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SBD Dauntless

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  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, July 22, 2017 3:32 PM

Back to the main subject:


The last texture for my model contains various elements that in the plastic kits are delivered as the decals: national insignia, radio-call numbers and various service labels. I prepared it as another vector drawing in Inkscape:

I exported this picture to a raster file named color-decals.png. It has transparent background, because I will combined this image with the other components of the color texture, prepared in previous posts.

The U.S. national insignia passed various transformations during the WWII. Between December 1941 and May 1942 the roundels on the Dauntless wings were enlarged, so they spanned over the ailerons (see figure "a", below):

However, as you can see in the photo of the USS Enterprise deck, there were exceptions: some aircraft preserved the older, smaller roundels. After 6 May 1942 all the roundels reverted to their “standard” size (72 in). Note that in this case they did not “touch” the aileron, but still their outer edge was very close to the leading edge (as in figure "b", above).

All of this means, that I cannot use for these wing roundels the same UV map as for the camouflage (UVMap). Although in this default UV layout the ailerons are in-line with the main wing surface (so they also fitted for the “decals” image), the problem occurs on the leading edge. In the UVMap layout its seam runs on the wing bottom surface, along the edge of the first panel. (I masked this seam on the camouflage texture in this way). Such a layout would split the bottom roundel into two parts – as marked in Figure "a", below):

To keep these roundels “in one piece”, I had to create another copy of the default UV layout (UVMap). I named it UVDecals. Then I modified it, adding an additional seam along the leading edge, and shifting appropriate faces from the upper to the bottom surface (as in figure "b", above).

In fact, I created this new UV layout only for the two objects: the outer wing meshes. This is possible in Cycles thanks to a special “fallback” node. In my previous model I worked out a node group, which can deliver the default (UVMap) coordinates for the all meshes that do not contain the requested (UVDecals) map. Such a group greatly simplifies using alternate UV layouts. You can find it in the material scheme as the UVFallback node:

Conceptually the color (diffuse) texture is composed from three images. The Decals image is placed over the camouflage (Camo), while the Dirt image is placed over them. Technically, the X.Textured Skin node internally places the decals image over the camouflage. Thus in the scheme you can see the Dirt image placed over the Camo and Decals images (it uses two Stack Image nodes for this purpose). If you want to learn more about these group nodes, see vol. III of the “Virtual Airplane” guide).

In the GIMP source, I shifted all the Stains layers from the color-camo.jpg into the color-dirt.png (see Figure 76-5 in this post). It allowed me to use the white stains layer for recreating weathering on the roundels located on the upper wing surfaces.

The stars on the wing bottom surface were also painted inside the letterbox slat. Initially there was something wrong with my UV mapping of this element (figure "a", below):

The pictures of the star on the slat inner surfaces were distorted (shifted). To fix this issue, I copied current UV layout (UVMap) into the UVDecals layout, and then shifted some of its inner UV vertices (figure "b", above).

Below you can see the first test of the “decals” texture:

At this moment it only contains the national insignia.

Now it is the time to “personalize” this aircraft. Let’s recreate the “black 4” from VSMB-241. As the first thing I added the radio-call numbers:

The single-digit number (“4”) was painted using the standard stencil. There was no problem in recreating this detail using the USAAF stencil font. (In fact – its vertical “stroke” was shortened. To recreate such a shape, I transformed the text into path and made appropriate modification). Then I exported from Inkscape the resulting color-decals.png picture and placed it as the reference in the source GIMP image, above the Camouflage layers. Finally I painted the darker background behind the radio-call number on a separate layer, as a new part of the camouflage image.

Using the USAAF font I am able to quickly recreate various service labels. In fact, most of them disappeared from this war-weary “black 4”. On the archival photo I can see only one label, on the life raft door (above left horizontal arm of the star – see figure "b", above). It is interesting to note how this detail appears on the restored aircraft:

As you can see, the labels on the restored aircraft are too large, and located in the wrong places. I recreated these elements in Inkscape, on a separate layer.

Restored aircraft can differ from the original in many details. In particular, their painting (the hue and the gloss of the camouflage, service labels fonts and sizes) leave much to be desired.

The last elements that I have to draw my “decals” texture are: the serial number (on the fin) and the model description (on the rudder). Unfortunately, the serial number is too small to be readable on the reference image, and the rudder is clipped out of its photo frame. All we can do is to use the photo of another aircraft from the same flight (as in figure "a" below):

Among the historical photos, I had only close shots of these numbers on some SBD-5s (figure "b", above). They showed me the proper font and size of these labels. For this aircraft I could only use a random serial number (figure "c", above). I chose one of the lesser ones from the two polls of the SBD-3 serial numbers (3185-3384 and 6492-6701). I suppose that the aircraft from this first pool were delivered before December 1941. On the historical photo (figure "a", above) of another aircraft from VSMB-241 you can still see the traces of the red and white stripes on the rudder, painted in December 1941. Then, in May 1942, the rudders were covered with the standard camouflage. You still can see these stripes behind the Blue Gray paint, because it was impossible to scratch the previous paint from their fabric skin. I reproduced this effect on my “decals” texture, drawing seven highly transparent stripes on the rudder.

Below you can see the final render of the “black 4”:

I also prepared for this model an alternate, sea environment:

I think that this picture of the Pacific Ocean creates a more familiar surroundings for such a naval aircraft. You can find the definition of this environment in the World tab of my Blender file. I named it Sea. Consequently, I renamed the previous environment to Land. You can easily switch between these two “worlds”.

In the next post I will work on the three-color Navy camouflage, used after January 1943 (you can find it mainly on the SBD-4s and SBD-5s). I will re-use in that new color scheme most elements from this two-color painting (the dirt texture, some of its weathering). Thus it will be a much quicker work.

In this source *.blend file you can evaluate yourself the current version of the model, and here are the Inkscape and GIMP source files of its textures. Because of the large size of the original GIMP file (*.xcf), this post is accompanied by its smaller version (2048x2048px), packed into *.zip file. I think that such a version is sufficient for checking all the details of this image (the structure of its layers, their opacities and mixing functions). The resulting textures (4096x4096) are packed into accompanying Blender file.

  • Member since
    January 2015
Posted by PFJN on Wednesday, July 26, 2017 4:46 PM


Thanks for the tips and feedback.

Your model is looking great, and your posts are super informative.  Can't wait to see more. Smile



1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, August 5, 2017 1:48 PM

Pat, thank you for following!

Today I am describing my work on the tri-color Navy camouflage:


In my previous post I finished the case of so-called “two-color” U.S. Navy camouflage, which was used between September 1941 and January 1943. You can observe on the archival photos that its non-specular Sea Gray / Light Gray combination was especially prone to weathering, and accumulated every grain of the soot and drop of the oil stains. Simultaneously the weathered Sea Gray paint became more and more white. The new, “tri-color” camouflage, introduced in January 1943, fixed these flaws, and provided better protection on the vast, dark waters of the Pacific. You can see an example of this pattern on an SBD-5 from VB-16:

However, this historical photo has a technical flaw: its colors are “shifted toward blue”. You can unmistakably see this “shift” in the color of the bottom surface (it was Intermediate White). I was not able to correct this deviation, finding acceptable. Below you can see another photo of a SBD-5 from VSMB-231, which colors are more balanced:

There were two variations of the tri-color painting scheme. While the most probably the “white 35” from the first picture represents the painting applied in the factory, the photo below shows a case of another variation:

The main difference is the dark Sea Blue section below the cockpit. It is creating a “bridge” of the Sea Blue color between the upper areas of the wing and fuselage. Most probably such a camouflage was applied by the Navy workshops, when the older aircraft were repainted from the “two-color” scheme. Note that all of the SBD-5s on this photo have larger national insignia than the “white 35” from the first picture. Their stars have precisely the same size and location as those in the two-color scheme. (It seems that the workshops just painted the two rectangles on each side of an existing roundel). You can also encounter aircraft that had the “bridged” camouflage and the smaller (i.e. standard) insignia, but it seems that all aircraft without the “bridge” below the cockpit had the standard roundels. This fact seems to confirm the “workshop” hypothesis of the “bridged” camouflage origins. Many modelers think that this variant of the tri-color scheme was created in the main Navy overhaul facilities at Norfolk.

In this post I will recreate the “white 35” shown on the first picture. This particular aircraft belonged to VB-16 squadron from USS Lexington (CV-16), and was flown by Lt. (Jg) George T. Glacken, with RM Leo Boulanger at the rear gun. There is another close-up photo of this aircraft, most probably taken during the same flight (early April 1944, over New Guinea):

This SBD-5 seems to be n much better condition that the weary SBD-3 from my previous post. From the photos of the other VB-16 aircraft it seems that the crew of this squadron had enough time to take care of their machines. All of them had uniform squadron emblems, the flying staff names were painted below the cockpits, and every mission was marked with a small “bomb” on the fuselage.

Unlike on the SBD-3, on this SBD-5 the anti-slip strip ends at the main spar (there is no forward part, painted in the glossy black). There are no visible deep (“bare-metal”) scratches on the center wing upper surface. Just some irregular areas and a few seams of the dome rivets are brighter. Most probably the paint was scratched from the heads fo these rivets. (There is no such a thing in the front of the main spar, because its seams were made of the “flat”, countersunk rivets).

I started my work on this camouflage by creating a new copy of the previous source GIMP file (Color.xcf). Then I modified its contents by repainting some key layers. Finally I exported the resulting pictures, overwriting the existing images (texture components in the skin material of my model).

The first repainted elements were the basic layers of the camouflage (color-camo.jpg image) – as in figure "a", below. This is one of the three color texture components. I simultaneously modified the ref-specular.jpg component of the reflectivity map, providing the “gloss” to the dark Sea Blue surfaces (figure "b", below):

I left the weathering layers of the camouflage image intact (hey are the same as in my SBD-3). You can see the first test render of this new camouflage (combined with modified color-dirt.png image) below:

This first render revealed that while the non-gloss surfaces look quite convincing, I had an issue with the more glossy upper surfaces. The dirt pattern disappeared on the highlighted areas. They look unrealistic smooth and clean (like on a polished airliner!).

The remedy for this issue is yet another texture, which will “modulate” the color of the specular reflections, making some areas darker than the others. It is quite simple – a neutral gray background and just some darker splashes. I named it color-specular.jpg. Figure below shows this image and its place in the material schema:

I also could put these splashes on a white background. However, I did not know if I would need some lighter elements. That’s why I used a neutral gray here.

Figure below shows the test render of this updated material:

I reproduced the scratches on the center wing in the same way as in the two-color SBD-3: using the scratches mask (mask-scratches.jpg image):

In this case the only bare-metal spots are the heads of the dome rivets. I recreated them using an inverted copy of the reference image. I also added some partially scratched areas in the front of the anti-slip stripes (they “reach” just the primer color).

