Allison Piston Engine Images
Courtesy of John Leonard and Dan Whitney. Unless otherwise noted, Images are Courtesy of the
Rolls-Royce Heritage Trust - Allison Branch
Published 8 Aug 2019; Revised 24 Sep 2019
Norman Gilman, Allison's chief engineer, began designing the GV-1710-A in May 1929. It was intended for development into an ethylene-glycol-cooled 1,000 hp aircraft engine. Both the U.S. Army Air Corps and U.S. Navy were interested. The Army version was rated at 750 hp, and the Navy version at 650 hp. Both versions were built and tested extensively by the U.S. Armed services, along with the National Advisory Committee for Aeronautics. Neither version flew.
GV-1710-A Images: F, LF, L, LA, A, RA, R, RF, T, B, T with Marvel Fuel Injection.
The V-1710-B was intended to replace German Mayback VL-2 engines that powered the airships USS Akron and Macon. No supercharger was required since the engines operated at low altitude. The V-1710-B had to be reversible and capable of going from full power forward to full power reverse in just eight seconds. This was accomplished by the introduction of 24-lobe cams that translated when engine direction was changed, magnetos capable of maintaining correct timing in either direction, and an accessory gear train that drove the accessories in one direction regardless of engine direction. A set of controls at the engine's rear controlled these reversing features. Although the V-1710-B passed a 150-hr type test, the project was cancelled after the USS Macon was lost.
V-1710-B Images: F, LF, L, LA, A, RA, R, RF, T, B
The Allison V-1710-C was the first engine to pass a 150-hr type test at 1,000 hp, which it did in April 1937. A total of 2,580 V-1710-Cs were built, with the majority being used in Curtiss P-40s. Aircraft that it powered included the Consolidated A-11A (Wiki), Curtiss (X)YP-37 (Wiki), Curtiss XP-40 (Wiki), P-40 (Wiki), P-40B, P-40C, and Lockheed XP-38 (Wiki). Allison proposed the V-1710-C power the Consolidated B-24, Douglas C-39 and Lockheed Loadstar.
V-1710-C Images: F, LF, L, LA, A, RA, R, RF, T
Allison V-1710-D models were designed for pusher propeller installations using a driveshaft. D-model design began in December 1935 and production ended October 1940. Two aircraft were slated for V-1710-D power — the Martin XB-16 and the Bell X/YFM-1. Only the X/YFM-1 flew.
V-1710-D Images: F, LA, A, RA, R, T
V-1710-E engines were designed for use with remote gearboxes. Three variants powered single-engine Bell P-39 (LF, RF, Firing), P-63 and XFL-1 fighters, all of which had the engine behind the pilot. This arrangement made room for a 37mm cannon firing through the propeller hub. A fourth variant powered the Douglas XB-42. P-39 engines used single-stage superchargers, while some P-63 engines added a variable-speed auxiliary altitude supercharger stage (LF, RA). The XB-42 employed two V-1710-E23 (L, RF) engines to drive contra-rotating pusher propellers. A turbocompound engine, the V-1710-E27 (L, A, R, T) was built and tested, as were numerous other variations on the shaft-driven remote gearbox (90°, Tandem, Tandem).
V-1710-E Images: F, LF, L, LA, A, RA, R, RF, T, B, with Driveshaft, Gearbox.
The V-1710-F featured a crankcase that was common to the -E engines, allowing the same reduction gear assemblies to be used on both engines. The V-1710-F was also capable of left-hand rotation by swapping the crankshaft end-for-end and fitting an idler gear to the accessory section so that supercharger, generator, pumps and magnetos all operated in the same direction. V-1710-F engines powered the Boeing/Lockheed/Vega XB-38, Curtiss P-40, XP-55 and P-60, Lockheed P-38, and North American P-51A and A-36. The V-1710-F32 featured an intercooled two-stage supercharger and was used in the two North American XP-51Js that were built. More V-1710-F models (about 48,700) were built than any other Allison engine.
