Tuning of foil kites

[jbrodin]

Over the past years I have gone through an at times frustrating process of figuring out how to keep my foil kites reasonably well tuned. The manufacturers (Flysurfer for me mostly) provide methods to reset the kites, but these do not always work, I therefore had the Idea to start a thread on the topic, to gather general insights and understanding on the topic. Some of what comes forth will be brand or model specific, but most foil kites are made by the same governing principles and have similar line plans.

To give context to the discussion I post here the line plan, for the 10 m2 Flysurfer Soul V1, which is the kite that I have spent the most time trying to figure out (I assume that Flysurfer is ok, with this).

Bridle and flying lines shrink over time. Over time the A row will shrink less and become longer than successively B, C and Z, as A is under more tension when the kite is flying. Generally, this will lead to the kite flying more slowly, with less performance, but possibly with added stability. As the Z-row is connected to the steering-lines the offset will also shift the trim of the kite, making the kite more prone to backstall whit the depower-trim fully extended (full power).

On Flysurfer kites you can use the so called mixertest, to adjust the B and C rows with loops, in nearly all cases C and then B have to be extended, to compensate for the mentioned difference in line-shrinkage. The Z-row can be extended to match the A-row again, either with an extension pigtail or by moving the steering lines further out, on the knots inside the bar floaters.

But what if the standard approach does not restore the kite, or if you want to change the characteristics of the kite? The goal here is to gather insight into how to remedy undesired behavior and to be able to tune the kite towards specific performance.

I am by no means an expert, so feel free to correct me and to contribute any insight or experiences you have on the topic.

I'll add links that are recommended here.

Method to restore the kite by measyring and extending every single bridle line:
viewtopic.php?f=197&t=2410952&p=1147911

[Jyoder]

Mixer test and long mixer test are ways to check the parts that are most likely to have changed: the heavier mixer lines. But at some point you have to go further into the kite bridle.

Flysurfer publishes a line plan with all the bridle measurements. It’s a time investment but you can check all the bridles this way and re-stretch any lines that have shrunk. Reminds me I have to do this on one of my old foil kites.

My understanding is that bridle Lines that are loaded sometimes shrink faster because the tension stretches the weave open and then when slack on the beach this lets micro particles in the gaps which clog up the weave and thus the line shrinks. With enough tension you can restore the line close by original length. Kind of counter-intuitive compared to other strings that stretch more and more until they break.

[keegster17]

great topic. It should probably be moved to the foil kite forum.

[jbrodin]

great topic. It should probably be moved to the foil kite forum.

Good point. Do you know how to do it, I tried but did not find a way.

[chaosgate]

On your Soul, have you tried to measure some of the bridle lines and compared them with the line plan? On a relatively new Sonic, I noticed that my measurements were consistently 2cm shorter than indicated, unless I applied very heavy tension (much more than the 5kg suggested for the mixer test). I wonder what other people's experience has been, since that could be a pretty big source of error when tuning the bridle (and if someone has a better procedure for measuring other than pulling like a maniac).

[joriws]

You probably scanned youtube for vids, but here are some good ones..

Bridle tuning video..


This is more mixer-test video..

Flysurfer publishes a line plan with all the bridle measurements. It’s a time investment but you can check all the bridles this way and re-stretch any lines that have shrunk. Reminds me I have to do this on one of my old foil kites.

Usually you should not try to stretch lines because it will help only for short period. Better approach is to use on Flysurfer-kites those LCL (little connector lines, the load fuse, I added this extra explanation what they are because they are not on every foil kite) on kite, add new LCL loop to lenghten by 1cm, or add new larks head to shorten.

Then one option is to tune PMA - but it is more for expert tuning if everything else fails.

[jbrodin]

Solution - Fixing unstable wingtips after the long Mixertest on a Soul 10 m

I have spent quite some time figuring out how to fix my Soul after the long mixertest made it completely useless. I have received a lot of different advice and tips, and have tried many things since. Basically, the long mixertest should restore performance and speed to the kite. Here is a post from the FB Fysurfer page about it, with a video of how the kite became after the long mixertest:



The kite can be made stable again by simply extending B and C in increments, but you don't want to extend by much, because then you are basically reverting the kite to the slow state the mixertest is supposed to remedy in the first place.

