THE 456th FIGHTER INTERCEPTOR SQUADRON
T PROTECTORS OF S. A. C.
The Allison V-1710
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The V-1710 engine was the first product of an extensive Army program to develop a high-power, liquid-cooled engine. Derived from a model designed in 1930 for airship use, the V-1710 was first used by the Air Corps in 1932. Rated at 1,000 horsepower, it was installed in the Consolidated XA-11A, an experimental attack version of the Consolidated P-25. By 1938, the engine's output had been increased to 1,150 horsepower and was used to power the Bell X/YFM-1 multiplace fighters. The V-1710 was continually improved and during World War II its output was increased to 1,475 horsepower in some series engines. During the war it was used primarily in the Curtiss P-40 "Warhawk", the Bell P-39 "Airacobra", and the twin-engine Lockheed P-38 "Lightning". It was also used in early versions of the North American P-51 "Mustang".
The engine on display, a right-hand drive V-1710-51, is of the series used primarily in the P-38G. When installed in a twin-engine P-38, it was paired with a left-hand drive V-1710-55 engine to counteract the effect of torque. The only difference between the two engines was the direction of propeller-shaft rotation.
Model: V-1710-51 (right-hand drive)
Type: 12 cylinder, supercharged
Displacement: 1,710 cu.in.
Weight: 1,345 lbs.
Maximum RPM: 3,000
Maximum Horsepower: 1,325
Cost: $19,000 (engine only)
PHOTOGRAPHS AND TEXT COURTESY OF THE AIR FORCE MUSEUM
The Allison V-1710
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The only American liquid-cooled inline engine to see service in World War II was the 1250 hp. Allison V-1710. Shown here is a Allison V-1710-F20R.
The only American liquid-cooled engine to see service in World War II was the Allison V-1710. Allison was an Indianapolis firm that had done well in a small way with Liberty modifications and with reduction gears for others' engines.
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The V-1710-E18 & E19 engine with extension shaft and outboard reduction gear box used on the P-39 Airacobra.
Around the time that the Army was washing its hands of the Curtiss Conqueror, Allison began to develop its own engine. The target was 1,000 hp, and Allison intended that the engine should be large enough to deliver this power easily. Development proceeded slowly until the Navy entered the picture. The Navy, while not losing its attachment to air-cooled power for airplanes, needed liquid cooling for dirigibles. Allison made a good dirigible power plant and awarded a development contract to the Indianapolis firm. The firm today remains a GM component under the style of "Detroit Diesel Allison Division."
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The front view of an Allison V-1710-F10R or F10I.
The V-1710-85 engine with extension shaft and outboard reduction gear box used on the P-39Q Airacobra.
The production Allison turned out to be the sturdy and reliable powerplant that its designers had striven for. The only thing that stood between the Allison and real greatness was its inability to deliver its power at sufficiently high altitudes. This was not the fault of its builders. It resulted from an early Army decision to rely on turbo supercharging to obtain adequate power at combat heights. Even this decision was not a technical error. A turbo supercharged Allison was as good a high-altitude engine as most. The trouble was that the wartime shortage of alloying materials, especially tungsten, made it impossible to make turbo superchargers for any but a small proportion of Allisons. Bomber engines got the priority.
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Allison engine installation on P-51A
The few turbo-supercharged Allisons that were made were allocated to P-38s, making the high-altitude performance of that plane its best feature. All 14,000 P-40s got gear-driven superchargers and, as a result, were never first-class fighter planes. Donaldson R. Berlin, the P-40 designer, has said that P-40s experimentally equipped with turbo-superchargers outperformed Spitfires and Messerschmitts and that if it had been given the engine it was designed for, the P-40 would have been the greatest fighter of its era. This may be to some extent the bias of a proud parent, but there is no doubt that the deletion of the turbo supercharger ruined the P-39.
Had Allison's engineers been able to put the effort into gear-driven superchargers that Pratt and Whitney and Rolls-Royce did, it might have been a different story. As it was, there can be little doubt that the V-1710 had more potential than was actually exploited.
Specifications: Allison V-1710-G6 Date: 1941 Cylinders: 12 Configuration: Inline V, Liquid cooled Horsepower: 1,250 hp (932 kw) R.P.M.: 3,200 Bore and Stroke: 5.5 in. (140 mm) x 6 in. (152 mm) Displacement: 1,710 cu. in. (28 liters) Weight: 1,595 lbs. (707 kg)
The Allison V-1710
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The Allison V-1710
Twenty days after the first NA-73X was rolled out of the North American Aviation factory at Mines Field in Los Angeles in September of 1940, the first Allison V-1710 (picture to right) engine arrived and was installed in the plane. The V-1710 was a 1710 cubic inch, inline 12 cylinder, liquid-cooled engine. With its single-speed, single-stage supercharger, the V-1710-39 developed 1120hp at 3000 rpm. On October 11, 1940, the V-1710 roared to life for the first time. The next two weeks were spent in engine and taxi tests. By October 26, ground testing was over and North American test pilot Vance Breese taxied the NA-73X to the end of the active runway. Checking that all his systems were in the green, Breese eased the throttle forward and released the brakes. NA-73X lifted easily off the runway. Five minutes later Breese landed. The NA-73X Mustang with the Allison engine had flown beautifully (Davis, 1981).
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The Allison engine was used in both the A-36 Apache (the US Army Air Force's derivative of the Mustang 1) and the P-51A. The new Allison V-1710-87 was installed in the Apache for better low level performance. The -87 developed 1325hp at 3,000 feet but power dropped off rapidly above 12,000 ft. The P-51A used the uprated V-1710-81 engine which had a much more efficient supercharger. Horsepower increased to 1330 and this, combined with the new, larger Curtis 10'9" propeller produced a top speed of 409mph at 10,000 ft. The rate of climb rose to 3800 ft/min with an absolute ceiling of 34,000 ft. This was still not great enough for a true fighter mission, as both the Spitfire and Messerschmitt could fly and fight above that altitude. New 150 gallon drop tanks, coupled with the more efficient -81 engine, led to an increase in the ferry range, by that time up to 2700 miles (Davis, 1981).
The P-51A (at right) was the last P-51 to use the Allison engine. The Allison, however, would return in the P-82E Twin Mustang. North American Aviation produced 1,570 Allison-powered Mustangs of all variants. Britain received 764 aircraft, either by outright sale or Lend-Lease, with a further ten aircraft going to the Soviet Union for trial tests. All the other went to US Army Air Force for use either on the fighting front or as Mustang trainers. Allison-powered Mustangs served on all fronts in a variety of roles. Unit commanders were constantly clamoring for more of the new fighters. Pilots and ground crewmen praised the Mustang for its high performance and reliability. Little did they know that on more modification would lead to a remarkable increase in the performance of the aircraft they came to know and love.
