Variable-incidence wing

A variable-incidence wing has an adjustable angle of incidence relative to its fuselage. This allows the wing to operate at a high angle of attack for take-off and landing while allowing the fuselage to remain close to horizontal.

An RF-8 Crusader using its variable-incidence wing during a landing approach

The pivot mechanism adds extra weight over a conventional wing and increases costs, however in some applications the benefits can outweigh the costs.

Several examples have flown, with one, the F-8 Crusader carrier-borne jet fighter, entering production.

History

Early designs used variable-incidence wings for control and trim, in place of conventional elevator control surfaces. A patent for a variable-incidence wing was lodged in France on 20 May 1912 by Bulgarian inventor George Boginoff.[1] The Zerbe Air Sedan was a tandem quadruplane flew only once in 1921. The French tandem-wing Mignet Pou du Ciel (Flying Flea) had a variable-incidence forewing and became briefly popular during the 1930s, but was discontinued following a series of fatal crashes.

During World War II, the German company Blohm & Voss developed the variable-incidence monoplane to provide increased lift at takeoff, where the rear fuselage was too close to the ground to allow rotation of the whole aircraft.[2] The fuselage of the Blohm & Voss BV 144 prototype transport sat low on a short undercarriage, allowing passengers to go on and off without the need for additional steps. Another proposal by B&V, the P 193 attack aircraft, was of pusher configuration and could not rotate its fuselage for takeoff without the propeller fouling the ground, so it was given a variable-incidence wing.[3]

Carrier-borne aircraft must have good forward visibility during the descent and approach for a deck landing. Without a variable-incidence wing (or other high-lift device), the pilot must pitch up the entire aircraft to maintain lift at the slow approach speed required, and this can restrict forward vision. By increasing the incidence of the wing but not the fuselage, both high lift and good forward vision can be maintained. The device also avoids the need for a long, bulky and heavy nose undercarriage to raise the angle of attack at takeoff. The Supermarine Type 322 prototype flew in 1943, having been developed at much the same time as the B&V types.

After the war the USA revisited the idea for the jet age. The Martin XB-51 prototype bomber of 1949 adopted variable incidence for much the same reason as B&V and flew in 1949. It was followed in 1955 by the Vought F-8 Crusader carrier-borne jet fighter, the only variable-incidence type to go into production and enjoy a successful service career.

See also
  • Stabilator - a variable-incidence horizontal stabilizer or tailplane.
  • Tiltwing - a type of vertical takeoff plane which tilts its wings and engines.
  • Variable camber wing - in which the aerofoil profile is changed rather than tilted.
  • Wing warping - in which the wing is actively twisted to change the incidence progressively along the span.

References
  1. FR 444010
  2. "Blohm & Voss Bv 144". 1000aircraftphotos.com. Retrieved 2020-07-02.
  3. Hermann Pohlmann; Chronik Eines Flugzeugwerkes 1932-1945, Motorbuch, 2nd Impression, 1982.
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