In my previous post I “fitted” my model of the P-40B into modern photo of a restored aircraft. (Precise speaking, it was a photo of the P-40C, but there were no external differences between these two versions). In general, I used Blender camera object to “pose” the 3D model so in the camera frame it looks just like the aircraft depicted in the photo. One of the key information that I used for this “fitting” was the lens focal length used for making the reference photo. (Modern cameras save key technical parameters in the resulting image file). I could just read this length from the photo properties, write it to the corresponding Blender camera Focal Length property, and focus on determining the remaining unknowns: camera location and direction.
However, how to use the historical “analog” pictures for such a match? (For example – this original Curtiss photo of the Tomahawk IA from November 1940:)
In the previous post I finally identified Curtiss layout sketch L-10202 as description of the XP-40 geometry, as it was in February 1940. In that time Curtiss was finishing preparations for serial production of the P-40. (The first P-40 from this batch was accepted by USAAC in April 1940). This final variant of the XP-40 resembled the serial P-40-cu, except the tail wheel cover and rear glass frames, “inherited” from the P-36. However, the archival photos revealed minor differences between engine cowlings of these aircraft: the serial P-40 had longer spinner and deeper radiator cover.
It seems that all the original drawings and sketches of the early P-40s that I collected from the AirCorps Library resources describe the XP-40. Thus, first I will prepare the XP-40 side view using this original documentation. Then I will draw a P-40B side contour, using these XP-40 lines and available P-40-cu/B/C photos.
As I showed in one of previous posts, the XP-40 sketches are not only rare, but also in poor shape:
Generally speaking, the early P-40s (-cu, B, C) were “P-36 airframes with inline engines”. Thus, the only unique first-order assembly in these P-40 variants was their engine compartment. So far it seemed that the documentation of this area was lost, and the restoration teams had to rely on archival photos and other restored P-40B/C. (A P-40B restoration teamfrom New Zealand mentioned this in their interview).
In my post from August 2019 (Fig. 98-13 and Fig. 98-14) I described a previously unnoticed layout sketch, that I found among the “uncategorized” P-36/P-40 drawings in the AirCorps “P-40” microfilm set:
It can describe the geometry of the “long nose Hawk” engine cowling. In the same AirCorps Library uncategorized “pile” I also found some regular XP-40 drawings (engine mount, radiator support) and other sketches. However, the lines in all these images are faded, making them nearly unreadable. The L-10202 sketch is the most promising blueprint that I have found. In this post I will try to match this layout to the P-40B fuselage that I prepared in my previous post. I will also use photos to evaluate the results (i.e. for checking if the sketched engine cowling layout matches the real aircraft).
As I mentioned in the previous post, I had to check if the “keel” under the wing that I draw according the P-40E blueprints and the “keel” in the P-40B were identical. I was forced to use the P-40E documentation, because the drawings of the earlier P-40 versions (B, C) are extremely rare and often dispersed among less important blueprints (like sketches or design proposals). Thus, to check the assumption that the P-40 “keel” was identical in the “short nose” and “long nose” Hawks, I had to use available photos.
The aircraft picture on most of the photos is deformed by the perspective distortion (which depends on the camera lens length) and barrel distortion (caused by imperfections of the optical system). You can quickly estimate the amount of these (combined) distortions on a side photo of an aircraft. Just look at the seam lines along the fuselage bulkheads. Usually they form “bulges”. If the seam lines on the aircraft nose are “bulged” in opposite direction than similar lines on the tail – then in this image you have a perspective distortion (as in this “Tomahawk” IIA picture, below):
As I wrote in the previous post, it is impossible to find a complete documentation of the early P-40 variants (so-called “long nose Hawks”: P-40cu, P-40B and P-40C). I collected all what is currently available from the Internet portals: blueprints of their direct predecessor (P-36) and drawings of the later variants (the “short nose” P-40D … P-40N). Using these scanned microfilm frames, archival photos and technical descriptions you can recreate the wings, empennage, tail and mid-fuselage of these aircraft.
