SBD Dauntless, from scratch

Very nice!

Wurger, SANCER, Gnomey, Lucky13, vikingBerserker - thank you for following this thread!

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

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


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

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


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


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


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


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


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

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


Figure "b" above shows the resulting surface.

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

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

Phenomenal work mate!

Nicely done so far!

Wurger, Lucky13, Gnomey - thank you!

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


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


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

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


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

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


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

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

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


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


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


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


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

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

Outstanding as always mate!

Lovely work so far!

Lucky13, Wurger, Gnomey: thank you! For this week I prepared the bottom of the SBD fuselage:

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


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

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



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

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


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

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


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

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


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

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


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


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

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



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

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


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

Looking good so far!

Wurger, Gnomey - thank you!

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


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


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


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

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


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

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


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


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


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

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


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

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


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

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

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

Extraordinary work mate!

Good work so far!

Wurger, Lucky13, Gnomey - thank you!

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

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

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


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

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

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


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


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

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


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

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


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

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


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

Using a side photo of a flying airplane, always try to estimate the elastic deformation of its wing, especially the wing tips! Usually such a deformation makes these photos less usable as the precise reference for a 3D model.

Click to expand...

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

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


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

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


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

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


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

The photos can be extremely useful reference, but they do not replace the traditional scale plans. First you have to create a 3D model that is close enough to the real shape, using the plans. Then you can project such a model onto a high-resolution picture for the further improvements.

Click to expand...

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

Last comments to my post #118 (I had to shorten it to fit into 10k characters limit):

To effectively match a 3D view projection to the photo, you have to be sure that at least some points of your model are in their real locations. In the case of my Dauntless model these "fixed points" were:

• Positions of the fuselage bulkheads (I read them from the stations diagram);
• The basic trapezoid contour of the wing (deduced from the general arrangement diagram dimensions);
• Positions, shapes and sizes of the root rib (the rib at the joint between the center wing and the outer wing panel. I deduced its chord and spatial location in relation to the firewall from the general arrangement diagram dimensions, while its shape is declared as NACA-2415 airfoil);

Then you can precisely determine the location of the camera and its lens by matching these elements to the photo.


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

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

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


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


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

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


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

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


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

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


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

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

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


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


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

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


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

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


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

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

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