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PostPosted: Thu Aug 08, 2002 3:42 pm 
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Location: Hamburg, Germany
just look at a four line softkite and you'll get how the tube is steered. . .

the lines mounted on the left and right side of the bar are called 'breaking lines' and are sinilar to the lines mounted on the bottom side of a 4 line handle.
pulling left will cause the left tip of the kite to get slower. the right tip keeps it's speed and the kite will turn left.


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PostPosted: Fri Aug 09, 2002 1:50 am 
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what a thread, I had no idea it would last this long. This reply could get long

First things first, foil kites fly/turn totally differently than LEI's. breaking the foil involves increasing the AoA beyond stall. A turn is just a stall on one side. LEI's depower by just presenting less surface to the oncoming wind.

The leading edge of a LEI kite generates no lift, only turbulent drag. Anything in the wind shadow of the LE generates no lift because it is sited in turbulent air flow. What is left is the back part of the canopy which to all intents and purposes is just a single sheet of fairly flat sailcloth obstructing the wind at a variable angle of incidence. Do the windtunel sim on this and you'll see it fails miserably. If U use the underside of the LE as the start of a double skin and you'll start to get a real aerofoil which drastically increases lift.....the windtunel sims I've checked on Yahoo look correct, but it doesn't agree with my sim's...I'll probably go back and check my stuff again (I was only dabbling). The sims often fail when airflow becomes turbulent so a true sim of LE and canopy is difficult to get right.

The turn theories on LEI's I'd sort of arrived at already and your comments clarified a couple of points, so here is a question : it takes very little material at the tip to slow it down/stall it when it is on the inside of a turn. The tip on the outside of a turn (travelling further) has its speed limited by its drag, which is related to the surface area of material...why arn't the tips of 4 line kites thin slithers ?

Royce, you're turning stuff is affected by the above...if the outside tip on a turn speeds up, it generates more lift, hence drag increases twice as much and the speed of the kite will be limited....reduce the drag (less canopy at the edges) and speed limitation increases.

For the guy who suggested that the underside of a wing has little effect...sorry...every flying vehicle in the sky (that uses the aerofoil effect) has a critical underside shape. Try dropping flaps by 20 deg in flight (or on your pc flight sim) and you'll see just how much a little change to a wings upper/lower surfaces makes to flying performance.

Something to leave you with : the kites are semi-circular...imagine a kite above you in the sky....the lift generated by any point on the kite is perpendicular to the surface (aerodynamics). So only the dead centre is actually giving 100% lift upwards, all the other points on the kite have a proportion of their lift vector acting sideways (the edges effectivly only produce horizontal lift)..how many hemispherical plane wings/parachutes/paragliders do you see ?

A kite designer please help !


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PostPosted: Fri Aug 09, 2002 12:04 pm 
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Location: www.tbks.net FL
Still trying..

Johnny

<font size=-1>[ This Message was edited by: Johnny TBKS on 2002-08-09 13:21 ]</font>


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PostPosted: Sat Aug 10, 2002 3:32 pm 
Here you hit the spot. A LEI kite, is a basic sled kite with a inflatable leading edge for water relaunch purposes. This means it retains it's shape by using the aerodynamic force's created by it's arc shape. A normal wing would need al complex bridle or a frame to keep it in the correct shape. By using the arc shape the kite can be flown directly on the steering line's without using any other form of support. If you are interested in this form of design you should check Peter Lyns patent in the foil design group @ yahoo.

Again I want to point out that the inflatable LE bladder does not support the wing in the air, it only keeps the kite open if it drops in the water!.

Continuing on the steering issue. Because of the arc shape the AoA of the wingtips do not change while pulling on the break line's. The wing however is being pulled in a twist creating a out of balance wing that will swing to one side. Sled steering is not optimal, that is one of the reason's why normal foil designs are so much faster.

Greet’s, Joost Moesker


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