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Aviation History
1953
1953 - 0031.PDF
9 January 1953 3i A hypothetical crescent wing, based on that of the Handley Page Victor it is not suggested that the aircraft has a wing of precisely this con figuration). The drawing has been prepared to show a possible location for the main spar, the decreasing thickness/chord ratio towards the tips and the arrangement of typical leading-edge flaps on the thin outer wings. say nothing of initial stressing) and the use of outer-wing sections of extreme thinness. But it is doubtful if the objections are really as formidable as has been supposed across the Atlantic: while it would be inadmissible to discuss relative merits of the Handley Page bomber and its con temporaries at this early stage, there is a strong body of opinion that the crescent wing is a very much better proposi tion than the thin conventional swept wing of the Boeing bombers. Most of the initial crescent-wing theory was formulated in Germany during the war, particularly by the firms of Arado and Blohm und Voss, although neither firm si'.cceeded in building a prototype for flight testing. At the end of the war Handley Page, Ltd., became interested in the possibilities offered by this layout, and proceeded to develop the crescent wing along their own lines. After extensive tunnel testing, a prototype wing was built and fitted to a Supermarine Attacker fuselage. Conversion of this aircraft, which also involved the fitting of a new tail, was carried out by Blackburn and General Aircraft, Ltd., in 1948. This test bed could probably have taken the wing to about Mach 0.9, but unfor tunately it was written off following structural failure during a high-speed pull-out, in which the test pilot, D. J. P. Broom- field, lost his life. Noteworthy features of the wing as seen on the H.P. 88 were the provision of large, area-increasing flaps inboard, and leading-edge flaps on the outer sections. Both these features have, as far as can be ascertained from the officially released photographs, been retained in the H.P.80 bomber. At this point it might also be mentioned that the H.P.88 featured an abnormally high tailplane and rear-fuselage air brakes; the former, at least, is prominent in the publishable photo graphs of the H.P.8O3 and it is quite likely that "Sabre-type" air brakes are also fitted. The drawing at the top of this page is not intended to represent the actual wing of the H.P.80; but our artist has included the leading-edge flaps of that bomber, because they are clearly visible in the released photographs and are of absorbing interest. These flaps are bigger than any previously seen, and their range of movement is very great. Further more, they are mounted on the outer wing panels only and are in two sections. In the photographs published in Flight last week these flaps were probably at their limit of downward travel, and the inner portions were seen to be depressed farther than the outer sections. Leading edge (or "droop-snoot") flaps have been found on several unswept aircraft in recent years, among which may be named the Supermarine 508 and the Grumman Panther. They are not added auxiliary surfaces, but are the leading edge of the wing itself, hinged at about 15 per cent chord. An upward deflection of the leading edge would result in an increase in lift and a considerable increase in drag, the overall gain being very slight. On the other hand, downward movement increases the maximum lift-coefficient and also increases the ideal angle of attack of the wing, the increase in lift being equal to that obtainable by depression of equal-area flaps beneath the trailing edge. It may be remembered that the H.P.80 has extremely thin outer wings; in fact, the thickness /chord ratio of these sec tions is undoubtedly less than that employed on any other aircraft of this size. Thin wings with sharp leading edges are particularly amenable to the leading-edge flap, which can provide a better nose entry at high angles of attack and increase the camber to afford a substantial increase in maxi mum lift coefficient. A further point, probably not applicable to the H.P.80, is that leading-edge flaps are far more effective than the conventional pattern at supersonic speeds; trailing- edge flaps obtain most of their lift increase by raising the pressure beneath the wing, but at supersonic speed the air beneath the wing cannot be informed of the presence of the flap—whereas the leading-edge flap can do its work by altering the pressure of the air behind it. A drawback to leading-edge flaps is the fact that they have an unstable hinge moment, i.e. when deflected they tend to move uncontrollably to the limit of their travel. This in turn demands the employment of extremely powerful long-travel jacks or, alternatively, an operating linkage driven by an irreversible motor; it will be interesting to see what arrange ment has been adopted for the inner and outer sections of the leading-edge flaps of the H.P.80. These devices are particu larly beneficial in the landing case, which requires a high angle of attack at which a thin, sharp-nosed wing is notorious ly inefficient. Depression of droop-snoot flaps when landing is preferably accomplished with drooping ailerons to obtain still further gains in lift coefficient. The crescent wing is claimed to be a particularly advan tageous layout from a number of structural and operational viewpoints—apart from the aerodynamic and aero-elastic gains which it affords. For one thing, the extreme sweep of the centre wing carries the main spar forward of the bomb- bay, so permitting the carriage of very large weapons. Behind the spar, the massive bogie undercarriage units can fold away forward without cutting any major structural members. The four Sapphire turbojets are also housed behind the main spar, and are consequently eminently accessible without incurring severe structural weight penal ties. Another advantage—pointed out by Handley Page's chief designer, in a contribution to his company's house journal—is that, since the main wing structure is ahead of the power plants, there is little likelihood of serious structural failure as a result of engine fires. The new Handley Page bomber is an unusually large aircraft, and it is a matter of great importance that it should be readily divided into sub-assemblies for transport. The crescent wing, at least, sub-divides easily by virtue of its inherent layout, with consequent gains in ease and cheapness of construction and in operational major overhauls. U.S. BASES IN SPAIN? SHORTLY after Mr. Eisenhower takes office as president—on January 20th—an agreement is expected to be signed between the United States and Spain for a mutual-aid pact. In return for the use of airfields, naval bases and other facilities, America would help Spain to improve her communications (particularly roads and railways), give general economic aid and, in addition, develop the bases granted. The American Assistant Secretary of State for Air, Mr. Huggins, with Brig.-General Washbourne, Director of Air Installations, visited Madrid a few weeks ago to work out details, but so far no definite announcement has been made about the selection of bases. Newsoaper reports mention Barajas (outside Madrid) and Seville as being two likely main air bases, while Cadiz and Cartagena, on the Adantic and Mediterranean coasts respectively, are likely to be the principal naval centres. At least six other subsidiary bases will probably be agreed upon. Some £454 million of mutual security aid has already been earmarked for Spain.
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