In 1971, a small piece of bent metal quietly transformed motorsport. American racer and team owner Dan Gurney attached a simple L-shaped tab to the trailing edge of his car's wing during testing at Phoenix International Raceway and discovered a breakthrough in aerodynamic control.

That modest invention, now known as the Gurney flap (or wickerbill), became one of the most effective tools for improving downforce with minimal drag. While similar devices had been studied in earlier aerodynamic research, Gurney's real-world application in racing proved its practical value.

Today, this same concept is applied not only in race cars but also in aircraft, helicopters, and wind turbines, demonstrating the power of simple engineering ideas executed well.

Who Invented the Gurney Flap? Dan Gurney's Race Day Innovation

Gurney and his team experimented with a simple, vertical lip spoiler on the rear bodywork of the GT40 prototypes during testing in the mid-1960s to improve high-speed stability. His later Gurney flap experiment began as a quick fix to improve handling but ended up reshaping aerodynamics. The added flap increased rear grip so dramatically that it initially caused understeer, highlighting its significant impact. After adjustments, the car achieved outstanding performance, helping Bobby Unser secure a record-breaking pole speed at the 1972 Indianapolis 500.

While earlier patents and aerodynamic studies had hinted at similar concepts, Gurney was the first to demonstrate the practical benefits in motorsport. The concept later influenced aviation and other industries, where small tabs are used to improve lift, stability, and efficiency.

What Is a Gurney Flap on a Car: Design and Physical Characteristics

A Gurney flap is a small but powerful aerodynamic device used on race cars, aircraft, and other high-performance vehicles to improve downforce and stability. Mounted at a right angle to the trailing edge of a wing or spoiler, it subtly changes airflow over and under the surface. Typically no taller than a few millimeters, it creates a pressure difference that boosts aerodynamic efficiency without adding significant drag.

Basic Design:

• A flat, vertical tab attached to the trailing edge of a wing or spoiler.
• Resembles a miniature L-shaped bracket that extends upward from the surface.

Size and Proportions:

• Typically, 1–2% of the wing's chord length (distance from front to back).
• They are usually only a few millimeters to a couple of centimeters tall, but their size is critical for performance.

NASA studies indicate that a Gurney flap sized at about 1.5% of the wing chord for certain wing profiles can increase the lift coefficient by roughly 0.3 and reduce the angle of attack needed for the same lift by several degrees.

Modern racing teams often build Gurney flaps from carbon fiber, which are valued for strength, light weight, and ease of modification. Aviation applications commonly use aluminum alloys or composite materials, balancing durability with manufacturability. Some advanced race cars even feature adjustable or variable-height Gurney setups, allowing engineers to fine-tune downforce and drag in real time.

How Does a Gurney Flap Work?

A Gurney flap improves aerodynamic performance by slightly disrupting airflow at the trailing edge of a wing. Normally, air flowing over the top and bottom surfaces meets smoothly at the back, a principle known as the Kutta condition. 

Adding a small vertical tab shifts that balance in a useful way:

• The flap creates a small wake and counter-rotating vortices behind the wing.
• These vortices keep airflow attached to the upper surface, delaying separation and reducing stall risk.
• A recirculation zone forms just ahead of the flap, increasing pressure on the lower surface and improving lift.
• The energized airflow acts as though the wing has greater curvature (camber), increasing lift without changing the wing's actual shape.

Wind-tunnel and computational studies show that properly sized Gurney flaps (typically 1–2% of chord length) can increase the lift coefficient by around 0.3, delay stall, and maintain stable flow at higher angles of attack, while only modestly increasing drag (Wadcock et al., 1987; Yang et al., 2020; Liu et al., 2025; Zhu et al., 2021)

What Is a Gurney Flap Used For? Applications Across Industries

The Gurney flap's simplicity and effectiveness have made it valuable far beyond racing:

Helicopters benefit from Gurney flaps because their stabilizers operate at extreme pitch angles. The Sikorsky S-76B incorporated a Gurney flap on its horizontal stabilizer to enhance stability, and other models, such as the Eurocopter AS355 TwinStar and Bell JetRanger, use similar devices for improved control. Wind turbines also leverage Gurney flaps to optimize pressure distribution along blade tips, increasing power efficiency.

Design Optimization: Getting It Right

Even though a Gurney flap is a small tab, design and installation significantly impact performance:

• Height Matters: About 1.5% of chord length usually hits the sweet spot—large enough to energize airflow, small enough to avoid excessive drag.
• Position and Mounting: Install within 0–5% of the trailing edge at a right angle; improper placement reduces effectiveness.
• Balancing Lift and Drag: Flaps improve downforce or lift but add drag, especially at lower speeds. Racing teams often adjust or remove them on high-speed tracks to prioritize straight-line performance.

Streetcar Applications: Practical Guidance

Performance enthusiasts can use Gurney flaps to fine-tune high-speed stability, but proper setup is crucial:

• Maintain aerodynamic balance to prevent understeer.
• Ensure secure mounting; loose tabs are hazardous at speed.
• Start small (around 1% of chord length) and test handling before increasing height.
• The budget for quality aftermarket setups is typically $50–$300 plus installation.
• Consider complementary modifications such as splitters, diffusers, or canards.

Experience Race-Inspired Performance with Hillbank Motorsports

Understanding aerodynamic innovations like the gurney flap enhances your appreciation for the engineering excellence behind legendary racing machines. At Hillbank Motorsports, we bring that same passion for engineering to every vehicle in our collection.

As an authorized Superformance and Shelby Cobra dealer, we offer meticulously crafted vintage sports cars, including the iconic Shelby Cobra, Daytona Coupe, GT40, Caterham classics, and Corvette Grand Sports, each representing decades of racing heritage and aerodynamic refinement. With over 40 years of family expertise spanning from South Africa to our locations in Irvine, California, and Jupiter, Florida, the Stander family's commitment to excellence means every vehicle meets the highest standards.

Whether you're looking for your dream performance vehicle or want to maximize your current car's aerodynamic potential, Hillbank Motorsports provides comprehensive solutions, including flexible financing, trade-ins, and consignment options. Our full complement of 1960s-era American sports cars combines authentic racing DNA with modern engineering precision—the same attention to detail that makes innovations like the gurney flap so effective. Experience the distinctive feeling of a big-block V8 roaring to life and the freedom of the open road.

Ready to experience legendary performance? Contact Hillbank Motorsports today at (949) 900-1960 or visit our showroom to explore our inventory. Your dream driving machine is waiting for you.