Continuing the discussion from Windswept and Interesting Ltd - #180
Before in this topic I wrote about that:
Let’s explore the topic a bit differently now. You want to use (semi-rigid) wings to be able to put clamps inside the wings, and to reduce needed bridling. I also say you want to use multiple bridles to reduce the needed strength of the cantilever beam that the wing is to resist the lift forces.
To make an efficient system that generates some power, and is also able to transfer torque to the ground, you want a wing with a high Reynolds number, so flying fast, with a reasonable chord length, and a high aspect ratio. That all points to a single ring of kites on the outside of the shaft. You also can’t make the wing too long however. Let’s go for 3 meters like you described in your recent end rapport.
Previously, the highwind group probably, said a good looping diameter was 9-10 times wingspan. If I independently think about this, I want to say that the unachievable ideal is (Velocity _{ \ inner\ wingtip})^2 : (Velocity _{ \ outer\ wingtip})^2 = 1 This is anyway I think a metric that takes into account the lower flying speed of a soft wing and allows that perhaps to fly in a smaller diameter.
Off-topic for this discussion maybe, but a different metric that I think is useful for a controlled shaft is minimum orbit time. You want to probably increase that as much is reasonable while you are trying to learn how to control the shaft, so you have more time to control the kites, so you’d increase the diameter of the shaft as much as possible. It also conveniently should make it more difficult to collapse the shaft, as you need to spend a lot longer at mismatched speeds to achieve that, at the expense of more line drag.
Without the tethers you’d end up with a polygon with the same number of vertices as kites I think. To prevent breaking connectors I’d use live hinges instead of rigid connectors, although maybe for a triangle you wouldn’t need to.
I don’t remember seeing recent videos where you show the polygon rings, maybe those work at this scale. I remember thinking the rings wouldn’t survive very long even at this scale from all the flexing.
If you were to go for a larger ring, I’d go for a bicycle wheel construction, maybe add a tensairity ring, which could scale more I think. But at that point I’d sooner drop the airborne part I think as you’d hopefully have a cheap and light rotor you could attach to any wind turbine.
Assuming the use of the back bot and now gliders connected together like I describe above, you would use the lifter kite to lift everything up and preload the shaft. Then you would slowly start spinning the shaft and let centrifugal force expand the shaft. Because you now have two tethers going through the wings, they stay at a fixed bank angle relative to the shaft helping them to catch the wind. Perhaps you would also need to pre-expand the shaft from both sides, or only the bottom side, or maybe the rotation is enough to fix any potential tangles and expand the shaft.
You could of course add as much complexity as you want… I would put the generator on a tower for example…