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Aviation History
1934
1934 - 1301.PDF
DECEMBER 6, 1934. FLIGHT. LIQUID-COOLED ENGINES Their Application to High-speed and Other Aircraft : A Resume of a Paper Read Before the R.Ae.S. by Capt. A. Graham Forsyth BEFORE the RoyalAeronautical Societylast Thursday, Capt. A. Graham Forsyth read a paper entitled " Liquid-Cooled Engines— Design and Application to High-speed and Other Air- craft." Although a cham- pion of the liquid-cooled en- gine, Captain Forsyth made it quite clear that he did not consider the air-cooled engine of no value. On the contrary, he thought it an excellent example of aero- nautical engineering, and recent flights had proved that the liquid-cooled en- gine had a real rival in the air-cooled. Owing to the great improvements made in the cowling of air-cooled engines, the difference be- tween the power absorbed by the cowled air-cooled as compared with the liquid- cooled type had been narrowed down, and on the latest type air-cooled cowlings the drag figures were nearly as good as those obtained from a normal water-cooled system. This meant that further improvements would have to be made in the installation of the liquid-cooled type in order that it might retain its supremacy over the air-cooled. The introduction of evaporative cooling and the use of ethylene glycol as a cooling medium had still further re- duced the drag of the liquid-cooled installation. While on the subject of improvements in aircraft the lecturer stated that in 1934 we were endeavouring to pro- duce single-seater fighters with speeds approaching 250 m.p.h., whereas with our experience we should be producing bombing aircraft with a speed of 250 m.p.h. and single- seaters capable of 300 m.p.h. In America commercial air- craft had been produced with speeds up to 220 m.p.h., fitted with air-cooled engines. The increase in speed had been gained by carefully studying the aerodynamic quali- ties of the aircraft. Generally speaking, the aircraft side of the American machines could not be greatly improved unless some revolutionary change in design came along. Speed of British Aircraft Of British aircraft the lecturer said that, although the construction left nothing to be desired, a great deal could be done to improve the speed by paying greater attention to details. Such items as projecting guns, oil coolers, navigation lamps, bomb racks, etc., required scrapping, and could easily be replaced by producing up-to-date equip- ment properly streamlined. The retractile undercarriage would also need developing if we were to have any hopes of competing against modern aircraft using every known device to improve speed. His reason for introducing the foregoing was to establish the fact that it was not worth while considering the engine side unless it was taken for granted that the aircraft in which it was to be installed would be of an up-to-date type. As it was his belief that for powers over 700 b.h.p. it might be necessary to revert to liquid-cooled engines, the lecturer stated he would indicate where he considered improvements could be made in regard to choosing the right type of engine for various types of aircraft. Fairing-in the cylinder blocks : some arrangements discussed by the lecturer. The installation of liquid- cooled engines had been simplified in recent years. Previously there were radiators on the side of the fuselage and header tanks in the top plane, with a considerable amount ol piping running everywhere in the fuselage. The raised position of the pilot had en- abled a simple installation to be adopted which con- sisted in a combined header tank and separator large enough to carry reserve water, coupled to an under- slung radiator. It was his opinion that ordinary water cooling would die out and would be replaced by eva- porative cooling or ethylene- glycol cooling. The radiator required for glycol cooling was approximately one-third the size of a water-cooling radiator designed for English summer conditions. There was a great deal to be said in favour of evaporative cooling with wing condensers, as their introduction eliminated all radiator drag. It had been demonstrated that there was very little steam lost when the condenser was punctured by gunfire. Advantages of Liquid'cooling Points advanced in favour of liquid-cooled engines were: the design allowed a small engine to be installed in the best fuselage shape ; when used in conjunction with a suit- able cooling system the drag was reduced to a minimum ; when tandem engines were used the engines would func- tion equally well as pushers or tractors; engines could be fitted with reduction gear which enabled the airscrew shaft to be located in the best possible position relative to the engine shaft, thereby producing the best cowling lines ; the construction of the airscrew shaft and drive made it possible to house the operating gear for a variable-pitch air- screw inside the engine, and in certain cases it was possible to arrange for a gun to be fired through the bore of the airscrew shaft; the engine speed was not so limited as on air-cooled engines ; owing to the high revs, it was possible to run with high compression ratios, which resulted in economic fuel consumption; oil consumption was difficult to control in any high-speed engine, but the liquid-cooled engines scored due to the possibility of adopting a lower piston clearance than was generally used in air-cooled en- gines ; liquid-cooled engines were generally lighter than air-cooled radials of the same power ; in large aeroplanes the coolant could be used for heating purposes ; in large flying boats, auxiliary sets were used for lighting, pumping, etc., which could be liquid-cooled and coupled to the main cooling system, thus providing a means of keeping the main engines at a temperature to prevent freezing ; liquid- cooled engines could be installed inside the fuselage or wings, thus making them accessible in flight; and, finally, the liquid-cooled engine was more silent in operation than the air-cooled. From the point of view of weight the liquid- cooled engines scored when the duration was over five hours. Criticising the policv of regarding the present aeroplane as the best method of wasting power, and the idea that
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