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Changing Mixer Line Length

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foilholio
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Re: Changing Mixer Line Length

Postby foilholio » Fri Jul 12, 2019 7:37 pm

PugetSoundKiter wrote: I was going to try and take the higher AR Aurora2 and make it more stable. Hoping to have a better upwind angle kite than the A15, in a smaller size, and easy riding for hydrofoil use.
Making it more stable is as simple as extending Z. You can get more involved and say extend more of the tip area of Z. Which will improve upwind even more. My mod improves upwind on the A15 too and involves extending Z at the tip. An 18m has quite limited range with a hydrofoil, low end is very good though.
PugetSoundKiter wrote: when I would sheet out with my long throw bar, the kite would recover from the back stall and shoot too far forward, I suspect due to the high camber/lift.
That is what high camber does. It causes the kite to rotate LE forward/down and reduce AoA and so fly forward. Doesn't help the rotation will cause a collapse too, as it is towards the lines and not away like low or negative camber.
PugetSoundKiter wrote: I’m going to follow your suggestion and go back the original A length and lengthen Z instead and then then make an adjustment to C as needed
Good you will find it works well. When you want to increase the depower and keep the ratio between ABCZ the same you will need to lengthen all BCZ together in ratio.
PugetSoundKiter wrote: So I’ve updated the diagrams:
- Changing Z line
- Changing A line
- Shrinking B pulley line
- Shrinking C pulley line
Only error is still in Z diagram. It doesn't change depower, well unless changed extremely.
kitexpert wrote: main reason for mixer tweaking is to correct changes which have happened because lines (pulley lines, bridle) have shrunk.
It should be to alter the kites behavior. Correcting for pulley length with say a level mixer like Flysurfer advise will usually make a kite fly wrong because of other bridle changes.
kitexpert wrote: Original factory settings are carefully designed and adjusted for the best general behavior of the kite (stability, performance).
The problem with original bridle lengths is they were designed for original canopy condition, which on an aged kites is not exact anymore.
kitexpert wrote: Then all line rows are level, canopy is clean and well supported. Kite air foil shape is kept original while kite changes AoA when kiter sheets in/out (with the possible small effect of line row locations).
I think there is many potential possibilities, some of them good to have the canopy distort for some of the sheet range. With this you have a mixed airfoil. Trick is how much and when. It seriously complicates foil kite design. Flysurfer seems to have explored it the most and given up on the more extreme implementations. Performance in a regard is certainly hindered by not keeping the skin smooth, but performance is not 1 dimensional.

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Re: Changing Mixer Line Length

Postby kitexpert » Sat Jul 13, 2019 11:31 am

foilholio wrote: I think there is many potential possibilities, some of them good to have the canopy distort for some of the sheet range. With this you have a mixed airfoil. Trick is how much and when. It seriously complicates foil kite design. Flysurfer seems to have explored it the most and given up on the more extreme implementations. Performance in a regard is certainly hindered by not keeping the skin smooth, but performance is not 1 dimensional.
That is correct. But it is a bit weird approach to distort canopy when great work has been done to design airfoil, cell shapes (incl. billowing), bridle, inner structures, LE stiffeners etc. to match precisely each other to keep canopy as clean as possible.

Most used and appropriate method to distort canopy is to increase camber when powered up. Then kite sits deep in the WW and maximum lift and resistance to backstall is needed, increased drag doesn't matter then much if at all.

To have to decrease camber by having more pull on B-C suggests there is stability issues with the design itself, usually meaning kite has too much camber in its airfoil.

It should be remembered that airfoils with different cambers do have quite different shapes, and comparable difference exist in every part of finished kites. For example if you had a high camber kite and you would like to convert it to stable depowerable kite by replacing profiles (ribs), you would find out that new low camber profiles (with same chord and thickness and other parameters) don't fit to old skins at all: lower skin appears to be too short, upper skin is too long and also both have wrong shapes by the chord. Also D-ribs and straps are of different lengths and shapes.

So it is not possible to adjust a stable depower kite to a high lift kite or vice versa. Fine tuning of bridle and mixer is possible and also necessary.
foilholio wrote: The problem with original bridle lengths is they were designed for original canopy condition, which on an aged kites is not exact anymore.
Main problem is that lines don't keep their lengths. If canopy has lost its shape kite is too far gone, and before that it very probably has lost its air tightness.

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Re: Changing Mixer Line Length

Postby foilholio » Sun Jul 14, 2019 2:27 am

I have seen some foil kites with some unbelievable amount of use. In one case the canopy had lost maybe 90% of it's color. It's a testament to truly how durable foil kites are. Having recoated porous kites and tuned many kites many times for many reasons, I can say a worn canopy is far from the end of the possible life of a foil kite.

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Re: Changing Mixer Line Length

Postby HALF » Sun Jul 14, 2019 10:12 am

foilholio wrote:
Fri Jul 12, 2019 7:37 pm
Correcting for pulley length with say a level mixer like Flysurfer advise will usually make a kite fly wrong because of other bridle changes.
Does the long mixer test introduced in the soul account for these changes?

foilholio
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Re: Changing Mixer Line Length

Postby foilholio » Sun Jul 14, 2019 11:34 am

Yes a long mixer test should somewhat account for them, except for spanwise changes and changes to the B limit. A long mixer test is certainly a good way to go at trying to resolve some issues. Personally my go to is always Z, correct for B limit at a level mixer then adjust Z. Playing with B and C is too complicated.

Also the long mixer test is not new, but been around since a long time now. I have till now never done it :-) I would suggest my full mixer test if all other things fail you which they shouldn't, but you will only address some things completely by mostly correcting all the bridles. Secret I think to that was reducing the measuring force to as little as possible.

Also "Playing with B and C is too complicated." just reminded of something PugetSoundKiter said.
PugetSoundKiter wrote: I’m going to follow your suggestion and go back the original A length and lengthen Z instead and then then make an adjustment to C as needed.
Making sole adjustments to C on flysurfer mixers is a PAIN. You adjust C and then you need to adjust B back. B is super sensitive, 2.5mm on B is like 1cm on Z. You can get 2.5mm from the loops in the rings tightening. Honestly I am no longer a fan of the flysurfer mixer. They could do much better.


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