Finally I prepared the “decals” picture in Inkscape, then exported it to the color-decals.png file. Analyzing various photos of other aircraft from the same squadron, I determined that the serial number on the fin was black, and small radio-call numbers (“35”) were also painted on the wing upper surface. I repainted in GIMP the VB-16 emblem (it seems to be in the contemporary cartoon style). Then I exported to a *.png file, and placed it in the SVG source image as a linked picture:

Below you can see another test render, featuring the complete texture set:

In overall, the tri-color painting looks acceptable. However, this model badly needs the details: the cockpit interior, radial engine, crew… Thus, in this post I am finishing the third phase of this project (“working with textures and materials”). Now I am starting the last, fourth phase: detailing. For most of the small parts that I will create in this last phase, I will use simpler materials that do not require any UV-unwrapping and texture images. For example – on the picture above the propeller hub requires different material (in this “white 35” it seems to be painted in a glossy Sea Blue). At this moment I kept the hinges and canopy rails in the natural metal color. I will have to “repaint” them, using simpler versions of the camouflage colors. Finally, it seems that I have to improve the glass material of the cockpit canopies (comparing with the archival photos, they are too “clear”). Anyway, I will describe my solutions to all these issues in the future posts.

In this source *.blend file you can evaluate yourself the current version of the model, and here are the Inkscape and GIMP source files of its textures. Because of the large size of the original GIMP file (*.xcf), this post is accompanied by its smaller version (2048x2048px), packed into *.zip file. I think that such a version is sufficient for checking all the details of this image (the structure of its layers, their opacities and mixing functions). The resulting textures (4096x4096) are packed into accompanying Blender file.

  • Member since
    January 2015
Posted by PFJN on Monday, August 7, 2017 12:21 PM


Thanks for the informative post.  I never had really though much about "toning down" white colors to keep them from coming across as too white.

Also, I see that you noted the squadron emblem was a raster image.  Out of curiousity, is pixelization an issue when you do your renderings and if so, how big a resolution did you have to have it so that you don't get any noticeable pixelization?

Can't wait to see more.


1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Monday, August 14, 2017 9:14 AM

Hi Pat,

thank you for following!



Also, I see that you noted the squadron emblem was a raster image.  Out of curiousity, is pixelization an issue when you do your renderings and if so, how big a resolution did you have to have it so that you don't get any noticeable pixelization?


In fact, when you examine the current "decals" texture of this model (4096x4096px in all), the resulting emblem is somewhat "pixelized". It just looks "good enough" on such a "general view" like the picture above.

However, in the source (Inkscape) vector drawing, this small circle is a 800x800px raster image. In practice, you cannot distinguish its pixels. This means that I am able to generate the resulting raster image of the "decals" texture in much higher resulutions (8192x8192px, or more), which will be apropriate for the close-ups. In this way I can control the "pixelization" of this and other details (for example: small labels).

  • Member since
    January 2003
  • From: Washington State
Posted by leemitcheltree on Saturday, August 19, 2017 4:13 PM

Good are....certifiable.  And astoundingly talented.  Your amazing dissection, interpretations, and renderings of the complex and esoteric shapes and details if the Dauntless are....just amazing.  I wow.  Superlatives seem....inadequate to describe your incredible work. 

If I may ask...what's the end game here?  What are your plans for this amazing rendering?  If you say it's to assist in the production of a 1/32 or 1/24 plastic model....I'll hand you my wallet right here, right now.


Thank you for your passion...your skill...and your desire to SHARE!!!  I'm in awe.

Kind Regards, Witold.  I'm a fan.

Cheers, LeeTree
Remember, Safety Fast!!!

  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, August 20, 2017 11:07 AM

leemitcheltree, thank you very much for following this thread!

In fact, you do not need "painting" with textures, as I described in the post above, when you are designing a new plastic kit. (On the other hand, you would have to prepare it in a NURBS-based modeler, like Rhino or a popular CAD system).

The goal of this project is a monograph of the SBD Dauntless. It will contain:

- detailed (1:48) scale plans of all its versions. (They will be generated automatically from my 3D model, and contain all the details, rivet seams included. This means that they will be much more precise than all other plans that are made from 2D silhouettes);

- some articles about this design and its use during WWII (this is not visible here, but I already gathered, red and indexed many books on this subject);

- color profiles of various SBDs, together with some visualizations (if my friend, who specializes in the ships, allows me to use his model of the Akagi, maybe I will even be able to prepare a scene from the Battle of Midway);

This monograph will be accompanied by the free Blender model (the ultimate version of the working files that accompany my posts). Its meshes can be used as a precise reference for designnig a plastic/resin kit (or a paper model).

As you can see, I work with a different, "virtual material" that is used to build computer models. It allows me to recreate all the aircraft details with the precision that is not possible in the world of the scale models. (I can "build" my model from the sheet metal that has the real thickness of 0.05", 0.03", or less). The only limit is your patience and available reference materials. The result can be shared - at least as a improved reference for the "real" models, or just as a model for a flight simulator.

Anyway, there is still a lot to do in this project - actually I am working on the details of the main landing gear. I suppose that I will publish a post on this subject next week.

  • Member since
    January 2015
Posted by PFJN on Sunday, August 20, 2017 12:50 PM

Witold Jaworski


Actually, your model has no shining elements, while in the real world everythng (more or less) reflects the light: add some rflectivity to your material. (Eventually you can expreiment with a ref texture - maybe some elements of your model should be more glossy than the others). If you using Blender / Cycles for this model, this book contains a "step by step" introduction to basic materials and lighting  - maybe it will be useful?



I just bought a copy of the "MAterials & Textures" chapter of your book last night, and am looking forward to reading it, as soon as I get the chance.  I suspect it'll take me some time though, as it looks very thorough and detailed. Smile

1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, September 16, 2017 2:06 PM



I just bought a copy of the "MAterials & Textures" chapter of your book last night, and am looking forward to reading it, as soon as I get the chance.  I suspect it'll take me some time though, as it looks very thorough and detailed. Smile


Thank you very much!
Feel free to ask me about any issue from this book!
  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, September 16, 2017 2:09 PM

I published my previous post a month ago, but the current stage of this project – detailing – requires less frequent reports. (Otherwise the posts would become rather monotonous: week after week they would describe making similar things, using the same methods). I started this last phase of the Dauntless project by recreating its main landing gear. First, I had to finish it, then I am able to write about this process. Thus I will describe it in this and next two posts. (I will publish them in a short sequence, week after week).

The retractable main landing gear of the SBD was probably a direct descendant of an experimental solution used in the Northrop 3A fighter prototype. In general, it looks quite simple: 

The upper part of the landing gear was an “L” – shaped tube, mounted between two wing spars. The lower part, visible below the wing, was a simple shock strut mounted to the wheel axle (see figure "a", below). The axis of the landing gear retraction was parallel to the thrust line and perpendicular to the walls of the spars (see figure above). The shock strut is deflected (by 6⁰) from the vertical axis, so that in the open position the wheel is directly below the axis of landing gear retraction (see figure "a", below): 

Figure above also shows various treads of the SBD tires. The tires of the earlier versions (SBD-1, -2 and -3) had no tread pattern (figure "b", above). The simple “straight grooves” treads appeared on the SBD-4 wheels (figure "a", above), while in the SBD-5/6s we can find a more elaborate, “brick” (figure "c", above) or “honeycomb” tread patterns.

Another interesting thing is the lack of the torque arms, that connect the cylinder and piston of the shock strut in most of the other aircraft (figure "a", below): 

The SBD manual explains that the designers used splined cylinders and pistons in their shock strut (figure "b", above). It looks like a quite elegant solution for the blocking random torsions of the shock strut piston (less outer parts that are prone to the eventual dust and jams). I did not find any complaints for this landing gear in the veteran memoirs and technical reports (usually they praise the “rugged structure” of the SBDs). However, all other aircraft designs use the torqe arms in their landing gear. Maybe they were just cheaper (i.e. easier to produce)?

Basically the work on the details means that you have recreate “in the mesh” all the parts you can see on the photos. Below you can see how I recreated the upper part of the landing gear leg: 

Recreation of such a die-cast part, with all of its additional walls, roundings, is a small challenge. To make it with as simple mesh as possible, I used several modifiers. First, I used the Mirror modifier to automatically generate the symmetric half of this object. (This symmetry was only possible because I decided to split this “L” – shaped part into two objects: this complex die-cast and a simple tube behind it. (This tube is not present in the picture above). Then I recreated all the rounded edges on this object using dynamically-generated fillets. Another modifier (Bevel) creates fillets along all the edges that I assigned a nonzero bevel weight. (The fillet radius is controlled by the value of this weight).

When this upper part of the landing gear leg was finished, I created the cylinder of the shock strut. It was just a tube with an octagonal flange *– nothing difficult. Then I had to create the lower part of the leg: 

It was another die-cast, which shaping required some time. (As you can see in the figure above, I formed this mesh from two crossing tubes).

While creating such a detailed assembly, I prefer to model each of its parts as a separate object. It gives me the opportunity to take advantage of its local coordinate system, when I need it. For example – the shocking strut is a tube rotated by 6⁰. When I formed it, I often extruded its faces along this local axis. Another advantage of such a model structure is the possibility of quick, “natural” adjustments of various parts. (For example – piston movement along the cylinder. In my model it occurs along its local Y axis).

Building the landing gear, I tried to check its retracted position as early as possible. Figure below shows first of these trials: 

As usual, a small fragment of the retracted landing gear leg protruded from the upper wing surface. I had to re-examine the photos, find which part has the wrong shape, and fix it.

I also used my photo references to recreate other landing gear elements, like the wheel brake disks: 

During this work I also found some differences between my model and the reference photo (see the notes in blue frames in the figure above). It seems that my landing gear is somewhat shifted forward.

Such a finding led to many rearrangements in the geometry of this assembly: 

In the background of figure "a", above) you can see my original drawing from 2015. After some deliberations, I decided to leave the center of the wheels at its current location, because it was dimensioned on the original general arrangement drawing. However, after measuring tire proportions on various photo, I decided that the SBD used slightly wider tires (30x7.5”) than the size (30x7”) specified in one of the comments placed on the original drawing from the SBD manual. (Sometimes draughtsman could make such a mistake). To fit the photo, I adjusted location of the shock strut, moving it slightly toward the fuselage. I also shifted downward the axis of retraction (rotation). Figure "b", above, shows how the updated model fits the reference photo. The tires on the photo still seems somewhat smaller than those from my model. However, I decided that this restored CAF aircraft could use a slightly smaller tires (29x7.5”). (This particular SBD-5 also uses at least another non-original part: a different version of its Hamilton Standard propeller).

Another element that requires some adjustments are landing gear covers. Although I created them during the modeling phase, now I have to compare their shape with the reference photo. Preparing for this test, I placed in my model a simple “stick” which I use as the hinge (I set it as the parent of the landing gear cover): 

The hard part was to determine the proper axis direction and the angle of this rotation. Surprisingly, the hinge was not lying directly on the aircraft skin (it would be the simplest solution). While it was relatively easy to find for a given hinge orientation a rotation which angle placed the left cover as on the photo, the same rotation applied to the right cover did not match the reference. It required some hours to find a combination that produced an acceptable (although not ideal!) match.

