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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 B-50 Superfortress
C-97 Stratofreighter
C-119 Flying Boxcar
Convair B-36
Number built 18,697
Developed from R-2180-A Twin Hornet
Developed into R-2180 Twin Wasp E

The Pratt & Whitney R-4360 Wasp Major was a large radial piston aircraft engine designed and built during World War II. 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 the last generation of large piston-engined aircraft before the turbojet and turboprop took over.


Design and development

The R-4360 was a 28-cylinder four-row air cooled radial engine. Each row of pistons was slightly offset from the previous, forming a semi-helical arrangement to facilitate efficient airflow cooling of the successive rows of cylinders. 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.

Although reliable in flight, the Wasp Major was maintenance intensive. Improper starting technique could foul all 56 spark plugs, which would require hours to clean or replace. As with most piston aircraft engines of the era, the time between overhauls of the Wasp Major was about 600 hours when used in commercial service.

Engine displacement was 4,362.50 in³ (71.5 L), hence the model designation. Initial models developed 3,000 hp (2,240 kW), but the final models delivered 4,300 hp (3200 kW) using two large turbochargers in addition to the supercharger. Engines weighed 3,482 to 3,870 lb (1,579 to 1,755 kg), giving a power to weight ratio of 1.11 hp/lb (1.83 kW/kg), which was matched by very few contemporary engines.

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

A derivative engine, the 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.


Pratt & Whitney R-4360 Wasp Major


  • 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-4360-51VDT - 4,300 hp (3,210 kW)
  • R-4360-53 - 3,800 hp (2,834 kW)
  • R-4360-B3 - 3,500 hp (2,610 kW)

Specifications (R-4360-51VDT)

Pratt & Whitney R-4360 Wasp Major (sectioned)

General characteristics

  • Type: 28-cylinder supercharged air-cooled four-row radial engine
  • Bore: 5.75 in. (146.05 mm)
  • Stroke: 6.00 in. (152.4 mm)
  • Displacement: 4,362.5 in³ (71.49 L)
  • Length: 96.5 in. (2 451 mm)
  • Diameter: 55 in (1397 mm)
  • Dry weight: 3,870 lb (1,755 kg)



See also

Related development

Comparable engines

Related lists


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

External links

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