Pratt & Whitney R-4360 Wasp Major

The Pratt & Whitney R-4360 Wasp Major was a large 28-cylinder supercharged air-cooled four-row radial piston aircraft engine designed and built during World War II. 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 the last generation of large piston-engined aircraft before the turbojet and turboprop took over.

Design and development
The R-4360 was a 28-cylinder four-row air-cooled radial engine. Each row of pistons was slightly offset from the previous, forming a semi-helical arrangement to facilitate efficient airflow cooling of the successive rows of cylinders, with the spiraled cylinder setup 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 reliable in flight, the Wasp Major was maintenance-intensive. Improper starting technique could foul all 56 spark plugs, which would require hours to clean or replace. As with most piston aircraft engines of the era, the time between overhauls of the Wasp Major was about 600 hours when used in commercial service.

Engine displacement was 4,362.50 in³ (71.5 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), which was matched or exceeded by very few contemporary engines.

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
• 2

Variants

 * 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. Turbo-supercharger exhaust used to augment thrust.
 * 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
Pima Air Museum, Tucson, AZ, has an electric driven cutway of this engine on display.
 * There is a R-4360 (TSB1-G) Wasp Major on display at the New England Air Museum, Bradley International Airport, Windsor Locks, CT.