I believe that a cable drive is the most economical method of converting flygen turbines, parotors, SuperTurbine™ etc. to a groundgen system where there are no heavy generators aloft and heavy electrical conducting tethers. The use of torsion shafts and tensegrity elements becomes problematic for true high altitude operation. The Kitewinder system works beautifully for small scale systems but many problems develop if we attempt to scale up the system:
• The size of the lifter kite increases to the point where it is difficult and dangerous to launch and land.
• A larger turbine will rotate at a much slower velocity requiring more gearing to operate the rope drive efficiently.
• The system is not easily adaptable to incorporate multiple turbines.
• The floating generator will become too heavy and an alternate support method will be required.
• Operating the lifter kite in figure-of-eight crosswind mode might cause the rope drive to rub against the walls of the pulleys causing wear and a reduction in rope drive efficiency.
None of the above factors are insurmountable and I feel that it is a well worthwhile effort to develop scaled up versions of the Kitewinder. I find it strange that there is almost no mention of cable drive systems in recent AWE literature.
I would like to add a «negative»: The lifter kite is stationary, thus the only way to limit the power which is dependent on w^2 (windspeed squared) is either reducing area or lift coefficient. I believe a stationary kite is difficult to depower in high winds. This leads to a system with a limited wind range.
Crosswind kites dont have this issue because you can additionally reduce the apparent windspeed. If the kite+tether has a high glide ratio, this reduction is quite significant.
I can think of many ways we can mitigate against high winds. The first an most obvious is to land the kite system and relaunch when winds are normal. If we are concerned with overspinning the turbines or generator we can brake the system and stop the turbines from rotating. If we are concerned with too much force on the Kite we can lower the angle of attack of the kite. This can be achieved by placing tensile springs in the bridling at the bottom of the kite. These springs will only extend during high winds.`
Have you tried that before Gordon? Did it works? I mean tensile string to de power the kite? Could be interesting
Don’t know if you guys follow us on fb, I just release some fresh photos of kiwee mechanics. That is the final update before release.
We have delay on delivery, shall have happened in August, will be more like November I think.
We deal with our customers… Not easy. I had a hard time today with one of them. God, BtoC is a challenge
Kitewinder operates crosswind, like all good wind energy devices.
I know Peter Lynn sr did quite a few tests. Getting low wind flight, gust absorption and depower at high winds is apparently quite difficult. And then there is the simple but difficult problem of single line kite stability in a big wind range.
Seeing that a talented kite designer like PL was not able to solve this in his career thus far (or at least not that Im aware of), we could conclude that the problem is hard or impossible to solve.
Which leaves us with a kite that is of use in a limited wind range only.
Again, crosswind flight and active control would be some easy ways around the problem. But it seems most people dobt want active control (for good reasons), and without that, crosswind motion is so much more difficult to achieve for a lifter type kite.
Anyways, I could suggest an alternative lifter with higher windrange: A smallish kite on top, then a ring with three bridled kites much like @Rodread ‘s Daisy. Add a means to depower the rings (eg a simple servo driven AoA control). And voila!
Thanks for the analysis. I had serious doubt that things would be so simple.
Lifter kite like pilot do become unstable above a certain wind speed and on special wind conditions but wind speed range remains large enough to use them.
The turbine in flight can contribute to the stability thanks to its (even small) weight below the kite, working a little like a boat ballast.
Kitewinder operates crosswind, like all good wind energy devices. Blockquote
Our definition of ‘crosswind’ is the movement of the whole device across the wind window and not the circular rotation of a turbine blade.
Control of the angle of attack by spring release might be much easier if the kite were restrained by diagonal stays at the four corners. The kite has to remain stable when changes are made. I am sure that all Peter Lynn’s experiments were on free flying kites. I wish Peter would participate in this forum to assist us.
Peter Lynn is not here, but he has written heaps about his efforts. Unfortunately his web page is being redesigned, but I found his old site with all the technical papers available still
https://web.archive.org/web/20180326044933/http://peterlynnhimself.com/
Well worth reading if you are into single line kites
@gordon_sp, you totally forget the user experience. Kiwee is a small device. It has to be simple. Imagine you have to deploy like 5 lines to operate it, that will simply not be used.
For bigger model it does not work too, too much complexity, fail case. Did you try to deploy and test a pilot in strong winds with a single line? 4line? Totally unrealistic. There a gap between drawings and reality, thus gap is called pragmatism. We have done 100 of ours of testing with rope drive. We know what is possible and what is not. Clearly what you describe is unrealistic
Blockquote
I’m thinking big! I’m thinking out of the box. Since the Kitewinder works so well on a small scale, why can’t we size it up to a permanent industrial scale energy generator? The lifter kite must be huge so rather than have a six man crew risk their lives launching the device, we have four diagonal unwind stands to control the kite position. We also need a device which will lift the kite to an altitude where it will catch the wind. Once humans are removed we can fully automate the launch and land operation. In this way we can favorably compete with conventional wind turbines.
I think a good next step for @gordon_sp would be to build a prototype. What you are suggesting should be built relatively easily, and give insight into the difficulties involved.
I think many of us thought through this and also provided some feedback. But I believe it would be unreasonable to expect anyone else to see this through. We all have ideas here, the problem is identifying the good ones and execution…
Isotropic kite has multi-lines and multi-anchors to improve passive safety, stability, and also scalability. So @gordon_sp’s idea about several lines and anchors is not new. Various multi-anchored AWES has been discussed in Yahoo forum. Multi-anchored kites have not the same purpose as Kiwee which carries a turbine. A multi-anchored kite carrying a turbine will multiply failure cases (turbine working as a pendulum hitting one of other lines, too long recovery time in storms…), without speaking about a probably low efficiency (that of the turbine) even for a gigantic installation. For small devices multi-anchored kites can be forgotten.
So @Kitewinder would likely lose half of the customers per line added.
I think even if it was discussed, execution is important. If something is not proved wrong during discussions one is free to start experimenting. Though some concerns were raised, I don’t think the idea of a multi line kite is impossible. Personally I am not sure which problem we would be solving, and I like better to simplify when possible rather than adding stuff
Improvements could be:
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for a static kite, perhaps scaling more with spaced anchors (I am not sure of it), and also a better control from the ground stations. But there are also issues like land use, complexity, tether drag.
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for both crosswind (example the 2 lines KSU of @Massimo’s KiteGen) and static kite, more safety as when a tether is broken, the kite is held by other tethers. However a single tether could be divided in several lanyards within a sheath.
But such improvements could lead to make other things worse.
The use of diagonal stays to control automatic launch and land is new. It is the only way I know of controlling the launch of a single skin lifter kite. Can you think of any other way? Once this method is developed, we can scale up to very large kite sizes which are necessary to support larger or multiple turbines and enable the operation of the cable drive.
The use of diagonal stays is not the same as a multi-anchored kite. The purpose of the stays is to stabilize the kite. Most of the lifting force of the kite is transferred to tension in the tether/cable drive.