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Aircraft Engines in Armored Vehicles
As military planners began to realize the need for armored vehicles prior to World War II, they were faced with the problem of powering such vehicles. The requirements were, aside from the weight issue, similar to those of aircraft—the engines needed to be compact, powerful, reliable and economical to operate. The use of aircraft engines in tanks was not a new idea. The V-12 Liberty from World War I developed Liberty 338 hp @ 1,400 rpm. Starting in 1920, it powered the Mk. VIII of which (100) were built.
The Continental R-670 first flew in 1931. In addition to its uses in aircraft, it became an extremely popular tank engine. It was a 7-cylinder radial that developed between 235 hp @ 2,400 rpm and 250 hp @ 2,400 rpm when used in armored vehicles. It powered the M1 (89), M1A1 (17), M1A2 (89), M2A1 (19), M2A2 (237), M2A3 (237), M2A4 (375), M3 (4,526), M3A1 (4,410), M3A3 (3,427), Turreted M1 (16), Barbette M1 (3), LVT2 (2,963), LVT(A)1 (509), LVT(A)2 (450), LVT4 (8,348), LVT(A)4 (1,890), and LVT(A)5 (269) (the number produced appears in parentheses after the designation).
Guiberson T-1020 was a 9-cylinder radial diesel was flight tested in a Stinson Reliant in 1940. In tank service it produced 245 hp @ 2,200 rpm and powered the M1A1E1 (7), M2 (34) and M3 Diesel (1,285).
Ford Motor Company thought it would be easier to produce an aircraft engine of its own design than to license-build the Rolls-Royce Merlin. A revolutionary and innovative 60° V-12 was designed and built, but before it could be fully developed, the US became involved in World War II. Ford removed four of the cylinders, resulting in a 60° V-8 for tank use that developed 450 hp @ 2,600 rpm. Several variants were produced.
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The Ford GAA was used in the M4A3 (1,690), M4A3(75)W (3,071), M4A3(76)W (1,400), M4A3 (105) (500), M4A3E5 (254), M4A3(76)W (3,142), M4A3(105) HVSS (2,539), M10A1 (1,413), and M7B1 (826).
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The Ford GAF powered the M26 (2,222), M26A1, and M45 (185).
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The Ford GAN, powered the T23 (248) and M4A3E5 (254).
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In order to meet the need for a larger engine, Ford resurrected the V-12 as the GAC, which produced 770 hp and powered the T29 (6).
Lycoming converted and aircraft engine to produce the O-435T, a 6-cylinder horizontally-opposed air-cooled engine. Used in the M22 Locust (830), it produced 162 hp @ 2,800 rpm.
A distant cousin of the J-5 Whirlwind that took Charles Lindbergh from New York to Paris, the 7-cylinder radial Wright R-975 variations developed between 340 hp @ 2,400 rpm and 400 hp @ 2,400 rpm. It powered the M2 (18), M2A1 (94), M3 (4,724), M3A1 (300), M3A2 (12), M3A5 (591), M4A1 (6,281), M4 (6,748), M4A1(76)W (3,246), M4(105) (800), M7 (7), M39 (640), M44 (6), M4A1(76)W HVSS, M4(105) HVSS (841), M18 (2,507), and M7 (3,490). Many R-975s were built under license by Continental.
Wright’s big R-1820 found limited use in armored vehicles in two forms. The G200 was a 9-cylinder gas-burning radial that developed 900 hp @ 2,300 rpm and powered the M6 (8), M6A1 (12). The Wright RD-1820 was converted to a diesel by Caterpillar and produced 450 hp @ 2,000 rpm in the M4A6 (75).
In addition to the use of aircraft engines, several manufacturers geared together multiple automobile engines to get the required power.
Cadillac built a 16-cylinder two V-8s. It developed 220 hp @ 3,400 rpm and powered the M24 (4,371), M5 (2,074), M5A1 (6,810), LVT3 (2,962), M8 (1,778), M37 (150), M19 (300) and M19A1.
Chrysler produced the A57 by combining five 6-cylinder in-lines for a total of 30 cylinders! The engine developed 370 hp @ 2,850 crankshaft rpm and was used in the M3A4 (109) and M4A4 (7,499).
