Shaping the Gun Troughs

The gun troughs in the aircraft usually are tricky elements. Their edges depends on the shape of two curved surfaces: the fuselage around the recess and the tubular inner surface. When you make mistake in any of these two shapes — you have to remodel the whole thing.

In the SBD there are two symmetric recesses in the upper part of the NACA cowling, in the front of its 0.5″ guns. Figure 44‑1 shows the left one:

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Figure 44-1 The gun troughs in the NACA cowling (SBD-3)

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Shaping the NACA Cowling Panels

In this post I will shape panels of the Dauntless NACA cowling. Working on the scale plans a couple months ago I came to the conclusion that the basic shape of this cowling was the same in all the SBD versions (see Figure 4.6 in this post). You can find the differences in their ‘ornaments’, like the sizes and locations of the carburetor air intake, or the number of their cowling flaps. Thus I used the high-resolution, long-lens photo of the SBD-5 (described in the previous post), to determine the ultimate shape of this cowling, and the split lines of its panels (Figure 43‑1a):

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Figure 43-1 Splitting the NACA cowling into individual panels

Basically, the SBD Dauntless NACA cowling was split into a single upper panel and two symmetric side panels. I started by copying corresponding part of the reference shape (created in this post) into the single side panel (Figure 43‑1b). The subdivision surface of such a 120⁰ mesh ‘arc’ is somewhat flat at both ends. Thus I had to tweak a little mesh edges in these areas, fitting them to the reference contour.

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Initial Approximation of the Engine Cowling (1)

SBD Dauntless had a radial engine hidden under typical NACA cowling. The Douglas designers placed its carburetor air intake on the top of this cowling, and the two Browning M2 guns behind it. In the result, the upper part of the SBD fuselage, up to the pilot’s windscreen, had a quite complex shape (Figure 40‑1):

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Figure 40-1 Complex shape of the upper cowlings

I am sure that I will tweak this shape multiple times before I reach the most probable compromise between all the reference photos I have. It will be much easier to do it by modifying a simple mesh instead of the complex topologies of the final cowling. Thus I decided to create first a simpler version of this fuselage section and adjust it to the all of the available photos. I will describe this process in this and the next post. Once this shape “stabilizes”, I will use it as the 3D reference in forming the ultimate cowling. Because I am going to recreate all the internal details of the engine compartment, I will create each cowling panel as a separate object.

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