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In order for a kite to produce lift, and remain in the
sky, it must be moving relative to the air around it.
This is most commonly accomplished by means of a
string which is anchored on the ground. From the kite's
point of view, the string is providing forward thrust
(and a downward load,
but we'll ignore that).
What if the kite was flown into an area with high-speed
wind, such as one of the world's four jet streams, which
has much lower speed wind around it?
A drogue parachute, inside the jet stream, could pull a
cable attached to a kite flying above the jet stream.
Drag on the chute moves the kite/chute system along,
and the tension on the cable provides thrust for the kite
(which is, after all, in slower air).
The kite would of course need flight control surfaces, in
order to keep the drogue centered within the width of
the jet stream, and at an appropriate height for the
drogue to be in the jet stream, with the kite outside it.
To keep the cable between the kite and the drogue
parachute from being too close to horizontal (which
would result in the the kite entering the jet stream, or
the drogue leaving the jet stream) there would need to
be a heavy weight somewhere in between the two.
Naturally, this would be the ideal location for whatever
payload the kite is to carry.
If the payload needs electrical power, a wind turbine
could be attached to either the kite or the drogue
chute. If the kite is to fly "forever," this would be
necessary, in order to provide power for the kite's
control surfaces.
To launch the system, the kite would be towed behind
a conventional airplane in the same manner as a glider
might be towed; once the airplane reaches the jet
stream, it turns to face upwind (if it isn't already),
moves above the stream, slowly lets out the payload,
then most of the cable that's between the payload and
drogue parachute, then finally releases the chute.
In order for the system to accurately locate the jet
stream (which certainly isn't a perfect circle around the
earth, and furthermore changes location seasonally), the
kite is equipped with a doppler LIDAR system which can
track the speed of the air in a 3D volume of space. This
is the same technology which is being tested with some
big wind turbines, to allow them to turn to face the
wind seconds *before* the wind shifts direction, in
order to produce more energy than they would if they
merely responded to a weather vane.
The most likely type of payload would be whatever
you'd normally stick in a weather balloon.
The existing technologies that this idea is in most direct
competition with are weather balloon, and satellites.
However, where a balloon might stay up for tens of
days (until the helium leaks out), this system can stay up
until a mechanical failure occurs.
And it takes lots of money to put a satellite into space,
so a jet stream powered kite is going to be much
cheaper, if it works.
Automated solar airplane that could fly 24/7 and never needs to land
http://www.physorg.com/news199158296.html
Maybe just every fortnight or so. [2 fries shy of a happy meal, Aug 18 2011]
[link]
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If someone could make an automated solar airplane that
could fly 24/7 and never need to land, this idea would
also compete with that. |
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If someone were to invent a helium balloon or blimp,
with atmospheric water extraction, PV panels, and a
device to perform electrolysis on that water, to replace
the hydrogen that's lost to diffusion quickly enough to
remain aloft indefinitely, then this idea would compete
with that technology. |
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Say, how halfbaked is that last idea? |
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Well, I baked the other half, and I'm afraid the prognosis
isn't good; you see it's this issue we always seem to have
with moving parts... |
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[+] I'll let you throw mine. It's a cool idea, even if it would
just get sucked into a jet turbine or eventually fall out of
the sky and cause a freeway pile-up. |
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In the event of the system leaving the jetstream, it shouldn't pose a danger. It already has a parachute and control systems, so it could easily put itself down somewhere safe and wait for re-deployment.
As for jet turbine suckage, to do anything useful it will need to be a decent size, therefore it will be visibly- and radar-detectable, and big enough to not (easily) be sucked in.
