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NASA Breakthrough For Solar Powered Aircraft

Posted by timothy on from the sunlight-is-free dept.

gilgsn writes "Planenews.com just received a news release from NASA's Dryden Flight Research Center about a breakthrough in fuel cell technology for solar powered aircrafts and how they used internet technology to broadcast data and HDTV video from the stratosphere above the Hawaiian island of Kauai. Their Helios Prototype could now fly through the night. I am sure that besides public communications, this will interest the military for their drones.."

4 of 23 comments (clear)

  1. Cancel that by MacAndrew · · Score: 3, Informative
    Forget what I said about getting shot down and weather. This thing flies higher than both. My eyes apparently skipped over the subhead of the Apple article:
    Powered by the sun and controlled by Power Macs, the ultralightweight Helios aircraft shattered the world altitude record in August 2001 when the remotely-piloted vehicle climbed to more than 96,500 feet (29,421 m.) -- three times higher than most commercial jets -- in a test flight over Hawaii.


    HAPPY NEW YEAR
  2. flying through the night still half a year off by js7a · · Score: 4, Informative
    Their Helios Prototype could now fly through the night.

    Not yet; that regenerative cell endurance upgrade is scheduled for completion by Summer 2003.

  3. Fuel cells turn out to store much more. by Christopher+Thomas · · Score: 5, Informative

    The energy obtainable by dropping a few kilometers -- hardly a big deal for a wing 40km up -- would be just as much as could be stored in fuel cells

    This turns out not to be the case.

    Energy stored gravitationally is F*d: 10N/kg * 1e3m, or 10 kJ per kg per km.

    Energy density for conventional batteries is at least 10 times this. Energy density for chemical fuels is several hundred times this. So, for a fuel cell power storage system representing a small fraction of the craft's mass, you get much more power storage capacity than you'd get from having the craft sink and rise again.

    The main problem will be keeping the weight of the hydrogen tank down (if stored at high pressure), or the volume down enough to fit in the craft's airframe (if stored at low pressure).

    1. Re:Fuel cells turn out to store much more. by Christopher+Thomas · · Score: 4, Informative

      I think you're missing the point. It does not matter at all how much potential energy is stored in a few kms of altitude. But if this craft is good at gliding, which it should be, being light with a large wingspan, it would only drop a few kilometers overnight through unpowered gliding.

      I find it doubtful that it would only drop a few kilometres after gliding for 12 hours.

      Back of the envelope calculation supporting this:

      From the Helios page cited by another poster, Helios weighs 1600 lbs, and has 14 moters rated to 1.5 kW each (2 hp). This gives a power consumption of 0.029 kW/kg, or about 1.25 MJ/kg over the course of 12 hours. Dropping 10 km gives you 0.1 MJ/kg. Power used in flight is far greater than gravitational potential energy for any practical drop, even counting the fact that the motors are not perfectly efficient at driving the craft.

      In summary, you'd hit the ocean quite early trying to glide overnight.

      The builders of the craft seem to agree, as the project page mentiones fuel cells being _required_ for operation through the night.