Recreating the Wright R-1820-52 “Cyclone” (1)

Following the conclusion from my previous post, I have to recreate yet another “Cyclone” version: the R-1820-52, used in the SBD-3 and SBD-4. Fortunately, the R-1820-32, used in the SBD-1 and SBD-2, seems to be identical (at least – as viewed from the front), thus I do not need to recreate this “Cyclone” variant. I will describe the modeling process of the R-1820-52 in the “fast forward” mode, compressing the whole thing to two posts: this and the next one.

Initially I identified just two differences: the shape of the front crankcase section and the different ignition harness. I assumed that I will be able to reuse most of the R-1820-60 components. I had discovered most of the issues described in my previous post while working on this R-1820-52 version. In fact, it occurs that such an attempt to create a 3D model of such an engine is like an scientific experiment: it verifies the initial hypothesis and reveals the new facts that otherwise would be overlooked.

I started by renaming in the source Blender file the scene that contains the previously finished engine as “R-1820-60” (the “military” symbol of an engine belonging to the “Cyclone” G200 family). Then I created a new scene, named “R-1820-52” (the G100 family). This is my new “working place”. I copied there (precisely speaking: “linked”) some of the “R-1820-60” parts that were common for the G100 and G200 family. In this “*-52” version I followed the same “building path” which I used for the previous one. So I began with the crankcase and the basic cylinder elements (Figure 91‑1):

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Figure 91-1 Forming the new crankcase

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Recreating the Wright R-1820 “Cyclone” (5)

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:

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Figure 87-1 Asymmetric 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.

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Recreating the Wright R-1820 “Cyclone” (4)

The fins of the air-cooled cylinder heads are a state-of-art piece of metallurgy (Figure 86‑1):

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Figure 86-1 Fins of the R-1820 cylinder head

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):

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Figure 86-2 Close-up of the fin details

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.

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Recreating the Wright R-1820 “Cyclone” (1)

The engine is the heart of every powered aircraft. In the case of the SBD it was the Wright R-1820 “Cyclone 9” (the “G“ model). In fact, this engine was one of the “workhorses” of the 1930s: designed in 1931, it was used in many aircraft, especially in the legendary DC-3. “Cyclone” was a reliable, fuel-saving unit for the Navy basic scout type. (Remember that the “Dauntless” was not only the bomber: it was also a scout airplane). In general, the R-1820 is a classic nine-cylinder, single-row radial engine (Figure 83‑1):

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Figure 83-1 The Wright R-1820 “Cyclone”, mounted on the SBD-5 airframe

The R-1820 G had been produced for over two decades, not only by the Curtiss-Wright, but also (under license) by Lycoming, Pratt & Whitney Canada, and Studebaker Corporation. Thus various less important details of this engine “evolved” during this period. In this post I would like to highlight some of these differences. I will focus on the forward part of this engine, because at this moment I am going to create a simpler model of the “Cyclone”, intended for the general, “outdoor” scenes. Inside the closed NACA cowling, you can see only its forward part. (Thanks to the air deflectors, placed between the cylinders – see Figure 83‑1). In such an arrangement, the visible elements are: the front section of the crankcase, cylinders, ignition harness, and the variable-pitch propeller governor. While the front section of the R-1820 crankcase remained practically unchanged in all versions, and the governor depends on the propeller model, I could focus on the cylinders and their ignition harness.

Identification of the version differences is the basic step, because otherwise you can build a model of non-existing object that incorporates features from different engine variants.

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Details of the Main Landing Gear

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):

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Figure 80-1 The fully extended shock strut

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”.

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Forming the Main Landing Gear

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:

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Figure 79-1 Main landing gear of a restored SBD-3

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Seamless Joining of Two Objects

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):

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Figure 72-1 The detail that I have to recreate

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.

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Tracing Aircraft Skin Details: Center Wing and the Fuselage

This week I continue mapping the SBD-5 Dauntless skin panels onto my model. After tracing the outer wing sections, described in the previous post, I traced the center wing section (Figure 65‑1):

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Figure 65-1 Traced panels on the center wing

As you can see in the picture, I also traced the contours of the wheel bay on the wing surfaces. (These openings disappear, when you enter mesh edit mode, because they are dynamically created by Boolean modifiers. Thus such contours will be useful during further work, because in this way you can see these edges while editing the mesh).

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A New Book — and New Fixes in the Model

Last week I found a new edition of Bert Kinzey’s “SBD Dauntless” book (Figure 59‑1). After ten years break, Bert started to continue his “Detail & Scale” series, this time in a different form: digital editions. This e-book is the “updated and revised” version of an earlier publication (from 1995). For me, the most important part of Kinzey’s books are the “walk around” photos. They differ from all other “walk arounds” by careful selection of the pictures and comprehensive comments that explain many technical details depicted on these images. Usually these comments are as important as the photos.

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Figure 59-1 Bert Kinzey’s book and one of the photos from inside

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Final Adjustments of the Model Shape

While working on the cowling details, I discovered that the SBD-5 from the Commemorative Air Force (“white 5”) uses a non-original Hamilton Standard propeller. It has larger hub and a pair of bolts in the middle of the hub barrel edges. (As I wrote in this post, the original Hamilton Standard hubs used in the SBDs were smaller, thus they had a single bolt in the middle of each barrel edge). What’s more, I also noticed that the centerline of my model does not precisely pass through the tip of the propeller dome visible in this photo. When I corrected this mistake, I also noticed that the edges of certain cowling panels in my model are minimally below their counterparts on the photo. I examined this difference and decided that I should fix it by rotating the camera of this projection around the fuselage centerline. It was really a “cosmetic” adjustment — the rotation angle was about 0.7⁰. However, suddenly everything in this model matched better the reference photo — except the horizontal tailplane (Figure 58‑1):

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Figure 58-1 Improved matching of my model to the largest reference photo

Continue reading Final Adjustments of the Model Shape