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P-40B (based on the original Curtiss blueprints)

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Yes, I suppose that modeling various cast details, like engine crankcases, hydraulic hubs, etc. is much easier in such a full-blown CAD/CAM like Fusion 360. The main reason is its advanced functionality for modeling various fillets. Blender lacks it (its bevels/fillets are restricted by the edges  of the two adjacent faces), which makes modeling such complex shapes quite difficult. This is the advantage of this Autodesk product.


However, for my ultimate goal (creating aircraft visualizations) Fusion 360 also has some drawbacks:

  1.  the lack of advanced, physics-based render engines like Cycles in Blender. Such an renderer is the ultimate tool for preparing convincing, photo-realistic visializations. If I would use Fusion 360 for modeling, then I should import these models to Blender for UV-unwrapping and further processing. I try to avoid workflows based on importing objects from one program to another. My workflow is not linear: it resembles a spiral of several turns. From time to time I have to go back and fix some meshes of the various model parts. Doing this in two different programs would be much more difficult;
  2. the sheer size of Autodesk products, and their poor quality! The response time of their programs is often slow, because of the poor quality of the underlying code. I remember AutoCAD 2.62 from 1986. Of course, now it is different program, but I could observe, decade after decade, how it grows into large, unmanageable "kludge".
  3. licensing model. Actually Autodesk offers a limited version of Fusion 360 for free, for personal use. Great, but who can guarantee that they will not change this policy next year? Some years ago Autodesk released similar 3D product for free, on similar conditions. As I remember, its name was "Ac3D", or something like this. Then, after three or four years, they closed this project and discontinued its licenses. It disappeared. After two decades of observing various corporate acts of sheer folly, I prefer to base my workflow on some stable, "long-living" Open Source projects. They will not disappear overnight;

Actually I am working on a new edition of my book on 3D aircraft modeling, thus I decided to stick to my current tools (eventually I will give a try to Substance Painter). I decided that I will form the small cast/forged parts, for which Fusion 360 excels, as previously, in the simplified form without fillets. Usually you even won't notice the difference in the final visualizations.


Edited by Witold Jaworski
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A little bit off-topic: An interesting project realized by BEK Milling Solutions. Their CNC machine is cutting out a P-40 model in 1:2 scale, from a styrofoam block. For the input geometry, they used my old model of the P-40B:


Actually, I am working on a more accurate one, based on the original blueprints. However, their deadlines did not allow them to wait for this update.

Edited by Witold Jaworski
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A new source of the accurate aircraft geometry and original blueprints!
(this is an update of post #1 from this thread, because the blueprint source I recommended there - the plans.aero portal - disappeared a year ago)



For over ten years Hugh Thomson has published marvelous posts in his blog about the historical aircraft. Just look there to see the P-51 Mustang, F6F Hellcat, F4F Wildcat and B-25 Mitchell CAD models and – what is sometimes even more important – compiled datasheets of their ordinates. The true, accurate geometrical data are usually dispersed and difficult to reconcile in the thousand sheets of the faded out, barely readable original blueprints. Hugh studied them all and is providing this information in the easy-to-use form. If you need such data on any of these aircraft – visit his page and choose any of these packages, or just make there a donation, to support his future projects!


Below I am enclosing some screenshots of his research work:





F6F "Hellcat"



P-39 “Airacobra”: Center-fuselage



P-39 “Airacobra”: wing geometry


Note that Hugh is also providing complete sets of the original blueprints scans. This is much better option than buying them from the source that I previously recommended (plans.aero). The big advantage is that by sending an e-mail to Hugh you are not contacting an impersonal Internet portal. Here is a real mechanical engineer, a specialist, who worked with these scans and knows all “pros and cons” of each package. Before buying any of these aircraft blueprints you can ask Hugh about its details, blueprint quality, image resolution. Highly recommended!

Edited by Witold Jaworski
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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:




In fact, both layouts are identical. I can read the maximum width of the fuselage from horizontal dimensions of stringer #8, which runs along the fuselage reference line. In addition, this blueprint also provides data points for the side contour, because there were stringers #1 (upper contour) and #13 (lower contour). I suppose that the black "masks" in the XP-40 drawing correspond to the Prestone and oil radiators. In the first variant of this prototype, they were located behind the wing trailing edge in a "box" cover (like in the Hawker "Hurricane").


There is also another diagram of the P-36 fuselage ordinates (dwg 75-21-020). However, this microfilm scan is partially unreadable:




In particular, the sketches in the lower left part of this drawing are dimmed, so I could not determine the meaning of the parameters listed in the ordinate tables.


I began by building the vertical and horizontal plane of the fuselage. Each vertex of these meshes corresponds to a point dimensioned in the layout drawing:




At this moment I do not want to speculate about the shape in between these points, so I connected them with simple straight edges. In this way this shape represents the "hard", dimensioned data.


For greater readability of these reference objects, I added here a few additional faces on the important contours, for example – behind the wing trailing edge. I drew them following the blueprint contours, which can be slightly distorted. Thus, they are less "confirmed" than the dimensioned datapoints. That's why I marked them in another color. When the fuselage surface in the final model reveals a contradiction in the reference planes, these additional vertices will be the first candidates for eventual adjustments.




I decided to mark faces connecting the "hard" (dimensioned) data points in blue, while the faces created by copying the blueprint contours are in green.


