parts of the reference drawings. On some textures (for example: the camouflage) it will be impossible to obtain an ideal continuation of the picture mapped along this seam. It is not a problem on the sharp edges, like the wing trailing edge. However, the rounded leading edge is a different case: I prefer to keep it “in one piece”, hiding the texture seam in the first original panel seam on the lower surface of the wing.

When the mesh is mapped on the reference picture, I use another, standard test picture to ensure that the mapped image is not deformed

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At this moment I have already unwrapped most of the model:

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I still have to unwrap the engine cowling. When I finish it, I will publish a full post about this process, as well as the updated model. (I will do it on next Sunday — July 24^th).

This week I finished mapping all the parts of my model onto a two-dimensional image. Figure below shows the test image, mapped on the model surface. (Its pattern helps me in keeping the same mapping “scale” for each object):

I did not “unwrap” the small details, like the parts of the propeller mechanism, because I will “paint” all the small parts using procedural textures.

Figure "a", below, shows how these meshes are distributed on the 2D UV map (you can see the reference image beneath). At this moment I mapped just a single (left) wing, the symmetric halves of the rudder and the fin, as well as the left side of the fuselage. The upper and lower part of the tailplane are symmetric, so I just mapped its left, upper side. I will create the other sides and symmetric elements later, at this moment I just reserved the necessary UV space for these objects.


In figure "b", above, you can see that the reference image looks like the first approximation of the skin details. In the next post I will draw an image of these details that fits these unwrapped meshes. It will be the base for all the textures I will create for this model.

In the rest of this post I will shortly describe my typical approach to UV mapping.

Let’s analyze the wing case. I am going to map its upper and lower surface separately. Thus I defined two auxiliary vertex groups, to easily select these mesh parts:

I use the Project From View command to create initial mapping. For the upper wing surface I use the projection from the local top view of the wing object:

I shifted and scaled this shape, fitting it to the reference image. I used “pinned” vertices from the flat part of the wing surface to this image (using the Pin command). Then I invoked (in the UV/Image Editor window) the Unwrap command:


It “relaxes” (unwraps) all the faces that are not pinned. In this case Blender unwrapped the leading edge and wing tip edge.

I unwrapped the wing bottom surface I the same way. At this moment the seam line between the upper and lower wing surface lies in the middle of the leading edge (figure "a", below). While it is OK for the relatively sharp edge around the wing tip, the minimal discontinuity of the texture image on the most exposed, forward part of the wing would spoil this model. Thus I usually hide such a seam, leading it along the nearest panel seam line on the lower wing surface (figure "b", below):


When I marked the seam line, I called another Unwrap command. In response, Blender “teared” the bottom part of the leading edge from the lower wing surface, and “glued” it to the upper surface:


As the final touch, I straightened the rib edges (it is much easier to draw the texture images on such an “orthogonal” wing layout). The only exception is the skewed inner edge of this wing segment:


When the wing surface was mapped, I replaced the reference image with the standard Blender test image (UV Grid). It is prepared for finding eventual mapping distortions:

As you can see, there was a serious distortion along the leading edge seam.

The remedy for such a flaw depends on the mesh local conditions. When it occurs on a flat surface, you can make the seam line sharp (setting its Crease coefficient to 1.0). However, in this case it would spoil the cross-section of the leading edge. The other, less preferable solution is to insert an additional, perpendicular edge loop. When you locate it in the proper place, it efficiently removes such a distortion:

(I do not like creating such additional edge loops, because each of them makes the resulting mesh topology more complex. However, sometimes you have no choice, as in this case).

In this source *.blend file you can evaluate yourself the current version of the model (as in the first illustration from this post).

After a long break in August and September (I had to finish a demanding project in my daily work) I am back. This week I made a “slow start”: because in my last July post I finished mapping the SBD-3, now I mapped in the UV space parts that are specific to the alternate Dauntless versions: SBD-1 and SBD-5.

Let’s start with the SBD-1: when you switch into its scene, you can immediately see the gray elements that are not mapped in the UV space (as in figure "a", below). These parts are specific for this version:

It did not require a lot of work *– just to unwrap few additional meshes in the UV space. You can see them in figure "c", above). I placed their faces in the same location, as their counterparts from the SBD-3. In figure "b", above, you can see the SBD-1 model after this update.

