Pratt & Whitney R-2800
| R-2800 Double Wasp | |
|---|---|
 |
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| A preserved R-2800 engine at the National Museum of the United States Air Force | |
| Type | Radial engine |
| National origin | United States |
| Manufacturer | Pratt & Whitney |
| First run | 1937 First flown May 29, 1940 |
| Major applications |
A-26 Invader B-26 Marauder Canadair CL-215 CH-37 Mojave Convair CV-240 family Curtiss C-46 Commando Douglas DC-6 F4U Corsair F6F Hellcat P-47 Thunderbolt P-61 Black Widow |
| Number built | 125,334 |
The Pratt & Whitney R-2800 Double Wasp is a twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of 2,800 in³ (46 L), and is part of the long-lived Wasp family.
The R-2800 is considered one of the premier radial piston engines ever designed and is notable for its widespread use in many important American aircraft during and after World War II. During the war years, Pratt & Whitney continued to develop new ideas to upgrade this already powerful workhorse, most notably water injection for takeoff in cargo and passenger planes and to give emergency power in combat.
First run in 1937, the R-2800 was America's first 18-cylinder radial engine design. The Double Wasp was more powerful than the world's only other modern eighteen, the Gnome-Rhône 18L of 3,442 in³ (56.4 L). (The American Wright Duplex-Cyclone radial of 3,347 in³ (54.86 L) was also under development at the time, and promised to be more powerful than either the P&W or Gnome-Rhone radials.) 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 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 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.
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