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I need convincing too:) Bar back lines!

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Matteo V
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Re: I need convincing too:) Bar back lines!

Postby Matteo V » Thu Apr 26, 2018 12:49 am

Matteo V wrote:
Wed Apr 25, 2018 5:56 pm
To me diameter shall be balanced with force repartition.
For optimum performance with respect to drag reduction, I agree that back lines can be reduced in diameter, and in some cases should be - specifically when you are racing. The kiting industry agrees with this concept - and has done all the proofs of it's validity.

Do you need to reduce the rear line diameter for regular recreational kiting (not racing where a fraction of a second counts)? I would say no, but I actually do with my line sets. I use 363kg front lines (because I weigh 100kg and really load up my lines in waves for strapped kitesurfing), and I use 225kg to 300kg lines on my rears depending on what line is handy. To me, I am not downsizing my rears as much as upsizing my fronts.

And here is where this thread is leading. Can you gain an advantage over your competitors in a freestyle or even in a boosting competition with reduced diameter rears (or fronts for that matter)? Would the answer take into account the likelihood of missing a heat due to a higher statistical chance of a broken line?

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downunder
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Re: I need convincing too:) Bar back lines!

Postby downunder » Thu Apr 26, 2018 2:18 pm

Hmm,

Now we know from where you are coming from, a 100kg bloke talking to a 57kg person about the safety of loading the lines :)


There is a reason why I mentioned English. And that is, the best and most progressive riders are from France. Not that many will dare to comment here coz of being scared of misinterpretation or whatever, English not being their first language. Hence, the difference in opinion comes only from Regis and a few other riders. Both Regis and me are under 60kg or so.
You’ll never understand this unfortunately coz we are in completely different league, as well as yourself.

We are feather light and you are heavy weight. Simple.

The equation might be complex, but it’s not a rocket surgery ;) it’s a number in grams as the result.

Sorry, did not bother to read anything else, and comps does not interest me at all.

Sincerely

D.

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Re: I need convincing too:) Bar back lines!

Postby foilholio » Thu Apr 26, 2018 2:48 pm

Matteo V wrote:
Wed Apr 25, 2018 5:56 pm
And foils have a more rigid structure than inflatables.
Well hmm ok, what can I say? Maybe if your are comparing the non inflated parts of an inflatable to the thicker parts of a foil kite? Honestly though I am dumb founded how you can make that observation. Maybe you can argue it with PMU, or I can quote you to troll him lol.

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Re: I need convincing too:) Bar back lines!

Postby downunder » Thu Apr 26, 2018 3:23 pm

^
Don’t bother, I think he just loves to be authority. Happens a lot when someone is 100kg and 1.8-1.9m tall. Plenty of examples everywhere. I’m the same tho :)

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Re: I need convincing too:) Bar back lines!

Postby Matteo V » Fri Apr 27, 2018 4:56 pm

foilholio wrote:
Thu Apr 26, 2018 2:48 pm
Matteo V wrote:
Wed Apr 25, 2018 5:56 pm
And foils have a more rigid structure than inflatables.
Well hmm ok, what can I say? Maybe if your are comparing the non inflated parts of an inflatable to the thicker parts of a foil kite? Honestly though I am dumb founded how you can make that observation. Maybe you can argue it with PMU, or I can quote you to troll him lol.
I claim no authority other than the validity of my argument. I also use both inflatables and foils, though I have no strong bias toward one or the other, outside of their actual strengths. Let me see if I can help you so you can find a weak point in my argument to make a case against. I am happiest when I am shown evidence that I am wrong, as that is how human beings learn. Everything else is "feels", and I am interest in "feels" mostly for how they are counterproductive with respect to understanding reality.

Foil kite:
With the ENTIRE underside of the kite supported by bridal attachment points, from leading edge to trailing edge, a FOIL KITE has more rigidity. Or rather, the bridals that are lightly loaded given their total number, take up all the stretch in the canopy (top and bottom, with connection via the vertical cell walls). This is because the load is taken where it is made at each part of the kite, and transferred vertically to the bridals in close proximity, NOT transferred horizontally a long distance to the leading edge or tips, and then to the bridals. Thus the air foil shape of a foil kite is prevented from warping by those bridals, via the reduction in horizontal forces over the entire canopy. Cord line, camber line, and thickness are all rigidly held in place by having so many bridal lines nearly in line with the forces generated by the foil section. Again, this is likely the reason for the difference in feel of a foil vs an inflatable.

