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Author: Subject: Speed Theory
pyro22487
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[*] posted on 19-8-2011 at 01:12 AM


Agreeing with ripsession now to many factors and talk. Just get out there and experience it for yourself. LOL



go fly a kite trainer 1.4 m
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Flexi sting 1.7m
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Feyd
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[*] posted on 19-8-2011 at 06:20 PM


Neeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeoooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooowwwwwwwwwwww!



Chris Krug-Owner @ Hardwater Kiting. Authorized Dealer of Ozone, Flysurfer, HQ kites.
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[*] posted on 23-8-2011 at 11:19 AM
Speed Theory -technical


I see a mix of posts here and I feel the need to comment.

The original question was can a large kite produce record speed in lower wind? My answer is that anything is possible but in practice it is much more difficult because power is linearly related to area (actually swept area) but it is proportional to air speed cubed.

Drag of the kite is also roughly proportional to the surface area -it rises as the square of velocity but it is since this is not the same velocity (as wind speed) we need to do more calculations.

Many smart posts keep pointing at drag and a limit that is reached for every foil. This is the most important point as long as we are limiting discussion to a beam reach 90 degree true wind angle (and all smaller angles).

If true wind angles greater than 90 are considered then bigger is always better and there is no theoretical limit short of c=the speed of light. But then all of your most heroic rides in high tech gear are nothing compared to some hick who got blown out of his trailer by an F5 tornado and reached 200+ mph from the pull of his mullet and pants around his ankles.

Not a very flattering accomplishment eh? So lets get back to the reaching condition for performance we can use and achievements worth bragging about.

Drag and coefficient of lift have been cited in several posts but nobody has pointed out why. When we start out from 0 the kite can pull at F0 at an angle of say 10 degrees to the direction you want to go. F0 is the force of the kite at true wind speed and 10 degrees attack. We quickly gain speed and now the kite is at say 45degrees to our direction. The kite is pulling harder now because it sees a higher wind speed =(true wind)cos45 + cart speed @angle , but because the angle is wider, less of this force is pulling us forward and more is pulling us downwind, increasing our drag. At top speed (say 3X true wind speed) the kite is leading us by only ~20 degrees so the majority of the pull from the kite is multiplying drag (drag is at best linearly proportional to orthogonal force) and a small portion is pulling us forward against that drag. There is no shortage of power because the air velocity is more than 3 times true wind speed (force is more than 9 times F0), but the angles of that force are increasingly contributing to drag and declining in forward thrust.

There are lots of factors, but when it comes to speed of a kite rig, the coefficient of lift of the kite is generally the dominant factor.
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Feyd
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[*] posted on 24-8-2011 at 05:01 AM


Sooooo, if I understand this correctly I have to grow a mullet and ride with my pants around my ankles to achieve maximum velocity on my kite?

Sweet!

Seriously tho, great description of what happens out there.

Another factor that dictates results is the drag on the rider. I usually wear fairly low profile clothing but a GS suit would probably give me a 5+ mph gain on whatever my end result would be without the GS suit. If I'm wearing a pack I'm usually slowed down 5-10mph.

I'm not gonna wear a GS suit all day in -20-30f windchills and have bits of myself falling off tho.:no:

Drag is obviously a huge factor for both the pilot and kite but ability to manage your edge and the lift coefficient are IMO the biggest deciding factors. There's a balance point there and if you get it just right AND CAN HOLD IT you'll really haul the mail.



Chris Krug-Owner @ Hardwater Kiting. Authorized Dealer of Ozone, Flysurfer, HQ kites.
www.hardwaterkiter.com 603-986-2784
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