Scientists have developed a flapping-wing robot capable of flying through the air, swimming underwater, and moving between the two environments to better understand how diving birds operate in both worlds.

Researchers said around 100 bird species can both fly and propel themselves underwater using only their wings. Although they use similar flapping movements in each environment, they slow their wingbeats and reduce wing area underwater to adapt to water being nearly 1,000 times denser than air.

The team noted that studying these movements in living birds is difficult, while computer simulations struggle to reproduce the complex interactions between flapping wings, fluid forces, and the transition between water and air.

To overcome these challenges, researchers created a modular aerial-aquatic robot weighing 250 grams. The machine features a streamlined body, two flexible membrane wings, a movable tail, onboard electronics, and a fully waterproof design.

The untethered robot can be controlled wirelessly, allowing scientists to adjust wing-flapping frequency and tail position to study how wing size, flexibility, and flapping affect movement in the air, underwater, and during transitions between both environments.

By comparing observations from diving birds with the robot’s performance, the researchers found that complex wing-folding systems are not required for movement in both environments.

Instead, they found that balancing wing flexibility, size, and flapping frequency was enough to achieve similar results.

Experiments showed that smaller wings increased underwater speed but did not improve swimming efficiency, while wings with intermediate flexibility delivered the strongest overall performance by improving underwater propulsion and still providing enough lift for flight.

Researchers also found that because flying requires less energy than swimming, it was more efficient for the robot to leave the water and fly rather than remain submerged over longer distances.

The study further demonstrated that wing-powered takeoff from water is possible without assistance from legs, although it requires substantial power.

Podcast: Play in new window | Download