wing were slowed because it was now producing so much downforce that the car was understeering. All that was needed was to balance this by adding downforce in front. Unser realized the value of this breakthrough immediately and wanted to conceal it from the competition, including his brother Al. Not wanting to call attention to the devices, Gurney left them out in the open. To conceal his true intent, Gurney deceived inquisitive competitors by telling them the blunted trailing edge was intended to prevent injury and damage when pushing the car by hand. Some copied the design and some of them even attempted to improve upon it by pointing the flap downward, which actually hurt performance. Gurney was able to use the device in racing for several years before its true purpose became known. Later, he discussed his ideas with aerodynamicist and wing designer Bob Liebeck of Douglas Aircraft Company. Liebeck tested the device, which he later named the "Gurney flap" and confirmed Gurney’s field test results using a 1.25% chord flap on a Newman symmetric airfoil. His 1976 AIAA paper (76-406) "On the design of subsonic airfoils for high lift" introduced the concept to the aerodynamics community. Gurney assigned his patent rights to Douglas Aircraft, but the device was not patentable, since it was substantially similar to a movable microflap patented by E. F. Zaparka in 1931, ten days before Gurney was born. Similar devices were also tested by Gruschwitz and Schrenk and presented in Berlin in 1932. Theory of operation The Gurney flap increases the maximum lift coefficient (CL,max), decreases the angle of attack for zero lift (α0), and increases the nosedown pitching moment (CM), which is consistent with an increase in camber of the airfoil. It also typically increases the drag coefficient (Cd), especially at low angles of attack, although for thick airfoils, a reduction in drag has been reported. A net benefit in overall lift-to-drag ratio is possible if the flap is sized appropriately, based on the boundary layer thickness. The Gurney flap increases lift by altering the Kutta condition at the trailing edge. The wake behind the flap is a pair of counter-rotating vortices that are alternately shed in a von Kármán vortex street. In addition to these spanwise vortices shed behind the flap, chordwise vortices shed from in front of the flap become important at high angles of attack. The increased pressure on the