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Much of the data about these engines comes from the Armored Fighting Vehicle web site.
Be sure to read the book review on the Rolls-Royce Meteor tank engine
Salmson Z-9
The Societe des Moteurs Salmson began development of aircraft engines in 1908 and started producing engines in 1913. No other water-cooled radial designs can boast such a long list of achievements. Salmson also built in-line and barrel engines, but the most famous Salmson engines are the water and air-cooled radials. The Z-9 model was widely used during World War 1.
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Salmson Z-9 |
Early |
Later |
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Type |
water-cooled 9-cylinder radial |
water-cooled 9-cylinder radial |
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Bore |
125 mm (4.92”) |
125 mm (4.92”) |
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Stroke |
165 mm (6.50”) |
170 mm (6.69”) |
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Displacement |
1,112 cu in |
1,146 cu in |
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Power |
230 hp @ 1,500 rpm |
250 hp @ 1,550 rpm |
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Weight |
? |
473 lbs |
Later Salmson Z-9s had a compression ratio of 5.4:1, a specific fuel consumption of 0.490 lb/hp/hr and a specific oil consumption of 0.077 lb/hp/hr.
Cylinders were constructed of steel with welded-on sheet-steel water jackets. They were captured by the two halves of the crankcase via two flanges at their base. Slightly inclined valves were actuated via rocker arms, pushrods and tappets running on three intake and three exhaust cams running in the same direction as engine rotation at one-quarter engine speed. Aluminum pistons were fitted with four compression rings and one oil ring. Intake valves opened at TDC and closed at 55 degrees ABDC. Exhaust valves opened at 65 degrees BBDC and closed at TDC.
Two nine-cylinder magnetos supplied dual ignition. Carburetion was via either Claudel or Zenith duplex carburetors. Oil was circulated by two oscillating-plunger pumps.
The two-piece crankshaft ran on ball-bearings and was joined via a short taper on the rear end of the crankpin, held to the rear crankcheek via a pin and nut. Several thousand of the later Z-9 models were produced during 1917 and 1918.
Not only was the Salmson Z-9 noteworthy as a water-cooled radial, but it also among the last production engines to successfully replace the usual master/articulated connecting rods with a true-motion Canton-Unne mechanism.
The idea of a water-cooled radial seems strange today, but such engines were quite common in the early days of aviation. The first US aircraft engine, the Balzer-Manly that powered Samuel Pierpont Langley’s ill-fated Aerodrome, was a water-cooled 5-cylinder radial. By 1939, others had been built by Albatross, Anzani, Clement-Bayard, Fiat, Garuffa, Rumpler and Salmson. During the Second World War, Wright Aeronautical tested a 42-cylinder liquid-cooled radial, Lycoming tested a 7,755 cu in, 36-cylinder liquid-cooled radial, and BMW built a 28-cylinder liquid-cooled radial.
The Canton-Unne mechanism was conceived by Georges Henri Marius Canton and Pierre Georges Unne, who filed their first patent application in France on December 15, 1908. Please refer to the diagram of the Canton-Unne mechanism. On the left is a transverse section of a representative radial engine. At the upper right is a detail of the Canton-Unne mechanism, a transverse section of which appears at the lower right. Each connecting rod (8) is attached to a single spool (9), which rotates on the crankpin (10) of the crankshaft (6). A gear (14), fixed to the spool (9), engages intermediate pinions (15), which also engage another gear (17) that is fixed to the crankcase (3). Gears 14 and 17 have the same number of teeth. Intermediate pinions (15) rotate on a shaft (16) that is fixed in place via an arm (18) that is an integral part of the crankshaft. As the intermediate pinions (15) “walk” around the gear fixed to the crankcase (17), they cause the spool (9) to rotate at the same angular velocity as the crankshaft, thereby eliminating the need for a master rod. A counterweight (19) balances the rotating and reciprocating masses attached to the crankshaft. While there have been many attempts to replace the master/articulated connecting rod scheme, none seem to have been worth the effort, although people continue to try.
