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Comment by JoeAltmaier | Hacker News Reader

Gotta be more to it. They blithly say, reeling it in takes a fraction of the energy it generates when it pulls the line out. But that's nonsense on the face of it.

I'm guessing, it changes it's wind profile, maybe going edge-on or closing up, to make it easy to pull down again. Gotta be something.

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On its face it sounds silly, until you get experience with wind surfing. It's using the same concept. Figure 8s generate the pulling force. When you stop the figure 8s, and change the angle of the kite, you get minimal pulling force.

Brake lines on a traction kite like that can cause the foil to fully de-depower and fall out of the sky. So you can let the wind pull it up, and then let gravity bring it down.

I think the kite might have control surfaces, thus would be able to control lift by changing its angle of attack.

Trailing edge control lines, pretty standard. You let them out and the kite will no longer be able to catch the wind and will float down. Keeping some tension on those lines and wenching it in will keep the kite controllable.

You're not wrong - they do that.

Have a look at https://thekitepower.com/products/ There's a diagram of the flight path and power generation over the cycles.

The flight path on the way out is much much longer going cross wind in figure 8s. On the pull back in it's a direct path back in, and it looks the kite shifts to point back at the base station more so there's a ton less resistance than on the way out.

>The energy generated by the system while reeling out is greater than the energy consumed to reel the kite back in.

There's something about it that just triggers the "perpetual motion machine" identification heuristic.

On a multi line kite you can control the angle of attack and speed. That gives you the ability to dial the pulling force up and down over a large range.

Only as much nonsense as rowing a boat without taking the paddle out of the water. In that specific example, you're going to be going in circles, but you will be moving.

You can propel a boat forwards with only one oar, without lifting it from the water. It's a useful skill, Kayakers use the same stroke to move sideways, and for stability in rough water. See https://en.wikipedia.org/wiki/Stern_sculling

Exactly, that's why calling this concept nonsense is so weird. It might be a tiny bit counterintuitive at first glance, but there's plenty of examples of it all around.

> Reeling it in takes a fraction of the energy it generates when it pulls the line out. But that's nonsense on the face of it.

Why is this nonsense on the face of it? This is just how kites work. Do you imagine that kite surfers just overpower the kite with their might and pull it back to the ground when they've had enough?

It’s also how turbines work. The fluid pushing on one side isn’t cancelled out by the drag created on the other.

No. I said I didn't. I said I believed there was more to it.

Others have actually elaborated on the likely mechanism. But sure, mocking people is a kind of post I guess.

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