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

The fuselage ordinates are organized into horizontal “water lines” (blue), vertical “buttock lines” (green) and resulting sections (red). Each vertex of these polygons corresponds to an original ordinate (data point). For simplicity, I connected these vertices using straight edges. (You can find more details about these “reference polygons” in this post).

As you can see, there are also original blueprints in this scene. In fact, they are the only reason of the large size of the uploaded *.blend file. In the initial view most of them is hidden because they would obscure all other objects. For example: I clipped from various assembly drawings silhouettes of the assembly frames. Each of these images is assigned to the corresponding section.

To manage this complex structure, I organized it into two basic collections named Wing and Fuselage:

Figure 119-2 Scene structure

Each of these collections contains a sub-collection named Blueprints and a sub-collection named Ordinates. Blueprints contains clips (raster images) of the original Douglas drawings. Ordinates contains the reference meshes (planes) recreated from the numerical ordinates provided in the Douglas blueprints.

Note the alphanumerical prefixes in the collection names (like “#5.A2a..”). I added them just to ensure that each name is unique. (This is a requirement in Blender.)

You can turn on/off visibility of these collections, as well as the individual visibility of their objects. For example: I manually turned off visibility of most of the reference images. I am turning them on when I need them.

The internal structures of the Blueprints and Ordinates collections differ from each other. In the case of the wing, both are split into three sections: center wing, outer wing, and wing tip. In the case of the fuselage, Blueprints contains just a sub-collection for the bulkhead blueprints (Frames), because there were so many of them. Fuselage ordinates (i.e. polygons) are organized into separate collections for the Buttock lines and the Water lines. There is another collection: Stiffeners, but its data are less reliable, because they were provided as single values per each fuselage station. For the stiffeners #0, #1, #2, #12, #13, #14, #15, which are closer to the fuselage centerline, ordinate tables provided their widths. For the other stiffeners (#3 … #11) ordinate tables provided their heights from the fuselage centerline. It seems that Douglas engineers “traced” them by projecting onto the surface described by the buttock lines and the water lines.

In the Sections collection I placed cross-sections of the fuselage buttock- and water- lines. The only additional information there are the arcs between these data points. (For example – in the fillets that span between the fuselage and the wing, or between the fin and the stabilizer.) I recreated them using the radii provided by Douglas (in the blueprint with the fuselage ordinates). These radii were not complete, but they are better than nothing. It seems that the SBD designers used a fixed 3” fillet radius where they could.

You can easily identify these assumed (non-confirmed) data points of the fuselage sections, because they do not belong to any horizontal or vertical line:

Figure 119-3 Details of a single section

These horizontal and vertical lines are the traces of the corresponding buttock planes and water planes. I left them in the resulting mesh as additional, disconnected edges.

In some water- and buttock- planes I also added a few additional vertices, to match better the eventual fuselage surface. (This is a purely aesthetic purpose.) They are non-confirmed by any numerical ordinate. For easy identification, I colored the additional faces created by such a vertex in brown:

Figure 119-4 Additional points on the water planes and buttock planes

The last Fuselage sub-collection, named Interpolation, holds my approximation of these ordinates. First of its sub-collections, named Surfaces, contains  smooth surfaces that I spanned over the buttocks- and water- lines:

Figure 119-5 Smooth fuselage surface spanned over the original ordinates

I described details of these surfaces in the previous post. They are something between a pure reference object and an initial attempt to forming the fuselage with smooth subdivision surfaces. (Shaping these contours, I learned about the minimum number of the control polygons that are needed to fit all available data points). You can also see there a windscreen “wireframe”. I built it using the dimensions from the cockpit assembly drawings. I needed these lines for reconstructing the shape of the guns cowling, which was not described by the original ordinates.

Two other Interpolation sub-collections, named Frames and Stiffeners, contain smooth interpolation of the fuselage bulkheads and longerons:

Figure 119-6 Smooth interpolation of the fuselage bulkheads and stiffeners

In addition, I also modeled the oblique parts of the bulkheads at station #4 (object: R1.Frame#04o), #5 (R1.Frame#05u) and #7 (R1.Frame#07b):

Figure 119-7 Additional frames, corresponding to the oblique bulkheads of the SBD skeleton

In the uploaded file their visibility is initially turned off.

Ultimately, this file also contains some reference photos. Each of them is assigned to an auxiliary camera which projects this model onto this photo. To easily switch between these projections, download this add-on and install it in Blender. It adds additional Cameras tab to the 3D View property pane (the one which you open using the [N] key). Use its contents to switch between available photos:

Figure 119-8 One of the reference photos, packed into this *.blend file

You can find more details about this add-on at the end of my tutorial on photo-matching (see the description around its Figure 104-26).

Playing with these photos, on three of them I observed a difference in the upper part of the windscreen contour:

Figure 119-9 Difference in the windscreen contour of the SBD-5 from the CAF

While the bulkhead and stiffener lines (thin black in the picture above) perfectly match the photo, there is a difference in the windscreen heights. This requires further investigation, because I formed this 3D shape according to the explicit dimensions from the original cockpit canopy blueprints. Of course, I could make an error while creating these lines.

I observed similar (but not identical!) differences in the photos of another SBD-5, from the Pacific Aviation Museum Pearl Harbor:

Figure 119-10 Differences in the windscreen contour of the SBD-5 from the PAM

The resolution of this photo is lower than the previous one. However, it is still enough to reveal this “offset”. At this moment I cannot exclude the possibility that these minor differences were created by the renovation teams. (It seems the least probable explanation, especially in the case of the Pacific Aviation Museum).