Jacobs Aircraft Engine Company

The Jacobs Aircraft Engine Company was formed in 1929 in Philadelphia. Later the company moved to Pottstown, Pennsylvania after purchasing the machine workshop of the Light Manufacturing and Foundry Company.

An early product of 1931 was the Jacobs L-3, a small 51 hp 3 cylinder radial air-cooled engine. Only 44 built.

By 1933, Jacobs had developed its most famous engine, the L-4 seven-cylinder radial air-cooled engine with a power rating of 225 horsepower and a displacement of 757 cubic inches (12.4 litres). It was better known as by its military designation, the R-755. At the time it became known as the best producer of engines in the 200-400 horsepower range. Jacobs was the first to start making engines using forged aluminum alloy pistons, sodium-filled exhaust valves and magnesium alloy crankcases.

The L-4 was used mostly on the Cessna UC-78 Bobcat, Cessna 195 and Stearman PT-18 Kaydet.

Due to the tendency of the L-4 engine to vibrate heavily at low rpms it was given the nicknames Shakin' Jake and Shakey Jake.

Later developments included the 285 hp L-5 or R-830, and 330 hp L-6 or R-915.

Jacobs engines were fitted to many US-built aircraft of the inter-war period, including several Waco models. They were in use in 26 different countries including in Canada, where 330 horsepower L6-MB engines were used to power the Royal Canadian Air Force's Avro Anson Mk. II aircraft.

In 1941 the American War Department gave the contract to Jacobs to produce Pratt & Whitney R-985 and R-1340 engines until 1945. Jacobs ranked 87th among United States corporations in the value of World War II military production contracts.

After World War II, Jacobs became a division of Republic Industries (not Republic Aircraft).

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