Davis, L. Carrollton
The Allison V-1710 Engine
Key Engine Specifications (Prior To Racing Modifications)
Model V-1710 G6R/L (V-1710-143/-145) Application All models: Major production included P-37, P-38, P-39, P-40, P-46, P-47, P-51A, P-63, P-82 Engine Type V-12 Piston Aero Engine, 60° "V" (angle between banks) Material Aluminum heads, water jacket, crankcase; Steel cylinder liners; Forged aluminum alloy pistons; Magnesium oil pan Bore x Stroke 5.5" x 6.0" Compression Ratio 6.00:1 Supercharger type Two stage engine driven supercharger, 10.25" engine impeller, 12.1875" auxiliary impeller Supercharger Ratio 7.48 engine stage, 8.087 (R) and 8.03 (L) auxiliary stage Anti-detonation 50:50 water-methanol injection anti-detonation injection (ADI) Fuel System Bendix-Stromberg SD-400D3 speed/density injection Weight 1,595 lbs Power 2,250 hp war emergency rating (WER) at 3,200 RPM & 101" Hg (35 psig) boost "wet" (w/ADI) and 115/145 PN fuel Performance 325 psi BMEP (brake mean effective pressure) Max. Piston Speed: 3,200 ft/min Firing Order RH turning: 1L-2R-5L-4R-3L-1R-6L-5R-2L-3R-4L-6R
LH turning: 1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R
Timing Ignition: Intake fires 28° BTDC, Exhaust 34° BTDC, Sparkplug gap = 0.012-0.015"
Intake: Valve opens 48° BTDC, Closes 62° ABDC, 0.015" clearance (cold), 0.533" lift
Exhaust: Valve opens 76° BBDC, Closes 26° ATDC, 0.020" clearance (cold), 0.533" lift
Total Manufactured 70,033 total, from #1 manufactured Aug 13, 1931 through s/n A-074125 completed June 2, 1948
Note: Many Unlimited Hydroplane Allison's originated from a batch of 750 V-1710 G6L/R engines intended for the North American P-82E/F. These engines were surplused in the 1950's by the Air Force. These engines differed from other Allisons primarily in the areas of lower compression ratio, an auxiliary supercharger and speed/density fuel injection. The boat racers routinely increased the compression, and discarded the auxiliary supercharger and injection system in favor of the more available Bendix-Stromberg Injection carburetors.
The Allison V-1710 was one of the most important large U.S. aero engines, with over 70,000 engines produced from the time of the first in 1931 to the last in 1948. The engine was produced in large quantities in the early1940's for several important fighters of WWII including the P-38, P-39, P-40, P-51A, P-63, and P-82. While the debate over the merit of air-cooled -vs- liquid cooled engines had raged in the 1920's, each was recognized to have certain advantages. As the only liquid cooled U.S. designed engine of the second-world war (the Rolls-Royce licensed Merlin being the other significant liquid cool manufactured by Packard as the V-1650), the V-1710 exhibited the advantages inherent with liquid cooled engines. These advantages include low frontal area and high short-term peak power output thanks to the coolant heat-sink, higher power because of the greater heat rejection capability of liquid coolant, and packaging flexibility. The air-cooled engines advantages are primarily the weight savings and reliability inherent in eliminating the liquid cooling system.
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Allison, which became a part of general motors in 1929, invested private funds in the development of a liquid-cooled V12 engine at the urging of Allison General manager Norm Gilman. While the U.S. Army Air Corp (U.S.A.A.C.) showed no interest, the Navy supported development of an experimental engine to test the basic design as a precursor to a reversible airship engine. The successful V-1710-A was test run in 1931 and delivered 650 hp at 2,400 RPM on 80-octane fuel. It featured the same 5.5" bore and 6.0" stroke as all succeeding V-1710's, weighed 1,010 lbs, had a 8.25" supercharger turning 7.3 times faster than the crankshaft, and had a compression ratio of 5.8:1. The engine featured a distinctive internal-spur gear propeller reduction drive (initial ratio was 0.66) which in late series models was replaced with more conventional external spur gearing. Modification were required half-way through the first 50 hr test run, and Allison took this opportunity to increase performance by increasing the supercharger gear ratio to 8.0:1. This engine completed its 50 hour test run in 1932 at a rating of 750 hp at 2,400 rpm.
Both the Navy and U.S.A.A.C. were now interested in the V-1710, the Navy placing the anticipated order for reversible airship engines designated V-1710-B and the U.S.A.A.C. designated V-1710-C. The Navy engine eliminated the supercharger (rotary induction blower) in favor of two carburetors placed in the Vee of the engine. The engine was designed to reverse from full power one direction to full power the opposite direction in less than 8 seconds, while driving a remote mounted propellers mounted on outriggers equipped with swiveling heads which allowed thrust to be directed vertically or horizontally. The engine power would be transmitted by 16' driveshafts to the remote transmission and gear arrangements in the swiveling heads. Allison had already designed such drive systems and transmissions for use in the Navy Airships USS Akron and USS Macon. The U.S.A.A.C. version was designated V-1710-C and featured a supercharger impeller enlarged to 9.5", a 2:1 propeller reduction drive in a longer nose casing, and a stiffened crankcase. Additional changes were required to overcome severe harmonic vibration problems caused by the long nose and change in reduction gearing which caused damage to crankshafts, reduction gears and cylinder blocks.
A significant redesign was undertaken by R.M. Hazen in 1936 which lead to an increased compression ratio of 6.0:1, improved combustion chambers which reduced the length of flame channel, improved piston and rings, and changed manifolds for better air-fuel distribution. This "C"-model passed its 150 hour type acceptance test in 1937, establishing a rating of 1,000 hp at 2,600 rpm at sea level. The definitive Allision which was the foundation for all future engines was now established -- penthouse-type combustion chambers with four valve per cylinder, overhead camshafts in each cylinder block with forked roller cam followers actuating pairs of valves in each cylinder, blade-and-fork connecting rods. Subsequent engines differing primarily in induction system and reduction gearing. A number of incremental improvements were made during the life of the "C"-model including increase in compression ratio to 6.65:1, eventually leading to "C"-models with takeoff ratings of 1,150 hp at 2,950 rpm and supporting 3,500 rpm for overspeed during dives.
The "D"-model featured a remote reduction gearbox in a pusher configuration for powering the Bell Aircraft XFM-1 Airacuda twin-engine fighter.
