UAVs Go Green With Fuel-Cell Powered "Ion Tiger"

Hugh Pickens writes "Increasingly, the military is deploying unmanned aerial vehicles, or UAVs, as eyes in the sky to scan the ground for targets and threats, especially for missions that are too dangerous for manned aircraft. Now Live Science reports that a new robotic spy plane called 'Ion Tiger' will harness alternative energy to make it more covert and longer lasting than battery-powered or engine-powered UAVs. A 550-watt, 0.75 horsepower hydrogen fuel cell will power the Ion Tiger with four times the efficiency of a comparable internal combustion engine and seven times the energy of the equivalent weight of batteries. When Ion Tiger took flight in October, it exceeded any demonstration of electrically powered flight so far, flying 23 hours and 17 minutes. 'And it carried a 5 lbs. payload to boot — enough to carry, say, a day-and-night camera,' says researcher Karen Swider-Lyons, head of the alternative energy section at the Naval Research Laboratory in Washington. 'No one has come close to flying 24 hours with a significant payload before.' Another big advantage is the Ion Tiger's reduced noise, heat and emissions. 'Think about lawnmowers or chainsaws — they're really loud,' says Swider-Lyons. 'It's hard to spy on people when they know you're there, so you had to fly them at high altitudes to keep them from being heard.'"

Comments

Huh?

[Rei]

When Ion Tiger took flight on October, it exceeded any demonstration of electrically powered flight so far, flying 23 hours and 17 minutes.

No it didn't. Have they never heard of the Qinetiq Zephyr? It flew for 82 hours.

Re:Huh?

[Rei]

Also on the subject of misleading claims:

A 550-watt, 0.75 horsepower hydrogen fuel cell will power the Ion Tiger with four times the efficiency of a comparable internal combustion engine

That would mean an efficiency of greater than 100%. Which is obviously nonsense. ICEs are generally 35-45% efficient in peak operation. If you want to say that you're not comparing peak operation, then you can't compare fuel cells at peak operation, either. For example, when driving the NEDC (the New European Drive Cycle, one that generally is gentler than our combined city/highway cycles), the tank-to-wheel efficiency of a fuel cell stack is about 36% (gasoline engines in the NEDC are generally 20-25% efficient, and diesels, 25-30%). Even at low, steady loads, fuel cells are about 45%. And that's tank-to-wheel -- i.e., doesn't include the losses in making hydrogen, which are significant. Yes, you can get really high efficiencies, 50-70% or so, with fuel cells in the lab. But to do that, you have to feed them pre-compressed oxygen rather than low-pressure air, and not count any accessory loads.

and seven times the energy of the equivalent weight of batteries

Notice they chose the one metric that favors H2 -- rather than, say, volume, durability, power, price per watt, fuel price per energy or fuel price per watt, or any other such metric that fuel cells bomb at. And they're almost certainly just comparing the fuel, ignoring how heavy the fuel cell stack is.

Another big advantage is the Ion Tiger's reduced noise, heat and emissions.

Fuel cells lose out to battery-electric in all three of those regards.

Now, I will say that UAVs are a better role for fuel cells than cars -- steadier loads, cost is less of an object, and a higher percent of the vehicle's mass needs to be energy storage. But they still aren't very attractive.

Re:Huh?

[Falconhell]

"Something else you seem to ignore is large wings, while providing for lots of lift, directly translate into higher drag"

WTF?

The higher the aspect rario of a wing the lower its drag.

As English designer and glide manufacurer Fred Slingsby famously put it, "There is no substitute
for span".(In terms of increasing a wings efficiency)

The smaller the chord of a wing the lower its reynolds number, hence less efficient.

Try googling Aspect ratio effects and reynolds numbers.

Green don't matter

[timpdx]

The military really doesn't care much it it is "green" or not, they just want the UAV on mission as long as possible. If it takes a "green" fuel cell, then fine. But if it took a ton of black coal to do the mission, then the dirty coal would be the fuel.

The hummingbird laughs at your 5 pound capacity

[Anonymous Coward]

Nobody has heard about the OFFICIAL holder of the rotocraft endurance tests? Boeings A160.

"It was the longest un-refueled flight of any rotorcraft, and the FAI has awarded Boeing the official endurance record in the 500 kg to 2,500 kg autonomously controlled UAV class for the flight.
-Staff. "Unmanned Aerial Vehicle (UAV) World Records". Fédération Aéronautique Internationale. http://records.fai.org/documents.asp?from=u&id=15059. Retrieved 2008-11-30."

http://en.wikipedia.org/wiki/Boeing_A160_Hummingbird

Why are they bragging about a damn plane that has to continuously change positions to stay in the air with only a 5lb capacity when the have a rotocraft that can remain stationary and carry 1000+ pounds!

Re:Thanks for the redundant unit conversion!

[mspohr]

Can't we all just stick to SI units to avoid problems like this?

"The dimension of power is energy divided by time. The SI unit of power is the watt (W), which is equal to one joule per second."

Horsepower is a non-SI unit. "One horsepower is equivalent to 33,000 foot-pounds per minute, or the power required to lift 550 pounds by one foot in one second, and is equivalent to about 746 watts."

550 watts would be 0.74 horsepower but why even bother with horsepower? Only cowboys and the idle rich use horses.