On the other hand, let's do not forget that these blueprints were drawn in the "analog era". This means that all the explicit dimensions you can see in these sheets were ultimately measured on a "master drawing" of the aircraft geometry. Such a physical measurement always produces minor, random deviations. You can find them by looking at a high angle along any of these contours, especially along a straight segment:




The bottom contour of the P-40 fuselage in the side view forms a long, straight line (see figure a, above). However, when you look along this shape in a large zoom, you will see the deviations of its vertices (figure b, above). It seems that typical tolerance of the measurements for this aircraft was +/- 0.02". I think that this value is possible since the typical skin thickness was about 0.03". However, among these datapoints you can encounter a few deviations which are greater three or four times.


In this early stage of building the 3D reference you cannot determine, if such an "outstanding" ordinate reveals a real, minor feature of the aircraft contour, or is a result of significant measurement error. Thus, I did not make any adjustments, just marking edges around such a dubious vertex as "crease", to easily find them later.


Sometimes you can identify such an ordinate as erroneous, when you find another blueprint which provides a different dimension for the same point. When I identified that the lower part of the tables from the partially unreadable diagram 75-21-020 (see the second figure in this post) contains stringer points coordinates, it became a great help for such verifications.


I created a reference "plane" for each of the fuselage stringers. Curtiss numbered them from 1 to 13, so I named accordingly each of these objects:




In addition, I found in diagram 75-21-020 a small table containing ordinates of the upper edge of the opening around the wing. I created from them another plane.


It is easier to find most of the "outstanding" data points when you build continuous faces from their ordinates, as in the illustration above. Then look along each edge of these contours. To give you impression, how many errors you can encounter in such a layout diagram, I am showing drawing 75-21-140 where I marked these identified wrong dimensions in red:




During this verification I studied again the diagram 75-21-020 (see the second figure in this post), and finally identified that its upper table contains widths and heights of the bulkheads. They are measured in the equal steps of 3" from the fuselage reference line. Using the readable areas of these tables, I was able to recreate tail bulkheads – from #5 to #16:




I used here the equally spaced widths from the fuselage diagram. Of course, I also used other blueprints. For example – drawings 99157 and 74-21-080 provided dimensions of the "turtledeck" and the glass spanning between frames #5 and #9.


Unfortunately, ordinates that describe frames #1..#4 are not readable. What's worse, the stringer ordinates provided only 5 data points for each of these bulkheads. I had to seek additional information among various detailed blueprints. Ultimately additional dimensions of the cockpit frame allowed me to recreate shapes of bulkheads #2 and #3, and determine the location and twist of the fuselage longeron:




As you can see, I did not find any additional dimensions of the firewall (#1), but I copied this contour from its assembly drawing. It fits the stringer points, but I marked it in green, to be fair. Dimensions of the frames #2 and #3 revealed that their contour between stringers 7 and 9 forms an arc. The upper contour of #2A is also a combination of two arcs. Knowing this, as well as the shapes of the stringers between frames #3 and #5, I concluded that frame #4 should be a linear interpolation between their contours.


The windshield can cause troubles when its intersection with the fuselage does not look like in the photos. This happens quite often. To avoid such surprises, I decided to check this edge in this 3D reference:




I assumed that the windscreen shape was identical in the P-36 and the P-40, so the P-36 drawings (75-26-001, -012, and -026) provided me its accurate dimensions. I formed the upper part of the fuselage basing on the bulkheads #1 and #2A and the cockpit frame. Then I compared the resulting intersection edge with the archival P-40 photos. I discovered that in the XP-40 this shape of the bottom cockpit frame was "angular", identical to the P-36, while in the P-40-cu its rear parts became somewhat smoother and moved rearward by about 0.8". This means that in the serial P-40s they modified the shape of the fuselage between stations #2A and #3A.


Two years later, when I projected this model onto some reference photos, I discovered that:

  1. The P-40 sliding canopy was ~1" shorter than in the P-36. In the effect, its 3A station which marked the base of the rear windshield frame, was 40.75" from the firewall. (In the P-36 it was 39.75").
  2. The P-40 windscreen preserved most of the original P-36 geometry, but was longer by about 0.8" (That's I wrote in the paragraph above that it was moved by 0.8");
  3. In the P-40 the rounded corners of the gun cowling cross-section at station #2A (and correspondingly, at #3A) were higher than in the P-36. This means, that while the overall dimensions of the cross section #2A (the width at the fuselage longeron and the height), are identical in the P-36, their contours in the P-40 are different. Most probably they modified them to better accommodate the pair of the M2 guns, mounted in the P-40.

All these observations contributed to the different shape of gun cowling-windscreen intersection edge which I observed in the photos. I recreated all these findings in this 3D reference, creating the P-40 gun cowling and the cockpit as gray, surface objects.


In the P-40B/C Curtiss introduced another modification to the windscreen frame, enlarging the inspection doors above the fuselage guns:




However, it did not alter the fuselage cross-sections, so I decided to skip this variant here. Because of this overlapped gun door, the windscreen frame in the P-40B/C is a quite complex shape. I think that it will be easier to form it starting with the previous, simpler variant of the P-40-cu, then apply the later modification.

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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 "a", below):




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 "b", above). This allowed me to interpolate these datapoint 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:




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:




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 "a", above). However, this contour still does not fit some of these datapoints (Figure "b". above). 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):




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:




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:




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




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":




Then I separated bulkhead curves from the auxiliary surfaces and "glued" them into complete 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:




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:




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




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:




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:




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:




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.

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