Then I had to make similar work in the SBD-5 scene. The engine cowling of this model contains more differences, thus it required much more work:

When all the meshes in all SBD models were unwrapped, I had to export them into a 2D drawing. (I will need such a picture as a reference for painting various textures). I prefer to keep it as a scalable vector drawing, thus exported it into an SVG picture, which I can edit in Inkscape:

The standard Blender command allows you to export only the single mesh of the active object. Some years ago I wrote an add-on which exports into SVG all selected objects at once. (You can find this add-on and learn how to use it in the III volume of this guide). It is extremely useful for such a model built from multiple objects, like this one.

Inside Inkscape I placed the exported objects onto a layer that has the same name as the defualt UV map in Blender: UVMap. (In the next posts I will prepare in Blender some other alternate UV maps, thus this naming convention is important).

Internally, I split in Inkscape the contents of the UVMap into five sublayers:

Two bottom layers (Color, Common) contains the elements that are common to all three models. I created Color layer for the future use. It contains just the fixed parts of the wing. I am going to use a separate texture for the national insignia and various technical labels. On some SBDs the stars on the wing lower surfaces were so large that they will require the seam line directly on the leading edge. Thus for this purpose I am going to create an alternate UV map for the wings. I will place it in Inkscape on additional Decals sublayer. Then, to create the UV layout for the insignia texture, I will hide the Color layer. When I will need the UV layout for the camouflage texture, I will turn off the Decals layer, and make the Color layer visible.

Why I did not simplify this drawing, creating in Inkscape a separate layer for each texture that would contain all the required objects? Because in such a case I would have to duplicate all of the common objects – sometimes several times.

The progress of my modelling project is not like a “waterfall”, it more like a spiral. From time to time I have to return to a finished stage, and fix something there. That’s why I always try to have just “one string that controls all”: in this case it means having single instance of every mesh in the Inkscape drawing. When I have to modify something in the corresponding Blender mesh, I will need to update just single element in this drawing, instead of multiple instances in the “simpler” version.

I use the same method as described above for obtaining the UV layout for a particular Dauntless version. There are three sublayers, named: SBD-1, SBD-3, and SBD-5. In each of them I placed just the elements that are specific for these version. For example, the figure below presents contents of the SBD-3 layer:

When you combine it with the basic layers (Color, Common), you will get the complete UV layout for the SBD-3:

(Of course, at this moment this layout contains only the left side of the model. I will update it later, adding the elements from the right side).

In this source *.blend file you can evaluate yourself the current version of the model, and here is the Inkscape file.

The progress of my work in this month will be relatively slow, because I still have some additional activities linked to my “daily” job. Nevertheless, it is going on.

The original texture map (UV map) finished in the previous post (as in figure below) is appropriate for the color textures (camouflage, national insignia and other markings). In this mapping various parts of the airplane overlap each other, so the pattern of the test image remains continuous:

While such an arrangement makes the camouflage painting easier, it would be impossible to use such a map with overlapping elements for another important texture: the image of the aircraft skin details. In this post I will shortly describe, how I prepared an alternate UV map for this purpose.

I am going to recreate all the panel seams, rivets, and hatches that you can see in the reference drawings using a height (bump) texture. The final effect will look as good (or even better) as with the details modeled “in the mesh”, while drawing these elements in 2D is much simpler and requires less work than the modeling in 3D. What’s more, I will use this image as the base for other important textures (reflection texture, transparency texture).

I prepared for this texture an alternate UV map:

To get decent results even in the close-ups of the final model, I need for the texture of the technical details a high resolution image. The simplest way is to enlarge the image, but it consumes the computer memory and increases the rendering time. To make better use of the available image space, I “packed” all the airplane elements more tightly. I also used another trick: because the left and right side of this airplane differ only in a few relatively small areas, I decided to map here only the left side of this model. I will use the same map for the right side. Later I will map the few faces from the right side that contains the differences in the empty fragment of this image.

To determine new size and locations of all model parts on this new map, I copied in Inkscape the UVMap layer (see previous post) with all its sublayers. I named this alternate map UVTech. I played for a while with the wings and main part of the fuselage. Ultimately I decided that I have to enlarge their size by uniform coefficient: 130%. The same coefficient applies to all other model parts. (The most important thing is to keep all these elements in the same “scale”. Otherwise you would have on the final texture rivets of different sizes, and other, similar errors). Then I moved and rotated some of the model elements, fitting them into the available space. In this way I created the first approximation of the new alternate UV map:

Using fragments of the scale plans, I also prepared an alternate reference picture that matches this layout (you can find it in the Blender file, linked at the end of this post). I used both of these pictures in creating this UV map in Blender.

