Details around Gunner’s Cockpit

The last details that I create in this project stage are the gun doors behind gunner’s cockpit. In the SBD-1 they covered a single Browning gun. Fortunately, they were wide enough for stowing the double guns, which were mounted in the SBD-2 and SBD-3 by the Navy workshops (Figure 57‑1):

Figure 57-1 Evolution of the SBD gunner’s cockpit

Note that stowing the ammunition belts of this double gun required additional cutouts in the cockpit rear border. They were covered by slide plates on both sides of the gun doors (Figure 57‑1). In this post I will recreate these details.

Before I do it, I have to fix a certain error that I have recently found: the shape of the tail cross-section, near the cockpit edge. When I formed it, I relied on the photos from a certain restoration project (Figure 57‑2a):

Figure 57-2 Difference in shape of the bulkhead at station 140

The upper part of the first bulkhead behind the cockpit (at station 140) in Figure 57‑2a) was shaped along a single, gentle arc/curve. Looking on the other photos I assumed that in the front view the gun doors formed an arc, and this arc smoothly joins the curve of the bulkhead contour at the hinge line. Basing on these assumptions (marked in Figure 57‑2a) in blue), I prepared appropriate mesh topology (as in Figure 57‑3a). I created a “sharp” edge along the future gun doors hinge line, which enables me to cut out the inner area for the gun doors (as you can see in this post, Figure 24-9).

However, since that time I still had an impression that something is wrong with this tail shape. Finally, when I started to look at the sliding panels behind the gunner’s cockpit, I found that their cross-sections are different than I expected. I have found the ultimate confirmation in the picture from SBD-1 manual (Figure 57‑2b). The top arc of this contour had larger radius, and its endpoints were outside the hinge lines. It was smoothly combined with a straight contour segment, spanning from the topmost longeron of the fuselage (the same that runs along the canopy side border).

Well, great! This means that I have to modify the concept of the mesh topology for this area in my model! Figure 57‑3a) shows the original layout, while Figure 57‑3b) shows the modified mesh:

Figure 57-3 Fixing the shape difference of the tail cross-sections

The enlarged arc of the tail cross-sections forced me to shift the mesh edges away from the gun door hinge line. In the effect, I had to switch to the “plan B” for this opening: I will create it using a Boolean modifier. (Never mind, I was going to use it anyway during the detailed phase, for the other openings in the fuselage).

To better fit the fuselage to the straight edges of the gun doors, I already placed their hinges on the tail upper surface (Figure 57‑4a):

Figure 57-4 The modified shape around the rear border of the cockpit opening and its mesh faces

I tweaked the mesh edges around the cockpit rear border, obtaining the shape that closely resembles the original part in the reference photos (Figure 57‑4b). However, I do not like their complex topology: such a thing can be an obstacle for eventual further modifications.

After this, I decided to verify how the last cockpit canopy slides under the previous segment. (This is another test before I start to work on the cutouts in the tail surface). In general, the gunner had to rotate it first into horizontal position, then slide it under the previous canopy (Figure 57‑5a):

Figure 57-5 The last canopy segment does not fit the others!

However, when I started sliding it, I had to stop: its rear edge was too wide (Figure 57‑5b)! It seems that its radius is exaggerated: it was larger than the radius in the forward section of this canopy (Figure 57‑6a):

Figure 57-6 Fixing the shape of the last cockpit canopy

Well, I adjusted the size of this last section, so that in the rotated position the last canopy segment fits the previous one (Figure 57‑6b). Of course, then I also had to adjust the corresponding frame object to this new glass shape. I definitely should check it earlier! On the other hand, after this modification the gunner’s cockpit of my model better resembles the original photos.

The decision of using the Boolean operator for the gunner’s opening allows me to simplify the fuselage mesh (Figure 57‑7a):

Figure 57-7 Ultimate solution for the cockpit rear border

As I mentioned earlier in this post, I was not satisfied with the complex topology of the cockpit rear border. Now I decided to create it as a separate panel (i.e. separate object). It will differ between the SBD-1 and the later SBD versions, because in the SBD-1 (and SBD-2) the fuselage did not have the side cutouts (see Figure 57‑1 and Figure 57‑8a). That’s why the auxiliary “cutting object” for the Boolean operation has a shape that resembles the “T” letter (Figure 57‑7b). In this way I created the main fuselage part that fits all the SBD versions. The topologies of both meshes — the fuselage and the rear panel around the gunner’s cockpit — became simpler. It means that it will be easier to introduce eventual further modifications.

Figure 57-8 Further elements of the fuselage assembly

There was an issue with the internal hierarchy of this model: the fuselage could not be the parent of the auxiliary “T”-like object, because it “cuts” its shape. (Such an arrangement causes problems with displaying the model — I already encountered it in the case of the wing fixed slats). The obvious solution was to assign both objects used by the Boolean modifier to a common parent. In the case of the wing it was its root rib. However, so far this main part of the fuselage was the root object of the whole model hierarchy. To resolve this problem I decided to create a new root: an Empty object. Because I will need it for posing the airplane in an eventual final scene, thus I placed it on layer 19, among other auxiliary handles (Figure 57‑8b).

After these preparations I was finally able to make the sliding panels and their rails (Figure 57‑9):

Figure 57-9 Sliding panels (in the SBD-5)

I used the reference photos to precisely recreate these elements. (The picture of a SBD-5 wreck in Figure 57‑9 comes from Pacific Aviation Museum Pearl Harbor. I decided that when I work with the details, I can more trust the wrecks than the restored aircraft). The cutout for the ammunition belt was made between two fuselage stringers and the bulkhead at station 140 (see Figure 57‑9a). Note that it creates a triangular hole between the sliding plate and the canopy rear frame (Figure 57‑9c). Ultimately it was covered by a rubber band, attached to the canopy. (I will recreate it during the detailing stage of this project).

I created the sliding panel from a rectangle, which received the oblique forward edge. Initially I created the shapes embossed on its surface from separate cylinder halves. Then I recreated the faces around their edges, integrating these shapes with the base plate.

The “rails” of this sliding panel were made from simple duralumin stripes, folded inside. They were riveted to the fuselage stringers. Because these rails had to be parallel to each other, the axis of the fold in the bottom rail was deflected from the stringer axis (Figure 57‑9b). That’s why this element had a wedge-like shape.

The archival photos revealed that there was also an alternate version of the sliding plates, which appeared in the SBD-3s. You can see it in Figure 57‑10:

Figure 57-10 Alternate sliding panels (SBD-3)

I think that the photo in Figure 57‑10a) was taken during operation “Torch” (November 1942), because the star on this picture has a wide light outline, most probably in yellow. Note that the gun has no armor plates there, and the sliding panel has no embossed stiffener along its rear edge. Figure 57‑10c) shows such a panel in a restored aircraft. (I have found it in the photos from the Kalamazoo Air Museum). We can see clearly here that the lower rail strip is not folded like in the Figure 57‑9, but just bent upward, and it is riveted to the stringer along its lower edge. This means that this sliding panel is somewhat narrower than the one from the SBD-5. (Why? Because the lower edge of this panel lies above the stringer axis, while in the SBD-5 it is slightly below the stringer axis). I suppose that it can be a field modification of an original SBD-3, adapting it for the double gun. However, I am not sure that all the SBD-3s had such sliding plates. Anyway, I recreated it in my SBD-3 model. The other version of the sliding panel, as in Figure 57‑9, you can find in the SBD-5 model.

In this source *.blend file you can evaluate yourself the SBD-1, SBD-3 and SBD-5 models from this post.