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Aviation History
1976
1976 - 0087.PDF
CONCORDE NOW ARRIVING could be reduced or delayed by using thin aerofoils and swept- back wings. The problem of how to manu facture structurally sound thin sections, and how to make them generate lift at subsonic speed, seemed daunting. So did the attainment of the great engine powers required. Coincidentally, the jet engine was being indepen- Below, man's first supersonic flight was America's rocket-propelled Bell XS-1 in October 1947, although it is almost certain that Europe was first with Britain's turbojet D.H.108, top, in September 1946, in a flight which resulted in the loss of this tail-less, swept-wing aircraft and its test pilot. dently developed in Britain and in Germany during the 'thirties. The jet engine was, of course, to prove crucial to the achievement of prac tical supersonics, although a rocket engine would first propel man through the "sound barrier," as the compressibility drag rise be came popularly known. The competition of war in 1939- 45 brought home to both sides the speed limit of the traditional pis ton-driven fighter. The squadron pilot discovered in combat, often by accident, the effects of com pressibility and wave drag control. The inefficiency of the propeller above about 450 m.p.h. (700 km/ hr) was well enough known. The ultimate piston - engined wartime fighters on both sides were achiev ing such speeds in level flight at altitude. The fastest British piston fighter of the war, the Spitfire XIX, was a good example. As the Spit fire's free-stream Mach number passed Mach 0-8, airflow over critical parts of the airframe would reach Mach 1 and shock waves would form. Although the Spitfire had remarkably thin aerofoils and control surfaces (compare them with those of the Hurricane), very little was known by R. J. Mitchell and his designers about the be haviour and management of shock waves. When these formed, dur ing high-speed dives from high altitudes, they would produce loss or even reversal of control as flow broke down behind the shock, and as the aerodynamic centre of pres sure (CP) moved aft. The opening of the early-fifties film "Sound Barrier" dramatically portrayed the early mysteries of supersonics, as a Spitfire pilot found he could not recover from a prolonged high speed dive. The future was to be with the explorers and exploiters of power controls, thin aerofoils, swept wings and the jet engine. For the record, the fastest speed ever attained by a piston-engined aircraft—or indeed by any propel ler-driven machine—is believed to have been when Squadron Leader Martindale of the Royal Aircraft Establishment flew a Spitfire XI at Mach 0-92 in 1944. Even allowing for the possible compressibility errors of pitot-static airspeed in struments, air flows over major portions of the airframe must have been well supersonic. By the end of the war, Europe was well ahead with high-subsonic developments. The first swept-wing aircraft to enter combat was the rocket-powered Messerschmitt Me 163. It was a sharply swept, tail less fighter designed to intercept the high-flying US Eighth Air Force B-17G Flying Fortresses. The Me 163's swept wing was not troubled by compressibility until well over Mach 0-8, when the pilot felt the lack of a tail to trim out the rearward GP shift and resultant pitch-down. The Me 163 was not a great success opera tionally, mainly because of its limited endurance and stability. The aircraft came late in the war, and there was not enough time for development. In fact, as post war work in Britain, America and Russia showed, the tail-less swept wing was not the best way into supersonics. In Britain, the de Havilland company tried this for mula, and the D.H. 108—basically a Goblin-engined Vampire nacelle with a sharply swept wing—was flying as early as 1945. The Swallow, as it was popularly known, was intended to be a scale flying model of the D.H. 106 (later the Comet). It was also a research vehicle for advanced new military types such as the fighter that was to become the D.H. 110 Sea Vixen. Experience with the 108 and with the Armstrong-Whitworth A.W. 52 flying wing brought the tail- plane and elevator back. Indeed, power controls and all-moving tails became essential gear in the ascent and conquest of the tran sonic peak. The delta wing and its
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