Pratt & Whitney R-2800 Double Wasp
18-cylinder radial piston engine family by Pratt & Whitney
The Pratt & Whitney R-2800 Double Wasp is an American twin-row, 18-cylinder, air-cooled radial aircraft engine with a nominal displacement of 2,800 cu in (46 L), and is part of the long-lived Wasp family of engines.
Produced from 1939 to 1960, the R-2800 saw widespread use in major American aircraft during and after World War II, including the Grumman F6F Hellcat, Vought F4U Corsair, and Republic P-47 Thunderbolt. It was developed into numerous military and commercial variants for fighters, attack aircraft, patrol aircraft, transports, and airliners, with changes in supercharging, fuel systems, water injection, reduction gearing, and accessory arrangements.
Design and development
First run in 1937, near the time that the larger 3,347.9 cu in (54.862 L) competing 18-cylinder Wright Duplex-Cyclone's development had been started in May of that year, the 2,804.5 cu in (45.958 L) displacement R-2800 was first flown by 1940, one year before the Duplex-Cyclone. The Double Wasp was more powerful than the world's only other modern 18-cylinder engine, the Gnome-Rhône 18L of 3,442 cu in (56.40 L).
The Double Wasp was much smaller in displacement than either of the other 18-cylinder designs, and heat dissipation was a greater problem. To enable more efficient cooling, the usual practice of casting or forging the cylinder head cooling fins that had been effective enough for other engine designs was discarded, and instead, much thinner and closer-pitched cooling fins were machined from the solid metal of the cylinder-head forging. The fins were all cut at the same time by a gang of milling saws, automatically guided as it fed across the head in such a way that the bottom of the grooves rose and fell to make the roots of the fins follow the contour of the head, with the elaborate process substantially increasing the surface area of the fins.
The twin distributors on the Double Wasp were prominently mounted on the upper surface of the forward gear reduction housing - with one of the pair of magnetos mounted between them on most models - and almost always prominently visible within a cowling, with the conduits for the spark plug wires emerging from the distributors' cases either directly forward or directly behind them, or on the later C-series R-2800s with the two-piece gear reduction housings, on the "outboard" sides of the distributor casings.
When the R-2800 was introduced in 1939, it was capable of producing 2,000 hp (1,500 kW), for a specific power value of 0.71 hp/cu in (32 kW/L).
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