In this post I will begin the wing root fairing and recreate the tail of this SBD fuselage.
To be able to fit the fuselage to the wing, I started by creating a new set of the “bulkhead” edges. I placed them at the stations of the original bulkheads (Figure 24‑1):
In most airplanes the wing root fairing and tailplane fairing are created from additional sheet metal elements, fastened to the fuselage with multiple bolts. In the case of the SBD lineage — Northrop Alpha, Gamma and BT-1 — the wing root fairing was the integral part of the fuselage structure. (However, the SBD tailplane fairing had the conventional, “fastened” design).
At the beginning I decided to form the rear part of the wing fairing as a separate object. In this way I will avoid the messing with the topology of the existing mesh. I will merge these two meshes later. Thus I copied into this new object a part of the fuselage mesh, and combined it with the initial part of the fairing cone (Figure 24‑2):
It is always worth to analyze how the modeled element was built in the real aircraft. Let’s look on the photos (Figure 24‑3):
On the picture above I marked straight lines in white, circular cross-sections in red and other curves in yellow. Note that the stringers connecting the circular sections are straight or gently curved. If you would think how this part was built in a workshop, it makes sense. It is not too difficult to recreate the circular cross sections of the fairing in the subsequent bulkheads. Then you have to set these bulkheads at the corresponding stations and connect them with the thin stringers. In this process you can always bent (a little) the initially straight stringer. That’s why all the lengthwise lines on the photo are straight or form a gentle curve.
To ensure that I will recreate this shape properly, I placed three auxiliary stringers as they were located in the real airframe (Figure 24‑4):
Ideally, the outer edges of these test stringers should protrude a little from the wing root fairing surface. Using such them as indicators, I added new edgeloops in the middle of this mesh, and adjusted its bottom shape, fitting it to the wing (Figure 24‑5):
For the further work on the wing root fairing I need the tail. I extruded it from the station 140 up to station 271. Then I put one of the middle bulkheads at station 195 as a reference. Finally I adjusted the shape of this surface to the contours drawn in the side and top views. I did it using three new “bulkhead” edge loops, inserted in the middle of the tail (Figure 24‑6):
Evaluating the shape of this newly created part I examined not only the resulting surface, but also the control mesh. In the case of a fuselage, some geometrical problems are more evident when you check the flow of the lengthwise (“longeron”) edges. In this case I noticed that something is wrong with the last segment of the tail (see Figure 24‑6).
The edge marked in yellow in Figure 24‑7 corresponds to a real longeron on the fuselage. On the photos this longeron seems to be nearly straight. However, in the last segment of my tail its direction is altered:
I re-examined my photos and concluded that I made mistake in the shape of the bulkhead at the end of the tail (station 271). The top contour of this bulkhead had larger radius than in my model. (However, I have an excuse: this part of the last bulkhead is an extrapolated shape, because its upper part is inside the tailplane — see Figure 22-4 in one of my previous posts. In Figure 22-4 you can also notice that I proportionally decreased width of the whole bulkhead contour. This deformation was the direct reason of this mistake). I corrected the tail shape, increasing the corresponding radii in the two rear bulkheads (Figure 24‑8):
Finally I modified edges around the gun door opening (Figure 24‑9):
I prepared horizontal edges of this opening earlier, while shaping the upper part of the station 140 bulkhead (see Figure 23-6 in the previous post). Now I added another sharp edge that closes this opening. Note that for such a rectangular border I avoid crossing two sharp edges — because the resulting corner would create additional elevation above the smooth fuselage surface.
In this source *.blend file you can check all details of the model presented in this post.
In this file you can delete the vertices inside the gun door opening (as in Figure 24‑9), and check that the shape of the fuselage around the gun bay remains unaltered. I “programmed” such a result into this mesh from the beginning. (I did it by appropriate adjustment of the few vertices in the first tail bulkhead).
In the next post I will form the difficult, rear part of the wing root fairing.