SBD Dauntless

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.}

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

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.

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.

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.

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

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.

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...

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.

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.

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.

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 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.

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.

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!

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!!!!

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.

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 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.

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.

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 :).

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

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.

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.

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.

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).

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 )

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.

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

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...