The Allison V-3420 was a large experimental piston

aircraft engine An aircraft engine, often referred to as an aero engine, is the power component of an aircraft propulsion system. Most aircraft engines are either piston engines or gas turbines, although a few have been rocket powered and in recent years ma ...

, designed in 1937 by the American

Allison Engine Company The Allison Engine Company was an American aircraft engine manufacturer. Shortly after the death of James Allison in 1929 the company was purchased by the Fisher brothers. Fisher sold the company to General Motors, which owned it for most of it ...

Design and development

In 1937, at the behest of the

United States Army Air Corps The United States Army Air Corps (USAAC) was the aerial warfare service component of the United States Army between 1926 and 1941. After World War I, as early aviation became an increasingly important part of modern warfare, a philosophical r ...

, the

agreed to design and build a large-displacement high-power aircraft engine. The resulting V-3420 was essentially a pair of 12-cylinder

Allison V-1710 The Allison V-1710 aircraft engine designed and produced by the Allison Engine Company was the only US-developed V-12 liquid-cooled engine to see service during World War II. Versions with a turbocharger gave excellent performance at high ...

engines mated to a common crankcase with a 30° angle between the inner cylinder banks. The crankshafts of the two V-1710 engines were geared together to drive a common propeller shaft. Most V-3420 parts were interchangeable with those for V-1710-E and -F engines. The V-3420 had a power-to-weight ratio of 1.6 kW/kg or 1 hp/lb, excellent for its time. It was envisioned as a powerful yet compact engine for several advanced USAAF projects of the day, including the

Douglas XB-19 The Douglas XB-19 was a four-engined, piston-driven heavy bomber produced by the Douglas Aircraft Company for the United States Army Air Forces (USAAF) during the early 1940s. It was the largest bomber built for the USAAF until 1946, and was or ...

, the

Boeing XB-39 Superfortress The Boeing XB-39 Superfortress was a United States prototype bomber aircraft, a single example of the B-29 Superfortress converted to fly with alternative powerplants. It was intended to demonstrate that the B-29 could still be put into service ...

, the Lockheed XP-58 Chain Lightning, and the Fisher P-75 Eagle. As none of these designs saw more than limited production, only about 150 V-3420s were built.

Variants

;V-3420-A16R (-11) ;V-3420-A16L (-13) :left-hand rotation of propeller, single-stage supercharger with single-stage turbocharger and intercooler ;V-3420-A18R (-17) ;V-3420-A24 :Supercharger ratio 7.2:1 ;V-3420-B (-23) :Similar to the -A but with mechanically driven supercharger in two variable-speed stages

Applications

* Fisher P-75 Eagle * Lockheed XP-58 Chain Lightning

Engines on display

* A V-3420-23 (B10) is on public display at the

Aerospace Museum of California The Aerospace Museum of California is a private non-profit aviation museum located in North Highlands, California, outside of Sacramento, California, on the grounds of the former McClellan Air Force Base. The museum has a 4.5-acre outdoor Air Pa ...

in North Highlands, California. * A V-3420 is on public display at the

Glenn H. Curtiss Museum The Glenn H. Curtiss Museum is a transportation museum in Hammondsport, New York with a focus on the early aviator Glenn H. Curtiss. The 60,000 square foot facility has a collection of aircraft, vintage motorcycles, automobiles, and aircraft eng ...

Hammondsport, New York Hammondsport is a village at the south end of Keuka Lake, in Steuben County, one of the Finger Lakes of New York, United States. The Village of Hammondsport is in the Town of Urbana and is northeast of Bath. History Lazarus Hammond founded ...

. * A V-3420-23 engine is on public display at the

National Museum of the United States Air Force The National Museum of the United States Air Force (formerly the United States Air Force Museum) is the official museum of the United States Air Force located at Wright-Patterson Air Force Base, northeast of Dayton, Ohio. The NMUSAF is the ...

Dayton, Ohio Dayton () is the List of cities in Ohio, sixth-largest city in the U.S. state of Ohio and the county seat of Montgomery County, Ohio, Montgomery County. A small part of the city extends into Greene County, Ohio, Greene County. The 2020 United S ...

alongside a Fisher P-75 Eagle

Specifications (V-3420-A18R (-17))

References

Notes

Bibliography

* Bridgman, Leonard. ''Jane's All the World's Aircraft 1945-46.'' Hammersmith, London: HarperCollinsPublishers (1994 reprint). *Gunston, Bill. ''World Encyclopedia of Aero Engines: From the Pioneers to the Present Day''. 5th edition, Stroud, UK: Sutton, 2006. *White, Graham. ''Allied Aircraft Piston Engines of World War II: History and Development of Frontline Aircraft Piston Engines Produced by Great Britain and the United States During World War II''. Warrendale, Pennsylvania: SAE International, 1995. * {{US military piston aeroengines V-3420 1930s aircraft piston engines Abandoned military aircraft engine projects of the United States