The Pratt & Whitney R-4360 Wasp Major is a twenty-eight-cylinder air-cooled radial engine developed near the end of the Second World War. Its four rows of cylinders and 4,360-cubic-inch displacement placed it among the most complex large piston engines produced in quantity in the United States.[1]
Architecture
The cylinders are arranged in four rows of seven, staggered around the crankcase in a spiral pattern often described as a corncob. This arrangement helped cooling air reach the cylinders despite the engine's depth. The Air Force museum lists 3,500 horsepower at 2,700 rpm and a weight of 3,404 pounds for its R-4360-4 specification, illustrating the power available from the large radial assembly.[1][2]
Aircraft applications
The Wasp Major was developed for the Boeing B-50, an improved derivative of the B-29. It also powered the Convair B-36 and Northrop B-35, and transport aircraft including the C-74, C-97, XC-99 and C-124. Its service therefore encompassed heavy bombers, cargo aircraft and aerial tankers during the period before turbine propulsion became dominant in those roles.[1]
Maintenance demands
The engine's output came with substantial maintenance requirements. Each engine had fifty-six spark plugs, and an incorrect starting procedure could foul or damage the entire set, leaving maintainers with hours of cleaning or replacement work. The museum's account describes the Wasp Major as reliable in flight but intensive to maintain, a useful distinction when considering its operational reputation.[2]
Place in aviation history
R-4360 engines powered the B-50 Lucky Lady during the first nonstop round-the-world flight in 1949. The type also represents the practical culmination of large American piston-engine development. When the C-97 and KC-97 families left US Air Force inventory in the late 1970s, they brought this era of large radial engines and their associated supercharging systems to a close within that service.[2][1]