As you can see, I performed a lot of various checking, adjusting and matching while forming the key elements of the landing gear. All of this because it is still quite easy to correct the geometry of this assembly while it is relatively simple. It would be a nightmare, when I did such a thing on the final, detailed assembly, which you can see in figure below: 

However, before I finished this landing gear in such a state depicted in the figure above, I had to create several dozen bolts of various size, as well as other details. I also discovered some small secrets of its retraction mechanism. You will find a short description of all of these findings in my next post (to be published next week).

I decided to not enclose the source Blender file to this post, because it would contain just these few basic landing gear components. I will add it to the next post, which describes this assembly in the finished state.

  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, September 17, 2017 8:37 AM

Indeed! I used some photos of the center wing from this restoration... Great thing that they managed to finish this aircraft - it was an ambitious project!

Following your note, I have even found a short video from the taxi test of this SBD-4.

Maybe the owner corporation is registered as inactive, because they have not started to build their planned San Diego Naval museum, yet? (Maybe they are just collecting their exhibition?)

  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, September 24, 2017 4:49 AM

The SBD shock absorbers had to disperse a lot of the kinetic energy of landing aircraft, minimizing the chance that the airplane accidentally “bounce” back into the air. (This is a key requirement for the carrier-based planes). For such a characteristics you need a relatively long working span between the free (i.e. unloaded) and the completely compressed (i.e. under max. load) strut piston positions. Indeed, you can observe that the Dauntless landing gear legs are much longer in the flight than in their static position on the ground: 

The working span of the SBD shock strut piston was about 10” long, while the difference between the static and the free (extended) piston positions was about 7.5”.

In the most of the aircraft the landing gear retracts with the shock struts fully extended. When I tried to do such a thing with the Dauntless landing gear, as in the figure above, I discovered that it definitely does not fit its recess in the wing! (see the figure below): 

It seems that there was something that compressed SBD landing gear during retraction by about 7”. In the case of the Republic P-47 (which landing gear leg shortened during retraction by 9”), such a thing was widely discussed as an exceptional achievement of its designers. However, nobody even mentioned that the same issue was already resolved several years earlier by the Northrop/Douglas SBD team.

The SBD landing gear leg was made shorter during retraction by compressing its shock strut piston. This “compressing” mechanism starts with the cable that pulls the piston upward. The cable is attached to a quadrant, which rotation is controlled by the rail, fixed to the wing spar: 

An additional spiral spring, attached to this quadrant (as in figure above), tightens the cable when the landing gear is extended. In this landing gear position the spring “freely” rotates the quadrant, just following the shock strut piston movements: 

(You can also see how it works in this short video sequence). Note that this spring ensures that in the fully extended (free) position of the landing gear the tip of the quadrant arm nearly “touches” the rail.

This is the starting position for the piston compression. During the retraction the quadrant rotation axis is elevated upward, while its arm is dragged along the rail (there is a small roller on its tip). In the effect, the quadrant rotates, pulling the cable that compresses the shock strut piston: 

You can also see how it works in this short video sequence. (Note that in this video the path of the quadrant arm tip is not perfect. This is the result of a relatively simple real-time rigging. Anyway, it gives the general idea how this mechanism works).

I also recreated the inner details of the landing gear recess: 

During the modeling phase I already recreated two spars and two main ribs in the wheel bay. Now I refined their shape, following the available photo reference. I added also the remaining ribs as well as the stringers and the covers (at the rear part of the bay).

As you can see in the picture above, I did not model the lightening holes: as in the case of the wing flaps, I recreated them using textures: 

I unwrapped meshes of all these new wing structure elements into the available space on the UV layouts that I used in the outer skin material (B.Skin.Camouflage, refined in my previous posts). The Navy painted the inner space of this wing recess in the same color as the wing bottom surfaces, so there was not any problem in assigning the B.Skin.Camouflage material to these objects. As you can see in the picture above, I also recreated the internal reinforcements of the landing gear cover. The inner side of the aircraft skin is covered with a generic material, named B.Skin.Details.Bottom. (It is assigned to the second material slot of the wing skin mesh, and set in the Material Index Offset field of its Solidify modifier). This simpler material is intended for the smaller details, and uses exclusively the generic, procedural “noise” textures for the dirt/ref effects. Thus it does not require any time-consuming UV unwrapping. In the figure above I used it also in the cover fittings. I only have to remember to alter the basic color of this simpler material when I switch to another camouflage scheme. (In the future, I will also create a similar material for the details on the upper surfaces – it will only differ in the basic color).

Because this B.Skin.Details.Bottom material has no regular bump map, I had to recreate more landing gear details “in the mesh”. In particular, I had to add the bolts (and nuts) visible on the reference photos. I created each of them as a separate object: 

All these bolts are clones of a few basic original bolt meshes (one with the octagonal head, others with the flat one). Among these originals there are also two or three variations of the bolt length. By default these bolt meshes are covered with a generic “steel” material. When I needed to “paint” them into different color, I alter their material assignment. (In such a case, I had to switch them into the object – based material mode).

Sometimes some of these bolt objects are also useful as the reference objects in the rigging, but I will discuss it in the next post.

I also like to have a look at the retracted landing gear inside the wing structure. When you can see these two assemblies together, suddenly the reason for some strange features of the particular rib or spar shape becomes clear: 

In figure above you can also see a couple of bolts forming an octagonal group on the rear spar. In general, I recreated most of the bolts and rivets on this spar using the bump texture. However, this was a special case: in the original airplane these bolts had quite large heads. What’s more, they were placed on a “stack” of two subsequent panels. I simply run out of the available grayscale of the bump texture in this particular place, thus I decided to recreate these “topmost” details in the mesh. (Just an exception from my general modeling tactics of using the textures as often as possible).

Figure below shows the complete landing gear in the open position, the shock strut fully extended: 

The decision to use a simpler materials that do not require UV-mapping has certain disadvantages. The most important of them is that I am not able to paint the small stains around the landing gear bolts and other kinds of the local dirt. But this is just the consequence of the level of details that I assumed for this model.

I have to reveal that this project has a certain deadline: I promised a local modelers’ magazine to deliver detailed SBD scale plans and a couple of color profiles in January 2018. Thus currently I am focusing on the external details, because I have to recreate them to the end of this year. It includes the landing gear and a simpler version of the engine (not intended for the extreme close-ups). When it will be done, later in 2018 I will recreate the cockpit interior, as well as the detailed engine compartment and wing flaps mechanism. This more enhanced version of this model will be intended for a SBD monograph (a book). I will publish it much later.

Among the materials that I have to deliver in winter 2018 I will not enclose any close-up pictures of the landing gear or other details, thus I can use the simpler materials here. However, in such a harsh light as in Figure 80‑10 the elements covered by the B.Skin.Details.Bottom material seem too “clean”. I will definitely work on this issue, increasing the contrast of its “noise” textures to give these landing leg and brake disk a more “dirty” look.

In the next post I will describe how I rigged this landing gear. (I will describe building a kind of “virtual mechanism” that allows me to extend/retract the undercarriage using a single slider. I already used it, making the video sequences presented in this post).

In this source *.blend file you can evaluate yourself the current (i.e. non-rigged) version of this model.

  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, September 30, 2017 1:31 PM

In previous post I discussed how the SBD landing gear retracts into its wing recess:

In principle, it is simple: the landing gear leg rotates by 90⁰. However, the parts responsible for shock strut shortening during this movement increase mechanical complexity of this assembly. The figure above does not even show the deformations of the brake cable, which follows the shock strut piston movements.

For some scenes I will need the landing gear extended, while for the others – retracted. In practice, moving/rotating each part individually to “pose” my model would be a quite time-consuming task. That’s why I created a kind of “virtual mechanism”, which allows me to retract/extend the landing gear with a single mouse movement. In the previous post I already presented its results in this short video sequence. In this post I will shortly describe how I did it.

In general, I coupled some key elements (objects) of the landing gear using so-called constraints. For example, I connected the rotation of the landing gear leg with the movement of a special “handle” object. To do it, I used a Transform constraint, attached to the parent object (the axle of the retraction) of the landing gear leg:

I created an auxiliary (non-rendered) “handle” object (X.600.Wheel.Handle). The Transform constraint of the landing gear leg axle (0.604.Strut.Axis.L object) converts the handle linear movement into landing gear rotation. Thus when I shift the handle object upward, landing gear leg rotates, retracting into its place in the wing. To restrict the range of this rotation, I assigned to the handle object additional Limit Location constraint. It restrict its possible movement to a 40-unit long span along local Z axis.

The more detailed explanation of my methods for the “mechanization” of the landing gear would take too much space in this post. However, some years ago I published an article on this subject (in “Blender Art Magazine”): 

To read this article, click the picture above or this link. I hope that this publication will explain you the general idea and typical implementation of such a “virtual mechanisms”.

The format of my posts (10-11 pictures) allows just for a quick review of the SBD landing gear constraints (one picture per a subassembly). Thus the next element coupled with the handle object (using another Transform constraint) is the landing leg cover: 

In the previous post I added many bolt objects to the landing gear, and mentioned that some of them will have an additional use. So this is just such a case: I set the forward bolt of the cover hinge as the parent of the whole cover assembly. (Because it lies on its rotation axis). A Transform constraint, assigned to this bolt, forces it to rotate in response to the handle vertical movements. Note that the range of rotation of this cover (101⁰) is greater than the range of the landing gear leg rotation (90⁰).

Another Transform constraint converts the rotation of the quadrant object into movements of the shock strut piston: 

This relationship seems quite straightforward: when the quadrant rotates upward, the piston shifts up, when it rotates downward, the piston shifts down – as if they really were connected by the cable. Rotation of the quadrant is forced by its Locked Track constraint, which arm “tracks” the auxiliary (non-rendered) target object (the red, small circle in the figure above). Effectively, location of this quadrant target controls the shock strut position.

The full motion path of the quadrant target object contains an arc and a straight segment: 

The arc corresponds to possible piston positions for the extended landing gear (see this short video sequence). The linear segment corresponds to the forced compression of the shock strut during retraction, when the quadrant arm tip slides along the internal rail. (You can see this motion here, although in this video the path of the quadrant arm tip is not ideal).

I did not want to use the animation motion path here, because it creates a “deterministic” movement (“frame by frame”). Instead, I wanted a general solution, controlled by a handle object instead of the animation frames. Thus this is the most complex subassembly in this landing gear rig. I will describe it in two pictures: one for the extended landing gear (implementation of the movement along the arc), the other for the landing gear retraction (movement along the linear segment).

When the landing gear is extended, the rotation of the quadrant target is forced by its “grandparent” object. This is an Empty instance, named after the source of the original movement it mimics: X.Quadrant.Spring.Control

A Transform constraint converts the vertical movement of the additional handle object (X.600.Strut.Handle) into rotation between -24.7⁰ and +118⁰. There is another Empty object (0.607.Target.Left.Parent), attached (by the parent relation) to the X.Quadrant.Spring.Control. Simultaneously, 0.607.Target.Left.Parent is the parent of the quadrant target object. (The reason for such an indirect relationship will become clear in the next figure). When the landing gear is extended, this chain of “parent” relations forces the quadrant target object to move along the arc path when the handle object moves up and down. To not exceed the minimum and maximum angles of this movement (and in the effect – the lowest and highest shock strut piston position), the location of the handle object is restricted by a Limit Location constraint.

Note that this smaller handle is the child of the main handle, used for the landing gear retraction (X.600.Wheel.Handle). Note also that the Transform constraint that forces this rotation, evaluates the handle position in the World Space (figure above, bottom right). This means that regardless of the position of the smaller handle, the shock strut will be fully extended after moving the main handle along the first few units along its way up. (So that I do not have to care about the initial piston position when I am starting landing gear retraction: it will set up itself).

During landing gear retraction the locations of the quadrant target, its parent, and “grandparent” become dispersed. Figure below shows how it looks like in the middle of the main handle (X.600.Wheel.Handle) movement: 

The parent (0.607.Target.Left.Parent) of the quadrant target object just “delivers” it to the rail line and stops there. (This is the end point of the rotation of its parent: X.Quadrant.Spring.Control object, as you can see in the previous figure). Then the quadrant target object is “dragged” by the landing gear retraction along the rail. I tried to obtain this effect by assigning it two constraints:

  1. Limit distance, which forces a fixed distance between the target object and the quadrant axis;
  2. Limit location, which restrict the possible location of the target object just to a certain span along its parent X axis (which I set parallel along the rail);

In theory, for such a constraint combination there is always just a single possible location of the target object (marked in the figure above). Unfortunately, it seems that Blender treats these constraint with certain “flexibility”. In the effect, the quadrant arm tip “sinks” into the rail. This effect is especially visible at the beginning of the landing gear retraction. Well, I tried hard but I could not find a better solution for this movement. Finally I concluded that I can left it in this state: this is a small part, which movements are partially obscured by the wing recess. When I need to make a close up, I can prepare a “deterministic” animation motion path for the quadrant target object.

The last rigged subassembly of this landing gear was the elastic brake cable. Because I used in this implementation another (better) solution than described in my article and book, I will discuss it shortly below: 

First, as in my previous model, I formed the curve (figure "a", above), that deforms the simple tubular mesh into the brake cable. (I used a Curve Deform modifier here). Then I created a simple armature consisting two bones: upper and lower (figure "b", above). The armature object is attached (by a parent relation) to the strut cylinder. Thus the origin of the upper bone is also fixed in this way. I assigned to the lower bone an Inverse Kinematics constraint, and set its Target to an auxiliary Empty object at its end. This target object is indirectly (via the brake disk) attached to the piston. In the effect, this armature follows every piston movement in a natural way – like a pair of the torque scissors. Finally I attached subsequent curve vertices (control points) to the nearest armature bone (figure "c", above). I also attached (via parent relation) the ankle object (at the bottom end of the brake) to the bottom bone. (So that it will follow its rotation). In the effect, the brake cable deforms when the shock strut piston is shifting, following its movement in a natural way. See this short video how it works.

In my previous model (the P-40B) I used for the same purpose a different, less effective combination of the constraints. I think that in the future I will always use the solution as in figure above, not only for the brake cables, but also for the torque scissors (the SBD landing gear did not have such an element).

Finally, I applied my Handle Panel add-on to create a convenient landing gear controls among the Blender panels: 

See this short video how it works. Now I can extend/retract the landing gear with a single mouse movement. I even do not have to know, where their handle objects are – the add-on will discover them automatically. (I just have to arrange them in the model space in a certain way – see the add-on description for details. This is a general utility, you can use it in your own Blender models).

The next part to recreate is the tail wheel assembly. I will report this step within two or three weeks.

In this source *.blend file you can evaluate yourself the current version of this model.

  • Member since
    January 2015
Posted by PFJN on Sunday, October 1, 2017 8:30 PM


Thanks for the detailed posts.  They are very helpful in understanding not only how you have done your modeling but also in understanding how the full scale aircraft worked.

Can't wait to see more Smile


1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, December 16, 2017 11:39 AM

Pat, thank you for following!

Well, for reasons beyond my control I had to take a break from this project. Today I am publishing the post about the tail wheel (see below), but this is my last article for the nearest three or four months.

I will resume my work on this Dauntless in the spring 2018.

  • Member since
    June 2014
Posted by Witold Jaworski on Saturday, December 16, 2017 11:41 AM

The Dauntless had fixed tail wheel of a typical design among the carrier-based aircraft. The tail wheel assembly consisted a fork connected to two solid-made beams, which movement was countered by a shock strut. The beams and the shock strut were attached to the last bulkhead of the fuselage:


The bottom part of this assembly was covered by a guard and a fairing. Both of these elements were attached to the lower beam. The archival photos reveal that the bulky fairing was often removed:


There were two tail wheel versions: the smaller, solid-rubber wheel for the carrier-based aircraft (as in figures above), and the larger, pneumatic wheel for the ground-based aircraft. As you can see on the example of a SBD-1 (below), they could be replaced in a workshop:


Figure above shows two SBD-1s, which were exclusively used by USMC squadrons in the continental United States. All of these 57 aircraft were built in 1940. As you can see in the photo above, they were originally delivered with small, solid tires. However, in the photo below, taken a year later, one of these SBD-1s has the large, pneumatic tail wheel. It seems that Douglas delivered these large wheels to the Navy / USMC as an optional kit, which could be mounted when needed.

The smooth tip of the tail was mounted to the last bulkhead as a light, easily detachable tail cone. It covered the tail wheel shock strut, as well as the rudder and elevator control mechanism. There was a large opening in the bottom of the tail cone. For certain sunlight directions (for example, in a dive) you could “look inside” the fuselage:


As you can see in the figure on the left, the tail wheel fairing effectively closed most of this view (figure "a", above), so that you could see just the catapult holdback fitting, two ribs and their stringers. However, when you remove this fairing, you can see many details inside (figure "b", above). Of course, they are not visible on most of the photos. These details are hidden in the pictures taken on the ground. In most of the in-flight photos this opening seems to be too small to reveal the interior details. However, thinking about the future scenes of diving bombers, I decided to recreate at least the key internal elements of this tail cone.

While the tail wheel in the SBD does not retract, it follows the shock strut compression. Thus recreation of this assembly requires some initial adjustments of these moving parts. (For example: I had to make sure that the wheel leg will fit into the tail cone). I am shortly describing this process below:


I started with the tire, its fork and the guard, which are present on my reference photo (figure "a", above). I also added the stringers along the border of the opening in the tail cone. Then I placed the simplified shapes of the tail wheel beams. At the beginning I did not know their proper width, thus their initial mesh was a simple, four-vertex trapeze, ready for eventual adjustments. In figure "b", above, you can see also a bolt at the end of each beam. They were important parts of this “virtual mechanism”. No armature was needed in this case. I decided that the lower beam will be animated by the handle movement. Thus I forced the upper beam to follow its rotation using a Copy Rotation constraint. Each of these two bolts is attached (by parent relation) to the corresponding beam. The tail wheel fork is attached (by parent relation) to the lower bolt. Simultaneously this bolt rotates, tracking the center of the upper bolt (using a Locked Track constraint). Thus, when I rotate the lower beam, it rotates the whole assembly (as in figure "c", above). Then I adjusted the width of the guard and the beams so that in the fully deflected position it fits the opening in the tail cone (figure "d", above).

Once the overall size of the beams was determined, I recreated their shapes, as well as the catapult hold back fitting, shock strut, and the tail wheel fairing:


The catapult fitting was attached to the ribs of the tail cone. Its side arms were fitted between the tail wheel fairing and the stringers running around the border in the tail cone opening. As you can see in figure "a", above, I started with the conceptual lines of this part. Then I used them to form the final “Y” – shaped fitting (figure "b", above). Using similar methods I recreated the beam details. (I could do safely, because they were already fitted to the tail cone, and I do not expect any further changes in their shape). Finally I also added the internal ribs of the cone (figure "c", above).

In the next step I recreated the rudder/elevator torque tubes and their fittings:


Figure "a", above, shows the rudder torque tube. It was mounted on a tripod. Note, that the rudder rotation axis lies in the front of this tube. (It rotated around the bolt that joined the torque tube with the tripod). For this level of detail I did not recreate the control cables. (Perhaps I will do it in the future). I also formed the elevator torque tube (figure "b", above). Its rotation axis also lies in the front of the tube. According the maintenance manual, there were also two pulleys for the elevator trim tab cables (figure "c", above). Unfortunately, I do not have any precise photo of this detail. I recreated their brackets using two rough sketches from the maintenance manual, but about 50% of their size and shape is just my guess. If any of you have a photo of the details from figure "c") (for example – from a restored SBD), let me know. I would appreciate any of such pictures.

Figure below shows all of the tail cone internal details that I have recreated so far:


For the assumed level of details I simplified some small elements, like the trim tab pulleys. I also did not recreated other minor, less visible elements like control cables, electric cables, some additional fittings and bolts. I will recreate them later, when I decide to make cutaway pictures of this model.

To recreate the alternate, “solid” version of the tail wheel, I switched to another reference photo:


The SBD on this reference photo was restored for Pacific Aviation Museum Pearl Harbor. Although the restoration teams do their best to recreate their “birds”, sometimes you can find a non-original part on their aircraft. In this case it was the tail wheel fairing: it is smaller and simpler (figure "a", above) than the original part (figure "b", above). However, the rest of the tail wheel assembly seems to be original, thus I used this photo as the reference for the “carrier-deck” version of the tail wheel and its fork.

Finally I also added the tail hook (it was removed only from the A-24s, delivered to the Army). As you can see, it was accompanied by some minor details:


Figure below shows the final result: the complete tail wheel and hook assemblies:


As you can see, I initially painted the internal surfaces using the standard Interior Green color, but then I was starting to have doubts. In the restored aircraft these surfaces are usually painted in the gray camouflage color (the same as used for the aircraft underside). Unfortunately, I did not have any historical photo of this area to determine how it was painted in the original SBDs. Most probably I will update the color of this detail according the restored aircraft.

The next part I am going to recreate is the R-1820 engine (a simplified version, for the external pictures). However, for reasons beyond my control I have to take a break from this project. I will write next post in the spring (2018). So, for time being my SBD will look like this:


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

  • Member since
    January 2015
Posted by PFJN on Saturday, December 23, 2017 9:58 PM


Thanks for the status update on your model and the info about the tail wheels.  I had heard similar things for other planes of the period.

I can kind of see why they would want an inflatable tire when operating from land bases, but I am kind of surprised that they used such a small hard wheel when operating from a carrier.  I would have thought that a larger inflatable tail wheel would help prevent too much wear and tear on the wooden deck cov erings of that era.



1st Group BuildSP

  • Member since
    September 2012
Posted by GMorrison on Tuesday, December 26, 2017 3:35 PM

Fascinating. I haven’t looked at this before.

