h a l f b a k e r yAssume a hemispherical cow.
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solar powered jet
a flying wing air plane with fresnel lens or parabol concentrate sun's light to a jet engine | |
a large 100x100 meter flying wing would generate more
than
10MW enough to keep the airplane flying at a high speed.
Fresnel lenses in the transparent hull gives maximum
design
freedom, but a parabola would also work.
Above the clouds there are 30% more sunlight and no
clouds,
enough to
keep up the speed of the earth's rotation and
become a virtual satellite. (see image)
image of jet
http://4.bp.blogspo...03-29++08-42-34.jpg
sketch of flying wing with jet [janpeternordin, Apr 01 2013]
Reactor-derived heat for aircraft propulsion
http://en.wikipedia..._Nuclear_Propulsion
[bs0u0155, Apr 01 2013]
Laser powered ramjet
http://www.dtic.mil...text/u2/a442467.pdf
[Kansan101, Apr 01 2013]
Solar Impact
http://www.thephuke...ss-the-us-38583.php
Transcontinental flight of solar aircraft. [whlanteigne, Apr 13 2013]
[link]
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I have no idea whether this would work, but it's a beautiful idea. [+] |
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Welcome to the 'bakery, by the way. |
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Your 100mx100m surface will intercept 10MW, but
how are you converting that to usable energy?
The current best research grade PV cells are only
~45% efficient, and they aren't on the market yet. |
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If you're going purely solar thermal, you could, in
theory, approach the Carnot efficiency which is
86% based on the sun's temperature, but the
competing requirements of aerodynamics and
optics are going to keep you well below that, even
before you account for the real world nature of
the engine. |
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Not saying it's impossible, just run the number for
something more like 3-4MW for that size wing,
rather than 10. |
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And welcome to the bakery. |
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Nice idea! I'm not entirely clear how the jet is going
to use the 10MW of focussed heat, though... |
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And, indeed, welcome to Care in the Community. |
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"Fasten seat belts" light stays on above 30 degrees latitude,
particularly in winter. |
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I like the idea of each wing doing double duty as a lens. I would like the hull opaque, if you don't mind, as my piloting regalia might attract comment from the unenlightened. |
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The mechanics of it: one could make a hunk of stuff very hot with a big Frensel lens. I am less clear on how one could make that hot hunk of stuff generate directional thrust. Hot air will surely shoot out the back. But it seems to me that getting cold air into the front of the hot hunk would be difficult. Would a ramjet style thing work? Fuel combustion seems to me directional in a way that conductive heating is not. |
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The best I can come up with for simple heating is
pulsejet. I suppose you could always use an PV
electric compressor fan. |
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I'm thinking this type of concept wants to lean closer to an assisted lighter-than-air type of craft, or perhaps an almost-lighter-than-air craft. |
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I think it would be nearly impossible to orient the wing correctly for both horizontal flight and energy capture except at the one place on Earth where the sun is directly overhead. |
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So if you have a flying wing, with a
transparent/fresnel lens upper surface, you've got
to get your focused radiation to one or two spots.
Common sense dictates that you want your jet
engines in the centre, so you've got to get the
energy there. |
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Now, the engines I can see working, standard jet
engines more or less with the energy coming from
sunlight rather than burning kerosene. You'd have
to get the light in via some form of super-tough
window, diamond or whatever, but after that it's
doable. Nuclear aircraft have been designed and
tested, and all their engines did was inject heat at
the right point. |
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The difficulty is going to come in non-lossy optics
and the angles you have to play with. Put simply,
you'll need some pretty convoluted optics to get
your radiation where it's going without having a
prohibitively thick wing. You're also not going to
have very much interior space.... there will be
wave guides filling the wing. |
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How about a flying wing with a large parabolic
collector in the centre.... using focused sunlight
from a huge orbital mirror? The mirror could track
the aircraft. |
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Perhaps Fresnel lenses focusing on a great many
vacuum-insulated liquid sodium tubes? |
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Here's how I would build it, assuming that the plane could be restricted to flying at noon with the sun straight overhead: |
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The wing would be a Fresnel lens. The engine would be slightly below the wing, mounted forward of the center. The focusing light would strike a parallel flat mirror positioned halfway between the wing and the focal point. The beam would be reflected upwards, where it would focus at the center of the wing. A convex mirror at the center of the wing would reflect directly into the rear of a ramjet, where mirrored surfaces would direct the light to the center of the engine where the air needs to be heated, where all the surfaces would be black. |
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Link to laser powered ramjet that NASA built. |
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Link to Solar Impact, Swiss-made solar-powered
airplane. |
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