Finally, upon advice from the service people at Flysurfer, I have landed on the following:

- If you want to be able to go back, in case the kite becomes worse, make marks on the lines by the adjustment loops, i put a stitch with white thread there.

- Do the long mixertest.

- If the wingtips fold in you can tighten the B-row with one cm increments and shorten lines B8, B9 and B10 from the line plan in the post that started this thread (they might have different labels for other models, the important thing is their position on the kite). It is the three points closest to the wingtip, on the second row, behind the leading edge. I shorten them by simply laying a twisted loop on the thin white bridle over the tiny attachment pigtail on the canopy attachment point.

- On my kite there was some asymmetry from left to right, the left was more unstable than the right, so I had to tighten B a bit more on the left side, I then tightened B8, B9 and B10 a bit more on the left, so that these lines matched the equivalent on the right upon tension, pulled from the attachment points at the canopy with all four front and rear lines attached together to a point by the rings that connect to the bar lines.

[jbrodin]

On your Soul, have you tried to measure some of the bridle lines and compared them with the line plan? On a relatively new Sonic, I noticed that my measurements were consistently 2cm shorter than indicated, unless I applied very heavy tension (much more than the 5kg suggested for the mixer test). I wonder what other people's experience has been, since that could be a pretty big source of error when tuning the bridle (and if someone has a better procedure for measuring other than pulling like a maniac).

I suppose that as long as the shrinkage is consistent, it is not a big issue. I have not tried to compare line lengths with the plan, it just seems too boring. I am more attracted to try to build an understanding of how the kite behaviors correlate with the tuning on a general level. The most tedious thing I do is left/right comparisons, point by point, on the canopy. I find that the center of the kite remains symmetric, but that the shrinking is less consistent towards the tips.

[downunder]

On your Soul, have you tried to measure some of the bridle lines and compared them with the line plan? On a relatively new Sonic, I noticed that my measurements were consistently 2cm shorter than indicated, unless I applied very heavy tension (much more than the 5kg suggested for the mixer test). I wonder what other people's experience has been, since that could be a pretty big source of error when tuning the bridle (and if someone has a better procedure for measuring other than pulling like a maniac).

Actually 12cm shorter on my well used 10m. This are green lines, correct?

Replaced them with spares, flies like new.

That is the first thing ppl should replace from my experience.


D.

[Breze]

On your Soul, have you tried to measure some of the bridle lines and compared them with the line plan? On a relatively new Sonic, I noticed that my measurements were consistently 2cm shorter than indicated, unless I applied very heavy tension (much more than the 5kg suggested for the mixer test). I wonder what other people's experience has been, since that could be a pretty big source of error when tuning the bridle (and if someone has a better procedure for measuring other than pulling like a maniac).

I suppose that as long as the shrinkage is consistent, it is not a big issue. I have not tried to compare line lengths with the plan, it just seems too boring. I am more attracted to try to build an understanding of how the kite behaviors correlate with the tuning on a general level. The most tedious thing I do is left/right comparisons, point by point, on the canopy. I find that the center of the kite remains symmetric, but that the shrinking is less consistent towards the tips.

I measured some DC40-DC100 new fabricated lines of the Sonic2 and compared them to the line plan they were all equally shorter 7-9mm (hand loading). I guess the cutting length minus the 2 two cm loops and the 2 splices of 6cm gives the calculated length. The real length is shorter bc of the splices. Not a big deal if the quantity of lines in each row of ABCZ would be the same. Keep in mind the Z row has only 3 lines vs ABC has 4 on Soul & Sonic . The breakes are therefor 10mm shorter than calculated.(supposition!!)
The paraglider trim checker Ralf Antz: 10mm differenz should be trimmed, 5mm diff could make a wing feel different- talking about 26qm and bigger gliders. To compare two lines by hand tensioning each and holding the ends together, makes it prone to errows.The wish for equal lenth makes on one side uneven tension.