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?

[Rei]

Oh, I'm sorry -- point to me where they had a wingspan restriction in their unconditional statement.

Re:Huh?

[Rei]

"Fuel cell plus solar powered electrolysis"? Yeah, throwing away 70-80% of your energy is a good way to stay aloft, right? Low loads on a fuel cell means tank-to-drive efficiency of ~45%, and small-scale electrolysis tends to be very inefficient, generally 50% or less (the big steam electrolysis systems are more efficient).

The Zephyr stayed aloft with lithium-sulfur batteries. Being still experimental, they don't have a very long cycle life yet (although there have been some big lab breakthroughs in this regard), but they have more energy storage capacity than li-ion. And more importantly, they don't throw away the overwhelming majority of their collected energy.

Re:Huh?

[mcrbids]

That would mean an efficiency of greater than 100%. Which is obviously nonsense. ICEs are generally 35-45% efficient in peak operation.

Yeah, that thought crossed my mind, too. But "efficiency" can mean different things depending on context. You could mean "time efficiency" - how much time gets wasted getting a job done, which would be irregardless of other resource usage. You are talking about "efficiency" in terms of ability to convert chemical energy into mechanical energy, and you are right, there.

But read the article. By context, I think they are actually talking about strength-to-weight ratio - how much useful power you get per pound of fuel/battery/engine. Combine that with the informal nature of the article, and it kinda makes sense that way.

Me? I'm curious about a system with obvious advantages for private aviation:

1) Better power/weight ratio, which is big. Even in a fairly substantial Cessna 182, when you take off with full fuel, you have to be honest in considering the actual weight of your passengers.

2) Fewer moving parts: Few pieces of equipment rival the reliability of an electric motor. If fuel cells are a simple chemical process without moving parts, the chances of failure could potentially drop through the floor. And that makes flying safer for everyone - most importantly, me.

Everything about a plane is about reducing failure rates. They are expressly designed to reduce mechanical complexity to reduce the chances of failure. The fuel mixture on a private plane is adjusted manually. The throttle is very simple. There are actually two ignition systems on each plane, and rather than use an electrical coil like a car, they each use an independent magneto system, like a lawn mower, so that an electrical failure (like a blown fuse) won't stop the engine from working.

If you could reduce the number of moving parts to ONE.... wow. That would be... AWESOME.

Re:Huh?

[X0563511]

He's not talking about a commercial airline. He's talking about small private planes for private use.

Re:Huh?

[TheLink]

That's true.

But still it's for spying. Everything else being equal, it's harder for something with a 2.5m wingspan to be spotted than something with an 18m wingspan.

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.

Re:Green don't matter

[PhantomHarlock]

The fuel cel is only green if you are separating the hydrogen and oxygen using power from a nuke plant. Otherwise it costs a tremendous amount of fossil fuel energy to separate the hydrogen.

The only truly green fuels at this point are hydrogen and electricity from nuke plants, perhaps supplemented by solar and wind, although the later two are extremely expensive per watt in comparison, as well as extremely inefficient land-usage wise.

--M

Re:Green don't matter

[Anonymous Coward]

Right. How does the army get its electricity in Afghanistan? A very long cable from the ÜS, or Europe, or India?

Of course energy efficiency matters for the army. More often than not they have to bring diesel in with trucks and run generators.
These convoys are expensive and vulnerable. Tons of black coal are definitely out of the question.

easy fix

[Tablizer]

Think about lawnmowers or chainsaws -- [conventional UAVs are] really loud...It's hard to spy on people when they know you're there

Just pay some neighbors to mow their lawn all day so that nobody knows the difference.

Re:easy fix

[MoeDumb]

Honey, is that you posting? All right all right, I'll get off the computer and mow the lawn! Although I never thought you'd stoop so low to troll here just to get my attention.

ion + tiger =

[threexk]

iger?

Great place for a fuel cell

[WindBourne]

In general, Fuel cells (and oil powered engines) are going to lose out to batteries. Battery (and ultracaps) tech is improving at a quick rate. HOWEVER, at this time, hydrogen fuel cells will win out if you disregard costs. I have little doubt that this craft will costs more to build than will either battery or engine based, but it does something that the other 2 do not do; The demands of the job.

Re:Great place for a fuel cell

[WindBourne]

I'll take those fuel cells and raise you by more than 10x the li-ion I will also note that those fuel cells who were developed in the 80's have gone nowhere. In addition, I am guessing that not too many will want molten coke in their crafts or car.

Thanks for the redundant unit conversion!

[voltaicsca]

Ok, great. 550 watts is approximately equal to 75 horsepower... Did they really need to include that? And that's before the energy is converted from electrical to mechanical, so that is, in fact a completely useless number. I understand goverment reporters not fully grasping units of measure, but slashdotters?

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.

Just the opposite

[WindBourne]

hydrogen Fuel cells will ALWAYS be expensive.

Far more problematic, production and transportation of hydrogen will remain highly inefficient compared to battery or far more likely ultra-caps. Oddly, I have seen the pro-h2 side claiming that it is more efficient to build fueling stations in which the hydrogen is generated from water vs. batteries. So, now, they want to transmit the power the same distance and then convert, store locally, fuel a car, store on the car, convert to electricity vs. storing on a battery. Keep in mind that each step has lose of efficiency, and batteries are more efficient than any of the steps just mentioned (and one step vs 4).

The only issue will be energy density of a battery/ultra cap. And that is increasing rapidly. Even now, the lithium air with 10x increase in energy density over lithium ion, will likely take out all hopes of the fuel cell being a commercial success.