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Aviation History
1951
1951 - 1439.PDF
106 FLIGHT SIKORSKY LECTURE . . . had been experimenting with how to use the helicopter in trans-pott. They had found it an excellent aircraft, and foresaw that, within ten years' time, the bulk of all (air) transport in this countrywould be undertaken by helicopter. We had the ideal conditions for it, i.e. large centres of population separated by comparativelyshort distances. Cruising speeds of the order of 150 m.p.h. could be expected, for experience had shown that with present cruisingspeeds the effect of head winds was great, and this made heli- copter operation uneconomical. Concerning the use of centre-drive and tip-drive, and theweights at which they would be used, he would like to ask if Mr. Sikorsky saw any difficulty in the transmission from turbo-prop-type engines. There were the problems of noise, gears and so on: there might be limitations to disc loadings for passengertransport; engine failure had to be catered for. These might have a strong bearing on the speeds which were practicable for cruisingflight. Mr. Sikorsky replied that he would repeat once more hiscomplete conviction that a good, reliable and practicable trans- mission could be worked out. Present types were quite good, andthe limit was in no way in sight. Practically all modern aircraft engines, and particularly turboprops, used transmission systemsto the airscrew. There was no need to be overawed by the trans- mission problem; there were ways and means of designingreasonable transmissions with respect to weight; systems con- siderably larger than those at present in existence would certainlycome. The future would show. Turning to the subject of higher disc-loadings, Mr. Sikorskyagreed that, at the higher values, landings would certainly become more difficult: but even if high disc-loadings resulted in damageto the aircraft (in an emergency landing) they should not result in damage to the passengers. In the multi-engined helicopter, itmight well be possible in such circumstances to reduce consider- ably the force of landing in precisely similar a way as applied tothe large, multi-engined fixed-wing aircraft. Mr. Raoul Hafner (Bristol Aeroplane Co.) said that nobodycould be more satisfied than he to hear Mr. Sikorsky's opinion that helicopters had come to stay. He then went on to say that,after investigations, he had tentatively come to the conclusion that there was a tendency towards favouring tip-drive as a functionof size. There was the limit imposed by tip speed, and it was patent that, as rotor diameter increased, r.p.m. went down, and the gap between engine speed and rotor speed became considerablefor rotors of great diameter. Gears also became heavier as rotor size increased. Perhaps the very large rotors would be jet-driven,whilst the smaller types would be gear-driven; somewhere, there was a criterion of size, above which jet-drive would be used, andbelow which gear-drive would obtain. He agreed with Mr. Sikorsky that gearing problems were difficult but were notinsurmountable. Mr. Sikorsky replied that there seemed a certain limit beyondwhich tip-drive would become considerably more attractive than centre-drive. Where that limit would come was hard to say,but the sizes with which we dealt were considerably below that limit. For a really large helicopter, the transmission wouldprobably not be of the kind we now knew. It might well be that the shaft would not carry torque but that, instead, a large gearmight form the basis of the rotor hub, torque forces being directly transferred from gear to hub. It might be that the gear would bedriven by (say) four pinions, each from an individual engine, through whatever reduction gears might be necessary. Byincorporating a freewheeling unit close to each pinion, the loss of an engine would not affect the transmission, and the helicopterwould still fly. In general, however, as size increased, there was no doubt that the preference for jet-drive would increase. On behalf of the audience, Mr. Wigdortchik (B.E.A.) accordedan expression of thanks to Mr. Sikorsky. Throughout aviation, he had been a leader, and now the fruit of his life's work wasbeginning to show itself: they could not hear from anyone in a better position to put the helicopter in true perspective. EXHAUST GAS ANALYSISA NEW line of attack is now being taken by Armstrong SiddeleyMotors, Ltd., on the difficult problem of determining the optimum combustion efficiency of a gas turbine. It has long beenknown that analysis of the exhaust gases of an internal combustion engine can give a direct indication of the combustion efficiency,and Armstrong Siddeleys are now applying this technique to the gas turbine. Samples of the exhaust gas are taken during flighttests, and are then sealed in special containers for subsequent analysis in the laboratory. From these samples an accurateestimation can be made of the combustion efficiency under various engine operating conditions, and, although it is early yet to pro-phesy the degree of improvement that may be expected from this new test development, there is little doubt that it can resultonly in advantage to the performance of the engine. NEW RUSSIAN HELICOPTERS DEMONSTRATED AT TUSHINO DISPLAY This photograph, secured at the Soviet Aviation Day display at'Tushino Airport, Moscow, on July 8th, is of unusual interest not only in providing the first views of a new type of Russian helicopter now in service, but in coinciding with our report, on this and the previous page, of Mr. Igor Sikorsky's paper "Helicopters in Peace and War." It will be seen thot the Russian machines have certain features in common with Sikorsky and Bell types, and with the Bristol 171. They are apparently used for military purposes.
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