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Aviation History
1962
1962 - 2326.PDF
THE P.1127 ANALYSED BY TWO CHIEF TEST PILOTS AND AN ENGINE DESIGNER WITH the greatest of all SBAC shows still fresh in our memory, it is already easy to make a considered and objective choice of the most outstanding aeroplane which took part in the flying display. As we have already recorded, an eminent American editor has written that the Hawker P. 1127 "had to be seen to be believed"; and there is little doubt that posterity will accord this aircraft a place ranking with that held by the Wright Flyer and the original Sikorsky helicopter. Valuable accounts of flying the P. 1127 have recently been read by the chief test pilots of the companies responsible for the aircraft and for its engine: Tom Frost, of Bristol Siddeley Engines Ltd. and A. W. "Bill" Bedford, OBE, AFC. AFRAes, of Hawker Aircraft Ltd. In fact, the two papers differ only in various minor details, for their authors collaborated to present a single basic draft for security clearance by the Ministry of Aviation. Mr Frost read his papsr in Los Angeles before the annual symposium of the US Society of Experimental Test Pilots (winning the award for the best contribution) while Mr Bedford presented his as a Main Lecture before the Boscombe Down Branch of the Royal Aeronautical Society. The following text is a synthesis of both papers. In the past, air power could be concentrated at locations overseas only because there existed long lines of communications and well- equipped overseas bases. But the trend is towards the progressive elimination of overseas bases, and only the introduction of V/STOL aircraft will in future permit aircraft to be swiftly brought to bear. It was this consideration, coupled with an eye to a naval application, that prompted Hawker Aircraft and Bristol Siddeley Engines to co-operate early in 1957 in the development of a single-seat strike fighter powered by a single turbofan discharging its whole efflux through two pairs of nozzles capable of being rotated in unison to provide either thrust or lift. There is a fundamental difference between the thrust requirements of a V/STOL aircraft compared with a conventional runway air craft, in that—although both require the same thrust loading, assum ing the same wing loading and L/D, to carry out a given wingborne mission—the V/STOL aircraft must have an installed vertical thrust greater than its weight to achieve a full vertical take-off. Bearing this in mind, it is appropriate to consider how it can be achieved in practice. In the single-seat strike aircraft the two extreme solutions are represented by, on the one hand, the separate lift and propulsion engine approach, and, on the other, the single engine having the ability to vector the total installed thrust by mechanical means so that it can provide both lifting and propulsive thrust. In 1956 Monsieur Wibault submitted an idea to Bristol Aero Engines Ltd using an 8,000 h.p. Bristol Orion engine to drive four centrifugal blowers distributed round the main engine casing like the four wheels of a car. By rotating the casings of the centri fugal blowers it was possible to direct the compressed air, and therefore the thrust, in any direction between the horizontal and the vertical. This arrangement achieved two important features of a lift/thrust engine, namely: fully rotatable thrust; and resultant thrust acting near the e.g. of the powerplant. Unfortunately, this arrangement was clumsy and too heavy for a useful aircraft, and the first step was to substitute for the four centrifugal compressors a single axial compressor, and achieve thrust rotation by means of swivelling nozzles. Following dis cussions with Hawker Aircraft the engine arrangement was finalized in 1957, and became the BS.53 Pegasus ducted-fan engine with both fan air and gas-generator exhausting through rotating nozzles. In this form the Pegasus ran in September 1959. The major part of the fan delivery air is ducted through two outlets situated on either side of the engine, whilst the remainder is passed through the h-p. compressor, combustion chamber and turbines before exhausting through two nozzles at the rear of the engine. Fan and h-p. compressor contra-rotate to eliminate gyro scopic couples. The dominating feature of the engine is the system of rotating exhaust nozzles on both the fan and exhaust streams. How the aircraft might have looked: the Michel Wibault Type 1-4-212 "Gyropter," with four centrifugal blowers drifen by an Orion turboprop
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