Low radius loop


#21

There are various kite power simulators now available as stand alone open source software or MATLAB simulations. You can likely program an altitude maintaining near-circular flight path into these simulators and be fed line tension parameters as output… Any experts on the packages available available?


#22

Pierre: I’m not convinced that even if you had some free (zero cost) source of “pull”, on the ground, that “reeling” would form an economical electricity-generation solution.


#23

Doug,
My purpose is the maximization of the space. Preliminary experiments about low radius loop with a wing show that it is possible to generate the same power by using far less space, using also some passive steering as autorotation.
Among AWES that has been tested only two systems produce 10 kW or more at several hundreds meters in height: flygen and yoyo methods.


#24

So you’re making so much power now, the only thing holding you back is you’ve used all the available space?


#25

I admit that was funny. Though the discussion is worthwhile


#26

I have two old paragliders. I don’t still know if they can generate 10 kW or more by staying in the room, perhaps yes if I open all the windows…


#27

http://twingtec.ch/ Twingtec (using yoyo method) flies by large loops, perhaps 10x wingspan. The same for Makani (using flygen method) as shown on their document.FAAfromMakani.pdf (3.5 MB)


#28

Low radius may also apply in figure-eight. Some arrangement for a kite-farm where kites fly in figure-eight can allow a better maximization of the space use. I may describe how in a further topic.


#29

On the video at 1’10" from the beginning we can remark the fast turn of 25 stacked kites What kite plans do you like?.
Increasing the power by keeping a low radius turn could be interesting for AWES.

2 stacked kites would be a beginning of a possible High lift coefficient and biplane kite in a flexible kite version.


#30

What this stack of flexifoils shows is how weak the kites are when crowded together, the high pressure wanted under a kite cancelled by the low pressure over a kite below. That’s why one skinny guy can fly them all, and they fly very slowly compared to a single flexi, which helps the pilot manage. An old heuristic is to space kites in a power stack at least 3 Wing Spans apart, and there is still considerable loss of power. A properly staggered multiwing has a different (trailing) geometry than a (vertical) stack, and even then may not beat one good kite matched to conditions. That this stack may do a low-radius loop does not offset the other losses.


#31

Thanks for some interesting input on the distance between kites heuristic. Would it be safe to extend the heuristic to a looping kite, such that wind must travel 3x the wingspan og the kite between every loop? In that case this could be a rule of thumb to design minimum flying radius for a given wing and windspeed…


#32

3 x wingspan is also roughly the diameter of the loop during my experiment on Low radius loop and


If the loop diameter is lower, so only 2 x wingspan, there is more loss due to the no speed of the chord toward the center, in a similar way as a classical wind rotor.

If the loop diameter is higher, from 4 x wingspan and more, the benefit of the higher swept area is annulated due to both the higher variation of power by the variations of the cosine, and a lesser power far from the central zone of the flight window.


#33

No, in principle an Archimedes Screw is effective (at low Re), and the stacking heuristic is mostly independent of wind velocity factor you introduce (that ranges toward high Re).

There is an optimal proportion to drogue apex holes, as an annular sweep analogue, if one is seeking Betz disc efficiency. Wingtip is traded for hub area.


#34

Reminds me of the early ship propeller development. They moved away from an archimedes screw very quickly.


#35

Yes, ship screws operate at high Re, so long screw is not preferred. The odd fact is a long screw turbine in an open flow can develop more power along its axial-depth than the Betz disc assumption allows, by entraining flow all along itself.

Other close real cases are high solidity rotors like irrigation wind turbines and stealth submarine propellers, where they have not “moved away” from the form.

Note: I will now desist from posting in Rod’s favor, as he seems to think I posted improperly on the reeling topic, but I don’t see the error.