I started with the most obvious part of the side view: the fuselage. Behind the firewall it was basically identical to the P-36, except the tail wheel cover:
Before you organize the original blueprints of an aircraft, collect as many reference photos as possible, and familiarize yourself with the aircraft shape, main assemblies and – especially – their joints. You will need all this knowledge to quickly recognize the drawings you need. About 60% of the original blueprints depict various small, internal details (tubes, brackets, plates, etc.) which are necessary only when you would like to build a real, flying airplane.
To select a useful subset of these blueprints, I had to review all the drawings in the microfilm set, and copy some of them into one of the target folders:
You can do such a “review” using two File Explorer windows: one for the source drawing list (of course with the preview pane), and the other for the target folder.
Recreating geometry of a historical aircraft is usually a painstaking, iterative process. You can see this in my work on the SBD Dauntless. During the long hours of studying the photos and trying to figure out the precise shape of this plane I often wished to have its source blueprints! For many years the access to the original documentation was “the Holy Grail” of the advanced modelers. (Everybody wished to have this ultimate resource, but only few saw it. And even those, who saw these drawings, often did not know what they are seeing).
When the production of an aircraft is definitely closed, and it quits the service, its blueprints are packed into manufacturer’s archives. After a few decades most of these companies are sold, while the less successful ones are out of the business. The original technical documentation of an aircraft usually becomes a bunch of useless, unreadable paper rolls that disappear in trash bins.
This winter I was busy with my daily business and took a break from the SBD model. However, in February and March I spent few Sundays helping in another project: the Fokker D.V biplane, used in 1917 as an “advanced trainer” by German Air Corps:
I was asked to take part in this project by C. West. He did all the research and provided all the materials: blueprints and photos. My part was recreating the geometry of this aircraft, especially its fuselage frame made of steel tubes. All what we had was a dozen of various archival photos, a poor general drawing, and the landing gear dimensions:
In this case I had to turn the available photos into the precise reference, as I did for the SBD, then use them to determine the required geometry details.
After “mounting” the R-1820 engines into my SBD models, I decided to recreate some details of the inner cowling (the cowling panels placed behind the cylinder row). In this post I will form the missing parts of the carburetor air ducts, hidden under the NACA ring. There are significant differences in this area between various SBD versions, which never appeared in any scale plans, or in any popular monograph of this aircraft. I think that the pictures presented below highlight these differences. They can be useful for all those scale modelers who are going to build the SBD “Dauntless” models with the engine cowlings opened. (Sometimes you can encounter such advanced pieces of work on the various scale model contests).
Let’s start with the SBD-5s (and -6s), which are better documented (because they were produced in much larger quantities). They had a dual intake system, of the filtered/non-filtered air, which I discussed it in the previous post. I already recreated the two intakes of the filtered air, placed between the engine cylinders. Now I have to create the central, direct air duct and its opening at the top of the internal cowling.
Figure 94‑1 shows the initial state of my SBD-5 model:
In my previous post I have finished the second variant of the R-1820-52 “Cyclone” engine, which was used in the SBD-3 and -4. (It looks like the earlier R-1820-32 model, mounted in the SBD-1 and -2). In the resulting Blender file linked at the end of that post you will find two “Cyclone” versions: the R-1820-52 (for the earlier SBD versions, up to SBD-4) and the R-1820-60 (for the SBD-5 and -6). Each of these engines has its own “scene”.
To “mount” these engines into my SBD models, I imported both scenes to the main Blender file. I defined each engine variant as a group, to facilitate placing them in the aircraft models as the group instances. I also added the firewall bulkhead and updated the shape of the cowling behind the cylinder row. (I will refer to this piece as the “inner cowling”). So far I did not especially care for the shape of its central part, hidden below the NACA ring. Now I updated it for the real size and shape of the engine mounting ring (Figure 93‑1a):