WJ I gather your model is the drawings you are creating, correct? 

As for the solid tail wheel, look at it from the other point which is that a pneu tire is just one more thing to have go wrong or be damaged in battle, and a landing accident is more catastrophic than a torn up deck.

 Modeling is an excuse to buy books.


  • Member since
    June 2014
Posted by Witold Jaworski on Wednesday, December 27, 2017 8:18 AM

Thank you for visiting this thread Smile!


WJ I gather your model is the drawings you are creating, correct? 

Yes, this is a computer model, so its "real" representations are the computer-generated pictures: various visualizations, scale plans, color profiles. This particular model is not directly intended for the 3D printing. (However, it can be used as a base for such a copy).

About the pneumatic tail wheel: I think that it was helpful for various ground airfields, which surface was often soft (because of rains or other reasons). The Marston mats did not always resolve this problem and the solid wheel colud "sink" into the ground, making the take off more difficult (especially with a heavy load). Of course, all depends on the local supply: for example, the SBDs from Henderson Field (Guadalcanal) retained their solid tail wheels. But the USMC SBDs that bombed the Rabaul in 1944 and 1945 had the large, pneumatic tail wheels. (I suppose that a perforated tail wheel was not a big problem - just more drag during the landing. The real danger for the aircrew was the perforation of one of the main wheels).

  • Member since
    June 2014
Posted by Witold Jaworski on Wednesday, April 18, 2018 2:19 PM
The engine is the heart of every powered aircraft. In the case of the SBD it was the Wright R-1820 “Cyclone 9” (the “G“ model). In fact, this engine was one of the “workhorses” of the 1930s: designed in 1931, it was used in many aircraft, especially in the legendary DC-3. “Cyclone” was a reliable, fuel-saving unit for the Navy basic scout type. (Remember that the “Dauntless” was not only the bomber: it was also a scout airplane[1]). In general, the R-1820 is a classic nine-cylinder, single-row radial engine:


The R-1820 G had been produced for over two decades, not only by the Curtiss-Wright, but also (under license) by Lycoming, Pratt & Whitney Canada, and Studebaker Corporation. Thus various less important details of this engine “evolved” during this period. In this post I would like to highlight some of these differences. I will focus on the forward part of this engine, because at this moment I am going to create a simpler model of the “Cyclone”, intended for the general, “outdoor” scenes. Inside the closed NACA cowling, you can see only its forward part. (Thanks to the air deflectors, placed between the cylinders - see picture above). In such an arrangement, the visible elements are: the front section of the crankcase, cylinders, ignition harness, and the variable-pitch propeller governor. While the front section of the R-1820 crankcase remained practically unchanged in all versions, and the governor depends on the propeller model, I could focus on the cylinders and their ignition harness.

Identification of the version differences is the basic step, because otherwise you can build a model of non-existing object that incorporates features from different engine variants.

BTW: do you know, that the R-1820 design had remarkably long life? The United States factories produced the last batch of these engines in 1964. The metric version of the earlier “F” model had been produced in Soviet Union under Wright’s license since 1934. A few years later Soviet engineers developed its enhanced version: Ash-62 (resembling the “G” model of the “Cyclone”). Ash-62 was widely used in 20th century aircraft of the former eastern block (especially – in the popular Antonov An-2), and had been produced under Soviet license in many countries. Actually the last factory that still produces these engines is PZL WSK-Kalisz in Poland. They provide new units for the last flying DC-3s, An-2s, and M-18s, as well as the overhauling services. Who knows, if this “eastern branch” of the R-1820 will last long enough to celebrate the 100th anniversary of the famous Wright design?

While looking for the reference materials, I have also found an interesting article about the development of air-cooled aviation engines (more precisely, their most important parts: cylinders). I think that it provides a valuable “technical context” for the visual differences that I am describing below.

Searching for the reference photos, I have identified two basic variations of the “Cyclone” cylinder shape:


Figure "a" above shows the classic version, produced to the end of the WW2, while the cylinder from Figure "b" comes from the post-war production. I will refer this earlier one as the “classic” version. This is the engine used in all SBDs. You can quickly identify this version by the characteristic “L”-shaped fins on its cylinder head (Figure "a"). The “classic” head has also curved contours, while the head of the post-war version has different style, and its contour is based on the straight lines. Both heads are aluminum die-casts. The critical element in this design was the overall area of their fins. Greater cooling area of the cylinder head allows you to obtain more power from the same piston volume. Thus the fins of the “classic” head are small wonders of the 1930s metallurgy: they are evenly spaced at 0.2” (5mm) along the head, and the widths of their tips do not exceed 0.05” (1.2mm). The fin at its base is about 0.1” (2.5mm) wide. Die-casting of such an object is extremely difficult. It requires not only the “written down” engineering knowledge, but also individual artisanship of the key workers. Note that the spaces between the fins of the post-war head are two times wider than in the “classic” version. However, between each pair of these “full-size” fins there is a smaller, much shorter “inner” fin. It is much easier to die-cast such a head. I suppose that the post-war heads are cast from an aluminum alloy that has better heat transfer characteristics. It would allow their cylinders to maintain similar power output using somewhat smaller cooling area.

The cylinders of the last R-1820 versions had yet another, conical shape:


In this photo you can also see here the propeller governor (in the first photo in this post it is hidden behind the propeller blade), and another version of the ignition harness.

The “classic” and the “post-war” cylinder heads have different orientations of their intake openings, which results in different shape of the intake pipes:


The classic version has a simpler, L-shaped intake pipe, which fits to the oblique opening of the intake valve (Figure "a", above). In the post-war version planes of both valve openings (exhaust and intake) are parallel (Figure "b", above), thus the intake pipe has a more complex shape (resembling “S”).

In fact, Figure "b" above shows the smaller, 7-cylinder version of the Wright Cyclone (R-1300). However, it used the same cylinder and intake ducts as the late R-1820. (I just could not find a shot similar to the Figure "a" of the late R-1820 version, so I used the picture of its “smaller brother” instead).

There are also minor differences in the rocker covers:


The classic version has simpler, four-bolt rocker cover (Figure "a", above), while the post-war covers uses two bolts more. The head of the post-war engine has some additional features (Figure "b", above), which do not exist in the classic head.

Finally, the ignition harness:


Classic ignition harness has a “collar” shape, smaller radius, and individual spark plug cables organized in pairs (Figure "a"). Post-war harness has a ring shape, somewhat greater radius, and evenly spaced spark plug cables (Figure "b"). Although each of these photos is taken from different side, it seems that both versions use the same propeller governor.

Having all these issues identified, I could select appropriate reference drawings. They came from “Cyclone 9GC Overhaul Manual”, published in 1943. I expect that even the simplified model of such an engine can have many hundred thousand faces, thus I decided to build it in a separate Blender file. I use the same “scale” as in the SBD model: 1 unit = 1 inch. When it is ready, I will import it into the SBD model.

In this new Blender file I decided to give chance to the alternate method of setting up the blueprints: using Empty objects with the attached image:


First I placed on the perpendicular planes the four views of the original installation drawings (Figure "a", above). Note that they contain a lot of the explicit dimension values – such information is an invaluable help in recreating this engine.

I quickly realized that the Empty objects with the reference images allow you to use simultaneously several alternate sets of the blueprints. Just place each of them on a separate layer. It will be a great tool in the Blender 2.8, which has to have unlimited number of layers. While working in the actual Blender 2.7, I placed these planes on layers 7…10, practically reserving them for the reference pictures. The second blueprint set contains the images from the original “Limits and Lubrication Chart” (Figure "b", above). These two views (side and rear view) are much more detailed than the installation drawings (presented in Figure "a", above). Of course, these images do not match each other in a perfect way: there always are some differences. However, I did not fix them, as in the case of the SBD planes, because all the key dimensions of this engine are specified in the installation drawings. I will just use these explicit values.

Following the standard of my posts, I am enclosing the current state of the source *.blend file. While there is no model, yet, you look inside to check the arrangement of the reference pictures. Next week I will report the first stages of building this model: forming the central crankcase and the basic cylinder shape. (Cylinders of this engine are identical with each other. Once you prepare one of them, you can quickly “populate” the crankcase with its eight clones. However, as you will see in the next posts, the die-cast, air-cooled cylinder head is one of the most complex objects to model…).

[1]The SBD Dauntless was a new implementation of the US Navy carrier doctrine, worked out in the preceding decade: in the clash of the carriers always wins those, who first finds carriers of their opponent. In fact, the best option was to find, report, and immediately make the first attack – that’s why all SBDs carried a 500-pound bomb on their scout missions

  • Member since
    March 2012
  • From: Corpus Christi, Tx
Posted by mustang1989 on Wednesday, April 18, 2018 2:43 PM

Hold on to yer hats folks. Brilliance present in this thread!!!! Wow WJ!!!



  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, April 29, 2018 9:33 AM


Hold on to yer hats folks. Brilliance present in this thread!!!! Wow WJ!!!

Thank you for following!

Well, my further work on the R-1820 engine lacks spectacular effects, I hope that you will enjoy its details in the next posts on this subject :).

  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, April 29, 2018 9:35 AM

In this post I will recreate the main and the front sections of the R-1820 crankcase, and the cylinder basic shape. Let’s start this model by forming the main crankcase:


This section is always obscured by the cylinders, so you cannot see it clearly on any photo. That’s why I used here the original drawing from the manual. Generally, this barrel-like shape contains nine cylinder bases. It is formed by two steel castings, bolted to each other. (These bolts are hidden inside the crankcase, between the cylinder openings).

It is always a good idea to start with a simplified model. It allows us to check all constrains of the geometry that are not obvious at the first glance from the reference drawings. In this case started by forming a symmetric half of the crankcase:


This is a simple barrel, smoothed with a Subdivision Surface modifier. Then I placed the flat piston bases along the circumference of this crankcase. I quickly realized that the side contour of this barrel depends entirely on the size and shape of these piston bases. After a few quick adjustments of the control edge loops, the barrel surface “touched” the outer edges of the piston bases along their whole length (as in figure above).

Note that these piston bases are so tightly packed around the crankcase, that they nearly join each other along a short, straight edge:


This means, that the crankcase barrel contains a cylindrical strip in the middle, which matches this straight edges on the piston bases. In fact, the sharp corners of these edges forced similar sharp edge on the barrel side contour.

When the general shape of the crankcase barrel looked right, it was time to create the final mesh. I decided that I will not use the dynamic effects of the subdivision surfaces for such a complex objects as the engine parts. (Because I want to keep the polygon count of this engine model below 1 million). Thus I “fixed” this subdivision effect, converting it into the normal faces (by “applying” the modifier). Then I took take the advantage of the “repeatability” of this shape. I deleted all the faces of the original “barrel”, leaving just the 20⁰ “slice” (as in figure "a", below):


The opposite 20⁰ of this “slice” is generated by the Mirror modifier. Then I made further modification to this mesh, removing all the faces from above the piston base (figure "b", above). I also copied and inserted into this mesh a quarter of the piston base contour. Then I started to join this contour and the mesh around it with new faces. You can see the result in figure "a", below):


As you can see, I also recreated the rear part of this crankcase section, just adding another symmetry axis to its Mirror modifier. The whole body of this crankcase can be built from 9 clones of such an object (as you can see in figure "b", above).

