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):

0043-01
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.

In the next step I extruded the ‘strip’ that overlapped the upper panel (Figure 43‑2a):

0043-02
Figure 43-2 Extruding the fastening strips

I also marked the bottom edge of this panel as sharp (Figure 43‑2b). In fact, the right panel overlapped the left panel along this line (they were similar, but not identical).

What’s more, in the SBD-5 and -6 the split line between these panels was shifted left by about one inch. Nevertheless I decided that I will split these two panels later, during the detailing phase. At this moment I just dynamically mirrored the left panel using modifiers. It will be easier to unwrap in the UV space this single element, then copy its unwrapped mesh and form the right panel during the detailing phase.

To keep the topology of this mesh as simple as possible, I decided to cut out the exhaust stacks openings using a Boolean modifier (Figure 43‑3):

0043-03
Figure 43-3 Cutting out the openings for the exhaust stacks

The high-resolution photo was a very useful reference for the ultimate check of the shape of this opening. (Its contour contains two arches connected by short straight lines).

In a similar way I cut out the space for the cowling flaps (Figure 43‑4):

0043-04
Figure 43-4 Cutting out the area for the cowling flaps (as for the SBD-3)

Actually, I am preparing the three-flaps sections, as used in the SBD-1.. -4. Note that I used the same auxiliary object to cut the upper cowling panel.

The overlapping ‘strip’ along the upper edges of the side panels was chamfered just on the cowling leading edge (Figure 43‑5a):

0043-05
Figure 43-5 Fine details of the forward part of the panel

It would be very difficult to shape such an effect ‘in the mesh’ here, because of the two-dimensional curvature of this area. That’s why I created it using two auxiliary objects and another Boolean modifier (as in Figure 43‑5b). This was the last detail of this panel, for the modeling phase.

The next element are the cowling flaps. Initially I created them as a three-segment ‘strip’ (one quad face per each flap). I marked all edges of this initial mesh as ‘sharp’ (Crease = 1). Once I determined the size and shape of these basic faces, I added new, internal edges and started to bend this ‘strip’ along the reference shape (red object in Figure 43‑6):

0043-06
Figure 43-6 Forming the cowling flaps

When this ‘strip’ was fitted to the reference cowling panel, I added temporary edges connecting their opposite vertices. These auxiliary lines helped me to determine direction of individual rotation axes of these flaps, as well as their origins (Figure 43‑7a):

0043-07
Figure 43-7 Splitting the cowling flaps into individual objects

Then I separated appropriate fragments of this mesh into three cowling flaps (Figure 43‑7b).

Finally I cloned and mirrored the three left cowling flaps into the three right cowling flaps (Figure 43‑8a):

0043-08
Figure 43-8 Completing and testing the cowling flaps

At this moment the right flaps objects have a negative scale, thus for the movement test I have to rotate these left and right flaps separately (along their local Z axes, using the Individual Centers pivot point mode — Figure 43‑8b).

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

In the next post I will form the gun recesses in the upper cowling panel. It will be a quite difficult detail!

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