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 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. 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 , hence the model designation. Initial models developed , and later models . One model that used two large
turbochargers in addition to the supercharger delivered . Engines weighed , giving a
power-to-weight ratio of . 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. ==Applications==