The power unit on the "E" and "F" engines were identical, with crankshafts, connecting rods, pistons, cylinder blocks, valve gear, and intake manifolds among other components completely interchangeable. The "E" featured a remote propeller reduction gearbox for the Bell P-39 Airacobra (and P-63 Kingcobra) driven with a 10 ft extension shaft turning at crankshaft speed between the engine and reduction gear. The "F" had a conventional integral tractor propeller reduction gear Lockheed P-38 Lightning and Curtiss P-40 Tomahawk. A turbocharged V-1710-F17L/-F17R engine equipped with ADI produced a WER of 2,300 bhp at 3,000 rpm with 90 in hg,, developing a BMEP of 355 psi. The "E" and "F" engines were the bread&butter Allisons, with these engines used in large volume on several major fighter programs of WWII. A total of 66,658 "E" and "F" types were built -- 18,998 "E"-type extension shaft engines were shipped, mainly for P-39 and P-63 aircraft, and 47,660 "F" models were shipped, mainly for P-38 and P-40 airplanes.
The ultimate V-1710 was the "G" series which brought together all of Allisons design and manufacturing experience to produce an outstanding engine in almost all respects from earlier engines. The V-1710-G was incorporated a number of desired improvements identified in 1943 by Wright Field (U.S.A.A.F. engineering/procurement organization) and improve performance to 1,725 bhp at 3,400 rpm. To improve performance, the 12-counterweight crankshaft developed in late 1942 was used to increase the maximum rpm to 3,400, the induction path was improved to increase flow, and improvement were also made to the supercharger, cylinder heads, and accessories section. One interesting characteristic of the "G"-series was the large proliferation of features and configurations -- short-nose integral reduction gears or extension shafts, with and without auxiliary superchargers, both 9.5" and 10.25" engine supercharger impellers, one or two-speed supercharger drives, a range of supercharger drive ratio's, three compression ratio's, pressure (injection) carburetor, speed density injection, or port fuel injection, and both left and right hand rotation. These engines became the most desirable to racers because of the high-revving crankshafts and improved detail design. A total of 763 were produced -- a batch of 750 V-1710-G6R/-G6L consisted of virtually all the "G" series production. When this batch of engines were declared surplus in the 1950's, they were said to to have been the engines which powered Unlimited Hydroplanes into the 1990's (Daniel D. Whitney, "Vee for Victory", pg 278). This same source describes how the Unlimited Racers traded performance for engine life, modifying engines to deliver as much as 4,000 hp.
The most remarkable engine was probably the V-1710-E27 experimental turbo-compound engine. This unique engine was the first turbo-compound or "power-feedback" engine and was way ahead of its time. Based on an E-22 power section with auxiliary stage supercharger, it used a General Electric CT-1 power turbine which was adapted from the exhaust turbine of a CH-5 turbosupercharger. The turbine drove the crankshaft through a 5.953 reduction gear. The engine compression was reduced to 6.0:1 to facilitate high supercharger boost pressure of 100 in hg (35 psig). Using 115/145 PN fuel with ADI injection, this engine was able to develop 2,980 hp at 3,200 rpm and 100 in hg boost from sea level to 11,000 feet. In addition to the remarkable power output, the engine demonstrated a 19% improvement in specific fuel consumption during cruise. Had the inlet exhaust temperature not been limited to 1750° F, it is certain even more power could have been developed. The temperature proved to be easily exceeded during full-power operation, so the engine was never placed into service with the P-63 as intended.
Allison Powered Hydroplanes
The Allison V-1710 was an important hydroplane powerplant from the dawn of the modern piston era after WWII until the turbine engine retired these engineering marvels. Thanks to the availability of high-powered airplane engines from WWII, the Gold Cup class metamorphosed into the Unlimited Class, a true national circuit which remains active to this day. In 1946 the Miss Golden Gate III became the first hydroplane to be powered by an Allison V-1710 -- she was designed and driven by Dan Arena. She was a three-point tail-dragger (tips of the two sponsons and the tail of the hydroplane). While she set a competition lap record of 77.9 mph during the1946 Gold Cup in Detroit, the Allison over-powered the 26-1/2 ft hull making her very difficult to control. The next year the Dossin Brothers of Detroit introduced their Allison powered Miss Peps V which was driven by Danny Foster. This boat earned both major Unlimited Hydroplane titles for 1947 -- the Gold Cup and the National High Points Championship.
In 1950 another significant milestone was established by an Allison powered hydroplane -- the Slo-mo-shun IV, owned and driven by Stan Sayres set a new mile straightaway record of 160.322 mph, topping the previous record set by Sir Malcom Campbell's Bluebird II by almost 20 mph. Two years later the Slo-mo-shun IV raised the mark to 178.497, with a one-way run of 185.627 on Seattle's Lake Washington. This boat was the first successful "prop-rider", with the rear of the boat riding on a half-submerged propeller instead of the tail of the boat as with the previous "tail-draggers". For the next 20 years boats used a Slo-mo type design or they were not competitive. The Slo-mo-shun boats brought the Gold Cup to the West for the first time, and would keep the Cup in Seattle for 5 years, with Allison powered Slo-mo's retaining the Cup from 1950-1953, and a Rolls-Royce Merlin powered Slo-mo successfully defending in 1954. This era marked the dawn of the enduring Seattle-Detroit hydroplane rivalry.
Some of the more interesting Allison boats include the 1950's G-22/U-70 Such Crust III, a huge 10,000 lbs hydroplane using two Allison V-1710's in tandem and another giant 10,000 lbs boat, the twin-tandem Allison powered Gale VI. Both of these big boats were designed to handle the rough East-coast river courses. Another significant Allison-powered boat was the Miss Madison of 1971, which overcame long odds to win the Gold Cup in her home town to the delirious delight of the home-town fans.
Another significant Allison milestone was the 1962 mile straightaway record set by the Allison-powered Miss U.S. I of 200.419 mph set at Gunthersville, Al, driven by Roy Duby. This was the first boat to break the 200 mph barrier, and this record stands to this day for piston powered boats. In 2000, a second tier turbine team eclipsed the 38 year old record for propeller driven boats by establishing a 202 mph mark. It is expected that the top turbine teams will attempt to establish a meaningful propeller-based record at the end of the 2000 season now that the revered 38 year old standard has been broken.
The last significant Allison-powered boat was 10th hull to be campaigned under the Miss U.S. banner. She began competition in 1974 and finished in 1976, when she became the first and only turbocharged Allison to win a gold-cup, the last Allison-powered boat to ever win a Gold Cup, and the last Detroit-based boat (at least up to the present) to win the coveted Gold Cup. This is the boat now owned by Unlimited Excitement and featured elsewhere at this site.
However, the history of Allison boats is not closed. Throughout the turbine era which began in 1985 with the National High Points Championship by the Miller American equipped with a Lycoming T-55 turboshaft engine, Allison-powered hydroplanes continue to challenge the supremacy of turbine boats. There is still one Allison-powered boat competing in the 2000 season. While the odds are long, many fans are pulling for the boat filling the air with the great roar from the past -- the warbling growl of an Allison-powered boat with its prop loading and unloading as it bounces across the water. The whoosh of a turbine will never fill the air like the growl from an Allison!
