Flap Height Research Articles

Gurney Flap Scaling for Optimum Lift-to-Drag Ratio

This note aims at providing evidence that there exists a flow-based scaling for the Gurney flap heights that yield an increase in lift-to-drag performance compared with the baseline airfoil at the same angle of attack (beneficial Gurney flaps). The results presented here, support this statement and further suggest that the boundary-layer thickness δ, measured at the trailing edge on the pressure side of the baseline airfoil, is not only an appropriate flow-based normalization for the flap height but is also a proper order of magnitude for the flap height providing the largest increase in the lift-to-drag ratio (optimum Gurney flap)

Lift enhancement of an airfoil using a Gurney flap and vortex generators

Experimental measurements of surface pressure distributions and wake profiles were obtained for an NACA 4412 airfoil to determine the lift, drag, and pitching-moment coefficients for various configurations. The addition of a Gurney flap increased the maximum lift coefficient from 1.49 up to 1.96, and decreased the drag near the maximum lift condition. There was, however, a drag increment at low-to-moderate lift coefficients. Additional nose-down pitching moment was also generated by increasing the Gurney flap height. Good correlation was observed between the experiment and Navier-Stokes computations of the airfoil with a Gurney flap. Two deploy able configurations were also tested with the hinge line forward of the trailing edge by one and 1.5 flap heights, respectively. These configurations provided performance comparable to that of the Gurney flap. The application of vortex generators to the baseline airfoil delayed boundary-layer separation and yielded an increase in the maximum lift coefficient of 0.34. In addition, there was a significant drag penalty associated with the vortex generators, which suggests that they should be placed where they will be concealed during cruise. The two devices were also shown to work well in concert.

Increasing the lift:drag ratio of a flat delta wing

SummaryLift and drag measurements were made to determine the effects of vertical flaps when positioned along a ray on the upper surface of a sharp-edged, flat, 60° delta wing. Six flap heights were tested at each of four semi-span positions.Results showed that all configurations gave improved lift-drag ratios. The maximum improvement was 33% using a flap of height 6·1% of the local semi-span placed at the 84% semi-span station. The flaps did not affect the lift but reduced the drag by generating a thrust force on the vertical flap surfaces.Flaps at the 84% position were modified to investigate the possibility of obtaining further increases in lift-drag ratio. In practice these modifications, inward inclination of the flaps, and fairing the inboard side of the vertical flaps, slightly reduced the flap effectiveness and were hot pursued further. Part chord flaps were also tried and showed that the reduction in benefit was roughly proportional to the length of flap removed.