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How to tune leading edge collapse

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Slyde
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How to tune leading edge collapse

Postby Slyde » Tue Sep 18, 2018 10:13 am

Advice needed. I recently reset my bridles to factory spec. B line had shrunk about 1cm, C line about 3cm and z line presumably more. When I first flew it the leading edge inverted as soon as the wind speed across the kite increased eg at speed and when rounding up. Z line was obviously too long as the bar felt really heavy and the kite would shoot right to the edge of the window without being able to stop it. Shortened z some but still inverting leading edge. Checked my line lengths agin and I seem to be good so what’s the problem? It flew better before I started fiddling. I could restore it to where it was but this seems counterintuitive. What is it that makes a leading edge invert? Some sort of flow separation or stall effect? Any foil geeks able to enlighten me?

foilholio
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Re: How to tune leading edge collapse

Postby foilholio » Tue Sep 18, 2018 11:29 am

What kite is it?

A shorter Z line causes heavier bar and instability. Lengthen it. Lengthen C may help or may not.

It is unlikely but possible your B limit is too long. It more sounds Z is too tight.

The obvious solution though is to set it back as it was. What were you trying to fix?

I will just explain something. Most foils shrink all bridles but much more with Z. Which will give positive camber. The mixer shrinks to reduce more B and C. Which will give negative camber. The two tend to cancel each other , resulting in little camber change. The problem is when you use something like a mixer test which negates the camber change from the mixer shrink, leaving only the bridle shrink, then leaving you with higher camber. Higher camber is less stable with higher bar force and more power. People do a mixer test then have these issues. The mixer test is a bit stupid like that. It sounds like that is what you have done.

Mossy 757
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Re: How to tune leading edge collapse

Postby Mossy 757 » Tue Sep 18, 2018 1:50 pm

Too much camber in the kite can cause the airflow over the top skin to be disrupted and cause a front collapse at speed. Reduce the camber in the kite by tightening C or B, or by lengthening Z a bit.

Before you do anything to the bridle, though, make sure your lines and bar are in proper trim. Sometimes you can fly a kite with a shitty bar tune, and then when you tune the bridle to where it's supposed to be, everything goes haywire. I tune my bar to leave about a 2 finger gap (1"?) between the bar and chicken loop when the line ends are even. This gives me just a tiny bit of backstall with the trimmer at full power, which is helpful going downwind and for landing/launching.


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