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Aviation History
1946
1946 - 1696.PDF
228 FLIGHT AUGUST 29TH, 1946, The Piston Engine Some Suggestions for its Further Development Within a Limited Power Range : "Halving" Existing Radial and In-line Types By C. D. SOLTZ THE aircraft industry is at an extremely interestingpoint in its career, brought about by the new develop-ments in power-unit design. The jet-propulsion engine in its many variations has already opened up im- measurable future possibilities of flying and has inevitably- brought in its train a series of problems yet to be overcome before its true worth is fully revealed. In this article it is not proposed to indulge in speculations concerning futuristic designs but to loiter somewhat in the realms of the poor obsolescent piston engine which still, I believe, has a future, however constricted it may be. Too much work has been put into this engine for it to be lightly discarded, and perhaps one of the main advantages of the new jet propulsion and turbine-airscrew power units, namely their relative ease of development, may allow a certain proportion of our research and development resources to be concentrated on our first pet whilst still maintaining an economically consistent development staff. It is assumed, maybe erroneously—the writer is merely expressing his personal opinion—that the field of the piston engine for all practical purposes will be limited to 1,500 h.p. as an absolute maximum and to an altitude of 10,000ft. Above that power and altitude the athodyd, the jet-propul- sion engine and the turbine-airscrew will be masters of all they survey. But up to this power it would seem, at the moment, to be economically desirable to utilize our exist- ing knowledge of the habits of the piston engine and not to spend time and labour on attempting the production ol other forms of prime mover. If this view is accepted, the piston-engine designer is confronted with a narrow but extremely interesting field of research in which he should be able with* say, one-tenth of his present resources to increase considerably the efficiency of his engine. A Wartime Handicap • The development history of the piston engine for most designs usually shows an increase in weight /power ratio above the 1,000 h.p. mark. This is surely not inevitable but merely due to the fact that the majority of aircraft- engine designers were caught at the outbreak of the war with a production engine of 1,000 h.p., and in the war years their main energies were concentrated on producing more horse power rather than in fining and paring existing designs down to better weight limits. The impetus that the war years have given to engine and material develop- ment will, without any doubt, have shown us how to do it, and it should be possible now, with all our wartime experience, to lay down the design and development pro- gramme of a successful piston engine of 1,000 to 1,500 h.p. with a weight/power ratio of, say, 0.7 lb/h.p. The follow- ing suggestions on the lines of research and development for a 1,000-1,500 h.p. engine of this weight/power ratio are offered, always assuming that only a small proportion of our labour resources can be devoted to this field. Some of the lines are naturally applicable to designs of lower horse power. It is always assumed in the design of a high-efficiency engine that the power developed is raised to the limit of the anti-knock rating of the fuel. Although the war was really fought on 100 octane fuel (160/130 grade) much development work has gone on, and fuels at least 25 per cent better (130/160 grade) are immediately available. The cost of such fuel is usually not intrinsic but merely a question of potential demand. Increasing the fuel quality immediately allows (always assuming that engine reliability can be maintained) an increase in compression ratio and/or boost pressure, with consequent increase in power from a given cubic capacity and thermal efficiency, the last being the main virtue which the piston engine still possesses. Six years of wartime development should allow this to take place without the previous proportionate increase in weight. If one surveys the materials necessary for the high-effi- ciency piston engine, the one which has progressed least, and perhaps for that reason alone should have inherent major possibilities, is the lubricating oil. Within the last few years slight developments have taken place in the use ditives, mainly of detergent qualities, which have The Merlin has shown how extra power can be obtainld from a given engine size by development. A "half Merlin " issuggested for further improvement. shown considerable promise in the fields of ring-gumming and sludging, and in automotive design the E.P. range of lubricants for hypoid axle designs are established. Such developments should continue to be pursued actively by the engine and oil companies, but the main line of lubrication development should be intensive col- laboration with the metallurgist to produce chemically reactive and adsorbent surfaces, a field of research rela- tively neglected but one which should be exploited no only for its bearing on aviation problems—and this pisto engine must have a long life—but for its importance in connection with practically every mechanism which needs a lubricant. I am not against the theorists of fluid lubrica- tion, but let them not be too one-sided on this matter, and let us have a little boundary lubrication too if it helps the engine designer and can be satisfactorily handled. The fuel and oil development sides have been mentioned first, not because they are the most important but first, because the combustion of the fuel is what forces the piston down and the airscrew round; secondly, because the fuel has already been partially developed to the required standard; and thirdly, because the resources of the oil companies, hitherto fully utilized, may find themselves
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