To create an alternate map (named “UVTech”) in Blender, I had to repeat following steps for every mapped mesh in the model:

1. Copy the existing UVMap into new map, and rename it to UVTech:
   
   
   
   
   
   
2. Resize the mesh faces on this new map by 130% (I typed the exact value of “1.3” using the keyboard input feature):
   
   
   
   
   
   
3. Place the enlarged mesh faces as in the reference drawing:
   
   
   

Sometimes during this process I introduced small improvements: for example, I decided that I can shrink the areas on the control surfaces leading edges. (They do not contain any details, and are obscured by the wing or the stabilizers). It allowed me to fit these elements into the reference drawing:

When this work was over, I replaced the contents of the UVTech layer in Inkscape with the final shape of the UVTech map. (I exported it from Blender as an SVG file, as I did in the previous post).

In this source *.blend file you can evaluate yourself the current version of the model, and here is the Inkscape file.

In next week I will start to draw the image of the technical details of the aircraft skin.

This week I continue mapping the SBD-5 Dauntless skin panels onto my model. After tracing the outer wing sections, described in the previous post, I traced the center wing section:



As you can see in the picture, I also traced the contours of the wheel bay on the wing surfaces. (These openings disappear, when you enter mesh edit mode, because they are dynamically created by Boolean modifiers. Thus such contours will be useful during further work, because in this way you can see these edges while editing the mesh).

I also outlined contours of the bomb bay panels, which are modeled separately “in the mesh” (every panel is a separate Blender object). I did it, because the panel lines that I draw on this image will be used as the input for various final textures. In some case I will use them as the source of “dirt” that occurs around every cleft in the aircraft skin. These thick lines will provide a decent effect on the textures.

Of course, I also used the reference photos to verify panel locations:



When I compared panel lines in the photo and my scale plans, I discovered that I have to make some corrections. There was a significant difference in the size of the fuel line covers (see figure above). In the real aircraft they were somewhat larger than on my drawings.

In similar way I mapped the empennage panels. The growing number of identified differences between the reference drawings and real airplane forced me to use these panel lines as a kind of additional reference picture. That’s why I also decided to trace the ribs on all of the aircraft control surfaces.

Once I mapped these details, I started tracing fuselage panels. First I drew their “horizontal” lines that run along the longerons:



Fortunately, it was quite easy, because during the modeling phase I intentionally placed some edges of the fuselage mesh along rivet seams. Now this effort pays off.

Then I verified these new lines on the reference photo. I discovered that while the aileron and elevator ribs on the photo match my scale plans, the rudder ribs have different locations:



I also noticed another difference in the upper part of the tailplane fairing. Its outer edge runs along one of the fuselage longerons. In my model it is placed somewhat higher than in the photo:



When the other fuselage lines match their counterparts on the reference photo, this difference means an error in the shape of my model. I analyzed this area, and I started to suspect that the gap between the real line and line on my model is caused by the difference in the fairing shape. However, to be sure, I needed more evidence to proof this hypothesis. I carefully checked all available photos of this area:



Ultimately, I had found that the upper edge of the tailplane fairing is too high. In my model it overlaps the longeron line, while it should be adjacent to this panel seam. Lowering this edge will decrease the fillet radius in the upper area of the horizontal stabilizer fairing.

Well, it means that I have to revert to the modeling, and adjust the shape of this part:



I did most of the modifications shown in figure above by shifting mesh vertices along their edges. Fortunately, this command has an “update UVs” option, which automatically updates the mesh UV layout. Thus when I updated the fairing mesh and I looked on its UV map, the mesh was already updated there. I just had to export it to the reference image, and shift few lines into new location (as in figure "a", below):



After these modifications, fuselage panel lines match the photo (as in figure "b", above).

I had another kind of troubles with the lower part of the fuselage, behind the wing trailing edge. The UV layout of this mesh fragment has a significant distortion. A straight line on the model maps to a curve in this area. What’s more, I had to split this area (using seams) into two separate parts, which also creates some continuity issues:



It was quite difficult to find a proper curve on the UV plane that transforms into a straight line on the model. This process required several iterations. After I managed to keep shapes of these lines within acceptable tolerance, I identified another difference between my model and the photos: a short seam below wing fairing trailing edge (see figure above). While in the real airplane it was a nearly straight line, in my model its rear part reproduces the conical shape of the trailing edge cross section. I suppose that this fuselage area had a visible deviation from the “ideal” conical shape, caused by the technological constrains. (It is difficult to apply such a more pronounced curvature, as you can see in my model, to the aircraft skin stringer). I will deal with this issue in the next post.