A Description Of The Allison V-1719
The V-1710 is a conventional overhead cam liquid cooled Vee-type engine with 4-valve pentagon roof combustion chambers using two 6-cylinder monoblocks bolted to a split crankcase. The engine has a propeller reduction gear or extension drive on the "grunt" of the engine as defined by Allison and an auxiliary case on the rear. Cylinders were numbered from the rear, with the bank to the left when viewed from the rear (auxiliary section) called the left bank and the other bank the right. Unlike automotive engines, the cylinders were numbered 1L to 6L on the left and 1R to 6R on the right, 1L being the the cylinder next to the auxiliary drive on the side of the coolant pump, the 1R cylinder being located next to the auxiliary section above the oil pump.
12 cylinder 60° Vee liquid cooled
Bore 5.5 in (139.7 mm), Stroke 6 in (152.4 mm), Displacement 1,710 cubic inches (28 liters). Compression ratio 6.0:1 (other versions typically use 6.65:1). Two cylinder blocks of six cylinders each comprising a cast aluminum-alloy cylinder head, six hardened steel cylinder barrels and a cast aluminum-alloy cooling jacket. Barrels held in head by a shrink-fit and are enclosed by coolant jacket. Jacket secured to head by studs and to cylinder by nut threaded over each barrel (and torqued to 2,200 ft-lbs!). Each cylinder-block secured to upper half of crankcase by 14 studs extending through the head. Combustion chamber has two intake and two exhaust valves and two diametrically opposed park plugs. Steel intake valve inserts, forged steel stellite-faced exhaust valve inserts.
Machined from aluminum-alloy forgings. Three compression rings above piston pin -- one keystone ring in the top groove and two conventional rings, and two oil-control rings in a single groove below. Floating piston pin retained by snap-rings at each end.
Fork and blade type made from steel forgings machined and shot-peened. Connecting rod bearings consist of two flanged steel thin shells lined with nickel-silver-tin, and clamped in the forked end by two bearing caps. Center portion of the outside diameter of the bearing is covered with an overlay of nickel-silver-tin which acts as journal for the blade rod. Blade rod fits around the overlay and is held in place by a single steel cap. Bronze bearing pressed into the small end for the piston pin. Big-end bearings lubricated under pressure from crankshaft, small-end bearing lubricated by splash.
Counter-balanced six-throw seven-bearing type. Each end of the shaft has a bolt flange which provide mountings at the front for a flexible splined coupling for driving the reduction gear pinion and at the rear for a dynamic torsional vibration balancer. Splined to the hub of the dynamic balancer is the outer member of a hydraulic damper. An inner member is connected to the outer rigid member by a flexible quill shaft and reacts against the outer member through a hydraulic fluid to minimize single-node low frequency torsional vibration. This damper provides the driving connection between the accessories housing and the crankshaft.
Two aluminum castings split on horizontal centerline. Large studs on the face of the upper half pass through main bearing webs on lower-half to clamp the two halves over the bearing shells. All main bearings are steel flanged shells lined with nickel-silver-tin. Center main bearing provided with faced flanges which bear upon the center crank cheeks to provide axial location (and absorb thrust loads) for the crankshaft. Cast magnesium-alloy oil pan bolts to the bottom of the crankcase lower half. Oil is scavenged from front and rear or the oil pan.
Two intake and two exhaust valves per cylinder. Stellite-faced sodium-cooled nichrome-alloy valves. The stems of the exhaust valves are parallel to each other and angled 22.5° with respect the the cylinder axis. The intake valves are also parallel to one another and angled 22.5°, the resulting angle between intake and exhaust valves being 45°. The exhaust valve seat was cut at a 45° angle to the valve stem, while the intake was cut at a 30° angle. Single camshaft operates six rocker arm assemblies top of each cylinder bank -- each rocker arm assembly consists of a two forked rocker arms pivoting on a plain bearing (one for the exhaust valves and the other for the intake valves), each with a single rolling cam follower which forks to actuate both intake or exhaust valves by means of articulated lash adjusting screws. Each camshaft is driven by bevel gears through separate inclined shafts from the accessory housing. Pressure lubrication to cam bearings supplied through hollow camshaft.
Accessory housing mounted directly to the rear of the crankcase and is driven from crankshaft through harmonic balancer/hydraulic vibration damper. Contains supercharger and auxiliary gearing, with drives for the engine supercharger impeller, auxiliary stage supercharger, camshafts, magneto, starter, oil pump, water pump, tachometer, fuel pump, generator and vacuum pumps. The housing also contains the supercharger and provides mounting provisions for the carburetor and those accessories listed above which are not contained within the engine.
Bendix Stromberg SD400B3 speed/density injection system consisting of a injection pump which meters fuel based on engine speed and fuel-air density (charge pressure and temperature) and a throttle contained in a throttle body located between the auxiliary stage and engine stage superchargers. The throttle is normally open with speed being regulated by varying the speed of the auxiliary stage supercharger as described below. All metering is accomplished within the engine-driven injection pump. Fuel injected into the engine stage supercharger impeller (as was ADI when activated). ADI derichment by means of ADI pressure sensing in the injection pump. The engine supercharger feeds the intake ports by means of a induction pipe which feeds rams-horn type intake manifolds at the center of the engine, the induction pipe is located in the "Vee" of the engine below the intake manifolds.
The engine supercharger (second stage supercharger) is contained in the accessory housing and is driven from the flexible inner member of the hydraulic vibration damper. The impeller is 10.25" diameter with 15 vanes and includes a separate rotating reverse-curved inducer guide vane inlet guide, the relationship with the impeller being maintained by the common splined shaft. The diffuser is cast integrally with the supercharger cover, which also contains the inlet to which the injector throttle body mounts. The impeller is overhung, with the shaft supported by two floating lead-bronze steel backed bearings placed on both sides of the supercharger drive gear. The bearing are pressure lubricated with engine oil.
The auxiliary stage is contained in a separate assembly coupled to the engine accessory section. It is intended to provide a critical altitude of 25,000 ft by delivering air to the engine supercharger at pressures close to sea-level when at critical altitude. This requires large volume of low density air to be handled by the auxiliary supercharger -- because of the density of the air at 25,000 ft the supercharger must move 2.23 times more air volume than the engine supercharger, and compress the air to about 2.7 times to deliver sea-level conditions. The auxiliary stage drive was obtained by a power-takeoff from the starter gear which connects to a driveshaft incorporating a universal joint, the driveshaft being contained in a tube coupling the engine accessory section with the remote auxiliary stage. The driveshaft hydraulic torque converter connected to the step-up gears contained in the auxiliary supercharger housing. The torque-converter provides variable speed for the supercharger by varying the amount of oil and therefore the coupling of the torque converter. The speed controlled by a boost-regulating system, permitting infinitely variable control of the speed of the auxiliary stage which was used to control manifold pressure so that power could is controlled while the throttle remains wide-open. The auxiliary supercharger consumes 490 hp from the crankshaft at the 2250 hp WER rating.