The shading of the crankcase faces is set as Smooth, except the faces around the piston base (which are marked as Flat).

I would like to mention a little “trick”, which can be useful in many other cases. To obtain a seamless join between the crankcase “slices” (as in figure "a", below), I added an additional, thin “strip” of the faces around the slice edge. These faces are parallel to the faces of similar strip in the adjacent slice (as in figures "b" and "c", below):


Once the middle section of the crankcase is ready, I started working on its front section. Generally speaking, this part looks like a combination of a cone and a cylinder, with many “protrusions” of additional details:


Actually, I recreated the basic shape of this section. (I will recreate the remaining details later). I did it using the same workflow as in the case of the previous section. First, I made a simple, “conceptual” model of this part. It was smoothed using a Subdivision Surface modifier. When the shape seemed to be OK, I converted the result of this modifier into normal mesh faces. Then I removed all the unnecessary edge loops and created the basic 20⁰ “slice” of this section:


To obtain the smooth shading between slices, I also created the additional thin strips of parallel faces along their adjacent edges. The basic slice of this section was easier to form than the one from the middle section, because it did not contain any opening.

Just to make the front of the engine more complete, I created the front disk (in a classic way, no “slicing” here) and the propeller shaft.

Finally I started working on the cylinder. Because all cylinders of this engine are uniform, I will complete a single (the topmost) one. The complete cylinder will be an assembly of many objects. Then, when it is finished, I will clone it around the crankcase.

As the first object in this assembly I created the simple, basic cylinder (i.e. the cylinder and its head without the fins and rocker covers):


It will be the parent object of all further elements of the cylinder assembly. As in the case of the crankcase, it does not use any Subdivision Surface modifier, just the “fixed” mesh faces with the Shade Smooth option (and Mirror and Bevel modifiers).

You can check details of this model in the source *.blend file. In the next post I will model the rocker covers and the covers of the intake/exhaust valves. (In the R-1820 they are just fragments of a single-piece cylinder head).

  • Member since
    June 2014
Posted by Witold Jaworski on Monday, May 7, 2018 11:17 AM

In this post I am wrestling with the partially hidden shape of the cylinder head:

One of the most prominent features of the R-1820 engine cylinders are their rockers. More precisely – their covers, cast as the part of the cylinder head:


The R-1820 was a classic four-stroke engine. Its cylinders had two valves: single intake valve, connected to the supercharger via a wide pipe, and single exhaust valve. Movements of these valves were controlled by cams, via pushrods and rocker arms mounted in the cylinder heads. The covers housing these valves and rocker mechanisms were placed on the right and left side of the cylinder head.

To simplify my model, I decided to separate the cylinder fins from its “solid” body (i.e. to create them as separate objects). However, because in the reality the cylinder head was cast as the single piece, it is very difficult to precisely determine its shape hidden between these fins:


While you can see the upper parts of the rocker covers on the reference photos, you can only guess their contours below the “fin surface”.

There is a blueprint that provides some additional clues:


However, I have some doubts about details of the contour that you can see on the rear view above. (I marked it with thick dashed lines in the picture). Look at the lowest part of this top contour: it should correspond to the upper (outer) surface of the combustion chamber. According other drawings, the shape of this chamber resembled a regular dome. If so, why the fragment of its contour visible in this drawing seems to be (a little) oblique? In the cutaway depicted in the first photo in this post I cannot see such an oblique shape. And why the side contours of this heads (the vertical dashed lines below the valve openings) are not symmetric? Thinking about it, I concluded that this drawing was not focused on the precise representation of the cylinder geometry: its main goal was to show the lubrication areas. Thus all these details, which we can see here, were drawn thanks to a “good will” of its draughtsman. They were hand-made, ink-traced drawings, and we can be just thankful to this technician for such a detailed piece of work. Still, I assumed that these lines can differ a little from the real contours – just because of the plain human error.

I formed the basic shape of the rocker cover using two clones of the same mesh: I placed one instance on the auxiliary drawing, while the second instance is located in its proper position on the cylinder (Figure "a", below):


Modeling this cover as a separate object allowed me to switch between its local (along the valve axis) and global coordinate systems. I could also modify this mesh switching between its clones. I used the instance, located on the cylinder, to fit its base into the combustion chamber dome. The other instance of this cover, placed over the auxiliary drawing, allowed me to follow the shape of this element. (In fact, I could also put another instance of this mesh over the top view of the rocker cover. However, I did not do it - just because I used this view only during the initial phases of the modeling, and it was relatively easy to rotate the modeled object and move it over the side view).

This is the initial, “conceptual” model of the cylinder head, so I split it into the key “solids” and formed the semi-spherical cover of the exhaust valve as another object (the red one in figure above). Such an arrangement allows for easy manipulating of these parts. During this phase I have to determine their most probable sizes and locations. For example – following the precise location of the exhaust opening, I discovered that for the size as in the “Lubrication Chart”, it has to be placed in a slightly different position (as in Figure "b", above). Otherwise, the right-bottom corner of the rim around exhaust opening would “sink” into the combustion chamber dome. (Of course, I also checked multiple times the most probable radius of this dome!).

When the whole thing seemed to match the photos, I made the rocker cover asymmetric (by “applying” its Mirror modifier and modifying the resulting faces). Then I modeled the oblique pushrod base (Figure "a", below):


To avoid some potential errors in the future, I started with placing the pushrod (another object) in the proper position, then formed the base around it. Figure "b", above) shows the resulting mesh. Note the sharp edges in its upper part. In the next step I rounded them, using a multi-segment Bevel modifier (Figure "a", below):


To have more control over these fillets, I used the weight-based version of the Bevel. Figure "a", above, shows the mesh edges that have a non-zero bevel weight marked in yellow. However, even in such a case, I could not avoid an artificial sharp edge between two fillets that were too close to each other (Figure "b", above). Well, in this situation I had to “apply” this modifier, and manually introduce small fixes to the resulting faces (Figure "c", above). I also dynamically created a “rim” around the upper edge of this cover. It is generated by the Solidify modifier, assigned to the thin face strip around this edge. Figure "d", above) shows the final result of these modifications.

While working on these parts, I simultaneously “scanned” the Internet, searching for more reference photos. Sometimes they just expose details, which were obscured in the reference materials that I already have. In this case – it was a protrusion on the rocker cover around the first and the last bolt (Figure "a", below):


I just had missed this tiny detail while forming the upper part of the rocker cover! Now I had a headache, how to fix it in a quick way. Ultimately I prepared two reference “cylinders” (I marked them in red, as you can see in Figure "b", above. Fortunately, there were many faces around the area that I had to modify. I placed these faces on the corresponding reference cylinders using the Blender Sculpt tool. (It allows me to push/pull multiple faces at once in a gradual manner).

You can see the final result of this modification in Figure "a", below:


Frankly speaking, I can see now that this protrusion had somewhat smaller radius. Ultimately I decided that it is “good enough” for the assumed level of details.

In the next step I cloned the rocker and valve covers onto the opposite side of the cylinder head: over the intake valve (Figure "b", above). In this first approximation of these parts, I rotated the intake valve cover (marked in red in the picture above), trying to find the proper location and angle of the intake opening. To fit it better, I also placed in this model the intake pipe. I knew, that in the future I will adjust its shape multiple times. That’s why I crated it initially as a simple cylinder, smoothed by the Subdivision Surface and bent along a parent curve using Curve Deform modifier. By controlling the location, rotation and shape of the parent curve I had full control over this pipe.

The intake rocker cover had also a unique feature: two bolts on its front and rear walls (Figure "a", below). They were intended for mounting around the engine an eventual NACA cowling. (Wright added these bolts on the Army request). For this “conceptual” stage of the modeling, I decided to add the bases of these bolts as a separate part. (Because I expect that I will move/modify shape of this element many times, before I reach the result that matches the reference photos). I will eventually join it with the cover (and add appropriate fillets around its edges) when it fits well.


In the next step I transformed the clone of the intake cover into a completely separate object (marked in blue in Figure "b", above). I also added the bolt bases around the exhaust and intake openings. (As you can see in the figure above, there are four of them on the exhaust cover, and three on the intake cover). Initially I created these bases as separate objects.

Once I verified their location, I joined these bolt bases with the cover mesh (Figure "a", below):


I joined these objects by applying a Boolean (Union) modifier. However, after such an operation the resulting edges required some manual “cleaning” (removing doubled vertices and edges).

I also formed an initial approximation of the rocker upper cover (Figure "b", above). I just placed it over the left rocker. The front contour of this part had to fit the circular contour of this engine (dimensioned on the original installation drawing). I also rounded its upper edge using a multi-segment Bevel modifier, but I can see that this part will require further modifications.

While working with these rocker covers, I discovered that I made a mistake in reading the original blueprints! I thought that one of the exhaust rocker cover elements was a cross-section, while it was oblique view of one of its fins (Figure "a", below):


On the reference photos I can also see that the bottom pushrod base plane was bent, with sharp side edges (Figure "b", above). Thus I had to modify accordingly the bottom part of this cover (Figure "c", above).

Well, such “discoveries” slow down the overall progress of the work, but they are inevitable, if you want to build a close copy of the real object. They happen all the time, as I am collecting growing number of the reference photos. In fact, I have measured that I spend at least half of the overall time on analyzing the photos. (Sometimes I also sketch on a paper the most complex shapes, before I start to model them in Blender. These sketches help me to better “understand” the objects that I want to recreate). The complex details of the cylinder head are often obscured by the fins, which makes this element an extremely difficult case. I am sure that I will identify and fix many of similar mistakes in the nearest future. For example: I will shift and rotate the cover of the intake valve multiple times, and then have to adjust the intake pipe after each of these updates. That’s why I prefer keeping this cylinder as an assembly of multiple, relatively simple objects. It would be much more difficult to modify this head, if it was a single, complex mesh. (In such a case you would have to care about all of its intersection edges!).

You can check details of this model in the source *.blend file. In the next post I will model the cylinder head fins.

  • Member since
    January 2015
Posted by PFJN on Monday, May 7, 2018 8:58 PM


Your work continues to amaze me.

I'm anxious to see more.


1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Sunday, May 20, 2018 5:59 AM

PFJN: thank you for following!

Today I will deal with the complexity of the cylinder head fins:


 The fins of the air-cooled cylinder heads are a state-of-art piece of metallurgy:


At the first glance, it is hard to believe that they were cast as a single piece. But when you look closer, you will discover that these fins “grow up” from the solid parts of the head as naturally, as the hair from the head:


Try to imagine the shape of molds used in the production of these parts, and the challenges faced by their manufactures! (See an interesting post about this. It describes production of the R-1830 Twin Wasp cylinders). Basically, modern producers of the heads for the air-cooled aircraft engines use the same technology as eighty years ago.

