Bird wings inspire improvements in airplane safety 

Inspired by bird flight, engineers have recently enhanced remote-controlled aircraft performance by adding rows of covert-inspired flaps to airplane wings. 

These flaps, modeled after the covert feathers birds deploy during certain maneuvers, help aircraft resist stalling and improve stability. 

Improvements in aviation performance

The research, led by Professor Aimy Wissa from Princeton University, suggests significant improvements in aviation performance by using lightweight, low-cost modifications that require no additional power.

“These flaps can both help the plane avoid stall and make it easier to regain control when stall does occur,” Wissa said. 

The technology echoes bird biology, specifically covert feathers that birds use when landing or facing turbulent winds. 

Although biologists have observed these feather movements, no study has precisely quantified their aerodynamic effects on bird flight. This study, however, demonstrates how similar flaps might function on aircraft.

Bird-inspired flaps boost aerodynamics

Postdoctoral researcher and first author of the study, Girguis Sedky, described the flaps as “an easy and cost-effective way to drastically improve flight performance without additional power requirements.” 

The flaps mimic covert feathers by deploying in response to changing airflow, with no need for external control systems. When strategically placed, these flexible flaps enhance performance and stability in aircraft without complex machinery.

Teardrop shape of bird wings

The principle behind the design lies in a wing’s teardrop shape, which accelerates airflow over the top, creating lift through a combination of low pressure above and upward force below. 

Under certain flight conditions, particularly at steep angles, the aircraft can stall as lift decreases sharply. By adding covert-inspired flaps, researchers discovered they could counter this drop in lift, allowing the aircraft to maintain control.

Wissa’s team conducted wind tunnel tests at Princeton’s Forrestal Campus to observe how these covert-inspired flaps affect air movement around the wings. 

“The wind tunnel experiments give us really precise measurements for how air interacts with the wing and the flaps,” Sedky explained. The setup included sensors that capture aerodynamic forces on the wings, as well as a laser and high-speed camera to record the airflow.

Unlocking secrets of bird wings 

Through their testing, the researchers identified two aerodynamic control mechanisms, one of which – called shear layer interaction – was previously unknown. 

This interaction occurs when a flap near the front of the wing adjusts the flow of air, enhancing stability. When placed near the back, the flaps engage the second mechanism, further aiding in lift.

Testing various configurations, from single to multiple rows of flaps, revealed that a five-row setup increased lift by 45 percent and reduced drag by 30 percent. 

“The discovery of this new mechanism unlocked a secret behind why birds have these feathers near the front of the wings,” Wissa said. 

Adding more flaps near the front of the wing enhanced performance benefits, indicating that birds’ covert feathers likely play a crucial role in their aerodynamic control.

From lab to field: Real-world testing

Following the success of wind tunnel experiments, the team moved to field testing on Princeton’s Forrestal Campus. 

They collaborated with Nathaniel Simon, a graduate student specializing in drone flight, to test the covert-inspired flaps on a radio-controlled (RC) plane equipped with an onboard flight computer. 

Simon programmed the computer to repeatedly induce stall conditions, allowing the team to observe the flaps’ deployment and performance.

“It’s cool to be able to collaborate in the shared space at the Forrestal campus, and to see how many areas of research this project touched,” said Simon, describing the flaps’ in-flight effectiveness in reducing stall intensity. 

The success in real-world conditions paralleled the wind tunnel findings, confirming that these flaps can significantly delay stall and stabilize flight.

Future applications beyond aviation

Beyond aviation, the researchers believe these bioinspired insights could benefit other fields where airflow modification could improve performance. 

“What we discovered about how coverts alter the airflow around the wing can be applied to other fluids and other bodies, making them applicable to cars, underwater vehicles, and even wind turbines,” Sedky said.

The study also opens new doors for collaboration with biologists to deepen our understanding of covert feathers in bird flight. Wissa sees potential for advancing both engineering and biological research through these discoveries. 

“That’s the power of bioinspired design. The ability to transfer things from biology to engineering to improve our mechanical systems, but also use our engineering tools to answer questions about biology,” she concluded.

The study is published in the journal Proceedings of the National Academy of Sciences.

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