This Duck Drone Could Spy on Enemy Subs

A model of the "Flimmer" in flight.

Naval Research Lab

AA Font size + Print

A model of the "Flimmer" in flight.

But building a flying-and-swimming robot is harder than nature makes it look.

Nature, which has no need for devices that spy on enemy submarines from the air and underwater, may nevertheless have invented their form: flying fish, for example, or ducks that can zoom over the water’s surface and dive beneath to feed. But the Navy Research Lab, or NRL, which is working on a new drone that can both fly and swim, is learning that combining robots for two different purposes is not as easy as nature makes it look.

Why does the Navy need duck drones? Simply put: flying is faster than swimming, largely because water is 1,000 times denser than air. Consider that the common MK 46 torpedo makes at best 50 mph, while sea-skimming missiles can do five times that speed.

While nature has found a way to accommodate the variety of physical forces that can act upon complex swimming and flying systems, humans have yet to figure this out. Submersible undersea drones, made thick-skinned to withstand water pressures, are generally heavy or equipped with complicated ballast systems. Aerial drones, conversely, are as light as possible, and rarely designed to crash into water.

(RelatedThe Marines Are Building Robotic War Balls)

“For a submarine to fly, the enclosed air volume, which is the main driver of weight for a submarine, needs to be reduced as much as possible. For an aircraft to land on the water, its structural elements need to be more robust to survive the high impact of splashdown.” Dan Edwards, a principal investigator for NRL, writes in the most recent issue of the lab’s Spectra magazine.

Under its Flimmer program (for “flying swimmer”), the NRL team built a “Test Sub” — basically a submarine with wings —and simply worked around the fact that it was heavier than the typical drone. They took it on at least three test runs, dropping it from a plane at 1,000 feet. The test sub flew well enough, according to Edwards’s account, performing “as any other aircraft, controllable in three axes and exhibiting sufficient stability for man-in-the-loop flight.” The team then guided it along the surface of the water at 40 knots (about 46 miles per hour) “before sending it beneath the waves where it performed like a regular UUV,” or unmanned underwater vehicle.

The “Test Sub was guided along a standard approach at an airspeed of approximately 40 knots before splashdown with wings level,” writes Edwards. “Upon touching the water surface, the aircraft saw a dramatic increase in drag and decelerated abruptly. After the splash, Test Sub submerged and started moving underwater and was responsive to human controls … Test Sub cruises well above 50 knots in the air, while top speed in the water is below 10 knots, illustrating the ultimate benefit of a flying submarine: assuring quick reaction access to underwater areas.”

The team is experimenting now with floodable wings and more fishlike designs such as the lab’s experimental “Wrasse-inspired Agile Near-shore Deformable-fin Automaton,” or WANDA. Built to mimic the movement of a fish called the bird wrasse, the WANDA’s moving fins may prove too fragile for a machine hitting the water at relatively high speed.

“A four-finned configuration provides high maneuverability and good stability underwater. In air, however, the fins add weight and are relatively fragile mechanisms that need to be able to survive the forces of splashdown. Bringing all these design elements together is the central challenge of the Flimmer program,” writes Edwards.

The team has begun to adjust WANDA’s design for flight and will spend the rest of the year fine-tuning and tweaking the design.

The future of flying fish drones looks neither like a bird, nor a fish, but something new entirely. 

Close [ x ] More from DefenseOne

Thank you for subscribing to newsletters from
We think these reports might interest you:

  • Software-Defined Networking

    So many demands are being placed on federal information technology networks, which must handle vast amounts of data, accommodate voice and video, and cope with a multitude of highly connected devices while keeping government information secure from cyber threats. This issue brief discusses the state of SDN in the federal government and the path forward.

  • Military Readiness: Ensuring Readiness with Analytic Insight

    To determine military readiness, decision makers in defense organizations must develop an understanding of complex inter-relationships among readiness variables. For example, how will an anticipated change in a readiness input really impact readiness at the unit level and, equally important, how will it impact readiness outside of the unit? Learn how to form a more sophisticated and accurate understanding of readiness and make decisions in a timely and cost-effective manner.

  • Cyber Risk Report: Cybercrime Trends from 2016

    In our first half 2016 cyber trends report, SurfWatch Labs threat intelligence analysts noted one key theme – the interconnected nature of cybercrime – and the second half of the year saw organizations continuing to struggle with that reality. The number of potential cyber threats, the pool of already compromised information, and the ease of finding increasingly sophisticated cybercriminal tools continued to snowball throughout the year.

  • A New Security Architecture for Federal Networks

    Federal government networks are under constant attack, and the number of those attacks is increasing. This issue brief discusses today's threats and a new model for the future.

  • Information Operations: Retaking the High Ground

    Today's threats are fluent in rapidly evolving areas of the Internet, especially social media. Learn how military organizations can secure an advantage in this developing arena.


When you download a report, your information may be shared with the underwriters of that document.