Researchers Unveil Separated-Flow Wing Design, Use Nature to Double Small-Drone Flight Times

Researchers from Brown University and the École Polytechnique Fédérale de Lausanne have published details of a bioinspired wing for miniature fixed-wing drones, offering notable improvements in efficiency and stability.

"Small drones can be really useful in many applications, including flights in populated areas as they are inherently safer for humans, but there are problems operating aircraft at those small scales," says Professor Kenny Breuer, the study's senior author. "They tend to be inefficient, which limits the battery-powered flight times of most drones to around 30 minutes or so. They also tend to get blown around by puffs of wind and turbulent air coming from obstacles such as buildings and trees. So we've been thinking about a wing design that might combat those problems."

The resulting design takes its cues from bird and insect wings, doing away with the traditional smoothly-contoured layout in favor of a smooth leading edge followed by rough and sharp leading edges designed to separate the airflow — hence the design's name: the Separated Flow Airfoil. The stability and efficiency gains come from separating the airflow at the leading edge, which paradoxically improves flow attachment at the trailing edge — aided by a small rounded flap placed near the trailing edge of the wing.

"When we purposefully separate the flow at the leading edge, we cause it to immediately become turbulent, which forces it to reattach at a consistent point regardless of atmospheric turbulence," explains Matteo Di Luca, who designed the wing. "That gives us more consistent lift and overall better performance. With the prototype we have, we're at a little less than three hours of flight time in the wind tunnel," Di Luca said. "The wind tunnel is an idealised environment, so we don’t expect it would last quite that long for an outdoor flight. But if it lasts half as long as it did in the wind tunnel, it’s still more than twice the flight of commercially available drones."

The new wing design isn't the first to take its inspiration from nature: Earlier this month researchers from Stanford University's Department of Mechanical Engineering unveiled PigeonBot, a morphing-wing system wearing real feathers and designed to offer 42 degrees of freedom (DoF).

The team's paper has been published in the journal Science Robotics under open access terms.