Adjusting the Tail Tip Shape

In the previous post I formed the shape of the SBD Dauntless tail tip. In this post I will finish its “closing strip” that contains the running light frame. I will also verify the overall shape of the tail tip using the available photos.

There is one thing I didn’t mention in the previous post, just to keep the narration focused on the pure modeling. Before the modeling I carefully studied the reference photos. In the result I found differences in the shape of the curved trailing edges of the fairing behind the elevator. On the photos you can see a straight fragment of this edge (Figure 39‑1a). Its presence means that the curve of the trailing edge was smaller, and the fuselage was somewhat thinner here. You can see the differences between the real shape and my reference drawing in Figure 39‑1b):

Figure 39-1 Another mistake that I found on my scale plans

I did not notice these detail before. As you can see, I applied this modification when I started to model this part.When the mesh of the tail tip was formed, I worked on the “closing” strip. I created a part of it as a separate object in the previous post (see Figure 38-5b). Now I extruded it along the side contour (Figure 39‑2a), then extruded the side faces of this strip (Figure 39‑2b):

Figure 39-2 Forming the band that closes the tail tip

I rounded the sharp edges of this element with a fillet. It is dynamically generated by a multiple-segment Bevel modifier — you can see the result in Figure 39‑3a):

Figure 39-3 Differences in the shape of the bottom opening

However, when I compared the bottom part of this tip to the photos, I saw that there are significant differences! Jut compare it in Figure 39‑3a) and Figure 39‑3b). The side edges of the tailwheel opening are less curved, and its rear edge is wider.

What is the reason of these differences? So far I tried to shape the bottom part of this tip as the smooth continuation of the previous tail segment (see Figure 39‑4b, Figure 39‑4c). It seems that I was wrong: these lines were broken at station 271, where the tip fairing was attached to the last bulkhead of the tail (Figure 39‑4a):

Figure 39-4 An analysis of the differences in the tip shape

To correct this shape, I first made the tailwheel opening wider by rotating the bottom part of the mesh (Figure 39‑5a):

Figure 39-5 Modifications applied to the fuselage tip

Finally I adjusted the shape of the “closing” strip to this new opening (Figure 39‑5b). Now it resembles the original as in the photo from Figure 39‑3b).

When I fixed the shape of this opening, I noticed another difference, this time in the shape of the tip cross-section. It is revealed by the vertical panel seam behind the tailplane (Figure 39‑6a):

Figure 39-6 Differences in the tip cross-section shape

This vertical seam seems to be flat, especially in the restored SBD from Figure 39‑6b). In my model this line is much more convex (Figure 39‑6c).

The primary reason of all these differences between my model and the real airplane is the lack of the reference: I have no photos of this fuselage tip taken from above. Thus I have to determine its shape on the plans by various indirect means — and assumptions. In such cases, when you shape it as a 3D model, you will often find errors in the reference drawing

Well, to make this section more “rectangular”, I have to make the fuselage even thinner in this area (Figure 39‑7a):

Figure 39-7 Flattening the fuselage tip

Yet the photos in Figure 39‑6a) and Figure 39‑6b) reveal another small difference, this time between the two different restorations of the SBD Dauntless. The aircraft from Figure 39‑6a) has the edges of the tailwheel opening bent inside, while in the SBD from Figure 39‑6b) the tip cross-section contour is straight to the end. Which one is true? At this moment I do not know! However, it will be better to modify the mesh of this tip in a way that makes such a rounding possible. (You can always straighten a curved surface. However, bending a flat mesh requires additional edges). That’s why I modified the mesh topology around this opening, adding another “longeron” edge (Figure 39‑8a):

Figure 39-8 Bending the edges around the tailwheel opening

Then I shifted two bottom edges a little (Figure 39‑8b), forming such a cross section as you can see in Figure 39‑6a) (compare it with the shape in Figure 39‑8c).

Figure 39‑9 shows the resulting tip:

Figure 39-9 Finished tail tip

I will recreate its internal reinforcements (bulkheads, stringers) later, during the detailing phase. At this moment I do not know whether I have to modify this part in the future. (It may happen when I find a better reference materials). Such a modification would require adjusting these internal structures, so it is better to postpone their creation as long as possible.

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

In the next post I will start to work on the engine cowling.

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