Liquid Hydrogen Powers a UAV For a Cool 48 Hours 72
An anonymous reader writes "While liquid hydrogen may not be a mainstream fuel for drones, the aerospace industry has said it holds the promise of flight endurance on the order of days, seemingly just another far-fetched aerospace industry pitch ... until now. The Naval Research Laboratory just announced that the Ion Tiger, a diminutive 37-pound airplane with a 17 foot wingspan, flew for 48 hours and 1 minute on liquid hydrogen and a fuel cell (anyone else notice the oddly specific duration? Guess it's better than 47 hours 59 minutes). This is a dramatically different scale than the liquid hydrogen powered 150 foot wingspan Boeing Phantom Eye and 175 foot wingspan AeroVironment Global Observer, which have yet to live up to their multi-day endurance projections. Interestingly enough, the well-known Global Hawk only has an endurance of 33.1 hours, which barely cracks Wikipedia's list of notable UAV endurance flights. Of course, solar-electric airplanes have flown for two weeks continuously, but that sure seems like refueling!"
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Why would you think so?
Does the idea of planning a '48 hour flight', and then spending a minute extra on landing after achieving the mission goal, seem strange to you?
All those extra minutes add up over time. IMO, all drones should have "instant landing" maneuvers. Simply start by pitching the nose to a moderately steep angle of 90 degrees down to cut out a lot of that landing time. Bonus: no need to calculate fuel usage time for any future flights...
Alternatively, as soon as the drone gets to its destination air-space, it could simply detonate any remaining fuel. ::KaBang:: - The sound of a drone reaching a state of perfection in usefulness to mankind.
Protip: Rem
There's something odd about the discrepancy (Score:1)
More like marketing: "Over 48 hours!" (Score:2)
The odd minutes may add up but I suspect it sounds better in marketing-speak: "Over 48 hours!" sounds more impressive than "48 hours 1 minute" or "2 days" perhaps?
Plus as somebody else had noted maybe there's a government contract which specifies money will be given if a prototype can be shown to run for at least 48 hours. Over 48 hours? 48 hours 1 minute, send us the money!.
These guys aren't into marketing... (Score:5, Informative)
I worked with this group and I can tell you they're not into marketing, but the press people that prepared the release probably are.
The bulk of what this NRL section does is technology demonstrators. They were also the first to air drop a drone from another drone. The odd number is probably an exact accounting of the time spent on powered flight; climb, cruise and loiter segments are the most significant for accounting for energy use during flight. Gliding and coast segments are not so interesting.
Props to my old crew at NRL, and to the memory of Jim Kellog who developed the first prototype of what became the Ion Tiger.
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Gliding and coast segments are not so interesting.
In this case, they are. The aircraft was powered by cryogenic liquid hydrogen. Even when they were coasting, they were still generating fuel (hydrogen gas), and that fuel could only be stored for a short period before rising tank pressures would have necessitated venting. Their fuel had a limited lifetime regardless of whether they were actually using it.
Re:There's nothing odd with 48 hours 1 minute (Score:5, Insightful)
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It's so no pedantic arseholes sneer about them probably rounding up.
This has everything sneering pedantic arseholes, refueling solar planes, and rounding.
Re:There's nothing odd with 48 hours 1 minute (Score:5, Interesting)
also if you say '48 hours' it sounds like you are approximating. but 48:01 is precise enough for people to know that you are serious.
The first man to calculate the height of mt everest calculated it to be 29,000 feet exactly. To make it sound as precise as it was, he said it was 29,002 feet.
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Another way to do it without lying is to slap a .0 at the end.
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Actually hydrogen mixed with oxygen in the relation 2:1 is much worse than hydrogen as a concentrated cloud.
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That is.... Water!
Re:I think liquid hydrogen is dangerous as hell (Score:4, Funny)
That is.... Water!
After the explosion, yes.
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Obligatory http://www.dhmo.org/ [dhmo.org]
Re:I think liquid hydrogen is dangerous as hell (Score:4, Insightful)
Like all mono propellants, it can break down to a more stable less energetic configuration without the need of getting mixed with anything. So say the fuel tank wasn't cleaned properly? Well we get H202 decomposition which liberates O2 and heat. Now its hotter and it decomposes faster, which produces more heat and faster decomposition.... I have personally seen this with my own monopropellant rocket.
Can you handle H202 safely? Yes. But you can also do that just fine with LH2 with the added benefit its pretty safe till you mix it with oxygen, and its has much more energy per kg. An important feature for long endurance flights.
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Two furlongs a fortnight... (Score:5, Funny)
How about you try to use units that make sense? Here's a diagram that illustrates the sillyness https://7chan.org/sci/src/132255181954.jpg [7chan.org]
Re:Two furlongs a fortnight... (Score:4, Funny)
Yes, they certainly should have used "172.86 kiloseconds" instead of "48 hours, 1 minute". Those odd factor-60 minutes and hours should die. It's not that hard to remember that a day is 86.4 kiloseconds and a year is about 31.5 megaseconds, after all.
