Liberty 12

Liberty L-12
Liberty L-12 aircraft engine
Type	Piston aero engine
National origin	United States
Manufacturer	Lincoln, Ford, Packard, Marmon, Buick
Designed by	Jesse G. Vincent and Elbert J. Hall
First run	about 1917
Number built	20,748
Variants	Liberty L-4, Liberty L-6, Liberty L-8

The Liberty L-12 was an American 27-litre (1,649 cubic inch) water-cooled 45° V-12 aircraft engine of 400 hp (300 kW) designed for a high power-to-weight ratio and ease of mass production. It was succeeded by the Packard 1A-2500.

In May 1917, a month after the United States had declared war on Germany, a federal task force known as the Aircraft Production Board summoned two top engine designers, Jesse G. Vincent (of the Packard Motor Car Company of Detroit) and Elbert J. Hall (of the Hall-Scott Motor Co. in Berkeley, California), to Washington, D.C.

The two left their positions at the Fageol Motors Co., putting an end to the short production of the most luxurious automobile of the period. They were given the task of designing as rapidly as possible an aircraft engine that would rival if not surpass those of Great Britain, France, and Germany. The Board specified that the engine would have a high power-to-weight ratio and be adaptable to mass production.

The Board brought Vincent and Hall together on 29 May 1917 at the Willard Hotel in Washington, where the two were asked to stay until they produced a set of basic drawings. After just five days, Vincent and Hall left the Willard with a completed design for the new engine, which had adopted, almost unchanged, the single overhead camshaft and rocker arm valvetrain design of the later Mercedes D.IIIa engines of 1917-18.

In July 1917, an eight-cylinder prototype assembled by Packard's Detroit plant arrived in Washington for testing, and in August, the 12-cylinder version was tested and approved.

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