Pratt & Whitney R-4360 Wasp Major

R-4360 Wasp Major
Pratt & Whitney R-4360 Wasp Major on display at Travis Air Force Base Aviation Museum
TypeFour-row Radial engine
National originUnited States
ManufacturerPratt & Whitney
First run28 April 1941 (prototype)
1944 (production)
Major applications
Manufactured1944–1955
Number built18,679
Developed fromPratt & Whitney R-2800 Double Wasp
Pratt & Whitney R-2180-A Twin Hornet
Developed intoPratt & Whitney R-2180-E Twin Wasp E

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. At 4,362.5 cu in (71.5 L), it is the largest-displacement aviation piston engine to be mass-produced in the United States, and at up to 4,300 hp (3,200 kW) the most powerful. The prototype first ran on 28 April 1941, with production-standard engines running in 1944. It was the last of the Pratt & Whitney Wasp family, and the culmination of its maker's piston engine technology.

The war was over before it could power airplanes into combat. It powered many of the last generation of large piston-engined aircraft before turbojets, but was supplanted by equivalent (and superior) powered turboprops (such as the Allison T56).

Its main rival was the twin-row, 18-cylinder, nearly 3,350 cu in (54.9 L) displacement, up to 3,700 hp (2,800 kW) Wright R-3350 Duplex-Cyclone, first run some seven years earlier (May 1937).

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 first prototype R-4360 was assembled using a modified H-3130 nose case and reduction gear, a supercharger and Bendix PT-13 carburetor from the R-2800 “B” series, and connecting rods from the R-2180. It was successfully test-run on 28 April 1941. The first airborne tests followed shortly thereafter. A modified Vultee A-31 Vengeance, designated V-85, served as the testbed, and the R-4360 made its maiden flight on 25 April 1942.

The engine was a technological challenge and the first product from Pratt and Whitney's new plant near Kansas City, Missouri. The four-row configuration had severe thermal problems that decreased reliability, with an intensive maintenance regime involving frequent replacement of cylinders required.[citation needed] 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 costly to operate and suffered decreased availability. Its commercial application in the Boeing Stratocruiser was unprofitable without government subsidy. 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 (71.5 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; 18,679 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.

Variants

Sectioned R-4360 Wasp Major

The following is a representative list of R-4360 variants. Power ratings varied by model, installation, supercharging arrangement, and operating limits. Data from the Aircraft Engine Historical Society, Graham White's "R-4360: Pratt & Whitney's Major Miracle", and a Pratt & Whitney variant index unless otherwise noted.

Wasp Major B3
3,500 hp (2,600 kW)
Wasp Major B6
3,500 hp (2,600 kW)
R-4360-4
3,000 hp (2,200 kW)
R-4360-10
3,000 hp (2,200 kW); two-stage, dual-rotation engine for the Boeing XF8B.
R-4360-17
3,000 hp (2,200 kW); XB-35/YB-35 outboard engine.
R-4360-19
Republic XP-72 engine with remote auxiliary supercharger.
R-4360-20
3,500 hp (2,600 kW)
R-4360-21
3,000 hp (2,200 kW); XB-35/YB-35 inboard engine.
R-4360-25
3,000 hp (2,200 kW)
R-4360-35
3,500 hp (2,600 kW); Boeing B-50 engine.
R-4360-41
3,500 hp (2,600 kW)
R-4360-43 VDT
4,300 hp (3,200 kW) VDT-type tractor engine for the YB-50C/B-54. A modified B-50, redesignated B-50C, was flight-tested with one VDT nacelle in 1947.
R-4360-45
3,000 hp (2,200 kW); XB-35/YB-35 outboard single-rotation engine.
R-4360-47
3,000 hp (2,200 kW); XB-35/YB-35 inboard single-rotation engine.
R-4360-51 VDT
4,300 hp (3,200 kW); intended for the B-36C, but the program was cancelled before deliveries to the Air Force.
R-4360-55 VDT
4,300 hp (3,200 kW) low-compression VDT pusher development for the B-36C. Its high-altitude triple-turbosupercharger installation used two CHM-2 turbosuperchargers in parallel and one CH-8 in series, and demonstrated normal rated power at a simulated altitude of 50,000 ft (15,000 m).
R-4360-53
3,800 hp (2,800 kW)
R-4360-57 VDT
4,300 hp (3,200 kW) high-compression VDT development of the R-4360-55, with a 7.5:1 compression ratio. Some examples were built, but the engine did not enter production.
Note: VDT stands for "Variable Discharge Turbine".

