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A variable-sweep wing, colloquially known as a "swing wing", is an airplane wing, or set of wings, that may be modified during flight, swept back and then returned to its previous straight position. Because it allows the aircraft's shape to be changed, it is a feature of a variable-geometry aircraft.
Sweeping the wing has the effect of reducing the curvature of the body as seen from the airflow, by the cosine of the angle of sweep. For instance, a wing with a 45 degree sweep will see a reduction in effective curvature to about 70% of its straight-wing value. This has the effect of increasing the critical Mach by 30%.
The first successful wing sweep in flight was carried out by the Bell X-5 in the early 1950s. In the Beech Starship, only the canard foreplanes have variable sweep. Oblique wing: a single full-span wing pivots about its midpoint, as used on the NASA AD-1, so that one side sweeps back and the other side sweeps forward.
One problem with the forward-swept design is that when a swept wing yaws sideways (moves about its vertical axis), one wing retreats while the other advances. On a forward-swept design, this reduces the sweep of the rearward wing, increasing its drag and pushing it further back, increasing the amount of yaw and leading to directional instability.
The L-39-2 was retained by Bell to support their X-2 program, being modified with a new fully swept wing of a design intended for the X-2. [ 1 ] [ 3 ] On December 12, 1949, both aircraft were transferred to the Lewis Research Center before being sold for scrap in 1955.
The export version was designated Su-20, and was first flown on 15 December 1972 by A. N. Isakov. The Su-17M was manufactured between 1972 and 1975, and entered service in 1973. The Su-20 was exported to Egypt, Poland, and Syria. The Su-17M was fitted with a modified fuselage and wing-sweep mechanism (without driveshafts).
Four basic configurations which have used vortex lift are, in chronological order, the 60-degree delta wing; the ogive delta wing with its sharply-swept leading edge at the root; the moderately-swept wing with a leading-edge extension, which is known as a hybrid wing; and the sharp-edge forebody, or vortex-lift strake. [7]
The P.1101 V1 prototype was of duralumin fuselage construction, retaining the outer wing section of the Me 262, but with larger slats and, as mentioned previously, the wing sweep could be adjusted on the ground from 30, 40, to 45 degrees; this was for testing only and never intended as an operational feature. [2]