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Aviation History
1954
1954 - 1872.PDF
25 June 1954 Vickers-Armstrongs Valiant B.1 (four Rolls-Royce Avon). and high sweep, tip-stalling problems becoming particularly acute. The adoption of the crescent wing was essentially a working 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 did not prove too great. Handley Page interest in progressive reduction of sweep was first awakened 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 it was found that detail design of the wing/fuselage intersection could remedy this difficulty. Under high-speed stall conditions, the performance of the crescent wing showed to advantage, 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 involved much calcula tion and experimental work in order to determine the pressure distributions and the most suitable wing geometry, and the Royal Aircraft Establishment co-operated in the necessary high speed tunnel tests. Stability and control characteristics under conditions of unseparated flow were little different from those of a conventional swept wing of the same average sweepback angle. The sweepback reduction at the tip of the wing, however, had to be limited because of the danger of a loss of aileron effect. Nevertheless, 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. A possible solution was to move the spar farther back to give a twisting effect in me opposite direction, but this was not prac ticable; neither was it permissible to increase the flexibility of the wing, due to flutter problems and the danger of aileron reversal. In the event, the twisting effect was largely overcome by the progressive reduction in sweep of die wing. As for flutter, no special characteristics were found which could be attributed solely to the shape of the crescent wing; in fact, general behaviour of the wing was similar to mat of any swept wing. It must be noted that, whereas Handley Page's technical direc tor claims mat the crescent wing is "die complete and^only answer to the demands of a most exacting specification" the Boeing company, makers of die B-47 and B-52, hold it to be "a fancy wing, too heavy to be practical." Design features of the Victor include "droop-snoot" leading edges—each in two sections—on me outermost panels; rear ward-moving, trailing-edge flaps, shaped to the jet-nacelle con tours; and large, hinged air-brake panels (mounted on the tail cone) to increase drag for deceleration in flight and on landing. Whereas what appears to be a visual-bomb-aiming position is buik into the nose, mis feature does not appear on enher the Valiant or die Vulcan. Early test flights showed the Victor to have a strong tendency to trim nose-up as ground effect came into play, thus conferrmg valuable "self-landing" characteristics. According to Handley Vickers-Armstrongs Valiant 6.2 (four Rolls-Royce Avon). Page's chief test pilot, any pilot can bring the Victor in gently with power on and with flaps and air brakes in operation, in rain or bad visibility; all tiiat is required of him is to correct for local air disturbances affecting lateral trim until the wheels of the main bogie undercarriage touch down. Then the nosewheel is brought on to the runway and the brakes applied. The Victor has powered controls, wim progressive feel simulation. Vickers-Armstrongs Valiant B.l. First of Britain's V-bombers, the Valiant B.l (B.9/48) is a more conventional design than either the Vulcan or Victor, though it displays great ingenuity in general layout and detail treatment. The first prototype flew in May 1951, and the second in April 1952. Production machines are now being delivered to the R.A.F. The Valiant's high-mounted wing is of generous area and of about 114ft span. Mean sweepback is about 20 deg and the four Rolls-Royce Avon turbojets are housed snugly in the inboard sections. There are no leading-edge slats or other attachments, but boundary-layer fences are fitted in line with the inboard ends of the ailerons. Double-slotted flaps extend outboard almost to the same position. Tail surfaces are slightly swept, and the nosewheel undercarriage has paired main wheels in tandem Very large Russian bomber, apparently with four turbojets.
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