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
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
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:
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.
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.
Since all of the windup stations are slaved to the main windup reel, why would the landing operation with multiple lines take any longer?
The idea of multi line kites is not new, but “the use of diagonal stays to control automatic launch and land” can be new if there is no prior art.
Have you tested it?
Some simpler and more reliable ways can be studied, comprising a light mast (a little like SySails’ mast), or a drone, or a ground station as wide as the kite in order to expand it before launching…
As the kite flies in a definite place due to the wind direction, the unrolled ropes will not be the same length for the four stations, which imposes a differential control. If such a control is not perfectly coordinated the angle of attack and the bank angle of the kite will change during landing (and also launching). So landing could be likely longer, not to mention the risks of malfunctions resulting from the complexity.
My concept of a restrained kite is not the same as a free flying kite. It will stay in a fixed place determined by the length of the tether and diagonal stays. If the wind changes, then the kite will lose lifting power and probably the diagonal stays will become slack on one side. We might be able to move the unwind stations to compensate for this but it might be better to land the kite, relocate the diagonal stays and relaunch. In all cases during launch and land the length of the stays are slaved to the length of the main tether/cable drive. It does not matter if some of the stays become slack because they will be corrected in the low wind region and the kite will be forced to land precisely on the lifting frame ready for the next launch.
I don’t see the aim to make the kite static? What is the benefit of that? Bring the kite back at each wind turn… Ouch that hurt. Why so much complexity? Having slack lines means getting stuck in the trees or whatever. I don’t think lines will behave has you say and all will be simple to operate. Test you own stuff and see by yourself if it is good or not.