Effects of Plain and Gurney Flaps on a Nonslender Delta Wing

A low-speed wind tunnel investigation was conducted to characterize the performance of plain and Gurney flaps on a 55 deg sweep delta wing. The geometry of the plain trailing-edge flaps was varied in terms of their length and setting angle. The height of the Gurney flaps was altered. Both the trailing-edge flaps and the Gurney flap are effective at lift augmentation; however, the plain flap has only a moderate associated drag penalty, while that of the Gurney flap is large. The drag increment of the Gurney flap is proportional to its relative area compared to that of the wing and far outweighs the Gurney flap's associated lift increment. Consequently, this leads to a significant drop in wing efficiency compared to the trailing-edge flap or planar wing. The addition of either type of flap causes a pitching moment reversal. Analytic modeling of both flaps successfully captured the aerodynamic effect of the flaps as a function of their geometric variables.