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Aviation History
1920
1920 - 0126.PDF
JANUARY 29, 1920 TWO NEW FIAT AERO ENGINES THE A-15 R. 400 H.P. 12-CYL. "V"A SHORT time before the end of the War the Fiat Co. pro-duced a new type of twelve-cylindered aviation engine de- veloping more than 400 h.p. With the signing of the Armis-tice immediate construction was not undertaken, but this engine has given such excellent results under test that it hasnow been decided to place it on the market. „ . The Fiat A-15 R. 400 h.p. twelve-cylindered " V " aero engine—aremarkably" clean " design The main objects sought in this engine were completeaccessibility of all organs requiring regular attention, such as magnetos, carburettors, valves, water pump, oil pump, etc.,and at the same time to reduce area and weight in relation to the power developed. This engine, which is officiallydesignated A-15 R. is one of the cleanest-cut and most pleasing-looking aviation engines ever built. While externalpipes and exposed mechanism have been avoided throughout, accessibility has not been diminished, but is much greaterthan on other engines produced up to this time. The V-type twelve-cylindered engine possesses considerableadvantages over the vertical six of equal power. The crank- case and the crankshaft are shorter, the shaft diameter issmaller, while the effort exerted on the individual cranks is smaller, all of which tends towards a reduction in weight.In the twelve-cylindered engine the equilibrium of the inertia and centrifugal forces is perfect, while the more regularimpulses reduce vibration to a minimum, to the great advantage of the propeller. Theonly objection which can be brought against the twelve-cylindered V-engine is that itrequires more attention than a six-cylindered engine by reason of the greater number ofplugs, carburettors, valves, etc. In the new Fiat this objection has been diminished, if notentirely removed, by careful designing with accessibility prominently in view.The cylinders are separate steel forgings welded together in groups of three, with acommon water-jacket for each line of six. An interesting feature is that the intake manifoldsare of sheet steel passing inside the water- jacket between the centre and the outercylinder of each group of three. This is a very fine example of the art of acetylene welding,and has th^ advantage of providing internal manifolds heated by the circulating water,with carburettors bolted up direct to the outside of the cylinder-blocks. It avoids theusual complication and inaccessibility of car- burettors placed in the angle of the cylinders.There are four valves per cylinder mounted in the head, with the exhaust led away fromthe outside from four ports for each line of six cylinders. The valves are operated by anoverhead camshaft for each line of cylinders. Rocker arms with an adjustable mechanismfor valve-stem clearance are used, and the whole is covered by a sheet steel housing,which both prevents oil leakage and adds to the clean appear- ance of the engine. Each overhead camshaft is operated by a bevel-gearmounted on the centre of the crankshaft and an inclined and enclosed shaft. These two drive-shafts are telescopic, inorder to allow for expansion by reason of heat, and the central location of the valve-operating gear adds to the purity oflines of the entire engine. The bevel-gear which serves to drive the camshaft also operates the gear-type oil pumpplaced in the lowest portion of the base-chamber. The water pump is at the rear of the engine, driven direct from The Fiat A-18 300 h.p. nine-cylindered radial water-cooled aero engine : View of the front or air-screw end The rear or magneto end of the Fiat A-18 300 h.p.radial aero engine 126
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