Modeling Bottom Fuselage (1)

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 27‑1a). (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 (as in Figure 27‑1b). They were bolted to the flanges punched in the fuselage skin along edges of this opening:

Figure 27-1 Bottom part of the SBD fuselage

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 27‑2a it is in red):

Figure 27-2 First two segments of the new mesh

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 27‑2b). 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 27‑2c). 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 the extrusion of these initial two segments I extruded four more, up to the flap hinge (Figure 27‑3a):

Figure 27-3 Extruding further segments

I consequently marked as sharp the edges that follow the opening borders (Figure 27‑3b).

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 (Figure 27‑4a):

Figure 27‑4 Preparing the bomb bay opening borders (1)

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 (Figure 27‑4b). 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 (Figure 27‑5):

Figure 27‑5 Preparing the bomb bay opening borders (2)

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 (Figure 27‑6):


Figure 27‑6 Preparing the opening borders (3)

When the central opening was formed, I extruded the tip of this body (the part below the flap — as in Figure 27‑7):

Figure 27‑7 The tip of the bottom fuselage

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 (Figure 27‑8a):

Figure 27‑8 Creating the wheel bay openings

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 (Figure 27‑8b).

Figure 27‑9 shows the final object I created in this section:

Figure 27‑9 The bottom fuselage — as formed in this post

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

In the next post I will continue my work on this assembly. I will recreate the covers for this opening, as well as their mounting flanges.

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