In my model I will recreate these fins in a somewhat simplified form, as a few separate Blender objects. I will also skip some fine details of their shape (for example the small features that I marked in the figure above). Such a simplification conforms the moderate level of details that I assumed for this model. It is always possible to make a more detailed version of this object later.

I began by forming the “external boundary surface” of the fins. After revising many photos I decided that it has a circular base. This base is combined with a shape extruded from a perpendicular arc:


The rocker covers, formed in the previous post, helped me in estimating the shape of this object. In general, the cylinder head fins are not symmetric, since the exhaust valve produces much more heat than the intake valve. Thus there are more fins around this area. Initially I formed the basic shape, leaving gaps around the rocker covers (as in figure above).

In the next step I filled these gaps (figure "a", below):


In fact, it was sometimes quite hard task that required careful analyzing the shape of the head fins in these areas. Note that fragments of the rocker pushrods were partially “sunken” in this object (as in figure "b", above).

I cut out the areas around these pushrods using the Boolean (Difference) function. To do it, I placed along the rockers two simple “boxes” (figure "a", below). Then I used them as the “tools” in a Boolean modifier that cuts out from the boundary shape the difference of their volumes (figure "b", below):


(Note that I rounded the original sharp edge of the “cutting box” using a multi-segment Bevel modifier). Then I “fixed” (applied) results of the Boolean modifier. After removing unnecessary vertices and edges from this area, I obtained the shape shown in figure "c", above. Finally I dynamically rounded the external edges of this cut out, using a multi-segment Bevel (Weight) modifier.

In similar way I created the hollows for the spark plugs. First I created two objects that have the shape of these cutouts. (As you can see in figure "a", below, their shape was more complex than the pushrod “boxes”):


I used these two objects in a Boolean modifier, which I applied to the boundary shape object. Figure "b", above, shows how this mesh looks like after “fixing” the results of this modifier. I also dynamically smoothed the resulting mesh using a moderate (level =1) Subdivision Surface modifier.

Finally, when the boundary shape was formed, I started to add the head fins. In the simplest case the mesh of a single fin can be just a single square face (figure "a", below):


Then I obtained the results shown in figure "b" (above) in a dynamic way, by adding to the fins object a stack of three modifiers:

  1. Boolean (Intersect) modifier, which uses the boundary object as the “cutting” tool;
  2. Solidify modifier, which gives the fins their thickness;
  3. Bevel (Angle) modifier, just to “round” the external edges of the resulting fins;

As you can see above, their cumulative effect is quite interesting.

All what I have to do now is to add to this “fins” object subsequent faces. The “L”-shaped upper fins have somewhat more complex topology:


It is built from a dozen of elementary square faces. I crated the rounded edge in the middle of this fin by adding another multi-level Bevel modifier to the top of the modifier stack. It rounds selected edges – those, where I set the so-called Bevel Weight coefficient to a nonzero value.

Sometimes the results generated by the Boolean and Solidify modifiers look strange. To fix these problems I had to be careful with the normal direction of the newly created mesh faces. Sometimes I even had to add an additional edge loop – because it alters the results of the tessellation that Blender performs for each face.

The R-1820 cylinder head also contains some “M” – shaped fins (as in figure "a", below):


I built such elements using an outer “U”-shaped surface combined with the inner, flat face (figure "b", above). The faces of the “U”-shaped surface have their normals directed outside, so the Solidify modifier generates the thick “walls” around it. The two edges at the “bottom” of this “U” are rounded (figure "b", above), as in the case of the “L”- shaped fin. The inner surface extends a little (by less than the fin thickness) outside the original faces of “U”-shaped surface. After applying the modifiers, this “overflow” creates an impression that both surfaces are joined.

As you can see in figure "a", below, the final mesh of the head fins resembles somewhat a Minecraft object:


However, when you switch into the Object Mode, in a split second the modifiers transform it into the desired shape (figure "b", above).

Do not be mistaken by this “smooth” workflow description. In practice I often had to make minor adjustments to the boundary surface mesh, to correct some unexpected effects of the Boolean modifier. Fortunately, the mesh of each fin is disconnected from the others, so all these issues appeared gradually, and I was able to resolve them in a systematic way. I had also made other adjustments: for example, in the middle of the work I discovered that the spacing between the fins was 0.215” instead of 0.220”. (I know that this distance seems extremely small, but for the 30 fins in a row, it really makes a difference!). Thus I shifted - vertically or horizontally - about two dozen fins. Fortunately, the Boolean modifier took care for the resulting adjustments in their shapes.

What’s more, it occurred that these dense, evenly spaced fins act as a kind of additional reference grid. While forming them, I found and corrected some inaccuracies between the fins and the valve and rocker covers.

For example: while forming these fins, I adjusted at least four times the angle, location and shape of the intake valve. And after each of these modifications, I had to fit anew the intake pipe. That’s why I prefer to keep such complex elements as this cylinder head split into various simpler objects as long as possible: you never know, when you have to modify them again!

You can check details of these fins in this source *.blend file. The model starts to resemble the real cylinder, but it still lacks many details. I will describe them in the next post.

  • Member since
    June 2014
Posted by Witold Jaworski on Wednesday, June 6, 2018 11:45 AM

In this post I will finish the first cylinder of the R-1820 “Cyclone”. It will be the “template” object, which I will clone eight times around the crankcase when I finish the other parts of this engine.

Although in my previous post the cylinder head received the full set of its cooling fins, it still lacks some details. One of them are the reinforcements of the valve covers:


As you can see, these reinforcements break the symmetry of the left and right valve covers. Both of them resemble a thick plate, but one is oblique, while the other is vertical. They are not the most prominent features of this cylinder head, and it took me some hours to determine their probable shape. Finally I classified them as the secondary features of the covers, which I have to recreate, for the assumed level of details.

First I formed the oblique reinforcement of the intake valve cover. I extruded it from the existing mesh:


When you compare this mesh (in Figure "a", above) with the last picture in my last-previous post (its Figure 85‑11), you will clearly see that I had to remake this shape again. (I was wrong, then). At this moment I declined to create the last “block” that closes the array of the vertical fins at this cover (Figure "b", above), because it would be too difficult to merge such a feature within the current mesh. I will come back to this issue later in this post.

In the case of the vertical reinforcement of the exhaust valve, I encountered similar problem: it would be quite difficult to extrude such a shape from the existing mesh. However, this time I decided to make it as a separate object:


The next element that I recreated is the top cover of the rocker (Figure "b", below):


After some initial trails, I decided that the previous, simplified version of this element that I made some weeks ago is useless. (You can still see it in Figure "b", below). Thus I started a new top cover from the scratch. I formed it using the same reference drawings that I used for the main rocker covers (Figure "a", above). The fillets of this shape (I marked them in yellow) are created using a multi-segment Bevel modifier. However I had some troubles with the radius of the upper fillet (Figure "c", above). It occurred that the Bevel modifier can alter the fillet radius along the rounded edge. What’s worse, I could not obtain the larger radius at the higher corner of this cover, because their proportions and sizes were restricted by the height of the cover shorter side (Figure "c", above). Well, the difference was not so big, thus I accepted it.

In the next step I prepared four conical shapes in the places where this cover had recesses around the bolts (Figure "a", below):


In the “old” object, still located on the top of the rocker cover, I also created a perpendicular “T-beam” (Figure "b", above). I formed it there, because I needed to use the outer, circular contour of this engine as the reference. It was just prepared for later.

Then I started to create the recesses around the bolts. After applying each of the Boolean modifiers I had to “clean” this mesh by removing the extra vertices and edges (Figure "a", below):


Then I spent significant amount of time on improving the shape of the fillets around these recesses (initially they were in a really bad shape). Basically, I had to disperse the fan-like edges from the forward recess along the mesh, and add some new “middle” edges (Figure "b", above). Finally, I placed this rocker top cover on the cylinder head and joined it with the “T-beam” object that I had prepared some steps before. Note that I left these two meshes disconnected – it looks quite good as it is (especially in black – see figure below). Joining faces of this “T-beam” and the rest of this cover would require significant amount of work.

These top rocker covers are examples of the parts that do not seem difficult at the beginning. Then, after many hours spent on their vertices and edges you are discovering their true nature . In this case I lost most of the time on fixing the various issues along the rounded edges of the bolt recesses. If I had to make this cover again, I would sculpt these fillets manually, then eventually smoothed them using a Subdivision Surface modifier.

Comparing to these top covers, the details of the cylinder barrel were easy. In the real R-1820 its fins were made separately, from steel rings. I created them from a quarter of such a ring:


I just used a Mirror modifier (along X and Y axis) to convert this mesh into a full ring, then multiplied it down along the barrel using an Array modifier. Finally I added the Solidify modifier, which gave these plates some thickness.

I also used a large-radius multi-segment Bevel modifier to profile the cylinder base (as in figure above).

Finally I added the first bolts to this engine. Each of these objects is a clone of the same mesh. Initially I prepared two such meshes: the classic nut for the rocker top covers, and the massive head for the bolts around the cylinder base (Figure "a", below):


I also recreated recesses in the cylinder base around these bolts. I made it using an auxiliary object and a Boolean (difference) modifier (Figure "b", above). (In fact, to make the edges of these recesses more regular, I had to alter a little some faces of these auxiliary objects).

The last element of the cylinder was its upper deflector. Basically, this is just a piece of the sheet metal, “wrapped” around the cylinder head:


Although most of this deflector surface lies in the “invisible” back area of this engine, I decided to recreate it as a whole – just for the eventual future use. (In fact, the most difficult part was to determine the approximate shape of this part). It was made from a single smoothed (by the Subdivision modifier) mesh surface. The vertical reinforcements on its sides are created as separate objects, also made from a single surface. Additional Solidify modifier gives them a non-zero thickness. Because this is the “invisible” zone of my model, I did not recreate such minor details as the bolts and rivets, here.

In general, this deflector was the last part of the cylinder. However, you never know when you find something new and will have to modify your model.

I finished this cylinder about two months ago, and then worked on the other parts of this engine. (Yes, my reports are always a few weeks late). After a month I finally decided to recreate the closing block of the fin array at the intake cover (marked in red in Figure "a", below). This time I made it as a separate object, to avoid tedious work of rounding all of the eventual intersection edges. I also looked for more reference pictures. One day in May I found additional detailed photos of the R-1820 cylinder head in a certain e-bay auction. When I compared them to my model, I discovered that my cylinder is missing one fin at the intake cover:


(There were three such fins in the photo, while my model had only two). The new photos quickly revealed my error: I have to shift the forward faces of nearly all existing vertical fins to the right! (To the next fin).

 In this and next paragraphs I use the “left” and “right” directions as you can see them in figure above. The intake valve is on the left, while the exhaust valve is on the right side.

Such a movement of the 26 fins will create space for additional “shorter” fin on the left and discard one fin on the right. It also will shift the central segment of these fins that contains the hollow for the forward spark plug.

