Foil kite tuning paraglider style with laser and weird results

[derek440]

I've got a couple of race foil kites that are having some performance issues as they have racked up the hours. Have tried the usual tricks of adjusting mixer and some stretching in the bridle but still having some performance issues, namely when trying to light it up and head deep downwind at pace the kite won't light up and you have to go higher angle/less performance. So now I have started comparing parts of the kite to the line plans and finding some deviations. In wanting to do a thorough job and watching how the paraglider servicing place check their bridles I have decided to try somethign simlar and added up the line "check lengths" for each attachment point through to the mixer - kinda like a long mixer test but not just at one part of the canopy but at each attachment point. Before you think wow that's impossible, if you have a spreadsheet of the check lengths (sum of A1, AM1, ML1 and Main 1 for example and for each attachmnent point it doesn't take too long to measure each one if you have a measuring laser and the tables arranged right and a weight on the mixer end with the correct line tension for the measurement. So I have done these things, bought a laser measure for $40 and set it all up and have measured A and B rows on one side. So first question, has anyone else done this type of approach, I know i saw someone say they measured their whole kite line by line, but possibly not the entire length totals??

Anyway now I've done one side of the kite I can see some weird things. As expected B row has shrunk more than A row which hasn't shrunk much, but I can see two issues in the data. First one is that the wing-tips seem to have not shrunk as much as the centre part of the kite on both A and B rows (its a three row race kite- a Flymaax Boomv2). So i think i have to rectify this but i can't understand why that has happened and not sure if this is something that can cause this type of perfromance issue but i guess we'll find out by rectifying and testing. Also part of the A row- A9,10,11 are much shorter than the rest of the A row. no idea how this has happened but I'm pretty sure this is causing a deformation in the Leading Edge which is visible when flying creating a bit of a pronounced "shoulder" on the LE. So my plan is to create new bridle sections for A9,10,11 and also the wingtip areas to make the A row back to factory shape and same for B row. Then I'll adjust the mixer/make new mixer lines to make A to B to brake the correct ratios/bar position.

So I think I am on the right path with this but just wondering if anyone else has tuned foil kites in this way and wants to give some advice? Thanks in advance. When I am done I might make a youtube video about how I am tuning these race kites, its a bit time consuming but with racing its pretty necessary and I don't think many racers actually know how to do this and I think most paragliders aren't seeing the same kind of wear patterns that water foil kites are getting and especially minimal bridle race kites. I can also share the data once I have verfied it all but if anyone is interested in how this type of bridle data looks in a spreadsheet you can just google for paraglider servicign reports and see how this type of report looks with delta's/variances and adjustments and post-change variances etc. Cheers!

[airsail]

Hopefully you have watched this video, sounds similar to what your doing. The long mixer test will adjust for chord wise bridle irregularities but not spanwise.

[PugetSoundKiter]

Great topic, I'll be following it as I have a few ex-race kites that could use some TLC beyond brute mixer changes. Interested in your test setup with the laser and line tension rigging. A video would be helpful.

For why the tip lines have shrunk less even tho they should be under less tension may be because they are different line strength/weave/type than the other mid-kite lines?

Wonder if the laser could be rigged to evaluate if there is some stretch in the kite fabric/stitching (race kite fabric is light and sometimes the internal structure is reduced for weight savings). Not likely, but it would be interesting if there were some ideas. Without the OEM dimensions/CAD file/top drawing there is really nothing to compare, and the surfaces are curved so this might not be a frustrating effort all for not.

[derek440]

Thanks for the replies, I did consider there may be a problem with my measuring of the wing-tips giving inaccurate data but I checked the line plan again and there is uniformity of the line types across the span which are in the bridle plan at https://ginkites.com/en/produit/boom-v2/ (down the bottom there is a line plan button). I am going to measure some more of these race kites to get some more data to compare, if i measure an almost new kite the same model i'll be able to see if my measuring process is flawed or if the more warn kite definitely is changing bridle shape in that way, I'll post back here when i have more data.

RE the measuring technique I am doing something similar to this video:
To make my life easier I just put the mixer end on a short rope on a bench and over the corner of the bench I hang 4kg of weight and the line holding the weights has a knot in it so I know how far to pull up, then i have a box on the bench at that point so I can point the laser at it. I'll do a video when i get more time and have the process working better, but for now i think my measurements are right, for sure there is a big deviation in teh A row at A9,10,11 which are all about 30cm shorter than original where the rest of the A row is about 1-1.5cm shorter than original. The B row is approx 4cm shorter than original, and aside from those issues the wingtips aren't as short as the rest of the row (about 5mm shorter than original on the A row and about 15mm shorter than original on the B row). Either way i think the wingtip thing may be a red herring, but I'll rectify the A row issue first and test and then rectify the wingtip issue second and test and hopefully one of them makes this awesome kite hammer downwind like it used to when it was new.

[lightandfrost]

This is how L&F solve the problem.

viewtopic.php?f=197&t=2410952

There is an XLS spread sheet in the download at the bottoms of the below thread. You can adapt it to meet your kites line plan easily

viewtopic.php?f=197&t=2411985

[derek440]

Interesting work on the Pansh tuning and similar outcomes with a slightly different method. The benefit of the laser measure from cloth to top of mixer is once you have it set up right and have a simple spreadsheet of the check-length values (took about an hour for me to make the XLS for my kite i was tuning) then the measuring is pretty quick. I don't have a fancy USB interface laser device so I just use earbuds with my iphone voice control to dictate the numbers as I feed them through the laser device one after another. Makes it reasonably easy to measure the kites definite lengths and therefore shape of the canopy and compare to factory. The good thing is once you have the data on your kite you have made a physical problem into a software problem so you can work out the changes you'd like in software and model the changes to get a clear "after" picture. Once you know exactly what change you are going to make you can splice up some lines to the right length and the hard part is add/replacing the lines but if you have done all the prep it shouldn't be too hard. Then fly and test. And if the bridle is back to factory lengths/shape and it still doesn't fly right then you have a canopy problem.

