"Wasp Major" Engine
Published January 30, 2007
Pratt & Whitney R-4360 "Wasp Major" Engine
The Pratt & Whitney Aircraft Division of the United Aircraft Corporation in East Hartford, Connecticut, concentrated during World War II on the manufacture of high-powered air-cooled radial engines. Military requirements for Pratt & Whitney engines during the war necessitated the opening of six company-owned manufacturing facilities and licensed production of Pratt & Whitney designs by four automotive companies and two other aircraft companies.
The remarkable R-4360 Wasp Major was developed by Pratt & Whitney beginning in 1942, but culminated twenty years of piston engine development at the company.
For all its mass, this 28-cylinder, 4,360 cubic inch powerhouse was the lightest engine for its horsepower of any aircraft powerplant of its time. It weighed 3,405 pounds but produced 3,650 horsepower, a ratio of .93 pounds per horsepower. It was fuel-injected, gear-supercharged, and featured one crankshaft with four throws, each throw connecting seven cylinders to the crankshaft. One of each throw's pistons was a "master" piston, having the connecting rod form the crank bearing, maintaining alignment of the bearing with the crankcase. The other six piston connecting rods were connected to the master rod's bearing with pinned hinge connections. Each cylinder had two spark plugs and was offset to maximize cooling as air moved across the engine.
The supercharger revolved six times for each revolution of the crankshaft and the propeller shaft turned once for every two revolutions of the crankshaft. The revolutions of the propeller had to be slowed to avoid exceeding the speed of sound at the tips, which would have drastically reduced propeller efficiency.
The R-4360 was a very reliable engine, but each flight usually required that aircraft mechanics re-tighten all engine mounting bolts! The Wasp Major was intended for use on the Boeing B-29D Superfortress, which ultimately evolved into the B-50 bomber project. The engine was subsequently used on several variants of the B-50, the Boeing C-97 Stratofreighter transport (which was based on the basic B-29 design), and the Douglas C-124 Globemaster II. Later versions of the engine were used on the Fairchild C-119 Flying Boxcar and Convair B-36 Peacemaker. The Engine Repair Shops at Hill Field repaired and overhauled variants of the Pratt & Whitney R-4360 Wasp Major engine during World War II and for years afterward.