Ignition is a Bendix-Scintilla DLFN-6 magneto unit which combines two magnetos into one unit driven by a single drive shaft. The 4-pole magneto mounts to the top of the accessory section, with the driveshaft passing through the supercharger induction outlet pipe. The magneto is driven at 1.5x engine speed to obtain 6 sparks per engine revolution, and the exhaust magneto timing leads the intake timing by 6° (points open/coil fires at 34° BTDC for exhaust and 28° BTDC for intake), and is composed of two independent high-tension magneto coils excited by the engine driven magneto shaft's 4-pole rotating magnet. Each coil is connected to a set of points is actuated by a 4-lobe breaker cam on the magneto shaft. The points are connected to a condenser inside the magneto and to the coil and "P-lead" which connects the magneto to the cockpit magneto switches.
Separate high-tension (HT) leads from each magneto connect to distributors located on the accessory end of each head and driven by the camshaft. The intake distributor (which distributes the HT voltage to the intake spark plugs which are located in the "Vee" or inboard spark plug location) is located on the left bank and the exhaust distributor is on the right bank.
Each distributor rotor has two independent terminals -- the "M" terminal which connects the the magneto HT lead by a center spring terminal, and a "B" or booster sliding ring connection. The "B" distributor finger leads the "M" by 30° and is used only on the intake distributor side. During starting, a battery powered booster coil is energized by the starting switch to facilitates starting by retarding the ignition timing 30° during cranking (which reduces the torque produced by the engine due to the fixed ignition advance) and provides a hotter spark than the magneto can produce at low cranking speed.
Dry-sump pressure system. Circulation maintained by a single pressure pump and two scavenge pumps, all of the gear-pump type. Pressure is regulated by a pressure-sensitive balanced relief valve. Spring-loaded check valve prevents oil entering system when engine is stopped. Large tube in upper half of crankcase distributes oil to main bearings, through which it enters hollow portions of the crankshaft. This tube also carries oil to reduction gears, reduction gear pinion bearings, and propeller governor pad. Oil for accessory drives and valve gear is carried by tubes and drilled passages in accessory the housing. Oil from valve gear drains to crankcase through passages at both ends of the cylinder-block. Oil for the hydraulic vibration damper operation is also supplied from the engine pressure system.
The coolant employed is a mixture of 70% water and 30% ethylene glycol. The coolant in the closed loop pressurized system is circulated by a centrifugal-type pump to the cylinder blocks and from the cylinder blocks to a small-capacity header tank and from the header tank via a radiator to the coolant-pump inlet. The flow of coolant air through the radiator is controlled, whether manually or automatically, through a temperature-sensitive device which controls radiator shutters. The header tank, which incorporates features to ensure the efficient separation of steam and coolant, is provided with a loaded relief valve which seals the whole coolant system up to a predetermined pressure. This pressurizing of the system raises the boiling point of the coolant and permits the use of smaller radiators. The header tank relief valve maintains the pressure in the system and also incorporates a suction-operated valve which admits air, if for any reason the pressure falls below atmospheric.
Direct cranking electric starter motor composed of 28V series would electric motor with integral 3-stage planetary reduction gear (approximately 100:1 reduction gearing) engaging a dog geared (1:1) to the crankshaft. Booster coil employed to retard and increase ignition during low-speed cranking. Primer system consisting of one injector nozzle in each of the four legs of the rams-horn intake manifold, fuel being controlled by solenoid valve from the pressure fuel supply.
Mounted to and driven by takeoffs on the accessory section. Include starter, tachometer generator, fuel pump, generator and vacuum pumps.
External spur-type reduction gear supported at front by ball thrust bearing and at the rear by a large roller-bearing. The pinion gear is mounted between two plain bearings and is splined to and driven by the crankshaft by a flexible coupling. The front scavenge oil pump is located in the reduction gear housing and the propeller governor is mounted on the rear of the housing in the Vee of the cylinder-blocks. The housing is provided with oil passages to supply both the governor and engine oil pressure for the hydraulic propeller blade pitch actuators. Reduction gear teeth are lubricated by an oil nozzle supplying three jets of oil directly on the teeth.
Engine Models and Applications:
Because of the vast number of V-1710 derivatives which were generated, the following table in necessarily incomplete, but includes representative models from the major series. Many of these deviates stem from early development, for example the "C" series consists of 13 unique models with total production of 2,582, yet 2,550 of those engines belonged to one model type (and of the 32 remaining engine, 19 belonged to another model type!). For a more complete, readers are suggested to Daniel Whitney's "Vee for Victory!" or Graham White's "Allied Aircraft Piston Engines of World War II". Note that both Allison and Service designations are used to refer to Allison models, the Allison designation consists of a letter followed by a number with an optional letter suffix, while the service designation is just a number. The service numbers are shown in parenthesis in the following table (some engines were experimental or developmental and not issued a service number).
Dash Application hp/rpm/altitude Comments A1 (-2) Navy Prototype 795/2480/SL (build 2) Prototype for Navy, first Allison V-1710, 87 PN fuel , 5.88 CR A2 (-1) Air Corp Prototype 1070/2800/SL (46" Hg abs) Prototype for Air Corp, 92 PN fuel, 5.75 CR B2R (-4) Dirigible 690/2400/SL Cancelled after loss of both USS Akron and Macon, R for reversible C15 (-33) Curtiss P-40 1040/3000/SL (42" Hg abs) 1,870 units delivered to British, long nose, Bendix Injection carburetor D2 (-9) YFM-1A 1150/2950/SL Pusher extension shaft engine E4 (-35) Bell P39 1150/3000/SL Extension shaft tractor, cannon fired through remote reduction gear F2R (-27) Lockheed P-38 1150/3000/SL First "short-nosed V-1710", internal spur gear replaced w/external gear F15R (-75) Lockheed P-38K 1425/3000/SL Water/Alcohol anti-detonation injection (ADI) F17R (-89) Lockheed P-38H/J 2300/3000/SL (90" Hg abs) WER, Turbosupercharged, w/115/145 fuel and ADI G6R (-143) N.A. P-82E/F 2250/3200/SL Used Bendix speed-density injection, 115/145 fuel with ADI E27 (-129) Bell XP-63H 2980/3200/11,000 (100" Hg abs) Most powerful V-1710, Turbocompound experimental engine
The total number of engines built for each series were:
A-series 2 B-series 3 C-series 2,582 D-series 44 E-series 18,998 F-series 47,660 G-series 763 Total 70,052 (note only 70,033 engines delivered because some prototypes were converted to later models)
Allison Powered Aircraft
P-38 Lightning (Lockheed)
The P-38 Lighting was one of the major fighters of WWII. The big twin-engined fighter, designed by Kelly Johnson (of later Skunk Works fame) and Hall Hibbard, featured twin-booms, tricycle landing gear, and boosted controls. The Allison engines were turbocharged and were "handed" -- the right engine rotating the opposite direction of the left -- to reduce rotational inertia effects. Two stress-skin monocoque booms supported thin engine nacelles, with the engine located immediately behind the propeller and the supercharger further aft. The booms were connected at the front by a central section of the wing, which also supported the central fuselage nacelle which housed the cockpit, and at the rear by a horizontal stabilizer. The main structural member of the cantilevered mid-mounted wing was a box-spar with front and rear shear members tied together with corrugated and flat sheet stock which made the whole assembly very strong and stiff. The wing included a slotted "Fowler" flap to enhance low speed operation, and later models featured mid-chord maneuvering flap located between the engine and fuselage nacelles.
