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.

Recreating the P-40B: 3D Reference of the Fuselage (1)

At this moment I am working on second volume of my book about 3D modeling.  It describes building a 3D model of a WW2 aircraft on the example of the P-40B. Preparing for this work, I discovered that the original documentation of this early P-40 variant (also known as “long nose Warhawks”) is missing. On the other hand – you can find plenty of the “short nose Warhawk” blueprints (related to the P-40D later variants), as well as some P-36 drawings. I started by picking over 1000 original Curtiss blueprints and sketches related to the P-40, XP-40, and the P-36 from the vast resources of the AirCorps Library. Then I analyzed their contents, comparing them to the available historical photos. I described this process in this and following posts, written in 2019. Ultimately I traced side view of the P-40B. I also concluded that a 3D visualization of the available ordinals will be a better reference. In the previous posts I built such a reference for the SBD Dauntless. In this and the next post will I describe similar work on the fuselage of the early P-40 variants (P-40-cu, P-40B, P-40C).

I prepared an empty Blender file. For the convenience, I placed there my side view (from this post, see Figure 102-15). As for the SBD model, I assumed that 1 Blender unit = 1 in. For the main part of this fuselage, spanning from the firewall to the rudder, I used two P-36 diagrams. First of them (dwg 75-21-140) provides locations of the fuselage stiffeners at each bulkhead. There is also its modified variant (dwg 75-21-836) for the XP-40:

Figure 120-1 XP-40 fuselage stiffener dimensions (dwg 75-21-836)

Original SBD Dauntless Blueprints: Ordinates

I decided to upload the Blender file in which I reproduced in the 3D space the original ordinates of the SBD fuselage and wing. (I described creation of this 3D reference in my previous posts). I think that in this form they can be useful for other modelers, who would like to recreate the geometry of this aircraft. Here is the link to the *.blend file (102MB) that contains the model presented below:

Figure 119-1 3D reference of the fuselage and wing ordinates

Original SBD Dauntless Blueprints: Fuselage Geometry (4)

In the previous post I used ordinals from the newly found fuselage geometry diagram for creating a set of the 3D reference planes:

Figure 118-1 Fuselage data points, grouped into intersecting planes

In this post I will span a smooth subdivision surface between these points. I think that such an interpolation will provide a more accurate reference than the longerons (stiffeners), which I previously shaped in this post (see there Figure 112-07).

Original SBD Dauntless Blueprints: Fuselage Geometry (3)

This February I found among the SDASM resources a diagram (dwg no 5060837), which describes the geometry of the SBD fuselage. This is the key piece of the information that was missing in the NASM microfilms I used before. Below you can see these lines:

Figure 117-1 SBD fuselage lines

The Overall Lengths of the Douglas SBD Variants

Since 2015 I have tried to determine the true length of the early SBD Dauntless versions (the SBD-1, -2, and -3). There was something wrong with the source of this information: the original BuAer performance data sheets. You can find there different lengths of the SBD-2 (32’ 2”) and the SBD-3 (32’ 8”), while the differences between these variants cannot explain the reason of such a longer fuselage in the SBD-3. The other sources repeat these figures without any reflection. Fortunately, last month I found in the SDASM resources two interesting drawings of the SBD-1. One of them is a general arrangement diagram, which clearly specifies its overall length (and how it was measured):

Figure 116-1 The overall length in the general arrangement diagram of the SBD-1

Original SBD Dauntless Blueprints: Fuselage Geometry (2)

In previous post I started creating 3D reference objects for the SBD fuselage. In this post I will complete this work. I will focus here on the difficult part: the wing fillet. It spanned along more than half of the SBD fuselage length. In this post I am going to prepare reference geometry that describe its shape from bulkhead #4 to bulkhead #13. Unfortunately, in drawings from the NASM microfilms I found just a few contours related to this feature:

Figure 113-1 Identified wing fillet contours

Original SBD Dauntless Blueprints: Fuselage Geometry (1)

As I already mentioned in this post, my microfilm set does not contain the fuselage geometry diagram. (I suppose that it was included in the missing roll C). Thus, this part of my work will be much more difficult, because I even do not have complete set of the bulkhead drawings! Just found a structure assembly drawing (i.e. side and vertical views), skin panels assembly drawing, mid-fuselage bulkheads, and some bulkheads of the tail. In the picture below I marked these undocumented areas of the fuselage in transparent red:

Figure 112-1 Fuselage structure: documented and undocumented areas

Douglas blueprints refer to the fuselage bulkheads as “frames”. They are numbered from 1 (the firewall) to 17 (the mounting base for the tail wheel and horizontal stabilizer). Of course, the fuselage assembly drawings provide their positions, measured from the firewall. (You can find them in this assembly drawing of the skin panels). In this post I will refer to fuselage bulkheads using their ordinal numbers, shown in the picture above (for example: “frame #05”).

Original SBD Dauntless Blueprints: Arrangement Drawing Issues

In some aircraft it is difficult to provide the precise value of overall length. One of them is the SBD Dauntless, because of its easily demountable spinner used in the first three variants (SBD-1…-3). Also the length of the Hamilton Standard Hydromatic spinner hub, used in the later SBD variants, can vary – especially in the restored aircraft. Thus, for verification of model kits or similar purposes I would suggest checking the distance between two easily distinguishable points: from the firewall to the tip of the tail cone. This dimension remains the same in all SBD variants. Preparing the fuselage blueprints for my model, I could determine this distance using the tail cone assembly drawing:

Figure 111-1 Using the marked stations to measure distance from the firewall

The key information is provided by the stations marked in this drawing: their names describe distances from the firewall. (You can read them yourself from the high-resolution version of this drawing).

Original SBD Dauntless Blueprints: Initial Findings

In general, the set of 7 SBD/A-24 reels from NASM contains 3308 unique microfilm frames, belonging to 3022 drawings. On reels “XA” and “XB” you can usually find updated copies of the previous reels (“A”, “B”,.. “F”). However, 350 frames from “XA” and “XB” are unique – most probably this is a part of the missing roll “C”. Duplicates from these “X*” reels are also useful, when a drawing from one of the previous reels is unreadable.

I chose about 1000 frames (mostly assembly drawings) from this microfilm set, and organized them into a tree-like structure as in Figure 108‑1:

Figure 108-1 Folder structure for the SBD blueprints

To preserve disk space, I placed in these folders shortcuts to files located in the original directories (These original directories correspond to microfilm reels: “A”, “B”, …, “XB”). I practiced that when I click such a link, it opens the image in Photo Viewer, as if it was the original file.