h a l f b a k e r y
It's the thought that counts.

meta:

account: browse anonymously, or get an account and write.

 user: pass:
register,

# Air tethered kite

Ride the jetstream, using drogue parachute to create thrust
 (+7, -1) [vote for, against]

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.

 — goldbb, Aug 18 2011

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]

 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.

 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.

Say, how halfbaked is that last idea?
 — goldbb, Aug 18 2011

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...
 — Alterother, Aug 18 2011

[+] 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.
 — Alterother, Aug 18 2011

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.

 [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.

 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.

[BS] What's to prevent your nanobots from swimming into someone's pants? Or worse, into their bladder?
 — goldbb, Aug 18 2011

 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).

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.
 — Alterother, Aug 18 2011

I'd ride one. Does the insurance package cost very much, and does it include something to eat while you wait for helicopter pickup?
 — normzone, Aug 18 2011

 I don't really grok the idea except for "put a bunch of stuff into the atmosphere".

 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.

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.
 — FlyingToaster, Aug 18 2011

 //Unless your two airflows are in opposite directions you will not be able to maintain position by any sort of vanes//

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.
 — MaxwellBuchanan, Aug 18 2011

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.
 — FlyingToaster, Aug 18 2011

You could probably build a rig that would keep station. You could also launch this from the ground like a train of kites.
 — baconbrain, Aug 19 2011

 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.

 I vaguely remember a similar machine that would move upwind.

 This leads me to two conclusions:

 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.

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.
 — caspian, Aug 20 2011

[+] 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.
 — FlyingToaster, Aug 20 2011

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"
 — afinehowdoyoudo, Aug 20 2011

 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.

 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.

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.
 — baconbrain, Aug 20 2011

 // you can tack a boat into the wind, //

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.
 — Alterother, Aug 20 2011

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.
 — MaxwellBuchanan, Aug 20 2011

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.
 — Alterother, Aug 20 2011

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.
 — goldbb, Aug 21 2011

 //it's not a purely "higher is faster" thing//

Fair comment. But in any case, I reckon you want the bigger, draggier kite in the slower air.
 — MaxwellBuchanan, Aug 21 2011

 [annotate]

back: main index