For each engine, the exhaust was collected in a "Y"-shaped manifold which combined the two engine exhaust manifolds into a single pipe which was routed above the wing to a General Electric type-B turbocharger located behind the wing at the top of the Nacelle. The turbocharger and exhaust pipe were exposed to the slipstream to facilitate cooling, and the compressed intake charge was intercooled in early models by ducting through the leading edge of the wings and in later models by air-to-air intercooler mounted under the engine. The planes cockpit and other vital area's were protected by armor, and the plane had a single 20mm cannon and four 0.50in machine guns in the central fuselage nose, the plane could also a bomb load of 4,000 lbs under the wings.
First flight for the XP-38 occurred in 1939, and by the end of the war 10,036 P-39's had seen service in all the theatres of WWII, including the Europe, North Africa, Pacific, and China-Burma-India. In some theatres, like Europe, pilots struggled to cope with the low temperatures due to inadequate cockpit heaters and very low (-60° F) temperatures, while in others like the Pacific the Lightning was perfect for the mission.
For the first high-performance airplane developed by Lockheed, the P-38 was very successful. The P-38J had a gross weight of 21,600, used 2 V-1710-89/-91 engines producing a combined total of 2,850 hp. These engines could propel the airplane to 414 mph with a range of 2,260 miles using external tanks.
P-39 Airacobra (Bell)
The P-39 was an unconventional aircraft from fledgling Bell Aircraft Company. Developed from 1937-1939, the most unusual feature of the airplane was the placement of the V-1710 engine amidships behind the cockpit. This location was chosen to make room for a huge 37-mm aircraft cannon in the nose firing through the propeller capable of firing 15 or 20 rounds. This plane also used the "tricycle" landing gear for the first time on a U.S. fighter -- a configuration dictated by the engine location. Allison developed the "E" series of engines to accommodate the engine location -- the power section was adopted from the "F" series, with propeller reduction gear removed and a crankshaft-driven shaft passing under the cockpit to a remote gear-reduction unit with a hollow passage for the cannon through the center of the propeller shaft.
The prototype plane was equipped with a GE turbosupercharger and exhibited good altitude performance. Performance was good enough to earn a pre-production order of 12 airplanes. Problems with the GE turbosuperchargers (especially turbocharger boost control) led to their deletion from the Airacobra -- without the turbosuperchargers the single-stage Allisons were unable to deliver adequate altitude performance so their mission was hanged to low-altitude interceptor. It became apparent that the early enthusiasm would not be achieved by the design, but France and Britain were desperate for any kind of interceptor with both governments placing substantial orders. France was occupied by Germany before their planes could be delivered, as a result Britain received these planes, too. The British were bitterly disappointed in the planes performance, abandoning them after just four missions over occupied France. Britain shipped most of the planes to the Soviet Union, where they were successfully used for low-level air support on the Eastern front, and were particularly successful as tank-busters because of the cannon. The remaining British planes were shipped to Australia.
Ultimately, the Soviets received almost half of the P-39's manufactured (4,773 of 9,585 produced). The P-39 also played a significant role for the U.S. in the Pacific, where alongside P-40's the Airacobra bore the brunt of the Japanese onslaught at the time of Pearl Harbor. Production ended in 1943 so the factory could focus on P-63 production. The plane was quickly withdrawn from service at the end of WWII.
P-40 Tomahawk/Kittyhawk/Warhawk (Curtiss)
This conventional fighter airplane was designed with best known practices of the 1930's. It was also the first airplane to make large-scale use of the V-1710. Its ancestor was the R-1830 powered Curtis P-36A, which was converted to the P-40 by swapping the Allison engine for the Pratt and Whitney radial. Performance consistent with 1930's era's fighters but was not awe-inspiring by WWII standards, especially when compared to contemporary British and German fighters.
The prototype flew in 1938 and the U.S.A.A.C placed an order for 524 planes in 1939, which was the largest contract issued for planes since WWI. The British were first to use the P-40, using planes they began receiving in early 1941. The planes were originally intended for French use, but were redirected to the British after the German occupation of France. The lackluster performance and lack of armor-plating and self-sealing fuel tanks, which were not required by the French, caused the British to transfer these planes out of the European theatre. The British transferred the planes to North Africa where they performed well against Italian and Luftwaffe planes.
Clair Chennault's American Volunteer Group and his small band of pilots made the P-40 memorable. Chennault's 'Flying Tigers' campaigned ex-British P-40 Tomahawks in China and Burma.
At the time of the Pearl Harbor attack, the P-40's were the best fighter in the Army Air Corp inventory. While obsolete by 1941-1942 standards, these planes bridged a critical gap between the rise in tensions and the delivery of more advanced fighters which were underdevelopment at the start of the 1940's. The P-40 was responsible for defending the Pacific at the start of hostilities, and performed admirably in the theatres not dominated by advanced fighters. It was also deployed by a remarkable array of Allied countries, including Australia, Canada, China, Egypt, France, the Netherlands East Indies, New Zealand, South Africa, Turkey, the UK, and USSR. A total of 13,732 were produced in two major series (P-40, P-40D/E).
P-51 Mustang (North American)
The North American Aviation P-51 Mustang was designed to meet a request byt the British purchasing commission, which in 1940 was anxious to purchase U.S. fighter aircraft. The commission originally approached North American and asked them to build the Curtis P-40 under license for the RAF, since this fighter was already in mass production. Instead, the British were convinced to support a new North American design which took advantage of recent laminar flow research. In a remarkable 100 days from the signing of the contract, North American had the prototype flying.
The P-51A was powered by the 1150 hp V-1710-F3R (V-1710-39), the same engine used in the P-40D. Later P-51A's were upgraded to the 1200 hp V-1710-F20R (V-1710-81), the same engine used in the P-40M. A monocoque fuselage with laminar wing supported the engine with two box-section sheet metal cradles attached to the firewall. A belly-mounted circular oil-cooler was surrounded by an annular radiator which were housed in a low drag belly scoop -- under ideal conditions the heated air existing produced slight positive thrust. Variable inlet and discharge openings were used to maintain optimal temperatures while minimizing drag. A ground attack/dive bomber version of the P-51A was designated A-36A -- this version had fixed inlet/discharge opening.
