EDITORS NOTE: The 1710 cubic inch, Allison V-12 was our liquid cooled aircraft engine of World War II. Build in Indianapolis, Indiana, it was a Midwestern entry into the war’s diverse manufacturing effort. You will still see the Allison V-12 in use today as tractor pull engines.
|The all American Allison V-12 finds much work as a tractor pull engine … in this case two engines are used.|
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From November, 1943 Air Trails magazine.
FOR a long time previous to the most disastrous Sunday in American history there had been a considerable body of thought in American aëronautics which tended to insist that there was wisdom in putting all of one’s eggs in the same basket.
This was not the opinion of the engineers of the U. S. Army Air Forces. It was not the opinion of a small group of pioneering engineers working together in a machine-shop engine-building plant in the cornfields of Indiana.
Their reasoning led to the conclusion that there might be some sense in fitting the engine to the airplane, rather than simply providing an engine to which a flyable airframe had to be designed. The result of the co-operation of these two groups is a typical American product which today is making an outstanding contribution to the United Nations’ military air effort around the world.
The size of this contribution, for military reasons, cannot, of course, be revealed, but the worth of the resultant product is easily discoverable in the Russians’ enthusiasm for their Lend-Lease Airacobras; in the spectacular performance of the Lightnings in the Aleutian and African campaigns; in the surprising and full-hearted approval of the English for a thing wholly American, the Mustang; and by the way in which the men with Chennault swear by their Warhawks as the finest aerial fighters in the world.
All these planes are powered by the Allison engine.
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|Big reason for long life of American engines is constant checking during manufacturing. Height gauges here check alignment and dimensions before assembly.|
The Allison is a 12-cylinder, 60° V-type liquid-cooled engine of 1,710 cubic inches piston displacement and rated at 1,325 horsepower. The cylinders are arranged in two blocks of six cylinders each, in line; the result is an engine of surprisingly small frontal area.
|Typical of the machine marvels at Indianapolis is this boring machine which simultaneously bores in the crankcase, all six holes for a cylinder bank.|
Each cylinder block is a complete unit, consisting of a single aluminum casting for the combustion chambers, six steel barrels and a cast aluminum jacket.
|Hardness of inside of cylinder barrels is tested with diamond-edged apparatus. The Allison engine has only 720 parts compared with 2,300 of the British Merlin.|
|On a heavy steel-topped table, this expert Allison craftsman is using a height gauge to check height and parallelism of cylinder-head cooling jacket.|
|Vertical honing machines grind insides of cylinder to extreme accuracy. With a reciprocating rotary motion, tools smooth cylinder wall to mirror-like surface.|
There are four valves per cylinder, two intake and two exhaust, which are operated by a single overhead camshaft and rocker arms. The heat-treated steel cylinder barrels and the valve seats are shrunk into machined recesses in the head, and the bronze valve guides are pressed into the heads.
|This machine laps the cylinder heads by sliding them over an abrasive-faced platform. Operation was formerly a tedious hand job. Precise fit is essential.|
Both the intake and exhaust valves are sodium cooled and have stellite facing on the valve-seating faces. The exhaust valve-seat inserts are of steel with a stellite facing, while the intake valve seats are of forged steel.
The crankcase consists of upper and lower aluminum alloy castings which split on the horizontal crankshaft center-line. The bearing caps are integral with the lower half.
The crankcase decks, on which the cylinder blocks are seated on solid copper gaskets, have fourteen long hold-down studs for each block. These studs transmit gas loads directly to the crankcase.
The crankshaft is a conventional six-throw. Partially counter-balanced type,—nitrided for journal hardness and resistance to fatigue. The crankshaft journals are hollow and fitted with removable aluminum alloy plugs. The counterweights are welded to the forged shaft, providing a dependable and easily-produced design.
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|Finished crankshaft is held in jig while connecting rods are attached. Shaft is supported in engine crankcase by seven steel-backed, silver-lined bearings.|
Each end of the shaft has a nine-bolt flange, which provides a mount at the rear for the dynamic balancer hub, into which is splined the outer member of the hydraulic vibration damper unit.
