Allison V-3420

In 1937, at the behest of the United States Army Air Corps, the Allison Engine Company 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 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 Boeing XB-39 Superfortress, 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==

with V-3420 engines • Boeing XB-39 Superfortress • Douglas XB-19 • 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 in North Highlands, California. • A V-3420 is on public display at the Glenn H. Curtiss Museum in Hammondsport, New York. • A V-3420-23 engine is on public display at the National Museum of the United States Air Force in Dayton, Ohio alongside a Fisher P-75 Eagle ==Specifications (V-3420-A18R (-17))==