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 cuin, it is the largest-displacement aviation piston engine to be mass-produced in the United States, and at 4,300 hp the most powerful. First run 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 3350 cuin displacement, up to 3,700 hp 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 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 4362.5 cuin, hence the model designation. Initial models developed 3000 hp, and later models 3500 hp. One model that used two large turbochargers in addition to the supercharger delivered 4300 hp. Engines weighed 3482 - 3870 lb, giving a power-to-weight ratio of 1.11 hp/lb. 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

Applications

• Aero Spacelines Mini Guppy • Aero Spacelines Pregnant Guppy • Boeing 377 Stratocruiser • Boeing B-50 Superfortress • Boeing C-97 Stratofreighter • Boeing KC-97 Stratofreighter • Boeing XF8B • Boeing XB-44 Superfortress • Convair B-36 Peacemaker • Convair XC-99 • Curtiss XBTC • Curtiss XP-71 (not built) • Douglas C-74 Globemaster • Douglas C-124 Globemaster II • Douglas XTB2D Skypirate • Fairchild C-119 Flying Boxcar • Fairchild XC-120 Packplane • Goodyear F2G "Super" Corsair • Hughes H-4 Hercules ("Spruce Goose") • Hughes XF-11 • Lockheed R6V Constitution • Martin AM Mauler • Martin JRM Mars • Martin P4M Mercator • Northrop YB-35 • Republic XP-72 • Republic XF-12 Rainbow • SNCASE SE-2010 Armagnac • Vultee XA-41

Engines on display

Specifications (R-4360-51VDT)