Pratt & Whitney R-1535 Twin Wasp Junior

The Pratt & Whitney R-1535 Twin Wasp Junior is an American aircraft piston engine developed in the 1930s and introduced in 1932. It is a fourteen-cylinder, two-row, air-cooled radial that Pratt & Whitney built as a larger relative of its nine-cylinder R-985 Wasp Junior, and it belongs to the company's Wasp series of radials. Bore and stroke were both about five and three sixteenths of an inch, giving a displacement of 1,535 cubic inches, about 25.2 litres. The variants listed for it range from 625 to 950 horsepower, with the R-1535-SB4-G rated at 825 horsepower for takeoff, burning 87 octane gasoline through a single-speed centrifugal supercharger and a carburetor. Surviving engines are on display at the New England Air Museum in Connecticut and at the San Diego Air and Space Museum.