Applications

Engines on display

R-4360 cutaway
R-4360-4 on display at the Air Zoo
R-4360 on display at Museum of Aviation, Robins AFB
R-4360 on display at the National Museum of the United States Air Force in Dayton, Ohio

Specifications (R-4360-51 VDT)

Pratt & Whitney R-4360 Wasp Major (sectioned)

Data from White, 1995

General characteristics

Components

Performance

See also

Related development

Comparable engines

Related lists

Footnotes

  1. ↑ 15,600 were built by Pratt & Whitney and the remainder by Ford Motor Company under license.

References

Citations

  1. 1 2 3 White, Graham (2006). R-4360: Pratt & Whitney's Major Miracle. North Branch, MN: Specialty Press. p. 35. ISBN 978-1580070973.
  2. ↑ White 1995, p. 212.
  3. ↑ White, Graham (2006). R-4360: Pratt & Whitney's Major Miracle. North Branch, MN: Specialty Press. p. 37. ISBN 978-1580070973.
  4. ↑ Gunston 2006, p. 132.
  5. ↑ "Ernest K. Gann's Flying Circus: Lady with a past". Ovi.ch. Archived from the original on 2004-12-18. Retrieved 2012-06-18.
  6. ↑ White, Graham (2006). R-4360: Pratt & Whitney's Major Miracle. North Branch, Minnesota: Speciality Press Publishers and Wholesalers. pp. 161–162, 169. ISBN 978-1-58007-097-3. Retrieved 3 September 2026.
  7. ↑ "Pratt & Whitney Piston Engine Production". Aircraft Engine Historical Society. Archived from the original on 6 December 2025. Retrieved 3 September 2026.
  8. ↑ Gunston 2006, p. 164.
  9. ↑ McCutcheon, Kimble D. (18 April 2025). "R-4360 Wasp Major Development History". Aircraft Engine Historical Society. Archived from the original on 23 June 2026. Retrieved 23 June 2026.
  10. ↑ "Index of Wasp Major & R-4360 Designated Engines" (PDF). Pratt & Whitney Aircraft. 15 May 1955. Archived (PDF) from the original on 23 June 2026. Retrieved 23 June 2026 – via Aircraft Engine Historical Society.
  11. 1 2 3 4 White, Graham (2006). R-4360: Pratt & Whitney's Major Miracle. Specialty Press. pp. 179, 196, 200–203, 273–274. ISBN 1-58007-097-3.
  12. ↑ "About the Museum". Mid America Museum of Aviation and Transportation. Archived from the original on 4 May 2014. Retrieved 18 February 2018.
  13. ↑ "Goodyear F2G-1 Super Corsair". The Museum of Flight. The Museum of Flight. Archived from the original on 23 December 2008. Retrieved 18 February 2018.
  14. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Huff, Randy. "Engines in North American Museums". Aircraft Engine Historical Society. Aircraft Engine Historical Society. Archived from the original on 18 February 2018. Retrieved 18 February 2018.
  15. ↑ "Pratt & Whitney R-4360 Wasp Major". Heritage Flight Museum. Avada. Archived from the original on 11 February 2016. Retrieved 18 February 2018.
  16. 1 2 "ENGINES ON DISPLAY". Combat Air Museum. Combat Air Museum. Archived from the original on 9 May 2008. Retrieved 18 February 2018.
  17. ↑ ""Wasp Major" Engine". Hill Air Force Base. United States Air Force. 20 January 2007. Archived from the original on October 19, 2016. Retrieved 18 February 2018.
  18. ↑ "R-4360 Wasp Major". Air Victory Museum. Air Victory Museum. Archived from the original on August 19, 2015. Retrieved 18 February 2018.
  19. ↑ "Pratt & Whitney Wasp Major R-4360-59B, Cutaway, Radial Engine". Smithsonian National Air and Space Museum. Smithsonian Institution. 2016-04-05. Archived from the original on 2024-07-26. Retrieved 18 February 2018.
  20. ↑ "Exhibits". SUN 'n FUN. SUN 'n FUN. Archived from the original on 13 January 2017. Retrieved 18 February 2018.
  21. ↑ "WELCOME TO THE MID-ATLANTIC AIR MUSEUM". www.maam.org. Archived from the original on 2000-04-08. Retrieved 2018-09-07.
  22. ↑ "Pratt & Whitney R-4360 "Wasp Major"". National Museum of the US Air Force™. Archived from the original on 2018-09-07. Retrieved 2018-09-07.
  23. ↑ "main exhibits". penngrovepower.org. Archived from the original on 2014-10-19. Retrieved 2019-07-11.
  24. ↑ Stoneberg, David (September 16, 2020). "A piece of military aircraft history sits in St. Helena, just waiting to put on a show". Napa Valley Register. St Helena, CA: Lee Enterprises, Inc. Archived from the original on September 19, 2020. Retrieved September 17, 2020.
  25. ↑ White 1995, p. 222.

Bibliography