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Aviation History
1931
1931 - 0100.PDF
SUPPLEMENT TOFLIGHT JANUARY 30, 1931 THE AIRCRAFT ENGINEER definitely adopting the geared type; Farman engines are also geared, but many of the ergines by other makers are of the direct-drive type, although an alternative geared type is sometimes available. The incorporation of a gear reduction to the airscrew would appear to be a wise step, in view of the higher engine-rotation rates now being sought and the relative inefficiency of the airscrew at these high speeds. The reduc- tion in airscrew noise with the lower tip speed possible in the geared engine is also very appreciable, and particularly valuable for commercial transport. The Gnome-Rhone " Mercure." (PLK;HT Phcto.). The tendency to offer alternative gear ratios on~engines is a noticeable feature. The Bristol Company were showing the Jupiter IX F and Mercury IV A and V A engines, all of the established Bristol nine-cylinder radial design, and each engine was fitted with a Farman reduction gear adapted to Bristol requirements. This gear in its simplest form gives a 0-5 gear ratio, and in a specially designed form it is now being made to give an alternative ratio of 0-656. The Rolls- Royce engines of the " F " and " H " series are all geared, there being three ratios available in the former series, namely. 0-632, -0-552, and 0-475. Straight spur gearing is employed throughout, and the crankshaft pinion is supported by roller bearings in a special manner to avoid transverse loads from the reduction gear affecting the crankshaft. Of the wide selection of Armstrong Siddeley engines shown. the larger types—namely, the Jaguar, Panther and Leopard— can be fitted with reduction gear. The gear employed consists of a fixed sun wheel and five planet wheels meshing in an internally toothed ring driven by the crankshaft. The airscrew shaft is integral with the spider on which the planet wheels are mounted, and is therefore on the same centre line as the crankshaft. The Farman engines, both radial and water-cooled types, were fitted with their proprietary gear reduction, and several other engines by other makers— notably the Gnome Rhone engines, the B.M.W. 12-cylinder, 600-h.p. water-cooled V-engine, and the Siemens nine- cylinder air-cooled radial of 500 h.p.—were fitted with the same type. Supercharging has now more advocates than formerly, many of the engines being made alternatively supercharged or unsupercharged. The supercharger employed exclusively is the high-speed centrifugal compressor, gear-driven by the engine. A division in this class is now becoming more general, in that to the category of supercharged engines with a full-throttle height of 10,000 to 12,000 ft. there is now being added a class with a smaller compressor to give a full throttle height of 3,000 to 5,000 ft. Section of Rateau supercharger. The Rateau type of supercharger is fitted to the Farman engines, and in the drive is incorporated a plate clutch held in contact by the centrifugal force of suitably pivoted levers. Engagement is then smooth, and in addition the gear and impeller is not rapidly decelerated on shutting off the engine. The supercharger can be disengaged if it is desired to econo- mise power when a supercharge is not required. On the Rateau stand were shown several superchargers of similar type, including an exhaust-driven one, but there was no engine with this latter type fitted. To judge by the engines shown, the problem of super- charging to very high altitudes is not being given much attention, except that in one case a two-speed compressor is receiving consideration, so that by its employment the power lost by the normal centrifugal supercharger at low altitudes, when little or no compression of the air is required, may be reduced. Such a supercharger will then work in two stages, the low-speed gear operating for the first few thousand feet and the high-speed gear from there to full- throttle height. Of displacement blowers, which also haw some benefit in economy of power at low altitudes, there was no example in any of the engines shown. Minor points of note in the designs shown were the more common use of a geared fan, as has been used on Armstrong Siddeley engines for some time, to improve the charging efficiency and distribution to the engine ; the provision for starting by hand turning and hand or electrically operated inertia starters, in addition to the standard gas starting; the fitting of an automatic ignition control and automatic boost control on the Bristol Mercury series of engines, and the provisioning on this same series for drives to other accessories. such as a generator, which may be later required ; the general use of petrol pumps, the A.M. and Lamblin pumps being particularly favoured by Continental firms ; and the tendency in many radial designs to place accessories such as the magnetos and fuel and oil pumps, in front of the engine. Section of A.M. fuel pump, type 4. 96/
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