Abstract: A Kreuger flap is hinge-mounted to the leading edge of an aircraft wing by a plurality of hinges hinged at one end internally of the wing, near its leading edge, and at the other end to the rear surface of the Kreuger flap. A torsion tube extending longitudinally through the wing over the length occupied by the Kreuger flap and to the rear of the hinge connection to the wing, is forcibly rotated by a single hydraulic cylinder connected to a crank arm fixed to and projecting radially from the torsion tube. A coil spring fixed at one end to the wing and at its opposite end to a second arm projecting radially from one end of the torsion tube, is moved overcenter during arm movement between first and second position during Kreuger flap extension and retraction and biases the Kreuger flap towards retraction.