BTI original illustration based on the published mechanism; not a prototype photograph or engineering drawing.
New robotics, plain English
MIT FAAV: The Robot That Swims and Flies
The same flexible wings swim, cross the surface, and keep flapping in flight. The clever part is how one lightweight machine handles two fluids with radically different density.
MIT and EPFL built a robot that swims and flies without changing vehicles. The flapping-wing aerial-aquatic vehicle, or FAAV, swims underwater, breaks through the surface, and continues through air. It weighs less than 300 grams and uses two flexible wings plus a steerable tail. The research appeared in Science on July 9, 2026.
The visible trick is the leap. The engineering problem begins earlier: water is about 1,000 times denser than air. A wing firm enough to hold a small robot aloft can meet enormous resistance underwater. A wing optimized only for swimming may bend too much to support flight. The team searched for a useful middle ground by changing wing span, flapping frequency, and tail pitch.
The successful published setup used medium 80-centimeter wings, roughly five flaps per second, and a steep 70-degree exit angle. In the reported tests, the robot moved at almost 1 meter per second underwater and around 6 meters per second in air. Those figures describe experimental runs, not range, battery life, payload, commercial availability, autonomous operation, or performance in rough ocean conditions.
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Robot that swims and flies: the quick answer
FAAV has a waterproof electric motor that drives a crankshaft. The crankshaft moves both wings up and down. Thin wing membranes flex under load and carry a hydrophobic coating that helps shed water. A motorized tail changes angle so the vehicle can aim down for a dive or pitch steeply upward for the transition into air.
Underwater, dense water pushes hard against each wing. The flexible structure reduces its flapping amplitude rather than forcing the full airborne stroke through that resistance. In air, where the fluid is much less dense, the same wings can move through a larger useful stroke and remain firm enough to generate lift and thrust.
The launch does not require a separate propeller, rocket, or pair of paddling feet. The robot swims upward, aims at about 70 degrees, and keeps flapping. That angle raises the wingtips away from the surface while the body crosses the boundary. Once clear, it continues into forward flight.
Five published results without the missing context
| Published result | What it means | What not to assume |
|---|---|---|
| Less than 300 grams | The battery-powered research vehicle weighs under about two-thirds of a pound. | That is the reported prototype mass, not a payload, endurance, or retail specification. |
| 80-centimeter wings worked across both media | The medium test wings balanced underwater resistance with enough shape for flight. | The team also tested 60- and 100-centimeter wings; one size is not proven best for every mission. |
| About five flaps per second | One similar wing rhythm moved the robot underwater and through air. | The result depends on wing size, flexibility, tail angle, test conditions, and control timing. |
| Nearly 1 m/s underwater and about 6 m/s in air | The same small vehicle moved much faster in the less-dense medium. | These are reported experimental speeds, not range, endurance, or guaranteed field performance. |
| A 70-degree pitch cleared the surface | The steep launch angle kept the wingtips out of the water while the wings continued flapping. | A steeper angle tipped the robot back, and the result does not establish all-weather launches. |
Why one wing normally struggles in both water and air
A wing works by pushing on a surrounding fluid. Air and water are both fluids, but their densities are so different that the same motion produces very different forces. Move a hand quickly through air and it feels easy. Repeat that motion underwater and the resistance becomes obvious. A robot wing experiences the same contrast across every flap.
An ordinary aircraft wing is built to remain stiff enough for predictable aerodynamic shape. Underwater, a large stiff wing can create high drag and large structural loads. An underwater propulsor is usually compact and designed around the density of water. Carrying separate flight and swimming systems would add mass, complexity, seals, actuators, and failure points to a vehicle that must stay light enough to fly.
FAAV tests a more economical idea: let one compliant structure adapt passively. The wing bends more when the water pushes back and less when it moves through air. That does not make the two environments identical. It gives the controller and tail a workable shared mechanism instead of two complete propulsion systems.
The robot’s four useful parts
| Part | Job | Why it matters at the surface |
|---|---|---|
| Waterproof fuselage | Holds the battery, electronics, and electric motor. | Keeps the drive system operating before and after immersion. |
| Crankshaft | Turns motor rotation into repeated wing strokes. | Lets the same actuator continue flapping through the transition. |
| Flexible coated wings | Deform under dense-water loads and generate force in air. | Reduce underwater stroke while retaining enough airborne structure. |
| Steerable tail | Changes the vehicle’s pitch. | Sets the steep exit angle that keeps wingtips from catching the surface. |
Why the medium wing won the published test
The researchers made three interchangeable wing sets: 60, 80, and 100 centimeters wide. They first tested in a small tank, then moved to Lake Geneva. For each configuration, they varied wing frequency and tail angle and watched whether the vehicle could swim up, clear the surface, and establish flight.
The 80-centimeter wings provided the successful balance reported by MIT. A smaller wing offers less area to push against the fluid. A larger wing can generate more force but also meets more underwater resistance and places greater demands on the drive. The medium span, combined with suitable flexibility, gave enough underwater propulsion without losing airborne support.
That result is a design point, not a universal law. A heavier sensor package, different membrane, larger battery, stronger current, higher waves, or longer endurance target could move the best compromise. The useful lesson is the method: test the whole transition rather than optimizing swimming and flying as separate demonstrations.
Five flaps per second does two different jobs
MIT reports that the robot swam at nearly 1 meter per second when its wings flapped around five times each second. It flew at around 6 meters per second with a similar frequency. The shared number does not mean each flap behaves the same way in both environments.
Underwater, the wing bends against much greater resistance and transfers force into dense water. In air, it can sweep farther and faster through a lower-density fluid. Flexibility changes the actual wing shape and stroke under load, so the structure helps translate one motor rhythm into two different motions.
