Fascination with Technology Inspired by the Puffin: Robot Flies, Swims, and Dives

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In our section "Fascination with Technology," we present impressive projects from research and development to engineers every week. Today: A wing-flapping robot that swims and flies like a diving bird.

Loons, gulls, puffins, and petrels are among the roughly 100 bird species that can both fly and swim. These diving birds plunge into the water to hunt for prey and then ascend back into the air. Inspired by these natural "amphibians," engineers from EPFL and MIT have developed a robot that can swim underwater and then take off out of the water—much like these birds.
The so-called "flapping‑wing aerial‑aquatic vehicle" (FAAV) weighs less than 300 grams (approx. 10.6 ounces) and aims to help researchers study the mechanics enabling diving birds to move both in the air and water. The robot consists of a central fuselage, two flexible, flapping wings, and a steerable tail. The wings and tail can be exchanged in different sizes. In trials conducted in a water tank and Lake Geneva, the engineers identified combinations of wing size, flapping frequency, and tail angle that allow for a seamless transition from swimming underwater, breaking through the surface, and into flight.

Robot Helps Explore Hard-to-Reach Marine Areas

The results published in Science help to understand how diving birds adapt their flight mechanics to the very different physical properties of air and water. At the same time, the design could inspire a new generation of air-water drones. The researchers envision applications in exploring hard-to-reach marine areas that are too dangerous for conventional ships. "Our vision is that oceanographers, marine biologists, and coastal communities can launch this robot from a boat or from the shore. It would fly close to a study area—such as an iceberg, a harbor structure, or over a pod of whales," says lead author Raphael Zufferey, now an assistant professor at MIT. "Then it dives into the water, takes measurements or samples, and flies back to deliver the data—at a fraction of the cost of conventional methods."

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Wing Size and Flexibility are Crucial 

Zufferey began working on the robot as a postdoctoral researcher in the Laboratory of Intelligent Systems (LIS) and the Biorobotics Lab (BioRob) at EPFL. He later continued at MIT, where he now leads the AURA Lab, which focuses on bioinspired aerial and aquatic vehicles. Based on the biomechanics of birds, the team developed wings made of thin membranes coated with hydrophobic nanoparticles to repel water. The fuselage houses a battery and a waterproof electric motor, which drives the wings up and down at predetermined frequencies via a crankshaft. The motorized tail can change its angle, aiding ascent or descent.
The experiments were initially conducted in a small water tank at EPFL and later in Lake Geneva. It was shown that wing size (about 80 cm / approx. 31.5 inches) and flexibility are crucial: the wings need to be flexible enough to minimize resistance in water, yet stable enough to support the robot in the air. The robot reached speeds of nearly one meter per second (approx. 3.3 ft/s) in water at a flapping frequency of about 5 hertz and flew through the air at about 6 meters per second (approx. 13.4 mph) at a similar frequency—comparable to real diving birds. To transition from water to air, the robot must be positioned at a steep angle of about 70 degrees to ensure that the wing tips do not touch the water's surface.

Like a Bird—But Without Feet

Remarkably, the robot manages without an element that many diving birds require: feet. "Most birds need to paddle with their feet at the water's surface to take off. The question was whether robots also need this—and the answer is no," explains Zufferey. "Until now, no one has succeeded in taking off from the water using only wings." In the future, the team plans to further develop the wings so they can also rotate. Additionally, tests will be conducted under more realistic conditions, such as in choppy water or windy environments. In the long term, the robot could contribute to new insights in marine research.