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Comment by robinhowlett | Hacker News Reader

Would it plummet out of the sky if the wind dropped suddenly?

At the altitude these will be flying at, the wind is pretty consistent compared to the wind at ground level we're used to. However, I would imagine that the on-board controller could kick on it's propellers or something if the altitude changes too much.

Stunt kite flyer here. Flying (both powered and unpowered) is about managing the mechanical energy in the kite/aircraft. If you have kinetic or potential energy available, you can always trade one for the other. If you have neither, you've almost landed.

This kite will always be doing quite significant movement, so the "apparent wind" on the airfoil surfaces should keep it moving even when the wind is dying down. Additionally, you can reel in the tether to give a little bit of movement to the kite. Typical kites can be flown by walking backwards at a normal walking speed (4-5 m/s or less).

This looks like a very controllable kite, I'm sure their control programs can land it in pretty adverse conditions safely.

presumably it would go into helicopter mode and return to base.

There's also autorotation, which means you need very little power for a controlled descent (still need some power to steer).

http://en.wikipedia.org/wiki/Autorotation

Autorotation only really works for large heavy propellers, like the ones on helicopters.

I don't know. It works for RC helicopters of 500 size or so. I haven't seen autorotation performed with multicopters, though, so not sure how it maps to this application. I'm guessing these are fixed-blade machines. RC heli's manage autorotation via their collective pitch, which RC quadcopters (or hexacopters) don't have (collective). So it might not be relevant. But on the other hand, if the value of avoiding a crash is high enough, they could make the blades collective just for that purpose. Or maybe make one or two of the multiple props collective... I'd assume they already have a working solution to avoid falling out of the sky, but then, it isn't mentioned in the copy.

EDIT: There are quadcopters that can fly inverted, but I think they use powered servos with a reverse polarity. The value of autorotation is that it works when your main power source dies. So it all depends on the context and parameters (is there a backup battery of lower capacity available for emergency situations, say).

If problematic wind was forecast, they could be automatically reeled in for some temporary period?

It has a generator.

That is to say, it has a motor.

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