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What are these archaic "day" and "year" units you're using? I haven't felt the need for units based on the orbital mechanics of one single planet for a significant fraction of a gigasecond. And besides, 10*PI megaseconds is a much more interesting period of time. :)
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Actually a good way to remember the length of a year is to remember that pi gigaseconds give (almost) a century.
decimal time (Score:2)
Those odd factor-60 minutes and hours should die
There has been an attempt at decimal time [wikipedia.org] during the french revolution, but it did not catch up
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Surely it was to meet a contract stipulation: "...shall fly for a period exceeding forty-eight (48) hours..."
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Why don't they have RTG's? When one crashes in your backyard you'll be glad.
Re:Wait..what?! (Score:4, Insightful)
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The ones sent into space are designed to withstand an uncontrolled reentry from space. The ones used to power lighthouses (for example) are significantly less durable, and I dare say that one built into an aircraft would want the minimum acceptable shielding.
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The ones sent into space are designed to withstand an uncontrolled reentry from space. The ones used to power lighthouses (for example) are significantly less durable, and I dare say that one built into an aircraft would want the minimum acceptable shielding.
Mass for a spacecraft is far more expensive then mass for an airplane.
Also, if the RTG falls out of a lighthouse it is not going to fall very far, so not nearly as much need for shock absorbing, while the uninformed people will go OMG NUCLUEAR! and aeronautic approved RTGs will need even more protections than those in spacecraft.
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It's my under standing that the few times those lighthouse RTG's or other non-space application RTGs have been opened and recovered by civilians the casualties were low. They didn't kill even 100's of peoples.
Total fatalities due to RTGs to date is probably less then 100. And this is a horrible estimate. Completely inaccurate and unscientific, but leaning on the safe side enough to make a point.
RTGs are not that bad when handled properly. Soviets screwed up by widely distributing them and not decommissionin
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The HINDENBURG carried engines + fuel totaling about 150,000 lb. Cruise power was 3200 hp (2400 kW) at 68 knots, but she could go 40 knots on 500 kW. That's 300 lb/kW. Is that close enough?
An airship that could travel at 40 knots for YEARS without stopping sounds pretty viable to me.
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I suppose I should have specified heavier-than-air-craft...
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I understand, but what does it matter by what design you achieve viable controlled flight a specified ratio of engine+fuel mass to engine power?
I am also pretty sure you could match that 40 knot figure with some kind of radical super-super-light huge-and-slow airframe such as is used in solar aircraft. Not sure if I would rate that viable except for special missions.
That's not long try 14 days (Score:2)
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Hate drones (Score:1)
Someone please come up with a small Arduino solution to shoot them down.
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I'd suggest some sort of catapult. Although I'm not sure Arduinos are the best type of ammunition.
Well they are (Score:2)
[x] useless
[x] have pointy edges
I say man the catapults!
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So it is OK to shoot down a plane just because it doesn't have a person in it?
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So it is OK to shoot down a plane just because it doesn't have a person in it?
That depends, are there a lot of people under it as well?
What's bad with solar? (Score:1)
Of course, solar-electric airplanes have flown for two weeks continuously, but that sure seems like refueling!"
Come on, that's terribly unfair! Refueling as you fly is not the same as having to return to base...
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Come on, that's terribly unfair! Refueling as you fly is not the same as having to return to base...
It's not refueling at all. Refueling would be swapping batteries. This is recharging. It's foolish to try to describe recharging as refueling when there's already a separate name for each. Or, in this case, it was prevarication on the part of the commenter.
Nice comparison (Score:3)
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For 'regular' turbine engines this is typically done with the 'specific thrust' and 'specific fuel consumption'. With these this allows you to make more reasonable comparison between engines of whatever size. Of course performance characteristics such as velocity of the plane etc should be the same.
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I am sure the OP meant 737.
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The Global Hawk isn't anywhere close to the size of a 747. A 747-8I is about 4x taller, 4x longer, 4x wider wingspan. It is a big drone but not especially large compared to other aircraft.
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I got the wingspan wrong but it still isn't anywhere close to a 747.
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Fuel cells can be anywhere from 1% to 90% efficient. In this case it's probably nearer the 90% limit, but that's not the general case.
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In general, the limiting factor is the quality of the hydrogen - the oxygen can generally come straight from the atmosphere. In this case, it's pure hydrogen stored as a liquid, so fuel cells tend to be fairly efficient.
Take Apple's fuel cells powering their data center, and they're running off natural gas, which is 20% carbon for the most part (by stoichiometry) which is impur
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If the clock read 48:01:00 then that is what the clock read.
No comparison with Global Hawk (Score:3)
It flies at 300 knots and weighs ~30,000 lbs (~14,000 kg).
I worked on the NASA Global hawks for a few years. They are incredible aircraft and certainly not in the class of the toys it is being compared with. Predator comes close (I was on an effort to put a sensor on the NASA Predator but funding got yanked) but Predator doesn't have nearly the capability of Global Hawk.
Naval Research Laboratory (Score:1)
Yeah, I've spent some quality time navel gazing myself.
Other benefit (Score:1)
The liquid hydrogen can be used to cool the infrared sensors as well.
not impressed (Score:2)
Not sure that says much about the power system.
The plane appears to be very close to a sailplane. Drop the weight a bit and i think it would run on watch batteries and thermals.
17 feet is a lot of wing for 40ish pounds of airplane.
hmm, can we make a powered glider that can find a big thermal and reverse the circuit to recharge a battery in a dive?