Allison V-1710
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The Allison V-1710 aircraft engine was the only indigenous US-developed V-12 liquid-cooled engine to see service during WWII. A sturdy and trustworthy design, it was at first overlooked for a number of applications due to supercharger problems. After numerous improvements it found great demand in the later stages of the war.
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History
The Allison Division of General Motors began developing the ethylene glycol-cooled engine in 1929 to meet a US Army need for a modern, 1000 hp (750 kW), engine to fit into a new generation of streamlined bombers and fighters. To ease production the new design could be equipped with different propeller gearing systems and superchargers, allowing a single production line to build engines for everything from fighters to bombers.
The Great Depression slowed development, it was not until December 14, 1936 that the engine first flew in the Consolidated XA-11A testbed. The V-1710-C6 successfully completed the Army 150 hour Type Test on April 23, 1937 at 1000 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. 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.
The Army had decided to concentrate solely on turbochargers for high altitude boost, believing that further development of turbochargers would allow their engines to outperform European rivals using superchargers. The high wartime demand for high-temperature alloying metals, notably tungsten, led to restrictions on turbocharger production.
Eventually the Army reserved the majority of the turbochargers for its few, high-priority, bombers. Most V-1710s were equipped with an underdeveloped, single-stage supercharger, satisfactory at low altitude but that severely limited high-altitude performance. About this time the US entered the war and some American fighter designs were changed to use the Packard built Rolls-Royce Merlin engine. Its long-tested, refined, two-stage two speed, supercharger gave excellent high-altitude performance.
A two-stage supercharger was introduced for the V-1710, improving the late-war versions of the V-1710 tremendously. It was later selected to power the Bell P-63 and North American P-82E/F series. In addition it was fitted, or studied, as the powerplant for many experimental and test aircraft such as the Republic XP-47A (AP-10), 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 in Indianapolis, Indiana.
Description
The V-1710 has 12 cylinders with a bore and stroke of 5.5 by 6 inches (140 by 152 mm), aggregating to 1,710 in³ (28 L) total displacement, with a 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 from which different installation requirements could be met by fitting the appropriate Accessories Section at the rear and a tailored reduction gear to drive the propeller from the front. This approach allowed easy changes of the supercharger(s) and supercharger drive-gear ratio. That gave different critical altitude ratings ranging from 8,000 to 26,000 feet (2,400–7,900 m).
The P-39, P-63, and XB-42 installations used V-1710-E series engines that exchanged the integral reduction gear for an extension shaft that drove a remotely located reduction gear and propeller. 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 its ability to turn the propeller either clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, installing an idler gear in the drive train to the supercharger and accessories and installing a starter turning the proper direction. The ignition wiring and firing order were re-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, and so on, 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 at a maximum, in the area, of 15,000 feet (5,000 m) they were available in comparatively large numbers and were the mainstay of some 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). However a lot of this improvement can be credited to the availability of higher octane fuels. 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 for the less stressed powerplants. 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, attracted by its greater reliability, adopted the V-1710. 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 that were 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 pursuit aiplanes are flying again, with freshly overhauled engines. The reliability, maintainability and availability of the engine has led others to use it to power flying examples of aircraft that people had otherwise been unable to find an airworthy example of the original engine. This includes newly manufactured Russian Yak-3 and Yak-9 airplnes as well as ambitious projects such as a replica Douglas World Cruiser and Focke-Wulf Fw 190D by Flug Werk of Germany.
Specifications (V-1710-85)
See also
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