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Aviation History
1929
1929 - 0910.PDF
FLIGHT, MAY fc 1929 The evolution of a " Ja- guar " cylinder barrel. push rod length takes the form shown in Fig. 2 on p. 361. This arrangement replaces that previously used, in which a ball-ended plug screwed into the end of the push rod was used. The tappets which actuate the push rods are operated from a common cam ring unit housed in the front portion of the engine body. The cams are formed in two rows on the outer surface of a steel ring which runs on a flanged cam bearer. The unit is driven at one-sixth engine speed in opposite direction to that of the crankshaft. Each row of cams includes employment of a one-piece crankshaft has been made pos- sible. In the two-row models the two crank throws are 180° apart, while in the single-row models there is, of course, but a single throw. The general appearance of the crank- shafts of the various models is well shown by photographs. The two main bearings for the crankshaft are of the plain uncaged roller type, and are located on the shaft next to front and rear webs respectively. The thrust bearing is, as already stated, housed in the front cover, and incor- porates a small roller bearing for steadying the front end of the crankshaft. Induction System.—The induction system of the Armstrong Siddeley engines is somewhat unusual in that use is made of a centrifugal fan mounted on and driven by the rear end of the crankshaft. This fan, it should be pointed out, is not to be confused with the blower in the supercharged types of engine, as its speed is too low for it to give any supercharging effect. Its function is to mix thoroughly the charge from the car- burettor and to assist in its conveyance, and even distribution, through the induction pipes which radiate Standardisation : These three sizes of cylinders and pistons serve the whole range of engines : Left, "Genet"; centre, "Mongoose," "Lynx," and "Jaguar"; right, "Leopard."three equally-spaced cams, the front ones operating the inlet valve tappets and the rear cams the exhaust valve tappets. Pistons and Connecting Rod Assembly.—The pistons are Y-alloy forgings, with two compression rings and one scraper ring in grooves turned just below the piston crown. There are no stiffening ribs below the piston head, the gudgeon pin bosses being supported by the special formation of the piston walls. The tubular gudgeon pin floats both in the bosses and in the small end bush of the connecting rod. The connecting rod assembly is of the type having a master rod and six auxiliary rods. The master rod has a split big end, which in the older models was a unit separate from the master rod. The latest version shows a different arrangement, that of the " Leopard " being illustrated by a photograph, while the new " Jaguar " and " Lynx " assembly is shown in a sketch, which is self explanatory. In the " Leopard " all the rods are of H-section, while in the new " Jaguar " and " Lynx " models the master rod is H-section and the auxiliary rods tubular. The Crankshaft.—By using a split master rod big end, the The " Genet " induction fan and covers. out from the fan casing, to the combustion chambers. The carburettor delivers the gas to the fan induction chamber on the back of the engine. This chamber is closed by the back cover. The shape of the fan varies slightly with the type of engine, but the photograph of the " Genet " fan is typical, in a general way, of all models. Lubrication System.—The dry sump principle of lubrication is employed in all Armstrong-Siddeley aero engines. An oil pump unit, incorporating a pressure pump and a scavenge pump, both of the meshed pinion type, is fitted below the front cover of the crankcasc. The upper is the feed pump, and is served direct from the tank. It delivers oil under pressure to the thrust bearing and to the big end bearings, while the two main bearings, the wrist pin and gudgeon-pm bearings, cylinder walls, cam gear, etc., are lubricated by splash. Superfluous oil collects on the inner walls of the engine body and drains to the sump, whence it is drawn by the scavenge pump via heater jackets around the induction fan casing and back to the tank, passing through filters on the way. Ignition.—In all types high-tension magneto ignition is employed, the ignition system being duplicated to ensure reliability. The placing of the magnetos varies somewhat with the type of engine. Thus, in the " Leopard," " Mon" The Armstrong-Siddeley reduction gear is very simple. The ratio is 0-657. goose," and " Genet," the two magnetos are mounted on the front of the engine, while in the " Jaguar " and " Lynx they are housed behind the engine bearer. The Geared Types.—Several of the Armstrong-SiddeJey models are now available in geared form, thus giving tiie advantage of better propeller efficiency and greater maximum power. The type of gear adopted is of a simple epicycle type, and is illustrated in one of our photographs. An inter - ally-toothed gear wheel rotates at the same speed as tne crankshaft, to which it is attached. This internally-tootneu gear wheel drives satellite gears housed in a cage on the ai screw shaft. These satellite gears revolve in the same dire - tion as the crankshaft and internally-toothed gear, and 358
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