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Aviation History
1929
1929 - 0909.PDF
FLIGHT, MAY 2, 1929 THE ARM O ENGINE! IN our issue of April 11, 1929, we published an illustratedarticle giving the chief characteristics of the remarkablerange of aero engines produced by Armstrong-Siddeley .Motors, Ltd. The present notes deal with some of the main features in the design and construction of these engines, and illustrations are given of some of the major components which go to the make-up of a range of engines which cover powers from 80 to 800 h.p. We have previously pointed out that three main types of engines form the greater portion of the Armstrong-Siddeley range by utilising a number of identical components. In this way are produced the " Jaguar," " Lynx " and " Mongoose " types, each of which may, in turn, be produced in different sub-types, although still retaining all or practically all of the original components common to the series. Thus, in the following notes, unless otherwise stated, the description of a part or assembly may be taken to refer to all three types. Where differences exist they will be indicated. The Engine Body.—Armstrong-Siddeley Motors, Ltd., employ the expression " Engine Body " to indicate the central structure around which the cylinders are arranged, and which carries the main bearings, gears, induction system, etc. As the term is descriptive we have retained it here. The engine body of the Armstrong- Siddeley engines comprises three separate units : the crank- tasc, the front cover, and the baik cover. The crankcase is an aluminium alloy casting, of cylindrical form, "around the circumference of which are arranged the fourteen sockets for tlie cylinders in two rows,st 'iKi;ered in relation to eachoth ^. (This applies to the Jaguar" series and to the Leopard " ; in the " Lynx "ai1 " "Mongoose," as well as in the " Genet," the crankcase "a but a single row of bosses, engines being of the ^•nglu-row type.) The forwardc "(1 ol the engine bodv is t-ios«d by the front cover, which '.'"uses the thrust bearing and wm(;s the mountings for oil _lImP. gas starter distributor, ™es T gear, taPP.ets (in the service sun? ? ) supports. •I he rear of the THE LATEST TYPE OF MOUNTING: A re-designed back cover forms the support for the engine instead of the separate mounting previouslyused. engine body is closed by the induction fan~casing, in the circumference of which are the sockets for the induction pipes. Finally, the rear cover closes the back of 'the induction fan casing, and carries supports for magnetos, tachometer drive, etc. Hitherto, a separate engine bearer has been used, in the form of a cupped steel pressing secured to the engine body by a number of studs. A more recent development is an engine bearer, which is integral with the induction fan casing. Such a bearer is illustrated in one of our photographs. Aluminium alloy is the material em- ployed for the engine body and covers. The Cylinders.—The cylinders of Armstrong Siddeley aero engines are of composite construction, having steel barrels and aluminium alloy heads. The upper end of the barrel is screwed into the head while the latter is hot, and the two are secured together by a locking ring shaped like a cooling fin, as shown in a sketch. The method of securing the cylinders to the engine body is unusual, and forms a patented feature. Instead of a flanged cylinder base, secured by studs to the engine body, as is more usually used, the cylinder of Armstrong Siddeley engines is screwed into a steel adaptor, and secured by a locking ring, in the manner shown in a sketch. The combustion chamber is approximately hemispherical, and has seating for two valves, one inlet and one exhaust, the valve seatings being of alumin- ium bronze, screwed and ex- panded into their sockets in the cylinder head. Valves and Valve Gear.—The valves are of the trumpet type, and are operated by rockers and push rods from the cam gear housed in the forward portion of the engine body. Tvra^oncen- tric coil springs returnreach valve to its seating, whne auxiliary springs of the y^jrasshopper " type maintain ^mtinuous con- tact between rocker and push rod and push rod and tappet. The lower end of each push rod engages with a tappet working in bearings in the engine body. In some of the engines the tappet ends in a spherical head, while the push rod end is cupped, while in others the reverse is the case. In the latest types of engine, the adjustment of the 357
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