The R-985 entered Army Air Corps service in 1932 at just 300 horsepower. Over the next decade, refinements pushed output to 450 hp, and the engine powered thousands of military and civilian aircraft—a modest-power radial that became one of the most ubiquitous trainers and light transports of the 1930s and 1940s .
R-985 Wasp Junior Overview
The primary subject of this technical guide focuses on the Pratt & Whitney R-985 Wasp Junior engine, engineered specifically for 9-Cylinder, Air-Cooled, Supercharged Radial applications. Below is an essential digest of this powertrain configuration.
• 9-cylinder radial
• 985 cu in displacement
• 300–450 hp range
• Powered trainers and light transports
R-985 Wasp Junior Technical Notes
985 cu in displacement; 9 cylinders; air-cooled and supercharged; maximum rpm 2,300; power ranged from 300 hp (1932) to 450 hp (WWII variants) .
The Wasp Junior’s small displacement relative to the R-1830 and R-1820 made it suitable for lighter aircraft where fuel economy and weight mattered more than raw power. Its supercharger maintained power at altitude, a feature that mattered for trainers operating from high-elevation fields. The engine powered primary trainers, light transports, and utility aircraft, serving as the first engine many wartime pilots learned to manage .
| Configuration | 9-cylinder, air-cooled radial |
|---|---|
| Supercharging | Yes |
| Displacement | 985 cu in |
| Max RPM | 2,300 |
| Power Range | 300–450 hp |
| Fuel | Aviation gasoline |
Aircraft Powered by the R-985
This engine model is deployed across various operational frameworks. Here is a breakdown of the typical machine or vehicle applications using this unit:
Primary trainers, light transports, utility aircraft (military and civilian)
Pros & Advantages
Lightweight; fuel efficient; supercharged for altitude performance; reliable and easy to maintain.
Cons & Disadvantages
Modest power output; limited growth potential compared to larger radials.
Frequently Asked Questions (FAQs)
Q1: When did the R-985 enter service?
A1: It was first used by the Army Air Corps in 1932, rated at 300 horsepower .
Q2: How much power did WWII variants produce?
A2: Up to 450 horsepower .
Q3: What was the R-985’s maximum rpm?
A3: 2,300 rpm .
Thousands of military and civilian aircraft, primarily trainers, light transports, and utility types .