Pratt & Whitney R-4360 Wasp Major


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, it is the largest-displacement aviation piston engine to be mass-produced in the United States, and at 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 powered turboprops.
Its main rival was the twin-row, 18-cylinder, nearly displacement, up to Wright R-3350 Duplex-Cyclone, first run some seven years earlier.

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 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. 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.

Variants

R-4360-4 - R-4360-17 - XB-35 and YB-35 outboard engines with 8-bladed contra-rotating propellersR-4360-20 - R-4360-21 - XB-35 and YB-35 inboard engines with 8-bladed contra-rotating propellersR-4360-25 - R-4360-41 - R-4360-45 - YB-35 outboard engines with 4-bladed propellersR-4360-47 - YB-35 inboard engines with 4-bladed propellersR-4360-51 VDT - "Variable Discharge Turbine" 4,300 hp. Intended for B-36C. Used on Boeing YB-50C Superfortress. R-4360-53 - R-4360-B3 - R-4360-B6 -

Engines on display