In this post I will finish all the remaining details on the front of the R-1820 engine. (As I mentioned in earlier posts, this model is intended for the outdoor scenes, with closed cowlings. That’s why I recreated the more complex rear part in a simplified form, just to check if it fits properly to the airframe).
One of the most exposed “Cyclone” details is the variable-pitch propeller governor (Figure 89‑1):
This is an additional unit that controls the pitch of the Hamilton-Standard propeller. (It controls the oil pressure, which determines the actual pitch of the propeller blades). You can find it in every aircraft, but it is often dismounted from the “standalone” engines, presented in the museums. The large wheel at its top is used as an actuator attachment. The actuator can be a pushrod or a cable from the cockpit. In the case of the SBD (and many other WWII aircraft) it was a control cable (Figure 89‑1b). The engine depicted in Figure 89‑1a) is a standalone museum exposition, thus it lacks such a cable.
In my previous posts (published in May and June) I focused on the cylinder. I think that it is the most difficult part of every air-cooled engine. Since that time I have made a significant progress, which I will report during nearest three weeks.
Let’s start with the rear section of the crankcase (behind the cylinders). Do you know how difficult is to find a decent photo of this area? The original pictures from the “Cyclone” manual are of moderate quality (Figure 88‑1a):
The modern photo (Figure 88‑1b) reveals more details. In general, it looks that the rear part of the crankcase is formed from two cylindrical segments. The intake pipes extend from the first (i.e. forward) of these segments. (There is a centrifugal supercharger inside). The upper part of the last segment contains rectangular air scoop, which also provides the mounting points for the carburetor (Figure 88‑1b). The rear wall of this segment forms the base for various auxiliary aggregates: magnetos, oil pump, starter, etc. As you can see in Figure 88‑1b), aggregates from the R-1820 exposed in the Pima Air Museum differ from the manual photo (Figure 88‑1a). I think that such equipment could be used in the B-17s. On this photo I also finally determined an important feature of the R-1820 geometry: its mounting points. (They are dimensioned on the installation drawings, but I had to find them among all these nuts and bolts that you can see on the crankcase).
In this post I will finish the first cylinder of the R-1820 “Cyclone”. It will be the “template” object, which I will clone eight times around the crankcase when I finish the other parts of this engine.
Although in my previous post the cylinder head received the full set of its cooling fins, it still lacks some details. One of them are the reinforcements of the valve covers:
As you can see, these reinforcements break the symmetry of the left and right valve covers. Both of them resemble a thick plate, but one is oblique, while the other is vertical. They are not the most prominent features of this cylinder head, and it took me some hours to determine their probable shape. Finally I classified them as the secondary features of the covers, which I have to recreate, for the assumed level of details.
The fins of the air-cooled cylinder heads are a state-of-art piece of metallurgy (Figure 86‑1):
At the first glance, it is hard to believe that they were cast as a single piece. But when you look closer, you will discover that these fins “grow up” from the solid parts of the head as naturally, as the hair from the head (Figure 86‑2):
Try to imagine the shape of molds used in the production of these parts, and the challenges faced by their manufactures! (There is an interesting post about this. It describes production of the R-1830 Twin Wasp cylinders). Basically, modern producers of the heads for the air-cooled aircraft engines use the same technology as eighty years ago.
In my model I will recreate these fins in a somewhat simplified form, as a few separate Blender objects. I will also skip some fine details of their shape (for example the small features that I marked in the figure above). Such a simplification conforms the moderate level of details that I assumed for this model. It is always possible to make a more detailed version of this object later.
One of the most prominent features of the R-1820 engine cylinders are their rockers. More precisely – their covers, cast as the part of the cylinder head (Figure 85‑1):
The R-1820 was a classic four-stroke engine. Its cylinders had two valves: single intake valve, connected to the supercharger via a wide pipe, and single exhaust valve. Movements of these valves were controlled by cams, via pushrods and rocker arms mounted in the cylinder heads. The covers housing these valves and rocker mechanisms were placed on the right and left side of the cylinder head.
In this post I will recreate the main and the front sections of the crankcase, and the cylinder basic shape. Let’s start this model by forming the middle section of the crankcase (Figure 84‑1):
This section is always obscured by the cylinders, so you cannot see it clearly on any photo. That’s why I used here the original drawing from the manual. Generally, this barrel-like shape contains nine cylinder bases. It is formed by two steel castings, bolted to each other. (These bolts are hidden inside the crankcase, between the cylinder openings).
The Dauntless had fixed tail wheel of a typical design among the carrier-based aircraft. The tail wheel assembly consisted a fork connected to two solid-made beams, which movement was countered by a shock strut. The beams and the shock strut were attached to the last bulkhead of the fuselage (Figure 82‑1):
The SBD shock absorbers had to disperse a lot of the kinetic energy of landing aircraft, minimizing the chance that the airplane accidentally “bounce” back into the air. (This is a key requirement for the carrier-based planes). For such a characteristics you need a relatively long working span between the free (i.e. unloaded) and the completely compressed (i.e. under max. load) strut piston positions. Indeed, you can observe that the Dauntless landing gear legs are much longer in the flight than in their static position on the ground (Figure 80‑1):
The working span of the SBD shock strut piston was about 10” long, while the difference between the static and the free (extended) piston positions was about 7.5”.
I published my previous post a month ago, but the current stage of this project – detailing – requires less frequent reports. (Otherwise the posts would become rather monotonous: week after week they would describe making similar things, using the same methods). I started this last phase of the Dauntless project by recreating its main landing gear. First, I had to finish it, then I am able to write about this process. Thus I will describe it in this and next two posts. (I will publish them in a short sequence, week after week).
The retractable main landing gear of the SBD was probably a direct descendant of an experimental solution used in the Northrop 3A fighter prototype. In general, it looks quite simple:
This post is a small digression about a modeling technique that you may find useful.
There is a detail on the bottom surfaces of the SBD center wing: an opening, made partially in the cover of the fuselage belly (Figure 72‑1):
The difficult part of this detail is its flange, stamped in the fuselage cover. I just have two photos of this element, both of average resolution. On both of them you can see a typical circular recession, made around the opening in the belly cover. In fact, such a feature is quite common in the sheet metal design (you can see plenty of such stamped flanges in various places inside your car). This is a minor detail, too small for any serious modeling, but too large for recreating it with the textures.