The purpose of this paper is to present principal aerodynamic characteristics of inverting flaps as determined in test flights and wind tunnel tests, and to review applications of this new device, and of its basic kinematic principle, to the V/STOL aircraft field.Two dimensional tests of double slotted inverting flaps show maximum lift coefficients of over four. Flight tests and three dimensional tunnel data show exceptional aerodynamic features for the new flap, including favorable lift-drag ratio and moment characteristics for high lift 90 deg flap position in approach and landing, and direct control of lift-drag ratio with flap position particularly advantageous for wave off and loiter. General considerations on mechanical, structural and operational aspects are reviewed.Inverting flap applications to specific VTOL configurations, including tilt wings, reversed modulated slipstream, direct jet lift, and rotor convertiplanes are discussed in terms of the characteristics of the flaps and of the V/STOL configurations under consideration. In this connection, the aerodynamic equivalence of the reversed modulated slipstream concept to partial wing tilt, with the corresponding aerodynamic equivalent movable stabilizer is presented; the exposable rotor convertiplane concept is reviewed briefly with inverting flap applications.Generalized V/STOL flow problems are discussed briefly in terms of the application of the kinematic principle of inverting flap to wing leading edge flaps, to boundary larger control, and to variable wing span. The wing span flaps concept is then introduced for in-flight variation of span, including a review of its principal applications on V/STOL aircraft field. Current developments of wing span flaps on aircraft are presented.