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Solar panels, will be sewn or pasted onto the para-sail.
There will be a need for a Solaredge type device that allows
for maximizing output although non equal sunlight on all cells.
If ultracapacitors work as said, and are lightweight enough,
use them for intermediate storage so we get a constant
current to the motor, or use a small battery if necessary.
See video of solar powered glider, by my friend the late
Hanan Einav-Levi, who passed away at young age this year.
solar powered glider
http://www.youtube....watch?v=sXC5tBVC0wE
[pashute, Jun 21 2013]
Solar powered plane
http://www.youtube....watch?v=H6chzgkA3xM
[pashute, Jun 21 2013]
Current situation
http://www.mothswor...wered-paramotor.asp
[pashute, Jun 21 2013]
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The beauty of the paraglider is that the inflatable
wing is lightweight, robust and can be packed into a
rig. These advantages offset the fairly draggy
nature of a flexible ram-air canopy. |
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If you start attaching solar panels, you will surely
lose many of those advantages, no? |
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Are these things flown at night or in cloudy weather? Solar will be weak or none at those times. |
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No. Each solar cell attached in a way that keeps the
wing quite flexible. Were talking about a motorized
paraglider. |
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And of course this is good for nice weather and
daytime only. I wasn't aware of people flying
paragliders of any kind at night or in fogs. I don't
think its much fun. |
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A typical paraglider engine is 20-30HP, which is 15-
20kW. Given an insolation of 1kW/m^2, and an
efficiency of 15%, you're going to need something
like 100 square metres of solar cell, whereas a
typical paraglider has a wing area of about 30
square metres. |
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It's a nice idea (and people have, as you know,
made solar-assisted sailplanes), but solar cells
would have to have a much higher efficiency than
they currently have. |
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Drat. I didn't check that. |
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Based on the third link, it looks like this isn't your idea. It's just the dream of the person who wrote that web page. (or is that you?) But yeah, I'd like to see this become a reality as well. |
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I'll trust [Max]'s calculations to the first order, though he didn't include the affect of the weight of the solar panels, but besides making solar cells more efficient, the other possiblities are making the paraglider more efficient and/or larger to have more surface area for solar cells. How much will the weight of the solar cells affect the power requirments? |
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Increasing solar cell efficieny to be above 45% is not something I expect to happen. I'm not saying there can't be a major breakthrough but my money is on incremental improvments that won't get to that level in my lifetime. |
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//I'll trust [Max]'s calculations to the first order// |
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MaxCo. cannot be held responsible for any damages,
loss or injury however amusing resulting from
decisions, actions or pharmaceuticals taken on the
basis of its calculations. All numbers are for
illustrative purposes only; actual digits may vary.
Orders of magnitude are shown larger than actual
size. |
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Actually, I have a not unrelated question for anyone
who knows aerodynamics. What is the minimum
thrust-to-weight ratio necessary for level flight in
still air? Is this ratio the same as the lift-to-drag
ratio? |
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//Is this ratio the same as the lift-to-drag ratio?// Yes, because, by definition, for steady level flight lift = weight, and thrust = drag (ignoring the signs). |
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[edit] That's non necessarily all that useful, though, because powering an aircraft is likely to alter its lift and drag. So the best achievable power to weight ratio may be (slightly) different from the best achievable lift to drag ratio (the glide ratio) of an un-powered glider. |
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That makes sense. And for an unpowered glider, lift-
to-drag is the same as the glide slope? |
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In which case, if an aircraft has a glide slope of 1 in
30, then a thrust equal to 1/30th of its weight
should (ideally) be sufficient to maintain level flight? |
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To a close approximation, yes (^^ see edit). |
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Thanks. Yes, point taken about the effect of
thrust on velocity and hence drag. |
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I was trying to work out if "lifter" technology
(basically in-air ion thrusters, which entrain air in
a stream of ions between two fixed electrodes)
could feasibly power an untethered aircraft. |
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Thrusts (measured as ability to lift dead weight,
including itself) of 100 grams have been generated
in air from 17W of power, and with a relatively non-draggy electrode
array. So I'm guessing that a
glider-style model with a decent (15:1) glide ratio
ought be able to have about 1.5kg of total mass.
The question then is whether sufficient solar
cellage (or battery) to furnish 17W, plus the
necessary hardware to step the voltage up to
several kV, can be built within that weight. |
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How do spiders lift themselves to the
stratosphere? or is that an urban legend? |
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This weekend the Motzash newspaper dealt with
four urban legends by Israeli youth, and found
THREE of FOUR to be surprisingly true and even
the fourth has a lot to it! a. Girl had skirt ripped
off by car door when getting out of ride she
decided not to take. b. Girl brought to summer
camp by rich parents with helicopter. c. Kids
ritually married as joke with a pretzel as ring,
received formal status of divorcees. d. Some real
weird names were actually given to kids by their
parents, but "Disappointment" and "Held an
Almond Tree Branch" never existed. "Like" in fact
does. |
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They spin fine threads which have sufficient drag to
be carried by air currents. |
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[max] Actually I was just thinking that if you are
right, it should be a phenomenon found in nature.
When observing the clouds it seems that air
currents from earth do not rise to such heights. |
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[scad] no, its mot ne. But my idea was to use the
current PV cells, rather than pasting them on rigid
panels, pasting them on the wings, which would
leave them flexible (to a point). |
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But it seems the amount of current produced is
powerfully the factoring limit. |
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// When observing the clouds it seems that air
currents from earth do not rise to such heights.// |
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Cumulonimbus (storm) clouds reach up into the
lower part of the stratosphere; and of course air
currents need not be associated with visible
clouds.
There are also all kinds of things like mountain
waves (ie, air rising up to pass over mountains). |
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Quick Google says that the world altitude record
for a glider is about 59,000ft, reached using the
lee waves off a mountain. |
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