New flapping robot swims and flies like a diving bird

6 min read

Loons, gulls, puffins, and petrels are among some 100 species of birds that can both fly and swim. These diving birds can plunge into the water to swim after prey, then leap back into the air to take flight.

Inspired by these natural aquatic aviators, engineers at MIT and EPFL in Lausanne, Switzerland, have designed a robot that can swim underwater and then flap its wings to lift itself out of the water and keep flying through the air, much like diving birds do.

The “flapping-wing aerial-aquatic vehicle,” or FAAV, weighs less than 300 grams (about half a pound) and was designed to help scientists study the mechanisms that allow diving birds to fly through both air and water.

The robot has a central body, or fuselage; two flexible, flapping wings; and a steerable tail. The wings and tail can be swapped for others of different sizes. In experiments in a water tank and a local lake, the engineers identified combinations of wing size, flapping frequency, and tail angle that allow the robot to smoothly transition between swimming underwater, breaking through the surface, and flying through the air.

The results, published today in the journal Science, could help scientists understand how diving birds adapt their flight mechanics to move through air and water — media with very different physical properties. The design could also give rise to a new class of drones and aerial-aquatic vehicles. The researchers envision that these winged robots could be used in oceanography to fly out to aquatic regions and collect samples in places too dangerous for traditional research vessels.

“Our dream is that oceanographers, marine biologists, and members of coastal communities could launch this robot from a boat, or from the shore, and it would fly close to the area of interest, such as an iceberg, a port facility, or over a group of whales,” says Raphael Zufferey, assistant professor of mechanical engineering at MIT. “It would dive into the water to take a measurement or collect a sample, and fly back to deliver the data at a fraction of the cost of traditional methods. Then it could take off again to dive once more.”

Zufferey is the lead author of the new study, which includes co-authors from EPFL and Northwest Indian College in Bellingham, Washington.

Flight mechanics

At MIT, Zufferey leads the AURA Lab, where he and his students design aerial and aquatic vehicles inspired by the biomechanics of nature. The robots they build are small and designed to discreetly explore and monitor the health of oceans and waterways.

For this new work, the team set out to design a vehicle capable of flying through the air and underwater. Any such vehicle would have to adapt and transition between two very different substances. Water is a thousand times denser than air, and moving through one or the other demands very different mechanics. Or so one might assume.

“You need to make some adaptations for that transition to work. But there is a solution in nature,” Zufferey says. “Birds like puffins can fly very fast through the air, and they can dive and swim in the water at speeds of 3 meters per second. They are capable of truly extraordinary things. So we knew it was possible. It is just that no one had tried it yet in a mobile robotic system.”

To understand how diving birds fly, the team consulted the scientific literature and gathered available data on puffins, petrels, kingfishers, and other diving birds. They observed that smaller birds flap their wings about 10 times per second when flying through the air, and about four times per second when swimming in the water. Larger birds have a slightly lower flapping frequency, both in air and in water, due to their greater wingspan.

Taking the biomechanics of the birds into account, the team developed a winged robot designed to flap its wings at frequencies similar to those of real diving birds.

Taking the leap

The new robot vaguely resembles a bird, with a body, two wings, and a tail. The body houses a battery and a waterproof electric motor that drives a crankshaft, which in turn moves the wings up and down at preset frequencies. The wings are made of thin membranes coated with hydrophobic nanoparticles to help repel water. And the tail is motorized, allowing its angle to change to help the robot climb or dive.

The wings can be swapped for others of different sizes. The researchers fabricated and tested three sets of wings: small (60 centimeters wide), medium (80 centimeters), and large (100 centimeters). They ran experiments, first in a small water tank and then in Lake Geneva, in Switzerland.

In their tests, they placed the robot underwater, about half a meter below the surface. They programmed the wings to flap at certain frequencies and the tail to tilt at certain angles over the course of the robot’s flight. They then observed under which conditions the robot could successfully swim up to the surface, exit the water, and take to the air.

The robot performed multiple flights with different wing sizes, flapping frequencies, and tail angles. Overall, the team found that the robot could fly, swim, and transition between water and air reliably when flying with medium-sized wings. The flexibility of the wings is key; the wings need to be flexible enough to minimize the flapping amplitude in the water, while being firm enough to keep the robot in the air when flying.

The researchers also found that the robot could swim through the water at speeds of nearly 1 meter per second when flapping its wings at a frequency of about 5 hertz, or five beats per second. The robot could fly through the air at about 6 meters per second, flapping its wings at a similar frequency. The robot’s speeds and flapping frequencies were similar to those of real diving birds.

To make the leap from water to air, the researchers found that the robot should be pitched at 70 degrees — a relatively steep angle that keeps the robot’s wingtips from touching the surface of the water as it flaps its wings to climb into the air. At a steeper angle, the robot would fall back into the water.

Interestingly, this combination of wing size, flapping frequency, and tail angle allowed the robot to swim underwater, launch itself from the surface, and fly, without something many diving birds require: feet. When birds such as puffins and ducks take off from the surface of the water, they paddle with their feet in addition to flapping their wings and tilting their tails. Surprisingly, Zufferey and his colleagues found that, at least in robotics, flying out of the water does not necessarily require a paddling maneuver.

“If you look at birds, most of them need to paddle at the surface to take off. And the question was: do robots need the same? And it turns out they do not,” Zufferey says.

Going forward, the team is refining the design of the wings so they can also pitch, in addition to flapping up and down. They will also test the robot’s performance in turbulent conditions, such as exiting rough waters and flying through wind. After that, they hope to put the vehicle to work in ocean science research.

“One of the big challenges in ocean science is collecting data frequently and in many different locations, something this robot may be able to do in the future,” Zufferey says. “You could send it out not just every week, but every hour. It could fly at high speed, dive, fly back, deliver its data, and head out again, over and over.”

This work was funded, in part, by a fellowship from the Marie Skłodowska-Curie Actions.

Sources and References

• Original article: “New flapping robot swims and flies like a diving bird” — MIT News
• Author: Jennifer Chu; MIT News
• Originally published: July 9, 2026
• https://news.mit.edu/2026/new-flapping-robot-swims-and-flies-like-diving-bird-0709
• English edition: CBT Intelligence Unit · August 2026