Pratt & Whitney R-4360 Wasp Major

The Pratt & Whitney R-4360 Wasp Major is an American 28-cylinder four-row radial piston aircraft engine designed and built during World War II, and the largest-displacement aviation piston engine to be mass-produced in the United States. It was the last of the Pratt & Whitney Wasp family, and the culmination of its maker's piston engine technology, but the war was over before it could power airplanes into combat. It did, however, power many of the last generation of large piston-engined aircraft before turbojets, and equivalent (and superior) horsepower turboprops (such as the Allison T56), supplanted it. Its main rival was the Wright R-3350 Duplex-Cyclone.

R-4360 Wasp Major
Pratt & Whitney R-4360 Wasp Major (sectioned)
Type Four-row Radial engine
National origin United States
Manufacturer Pratt & Whitney
First run 1944
Major applications Boeing 377
Boeing B-50 Superfortress
Boeing C-97 Stratofreighter
Convair B-36
Fairchild C-119 Flying Boxcar
Number built 18,697
Developed from Pratt & Whitney R-2180-A Twin Hornet
Developed into Pratt & Whitney R-2180-E Twin Wasp E

Design and development

The R-4360 was a 28-cylinder four-row air-cooled radial engine. Each row of seven air-cooled cylinders possessed a slight angular offset from the previous, forming a semi-helical arrangement to facilitate effective airflow cooling of the cylinder rows behind them, inspiring the engine's "corncob" nickname. A mechanical supercharger geared at 6.374:1 ratio to engine speed provided forced induction, while the propeller was geared at 0.375:1 so that the tips did not reach inefficient supersonic speeds.

The four row configuration had severe thermal problems that decreased reliability, with an intensive maintenance regime involving frequent replacement of cylinders required as a result. Large cooling flaps were required, which decreased aerodynamic efficiency, putting extra demands on engine power when cooling needs were greatest. Owing in large part to the maintenance requirements of the R-4360, all airplanes equipped with it were hugely expensive to operate and suffered decreased availability. Its commercial application in the Boeing Stratocruiser was unprofitable without government subsidy.[1] Abandonment of the Stratocruiser was almost immediate when jet aircraft became available, while aircraft with smaller powerplants such as the Lockheed Constellation and Douglas DC-6 remained in service well into the jet era.

Engine displacement was 4,362.5 cu in (71.489 L), hence the model designation. Initial models developed 3,000 hp (2,200 kW), and later models 3,500 hp (2,600 kW). One model that used two large turbochargers in addition to the supercharger delivered 4,300 horsepower (3,200 kW). Engines weighed 3,482–3,870 lb (1,579–1,755 kg), giving a power-to-weight ratio of 1.11 hp/lb (1.82 kW/kg).

Wasp Majors were produced between 1944 and 1955; 18,697 were built.

A derivative engine, the Pratt & Whitney R-2180-E Twin Wasp E, was essentially the R-4360 "cut in half". It had two rows of seven cylinders each, and was used on the postwar Saab 90 Scandia airliner.


  • R-4360-4 - 2,650 hp (1,976 kW)
  • R-4360-20 - 3,500 hp (2,610 kW)
  • R-4360-25 - 3,000 hp (2,237 kW)
  • R-4360-41 - 3,500 hp (2,610 kW)
  • R-4360-51 VDT - "Variable Discharge Turbine" 4,300 hp (3,210 kW). Intended for B-36C. Used on Boeing YB-50C Superfortress. 2-Power recovery turbines.
  • R-4360-53 - 3,800 hp (2,834 kW)
  • R-4360-B3 - 3,500 hp (2,610 kW)
  • R-4360-B6 - 3,500 hp (2,610 kW)


Engines on display

Specifications (R-4360-51VDT)

Data from

General characteristics

  • Type: 28-cylinder supercharged air-cooled four-row radial engine
  • Bore: 5.75 in (146 mm)
  • Stroke: 6.00 in (152 mm).
  • Displacement: 4,362.5 cu in (71,489 cm3).
  • Length: 96.5 in (2,450 mm)
  • Diameter: 55 in (1,400 mm)
  • Dry weight: 3,870 lb (1,760 kg)



See also

Related development

Comparable engines

Related lists



  1. "Ernest K. Gann's Flying Circus: Lady with a past". Retrieved 2012-06-18.
  2. "About the Museum". Mid America Museum of Aviation and Transportation. Retrieved 18 February 2018.
  3. "Goodyear F2G-1 Super Corsair". The Museum of Flight. The Museum of Flight. Retrieved 18 February 2018.
  4. Huff, Randy. "Engines in North American Museums". Aircraft Engine Historical Society. Aircraft Engine Historical Society. Retrieved 18 February 2018.
  5. "Pratt & Whitney R-4360 Wasp Major". Heritage Flight Museum. Avada. Retrieved 18 February 2018.
  6. Yankee Air Museum archive records and display
  7. "ENGINES ON DISPLAY". Combat Air Museum. Combat Air Museum. Retrieved 18 February 2018.
  8. ""Wasp Major" Engine". Hill Air Force Base. United States Air Force. 20 January 2007. Retrieved 18 February 2018.
  9. "R-4360 Wasp Major". Air Victory Museum. Air Victory Museum. Retrieved 18 February 2018.
  10. "Pratt & Whitney Wasp Major R-4360-59B, Cutaway, Radial Engine". Smithsonian National Air and Space Museum. Smithsonian Institution. 2016-04-05. Retrieved 18 February 2018.
  11. "Exhibits". SUN 'n FUN. SUN 'n FUN. Retrieved 18 February 2018.
  12. "WELCOME TO THE MID-ATLANTIC AIR MUSEUM". Retrieved 2018-09-07.
  13. "Pratt & Whitney R-4360 "Wasp Major"". National Museum of the US Air Force™. Retrieved 2018-09-07.
  14. "main exhibits". Retrieved 2019-07-11.


  • Bridgman, Leonard, ed. Jane's All The World's Aircraft 1951–1952. London: Samson Low, Marston & Company, Ltd 1951.
  • 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
  • White, Graham (2006). R-4360: Pratt & Whitney's Major Miracle. North Branch, Minn.: Specialty Press. ISBN 1-58007-097-3.
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