Updating the SBD-5 Model

I continue updating the Dauntless versions that I am building in parallel to the basic SBD-3. In the previous post I updated the one important element of the SBD-5 model: its propeller (SBD-3 used an older version of the Hamilton Standard propeller). In this post I will continue this update.

While I already recreated the SBD-5 NACA cowling (see Figure 46-8 in this post), now it is time to adapt the panels behind it. I started by copying the corresponding cowling from the SBD-3. When it appeared in the place, I discovered a 1” gap between this cowling and the SBD-5 inner cowling panel (Figure 56‑1a):

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Figure 56-1 Fitting the rear cowling from the SBD-3 into SBD-5

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Updating the Model of the SBD-1

As I described it in one of my previous posts, in parallel to the SBD-3 I build a SBD-1 model and a SBD-5 model. They are in the same Blender file, but in separate scenes. Since I completed the SBD-3 model for this project stage, now it is time to take care of these other versions. These models share all the common objects with the SBD-3, so I have to recreate a few different details. I already modified their NACA cowlings. In this post I will update the SBD-1, because there is just a single remaining difference: the ventilation slot in the side panel of the engine cowling.

The SBD-3 had this slot much wider than the SBD-1 and SBD-2 (Figure 54‑1):

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Figure 54-1 Comparison of the ventilation slots in the SBD-3 and the earlier versions

(I used here an archival photo of the SBD-2, because it had the same side cowling as the SBD-1. There were only 57 SBD-1s ever built, so the photos of this version are not as numerous as the later ones).

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Modeling the Upper Cowling of the Fuselage

In this post I will form the fuselage panels in the front of the windscreen. In the SBD there were two hinged cowlings, split in the middle. They allowed for quick and easy access to the M2 gun breeches and the internal cabling behind the instrument panels (Figure 49‑1):

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Figure 49-1 The hinged cowling in the front of the windscreen

The parts of the fuselage around the cockpit are always tricky to model. It especially applies to the panel around the windscreen. When you obtain the intersection edge of these two objects, it can reveal every error in the windscreen or the fuselage shape.

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Modeling the Rear Part of the Engine Cowling

In this post I will create the next section of the engine cowling. I copied its forward edge from the rear edge of the inner cowling panel. Then I extruded it toward the firewall (Figure 48‑1):

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Figure 48-1 Initial shape of the engine cowling behind the NACA ring

I am going to split this object into individual panels, thus I already marked their future edges as “sharp” (as you can see in the figure above). It allowed me to preserve continuity of the tangent directions around these future panel borders from the very beginning.

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Engine Cowling Details

In this post I will finish the engine cowling of the Dauntless (of course, for this stage of the project). In the previous posts I formed its outer panels. In the case of the air-cooled radial engines like the one used in the SBD, there is always another, inner panel: the central part of the cowling. It is located behind the cylinders and exhaust stacks. In the classic arrangement of the NACA cowling it is nearly invisible. In the SBD-1..-4 you could see only its outer rim. That’s why I had to use all available pictures of the Dauntless engine maintenance or the wrecks, to learn about its general shape (Figure 46‑1):

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Figure 46-1 The central cowling panel, behind the engine

This panel had two variants. The first one (let’s call it “flat”) is visible on the photo above. It was used in the SBD-1..-4. In the SBD-5 and -6 the engine was shifted forward by 4”, so the central panel became a little bit longer (“deeper”).

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Modeling the Carburetor Scoop

The carburetor scoop passed significant evolution in the subsequent Dauntless versions. In the SBD-1 there was a rather large air duct placed on the top of the NACA cowling (Figure 45‑1a):

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Figure 45-1 Evolution of the carburetor scoop in the first Dauntless versions

However, it was quickly discovered that it obscures one of the most important spots in the pilot’s field of view: straight ahead and slightly below the flight path. That’s why it was somewhat corrected in the next version (SBD-2). In this aircraft the designers lowered the scoop, increasing the field of view from the cockpit. Such a solution persisted in the SBD-3 and -4. In the SBD-5 they completely redesigned it, placing the carburetor scoops inside the NACA cowling (more about this — see in this post the paragraphs around Figure 11-6).

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Shaping the Gun Troughs

The gun troughs in the aircraft usually are tricky elements. Their edges depends on the shape of two curved surfaces: the fuselage around the recess and the tubular inner surface. When you make mistake in any of these two shapes — you have to remodel the whole thing.

In the SBD there are two symmetric recesses in the upper part of the NACA cowling, in the front of its 0.5″ guns. Figure 44‑1 shows the left one:

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Figure 44-1 The gun troughs in the NACA cowling (SBD-3)

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Shaping the NACA Cowling Panels

In this post I will shape panels of the Dauntless NACA cowling. Working on the scale plans a couple months ago I came to the conclusion that the basic shape of this cowling was the same in all the SBD versions (see Figure 4.6 in this post). You can find the differences in their ‘ornaments’, like the sizes and locations of the carburetor air intake, or the number of their cowling flaps. Thus I used the high-resolution, long-lens photo of the SBD-5 (described in the previous post), to determine the ultimate shape of this cowling, and the split lines of its panels (Figure 43‑1a):

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Figure 43-1 Splitting the NACA cowling into individual panels

Basically, the SBD Dauntless NACA cowling was split into a single upper panel and two symmetric side panels. I started by copying corresponding part of the reference shape (created in this post) into the single side panel (Figure 43‑1b). The subdivision surface of such a 120⁰ mesh ‘arc’ is somewhat flat at both ends. Thus I had to tweak a little mesh edges in these areas, fitting them to the reference contour.

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Initial Approximation of the Engine Cowling (1)

SBD Dauntless had a radial engine hidden under typical NACA cowling. The Douglas designers placed its carburetor air intake on the top of this cowling, and the two Browning M2 guns behind it. In the result, the upper part of the SBD fuselage, up to the pilot’s windscreen, had a quite complex shape (Figure 40‑1):

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Figure 40-1 Complex shape of the upper cowlings

I am sure that I will tweak this shape multiple times before I reach the most probable compromise between all the reference photos I have. It will be much easier to do it by modifying a simple mesh instead of the complex topologies of the final cowling. Thus I decided to create first a simpler version of this fuselage section and adjust it to the all of the available photos. I will describe this process in this and the next post. Once this shape “stabilizes”, I will use it as the 3D reference in forming the ultimate cowling. Because I am going to recreate all the internal details of the engine compartment, I will create each cowling panel as a separate object.

Continue reading Initial Approximation of the Engine Cowling (1)