Pratt & Whitney R-985 Wasp Junior
A dependable 9-cylinder radial that became one of the most widely used small aircraft engines of the 1930s. Compact, air-cooled, and reliable, it powered trainers, bush planes, and early light transports around the world. Its balance of simplicity and durability made it a favorite for operators flying in remote and demanding conditions.
Key Specifications
Type
Year Built
9-cylinder air-cooled radial piston engine
1929
Horsepower
300–450 hp at ~2,000–2,300 rpm
Weight
~650 lb (295 kg)
Power-to-Weight Ratio
~0.6 hp/lb (varies by model)
Fuel
Aviation gasoline
Cooling System
Ignition
Construction
Manufactuer
Air-cooled radial fin design
Dual magneto ignition system
Forged steel crankshaft, aluminum alloy crankcase, steel cylinder barrels with aluminum cooling fins
Pratt & Whitney Aircraft
Engineering Significance
•The R-985 became a backbone engine for utility aviation. It powered bush planes flying into the Canadian wilderness, floatplanes operating from lakes and rivers, and primary trainers preparing pilots for military service. Its strong low-altitude performance and simple maintenance requirements made it ideal for operators far from major maintenance bases.
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•The R-985 refined the small radial formula. Its supercharger improved high-altitude capability while maintaining mechanical simplicity. The dual magneto ignition increased redundancy and reliability, which was critical for overwater and remote-area flights. Its modular radial layout allowed for easier servicing compared to many inline engines of the era, reinforcing the radial engine’s dominance in pre-jet commercial and utility aviation.
Notable Aircrafts
•Beechcraft Staggerwing
•de Havilland Canada DHC-2 Beaver
•Lockheed Vega (some variants),
•Sikorsky S-38
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Beechcraft Staggerwing
Sikorsky S-38