The R-1820 “Cyclone” Versions

I decided to write a post about the first decade of the R-1820 “Cyclone” development (up to the R-1820-60 version, i.e. 1940). This engine was used in many designs from 1930s, and you can find the references to its various models in many technical specifications. However, sometimes it is difficult to determine how such a referenced version looked like! The early models of the “Cyclone” were produced in small batches, so there is less historical photos. Sometimes even the specialists from the museums are misguided: in one of them, you can find a SBD-3 fitted with the engine and the propeller from the SBD-5. My query, which resulted in this article, started with comparison of the R-1820-60 (used in the SBD-5) and the R-1820-52 (used in the SBD-3 and -4). I have found so many differences, that I started to wonder about the engine used in the pre-war SBD-1 and SBD-2. (They used the earlier “Cyclone” version: R-1820-32). The results presented below may be interesting to the modelers who recreate aircraft from this period (for example – the Curtiss “Hawk”, or the Grumman F3F-2 “Flying Barrel”).

Let’s start from the beginning: below you can see the first model of the R-1820 family, designed in 1931 (Figure 90‑1):

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Figure 90-1 One of the earliest R-1820s

Frankly speaking, there is only a general resemblance to the later “Cyclone” versions. Note the small crankcase front section and the “archaic” cylinder heads. (They have different shape, and their fins are much shorter and widely spaced: these are indicators of a simpler casting technology). Another strange feature is the exhaust, which could be also mounted in the reversed (i.e. forward) direction. (Some of the aircraft from this era used front exhaust collectors). This engine used large spark plugs, mounted horizontally (in parallel to the centerline). It was rated at 575hp on takeoff, and used in some contemporary designs, like the Curtiss “Hawk” biplane.

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