Recreating the P-40B: 3D Reference of the Fuselage (2)

In this post I will complete the 3D reference that I started in the previous post. Here is a link to the Blender file that contains 3D reference skeleton of the “long nose” P-40, described in the text below. It was compiled from all available blueprints.

Studying the dimmed blueprint scans, I was not able to read some horizontal ordinates placed close to the top and bottom segments of this fuselage. This created gaps in my 3D grid (Figure 121‑1a):

Figure 121-1 Additional vertical planes

Fortunately, in the fuselage ordinates diagram (dwg 75-21-020) I was able to identify ordinates of two vertical planes, placed at +3” and +6” from the symmetry plane (Figure 121‑1b). This allowed me to interpolate these datapoints with curves.

Why did I try to place in this “grid” all the available datapoints? Because you can interpolate these points in different ways. For example: in the picture below the same three vertices are interpolated by two different curves:

Figure 121-2 Different interpolations, based on the same datapoints

If you have more datapoints, you can trace the resulting contour with greater precision.

Of course, in determining ultimate shapes of the interpolation curves I also used contours from the assembly blueprints:

Figure 121-3 Fitting bulkhead drawing to the fuselage datapoints

Fitting these drawings to the datapoints can reveal additional group of wrong ordinals, which passed the previous verification. In the illustration above I adjusted the overall width and height of the blueprint fitting it to the outer vertices representing the fuselage ordinates (Figure 121‑3a). However, this contour still does not fit some of these datapoints (Figure 121‑3b). I suppose that the true contour should pass through point (3), but point (2) is located too high (by about 0.1”) to form a correct curve. In this case I decided to ignore vertex (2), because most probably this is an effect of measurement error.

Focusing on forming a single bulkhead curve does not guarantee smooth transition between the subsequent fuselage cross-sections. To avoid this class of errors, I generate their interpolations using auxiliary surface. In the few illustrations below, I am showing how I prepared the smooth contours of the tail bottom bulkheads.

I started by interpolating of the first and the last bulkhead with auxiliary surface (marked below in white):

Figure 121-4 Interpolating the first and the last bulkhead

These bulkheads form the outer edges of this “patch”. This is a subdivision surface, and its vertices are its control points – just like in the NURBS patches used in the CAD systems.

In the next step, I added a bulkhead in the middle:

Figure 121-5 Interpolating the middle bulkhead

Note that I marked these new edges as “sharp” (Crease = 1.0). In the effect, while the bulkhead contour is a smooth curve, perpendicular edges remain straight. In this way I can fit this surface to the stringer planes and avoid eventual problems with curvature in the planar view. (The goal of this auxiliary surface is to “produce” smooth bulkhead contours. I will deal with this two-dimensional curvature while forming the ultimate model).

In the next step, I inserted another contour between the existing ones:

Figure 121-6 Interpolating another bulkhead

In this way, by subdividing each new surface segment, you will obtain complete set of the smooth bulkheads:

Figure 121-7 Complete auxiliary surface

You can check in the rear view if the (control) vertices of this surface form a smooth-looking mesh. (When the control surface is smooth, the resulting surface is even smoother: this ensures that there is a proper transition between the subsequent bulkhead shapes.)

Interpolating the side and top portions of the bulkheads, I prepared two other auxiliary “patches”:

Figure 121-8 Other auxiliary patches for interpolating fuselage bulkheads

Then I separated bulkhead curves from the auxiliary surfaces and “glued” them into complete contours:

Figure 121-9 Interpolated (smooth) bulkhead contours

Of course, these interpolated shapes are “less certain”, but more useful than the discrete “hard” datapoints. That’s why I decided to mark them in a different color: red. What’s more, I preserved the original blue polygons that represent the original ordinates. If in the future I have doubts about any part of this interpolation, they will allow me to revise the basic data.

I did not interpolate stringer lines, because radii of their curves are much greater than in the case of the bulkhead contours. Usually, for such shapes the simple “blue” polygons created from the ordinates provide enough reference.

The number of objects in this scene is growing, so I grouped them in the four basic collections:

  • Blueprints – all reference images.
  • Ordinates – all “blue” objects, i.e. confirmed by the explicit dimensions or ordinates.
  • Interpolation – all “red” objects, i.e. smooth contours that interpolate spaces between the data points from Ordinates.
  • Auxiliary – surface “patches” and other helpful stuff.

There are no engine cowling ordinates for the P-40-cu/B/C. In 2019 I found in AirCorps Library a layout (dwg L-10202), which describes the last (pre-production) variant of the XP-40. I recreated these ordinates in the 3D space:

Figure 121-10 Cowling ordinates of the XP-40

In 2019, after detailed studies, I concluded that the X-40 radiator cover was lowered in the serial P-40s by about 1” (see this post). I assumed that the side and the upper cowling panels were the same as in this pre-production prototype. Thus, I decided that I will start by preparing an auxiliary surface for these original XP-40 ordinates:

Figure 121-11 Interpolation of the XP-40 engine cowling

In the next step I modified the bottom part of this shape, following the lines from my side view drawing:

Figure 121-12 Interpolation of the P-40-cu/B/C engine cowling

As you can see, I also recreated the complex shape of the coolers inlet frame. In the AirCorps Library resources I found a XP-40 layout drawing (L-10276). Initially, I concluded that similar frame was used in the P-40-cu/B/C. However, after studying more archival photos, I decided than in the production aircraft this frame was slightly moved down (by about 0.5”), and wider.

When this auxiliary surface was ready, I copied its curves into bulkheads:

Figure 121-13 Cross-sections of the P-40-cu/B/C engine cowling

Note that I marked the modified part of the cowling (as it was in the serial P-40s) in yellow. I reserved this color for the elements based on the photos.

In the final variant of this reference, I added some additional details, like the contours of the cutouts behind pilot’s headrest:

Figure 121-14 3D reference of the P-40 fuselage

I found their dimensions in the blueprint of the rear cockpit frames (dwg 75-21-078) and the geometry of the P-36 glass (dwg 99157, 75-21-80). I added these panels here because they are product of complex intersection of two curved surfaces.

Here you can download the *.blend file that contains complete reference skeleton of the “long nose” P-40:

Figure 121-15 3D reference of P-40B/C

In its Auxiliary collection you can also find other details, like the splitting planes of the cowling panels, gun fairings, and carburetor air scoop. I modeled their basic shapes, skipping most of the fillets. They are based on other XP-40 blueprints that from Air Corps Library.

I also placed here a simplified main landing gear. Its base (Empty) object is named S.LG Base. It is set in the “retracted” position, for which its local Y rotation is 0°. To extend this landing gear, set Y rotation of S.LG Base to +91° and rotate its leg (object S.LG Leg) around local Z axis by -96°.  

To use this model as a reference, import (File:Append) whole scene (named Reference) from this file into your project (*.blend) file. Then, in your default scene, go to Properties window, Scene tab, Scene panel, and in field Background Scene select the imported Reference scene.

This model still misses some elements, like the tail wheel assembly. In the early P-40 it resembled the P-36 tail wheel, but it was modified to fit under more streamlined doors. However, in 1941 it was modified – at least in the P-40s based in the continental U.S. Further modifications were introduced to the tail wheel leg in the “short nose” Warhawks (P-40D and later). Thus, do not use the available P-40D/E blueprints of this assembly, but recreate this detail basing on the photos.

3 thoughts on “Recreating the P-40B: 3D Reference of the Fuselage (2)

      1. I just tried to look at your post on the SBD and a bunch of errors is listed. I posted a message on this on the “Contact Us” today. Few others are this way but not all.

        If you try to post a message it shows up blank so the site is messed up.


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