Interestingly I have found paraglider repair centres that offer this as a service, I am going to ask one of them if they'll do kites and how much it would cost if I provide the spreadsheet. I am guessing its expensive, but still cheaper than a new bridle. Note that I probably would have just got a new bridle and/or kite for racing but can't get the bridle before an event that is coming up soon.

[evan]

Even with fairly new bridles you ideally want to check/tune after each handful of sessions when you want to have the best performance. Also good to check a brand new kite after the first few hours of powered riding, there is sadly no way to produce bridle lines to millimeter precision so you will always end up with slight differences that can have an impact on the performance.

Laser setup is great, but keep in mind that the cheaper ones often have a 2-5mm minimum precision if you check the documentation, ideally you want that an order of magnitude better in the 0.1-0.5mm range.
If you have a steady hand you can get away with a measuring tape and come close to 2mm precision.

[derek440]

I have measured two more kites (same model and one same size, one 13m) and found some interesting patterns and think I know how to get these kites flying fast downwind at good angles again. The wingtip issue I think was just misleading, I think its just an anomoly of the kite and the last few attachments have almost no load. The real issues have become clear with more data.

Firstly the kite is suffering from shrinkage faster than expected due to the very collapsed bridle -which was of course done to reduce drag. So the main issue is the B levels are all much shorter relative to A, but due to the way they ride mostly off the A level with very very low bar pressure and somewhat loose brakes a few racers haven't noticed as the brakes should have been let out and then when they have realised due to performance losses they have massively underestimated how much to let out the brakes, the main thing noticed after not tuning the kite for a few months is that eventually when you try to sheet in hard and power up downwind it doesn't work as well as it used to and you have to go higher mode to light the kite up. We are seeing about 2cm shorter B row than A row in the bridle (of course that very averaged) and also seeing in the short mixer test that after about 40h of hard use the B is again shorter than A by about 1.5 to 2cm. So a total of about 3-4cm shorter B than A which of course on a three row's of bridle kite you should let the brake out double that and of course the adjuster knots can only add about 6cm. One racer let the brakes out to the full extent of the adjustment knots and also did some stretching of the brake bridles and that kite went the longest performing well after those changes. The kites that weren't tuned at that point just started to suffer performance hits.

The second issue was harder to spot without more data but the outer half the A row is shorter than the centre half. Again its not exact and for every line but its generally what is happenign with these kites. The reason is that there is a collapsed gallery level/main trunks/branches in the bridle so there are only two main branches to the A row for each half of the kite, and the kite is designed to fly off the A row - which is set back from the leading edge. So the A main/trunk lines are a stronger line for the centre one than teh outside one and it turns out the outside trunk is shrinking more than the centre trunk. This is creating a "shoulder" on the leading edge between A8 and A9 which is shorter by about 2cm out to the wing tip. This is easily rectified by splicing up a new A main line out of 1mm dyneema that is 2cm longer (the factory length) and replacing.

So back to the point of this post, the laser measuring has been invaluable as its way faster than using a tape which is something I'd never do for three kites like I have just done with the laser. It also means you can re-do the measures quickly and easily and this method gives you the total picture of the shape of the canopy. I'm still not sure if I'll bother building more measuring rig/frames to make it more accurate I reckon I do a good enough job by hand and measuring a whole kite takes me less than an hour now once I have the XLS which takes about 30 in to enter. As I also sell kites I'll probably just offer this as a tuning service but if you only own a few foil kites I still reckon it would be worth it to keep them in tune, especially if you are racing. Anyway I hope this info helps someone. I'll make a youtube vid at some point about how I did all this and link it here if/when i get around to it.

[edt]

but i can't understand why that has happened

It seems obvious once you think about it (thought I never really thought about it until I had a foil kite) but the place on every kite where you have the most load is the a risers, next b has a little less load then c has a little less load and then finally z has the least, while the center of the kite is most loaded, then progressively as you go to the wingtips it gets less loaded. Any time you sheet out, the kite will have most of the load on the a risers. And the reason that the middle section has more load than the wings is that the middle section is flatter to the wind while the wingtips are at an angle. Also the way the bridles are built, the load is uneven so on some place like A9,10,11 you might have a lot more load than the rest of the kite (though it should be symmetric left and right but not always on my kites). anyway that's my theory.

These foil kites fly so good the first few years then . . . lasers and spreadsheets. Keep us updated, I'm trying to tune all my foil kites right now.

[Herman]

For why the tip lines have shrunk less even tho they should be under less tension may be because they are different line strength/weave/type than the other mid-kite lines?

But are the tip lines under less tension? The tension in the lines have to balance the lift force. If the angle of the bridle line to the cell attachment is more acute then the tension has to be greater so that the component of the tension resolved in the direction of lift still balances. Does tension depend on the bridle geometry as well as the variation in lift across the canopy? ( pressure in the cell has to be high enough to support any additional tension required by an attachment angle……..). Not sure how relevant any of that is ……need to observe some attachment angles. Any thoughts?

Thanks all above for the interesting thread!