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Aviation History
1942
1942 - 0653.PDF
MARCH 26TH, 1942 1 AMERICA'S ALLISON ENGINE DETAILS OF 12-CYLLNDER ^£TPE OF 1,710 CUBIC IWJIES CAPACITY, AN ENGINE APPLIED TO MANY U.S.A. TYPES. FLIGHT 281 V1810 C15 engine with long nose as installed in the Curtiss Tomahawk. By G. GEOFFREY SMITH, M.B.E. S OME weeks ago an oppor tunity was afforded by the Ministry of Aircraft Produc tion to examine in detail specimens of the Allison aircraft engine, which now figures in many U.S.A. types in service with the R.A.F. We were able to inspect raws of engines in various stages of assembly at a maintenance repair unit which is now well organised and practised in the overhaul of the Allison, so that servicing proceeds automatically and efficiently. The Allison is the only example of the liquid-cooled engine in American military aircraft save for the Packard-built Rolls-Royce Merlin. The U.S.A., as is well known, has hitherto specialised upon air-cooled radial engines, which, it must be confessed, have earned an enviable name for dependability and power output. It is ten years since General Motors Corpn. (which acquired the Allison Engineering Co. in 1529) set about the task of producing a 12- cylinder liquid-cooled. V- type engine. Among the attractions set forth by the Chief Engineer, Mr. R. M. Hazen, are (1) small frontal area ; (2) the pro mise of higher power out put .per c.c. due to the MjFpz and uniformity of JPooling; (3) greater reliability because it is less sensitive to temporary overloads. The type best known in this country is the V1710 C15, a designation which indicates the form of the engine and the cylinder capacity in cubic inches. Incidentally, it is. 61 cubic inches larger than the Merlin. Fitted to the Curtiss Tomahawk and a<so early examples of the Lockheed Lightning, the C15 engine differs mainly in appearance from the later E and F types applied to the Bell Airacobra, Mustang and Kittyhawk, Previous descriptions in recent issues of "Flight" of leading aircraft engines have appeared on the following dates : Bristol Hercules - - Nov. 27, 1941 Rolls-Royce Merlin - Feb. 26, 1942 Section through cylinder block of the V1710 type. in that it has a long nose integral with the crankcase, enclosing the 2 :1 reduction gear. This gear is an internal spur gear meshing with the pinion gear splined on the front end of the crankshaft. The E types, on the other hand, are used with an extension shaft and separate reduction gear, as on the Airacobra, whilst the F type on the Mustang, Kittyhawk and Lightning, has an offset spur-type reduction gear. Two models of the F-type engine fitted to the eagerly awaited Lockheed Lightning twin-engined fighters have exhaust-driven turbo superchargers and are rated at 1,000 b.h.p. at 2,600 r.p.m. and 1,150 b.h.p. at 3,000 r.p.m. It is the C-15 type power unit to which these notes primarily refer, and many entirely original features reveal themselves in a study of this product of one of the great American car manufacturers. General Features The bore and stroke are 5.5m. x6in., and the cylin ders are cast in two blocks each with six cylinders and set at 60 degrees. t The head is a separate one-piece alloy casting, and there are foilr valves per cylinder, set at 22J degrees to the cylin der axis, operated by a cen tral overhead camshaft driven by an inclined shaft at the rear of the engine through bevel gears from the accessories drive shaft. The rockers are .mounted on the top of the cylinder head. Hardened steel, carburised cylinder barrels are shrunk into the head. Enclosing the barrels is a jacket of light alloy secured to the head by studs, the lower connection being by a nut threaded on each cylinder barrel. Each block is secured by 14 stud bolts extending through the head, and so clamping the barrels between the head and the crankcase. Sodium- cooled exhaust valves are employed with seats of
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