Pratt & Whitney R-4360 Wasp Major

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R-4360 Wasp Major
Pratt & Whitney R-4360 Wasp Major.jpg
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
Hughes H-4 Hercules
Number built 18,697
Developed from Pratt & Whitney R-2180-A Twin Hornet
Developed into Pratt & Whitney R-2180-E Twin Wasp E

The Pratt & Whitney R-4360 Wasp Major was a 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 the turbojet, and equivalent and superior output level turboprop powerplants like the Allison T56 took over.[1]

Design and development[edit]

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.

Although mechanically reliable in flight, it developed an unenviable reputation for in-flight fires, particularly in its Boeing Stratocruiser application, and in addition the Wasp Major was maintenance-intensive. Improper starting technique could foul all 56 spark plugs, requiring hours to clean or replace.

Engine displacement was 4,362.50 cu in (71.489 L), hence the model designation. Initial models developed 3,000 hp (2,240 kW), and later models 3,500 hp, but one model 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).

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.


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-4360-51 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[edit]

R-4360 cutaway

Specifications (R-4360-51VDT)[edit]

Pratt & Whitney R-4360 Wasp Major (sectioned)

General characteristics

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



See also[edit]

Related development
Comparable engines
Related lists



  1. ^ Pratt & Whitney web site
  2. ^ "Museum Home". Retrieved 2015-09-15. 
  3. ^ Pratt & Whitney R-4360 (TSB1-G) Wasp Major
  4. ^ Hill AFB
  5. ^ [1]
  6. ^ [2]
  7. ^ [3]
  8. ^ [4]


  • 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[edit]