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Experimental UAV sets endurance record

For 26 hours and one minute — that’s how long the Ion Tiger circled nonstop over Aberdeen Proving Ground in Maryland.

The 37-pound experimental Navy unmanned aerial vehicle set an endurance record for fuel-cell-powered drones Nov. 16 and Nov. 17, more than doubling the flight time of its closest rivals.

On board: A five-pound payload, a 9.5-pound tank of compressed hydrogen and a lightweight but powerful fuel-cell engine.

The flight showed what can be accomplished with fuel-cell power and a small UAV. But it also revealed some of what still remains to be done.

With 26 hours of endurance, a UAV like the Ion Tiger could be sent on long-range missions. Or it could simply be launched to loiter overhead, ready to be used when needed, said Karen Swider-Lyons, head of the chemistry division of the Naval Research Laboratory’s alternative energy section.

Equipped with a day-night camera, the plane could become a reconnaissance and surveillance platform. With communications gear on board, it could serve as a relay node.

But at the moment, the UAV has no operational mission. “We’re just showing what we can do with the technology,” Swider-Lyons said.

The main goal was a display of endurance, and the research lab nailed that. “No one else has come close to flying for 24 hours with a significant payload,” she said.

But the aircraft was designed to fly 27 miles per hour. That’s 702 miles in 26 hours, a useful distance for a variety of missions.

The relatively slow speed is problematic when the weather is less than ideal. During an October flight, for instance, the unmanned aircraft encountered wind gusts of up to 40 miles per hour, so in effect it was flying backward some of the time.

The aircraft was designed to maximize flight time, so it was built a lot like a sailplane, Swider-Lyons said — light and with lots of lift. The fuselage resembles an 8-foot-long pollywog with thin, 17-foot-wide wings. A small propeller protrudes from the nose.

The key to the Ion Tiger’s performance is its fuel-cell engine, which turns its propeller and powers its communications package and payload.

Compared with other power sources commonly used on UAVs, the Protonex fuel cell produces seven times more power than batteries of the same weight, and four times more power than a comparable internal combustion engine, the Navy says.

And unlike larger UAVs that rely on internal combustion engines, the Ion Tiger is extremely quiet and has a low heat signature. That means it can fly lower to perform reconnaissance missions without being detected, Navy researchers say.

That’s good as far as it goes, but it doesn’t go far enough.

“The ultimate goal is to provide silent electric propulsion” for a UAV that has “real mil application,” said Jeff Baldic, director of unmanned power systems for Protonex, which built the aircraft. That will probably require a fuel cell that delivers three times more power and a UAV that is more than just a sailplane, he said.

The fuel cell part “is not hard,” Baldic said. “You could scale up the fuel cell and it would be only marginally heavier.”

As for the aircraft, “the design depends on the application,” he said. Mission requirements will dictate what the plane must do, which will dictate features like size and speed, which will determine its design.

“We have a long way to go with the technology,” Swider-Lyons said. But the Ion Tiger has demonstrated in a dramatic way the potential of fuel cells — and of UAVs, she said.

“We’re seeing the nano-ization of airplanes,” she said. Twenty-six hour endurance means “we can start doing big airplane missions with relatively small planes.” For the military, that means less cost and less risk.