Bird-Inspired Robot Swims and Flies: EPFL and MIT Develop Flapping-Wing Aerial-Aquatic Vehicle

Bird-Inspired Robot Swims and Flies: EPFL and MIT Develop Flapping-Wing Aerial-Aquatic Vehicle

By Jennifer Chu / Images: Raphael Zufferey

Loons, gulls, puffins, and petrels are among roughly 100 bird species capable of both flight and swimming. These diving birds can plunge into the water to pursue prey, then burst back into the air and take wing. Now, inspired by these natural dual-medium navigators, a team of engineers from the Swiss Federal Institute of Technology Lausanne (EPFL) and the Massachusetts Institute of Technology (MIT) has designed a robot that mimics this behavior — swimming underwater and then leaping out to fly using flapping wings.

What Is a Flapping-Wing Aerial-Aquatic Vehicle (FAAV)?

The Flapping-wing Aerial-Aquatic Vehicle (FAAV) weighs less than 300 grams and was designed to help scientists understand the aerodynamic and hydrodynamic mechanisms that allow diving birds to transition between air and water. The robot features a central fuselage (the "neck"), two flexible flapping wings, and a steerable tail fin — all of which can be swapped out for components of different sizes.

The engineering team conducted experiments in water tanks and on Lake Geneva, systematically identifying the optimal combination of wing size, flapping frequency, and tail angle to enable the robot to swim smoothly, break the water surface, and sustain flight. The findings have been published in the journal Science, shedding light on how diving birds adjust their biomechanics to cope with the vastly different physical properties of air and water — and potentially opening an entirely new category of aerial-aquatic drone.

The researchers envision such winged robots being deployed from ships or shore to reach waters inaccessible to conventional marine vessels, collecting samples or data along the way.

"Our dream vision is to have oceanographers, marine biologists, and coastal communities launch this robot from a boat or a beach and have it fly to a location of interest — near an iceberg, a port facility, or a pod of whales," said Raphael Zufferey, the study's lead author and an assistant professor of mechanical engineering at MIT. "It could dive underwater to take measurements or collect samples, then fly back to relay data at a fraction of the cost of traditional methods — and then head out again for another dive."

Aerodynamic and Hydrodynamic Design

Zufferey began this research as a postdoctoral researcher at EPFL's School of Engineering, working in the Intelligent Systems Laboratory (LIS) and the Biorobotics Laboratory (BioRob) under co-authors Dario Floreano and Auke Ijspeert. The work was later continued at MIT, where Zufferey now leads the AURA Lab, focused on bioinspired aerial and aquatic vehicle engineering. The study also includes co-authors from Northwest Indian College in the United States.

Drawing on avian biomechanics, the team used membrane wings coated with hydrophobic nanoparticles to facilitate rapid water shedding. The fuselage houses a battery and a waterproof electric motor that drives the wings in an up-and-down flapping motion via a crank mechanism at a set frequency. The tail fin is also motorized and adjustable, controlling the vehicle's pitch to climb or dive.

Key Parameters: Wingspan, Frequency, and Angle

Experiments revealed that an 80 cm wingspan and carefully tuned wing flexibility are critical: the wings must be supple enough to reduce drag during underwater strokes, yet stiff enough to generate sufficient lift in the air.

• Underwater swimming speed: approximately 1 m/s (flapping frequency ~5 Hz)
• Airborne flight speed: approximately 6 m/s (similar flapping frequency)
• Water-exit pitch angle: approximately 70 degrees nose-up, preventing wingtips from striking the water surface

These speeds and flapping frequencies closely match those observed in real diving birds.

No Feet Required for Takeoff

One of the study's notable findings is that this combination of wingspan, flapping frequency, and tail angle enables the robot to swim underwater, take off from the water surface, and sustain flight — without the feet or webbed flippers that most diving birds rely on during water takeoff.

"When you watch birds, you notice that most of them use their feet to paddle along the surface before lifting off. The question was: does a robot need to do that too? It turns out it doesn't," Zufferey said. "No one had ever managed to fly out of water using wings alone."

Next Steps

The research team is continuing to refine the wing design to enable lateral turning in addition to vertical flapping. Future work will also test the robot's performance in challenging conditions, including choppy water and strong winds. The ultimate goal is to deploy the vehicle in real-world ocean science missions.

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Research Citation: Zufferey, R., Jeger, S. L., Hüsser, M., Ruiz, F., Lapsansky, A., Ijspeert, A., Floreano, D. (2026). Leaping out of the water: Aerial-aquatic locomotion with flapping wings. Science.

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