Birdlike robot swims underwater, then flaps into flight without paddling

Engineers at MIT and EPFL have developed a bird-inspired flapping-wing aerial-aquatic vehicle that can swim underwater and then emerge into flight without paddling. The robot, called FAAV, weighs less than 300 grams and has a fuselage, two flexible wings, and a steerable tail. A battery and waterproof electric motor drive a crankshaft that moves the wings at preset frequencies. Its membrane wings are coated with hydrophobic nanoparticles, while interchangeable wings and tail components allow testing of different configurations.

In tank and Lake Geneva experiments, researchers started the robot roughly half a meter underwater and varied wing size, flapping frequency, and tail angle. Of three wing sets—60-centimeter, 80-centimeter, and 100-centimeter spans—the medium wings produced reliable swimming, water-to-air transitions, and flight. The wings needed enough flexibility to reduce flapping amplitude underwater, yet enough firmness to support aerial flight.

At about five flaps per second, the vehicle swam at nearly one meter per second and flew at about six meters per second, values similar to those reported for diving birds. A tail-controlled pitch of 70 degrees helped it clear the surface while preventing wingtip contact with water; a steeper angle caused it to tip back. The work, published in Science, aims to help study how diving birds operate in air and water, which have sharply different physical properties.

Researchers say future versions could add turning capability to the wings and be tested in choppy water and wind. They envision potential oceanographic use: a robot could travel to areas difficult or dangerous for traditional vessels, collect measurements or samples, and return data.