MINIMUM DRAG WING CONFIGURATION FOR AIRCRAFT OPERATING AT TRANSONIC SPEEDS

摘要

A wing extension or tip fin is disclosed wherein the tip fin is joined to an aircraft wing to form a nonplanar wing configuration which minimizes induced drag during both low speed and high speed operation of an aircraft. The tip fin which is of generally trapezoidal geometry, extends streamwise along the end of the aircraft wing and is canted to project upwardly and outwardly therefrom. Additionally, the tip fin is twisted to toe-out relative to the freestream direction with the angle of twist varying along the lower portion of the tip fin length. Viewed from the side, the tip fin has a sweep angle at least equal to the sweep angle of the aircraft wings with the leading edge of the tip fin intersecting the wing tip chord at a position aft of the wing leading edge. A strake which extends along the upper surface of the wing from the wing leading edge to the tip fin leading edge, forms a smooth transition between the wing and tip fin. To provide maximum aerodynamic efficiency, the length and cant angle of the tip fin are established to reduce the induced drag of the wing-tip fin combination below that exhibited by the wing alone or by a conventional wing of area and span equivalent to that of the combined wing-tip fin. Interference and compressibility drag of the combined wing-tip fin is minimized by controlling the chordwise position of the tip fin and by the strake which not only provides an aerodynamically smooth wing to tip fin transition, but establishes a vortical flow pattern that maintains boundary layer attachment under high speed flight conditions. Further, the area of the tip fin is established for minimum profile drag, the variation in tip fin thickness ratio further minimizing interference drag and the tip fin twist compensates for spanwise loading on the wing to reduce induced drag.