Pratt & Whitney R-4360

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Pratt & Whitney Wasp Major (sectioned)

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 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 planes before the jet engine and turboprop took over.

It was a four-row radial engine with 28 cylinders (seven per row); each row was slightly offset from the previous so that they formed a somewhat helical arrangement (as can be seen in the photograph) - this was to permit better cooling of the successive rows of cylinders. A mechanical supercharger geared at six times engine speed provided forced induction, while the propeller was geared at half engine speed so that the tips did not reach inefficient supersonic speeds.

The engine had many good and bad points. While it had a high power output, reliability was a persistent problem. Crankcase oil leaks were very common, as noticeable on many photos of the B-50 with long black streaks down each wing. This made long-distance overwater planes, like the Boeing 377 Stratocruiser, rather unpopular with passengers.

Engine displacement was 4,360 in³ (71.4 L), hence the model designation. Initial models developed 3,000 hp (2240 kW), but the final models delivered 4,300 hp (3200 kW). Engines weighed 3,482 to 3,870 lb (1,579 to 1,755 kg), heavy but giving a power to weight ratio matched by very few engines.

The engine was commonly nicknamed the Corncob, since its multiple, staggered rows of cylinders made it resemble one.

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

1 Aircraft usage
2 Specifications (R-4360)
3 Related contents
4 References
5 Further reading

[edit] Aircraft usage

The Pratt & Whitney R-4360 was intended as a new powerplant for the Boeing B-29 Superfortress; Wasp Major-powered Superfortresses were eventually designated B-50. They also powered the Convair B-36 as well as a broad assortment of other aircraft: