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Science Technology

Experimental Fuel-Cell Airplane's 2nd NASA Test 29

Posted by michael from the feeling-lucky dept.
js7a writes "The Helios prototype, holding the sustained flight altitude record, having unsuccessfully completed its first test with a fuel cell, is almost ready for its first night flight this Thursday, Friday, or Saturday. Helios uses solar panels for flight with payloads over 600 lbs. planned for up to six months using regenerative electrolysis. What good is a plane that will fly for six months without refueling? Besides providing a UAV alternative to AWACS, they can improve internet connectivity."
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Experimental Fuel-Cell Airplane's 2nd NASA Test More

Experimental Fuel-Cell Airplane's 2nd NASA Test

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  • I want one (Score:5, Insightful)

    by Beryllium Sphere(tm) ( 193358 ) on Wednesday June 25, 2003 @01:11AM (#6291868) Journal
    I wonder about the engineering tradeoffs. The electrolyzer and the tanks add weight, compared to the other approach to nighttime operation of solar powered aircraft -- drift downward. There's quite a bit of stored energy in an airplane that's been lifted to 100,000 feet. At low speed with a good glide ratio, you can coast until dawn.

    If you incur the weight penalty to stay at 100,000 feet, you get continuous radio coverage over a ~500 mile radius. If I were Indonesia and trying to deploy broadband over hundreds of islands I'd be really interested in this.

    • Radio Ground Coverage (Score:1, Interesting)

      by Anonymous Coward
      If you incur the weight penalty to stay at 100,000 feet, you get continuous radio coverage over a ~500 mile radius.

      Are you sure? I'm no expert, but I remember the flying wireless internet platform proposals from a few years ago flew pretty high - (50k feet, maybe?), but didn't aspire to cover anything more than a single city. 100K feet is only 18 miles - is that really high enough to get line-of-sight on something 250 miles away?

      • Re:Radio Ground Coverage (Score:3, Interesting)

        by js7a ( 579872 ) *
        There's more to it than that. Once you're above the troposphere, you get to use the ionosphere as a reflector with much less penalty. That's how over-the-horizon radars work.
    • At low speed with a good glide ratio, you can coast until dawn.

      Sounds like that old game F-19 Stealth Fighter [mobygames.com] from MicroProse.

      I used to be able to fly across the Persian Gulf with no fuel just by nosing down and up. Landing was a bit tricky though ;)

  • I wonder if it would be possible for a future aircraft to stay up most of the time by just gliding, using computer vision (low power laser rangefinders along with GPS, maybe?) to detect thermals, then computation to plan routes to ride those thermals upwards, then glide downwards to the next thermal. This could conserve a lot of power, which could be used only when absolutely needed.

    Yeah I know there are gliders now, but I'm talking about something that basically stays up for weeks or months at a time.

    • Re:Autonomous thermal surfing? (Score:5, Interesting)

      by dougmc ( 70836 ) <dougmc+slashdot@frenzied.us> on Wednesday June 25, 2003 @02:54AM (#6292167) Homepage
      I wonder if it would be possible for a future aircraft to stay up most of the time by just gliding ...
      The problem with this idea is that thermals are powered by the sun. Once the sun goes down, the thermals do too. You might have some thermal activity due to a large concrete item that retains heat well (I bring this up because I was slope/thermal flying an R/C plane over Mansfield dam [travis.tx.us] today) but even so it wouldn't last all night.

      That, and thermals do go up high, but not up to 100,000 feet. And a plane that stays at 1000 feet isn't nearly as useful as one that stays at 100,000 feet.

      Slope soaring would make more sense, as if you're in a coastal area is usually always windy and the wind direction is pretty well known, but this would require an appropriate slope and it's hard to gain signifigant altitude unless you have a full mountain for your slope.

      You could probably keep a plane up indefinately over a constant source of massive heat like a nuclear power plant or volcano, but that wouldn't be very useful.

      I believe that the world record duration for a R/C glider is 30 hours or so -- I don't know the specifics, but I'll bet this was on a slope. After 30 hours, he probably either got tired or his receiver battery died :)

      • At 100k feet they're above most of the atmosphere. I'm not sure that there would be enough thermal airflow to add much lift.
      • For serious high altitude sail plane action you need rotors...

        They are basically the eddys in the wakes of mountains, and they are what is used to set altitude and duration records in gliders. I only flew in Illinois, so I never experienced one, but I had a friend in my glider club who was from Germany (a grad student at U of I) who had been at 20,000 for 6 hours in a rotor before.

        I think (don't quote me) the unpowered altitude record is in the neighborhood of 60,000 ft.
    • Uh....Isn't that what this article is about? It doesn't have the friken lasers though....