Careful attention to detail and the laminar wing resulted in establishment of a new standard of low drag by the P-51A. When it entered service in November 1941 it was obvious to the British that they had a winner. The British experience with previous Allison powered-aircraft had been less the awe-inspiring -- the high drag airframes of the P-39 and P-40 consumed excessive horsepower -- in an efficient airframe like the P-51 the V-1710 would provide outstanding performance.
High altitude performance was a weak area of the V-1710. Since it was designed to be used with turbochargers, the V-1710 had much lower critical altitude than other engines when run without a turbocharger. Since suitable turbochargers were not available for the British (GE turbochargers being allocated to other strategic U.S. aircraft programs), the single-stage V-1710 powered P-51A were limited to relatively low altitudes. Rolls-Royce felt strongly that the North American outstanding P-51 airframe coupled with their two-stage supercharged V-1650 Merlin offer outstanding performance. This was proven when six Mustangs were converted to Merlin power and all performance parameters were dramatically improved. From the P-51B on all Mustangs used Merlin engines -- most Packard-built V-1650's under license from Rolls-Royce.
P-63 Kingcobra (Bell)
The P-63 was a completely new airplane based on the Airacobra. Significant improvements included a laminar flow wing, two-stage supercharged Allison V-1710's, fuselage stretched 2-1/2 ft to accommodate the increased engine length, relocated wing to accommodate Cg, and reconfigured radiator and oil coolers.
The U.S. and Britain already had other fighters in service which met their requirements when the Kingcobra entered service. The Soviet Union was continuing to heap praise on the Airacobra, and were the recipient of over 2/3 of all P-63's built, taking 2,421 of the 3,303 built. The Free French formed an air force in 1944 after the liberation of France, and the P-63 was one of their early aircraft. Some of the 400 aircraft supplied to France were still in service in the 1950's in Indochina.
The ultimate P-63 would have been the P-63H, which would have used the turbocompound V-1710-127(E29) engine which doubled the available power to almost 3,000 hp! While a testbed was constructed, it was never flown due to limitations of the turbine at the time -- the turbine had a 1,725° F temperature limit. Bench testing had shown power levels as high as 3,090 hp at 3,200 rpm and 28,000 ft with 100 in Hg abs boost and ADI, but even with rich 12.5:1 air-fuel ratios the exhaust temperatures were 1,825° F. To have enough safety margin, Allison believed they would need a turbine capable of handling 1,950° F temperatures, something the began working on until redirected to turbojet research. So the P-63H would become another victim of the jet age.
One of the stranger mission for the P-63 was the RP-63 "Pinball" variant. The plane was modified by adding over a ton of armor plating to the airplane. The plane was then used as a piloted gunnery target, with unique 0.50-caliber frangible bullets made from plastic, lead, and graphite being fired at the airplane by waist and turret gunners undergoing bomber training. A light in the cockpit and on the spinner would light when the plane was hit -- giving rise to the "Pinball" nickname.
P-82 Twin Mustang (North American)
Recognizing the need for a superior escort fighter to accompany long-range bombers over Europe, North American developed a twin-fuselage fighter based upon the very clean P-51 Mustang. The design included the features required for long-range fighter support -- high performance, reliability of twin engines, increased fuel capacity, and two pilots to share the workload. With unescorted bombers suffering large losses, the Air Corp placed priority on solving their long-range escort problem. The Air Corp responded to North American's unsolicited design in January of 1944 with an order for four experimental XP-82's. Although all four planes were originally to be Allison powered, plans changes so the first two, now designated XP-82A and using the V-1710-119, with the second two designated XP-82B and using Packard Merlin V-1650-23/25.
The all-new design looked like two siamesed P-51 Mustang's -- two fuselages were joined together with a central wing bridging the gap between fuselages, and a single horizontal stabilizer connected the rear fuselage. Two pilots flew the plane -- one was in the left fuselage cockpit and the other in the right. Tractor engines configuration was standard P-51 design, with one engine in each fuselage. The necessary communications, control cables, fuel lines, wiring, and other support was routed through the interconnecting central wing.
While the P-52A was cancelled when the war ended, work on the P-52B continued with the Merlin-powered plane's first flight in October 1945. Twenty production airplanes were built in early 1946 using Merlin engines previously purchased for the purpose. Production of Merlin's ceased at the end of the war, so when the Air Corp ordered 250 additional planes it was determined that they would be powered by the Allison V-1710-143/145 and originally specified by Allison specification V-1710-F36R/L but evolving to revised specification V-1710-G6R/L. The order was split between two groups -- the first group of 100 planes were P-82E escort fighters for use by Strategic Air Command to escort bombers, and remaining 150 were designated P-82F all-weather radar equipped interceptors/night fighters. The last 59 all-weather interceptors were actually delivered as P-82Gs. These planes entered air-defense service in the spring of 1948 and were based on both the east and west coasts of the United States, Alaska, and Japan. When the Korean war erupted, the Japan-based P-82's were the only planes with the necessary range to reach the battle fields, and a P-82G claimed the first aerial victory of the war. The last active duty mission by a P-82 was flown in Alaska in November 1953, the Twin Mustang having been replaced by jet-powered interceptors.
Boeing XB-15 -- This was the role the V-1710 had been designed for -- bombers. The Boeing XB-15 was a very long range bomber, designed to fly higher and faster than the opponents. It was the largest plane in the world, requiring four 1,000 hp engines. The V-1710 was selected to power this bomber, but continuing development problems led to replacement with Pratt and Whitney R-1830 radials in late 1935. The performance of the plane was reduced as a result of the substitution. Ultimately the Boeing B-17 was selected over the XB-15 for the long-range bomber role.
Martin XB-16 -- This plane began as almost identical to the Boeing XB-15 and intended for the same mission -- very long range bomber. The original normally aspirated plane evolved to a turbocharged configuration, the 65,000 lb four engined aircraft having a 2,600 square ft wing. Top speed was estimated to be 237 mph and cruise 120 mph, . As time went on, this plane grew to a gross weight of 105,000 lbs, which required more power so two additional engines were to be buried in the wing, adding two pushers to the 4 tractor engines. The plane used a tricycle landing gear configuration and the tail was modified from a conventional design to a twin-boom type on slender booms. The Air Corp purchased the design, but a prototype was never constructed. Like the XB-15, the economics of the Depression led to program cancellation when the B-17 won the Air Corp's long-range bomber contest.
Martin Twin Bomber -- This plane was a twin-boom twin-engine light bomber of 30,000 lbs gross featuring a central fuselage with a tractor and pusher propeller on the central axis of the plane. The plane was likely a competitor to the XFM-1/2, but did not progress beyond the preliminary Model 151K-1 presented to the Air Corp in 1936.
