MIT and EPFL Unveil Flapping-Wing Robot That Dives, Swims Underwater, Then Takes Flight

Seawater is roughly a thousand times denser than air, a contrast that usually demands completely different strategies for moving in each environment. Yet some seabirds manage both: gulls and puffins can dive beneath the surface, propel themselves underwater, and then burst back into the air to fly. Engineers at MIT and EPFL in Lausanne, Switzerland, have now built a small robot that pulls off the same kind of two-world transition.

The prototype, dubbed a flapping-wing aerial-aquatic vehicle (FAAV), weighs under 300 grams—about half a pound. Its layout is birdlike but engineered for waterproof resilience: a central fuselage houses the battery and a sealed electric motor, which turns a crankshaft to drive the wings at set flapping frequencies. Two flexible wings, built from thin membranes, are treated with hydrophobic nanoparticles intended to shed water quickly. At the rear, a motorized tail can change angle, helping the vehicle control its pitch to climb into flight or angle downward to submerge.

To understand how such a lightweight machine can both swim and fly, the researchers tested the system in controlled tank experiments and in open-water trials at Lake Geneva. Led by Raphael Zufferey, an assistant professor of mechanical engineering at MIT, the team systematically explored how wing size, wingbeat frequency, and tail angle interact during the critical moment when the robot must transition from the water to the air.

Those tests pointed to a sweet spot in wing design: medium-sized wings worked best. The successful wings were compliant enough to reduce flapping amplitude while pushing through dense water, yet stiff enough to generate lift once the vehicle cleared the surface. In the team’s best-performing configurations, the speeds and flapping frequencies landed in the same general range seen in real birds. They also found that a steep body pitch—about 70 degrees—helped the robot “pop” out of the water and establish flight.

One surprising result concerns what the robot doesn’t have. Many diving birds use their feet to paddle or kick against the surface during takeoff. The FAAV, however, managed the water-to-air transition without any feet at all, relying instead on the tuned interplay of flapping wings and tail control.

The researchers see the work as an early step toward amphibious drones that could reach places where conventional boats, buoys, or aircraft are impractical—or too risky. Zufferey envisions oceanographers, marine biologists, and coastal communities launching the vehicle from shore or a boat, sending it to a target such as an iceberg, a port facility, or even near a pod of whales. The robot could then dive to gather a measurement or sample and return to deliver data at a fraction of the typical cost, potentially repeating the cycle many times.

Next, the team plans to develop wings that can rotate as well as flap, a capability that could improve maneuverability. They also intend to evaluate performance in more challenging real-world conditions, including choppy water and windy air, before attempting deployments aimed at open questions in ocean science. One of the field’s persistent problems, Zufferey notes, is collecting measurements both frequently and across wide areas—something a fast, repeatable fly-dive-fly system could eventually provide, even on hourly schedules rather than weekly campaigns.

Why it matters

Tools that can seamlessly operate in both air and water could lower the cost and risk of collecting ocean data, especially near hazardous infrastructure, wildlife, or ice. If the design proves robust in turbulence, it may enable far more frequent sampling across many locations—changing how researchers and coastal operators monitor marine environments. The next milestone will be demonstrating reliable operation in rough water and wind, where most field systems struggle.