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Aviation History
1964
1964 - 2324.PDF
FLIGHT Internmtional, 27 August 1964 331 reheat system. This scheme was shown to be particularly unattrac- tive, since it aggravated the inherent e.g. problem. Further investigations led to the study of Pegasus-type nozzle configurations employing burning in both the hot and cold nozzles, the temperature in the cold nozzles being limited to 800°K. Detailed consideration of the design of an engine in which burning in the hot and cold nozzles was employed from initial development, suggested that three combustion systems would accentuate develop- ment problems. It was shown that, by raising the temperature of the cold burning system to l,200°K and using cold burning only, the same thrust level could be achieved as that obtained with the combination of lower-temperature cold burning together with the rear hot-nozzle burning. Some of the early studies were carried out in close co-operation with the Republic Aviation Corporation. Ultimately the BS.100 engine design was evolved for the P.I 154. Since the "go-ahead" on this engine, design work has proceeded in conjunction with Hawker Siddeley and various aspects of the installation have been progressively finalized. This has been a significant contribution to achieving the P. 1154 programme dates. A major development activity on the BS.100 has been the work carried out on PCB. This work started in the spring of 1961 on small-scale rigs, followed in November 1962 by a full PCB system- test on a Pegasus 2 engine. The basic problem was concerned with achieving efficient combustion in a restricted volume where the flow was not axial. Use was made of Bristol Siddeley ramjet experience, and water flow tests (an established analogy in simu- lating combustion problems). The latter assisted in the combustor design, later confirmed by constructing metal models representing the complete system. The more complex geometry of the final system was simulated in Perspex models for flow-visualization test- ing. These techniques assisted the full-scale combustion rig, where one complete side of the PCB system is represented, and bench testing on a Pegasus 2. These two programmes have demonstrated the feasibility of PCB, and confirmed that there are no fundamental problems associated with it. Intensive development will lead to the evolution of a flight-worthy system. Further development is anticipated by increase in PCB operating temperature giving increased thrust for take-off, and at altitude for improving supersonic acceleration and maximum speed. Altogether the experience gained in operating the P. 1127 has confirmed the claims made originally for the advantages of the Pegasus vectored-thrust turbofan. The larger BS.100 engine retains the turbofan and four-rotating-nozzle concepts of the Pegasus, and thus the powerplant and airframe of the P.I 154 supersonic V/STOL strike aircraft will benefit directly from the four-year experience already accumulated. Twin-engine V/STOL aircraft based on the vectored-thrust engine are now being proposed for long-range strike and intercepter roles. The vectored-thrust engine also has an important application in naval aviation, where significant reductions in approach speeds can be made. The vectored-thrust turbofan has equally important applications to transport aircraft, and extremely short field performance can be achieved by using thrust deflection, especially if combined with fig 7 Multi-intake sponson with lid-fixing wires in position Fig 8 Layout for a vertical-lift short-range military assault transport blown aerodynamic surfaces (Fig 9). Evolution of VTOL transport aircraft necessitates the development of lightweight lift engines, which should be turbofans to minimize the installed engine-plus-fuel weight. The optimum high-speed civil and military VTOL transport must be turbofan powered, and a common engine type of moder- ately high by-pass ratio should be evolved for the vectored-thrust and direct lift engines. Fig 9 Nozzle and wing-flap configur- ations (/) Take-off: flaps at take- off setting, intermediate nozzle deflection (2) (n flight: zero flop deflection, zero nozzle deflection (3) Landing: full flop deflection, full reverse thrust
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