On the front flange is mounted a female gear-tooth coupling for driving the reduction gear pinion.
The crankshaft is supported in seven steel-backed, silver-lined main bearings.
The drive for the overhead camshafts is provided by a gear train which starts at the rear end of the crankshaft and drives through a hydraulic vibration damper; then, in order, an idler gear, a cormbination spur and bevel gear, and inclined drive shafts to bevel gears at the rear end of the camshaft of each cylinder head.
The accessories housing is mounted directly on the rear of the crankcase and is a magnesium alloy casting. It contains the centrifugal supercharger and the drives for the coolant pump, camshafts, fuel pump, two vacuum pumps or hydraulic pumps, oil pump, starter, and generator.
The supercharger impeller is 91/2” in diameter and is driven at several different speeds depending on the specific model. The supercharger is driven by a gear train which starts with a spur gear on the outside of the hydraulic damper inner shaft, which is flexibly connected to the rear end of the crankshaft through a quill shaft and the hydraulic vibration damper. This gear drives an intermediate shaft, on the end of which is the final drive gear which drives the impeller pinion shaft.
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|Milling machine cuts out excess metal from supercharger impeller. In addition to this built-in supercharger, external turbo can be used, as on the P-38 Lightning.|
The impeller shaft runs in two steel-backed floating bushings which are faced with lead-bronze inside and outside. The inertia of the rapidly rotating supercharger impeller is utilized to maintain constant speed on the inner member, or “paddle,” of the hydraulic damper.
The torsional vibratory motion of the outer member of the hydraulic damper (and that of the rear end of the crankshaft, to which the outer member is splined) is effectively damped by oil pressure built up in the hydraulic damper by virtue of the differential motion of the inner and outer members.
The torsionally flexible quill shaft connecting the inner and outer members serves to limit the travel of the hydraulic damper and to hold the two members in proper mechanical relation. A take-off from this same gear train drives the camshafts and magneto.
|The complete engine disassembled. All engines are tested on stand, disassembled and inspected, reassembled and retested. First run is called “green test.”|
|In this department, engine parts are cleaned and inspected after “green test” by both army and Allison inspectors. Thus, possibility of failure is minimized.|
The V-type liquid-cooled engine has distinct advantages for the installation of an exhaust-driven turbo-supercharger which can be located immediately under or to either side of the engine with a short exhaust line and short air ducts to the intercoolers and the carburetor.
Liquid cooling also permits locating radiator equipment in such places on the plane where a minimum of drag is experienced, thus making more of the engine power output available for useful work. The chemical coolant used in the Allison is ethylene glycol.
Typically American in its design and creation, the Allison engine embodies an astonishingly low number of piece parts, (only 700 as compared with 2,300 in the most widely known European rival engine), facilitating ease of repair and overhaul through a high inter-changeability of parts.
This has proven to be a pearl without price where emergency overhauls have had to be made in the jungles of New Guinea, on the sandy shores of the Yangtze River, on African deserts, on the ice and the snows of Alaska.
When in May, 1939, the army issued Allison its first quantity order, the Allison V-1710 C-15 engine, rated 1,090 horsepower at altitude, was the production model.
In May, 1941, there were added to the production schedule the E, the F-2 and the F-3. Subsequently, these were replaced by newer models and today Allison has in regular production four models: the F-17, the F-20, the E-19-R and the E-19-L.
One of the outstanding engineering achievements has been the reduction in the weight of engines per horsepower. In 1940 this weight ratio to horsepower was 1.22 pounds; today it has been reduced to .93 pounds.
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|“V for Victory” has added point to Allison Workers who turn out thousands like this powerful V-shaped engine, Here shown on moving final assembly line.¬|
|With hairbreadth accuracy this big turret lathe turns and bore outer propeller shaft. In single operation, heat-treated shaft is reduced to exact size.|