Pratt & Whitney R-1535 Twin Wasp Junior

R-1535 Twin Wasp Junior
Pratt & Whitney Twin Wasp Junior, at the National Museum of Naval Aviation, Pensacola, Florida
TypeRadial engine
National originUnited States
ManufacturerPratt & Whitney
First run17 October 1931[1]
Major applications
Number built2,880[1]
Developed fromPratt & Whitney R-985 Wasp Junior

The Pratt & Whitney R-1535 Twin Wasp Junior is an American aircraft engine developed in the 1930s. The engine was introduced in 1932 as a 14-cylinder version of the 9-cylinder R-985, and was a two-row, air-cooled radial design. Displacement was 1,535 cu in (25.2 L); bore and stroke were both 5+3⁄16 in (132 mm).[1]

Variants

The following is a representative list of R-1535 variants. Data from a Pratt & Whitney designated-engine index and the U.S. Navy Aeronautical Engine Laboratory report index, unless otherwise noted.[2][3]

  • R-1535-11 - 750 hp (560 kW)
  • R-1535-13 - 750 hp (560 kW), 825 hp (615 kW)
  • R-1535-44 - 625 hp (466 kW)
  • R-1535-64 - 950 hp (710 kW)
  • R-1535-72 - 700 hp (520 kW) for takeoff; 650 hp (480 kW) normal at 7,500 ft (2,300 m)
  • R-1535-82 - 750 hp (560 kW)
  • XR-1535-86 - 825 hp (615 kW); experimental fuel-injection variant
  • XR-1535-88 - 825 hp (615 kW)
  • R-1535-94 - 825 hp (615 kW)
  • R-1535-96 - 825 hp (615 kW)
  • R-1535-98 - 700 hp (520 kW)
  • R-1535-SB4-G - 825 hp (615 kW)

Applications

Applications from the Aircraft Engine Historical Society, unless otherwise noted.[1]

Engines on display

Specifications (R-1535-SB4-G)

Data from [7]

General characteristics

  • Type: Fourteen-cylinder two-row supercharged air-cooled radial engine
  • Bore: 5+3⁄16 in (131.8 mm)
  • Stroke: 5+3⁄16 in (131.8 mm)
  • Displacement: 1,534.9 cu in (25.153 L)
  • Length: 53.27 in (1,353 mm)
  • Diameter: 44.13 in (1,121 mm)
  • Dry weight: 1,087 lb (493 kg)

Components

Performance

See also

Related development

Comparable engines

Related lists

References

Notes

  1. 1 2 3 4 McCutcheon, Kimble D. (20 April 2020). "Pratt & Whitney Twin Wasp Junior (R-1535)". Aircraft Engine Historical Society. Retrieved 28 August 2026.
  2. ↑ "Index of Twin Wasp Jr. & R-1535 Designated Engines" (PDF). Pratt & Whitney Aircraft. Retrieved 23 June 2026 – via Aircraft Engine Historical Society.
  3. ↑ "U.S. Navy Aeronautical Engine Laboratory Report Index". Aircraft Engine Historical Society. 12 December 2015. Retrieved 23 June 2026.
  4. ↑ "Potez 63.11". Cyber Aéro Breton. Retrieved 23 June 2026. Potez 63.12 : Version de chasse dotée de moteurs Pratt & Whitney R-1535 Twin Wasp Junior. Un prototype.
  5. ↑ "Pratt & Whitney R-1535-96 Twin Wasp Junior"
  6. ↑ "From lakebed to legacy at Patria's F-35 assembly and maintenance facility | Patria". www.patriagroup.com. Retrieved 2026-08-10.
  7. ↑ Tsygulev (1939). Aviacionnye motory voennykh vozdushnykh sil inostrannykh gosudarstv (Авиационные моторы военных воздушных сил иностранных государств) (in Russian). Moscow: Gosudarstvennoe voennoe izdatelstvo Narkomata Oborony Soyuza SSR.

Bibliography

  • Gunston, Bill. World Encyclopedia of Aero Engines: From the Pioneers to the Present Day. 5th edition, Stroud, UK: Sutton, 2006.ISBN 0-7509-4479-X
  • White, Graham. Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II. Warrendale, Pennsylvania: SAE International, 1995. ISBN 1-56091-655-9
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