Engineers build raptor-inspired feathered drone with morphable wings and twisting tail that can initiate banking

A pair of engineers at École Polytechnique Fédérale de Lausanne (EPFL) has designed, built and tested a feathered, hawk-inspired drone capable of carrying out banking maneuvers without using its wings.

In their paper published in the journal Science Robotics, Hoang-Vu Phan and Dario Floreano describe the factors that went into building their robot raptor and how well it performed during testing in a wind tunnel.

The work by the researchers began when they learned that many types of raptors have been found to initiate banking while soaring without moving their wings. The entire procedure is carried out by manipulation of the tail. In contrast, airplanes and drones carry out banks by manipulation of ailerons on the back of the wings.

Intrigued by the difference between the way human-built craft and raptors conduct banks, the pair designed and built a feathered, mechanical raptor capable of mimicking the technique of a hawk.

To build their drone, the researchers turned to the anatomy of the hawk. Using light materials, they created raptor-like bones and joints to make the wings and tail and fashioned them onto an equally light body and then covered them with foam feathers. The simple drone was held aloft by the attachment of a rod to the body—the other end of the rod was held in a researchers' hand. They called the result LisRaptor.

Next, they studied video of hawks in flight to learn how they manipulate their tails to initiate a banking maneuver and mimicked what they saw with their mechanical bird. They then put it in a wind tunnel for testing.

The researchers' artificial hawk was able to successfully bank inside the wind tunnel without using its wings. Instead, all it took was a certain twisting of the tail.

They found it worked due to the proximity of the tail to the wings—a slight twisting allowed for asymmetric wind flow over the wings and tail, resulting in asymmetric lift—which made the entire bird tilt to one side even as it pointed slightly upward, to prevent stalling.

The research pair suggest their robot not only helps explain certain aspects of raptor flight but might be useful in designing new kinds of drones that are able to turn more smoothly.