Experimental Investigation into the Effect of Gurney Flaps on Various Airfoils.

The aerodynamic effects of the application of Gurney flaps of different heights and chordwise locations to five airfoils have been investigated in the Pennsylvania State University low-speed, low-turbulence wind tunnel. The effectiveness of each Gurney flap/airfoil combination is measured by the change in the maximum lift coefficient of the airfoil. When grouped by flap height and plotted against chordwise location, there is considerable scatter in the data, indicating that the effectiveness of the Gurney flap is strongly influenced by airfoil shape. Two anomalous cases are considered in detail. In the first case, the increase in cl, max is considerably different for two airfoils with the addition of a Gurney flap having the same height and mounted at the same chordwise location. The second case is one in which a Gurney flap of a specific height and mounting location is found to increase cl, maxs on one airfoil and decrease it on another. For these cases, pressure distributions, lift curves, and drag polars are provided. An explanation for the mechanism for the change in lift due to a Gurney flap is presented [ABSTRACT FROM AUTHOR]