Given that water is 1,000 times denser than air, moving through those two mediums requires very different mechanics—or so one might assume. Yet birds like gulls and puffins can plunge into the sea, swim underwater, and leap back into the air to fly away. And now engineers at MIT and EPFL in Lausanne, Switzerland, have designed a robot that can do likewise. 

The “flapping-wing aerial-aquatic vehicle,” or FAAV, weighs less than 300 grams (about half a pound) and is equipped with a central fuselage, two flexible wings, and a steerable tail. The body contains a battery and a waterproof electric motor that drives a crankshaft, which pumps the wings up and down at preset frequencies. The wings are made of thin membranes that are coated with hydrophobic nanoparticles to help wick away water. And the tail is motorized, enabling it to change its angle to help the robot fly up or dive down.

In experiments carried out in a water tank and at Lake Geneva, a team led by Raphael Zufferey, an assistant professor of mechanical engineering at MIT, identified combinations of wing size, flapping frequency, and tail angle that enable the robot to smoothly transition from swimming to flying. 

The best results came with medium-size wings that were flexible enough to minimize flapping amplitude in water and also firm enough to keep the robot aloft in the air. The speeds and flapping frequencies were similar to those used by actual birds, and a pitch of 70 degrees—a relatively steep angle—allowed the robot to make the leap from water to air. Interestingly, although many diving birds paddle their feet to help them take off from the water’s surface, the team found that the bot didn’t need feet at all.

The engineers’ results could help pave the way for a new class of drones and vehicles that could fly to and sample from aquatic regions too dangerous for traditional vessels to access.

“Our dream vision is for oceanographers, marine biologists, and members of coastal communities to launch this robot from a boat, or from shore, and it would fly close to the area of interest, such as an iceberg or a port facility, or over a pod of whales,” says Zufferey. “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 go back out to dive for more.” 

The researchers are now trying to design wings that can turn as well as flap. They will also test the robot’s performance under turbulent conditions, such as swimming in choppy waters and flying through wind. Then they hope to deploy the vehicle to help answer questions in ocean science.

“One of the major challenges in ocean science is collecting data both frequently and across many locations, which is something this robot could do in the future,” Zufferey says. “You could send this out not just every week, but every hour. It could fly out at high speeds, dive in, fly back, deliver its data, and go back out, multiple times.” 

The average American throws out around 81 pounds of clothing each year, and there are few options for recycling it. MIT engineers hope to cut down on that textile waste with a new type of yarn. 

The thermoplastic yarn mimics the properties of conventional elastic yarns, which typically combine spandex with polyester or nylon. Those fibers would have to be separated for recycling—a process that isn’t practical. But the MIT team found a way to create a similarly stretchy yarn from two variations of polyethylene, a material commonly used in milk jugs and grocery bags. Because they come from the same chemical family, the yarn can be melted as is. Svetlana Boriskina, who led the work as a research scientist in the Department of Mechanical Engineering, says a garment made from this material could then be spun into new yarn for a next generation of clothing. Even after 10 cycles of melting and respinning, the yarn stays as strong and flexible as conventional thread. 

“Now we have something that can be knitted and woven,” Boriskina says. “That is the next stage.” Someday, the researchers hope, a polyethylene garment could be dropped in a collection bin and sent to a recycling facility, promoting a more sustainable, circular textile economy. 

When remotely operated vehicles settle on the seafloor or dig through a sand bed, they can kick up clouds of sediment that onboard cameras struggle to see through. Often, the only thing to do is wait until the dust settles. But a new system developed by Amy Phung, SM ’23, PhD ’26, and her advisor Richard Camilli, SM ’00, PhD ’03, of the Woods Hole Oceanographic Institution (WHOI), offers a solution. 

In this technique, the vehicle first uses sonar to quickly map its surroundings. That technology doesn’t provide detailed resolution, but it works equally well in cloudy and clear water. And it allows a vehicle to safely get close enough to specific objects for cameras to visualize them more carefully. To speed up the processing so the mapping can be done in real time, the researchers combined the sonar tech with an image-­matching algorithm developed by researchers in France that quickly estimates the relative depth of each pixel in a 2D scene.

“An analogy would be if you were to go into a china shop in the dark, and try to pick your way around to find a specific coffee mug without knocking things over,” Camilli says of their new technique. “This would allow you to do that.” He and Phung say applications could include scientific exploration, underwater construction and maintenance, and handling of unexploded undersea mines.