SBD Dauntless, from scratch

[Witold Jaworski]

Wurger, Gnomey - thank you! Today I will recreate part of the wing internal structure:

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

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

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

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

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

In the same way I created the second spar:

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

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

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

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

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

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

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

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

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

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

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

 

[Wurger]

 

[Gnomey]

Good work so far!

 

[SANCER]

I'm still in "WOW TIME" 😲😨
Felicidades por tan asombroso trabajo!! 👍👍👍

 

[Lucky13]

Splendid work!

 

[Witold Jaworski]

Wurger, Gnomey, SANCER, Lucky13 - thank you!

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

[Wurger]

Brawo !!!

 

[Witold Jaworski]

Wurger - thank you!

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

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

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

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

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

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

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

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

In the next step I recreated the mid-fuselage:

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

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

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

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

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

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

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

 

[gbr-22]

Awesome work so far!

 

[SANCER]

My dear WJ is a joy to observe the way on which you do these schemes !!
I insist that the photographs that you have as a reference are exepcional.

Encantado de seguir disfrutando tu trabajo!!

Luis Carlos
SANCER

 

[Wurger]

 

[Gnomey]

Nicely done so far!

 

[Witold Jaworski]

gbr-22, SANCER, Wurger, Gnomey - thank you!

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

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

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

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

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

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

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

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

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

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

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

You can learn more about this and other useful properties of the subdivision surfaces in Vol. II of the "Virtual Airplane" guide.

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

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

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

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

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

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

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

 

[Wurger]

To jest wspaniała robata. Brawo!

 

[Lucky13]

 

[SANCER]

With them too!!



Luis Carlos
SANCER

 

[Witold Jaworski]

Wurger, Lucky13, SANCER - thank you, this is just the beginning (It seems that I will report my progress on this fuselage in a few posts)

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

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

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

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

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

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

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

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

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

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

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

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

Finally I modified edges around the gun door opening:

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

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

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

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

 

[Wurger]

 

[SANCER]

...

 

[Gnomey]

Looks good so far!