F1MATHS: Why do teams use gurney flaps on their cars?

The Gurney flap is a standard tool in aerodynamic design. F1Technical’s senior writer Balazs Szabo explains the history of this aerodynamic device that has been used in Formula One for decades.

The Gurney flap is one of the simplest yet most influential aerodynamic devices ever introduced into motorsport and aviation. It consists of a small tab mounted at a right angle to the pressure‑side surface of a wing’s trailing edge, typically projecting only one to two percent of the wing’s chord.

Despite its minimal size, the device can significantly enhance the aerodynamic performance of an airfoil, often allowing a simple wing profile to achieve lift characteristics comparable to far more complex designs.

How the Gurney Flap Works

The flap operates by modifying the pressure distribution around the airfoil. By increasing pressure on the pressure side and reducing pressure on the suction side, it strengthens the circulation around the wing. This effect helps the boundary layer remain attached to the suction surface all the way to the trailing edge, delaying separation and improving lift. The result is a more stable and efficient aerodynamic profile, particularly at higher angles of attack where flow separation is more likely.

Because of these benefits, Gurney flaps are widely used in applications where high lift or high downforce is essential. They appear on racing cars, helicopter stabilizers, and aircraft such as banner‑towing planes, where low‑speed lift is critical.

Origins in Motorsport

Although similar concepts had been explored decades earlier, the modern Gurney flap is credited to American racing driver and team owner Dan Gurney. In the early 1970s, after retiring from driving, Gurney was managing his own racing team when his driver, Bobby Unser, struggled with the handling of a new car.

Seeking a quick solution, Gurney recalled earlier experiments with spoilers used to counteract aerodynamic lift and decided to attach a small right‑angle strip of metal to the top trailing edge of the rear wing.

The modification was fabricated in less than an hour. Initial lap times did not improve, but Unser privately revealed that the car now produced so much additional downforce that it was understeering. Once the front of the car was balanced with additional downforce, the performance gains became clear. The car could corner faster and achieve higher speeds on the straights thanks to improved stability.

Recognizing the competitive advantage, Gurney and Unser attempted to keep the device’s true purpose secret. Gurney even misled curious rivals by claiming the blunt trailing edge was intended to prevent mechanics from injuring themselves while pushing the car. Some competitors copied the idea but installed the flap pointing downward, which degraded performance and helped maintain the secrecy a little longer.

Scientific Validation and Wider Adoption

Gurney later discussed the device with aerodynamicist Bob Liebeck of Douglas Aircraft Company. Liebeck conducted wind‑tunnel tests using a 1.25% chord flap on a Newman symmetric airfoil and confirmed the performance improvements Gurney had observed. His 1976 AIAA paper formally introduced the concept to the aerodynamics community, and the device soon became known as the “Gurney flap.”

Although Gurney assigned his patent rights to Douglas Aircraft, the device itself was not patentable. Earlier work, including a 1931 movable microflap patented by E. F. Zaparka and experiments presented in Berlin in 1932 by Gruschwitz and Schrenk, had already established similar concepts.

Legacy

Today, the Gurney flap is a standard tool in aerodynamic design. Its effectiveness, simplicity, and versatility make it valuable across motorsport, aviation, and even renewable energy applications such as wind turbines.

What began as a quick, improvised fix in a racing paddock has become a fundamental aerodynamic principle — a testament to Dan Gurney’s ingenuity and the power of practical experimentation.