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Aviation History
1964
1964 - 2112.PDF
BAC.221 Slender-delta Research Aircraft BY THE TECHNICAL EDITOR T first glance, the British Aircraft Corporation 221 supersonic research aircraft appears to be an aerodynamic scale model of the Concord airliner. In fact, the wing of the 221 is not a direct scale of that of the Concord, and the new research aircraft is required for basic investigation into the general propertiesof slender- delta aeroplanes. In particular, it has been built to explore the behaviour of a slender delta wing at angles of attack high enough to generate a powerful vortex above the leading edge. Such a vortex increases the lift available at high angles of attack from a sharp-edged wing with this type of planform, and since about 1955 it has been one of the major subjects of interest to the Aerodynamics Department of the Royal Aircraft Establishment at both Farnborough and Bedford. It was at this time that work began on the long programmes of fundamental research into possible con- , figurations of the slender-delta form suitable for a supersonic transport, and numerous models were made for wind-tunnel investi- gations. The data on lift, drag and stability obtained with these models have provided the major part of the foundation upon which is based the aerodynamic design of the Anglo-French Concord. Neverthe- less, the precise behaviour of a slender delta wing varies with Reynolds number in a manner that cannot readily be predicted, and it was soon apparent that the RAE had a requirement for a full- scale research aircraft. With such an aircraft it would be possible to establish the correlation between tunnel models and full-scale results, and the ability to do so would in turn appreciably increase the accuracy of interpretation of data obtained from later models. Britain was timid in entering the supersonic era. She has so far flown only three types of supersonic aircraft, two of these being research designs, the latest of which is already a terminated pro- gramme. But the two Fairey FD.2 research machines have given an excellent return for the small outlay invested in them. In March 1956, Mr Peter Twiss, in the first FD.2 WG774, set a world absolute- speed record of 1,132 m.p.h., surpassing the previous record by no !ess than 310 m.p.h. Fully described in this journal on April 25, 1958, the FD.2s were instrumental in setting Dassault on the road which led to the family of Mirage aircraft which have become a world-wide success. In this country they gave valuable service at the RAE Bedford in providing data on the behaviour of an aircraft fitted with a 60° delta wing. From 1958 they were also used for other research, including investigations into ejector-type propulsive nozzles, which can provide substantially greater thrust at high supersonic speeds in return for a penalty in take-off efficiency. During 1958 the Fairey Aviation Co and the RAE discussed the possibls extension of FD.2 research by fitting a new wing of the curved "ogee" planform which preliminary tunnel investigations had indicated as having a favourable combination of lift, drag and stability characteristics at Mach numbers of the order of 2. In September of that year Fairey submitted a formal proposal for an aircraft based on the FD.2 but having an ogival wing integrated with the fuselage after the manner of the SST project at that time being investigated by Hawker Siddeley. As a result of the new wing plan Fairey proposed that the fuselage should be lengthened by 3ft, but despite this the downward-hinged nose still took with it the foremost portion of the wing. Moreover it was found impossible to locate the centre of gravity sufficiently far forward to match the forward migration of the centre of pressure; and the dorsally positioned engine intakes tended to swallow the leading-edge vortex, especially at low airspeeds when the vortex- generated lift is most valuable. In 1960 the UK aviation business of Fairey Aviation was taken over by Westland Aircraft. The latter company assumed respon- sibility for the Gannet programme, but the proposed modification of the FD.2 was given to Hunting Aircraft Ltd, and a Ministry of Aviation specification was issued to cover it. Finally, in July 1960, Bristol took over the programme to produce a modified FD.2 as part of a general redistribution of work-load within the newly formed British Aircraft Corporation. In August 1960 Bristol Aircraft, now British Aircraft Corpora- tion's Filton Division, proposed two types of modification of the FD.2 ; (1) with an optimum ogival wing,a 6ft fuselage extension and a much taller undercarriage; and (2) a minimum conversion, without fuselage extension and retaining the existing landing gear. Both proposals specified an Elliott Bros autostabilization system, and
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