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Aviation History
1954
1954 - 1386.PDF
FLIGHT, 14 May 1954 611 "FLIGHT" Photographs First prototype of the Handley Page Victor B.1 medium bomber, powered with four Arm strong Siddeley Sap phire turbojets and ex ploiting the principle of the crescent wing, dis cussed by Mr. Lee in his lecture. The air brakes are shown extended. AERODYNAMICS of the CRESCENT WING An R.Ae.S. Section Lecture by Mr. G. H. Lee SOME of the reasons behind the choice of the crescent wing for the H.P.80 Victor were described by Mr. G. H. Lee, B.Sc, D.I.C., F.RJV.e.S. (deputy chief designer, Handley Page, Ltd.), before the Royal Aeronautical Society in London on April 27th. The title of Mr. Lee's paper was Aerodynamic and Aeroelastic Characteristics of the Crescent Wing. This type of wing, began Mr. Lee, had been chosen on performance grounds. The specification to be met had called for long range, good load-carrying ability, high subsonic cruising speed and high cruising altitude, but no one layout was right for every application. In general, a moderately high aspect-ratio would be required, with a high angle of sweep- back to give the high critical Mach number. Unfavourable pitching behaviour at the stall, however, resulted from high aspect-ratio and high sweep, tip-stalling problems becoming particularly acute. The adoption of the crescent wing was essentially a work ing compromise between two methods of overcoming these difficulties—i.e., between high sweep with low aspect-ratio, and moderate sweep on a thin wing of reasonably high aspect- ratio. By progressively reducing both sweep and thickness/ chord ratio, a constant critical Mach number along the span was obtained; the thick wing-root was suitable for stowage purposes; and the overall structure-weight penalty had not proved too great. Handley Page interest in progressive reduction of sweep had begun in 1946. Early experimental evidence had shown that, in regard to behaviour at the low-speed stall, the three- stage-sweep configuration was better than one of constant sweep with high aspect-ratio. The highly swept root which did not stall easily resulted in a tip-stalling problem to some extent, but detail design of the wing/fuselage intersection could remedy this difficulty. Under high-speed stall condi tions, the performance of the crescent wing showed to advan tage, particularly good behaviour being apparent in high-g turns. The need to vary the sweep and thickness/chord ratio to obtain the constant critical Mach number had involved much calculation and experimental work in order to determine the pressure distributions and the most suitable wing geometry. The Royal Aircraft Establishment had co-operated in the necessary high-speed tunnel tests. The stability and control characteristics under conditions of unseparated flow were little different from those of a conventional swept wing of the same average sweep-back angle. The sweep-back reduc tion at the tip of the crescent wing, however, had to be limited because of the danger of a loss of aileron effect, but the aileron power at low speeds was an improvement over that of the straight swept wing. From the aeroelastic point of view, the effect of swept wings on manoeuvre margin had to be considered. Up-loads at the tip, and consequent wing-bending, would normally increase the amount of wash-out and cause a loss of lift at the tips. While a small amount of this effect might be desirable, too much of it would result in excessively violent pull-outs at high speed, the manoeuvre margin becoming either too small or negative. One solution would be to move the spar farther back to give a twisting effect in the opposite direction, but this was not practicable. Neither was it permissible to increase the flexibility of the wing, due to flutter problems and aileron reversal. This twisting effect was largely overcome by the progressive reduction in sweep of the crescent wing. Concerning flutter, no special characteristics had been found which could be attributed solely to the shape of the crescent wing. General behaviour of the wing was similar to that of any swept wing. To meet the specification mentioned, three solutions seemed possible. Examples of these three different approaches were: the Boeing B-47 (straight wings with moderate sweep, high aspect-ratio and podded engines); the Vulcan (delta wing with no tail); and the Victor. The respective solutions to the main problems of obtaining the high critical Mach number could be tabulated as follows: — Problem Tip stall Flaps Manoeuvre margin Flutter Podded engine nacelles Poor. Twist from engines is wrong engine mass- balance Solution Tailless Delta small aspect-ratio large wing area offsets low max C\_ stiff wing stiff wing Crescent less sweep at tip plan-form he'ps normal
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