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Aviation History
1953
1953 - 0030.PDF
3° FLIGHT How the H.P.80, or Victor—the name is now officially confirmed—appears inflight. This picture has been prepared from one of the two ground views, so far the only photographs released. The leading-edge flaps have been "retracted" by the artist. THE CRESCENT WING Brief Design-analysis of a New Shape in the Sky WHENEVER the aircraft designer has the choice of a number of fundamentally different structures, each of which suffers from individual disadvantages, it becomes extremely difficult for him to make the initial selection of a layout which, once adopted, can never be changed and the characteristics of which make or mar the aircraft concerned. Such a choice faces the designer of the bomber of today. In order that intercepting fighters shall be forced to reach supersonic speed at intervals during an attack all modern bombers must be capable of cruising at the highest possible subsonic speed. Transonic flight poses severe problems, and the recon ciliation of varying demands has led to a number of families of wings, each of which represents a compromise in the solution of the design requirements. From the aerodynamic viewpoint, a low thickness/chord ratio is essential to postpone drag-rise at high Mach numbers. Wing sweep is a straightforward way of delaying the onset of several transonic problems, and with it the critical Mach number can be raised by 0.3 or more. From the structural aspect, there must be enough area to support the weight of the aircraft reasonably, and sufficient wing-thick ness to carry bending loads. It is also advantageous if the wing has sufficient volume to house the engines, landing gear and fuel, although this procedure has not been followed in the United States. The performance of the aircraft invites a wing of high aspect-ratio to reduce induced drag and so confer good high-altitude performance and range. Equally important are the maintenance of low structure-weight—for the snowball effects of even a 50-lb increase are only too obvious in the final design—and the reduction of drag at cruising speed. Considerations of production recommend a structure with a skin of uniform light gauge, capable of being stretched, drilled and assembled by conventional methods. Finally, the stability and control characteristics of the wing must be impeccable at all speeds and altitudes. In this country, the decision to use large wings to reduce wing loading and add stowage space has resulted in a use ful gain in wing area denied to American bombers. Among the British types the greatest wing area is found in the Avro Vulcan, which represents an original and most interesting solution to the problem. On the other hand, the design staff of Handley Page, Ltd., under Mr. R. S. Stafford, F.R.Ae.S., have developed the crescent wing which is an attempt at achieving the best of both worlds. Their wing is designed for a cruising speed approaching Mach 1, and has FLEXURAL AXIS high aspect-ratio for long range flight at high altitude. The general configuration is shown in the illustrations at the top of the opposite page. With the untapered swept wing of conventional type, tip stalling is likely to occur as a result of outward spanwise airflow. The progressive reduction in sweep of the crescent wing results in an amelioration of the airflow over the tip which confers improved aileron control, particularly at low speeds. A fundamental characteristic of the crescent wing is the fact that the thickness/chord ratio and angle of sweep are varied to maintain the same critical Mach num ber throughout the span. Again, the conventional swept wing suffers from serious inherent aero-elas tic drawbacks, chief of which is probably the fact that loads applied at the tip cause wing twist. Thus, aileron deflection can cause wing twist sufficient to nullify or reverse the aileron rolling moment. By the same token, asymmetric flight loading can cause an aircraft with this type of wing to become danger ously unstable. The crescent wing carries its ailerons ahead of, or on, the flexural axis, as shown in the small diagram above. The applied rolling moment due to aileron deflection is thus augmented—instead of being opposed by—the wing twist which it introduces. It may be remembered that the Boeing designers had to resort to unconventional lateral controls for the B-52 (pages 702-704, Flight, December 5th, 1952), in which a con ventional swept wing is employed. It is appropriate to note at this point that this American company have declared themselves opposed to the crescent as being "a fancy wing too heavy to be practical," and they are believed to have adopted a B-52-type wing for their forthcoming turbojet transport. A report states that this B-52 wing showed "better wind tunnel properties than more complex pat terns." The obvious disadvantages of the crescent wing are a very slight increase in structure-weight, some increase in com plexity (which may be reflected in jigging and assembly, to Aileron "solidity" and rolling sta bility are enhanced by ensuring that the aileron does not lie behind the major axis of flexure.
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