The reported similarity to diving-bird frequencies is a useful biological reference, not proof that the robot duplicates a puffin or petrel. Birds actively adjust muscles, joints, feathers, posture, and timing. FAAV is a simplified research machine designed to reveal which mechanics matter most.
The 70-degree exit solves a wingtip problem
A shallow exit leaves the long wings close to the surface. If a wingtip strikes or remains buried in the water while the rest of the vehicle tries to fly, the uneven resistance can drag or rotate the robot. The team found that pitching the vehicle to about 70 degrees raised the wings into a better position for the final flaps out of the water.
More angle was not automatically better. MIT reports that a steeper setup tipped the robot backward into the water. The transition therefore uses a narrow physical tradeoff: steep enough to clear both wings, but not so steep that forward motion disappears and the body falls back.
Diving birds often paddle their feet while flapping to leave the water. The FAAV runs showed that this robot did not need a separate paddling action under the tested conditions. Removing that subsystem saves weight and mechanical complexity, but it does not establish that every aerial-aquatic robot can launch without one.
What an ocean-science version still needs
The research vision is compelling: fly quickly from shore or a boat, dive to take a measurement or sample, return through the surface, and deliver the data. One vehicle could connect aerial mapping with underwater observations around coasts, ports, ice, wildlife, or water-quality events.
The published result is a locomotion demonstration, not that complete field system. MIT says the team plans to improve turning and test turbulence such as choppy water and wind. A practical mission would also need navigation, sensing, communications, sampling hardware, collision avoidance, waterproofing life, battery endurance, recovery procedures, and rules for operating around people and wildlife.
Payload changes the central compromise. Every camera, sampler, modem, and larger battery adds weight. Added mass can require more wing area or power, which increases underwater loads. The next engineering question is therefore not only whether the robot can cross the surface, but how often it can do so while carrying useful instruments in realistic conditions.
How BTI checked the FAAV claims
BTI reviewed the MIT News report dated July 9, 2026, the MIT DSpace open-access record, the Science DOI record, and the MIT AURA Lab page on July 14, 2026. We separated measured prototype results from future-use statements and retained attribution for mass, wing spans, flapping frequency, speed, pitch angle, test locations, and planned turbulence work.
The visual package uses original BTI illustrations of the published mechanism. MIT News makes its download images available under a non-commercial, no-derivatives license, so BTI did not embed or alter those press photographs in this commercial website and social package. Readers can use the source links below to see the credited prototype photographs and official video in their original context.
BTI did not build, operate, inspect, time, weigh, or independently test FAAV. We did not verify battery endurance, payload, autonomous navigation, range, rough-water performance, long-term waterproofing, safety, environmental impact, manufacturing readiness, price, or availability. No affiliate link appears because this is science reporting rather than a retail comparison. No Product or Review schema is used.
What the study does not establish
- Routine launches from choppy ocean water, strong current, rain, or high wind.
- A complete autonomous mission from takeoff through sampling, return, and data delivery.
- Commercial range, endurance, payload, service life, maintenance interval, or manufacturing cost.
- Safe operation around boats, swimmers, animals, protected areas, or crowded shorelines.
- That an 80-centimeter wing and 70-degree pitch are optimal for every vehicle size or mission.
- Retail availability, pricing, ratings, reviews, awards, endorsements, or an investment outcome.
What to remember
The breakthrough is not simply that one robot can appear in two places. One pair of flexible wings changes its behavior under load, letting the same lightweight drive system work underwater and in air. A steerable tail then aims the robot at the narrow angle needed to cross the surface.
The saveable map is: flexible wings for two densities, about five flaps each second, medium 80-centimeter span, 70-degree pitch, then continued flight. The research team has demonstrated the transition in controlled tests and a lake. Turbulence, useful payload, autonomy, and repeated field missions remain future work.
Follow @besttechinsight for the mechanism behind each new technology in plain English. Related BTI explainers cover how 1X NEO senses a slipping object, how a cargo-ship wing turns wind into thrust, and why NASA Dragonfly needs eight rotor sets on Titan.
MIT FAAV robot FAQ
What is the robot that swims and flies?
It is FAAV, a flapping-wing aerial-aquatic research vehicle developed by engineers from MIT and EPFL. It uses the same flexible wings underwater and in air.
How heavy is the FAAV robot?
MIT reports that the prototype weighs less than 300 grams, or about two-thirds of a pound.
How does FAAV get out of the water?
It swims upward, uses its tail to pitch to about 70 degrees, and keeps flapping so its wingtips clear the surface and the vehicle continues into flight.
How fast does the robot move?
The published tests reported almost 1 meter per second underwater and around 6 meters per second in air at roughly five flaps per second.
Does the robot use propellers or paddling feet?
No separate propeller or paddling-foot mechanism was needed for the reported water-to-air transition. A motor, crankshaft, flexible wings, and steerable tail created the motion.
Can FAAV already run autonomous ocean missions?
The published work demonstrates locomotion and the surface transition. MIT describes ocean sampling as a future goal and says the team still plans to test turning, wind, and choppy water.
Sources
- MIT News: New flapping robot swims and flies like a diving bird: Primary university report for the July 9 publication date, robot mass, construction, test setup, measured speeds, launch angle, and future research goal.
- MIT DSpace open-access paper record: Open paper record for Leaping out of the water: Aerial-aquatic locomotion with flapping wings.
- Science DOI 10.1126/science.aeb6744: Publisher record for the peer-reviewed study; use the paper for experimental detail rather than treating a social clip as the source.
- MIT AURA Lab: Research-lab context for bioinspired aerial and aquatic robotics.