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Kitesurfing Brain Teaser

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peet
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Kitesurfing Brain Teaser

Postby peet » Fri Sep 07, 2012 2:43 pm

Just for fun, what would your kite do in the following scenario:

On a windless day, you're taken a few km up into the sky. Then you're dropped with your kite directly above you, with no horizontal speed.
Assuming you can survive the altitude, and nothing breaks, and you do nothing to turn/steer you kite, what will happen to your kite and you? Will it remain above you like a parachute, and you'll just fall straight downwards? Or will something else happen?

I'll be interested to hear your answers :)

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kitesurfingcollectiv
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Re: Kitesurfing Brain Teaser

Postby kitesurfingcollectiv » Sat Sep 08, 2012 5:44 pm

Would you be flying a LEI or a foil?

I was watching some people paramotoring a few weeks ago and I was thinking the same thing; if their motor cut out, would they still have enough forward momentum to bring them safely to the ground or would the loss of forward momentum kill the air in the foil and collapse the canopy?






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zfennell
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Re: Kitesurfing Brain Teaser

Postby zfennell » Sat Sep 08, 2012 10:42 pm

if you over-sheet the kite, it will remain stalled and fall straight down.

if you trim the kite to dive, it will generate lift and eventually allow you to travel forward at a speed determined by the overall L/D ratio of your kite ( as you keep trimming relative to the new forward direction of travel)


airplanes and gliders have no problem falling out of the sky if you increase angle of attack to the point where the vehicle stalls.

-bill

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yoav_at_blade
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Re: Kitesurfing Brain Teaser

Postby yoav_at_blade » Sun Sep 09, 2012 8:14 pm

Interesting topic.
I think zfennell is on the right track. If you over-sheet the kite, it will "stall" and crumble, loosing power and making you fall faster.
If your kite is trimmed properly, than you will fall a bit faster than you would if you were to jump on a windy day. I think if you aggressively turn the kite from 10-2, you could create lift and slow yourself down, but i wouldn't expect it to be much of a soft landing.

peet
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Re: Kitesurfing Brain Teaser

Postby peet » Sun Sep 09, 2012 9:15 pm

Yup, zfennell definitely on the right track.

This is what I think would happen (assuming you haven't stalled the kite by sheeting in to much):
I'm assuming the kites forward direction is opposite to your facing direction, just as it would be if you had it at the zenith when flying it on the beach.

As you accelerate downwards, the apparent wind on your kite will be directly upwards - it will effectively be sat at the centre of the 'wind window' and it will start flying forward out towards the edge.
This will mean the the kite will fly from directly above you to behind you, and may get quite close to being level with you (which would be the edge of the window position for downward flight).

I expect it wouldn't quite get there, as the kite would be generating horizontal lift, pulling you backwards (and upwards) towards it. This will cause you to accelerate horizontally, and also slow your descent.
As your horizontal speed increases, the apparent wind will shift from being vertical, to some combination of vertical and horizontal, and the kite will fall back, to fly at some angle above and behind you.

At some point both you and the kite will reach terminal velocity, and you'll be falling both horizontally backwards and downwards. I expect you may fly faster horizontally than downwards, but this depends on the L/D of the kite, and the drag of the falling rider.

Dan Glyaire
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Re: Kitesurfing Brain Teaser

Postby Dan Glyaire » Mon Sep 10, 2012 3:21 am

peet wrote:...............
Or will something else happen?

I'll be interested to hear your answers :)



i will poop my pants.


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