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Aviation History
1929
1929 - 0734.PDF
FLIGHT, APRIL 11, 1929 cylinders, and develops a normal power of 135 b.h.p. at a speed of 1,620 r.p.m. The two extremes, as it were, of the Siddeley aero engine family have this in common with the rest that they are radial air-cooled, and that many of their detail features are similar. They have not, however, actual components inter- changeable with the other three types, those of one engine being larger than the standard and those of the other smaller. These two engines are the " Leopard," of a normal power of 710 b.h.p., and the " Genet," with a normal power of 80 b.h.p. The " Leopard " is, like the " Jaguar," a fourteen-cylinder radial, but its cylinders are of greater bore and its pistons have a longer stroke than those of the " Jaguar." The " Genet " is a light 'plane engine, with five cylinders, similar to, but smaller than those of the three main types. Apart from the size of its cylinders, the " Genet " also differs in that its " odd " cylinder is at the top, while in the " Mongoose " the odd cylinder is at the bottom, with the two upper cylinders leaving a gap at the top centre line. This arrangement of the cylinders of the " Mongoose " has been chosen, we believe, in order to give the pilot a good view straight ahead, between the two top cylinders. The Armstrong Siddeley aero engines are produced on a large scale in a modern up-to-date factory equipped with the latest machine tools which it is possible to obtain, and hand fitting has been practically eliminated, so that strict interchangeability of parts is achieved. The result has been that, what with the care taken in manufacture and design, these engines have established an excel- lent reputation at home and abroad. The " Jaguar," hitherto the type most extensively used, has been fitted with excellent results in types of aircraft covering the entire range from single- seater fighters, through two-seater re- connaissance machines, deck fighters, seaplanes and flying-boats, to large commercial aircraft. In this connection it is of interest to mention that the " Jaguars " which have been in use on the London-Paris route of Imperial Air- ways, Limited, in the Armstrong Whit- worth " Argosy " machines, have estab- lished periods of running of 400 hours between overhauls. Three " Argosies " on the London-Paris route have, between them, now flown something like 5,000 hours, so that the total distance covered is somewhere between 400,000 and 500,000 miles, with excellent reliability, and without any machine sustaining any mishap resulting in injury to a fare- paying passenger. In service aircraft also, the " Jaguar " in its various types and forms has done remarkably well, so that it is small wonder that this engine is now in service in no less than twenty different countries throughout the world. The direct-drive " Jaguar " is, of course, the type which has so far done most to establish the reputation of the Armstrong Siddeley aero engines, but the geared version, now in production, promises ex- tremely well, and it should be noted that the new " Argosies " which have been ordered by Imperial Airways, Limited, and which are to be used on the London-Basle section of the Empire air route London-Egypt-India, will be fitted with geared Jaguars." The fourteen cylinders give extremely smooth running, while the 3 to 2 reduction gear enables better propeller efficiencies to be obtained in machines with rela- tively low cruising speed ; finally, the use of gearing permits higher engine speeds to be used for taking off, so that the very Ungeared JAGUAR Superchonjed "JAGUAR gratifying results obtained with the older " Argosies " should be consider- ably exceeded with the new types. For heavy types of service aircraft, the advantages of the geared engines are, of course, very similar to those obtain- ing in commercial types. The supercharged " Jaguar" is, of course, chiefly intended for service fly- ing, where the maintenance of full power to great altitudes is of importance. This type of engine has been in successful use by Royal Air Force squadrons for more than three years, and the supercharged " Jaguar " is claimed to be the first really practical supercharged aero engine in the world to be fitted as standard to service aircraft. This engine incorpo- rates the very latest developments in supercharging equipment, and must be regarded as in the very front rank of engines of this type. It is not intended to discuss in detail this week the constructional features of the Armstrong Siddeley aero engines. This must be reserved for a future occasion. But a few words to supple- ment the table of particulars given on page 293 and the power, etc., curves on page 296, may be of assistance. To fix one's idea of relative sizes, it is worth noting that the " Leopard " is of 47 litres capacity, the "Jaguar" of 24-8 litres, the "Lynx" of 12-4 litres, the "Mongoose" of 8-85 litres, and the " Genet " of 4-12 litres capacity. The standardisation of bore and stroke in the case of the " Jaguar " and " Lynx " types results in all the " Jaguars " being of the same capacity whether direct drive, geared or supercharged ; and similarly, all the " Lynx " types are of equal capacity and exactly one-half that of the " Jaguar." It will also be noted that standard compression ratio of 5 to 1 has been adopted for all thf engines, with the exception of the " Genet," in which the ratio is a little higher, i.e., 5J to 1. So man ' of the parts of the Armstrong Siddeley aero engines having been standardised, and the range in power obtained by varying the number ol cylinders, it is not without interest to examine the table of data given on page 293, and to ascertain what might be termed the relative "efficiency" «l the various engines. Choosing as a basis for such comparison the " horsepower per litre capacity," we find the httle "Genet" almost" ranking highest, with a figure of 19-4. For the " Mongoose, the figure is 15-25; for the super- charged " Lynx " 14-7 ; for the geare! " Lynx IV " 18 1 ; for the direct-driv. "Lynx IV" 17-35; for the_ super- charged and geared "Jaguar" \ii_; for the supercharged "Jaguar" 13-7; for the geared " Jaguar VI " 19-5 ; for the geared " Jaguar IV " 17-1 ; for th- direct-drive " Jaguar IV " 16 1, and for the " Leopard " 15-1. These figures al! refer to normal power. In the case oi the supercharged types, the figures are, of course, unfair, as these engines do not. develop their power at ground level but at some particular altitude. Taking, instead, the " power at rated altitude we obtain, for the supercharged "Jaguar ^ 15-5 h.p./litre capacity ; for the geareu Jaguar" 17-1, and for the supercharged "Lynx" 16 I. It is rather remarkable that, taking the two extremes of power, the 710 h.p. " Leopard" and w- 80 h.p. " Genet," the difference should be only 4-3 h.p./nt The question is often asked by people outside the avi^a°"world whyiit is that aero engines do not develop anytnin,, and supercharged 294
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