Abstract: A dual-configuration airfoil having a thin profile which is adapted to foster high-speed flight, and having a pivotable portion on the upper surface which is movable upwardly for selectively increasing the thickness of the airfoil. In one embodiment, the pivotable portion pivots about an axis which coincides generally with the leading edge of the airfoil. The thickness of the airfoil when the pivotable portion is fully raised is about twice the thickness of the airfoil when the pivotable portion is fully retracted. A rigid connecting section forms part of the airfoil's upper surface immediately behind the pivotable portion. The connecting section is also movable, such that a substantially continuous and rigid surface is presented to the air moving over the airfoil's upper surface during such times as the pivotable portion is being pivoted upward and downward--as well as when the pivotable portion is fixedly held.