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Lofting, Flat Kites & Aerodynamics Questions

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RickI
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Lofting, Flat Kites & Aerodynamics Questions

Postby RickI » Wed Jul 15, 2009 5:05 pm

Lets say you are lofted flying off the water and inland. You had your chance to Emergency Depower but as happens all too often, you fail to do so in time. Your kite is parked near the vertical, the wind comes and up you go, fast. As you pass overland you gain altitude, likely due to ridge lift and perhaps a near surface stagnant zone shifting the wind streamlines upward. As you are rising upward, you push out on the bar on your flat kite, reducing the angle of attack. A significant component of the wind velocity vector may be approaching perpendicular to the bottom area of the kite vs. the normal lateral projected area in conventional flight. As a result, reducing the AOA by pushing out the control bar has little effect on the kite's flight during this period of uplift.

1. Have folks experienced this before?

Also, when you are moving at unusually high speed downwind during a jump, do you find your kite still drops when you push out on the control bar? I believe this has been the case but usually if I am moving that fast horizontally there is very little height and term of flight. I recall some flat kite AOA seem to approach almost a negative value relative to the horizontal. If this is the case, it would seem that pushing the bar out should retard lift in normal horizontal flight, largely independent of horizontal speed? If it stays close to level on the other hand, potential inertial effects might maintain flight independent of AOA for a period of time.

2. Impressions on this?

Thanks!

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Re: Lofting, Flat Kites & Aerodynamics Questions

Postby DrLightWind » Wed Jul 15, 2009 11:51 pm

:jump:

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RickI
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Re: Lofting, Flat Kites & Aerodynamics Questions

Postby RickI » Thu Jul 16, 2009 2:29 am

Been talking to some in the industry, it seems feasible if your predominant direction of travel is up as opposed to laterally such as in a case of uplift lofting, pushing the bar out on a flat kite (or ANY other kite type that comes to mind for that matter), may not alter your rate of climb much much less cause you to descend. Once you come out of the climbing phase, ideally that function should return. I've heard about this being experienced in two loftings involving a strong uplift (ridge lift) component. Other related experiences out there?

Still wondering about the second part of the question though. If you launch an extremely fast jump downwind, do you still sink out readily enough by pushing the bar out or reducing the Angle of Attack, or not with flat kites? I suspect with slower, more routine jumps you would be able to easily sink the kite by pushing the bar out. Just not certain about high speed flight, like in a major lofting.

Input?

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Re: Lofting, Flat Kites & Aerodynamics Questions

Postby jakemoore » Thu Jul 16, 2009 2:52 am

If the wind suddenly changes direction so that it is going up and your kite is at the zenith the flight dynamic is going to be the same as hot-launching in the powerzone except with the kite above you. I.e. a brief yank until you are traveling at the wind-speed or the kite is at the edge of the window. Once you are traveling at the wind-speed (up sideways or whatever direction) this is the same as the maximum descent part of a jump. My experience flying flat kites since 2003 (Flysurfer Psycho 1 onward) demonstrates that if you are fully dangling and you depower the kite, it will fly behind you and you will drop.

Now I view the flying downwind fast scenerio as being similar to a chicken jibe. Once you are near windspeed, the kite has no power. I don't think an infinite drag downwind or up in the air is the real danger in these situations. I think the real problem is that you are already in the air, going fast and out of control, and unless you fly the kite like Len-10 you are going to land hot.

For updraft lofts (never happened to me) I like advice presented in Flysurfer's older kite manuals: Treat the kite like a small paraglider. Stay in control. Try to steer the kite upwind to minimize ground speed. Try to avoid obstacles. But if you are flying downwind at 30 mph, 10 feet in the air over concrete and out of control I don't think it matters what you do with your kite.

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DrLightWind
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Re: Lofting, Flat Kites & Aerodynamics Questions

Postby DrLightWind » Fri Jul 17, 2009 1:48 pm

Props for you Jake :thumb:
Last edited by DrLightWind on Sat Jul 18, 2009 3:32 am, edited 1 time in total.

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jakemoore
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Re: Lofting, Flat Kites & Aerodynamics Questions

Postby jakemoore » Fri Jul 17, 2009 8:35 pm

An interesting article on cloud-suck as it applies to paragliders:

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

20 (meters / second) = 44.7387258 mph

I am going to assume if she is in full backstall going up 44 mph then she was in a 44+ mph updraft with a 26 meter fixed bridle foil kite. But if the paraglider were to depower like a bow? I guess the question is how much wind could you hold the kite in?

We need Spork to figure this one out.


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