If you ever sitting on a plane row facing a wing, you’ll likely see multiple flaps along the edges that adjust during takeoff and landing. Like bird feathers, these components are necessary for controlling the vehicle’s rotation, lift and drag during flight. However, unlike their avian counterparts, these mechanisms are generally placed in single rows along a wing and require electronic components to control as they travel.
Birds have been taking to the air for millions of years, equipped with exponentially more ‘flaps’ in the form of hidden groups of feathers that passively adapt to the airflow. Some engineers are convinced that aircraft can be built more safely and energy-efficiently if they do so. Their results, published on October 28 in the Proceedings of the National Academy of Sciencesseem to support such breezy aircraft upgrades.
Researchers at Princeton University recently upgraded a small, remote-controlled model airplane with rows of flaps that mimic hidden feathers — the feather groupings in birds that passively adjust during complex maneuvers such as navigating wind gusts and landing. By doing this, the team believes that similar biomimicry-based designs could one day help aircraft improve overall performance and avoid potentially dangerous emergencies.
While previous “studies suggest [covert feathers] may improve flight during maneuvers such as landing or flying through gusty winds,” the team wrote that “there is no existing consensus on its underlying physics or the implications of having multiple rows.” To solve this, they first installed two to five rows of hidden flaps on 3D-printed, scale model airplane wings, then subjected their prototypes to wind tunnel testing in a 30-foot installation. Inside the tunnel, a combination of sensors, both laser and high-speed cameras, meticulously measured the airflow around the wings during various fitness simulations. They also used a wing model built with standard single-row flaps to serve as a control.
“The wind tunnel experiments give us very precise measurements of the interaction of air with the wing and the flaps, and we can see what is actually happening in terms of physics,” said Girguis Sedkey, a postdoctoral researcher and lead author of the study, in a university profile on Monday. After analyzing the data, Sedkey and their team identified specific ways in which flaps control airflow around a wing. One of these, the ‘shear layer interaction’, had never before been documented in aviation testing.
“The discovery of this new mechanism has revealed a secret of why birds have these feathers on the leading edge of the wings and how we can use these flaps for aircraft,” said Aimy Wissa, assistant professor of mechanical and aerospace engineering and principal investigator of the study. Wissa added that of all models, the five-row design performed the best, improving lift by 45 percent while reducing drag by 30 percent.
“[T]The more flaps you add to the leading edge of the wing, the greater the performance benefit,” she explained.
[ Related: How do planes fly? ]
After these initial experiments, Wissa’s team then moved to outdoor flight testing using a bird-sized R/C drone aircraft borrowed from Princeton’s Somerset RC model airplane club. Engineers first installed hidden flap rows and then programmed an on-board computer to turn autonomously. From there, researchers launched their model and watched how it navigated the aerial challenges. Each time the computer initiated a stall, the aircraft’s secret flaps deployed passively to reduce the stall intensity.
“That is the power of bio-inspired design,” says Wissa. “The ability to transfer things from biology to engineering to improve our mechanical systems, but also to use our engineering tools to answer questions about biology.”
Wissa and her colleagues believe that hidden bird feathers could lend themselves to more applications than just aircraft. Given the fluid dynamics of airflow, they note the potential to explore similar modifications to improve the efficiency and safety of cars, underwater ships and possibly even wind turbines.
