Abstract: An experimental wind-tunnel investigation was undertaken to determine the effects of Gur ney flaps on aNACA0012 air foil at a chord Reynolds number of 21 1@10⁶ . In comparison with the clean configuration r esults, theGurney flap increased the lift significantly. A higher lift-to-drag ratio was obtained by t he 0.5% C flap when thelift-coefficient exceeds 11 0, and a maximum increment of lift-to-drag ratio was obtained by the 2% C flap at a liftcoefficient of 1135. The pressure distribution r esults showed that the Gurney flap increased the suction of t he uppersurface and the pressure of the lower surface, and thus the total lift. The wake velocity profile indicated a significantdown-turning of the stream over the upper surface of t he airfoil, and this revealed t hat the camber of the airfoil wasincreased by t he Gur ney flap. When serrated, Gurney flaps produced less lift and drag than not serr ated ones, butt he variation of the lift-to-dr ag r at io depends on the effective ar ea of t he flaps1 T he Gurney flap should be employedat moderate2to2high lift-coefficient conditions such as takeoff and landing, while not advisable at low-to-moderatelift-coefficient conditions.

Key words: lift enhancement, airfoil, Gurney flap, wind tunne l tests