The History of the Pratt & Whitney R-985 & The List of Aircraft Powered by the Radial Engine

The Pratt & Whitney R-985 Wasp Junior is a series of nine-cylinder, air-cooled, radial aircraft engines built by the Pratt & Whitney Aircraft Company from the 1930s to the 1950s. These engines have a displacement of 985 in; initial versions produced 300 hp (220 kW), while the most widely used versions produce 450 hp (340 kW).

Wasp Juniors have powered numerous smaller civil and military aircraft, including small transports, utility aircraft, trainers, agricultural aircraft, and helicopters. Over 39,000 of these engines were built, and many are still in service today.

Begun in 1925 by former Wright Aeronautical employees as a spinoff from a machine tool company, Pratt & Whitney became one of the world’s largest manufacturers of aircraft engines, and the Wasp Jr. is one of the most successful reciprocating engines ever built. Pratt & Whitney introduced it as a complement to the highly successful Wasp and Hornet families of engines in 1930. The Wasp Jr. was essentially a Wasp of reduced dimensions. Pratt & Whitney and its licensees manufactured over 39,000 versions of the R-985 until 1953 for a wide variety of military and commercial aircraft, including light transports, trainers, sport aircraft, and helicopters.

The R-985-AN-14B powered the McDonnell XHJH-1 and XHJD-1 Whirlaway helicopters and the Avro Anson V trainer. This Wasp Jr.-aptly nicknamed “The Dancing Engine”- has been sectionalized and motorized to demonstrate the movements of its internal components.

The Pratt & Whitney R-985 Wasp Junior was a 9 cylinder, single-row, air-cooled radial engine with horsepower ranging from 300 hp to 450 hp, depending on the model and configuration. It was used in a range of aircraft that included the Grumman Goose, Lockheed Model 10A and Beechcraft Model 18. Jacqueline Cochran used the Wasp Junior to set speed and altitude records in a specially built D17W Beechcraft Staggerwing.
In the mid-1930s, Pratt & Whitney produced five basic engines:

  • The single-row Wasp Junior.
  • The single-row Wasp.
  • The single-row Hornet.
  • The double-row Twin Wasp.
  • The double-row Twin Wasp Junior.
history of the r-985
(Image: Griff Wason Art & Illustration.)

The Wasp Junior was a smaller version of the R-1340 Wasp designed to compete in the market for medium-sized aircraft engines. Development was completed in 1929 and the engine went into production in early 1930 at the new 400,000 sq./ft Pratt & Whitney plant that opened on January 1, 1930, in East Hartford.1 The original Wasp Junior was rated at 300 hp at 2,000 rpm and was similar in power and displacement to the J-6-9 Whirwind. A supercharged version developed 400 hp at 2,300 RPM at 4,000 ft. and by 1932 power was up to 420 hp with racing versions greater than that.2

In 1931, Pratt & Whitney developed a “hot spot” or heat exchanger on the oil regulator to improve engine performance. It was installed between the carburetor and the rear section of the engine. The regulator used the temperature drop of the gasoline evaporation to cool the oil and the same unit used the engine exhaust to heat the fuel/air mixture in cold weather.

More than 39,000 Wasp Juniors were produced from 1929 until the end of production in 1953.5It was considered the best engine in its class and many Wasp Junior engines are still flying today.

Specifications of the Pratt & Whitney R-985 Radial Engine

Pratt & Whitney R-985 Wasp Junior
Date: 1929
Cylinders: 9
Configuration: Single-row, air-cooled radial
Horsepower: 400 hp (298 kW)
RPM: 2,300
Bore and Stroke: 5-3/16 in. (132 mm) x 5-3/16 in. (132 mm)
Displacement: 985 cu. in. (16.14 liters)
Weight: 640 lbs. (290 kg)

Aircraft Powered by the Pratt & Whitney R-985

  • Airspeed Oxford (AS.46 Oxford V)
  • Air Tractor AT-300
  • Avro Anson (Mk V)
  • Barkley-Grow T8P-1
  • Beechcraft Model 18 and military derivatives
  • Beechcraft Staggerwing D17S, D17W, G17S
  • Bell XV-3
  • Bellanca 300-W
  • Berliner-Joyce OJ
  • Boeing-Stearman Model 75 (in aftermarket conversions)
  • Bratukhin G-3
  • CAC Winjeel
  • de Havilland Canada DHC-2 Beaver and L-20/U-6 military versions
  • Douglas C-26 Dolphin
  • Fleetwings BT-12
  • Gee Bee Model Z
  • Grumman G-164 Ag Cat (some models)
  • Grumman G-21 Goose
  • Howard DGA-11
  • Howard DGA-15P
  • Junkers F13 (Rimowa F13 replica)
  • Koolhoven F.K.51 (some models)
  • Lockheed Model 10-A Electra
  • Lockheed Model 12-A Electra Junior
  • Max Holste MH.1521 Broussard
  • McDonnell XHJH Whirlaway
  • Naval Aircraft Factory N3N (in aftermarket conversions)
  • North American BT-14
  • PWS-24bis
  • Seversky BT-8
  • Sikorsky H-5 helicopter (and S-51 civil version)
  • Sikorsky S-39 amphibian
  • Snow S-2B and S-2C
  • Spartan Executive 7W
  • Stinson Reliant SR-9F and SR-10F
  • Vought OS2U Kingfisher
  • Vultee BT-13 Valiant
  • Waco S3HD
  • Waco SRE Aristocrat
  • Weatherly 201 series
  • Weatherly 620

What’s your favorite part of a the Pratt & Whitney R-985? Our is the sound, so here is a video of that round sound:


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