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back to article Giant solar-powered aircraft takes to the skies

Swiss adventurer Bertrand Piccard today moved one step closer to fulfilling his ambition to fly a solar-powered aircraft round the world as his Solar Impulse completed its first full-fat test flight. The Solar Impulse The Solar Impulse boasts a wingspan as wide as a Boeing 747, with 12,000 solar cells powering four electric …

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      1. mahonj
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        The problem is holding position, not endurance

        It seems obvious that this is a test for a long endurance UAV where they put in a pilot during the test phase as they need the flexibility that a pilot gives during development.

        This I buy.

        However, I am not sure it will be able to remain circling around one point for a long time if the wind gets up. If you can only go 44mph, and the wind is > 44mph, you will start to drift off.

        What they need is more power, and hence solar cells that are more efficient for the same mass (check out their website). They would also like better batteries (as would the whole EV world).

        They may be in luck with the batteries as loads of people are working on this, it is likely to happen sooner or later. The solar cells are another matter. Lots of people are working on solar cells, but I have not heard of anyone working on very LIGHT ones. This they will have to pioneer themselves.

        Then there is the ultimate efficiency of solar cells. These seem to top out at about 38% at present for very expensive ones. They are using 12% ones (for lightness), and we could imagine they could get to say 18% with a little work.

        This is still only 50% more power, which might allow them fly 25% faster - say 55mph - this is still too slow to hold position in many stratospheric zones.

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        1. Nigel 11
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          Better than 18%

          You can buy 18%-effficient panels to go on your roof today. The gap between best and cheapest will narrow for solar cells, just as it has for CPUs.

          For light weight, one wants a thin film solar panel, rather than thick(ish) slices of silicon assembled into an array. Then integrate the thin film into the flight surfaces of the UAV. You can probably do that with CdTe or CIGS, and the technology of thin-film solar cells is rapidly advancing.

          It might not be the end of the world if one could not do stratospheric position-holding, though it would require some diplomatic effort to allow a large number of high-altitude unmanned communications platforms to "orbit" the planet in the stratosphere. Manouvering ability sufficient to avoid being blown over a few paranoid states like North Korea might suffice, if China, Russia, the major emerging economies and the West agreed to allow a worldwide UAV communications system.

          Air is much thinner at high altitude - doesn't that reduce the amount of power needed to fight a headwind?

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  2. Louis 3
    WTF?

    Flight, right!

    This is all well and good... in theory. But, everyone knows that you can't "fly" around the world!

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  3. SolarDude

    Better alternatives

    While this is cool, to me this seems much less promising than other technologies. Consider this:

    http://www.solarairship.net

    They also have a flying prototype. And their craft is faster, flies higher, is safer, wouldn't be affected by cloud cover, and most importantly can actually carry a useful load. I think the future of solar powered aircraft is more likely to take a shape like this than a heavy aircraft that can not lift anything.

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