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Aviation History
1933
1933 - 1340.PDF
FLIGHT, DECEMBER 28, 1933 Fig. 32 : Double-row radiais. The Armstrong-Siddeley " Tiger "' between a French " Mistral Major " and a Pratt &. Whitney " Twin Wasp." Gnome K.14 still having to meet at least as serious, and probably greater, cooling difficulties as on the radial type. I suggest that the most promising solution is the double row radial in compact form. There is at present a strong school of thought both in Europe and America in favour of the 14-cylinder double row staggered radial engine for this category, and Fig. 32 shows a composite picture of the British Armstrong- Siddeley " Tiger " engine of 32.7 litre (1,994 cu. in.) capacity, the French Gnome " K.14 " engine of 38.6 litre (2,360 cu. in.) capacity, and the Pratt & Whitney engine of 30 litre (1,830 cu. in.) capacity, representative of the most advanced conceptions along these lines, and it will be interesting to watch the development of these similar types. Fig. 33 shows side views of the Gnome " K.14 " and the Pratt & Whitney "Double Wasp" types. Although externally it would appear that all three engines present a strong family likeness, the American design differs considerably from the European types in several respects, the crankcase being built up of three forgings, with a central division wall, and it is of smaller swept volume, and would appear to have been laid out along the lines of high-speed development. I suggest that if the air-cooled engine protagonists are going to hold the field against the liquid-cooled engine in this category, where high efficiency will probably count more than in other types of aero engines, and light weight, compactness, and low specific fuel and oil consumption are of the utmost importance, neither the staggered radial nor the multi-bank in-line air-cooled engine may be the ultimate solution. I suggest instead the double bank in line engine as first seen in the design of the Curtiss " Chieftain " of some years ago. This layout lends itself to the use of both sleeve and overhead camshaft valve gear, one of which will be necessitated if a considerable increase of crankshaft rotation is to be satisfactorily em ployed, and it also enables a very stiff crankcase construc tion to be achieved. During the period under review I suggest that there will be a call for an engine of this type of 850 to 950 h.p., which should develop its power from 20 to 25 litre (1.220 to 1,525 cu. in.) capacity. Category (/)—Large Flying-Boat and Large Air Liner Type Engine Finally, with regard to the really large power plant for projected marine and civil aircraft, I am afraid that I have no slide from which to draw upon my fancy, but I suggest that, during the period under review, there will be a demand for a power unit of 1,000 h.p. to 1,200 h.p. which may be met by an air-cooled engine. Owing to the size of the aircraft, scale effect will come into the layout, and cooling conditions may not, therefore, be so severe, but considerable attention must be paid to fuel consumption, and the engine must be capable of run ning for long periods without attention or maintenance. If such an engine is required within the next five years, I think it must be of the four-cycle petrol type, but I would suggest that the most hopeful solution may be the compression ignition or Diesel engine of the two-cycle type, and of large swept volume of the order of 55 to 65 litre (3,355 to 3,965 cu. in.) capacity, and capable of maintaining a continuous cruising horse-power of 800 to 900. I am afraid these notes only provide a very precursory review of possible air-cooled aircraft engines for the future, but I hope they will provide some " food for thought." I wish to thank the British Air Ministry, the Bristol Company, and other constructors, for their permission to make use of certain data and to exhibit slides of their products. r~- Fig. 33 : Side views of the " Mistral Major " and " Twin Wasp." 1318
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