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Aviation History
1949
1949 - 0235.PDF
FEBRUARY IOTH, 1949 FLIGHT 153 JET LINERS FOR«- SHORT. RANGE Analysis of Ope rating Economy WITH the declared purpose of showing that the opera-tion of jet aircraft between London and Paris iswell worth while, Air Commodore Sir Frank Whittle, K.B.E., C.B., R.A.F. (Retd.), lectured before the Aero Club de France in Paris on January 20th, his subject being " London to Paris by Jet Plane." The problems and possibilities of operating pure jet transport aircraft over short ranges were presented with characteristic lucidity. The Air Commodore introduced his subject by observing that the distance from London to Paris is about 225 miles and that this distance can be covered in thirty minutes by an aircraft powered by simple turbojets. "Is it," he asked, " worth it? " Some people, he said, argued that since the traveller has been something like two hours in travelling to and from the airports at each end, and waiting about, a saving of half an hour in three hours was not of great importance. There might, he confessed, be some truth in this from the passen- ger's point of view, unless there were other advantages, such as increased comfort and safety, and reduced fares ; but from the operator's point of view, to be able to do the journey in half an hour instead of an hour meant a very big increase in the revenue-earning capacity of an aircraft, unless the increased speed had to be paid for heavily in reduced payload. Speed and Efficiency There followed a summary of the advantages of the turbo- jet as compared with the piston engine and airscrew, and a dissertation (the substance of which is already familiar) on thrust and power characteristics, weight and fuel con- sumption of the turbojet. Under the last heading one point invited special attention, namely, that at 600 m.p.h. the thrust horse-power was nearly three times its value at 200 m.p.h. but the fuel, consumption was only 1.3 times. This brought up one of the most fundamental characteristics of the turbojet—the dependence of overall efficiency upon forward speed. Air Commodore Whittle explained that a figure of 1.21 lb/hr/lb thrust at 600 m.p.h. corresponded to 0.755 lb/t.h.p. /hr, which was almost certainly lower than could be obtained with a piston engine and airscrew at that speed. Thus, even at high speed at sea level the turbojet The Avro-Canada C-102 (Four R.-R. Derwent Ss) A Paper read by A. Cdre. Sir Frank Whittle before the Aero Club de France was at least equivalent to the piston engine and airscrew in overall efficiency. At height there was a substantial improvement due to the effect of low air temperature. There were plenty of signs, said the lecturer, that the turbojet was going to live up to its promise of providing far greater reliability and less need for maintenance than the reciprocating engine. Already experience in R.A.F. fighter squadrons had shown that the man-power required foi sei\ icing and maintenance is about one-third of that for The Fokker F-26 Phantemt project (Two R.-R. Nenes) piston engines. There were signs that a much lower figure than this would be obtained in time. Several recent endur- ance runs in Britain indicated that servicing and main- tenance would require less than one man-hour per engine in 10,000 miles of flying. There would also be a large reduction in the man-power required for servicing the air- frame, etc., because a large proportion of troubles experi- enced were caused by engine vibration. Considering the question of first cost, A. Cdre. Whittle considered that there was a tendency to assume that the cost of the turbojet would be about the same as that of the piston engine. He had no doubt, however, that for compar- able quantities the turbojet would be cheaper, and in the case of types with centrifugal com- pressors, very much cheaper. It had to be admitted that operating conditions which re- quired fuel reserves to be carried for long periods of stacking at low speeds and low heights were very adverse to the jet aircraft which must fly fast and high for good . The Avro Tudor VIII (Four R.-R. Nenes)
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