The part that is in the jetstream will also need to be kite-ish; a simple drogue will want to 'fall' out of the stream. So it will basically need to be 2 kites fighting against their respective aerial environments. |
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[AO], first, which of your ideas consists of (half of) a
solar powered, self refilling, hydrogen blimp? And, how
many moving parts are involved with photocells and
electrolysis? I'll admit that atmospheric water
generation involves moving parts (namely, all of the
parts of a dehumidifier), but surely it should be possible
to make one which can function for a couple of years
without maintenance. |
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Second, an airplane flying in the jet stream will surely
have forward looking radar to detect other air vehicles,
even if those air vehicles are kites. Especially if the
payloads of those kites have radio beacons which
announce their presence to any nearby airplane. |
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[BS] What's to prevent your nanobots from swimming
into someone's pants? Or worse, into their bladder? |
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Alright, so I was being a little loose with my criticism. I
apologize for that. I was really just trying to point out the
more complex a machine gets, the less time it's going to
function autonomously before something breaks, and if the
sucker's just scooting along in the jet stream, there's no
telling where it's going to come down (probably in the
water). |
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In no way did I mean to imply I'd posted a similar idea; I
meant the 'baked the other half' comment as a way of
saying, 'here's the drawback I see'. Obviously I completely
missed the net with that one. |
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I'd ride one. Does the insurance package cost very much, and does it include something to eat while you wait for helicopter pickup? |
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I don't really grok the idea except for "put a bunch of stuff into the atmosphere". |
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Unless your two airflows are in opposite directions you will not be able to maintain position by any sort of vanes, unless the two ends are connected by a solid strut, ie: not a rope. |
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You will of course still be able to sail, just the same (more or less) as you could using water and air: just not stay still. |
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//Unless your two airflows are in opposite directions
you will not be able to maintain position by any sort
of vanes// |
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Is that right? After all, you can tack a boat into the
wind, fundamentally by exploiting the difference
between the movement of the air and the water. It
should be possible to do the same using a double-
kite. |
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yeah you're right, I keep thinking they're the same altitude. In which case why is this post not "aero-nautical sailboat" or something. |
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You could probably build a rig that would keep station. You could also launch this from the ground like a train of kites. |
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It is theoretically possible to make a machine with wheels
and a fan that, wind powered, travels down wind along the
ground faster than the wind. Partly due to the
implausibility of this fact, when alleged videos of such a
machine were published on the net there were enormous
arguments disputing it's validity and the physics explaining
it. |
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I vaguely remember a similar machine that would move
upwind. |
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This leads me to two conclusions: |
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To make a station keeping system that works suspended in
two air streams blowing the same way at different speeds,
it may be useful to have fans or turbines at both ends, one
powering the other. |
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If you succeed in making this you will get a lot of fame for
doing something that seems impossible but turned out not
to be. |
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[+] I'd really like to see this as an unpowered sailing airship. But it'd require probably thousands of feet of cordage/cabling to link the ship and keelboard. |
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I remember seeing a book that described box kites flown
without tethers, carrying water-filled jugs as ballast to
balance the lift. In the course of looking for a link (no
luck yet), I found this on wikipedia: " The mooring could
be another kite flying in a media stream distinct-enough
to provide coupling with the first kite, so the double-kite
system serves its designed purpose; kite-surfing is an
example, where the lower kite is a water-kiting board.
Richard Miller, in Without Visible Means of Support (Los
Angeles: Parker, 1967), described a double-kite system
where the upper kite flew in the jet stream and the
lower kite flew outside the jet stream" |
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Air-tethered kites, as in the title, have been done for years. I did one in 1980-something, after having read about it as an old trick. |
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The book said that a kite could sometimes fly if a very long string was let go and dragging through slower air layers below it. |
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I remembered that when I had a long line out and the wind was picking up as a storm rolled in. I didn't want to wind it all back in, so I tied a bunch of air-filled balloons that I had to the end of the line, and let the kite go. It seemed to be doing fine as far as I could see. |
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// you can tack a boat into the wind, // |
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Yes, but the thrust of the wind against the sail is directly
countered by the drag of the water against the keel;
barring currents, which have negligible effect in this case,
water is a relatively immovable substance when compared
with air. It will always provided sufficient drag to make the
sail efficient, whereas two air currents, one slow and one
fast but both moving in the same direction, may not. |
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Or then again they may. Assuming that the higher
winds are at the greater altitude, you'd probably
want a big draggy bottom kite, and more wingish
upper kite. |
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Maybe. Beyond my realm of expertise. I just wanted to
point out that we can't automatically assume similarity in
dynamics between a boat and a kite. |
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MB, It's not a purely "higher is faster" thing -- the air
within the jetstream is fast, while the air around (above,
below, north of, south of) the jetstream is slow. |
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//it's not a purely "higher is faster" thing// |
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Fair comment. But in any case, I reckon you want
the bigger, draggier kite in the slower air. |
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