V-1710-F Images: F, LF, L, LA, A, RA, R, RF, T, B
The Allison V-1710-G6 powered the North American F-82 (USAF Photo). Of 272 F-82s built, 250 were powered with V-1710s, the remainder by Rolls-Royce Merlins. An F-82 shot down a Yak 9 on 27 June 1950; this was the first enemy aircraft downed during the Korean conflict.
V-1710-G Images: L, R.
In the middle 1930s, U.S. Army Air Corps planners realized they would need a new, more powerful, class of engines to power the long-range superbombers they were contemplating. The Air Corps asked Allison to propose a double V-1710 in the form of the X-3420. As was often the case, Air Corps was its own worst enemy, insisting this be accomplished with a single crankshaft and using fuel injection. Allison objected, saying that the articulated rods were not strong enough for the engine speed contemplated and that fuel injection systems were not yet practical. Despite its misgivings, Allison submitted a proposal for an engine limited to 2,400 rpm that produced 1,600 hp. Sure enough, a reliable fuel injection system never materialized and the X-3420 project stagnated as Allison completed type testing of the V-1710.
In late 1936, Allison proposed a new carbureted V-3420 with two crankshafts and sharing 92% of its parts with the V-1710 design. In April 1938, testing began on this V-3420-A, whose crankshafts turned in the same direction. The V-3420-A had passed its 150hr Type Test by 3 March 1942, producing 2,600 hp and making it a candidate for replacement for troubled Curtiss-Wright R-3350s in the Boeing B-29 and Consolidated B-32. By the end of WWII some V-3420 versions were reliably producing 3,000 hp, yet it never saw service in a front-line aircraft.
The V-3420-A powered the Boeing/Fisher XB-39 (ground, flight), the Douglas XB-19A (R, RF), and the Lockheed XP-58. Allison proposed using it for the Curtiss C-46, Hughes HFB-1 Spruce Goose, Lockheed P2V-1 and Martin B-26.
V-3420-A Images: F, LF, L, LA, A, RA, R, RF, TF, TA, BF, BA.
The V-3420-B featured crankshafts that rotated in opposite directions, each driving one disk of a contra-rotating propeller. This engine was only used in the Fisher P-75. The off-center supercharger produced an uneven mixture distribution to the cylinder banks, which was remedied by changing the phase angle between the two crankshafts. In its final form, the V-34200-B12 (LA, LA with Extension Shafts and Gearbox, R with Extension Shafts and Gearbox) with a two-stage supercharger had a sea-level war emergency rating of 3,115 hp at 3,000 rpm. This engine was used in the Fisher XP-75A
V-3420-B Images: F, LF, L, RF, L with Extension Shafts and Gearbox, RF with Extension Shafts and Gearbox.
Unusual Single and Double V-3420 Studies
Rather than developing entirely new large engine models, Allison proposed several unusual geared single and double V-3420 (also called DV-6480) installations. These were presumably adaptable to many different aircraft types; some were to be submerged in the wing (suggesting minimal vertical dimensions), others featured fuselage-mounted engine(s) with remote reduction gear boxes driving either counter-rotating or contra-rotating propellers.
Proposed single V-3420 installations included an aircraft with twin pusher propellers driven from a centrally-mounted engine via drive shafts and remote right-angle gear boxes (top view, left aft view). Another scheme used a transverse mounted engine, buried in the wing, driving contra-rotating propellers through a right-angle gearbox.
Allison proposed double fuselage-mounted V-3420s geared to the same contra-rotating propeller, which Allison referred to as DV-6840, to power what appears to be a medium bomber. Martin propesed the Model 201 (3-view, cutaway) along similar lines. Allison also suggested twin transverse-mounted V-3420s driving contra-rotating tractor (or pusher) propellers, as well as contra-rotating tractor AND pusher propellers.