Liberty Aircraft Engine
1917 Liberty Aircraft Engine
Photo: Bill Vance

by Bill Vance

The automobile industry was called the “Arsenal of Democracy” because it possessed the skill, expertise and production capacity that could readily convert to high volume output of war material. During World War II, automakers made everything from tanks to torpedoes, helmets to helicopters, Jeeps to Jerry cans.

The industry also participated in World War I, and one of its outstanding achievements was the “United States Standard 12-Cylinder Aviation Engine,” quickly dubbed the “Liberty” engine.

When the U.S. entered the war in the spring of 1917, there was an urgent need for a powerful American aircraft engine for the increasingly important role of air power.

Existing European designs were ruled out mainly because of the necessity of converting from metric measurements. There was also a certain amount of pride involved in “Yankee ingenuity.”

When a V-type engine was decided upon, it was natural to turn to the Packard Motor Car Co., which had introduced the “Twin-Six” V-12 in 1915, the world’s first series-production 12-cylinder car.

Packard had also done considerable work on a V-type aircraft engine, and its engineers had amassed a great deal of knowledge that would be invaluable in the Liberty’s development.

Packard’s chief engineer Jesse Vincent, and E. J. Hall of the Hall-Scott Motor Co., an aircraft engine manufacturer, were placed in charge of the Liberty design program.

Project headquarters was a suite of rooms in the Willard Hotel in Washington, D.C. Under Vincent and Hall, draughtsmen began working around-the-clock on the new design in late May of 1917.

Eight- and 12-cylinder engines were planned, both with a bore and stroke of 127 by 178 mm (5.0 by 7.0 in.). The eight was ultimately abandoned due to lack of power, and all efforts concentrated on the 12.

Within a few weeks the Vincent-Hall group had produced the new engine’s design. It went to Packard where the drawings were finalised, and then checked by other industry experts, including Henry Leland, president of the Cadillac Motor Car Co.

With an agreed set of plans, Packard began work on a prototype. By July 4, 1917, just six weeks after the initiation of project, the first engine was delivered to the U.S. Bureau of Standards for evaluation. It produced 320 horsepower, and by August 25th had passed its 50-hour durability test.

The Liberty engine was a classically sound concept. The designers, in their haste, had not been shy about borrowing well proved features from other manufacturers such as Mercedes, Rolls-Royce, Hispano-Suiza and Curtiss.

The water cooled V-12’s cylinder banks were set at 45 degrees, keeping engine width to only 686 mm (27 in.). The 127 by 178 mm (5.0 by 7.0 in.) bore and stroke yielded a displacement of 27.0 litres (1,649 cu in.), and there was a single overhead camshaft in each cylinder bank.

The camshafts were driven by bevel gears and shafts at the rear of the engine. Aluminum was liberally used for such components as pistons and crankcases, and clever ideas like a hollow crankshaft, and tubular steel cylinders (a significant Ford contribution), kept the engine’s dry weight at only 383 kg (844 lb).

Although initially rated at 320 horsepower, the Liberty ultimately reached 421 at 1700 rpm in normal operating mode, with 449 at 2000 available for takeoff. This was approximately one-half horsepower per pound of weight, an excellent achievement at that time.

Once the military found the engine acceptable, the government placed orders for 26,500. Ford was to build 5,000, Lincoln Motor Co. (formed by Henry Leland after he left Cadillac) 6,000, Packard 6,000, Nordyke and Marmon, builder of the Marmon car, 5,000, Cadillac 2000, Buick 2,000, and the remaining 500 by a company named Trego Motors. Machine shops large and small produced the many tools, jigs, dies and fixtures required.

The first engines came by December, 1917, and by June, 1918, when Willys-Overland also came on stream, Liberty production reached 150 a day, certainly mass production for an aircraft engine.

By Armistice Day, 1918, a total of 15,572 Liberty aircraft engines had been built, an average of 865 a month from the initiation of design.

The Liberty engine was a significant factor in the allied success. It eventually became a peacetime workhorse of the sky, a kind of aeronautical small-block Chevy V-8 of its day. It would power record-breaking planes, boats and even cars, and was a favourite for rum-running boats.

The Liberty survived until World War II. It was used as a tank engine by the British until 1943 when it was superseded by the more modern Packard-built Rolls-Royce Merlin. The Liberty, born in the First World War, and dying in the second, was a leading aircraft engine of its era, and a fine tribute to the automobile industry.

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