Lockheed Vega XB-38 "Flying Fortress" -- V-1710-89's replaced the Wright R-1820-65 radials on a B-17E bomber airframe. Turbocharging was retained, and the radiators were placed in the leading edge of the wing, with the intercoolers under the engine. While the main motivation for this program was to provide an alternate engine supply in case R-1820 supply was interrupted, there was also considerable interest in the performance of a liquid-cooled bomber. With 1,425 hp to 25,000 ft in each of the four engines, considerably improved performance was established, with speed increasing from 317 mph to 327 mph, and similar gains shown in rate of climb, bomb load, and range. The first flight of the XB-38 was in May 1943, the last occurred nine flights later when an engine fire occurred during a speed run at 25,000 ft. The crew was forced to evacuate their burning airplane, which subsequently crashed. Brief consideration was given to continuing the program with a heavily armed version of the B-17/-38 being developed for the "escort" mission, but when improved supplies of the R-1820 were established, priority was placed on production of the B-17G.
Douglass XB-42 "Mixmaster" -- This was a unique pusher airplane using two V-1710 "E"-type engines placed side-by-side behind the cockpit and driving a contrarotating propeller extending out the rear of the empanage on the centerline of the aircraft. One engine was coupled to the right-hand turning propeller and the other engine to the left-turning through a reduction gear placed at the rear of the fuselage. The extension shafting was borrowed from the P-39 design. Electric fans were required to solve the cooling problem inherent in pusher designs, which don't have a significant propeller wash to supply cooling air as do tractor configurations. A persistent problem with oil escaping from the left hand breather eventually required a redesign of the front cover and crankcase breather on left turning high power "E" models. The first airplane was lost during an engineering test flight due to pilot error (fuel/aircraft configuration management) near Schenectady, New York in December, 1945. The second aircraft had jet engines added to the wings, being designated XB-42A. This aircraft was retired in 1948, and now is part of the Smithsonian Institution's National Air and Space Museum collection.
Douglass DC-8 "Skybus" -- This low-winged contra-rotating pusher transport powered by two V-1710's was announced by Douglas Aircraft in October 1945 as the "Transport of Tomorrow" -- the post-war successor to the DC-3. This airplane had a drive configuration similar to the XB-42 but placed the engines under the floor in the passenger compartment. It's 39,500 gross weight was sufficient to accommodate 48 passengers in a pressurized cabin sitting five abreast. The plane would have been 50% faster than the DC-3, at half the operating cost. The engine was expected to be a derivative of the V-1710-E29, but would have achieved the required altitude performance with a single-stage two-speed supercharger, an Allison first. The airlines were concerned about the maintenance costs of the unconventional propulsion arrangement and chose to purchase conventional Convair 240 and Martin 2-0-2 airlines. The DC-8 designation would be reused for the company's successful first jet transport a decade later.
Douglass XC-114/YC-116 -- This was intended to be a liquid-cooled variation of the DC-4/C-54 four engine transport which used Pratt and Whitney R-2000 air-cooled radial engines. The design would have accommodated the V-1710, the Rolls-Royce Merlin, or the Wright R-2180 engines. Ultimately Douglas continued with the R-2000 for the resulting C-54E, but the airforce assigned the XC-114 designation to a C-54E type fuselage which had been stretched 81 inches (the same fuselage at the soon to be introduced R-2800 powered DC-6) and acquired 4 V-1710-131(G3R) engines from Allison. The G3R featured the two-speed supercharger drive turning a one stage supercharger with a 10.25" impeller which enabled high-power takeoff with good medium altitude performance. The G3 delivered 1,600 hp for takeoff-vs- 1,350 hp for the R-2000 engine. Although American Airlines was seriously interested in the proposed plane in 1946, they ultimately declined to invest in the program and the plane was discontinued in 1946.
Brewster Model P-22 -- Brewster was one of several companies interested in integration the new Allison into their airplanes in the late 30's. Brewster proposed an airplane based on their F2A Buffalo which would use a two-stage supercharger. A maximum speed of 307 mph at sea-level and 347 mph at 12,000 ft, its critical altitude. The U.S.A.A.F. and French purchasing commission failed to issue contracts for the plane and it didn't enter production.
Bell Model 11 -- This was one of several Bell proposals in response to the 1939 Army fighter request for proposals (the other responses would lead to the P-39 Airacobra). This was a conventional taildragger powered by a tractor mounted V-1710. Projected performance was 411 mph at the 15,000 ft critical altitude. In the resulting competition, one of the company's XP-39 proposals placed second in the competition (and subsequently received orders), while the Model 11 placed 11th out of 19 designs offered. As a result, the company placed directed its resources to the P39 program, abandoning the Model 11.
Bell XP-52 -- This proposal was made to the Air Corp in response to their solicitation for advanced and unconventional aircraft. The Air Corp liked a proposal offered by Bell for a pusher airplane similar in size to the P-39 but with a wing 25% smaller. Rather than a design contract, the Air Corp offered to release the P-39 for foreign sale by Bell and pay Bell $50.00 (yes, fifty!). The plane would have been powered by a pusher V-1710-E9 two-stage engine with 1,225 hp available up to a critical altitude of 18,000 ft, with an expected speed of 443 mph. Bell had offered other proposals based on the Lycoming XH-2470 and the Continental I-1530-5 engines which have been incorrectly cited by some as the intended powerplants for the XP-52. The program was abandoned in favor of the later Bell Model 20 (XP-59) which was to have been a twin-boom pusher. That program was also abandoned so the XP-59 designation could be used as a cover for the first U.S. jet airplane, the Bell XP-59A.
Curtiss XP-55 "Ascender" -- This radical "tail" first canard was another plane which developed in response to the solicitation for advanced and unconventional aircraft proposals by the Air Corp. It was essentially a flying wing in a pusher configuration powered by the V-1710-95(F23R). The first of three prototypes flew in 1943, the performance achieved being 390 mph at 19,300 ft with a service ceiling of 34,600 ft. The advances by conventional aircraft and the development of the turbojet, along with the demands of high-priority production programs led to no interest in further development of the Ascender.
Curtiss XP-60A -- This was intended to be a modernization of the P-40 airplane. It incorporated a laminar flow wing and considerable detail to drag reduction. The prototype flew in September, 1941 and a production order for 1,950 planes issued in October, 1941. Following the attack on Pearl Harbor, the Army decided to concentrate production on proven types, leading to the cancellation of the production order. While work on several prototype airplanes continued, production capacity was absorbed by an order become a second source for Republic Aviation, producing the P-47D (Curtiss versions designated P-47G-1-CU). Flight test results show the performance of the XP-60 would have been comparable to th best-in-class fighters of the day.
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