Figure below shows the complete set of the panel lines, mapped on the SBD-5 surface:



I still have to map the differences that occur in the other Dauntless versions (SBD-1, SBD-3). Frankly speaking, I started to note some variations in the layout of the fuselage panels between various restored SBDs. Sometimes it is difficult to distinguish the real, historical differences between various versions from the side-effects of a particular restoration.

In this source *.blend file you can evaluate yourself the current version of the model, and here is the Inkscape file.

Wow, this is fantastic! It looks like a lot of strenuous work goes into the making of virtual aircraft. It's very intriguing to see what goes into making one. Your attention to every detail is striking. Well done!

Befudled - thank you! Well, as in the case of the "real" models there is alwyas a "quick way" for the less detailed replicase, and the "slow road" to the more precise works. The only difference is that you can make these digital models as detailed, as you wish. The only limits are your own skill and patience. Usually I determine the target level of details before I start recreating a new aircraft. This one has to be detailed.

In every creative process, after each “big step forward” you have to stop and carefully examine the results. Usually you have to make various corrections (sometimes minor, sometimes major), before taking the next step. This post describes such minor corrections that I had to make after mapping the key texture of the panel lines.

In my first post published in October, I drew the panel lines on the model, then compared them with the photos. Sometimes a minor difference between their layouts can lead to a discovery of an error in the fuselage shape. I in that post already found and fixed an issue in the shape of the tailplane fillet.

I also mentioned (see Figure 65‑9 in previous post) that I can see a difference in the bottom part of the wing fillet. Now I would like to resume my analysis at this point:

As you can see in the photo (figure "a", above) the shape of one of the seams on the bottom of the trailing edge (in red) differs from the photo (yellow dashed line). In my model this seam contains two segments figure "b", above): a straight line, corresponding to the flat, bottom surface of the fuselage, and a curved segment, resulting from the cross-section of the rounded trailing edge. From the geometrical point of view, such a shape is absolutely correct. However, it differs from the real airplane. Why?

Well, we should never forget about the way in which such an aircraft structure was built: there were fixed bulkheads of a fixed, determined shape, and the stringers (stiffeners) between them. It was possible to bend a little such a stringer between two subsequent bulkheads. However, the resulting curve always had a shape similar to a uniform, gentle arc – as you can see in the photo (figure "a", above). The combination of the straight segment and a curved segment (as in the model from figure "b", above) would require at least an additional bulkhead between these two segments. All in all, the real shape of the aircraft was not as ideal as you can see in my model. I had to modify its shape in this area.

Figure below shows the fuselage mesh before and after my modifications:

As you can see, in the final version I split the bottom of this fuselage into much more faces. It was one of these cases, when you try to change a single detail, then it occurs that this modification causes a “network effect”. Initially I rearranged faces on the fillet trailing edge, creating two additional n-gons. It improved the shape of the seam line. However, this removed small crease edge that was “fixing” the deformation around seam corner. Thus I had to find another place for the seam… Well, the resulting mesh does not look especially elegant, but it finally creates the desired effect.

Figure "a", below, shows details of my new concept for unwrapping this area in the UV space. I had to reduce the low-distortion area behind the wing. Actually it is just large enough to contain the identification lights. (It would be extremely difficult to obtain their circular frames on the highly distorted faces “glued” to the main part of the fuselage):

Figure "b", above, shows the modified UV layout of the fuselage mesh. This time I was able to not break any of the panel seam lines in the middle. Actually the new UV seam crosses just a single rivet line. (It does not create as many further complications as in the case of the crossed panel line).

Below you can see the panel lines on the updated model:

After so many modifications applied to the fuselage mesh, it is a good idea to check if they did not spoil something in the alternate UV layout. (This is second UV layout in this model. As you can find in the previous posts, I created the first UV layout, named UVMap, for the other textures, for example – for the camouflage).

Indeed, when I switched the current UV layout from UVTech to UVMap, I saw that I have some troubles here:

The primary reasons of these troubles are:

• Substantial modification of the mesh topology in this area (some of the original faces that were mapped in this layout have disappeared);
• Alteration of the seam line: seam lines are shared between UV layouts. I altered the original seam to another edge loop, while working on the UVTech layout;

In the effect, now I have now some highly distorted and stretched faces in the UVMap layout (as you can see in figure above).

