The Liberty Engine

America's major technological contribution to World War I was the "Liberty" aircraft engine. It was light, powerful and efficient. America's auto industry turned out 20,478 of them for the war. The Liberty engine continued in military and civilian use even into World War II.

This 12-cylinder, liquid-cooled 443-hp Liberty 12-B demonstrates the Army Air Service engineers' quest for higher flight and more efficient power. Its turbo-supercharger allowed aircraft to reach great heights by compressing the thin air at high altitudes to preserve engine power. A turbo-supercharger uses engine exhaust to power an air compressor, which in turn feeds dense, oxygen-rich air to the engine. A sturdy circular arrangement of reduction gears on this particular engine (called "epicyclical" gears, in the round silver case around the propeller shaft) allowed the propeller to turn at variable speeds for better performance. This method of changing the propeller's thrust by shifting gears eventually gave way to adjusting the angle or pitch of the propeller blades instead.

These kinds of experimental refinements were carried out at McCook Field and Wright Field, the Army Air Service's testing facilities near Dayton, Ohio. The tests led to greater knowledge and better aircraft in the 1920s and 1930s and paved the way for developing the superior aircraft the Allies would need in the Second World War.

The Liberty L-12 was a 27 litre water-cooled 45 degree V-12 aircraft engine of 400 horsepower (300 kW).

It was designed by Jesse Vincent and E. J. Hall of the Hall-Scott Motor Co. and manufactured by Packard, Lincoln, Ford, Nordyke and Marmon, and General Motors during the First World War. It was a modular design where 4 or 6 cylinders could be used in one or two banks. 20,478 were built between July 4, 1917 and 1919. A single overhead camshaft for each cylinder bank operated 2 valves per cylinder, in a similar manner to the inline six cylinder German Mercedes D.III engine. Dry weight was 383 kg (844 lb). Two examples of a six-cylinder version, the Liberty L-6, were produced but not procured by the Army. Both were destroyed by Dr. William Christmas testing his so-called "Christmas Bullet" fighter.

An inverted Liberty 12-A was also referred to as the V-1650 and was built up to 1926—the exact same designation later applied, due to identical displacement, to the World War II Packard-built Rolls-Royce Merlin.

The History Of The Liberty Engine

Smithsonian Annals of Flight

The Liberty engine, 1918-1942
Philip S. Dickey III
x, 110 p. illus.
1968
Number 1.3, Smithsonian Annals of Flight
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Full Description (from SIRIS)

The engine was also produced for tank use, including the UK Nuffield Liberty engine in World War II.

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