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Aviation History
1944
1944 - 1173.PDF
JUNE 8TH, 1944 FLIGHT 611 Power Plant — Past and Future Qeometric Layout and Number of Cylinders : Engines of 8,000 h.p. by I960 : Jet Propulsion and Qas Turbines : Qreat Britain's Pioneer Work (Concluded from page 583) THE first half of the precis of the 32nd Wright Memorial Lecture read by Sir Roy Fedden before the Royal Aeronautical Society was reported in last week's issue of Flight. Following are the remaining sec tions of the paper. Sir Roy pointed out that although when the war is won we shall obviously continue to provide power plant for our military air force for policing purposes, and also for civil aircraft, we shall employ engines that are available at the * time, but we have learned so much during the present war • thai there are considerable strides that can be made for the future. In principle. Sir Roy continued, I am averse to adapting military engines for peace time use although, ob viously, we shall not throw away all the remarkable ex perience we have gained during the war. As soon as is practical we must develop a new family of engines for civil use, and we must ap proach this goal with a different outlook, giving the maximum attention to long life between overhauls, minimum maintenance costs and servicing, and, above everything, low drag and low fuel consumption. Turning now to this new family of engines, one of the first big questions is that of the breathing mechanism, and I am of .the opinion that we should do well to select the Burt McCollom sleeve valve with bores of up to --* £4 inches for air-cooled cylinders, and j\ inches for liquid-cooled cylinders, in the latter case giving out puts of something hi excess of 200 h.p. per cylinder. It is difficult to be so categorical about- the pros and cons of air and liquid cooling for future high- power air transport power plants. dominant all over the world in ouuu 7000 6000 5000 4000 3000 2000 1000 1908-14; (1914 •18 BR f-'t 'I' 1918 39 1 | I 1 1 1 SP 1 ^ V 1 I —I ECIFIC, to LB/BH. / EICH' P WE 1 POWER 1 1939-4* I1 / J, r » | 1 1 1 1 1 r _4 1 1 1 1 n 1 1 SE "^ -1945-60-/—« X CD 4 x S2 1900 1910 1920 1930 YEAR This shows the progressive development of average engine powers and specific weights, over the last 40 years, and assumed curves for the next 16 years. Air-cooling was pre- civil aircraft before the war, due to the fact that early civil airliners had employed the old type of somewhat complex liquid-cooled engine with separate cylinders, presenting an entirely different proposition from the modern properly conceived, liquid- cooled, self-contained power plant. Further, the liquid- cooled engine should be slightly better on fuel consump tion, and should have advantages in buried installations, although there is much to be said for the air-cooled engine whilst the conventional nacelle mounting is retained. There is no doubt that for the air-cooled engine the ulti mate development of integral finning technique is being approached, and the latest type of special finning lathe completes the whole fin-cutting operation in six minutes, fc cutting 52 fins with 104 tools and removing 20 lb. of metal in the process. In view of the fact that there are likely to be big develop ments in the future on" the gas turbine, which may super sede the reciprocating engine in due course, it would appear that there is insufficient time left to develop piston engines incorporating any major new principles, and the builders of such power plants of the future should make hay while the sun shines with proven geometric layouts. Assuming the state of the war will allow us to devote sufficient energy to new designs during the next twelve months, and accepting that any large aircraft engine-takes five to six years to develop and bring to a satisfactory state of production, the post-war family of engines which are envisaged should come into use about 1950, and will then have a useful life of five to ten years, dur ing which time we are likely to see the gradual decline of the piston engine in favour of the gas turbine. It will be seen from the chart that the power/ weight ratio of conventional en gines which, in 1905, aver aged just over 4 lb. per h.p., dropped steadily until it stabilised at about 1.1 lb./ h.p. in the late 1930s, when outputs reached about 800 h.p. The curves have been extrapolated on what seems to be a reasonable basis, and indicate that by i960 we may expect to see engines of 8,000 h.p., while the power/weight ratio shows a slight upward trend. Basing our predictions on a maximum of about 200 h.p. per cylinder, it will be worth while devoting a short time to assess the potential power output of the various practical types of engines. It would seem the Rolls-Royce Griffon represents about the peak size for 12 cylin ders, and we may expect at least 2,400 h.p. from this type of engine in the next few years. The V-16 is attractive on account of its small cross- sectional area, but it is long and the crankshaft system is difficult. The X-24 has been constructed, in prototype form, in many countries during the last 25 years. In general terms it is not considered economical to transmit more than 3,000-4,000 h.p. through a single crankshaft: this layout is practicable for powers up to that figure. In order to alleviate these difficulties, the X-24 twin- crank is suggested, and although for high powers this engine has advantages for air-cooling, it does not seem as attrac tive as the H twin-crank for liquid-cooled engines. The W-24 twin-crank seems a logical development as an emer gency, but it is believed that this design could only be considered as a wartime policy, the H-24 twin-crank being a more compact solution. Trie Napier Sabre of 2,200 h.p. has already proved this design to be a classic liauid cooled 1940 1950 1960
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