Swept wing
Wing sweep at high speeds was first investigated in Germany as early as 1935 by Albert Betz and Adolph Busemann, finding application just before the end of the Second World War.
It has the effect of delaying the shock waves and accompanying aerodynamic drag rise caused by fluid compressibility near the speed of sound, improving performance.
[2] 3. most commonly to increase Mach-number capability by delaying to a higher speed the effects of compressibility (abrupt changes in the density of the airflow), e.g. combat aircraft, airliners and business jets.
Other reasons include: 1. enabling a wing carry-through box position to achieve a desired cabin size, e.g. HFB 320 Hansa Jet.
[18][19][20] On fighter designs, the addition of leading-edge extensions, which are typically included to achieve a high level of maneuverability, also serve to add lift during landing and reduce the problem.
"[24] To visualize the basic concept of simple sweep theory, consider a straight, non-swept wing of infinite length, which meets the airflow at a perpendicular angle.
Small amounts of sweep do not cause serious problems, and had been used on a variety of aircraft to move the spar into a convenient location, as on the Junkers Ju 287 or HFB 320 Hansa Jet.
[29][30] However, larger sweep suitable for high-speed aircraft, like fighters, was generally impossible until the introduction of fly by wire systems that could react quickly enough to damp out these instabilities.
The result is a weight distribution similar to the classic layout, but the offsetting control force is no longer a separate surface but part of the wing, which would have existed anyway.
He successfully employed swept wings in his tailless aircraft (which, crucially, used washout) as a means of creating positive longitudinal static stability.
The Dunne D.5 was exceptionally aerodynamically stable for the time,[36] and the D.8 was sold to the Royal Flying Corps; it was also manufactured under licence by Starling Burgess to the United States Navy amongst other customers.
[42] Hubert Ludwieg of the High-Speed Aerodynamics Branch at the AVA Göttingen in 1939 conducted the first wind tunnel tests to investigate Busemann's theory.
The Blohm & Voss P 215 was designed to take full advantage of the swept wing's aerodynamic properties; however, an order for three prototypes was received only weeks before the war ended and no examples were ever built.
[45] A prototype test aircraft, the Messerschmitt Me P.1101, was built to research the tradeoffs of the design and develop general rules about what angle of sweep to use.
[47] Germany's wartime experience with the swept wings and its high value for supersonic flight stood in strong contrast to the prevailing views of Allied experts of the era, who commonly espoused their belief in the impossibility of manned vehicles travelling at such speeds.
[49] The M.52 was envisioned to be capable of achieving 1,000 miles per hour (1,600 km/h) in level flight, thus enabling the aircraft to potentially be the first to exceed the speed of sound in the world.
[51] On 14 October 1947, the Bell X-1 performed the first manned supersonic flight, piloted by Captain Charles "Chuck" Yeager, having been drop launched from the bomb bay of a Boeing B-29 Superfortress and attained a record-breaking speed of Mach 1.06 (700 miles per hour (1,100 km/h; 610 kn)).
[34] The news of a successful straight-wing supersonic aircraft surprised many aeronautical experts on both sides of the Atlantic, as it was increasingly believed that a swept-wing design not only highly beneficial but also necessary to break the sound barrier.
[57] This world record stood for less than three weeks before being broken on 25 September 1953 by the Hunter's early rival, the Supermarine Swift, being flown by Michael Lithgow.
[58] In February 1945, NACA engineer Robert T. Jones started looking at highly swept delta wings and V shapes, and discovered the same effects as Busemann.
He finished a detailed report on the concept in April, but found his work was heavily criticised by other members of NACA Langley, notably Theodore Theodorsen, who referred to it as "hocus-pocus" and demanded some "real mathematics".
[40] However, Jones had already secured some time for free-flight models under the direction of Robert Gilruth, whose reports were presented at the end of May and showed a fourfold decrease in drag at high speeds.
In May 1945, the American Operation Paperclip reached Braunschweig, where US personnel discovered a number of swept wing models and a mass of technical data from the wind tunnels.
[40][66][67] The performance of the F-86A allowed it to set the first of several official world speed records, attaining 671 miles per hour (1,080 km/h) on 15 September 1948, flown by Major Richard L.
[68] With the appearance of the MiG-15, the F-86 was rushed into combat, while straight-wing jets like the Lockheed P-80 Shooting Star and Republic F-84 Thunderjet were quickly relegated to ground attack missions.
[69][70] Later planes, such as the North American F-100 Super Sabre, would be designed with swept wings from the start, though additional innovations such as the afterburner, area-rule and new control surfaces would be necessary to master supersonic flight.
[71][12] The Soviet Union was also quick to investigate the advantages of swept wings on high speed aircraft, when their "captured aviation technology" counterparts to the western Allies spread out across the defeated Third Reich.
[78][79] Germany's swept wing research was also obtained by the Swedish aircraft manufacturer SAAB, with the help of ex-Messerschmitt engineers that had fled to Switzerland during late 1945.
[82] The company incorporated both the jet engine and the swept wing to produce the Saab 29 Tunnan fighter; on 1 September 1948, the first prototype conducted its maiden flight, flown by the English test pilot S/L Robert A.
Swept wings would reach Mach 2 on the BAC Lightning, and Republic F-105 Thunderchief, built to operate at low level and very high speed primarily for nuclear strike, but with a secondary air-to-air capability.
