Experimental study on gurney flap and apex flap on a delta wing

The effects of Gurney flaps and apex flaps on the longitudinal aerodynamic performance of a delta wing with 70-deg sweepback angle were investigated in low-speed wind tunnel at a Reynolds number of 3.16 × 10⁵ based on the root chord of the delta wing. The experimental results indicate that the increment of lift coefficient can be obtained efficiently for different ranges of angle of attack with Gurney flaps and apex flaps, respectively. The study first tested the application of Gurney flaps together with an apex flap on the highly swept-back delta wing. The results show that they, used together, can greatly improve the longitudinal aerodynamic performance of the delta wing, and in this case the apex flap contributes much to the gains. The maximum lift-to-drag ratio can be achieved when the drooping angle of the apex flap is nearly equal to the angle of attack.