Allison V-1710
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Allison_V-1710.jpg
The Allison V-1710 aircraft engine was the only indigenous US developed liquid-cooled engine to see service during WWII. Known as a sturdy and trustworthy design, it nevertheless was overlooked in a number of applications due to problems with the supercharging. Newer supercharging in the engine's later models cured this, and it again found itself in great demand in the later stages of the war.
History
The Allison Division of General Motors began developing the ethylene glycol (Prestone) cooled engine in 1929 to meet a US Army need for a modern 1,000 horsepower (750 kW) engine to fit into a new generation of streamlined bombers and fighters.
Limited resources during the Depression years slowed development, and it was not until December 14, 1936 that the engine first flew in the Consolidated A-11A testbed. The V-1710-C6 successfully completed the Army 150 hour Type Test on April 23, 1937, at 1,000 hp (750 kW), the first engine of any type to do so.
The engine was then offered to aircraft manufacturers where it powered the Curtiss X/YP-37, and then in a new Pursuit competition that resulted in it powering the Lockheed P-38, Bell P-39, Curtiss P-40, and North American P-51A. It was later selected to power the Bell P-63 and North American P-82E/F series. In addition it was fit or studied as the powerplant for many experimental and test aircraft such as the Republic XP-47A, Curtiss XP-55 Ascender, Boeing XB-38, and Douglas XB-42 Mixmaster.
In total, over 70,000 V-1710s were built by Allison during the war, all at Indianapolis, Indiana.
Description
The V-1710 has 12 cylinders, each with a bore and stroke of 5.5 by 6 in (140 by 152 mm), aggregating to 1,710 in³ (28 L) total displacement, with a cylinder compression ratio of 6.65:1.
The engine design benefited from the General Motors philosophy to build in production and installation versatility. The engine was constructed around a basic power section to which different installation requirements could be met by fitting the appropriate Accessories Section at the rear, as well as a tailored reduction gear to drive the propeller from the front. This approach allowed easy changes of the supercharger(s), supercharger drive gear ratio, and gave different critical altitude ratings ranging from 8,000 to 26,000 feet (2,400 to 7,900 m). The P-39, P-63, and XB-42 installations used V-1710-E series engines, which exchanged the integral propeller reduction gear for an extension shaft that drove a remotely located reduction gear. Aircraft such as the P-38, P-40, P-51A, and P-82 used close-coupled propeller reduction gears, a feature of the V-1710-F series. Another feature of the V-1710 design was the ability to turn the propeller either clockwise, or counter-clockwise, by simply assembling the engine with the crankshaft turned end-for-end, installing an idler gear in the drive train to the supercharger and accessories, and having a starter turning the proper direction. The ignition wiring and firing order were also arranged to accommodate the direction of rotation.
The V-1710 has often been criticized for not having a "high-altitude" supercharger. The comparison is usually to the later "two-stage" versions of the Rolls-Royce Merlin V-12 engine, built by Packard as the V-1650, and used in the P-51B/C/D Mustang. The US Army had specified that the V-1710 was to be a "single-stage" supercharged engine, and if a higher altitude capability was desired the aircraft would use their newly developed turbosupercharger, as was featured in the P-37, P-38, and XP-39. Separately, Allison developed an engine driven two-stage supercharger that was a vital component of the P-63 and P-82 installations. Although the early V-1710 powered P-39, P-40, and P-51A airplanes were limited to combat operations in the area of 15,000 feet (5,000 m), they were available in comparatively large numbers and were the mainstay of Allied Air Forces in all but the European theatre of operations. In total over 60 percent of the US Army Pursuit aircraft operated during WWII were powered by the V-1710.
Allison continuously improved the engine during the war. The initial rating of 1,000 hp (750 kW) was increased in stages to where the final V-1710-143/145(G6R/L) was rated for 2,200 hp (1,600 kW). Early in the war Allison approved War Emergency ratings to be used in combat that allowed engines rated for takeoff at 1,150 hp (860 kW) to operate at up to 1,600 hp (1,200 kW), but required immediate disassembly and inspection of the motor before reuse. Improvements in manufacturability brought the cost to produce each engine from $25,000 down to $8,500, and allowed the installed lifetime of the engine to be increased from 300 hours to as much as 1,000 hours. Weight increases needed to accomplish this were minimal, with the result that all models were able to produce more than 1 hp/lb (1.6 kW/kg) at their takeoff rating.
Following the war North American built 250 P-82E/F airplanes that were operated in various air defense roles into the early 1950s. This was the final military role for the V-1710, but not the end of its useful life as thousands of the engines were available on the surplus market. In the 1950s many drag racing experimenters shifted to the engine from automotive engines because of its greater reliability. Unlimited hydroplane racing also became a big sport across the US at this time, and V-1710s were often tuned for racing at up to 4,000 hp (3,000 kW), power levels never anticipated when Allison designed the engine. Later, as purpose-built V8 engines became available for drag racing and unlimited boats shifted to turbine power, tractor pullers began using the engine, again developing unimagined power. Finally, the warbird movement began to restore and return to the air examples of the classic fighters of the war and many V-1710 powered pursuits are again flying with freshly overhauled engines. The reliability, maintainability, and availability of the engine has led others to use it to power flying examples of aircraft otherwise unable to find a airworthy example of their original engine. This would include the new manufacture Yak-3 and Yak-9 airplanes out of Russia as well as ambitious projects such as a replica Douglas World Cruiser.
See also
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