I believe such a system can not perform well in a wide range of wind conditions. Please prove me wrong…
I can only prove something when I can test in the heights. my hope is that the kite will automatically move up and down with the highest wind speed.
The energy band your are harvesting is reliant on the amplitude of modulation of line tension from gusts and how that resonates with your spring tensioning system.
My instinct is… It’s a limited resource in comparison to the constant mass flow energy of harvesting wind instead of gusts.
it may be that it is so. on the other hand, neither enerkite nor skysails has so far generated significant amounts of energy.
Have you contacted this center for advice?
Nationales Erprobungszentrum für Unbemannte Luftfahrtsysteme
https://www.dlr.de/ux/de/desktopdefault.aspx/tabid-13303/23288_read-67121/
Some of the interesting articles in their news section:
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no, I didn’t know that yet. thanks for the hint. I will try to get in touch with it
How can it suit your kite and spring selection, if you cont control the motion of the wing. Eg. in high winds the spring will be fully compressed resting towards end stop. Remember drag is windspeed squared. And in low winds, the wind may not be turbulent or if it is turbulent not strong enough to compress the spring significantly.
I think for this to make sense, you must have a way to power/depower on command. Relying on the natural wind to fit your control needs seems like a longshot
But Enerkite and Skysails at least have a good story to make people believe that they may produce power in the future. If someone were not convinced they would not get funding. And I am pretty sure people will not part with their money very easily.
I am not trying to kill your project here. Or I kind of am, but you should be able to convince me I’m wrong. I could even help you make an argument in the future for someone important to you. But I will not give you a BJ, i will say exactly what I believe is true, it may not be easy to hear…
i am in close contact with skysails. that is the reason for my development. from the beginning i was of the opinion that skysails was made too complicated. I have time. at some point is the right time. at the latest when there is no more oil for the aircraft, our kites can fly in the jet stream.
You could potentially change the hold point on a variable force coil spring…
e.g. by having a wider span of grip on the ends of the spring in light winds… more length and thinner material would be available for the central unwinding spool… You’d have to tighten up the grip ends towards the centre and take shorter strokes in higher wind
The interest of this system would be to be able to do without control. Indeed in areas of turbulence the wind changes in intensity and also in direction, which allows to alternate power and depower while letting it happen.
You just have to test it on very windy days, and not too far from the ground, to produce the curves in real time. More precise data would make it possible to extrapolate for use at higher altitudes, say a few hundred meters, where the Low Level Jet starts, allowing higher turbulence amplitude.
yes, but in my opinion the vibration behavior of the rope is of great importance. even if the length was realized on the floor, the necessary pulley would change the vibration levels
Debatable if that matters all that much. Here’s a test I suggest to get a feel for that:
This is an experiment you can do right now if you have a long enough rope.
A better experiment maybe: place two pulleys far apart and put equal weights on either end to simulate the weight and the kite pull. Now move one like you imagine it will be moved by gusts.
I understand what you mean However, the rope cannot move freely, it will not behave as it would in real operation.
You’re right. It’s a simplified model. It will still help with understanding though.
Too many ifs and buts, Thomas. Just do some tests.
I have done all the tests I consider to be useful at 100 meters. I will continue when I can test from 3000 meters
Let’s now put a placeholder on the line between the pulleys to act as our kite. Note how that placeholder will be able to move more freely than at the pulley and most freely toward the middle of the span, and that the tension in the line will act as our wind force.
We could add another line at that placeholder location and pull on that toward the ground pulley to simulate the assumed periodic lulls, or stick will pulling at the top pulley.
i suspect that the weight of the rope and the area exposed to the wind play a large role
Yes. You try to do the simplest and cheapest tests first where you ignore a lot of things. If your idea passes the simple test you can try to continue. If it doesn’t you think again, perhaps change something, and test again.
My hypothesis for this simple test is that it will fail if you make the rope too long because the inertia of the rope, and the different waves in the rope, will dampen your small and short oscillations before they get to the ground.
If the test is a success, you add a difficulty, perhaps by making the oscillations more random. If that is a success, perhaps you add a damper or a generator on the ground.