    • Re:Autonomous thermal surfing? (Score:4, Informative)

      by bobba22 ( 566693 ) on Wednesday June 25, 2003 @07:11AM (#6292755) Journal
      The BBC are reporting on a british version designed to go higher still. http://news.bbc.co.uk/1/hi/sci/tech/3016082.stm This will go to altitudes around low earth orbit. At these heights, surely gravity is less of an issue and the night-time drift downwards would be less significant, easily made up for when the sun rises (there would be a longer day high up, too). The ground coverage at such a height would be quite dramatic, the entire UK can be covered by one 'plane. What are the hazards from weather that high? Apart from temperature exrtemes, do high winds happen?

      • Re:Autonomous thermal surfing? (Score:5, Informative)

        by mess31173 ( 462954 ) on Wednesday June 25, 2003 @10:16AM (#6293965) Homepage
        surely gravity is less of an issue and the night-time drift downwards would be less significant

        Wrong. Gravity still has about the same strength there as it does with your feet securely on the ground. The difference is only negligible. The only reason that satellites and other orbiting objects stay in space is because they are moving very quickly. Imagine this; An object traveling so fast that it is trying to leave earth orbit but it doesn't quite have enough energy to overcome the force of gravity and fly off into space. So it is constantly falling at the same rate, it's just balanced at the perfect position to not fly off and not to fall. This is called orbit. It's not because at some magic spot gravity ceases to be as effective. Look at the moon. Cheers!

      • Re:Autonomous thermal surfing? (Score:1, Interesting)

        by Anonymous Coward
        Try http://www.qinetiq.com/news_room/newsreleases/2003 /2nd_quarter/qinetiq19.html [qinetiq.com] for a bit more information on this.

        If everything comes off, this will be a very public, practical usage of high altitude UAV, taking pictures of a record breaking high altitude balloon [qinetiq1.com], taking off from a triple hulled ship [qinetiq.com].

        Nothing like three birds with one stone.

  • Drag not gravity... (Score:4, Insightful)

    by mess31173 ( 462954 ) on Wednesday June 25, 2003 @10:37AM (#6294182) Homepage
    I feel compelled to add another comment here. Everyone is focusing on gravity here as the big factor as to this things glide time. Although this is obviously an issue in the big picture it's not the real issue. Didn't your teachers ever show you the experiments where people would drop a feather and a bowling ball in a vacuum and they would both hit the ground at the same time? Does this mean anything to anyone. I can hear the light bulbs go off now.

    The real issue is DRAG a.k.a. FRICTION. If there were no or negligible drag this thing could fly forever. It's the drag that slows it down and causes it to drift back to earth. So what do you need to increase your speed? Propellers. And what drives the propellers? Fuel cells. What these scientists are doing is trying to make their fuel cells more efficient so they can over come their ultimate enemy, drag. Just a little insight for everyone. Cheers again!

    • Surely, with, say, 1/10 of the real gravity, staying up there would be much much easier. Atmosphere probably would be denser there and motion caused by warming/cooling would be slower.

      Now, what makes the planes stay up? Antigravity? Drag? Anti-drag? No.

      Hot air balloons (or hydrogen/helium balloons (or even great balls of vacuum)) stay in the air the same way things float (or don't sink) in the water. Principally, water/air density is bigger under the object than it is above it. This always generates a f

    • The real issue is DRAG a.k.a. FRICTION. If there were no or negligible drag this thing could fly forever.

      No. If there were no drag, it would fall like a marble.

      Gravity is what airplanes fight, and they do this by passing an irregular surface rapidly through the atmosphere, creating an ineqity in the pressure of the air, and thus creating lift--which works directly against gravity once you have enough of it.

      You're right about the fuel cells and the propellors, but wrong about what they fight. Heck, if
    • It's the drag that slows it down and causes it to drift back to earth.

      There are two kinds of drag - parasitic drag and induced drag. Parasitic drag is drag that does not contribute lift. It increases with the square of airspeed. Induced drag is due to the fact that wings do not lift straight up - they lift slightly aft as well (well, that's the simplified explanation). The larger the lift coefficient, the more pronounced this aftward lift is.

      In this design, you can be sure that almost all of the drag is

  • I remember a discussion a while back dealing with small zeppelin/ballon networks placed around a metro area. Wouldn't this provide a better platform from which to launch city wide wans?
    • There are experiments going onin the UK but I doubt it will ever prove practical. The baloons are tethered via fiber links and float at about 5 mi elevation.

      On this hilltop where I live, we have at least one lightning strike every year. Just about a month ago my modem (again) was fried by a ground strike in the nearby pasture. A few years ago it hit the pole in the backyardand spread throughpout the house. A few years before that it hit the house directly and fried telephone wire, computer, televisions, st

  • Why do half of these look like they're straight out of a fark.com photoshop contest?
  • Thursday's skies show no clouds over Hawaii, and perhaps 15% scattered clouds out hundreds of miles. Go for it!

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