To fix this flaw, I modified the UVMap layout. I had to accept that there will be some distortion of the texture image on the bottom wing fillet areas, as you can see in figures "a" and "c", below. I decided that such a distortion is passable for the color textures (for the technical details I will use another, UVTech layout).

An important element of the UV layout for color textures is the location of the seam lines. (The unavoidable color differences between separate parts of the texture image always occur along the UV layout seams). Usually I try to hide them, marking as the UV seams the mesh edges that run along a panel seam (see Figure 60-2, in this post). That’s why I cannot use here the seams from the UVTech texture: they run across a “blank” area of the aircraft skin. However, there are no appropriate panel seams in this area. Thus I when I decided to create an additional seam, I placed it along one of the rivet seams (as in figure "a", below):

Then I had to modify the layout of the mesh faces in the UV space (figure "b", above). (I used a little Blender trick to quickly obtain such an effect. First I temporarily removed the seams from the alternate UVTech map. I also removed all the “pins” from the vertices around this seam. Then I invoked the “Unwrap” command, and all the mesh faces “reorganized” themselves around the new seam. Finally I had just to pin them again, and restore the removed seams from the other mappings.)

However, it seems that I went in my modifications too far, when I “improved” the upper part of the wing fillet:

I deformed its original, conic shape, unconsciously reducing the cross-section radii of this surface over the wing upper area. It seems that I had forgotten to look on the photos. Now I have to fix this error.

To ensure that the shape of the panel lines in my model will match the photo, I placed in the model space some auxiliary “stiffeners” (figure 'a", below):

The reference photos were a great help here: some of them depicted these stiffeners in the side view, the others – in the top view (figure "b", above). I used these pictures to precisely determine locations of these seams in the 3D space.

Using my auxiliary objects, I was able to recreate the wing fillet with greater precision:

As you can see in the figure above, I also created two auxiliary conical segments. They provide me a kind of “indicator” of the differences between the “ideal shape” and the fuselage surface.

Figure below shows the results. Because there are no panel seams along the inner stiffeners of the wing fillet, I drew their rivet seams on the model texture. As you can see, they match both reference photos:

In this source *.blend file you can evaluate yourself the current version of the model, and here is the Inkscape file.

Within two-three weeks I should prepare the first texture. It will be the bump map.

Small update: since November I am engaged in a time-consuming project in my daily job.
I will resume my work on this model in March 2017.

OK, I completed in March my "daily" project, so I am back at my work here.

In this and the next post I will describe my work on the first of the textures required for the SBD Dauntless model. It is called bump (height) map. I use it for recreating all of the minor details that are visible on the aircraft skin.

However, before I begin this work, I had to put my model into more “natural” surroundings. I imported the environment (World) and the material settings from my previous model (the P-40). You can see the initial results below:



Of course, the propeller of this aircraft is static, and there is nothing in the cockpit and under the engine cowling. Do not worry, this is just the first approximation! The principle is that you should work with the materials in the final environment. Otherwise the final result may not look as you want. In this case there is an outdoor scene, full of the sunlight. (Every painter will tell you, that everything on the picture depends on the light: many details would look quite different in the indoor lights and their soft shadows).
As you can see, I decided to start this work with an ideal, smooth and shiny material. Each new texture that I will apply will make it more realistic.

Note for those, who will examine the contents of the Blender file that accompanies this post: I am using the Cycles renderer to create this one and the future pictures. (Cycles is one of the Blender rendering engines). The node-based schemas of its environment and materials are quite complex. What’s more, I modified them after importing from my P-40 model, temporarily removing all of the original P-40 textures, and disconnecting many fragments that initially are not needed:



If you would like to analyze details of this setup – you can find its step-by-step description in vol. III of the “Virtual Airplane” guide. It shows how to obtain the required effects, and also discusses some of the possible alternatives.

Creation of the bump map resembles work on a new scale plan. I am drawing it as the scalable (vector) drawing in Inkscape, adding new details to the picture that I started in one of the previous posts. Keeping the source picture of this texture in the SVG format allows me to quickly generate image of any resolution.

I decided that it will be much easier to use the same texture for all of the SBD versions. Thus I had to shift the UV maps of some version-specific elements (mainly the engine cowlings) into the other, unused areas of this UV space.

Then I had to fill the areas between the panel lines with rivet seams, bolts and various inspection doors. I stared with the center wing area. I used the reference drawings (scale plans and the UV mesh layouts) to create the first approximation of these lines:



Technically, I sketched the rivet seams as dotted lines, using a customized dot pattern. (You can find how to do it in the “Virtual Airplane” guide, in the chapter about Inkscape, section titled “Drawing a dotted line (rivets)”).

