Pratt & Whitney R-4360 – The 28-Cylinder engine

In World War II, the United States developed and produced the Pratt & Whitney R-4360 Wasp Major, a 28-cylinder, four-row radial piston aircraft engine. This is the biggest airplane piston engine ever developed by Pratt & Whitney in terms of mass production.

It is a massive 71-liter, air-cooled, radial engine with up to 4,300 horsepower produced. Even the earliest R-4360 models were capable of producing over 2,500 horsepower. Although the Wasp Major began life as a “simple” supercharged engine, its ultimate form also had a turbocharger.

Source: Smithsonian National Air and Space Museum, NASM Original Photography, NASM Acc. 2012-0026

It was the final model in the Pratt & Whitney Wasp line. It represented the peak of piston engine development at Pratt & Whitney. However, it couldn’t power any planes until the war had already ended.

Design & Structure

There are four rows of 28 cylinders in the R-4360. The engine’s four rows of seven cylinders and 56 valves were offset radially to allow cooling air to reach the back rows. However, there were minor issues controlling temperatures in the engine’s rearmost cylinders.

Source: Robert Wahlgren / enginehistory

Two spark plugs per cylinder ignited the mixture that powered each piston. Therefore changing all 56 plugs will take a whole day for a technician to finish. A pressure carburetor distributing gasoline to the engine was used because fuel injectors were still in their beginnings when the R-4360 was being developed.

The engine has a 4,362.5-cu-in (71.489-l) displacement. Initial versions generated 3,000 horsepower, with subsequent versions going up to 3,600 horsepower. Another version with two big turbochargers in addition to the supercharger generated 4,300 horsepower.

Source: Robert Wahlgren / enginehistory

Depending on the model, engine weight ranged between 1,579 – 1,755 kg, resulting in a power–to–weight ratio of 1.11 horsepower per pound.

There were 18,697 Wasp Majors manufactured between 1944 and 1955.

What Planes did it power?

Source: By RuthAS / wikicommons

While the Wasp Major was primarily used to power the Boeing B-50 Superfortress and Northrop’s pioneering B-35 flying wing, it also powered some of the largest and most powerful Convair B-36 Peacemaker aircraft at the time. The re-engineered Hawker Sea Fury Dreadnought won gold in the Unlimited Class at the Reno Air Races in 1983 and 1986 using the R-4360.

Source: By U.S. Air Force
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