Fortunately, the structure of my model allows me to do such a modification in a relative easy way. (That’s why I hold myself in duplicating this cylinder to the latest stage of this project, and using in every of its objects as many modifiers as possible). I have introduced all these updates to the latest version of this R-1820 model, thus you will not find them in the example file that accompanies this post. (They will appear in the file that accompanies one of the future posts).

How I did it? First, I modified the shape of the “fin boundary” object, which I use to the Boolean modifier to “cut” the fins (Figure "a", below):


Then I shifted the “raw” faces of the fin mesh to the right by one “fin module” (0.215”). When I did it, I started switching these shifted faces to the adjacent fins (Figure "b", above). Finally I dropped the rightmost fin and added one fin segment on the left.

Figure "a", below, shows my results, while Figure "b", below, is the picture of an authentic R-1820 head:


The most obvious difference is the certain “angularity” of my model: it lacks many of the soft fillets and intermediate surfaces that you can see in the original head. This is the price for the relative simplicity and moderate polygon count. (The final model of this engine will have about 500 thousand faces). Making a more detailed version of this head would require much more time, and (at least) four times more faces in the final model.

However, I can also see various minor differences in the area around the exhaust (I marked it in figure above using a dashed line). It seems that I should shift the exhaust base to the rear, because you can see it on the photo, while it is hidden under the fins in my model. This is strange because I read the precise location of the exhaust opening from the explicit dimensions on the original installation drawings. I have also found another minor difference between this photo and the original Curtiss-Wright drawing. Thinking about it, I realized that I am using reference drawings from 1942, while the head in this photo comes from a B-17G (according the e-bay auction). This means, that it was produced no earlier than in 1944. It may happen that I found minor differences between various R-1820 production series. All in all, they appear on the rear part of the engine, which will be invisible in my model. Thus I decided to continue without fixing these findings.

Figure below shows the current state of the cylinder model:


You can examine my model in this source *.blend file. Just remember that this is the earlier version, saved in March (before I shifted the forward fins). In the next post I describe my work on the crankcase details. After this I will recreate the spark plugs, ignition harness and the side deflectors (between the cylinders).

  • Member since
    June 2014
Posted by Witold Jaworski on Friday, July 13, 2018 1:26 PM

In my previous posts (published in May and June) I focused on the R-1820 cylinder. I think that it is the most difficult part of every air-cooled engine. Since that time I have made a significant progress, which I will report during nearest three weeks.

Let’s start with the rear section of the crankcase (behind the cylinders). Do you know how difficult is to find a decent photo of this area? The original pictures from the “Cyclone” manual are of moderate quality:

The modern photo (Figure "b", above) reveals more details. In general, it looks that the rear part of the crankcase is formed from two cylindrical segments. The intake pipes extend from the first (i.e. forward) of these segments. (There is a centrifugal supercharger inside). The upper part of the last segment contains rectangular air scoop, which also provides the mounting points for the carburetor (Figure "b", above). The rear wall of this segment forms the base for various auxiliary aggregates: magnetos, oil pump, starter, etc. As you can see in Figure "b" (above), aggregates from the R-1820 exposed in the Pima Air Museum differ from the manual photo (Figure "a", above). I think that such equipment could be used in the B-17s. On this photo I also finally determined an important feature of the R-1820 geometry: its mounting points. (They are dimensioned on the installation drawings, but I had to find them among all these nuts and bolts that you can see on the crankcase).

I think that this rear part of this engine is much more complex than the forward section. Fortunately, it is invisible in my model (I am not going to open the engine cowling panels, at least not at this stage of the project). Thus I recreated them just as placeholder “blocks” (see figure below). In this simplified form they will allow me to determine the details of the SBD engine cowling geometry:


Once I saw these details on the photos, I was able to properly interpret the original installation drawings from the Curtiss-Wright manual. I recreated in the simplified form the intake pipe base (Figure "a", above). I will repeat these blocks for every cylinder. (I built this crankcase section from nine identical parts). Note the hole for the mounting bolt on the left side of the intake pipe. I just placed it there as a reminder for myself. The last crankcase section is created as a single (mirrored) part (Figure "b", above). I placed the simplified magnetos and oil pump on its rear wall.

In the next step I recreated there the details of the pushrod bases in the front of each cylinder:


The rim of the forward crankcase is usually obscured by the ignition harness. I managed to find some photos that show this part. They reveal that there is a cylindrical “strip” around this rim (Figure "a", above), which forms the base for the pushrods. The outer diameter of this “strip” matches the rim diameter of the crankcase main section (the section that forms the cylinder bases). It is larger than the diameter of the conical part of the forward crankcase. The forward edge of this strip has characteristic “stair” shape (Figure "a", above). This shape repeats in the front of each cylinder. Every “step” of these “stairs” matches the base plate of one of the pushrods, or forms a bolt head base.

As I described it in the first posts about the R-1820, I formed this forward section of the crankcase using nine identical segments (clones), placed in the front of each cylinder. Thus I just had to recreate this strip in the mesh of a single segment, and Blender automatically repeated it around the crankcase rim (Figure "b", above). In this mesh, I used a multi-segment Bevel (Weight) modifier to round some of the newly created edges. (I have some troubles with the intersecting beveled edges, here. Finally I decided to use the Bevel modifier for the “meridian” edges, only. I created the gentler, “parallel” fillets manually, placing 3 or 4 new edges at the rim strip base).

When I reproduced the “stair” forward edge of the pushrod bases, I discovered that:

  • For each cylinder, one of the pushrods is shifted forward. (This is a norm for every classic radial engine, because each of these two pushrods follows different cam. One of them uses the intake valve cam, while the other uses the exhaust valve cam);
  • The pushrod bases were closer to each other than they depicted them in the original installation drawings from the Curtiss-Wright manual. (It could happen, because this was not any important, “dimensioned” element of these drawings);

I moved accordingly the pushrod bases close to each other, and then I discovered that they no longer fit their troughs in the cylinder head (Figure "a", below):


Fortunately, the shape of the head fins is still controlled by the surface object (via a Boolean modifier). All what I had to do was a minor adjustment of its mesh (Figure 88‑4b). Then Blender took care for the fin shapes (Figure "c", above).

As you can see (Figure "b", "c", above), I also added to this model the pushrod seals and clamps. All of these details are clones (they share single mesh). These clamps will be useful in other places of this engine.

Another engine element hides among the lower cylinders (5 and 6): this is the oil slump:


While the forward part of the oil slump appears on many photos (as in Figure "a", above), all what I found about its overall shape were: two pictures from the manual (Figure "b", above), and the side contour on one of the blueprints. However, certain features became obvious, when you place this part into the model. The recesses on its sides fit the adjacent cylinders (Figure "c", above), while the Y-shaped “tail” bypasses the vertical intake pipe that belongs to cylinder 5.

I formed oil slump using subdivision surfaces. To keep the shape of the front crankcase as simple as possible, I modeled the oil slum base as a separate object. Its external edges blend smoothly with the two adjacent crankcase segments. (These segments are separated along the engine centerline).

On the forward part of the oil slump you can see a prominent engine data plate. I will recreate this detail later, together with similar elements that occur in the cockpit. (They will require a separate texture).

On the opposite side of the crankcase there is a more exposed feature: propeller governor base:


In general, its shape is a combination of symmetric cylinder and dome with an asymmetric “wedge” (Figure "b", "d", above). To find the proper proportions of these objects, first I prepared their simplified, conceptual model (the red blocks in Figure "c", "d", above). The most “sensitive” elements here are their intersection edges, especially on the oblique, left side of the “wedge”. I tried to obtain similar shapes of these curves to those visible on the photos. (However, in the real crankcase these edges are “soften” by the fillets. It is more difficult to determine their exact shape).

Finally, when the conceptual model was close enough to the original, I used it as the base for the final version:


First I joined the “cylinder” and “wedge” into single object, and added fillets (multi-segment Bevel modifier) along their intersection edges (Figure "a", above). Then I joined the three upper segments of the forward crankcase with this propeller governor base (Figure "b", above). It created additional intersection edges, which I also rounded using the same Bevel (Weight) modifier. Note that I did not “smooth” this surface with a Subdivision Surface modifier: it was dense enough without it.

There was also another reason: the optimal mesh topology for the beveled edges differs from the optimal topology for the subdivision surface. For the fillets created by the multi-segment Bevel modifier, the beveled edge has to be far away from the other parallel edges. To obtain similar effect using the Subdivision Surface modifier, you have to concentrate several parallel edges close to each other. Sometimes I use a mix of these two modifiers (Bevel + Subdivision Surface). However, for the more complex shapes, like this one, this combination can create certain artifacts by its own.

 The next element of the engine is the ignition harness. Figure below shows its rear part:


In fact, this part will be invisible in the final Dauntless model. I recreated it because I just do not like to “suspend objects in the air”. Still, while fitting this engine into the airplane, the simplified versions of these invisible parts can give you a valuable hint about potential collision/intersection. The harness in the engine from the Jimmy Doolittle Air & Space Museum (Figure "a", above) seems to be rotated upward on the magnetos. I recreated in the reversed position (Figure "b", above), as in the manual (see the first photo in this post).

Note the carburetor details in Figure "a", above. The complexity of their shapes exceeds by a magnitude the rest of this engine. I am really glad that they are hidden under the cowling, so I do not have to recreate this “mess” of intersecting blocks and pipes, all smoothed with hundreds of fillets. (I think, that it reminds the densely packed Maya sculptures, or some instances of the modern art  Wink).

The manifold of the harness is a simple tube, bent along the curve that controls its shape. (I used here the Curve Deform modifier). The forward part forms a 300⁰ arc around the crankcase:


I already placed along this manifold the bases for 18 individual spark plug cables (Figure "b", above). At this moment I recreated the first pair of these cables, for the topmost cylinder. Each of these two tubes has its own deforming curve. As you can see (Figure "c", above), I also recreated the spark plugs and the clamps that attach these cables to the pushrods. I will recreate the remaining 16 cables in the next post, when all of their cylinders will be in place. (Each of these cables will be bent along a slightly different shape). There are also four mounting brackets (Figure "d", above) that attach the ignition harness manifold to the crankcase.

I also recreated the deflector plates, mounted between the cylinders:


I decided to skip (simplify) some of their features that will be less visible under the NACA cowling. Thus I omitted the bolt holes at the cylinder sides, and various small holes in some of these plates. (The purpose of the two holes visible - in Figure "a", above - will become obvious in the next post).

Figure below shows the current state of this R-1820 model:


I will finish it in the next post.

You can examine the model depicted above in this source *.blend file. Just remember that this is the earlier version, saved in May (before the correction of the the forward fins, which I described in my previous post).

  • Member since
    January 2015
Posted by PFJN on Tuesday, July 17, 2018 7:25 PM


Oops I almost missed this latest update. It looks great Smile


1st Group BuildSP

  • Member since
    June 2014
Posted by Witold Jaworski on Friday, July 20, 2018 2:14 PM

Pat, thank you for following!Smile


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