Jacobs Aircraft Engine Company

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The Jacobs Aircraft Engine Company was formed in 1929 in Philadelphia. Later the company moved to Pottstown, Pennsylvania[1] after purchasing the machine workshop of the Light Manufacturing and Foundry Company.

Early engines[edit]

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

The Cessna UC-78 Bobcat used the L-4 engine

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.[2] 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.[3]

Later models[edit]

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.[4]

The Pratt & Whitney R-985 engine, produced by Jacobs during WWII

In 1941 the American War Department gave the contract to Jacobs to produce Pratt & Whitney R-985 and R-1340 engines until 1945.[4] Jacobs ranked 87th among United States corporations in the value of World War II military production contracts.[5]

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



  1. ^ "Occidental Chemical Corp". E.P.A. Retrieved 2 November 2012. 
  2. ^ "Jacobs Aircraft Engine Company aircraft engine specifications". www.pilotfriend.com. Retrieved 2 November 2012. 
  3. ^ "The Jacobs Radial Engine". www.gruner.com. Retrieved 2 November 2012. 
  4. ^ a b Hoult, Doug. "The Jacobs Engine". www.bombercommandmuseum.ca. Retrieved 2 November 2012. 
  5. ^ Peck, Merton J. & Scherer, Frederic M. The Weapons Acquisition Process: An Economic Analysis (1962) Harvard Business School p.619