Then I matched these seams against the reference photo. Initially these rivets were in red, because this color makes them more visible against the background picture:



During this work I had both: Blender and Inkscape windows on my screen, side-by-side. On the reference photo in Blender I could see the differences between the real rivet seams and my drawing. Using these findings, I updated accordingly the drawing in Inkscape. Then I exported it from Inkscape as a new version of the *.png file, reloaded it in Blender, and looked for the remaining differences. Refreshing the mapped image with these “export+reload” commands is quick and requires just two mouse clicks, and one keyboard shortcut in Blender. Usually I need between 3 and 6 of such iterations to obtain a satisfactory match between my drawing and the photo of the given part of the aircraft.

When the rivet seams are in place, it is good idea to check if the internal ribs and spars fit their lines. (While working on the wing, I created a few of these internal reinforcements inside the wheel bay *– see figure below):



In the 3D View mode Blender draws the texture on both sides of the surface, so such a comparison is pretty straightforward. To see the rivet seams “through” the elements being verified, I switched their display mode to Wire. When I identified a difference, the rule was that the rivet seams are in proper location (because they were already verified against the reference photos, while these ribs and spars were based just on the reference drawing). In the case depicted above, I had to move forward the front spar (by less than 0.5”).

When I verified all the rivet seams from the current area, I switched their colors. Because the leading edge of the SBD wing had smooth finish with flush rivets, I created for them new sublayer, named Flush. These seam lines are black. The remaining rivets had classic (dome) heads, thus they are white. I placed them on another sublayer named Dome. I also added to this drawing the inspection doors and the fuel filler cover:



In the bump map texture, the shade of the gray determines the height of an area. The highest element is white, while the lowest is black. Thus I switched the background color of my Inkscape drawing to the neutral gray (50% black + 50% white). Then I could recreate the aircraft skin panels. In the SBD Dauntless these panels overlapped each other. To achieve this effect, I used areas filled with linear gradient:



In this fragment of the aircraft skin I used only areas filled with vertical gradients. I placed them on Panels:Vertical sublayer. (In more general cases, I will also use another set of panels, from :Horizontal sublayer). There are always some sheets riveted atop other panels. In this drawing, I drawn them as the lightest areas, placed on Overlays layer. To decrease variation of the rivets height between the darker and lighter areas, I made their layers partially transparent. (See more details of this method in the “Virtual Airplane” guide, in the chapter about Inkscape, section titled “Mapping construction details of airplane surfaces”).

As you can see in the figure above, I also sketched various minor openings in the aircraft skin. Initially they are red (just for easier matching against the reference photos). Ultimately the verified elements from this layer are black. I will use them not only for the bump map, but also for another auxiliary texture: the opacity map (you will see it “in action”, soon).

OK, let’s check how this first fragment of the bump map looks on the model. I exported it from Inkscape as a raster image (4096x4096px) named nor_details.png. Then I added to the material schema an Image Texture node, which represents this image. It is connected to the Displacement slot in the material output:



As you can see in the figure above, I selected one of the available UV maps by name *– using the Attribute node. Usually in my schemes it is accompanied by a UV Fallback node. This custom (group) node provides the default UV map for the meshes that do not have the UV map specified in the Attribute node.

You can evaluate the results below:



The first thing that I noticed: the dark gray dots that I used to emulate the flush rivets should create less visible seams. Currently their rivets seems too deep – so I should make these dots lighter. The same applies to the small bumps around bolt heads (visible on the covers).

You can see the details created by the bump texture when you place the model between the camera and the sunlight. (Check it, playing with the rendered model that accompanies this post). These skin details can completely disappear, when you look at the model from certain directions. As in the real world, all these rivets and panel seams are mostly visible not because of their shape (recreated by the bump map), but because of the small amounts of dust and dirt that accumulate around them. In one of the future posts I will recreate this effect, using the reflectivity texture. For this purpose I will reuse most layers from the bump map image.

In this source *.blend file you can evaluate yourself the current version of the model.

As you can see in this post, you have to draw a lot of details while preparing the bump map. (I think that this is the most time-consuming texture). However, nearly all of the other textures will base its drawing. In the next post I am going to show you the finished version, so give me some time to complete its image. I think that I will publish this second article about bump map within two weeks (on April 8^th).