Inflatable kite:
ONLY the leading edge has multiple connection points to the kite in line with the forces generated by the foil section of an INFLATABLE. Steering connection points number only 2 (1 each side, with few exceptions) on most inflatable kites. Thus the canopy behind the leading edge, ALL THE WAY to the trailing edge, is free to warp and stretch according to load limits of the material over the entire span of the kite. The load generated at the center point of the foil section of the kite must be transferred to the leading edge bridals, or the steering lines via the canopy. And the trailing edge is only supported horizontally, not vertically as you approach the horizontal center section (lift producing) part of the trailing edge. Thus forces on the leech line in the trailing edge, that result in pull on the steering lines, are 90° to the resultant load at that particular section.

Think of two garbage bags filled with water:

One rounds out because the water filling it takes the shape of the bag is because the bag is only supported with its outside skin.

The other is an impossible flat bottomed bag, because you have a bunch precise length lines connected to the bottom to support it against "bagging out". Thus you could make a rigidly held (against outward forces, would not stand upright) flat bottom garbage bag with lots of little bridals holding that shape.

Which shape is more rigidly held in place? - Push on the bag without the lines and it will bulge in one direction, then the other, changing it's shape until the wave energy dissipates. But the flat bottomed trash bag will see much less distortion where supported by the lines because those lines limit the movement of the skin.

Many things in kiteboarding, physics, and even life are counter-intuitive. Heck, my view is that most of kiteboarding is learning how to stop yourself from doing what you think you should be doing.

And thanks for mentioning "Pumpy" - that's all we need here right now. :roll:

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Re: I need convincing too:) Bar back lines!

Postby edt » Fri Apr 27, 2018 7:02 pm

Matteo V wrote:
Fri Apr 27, 2018 4:56 pm

With the ENTIRE underside of the kite supported by bridal attachment points, from leading edge to trailing edge, a FOIL KITE has more rigidity. Or rather, the bridals that are lightly loaded given their total number, take up all the stretch in the canopy (top and bottom, with connection via the vertical cell walls). This is because the load is taken where it is made at each part of the kite, and transferred vertically to the bridals in close proximity, NOT transferred horizontally a long distance to the leading edge or tips, and then to the bridals. Thus the air foil shape of a foil kite is prevented from warping by those bridals, via the reduction in horizontal forces over the entire canopy. Cord line, camber line, and thickness are all rigidly held in place by having so many bridal lines nearly in line with the forces generated by the foil section. Again, this is likely the reason for the difference in feel of a foil vs an inflatable.
Very interesting. So I guess in practical terms this means that a foil kite doesn't twist like a pretzel as much as a tube kite does, also it holds the ideal wing shape better. Of course there is a lot more hoop pressure on a tube kite so a foil kite does things like taco, jelly fish, asymmetric wingtip wrap, double wingtip wrap and bow tie. If you completely release the wind pressure on a foil kite it's just a piece of cloth in the air, but a tube kite will hold its shape and start to fall down. When the wind starts up again, the foil kite can take many different shapes as the wind pressure is put on a shape the kite was never designed for. I do know that for my C kite it twists a lot in the air, a lot more than my bridled kite. I also know that when I do a really hard downloop (less often on a kiteloop) on my foil kites almost always the wing tip near the water starts to fold completely inward, I guess there's no wind pressure to hold the foil in its proper shape.

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Re: I need convincing too:) Bar back lines!

Postby Matteo V » Sat Apr 28, 2018 3:57 am

edt wrote:
Fri Apr 27, 2018 7:02 pm
Very interesting. So I guess in practical terms this means that a foil kite doesn't twist like a pretzel as much as a tube kite does, also it holds the ideal wing shape better. Of course there is a lot more hoop pressure on a tube kite so a foil kite does things like taco, jelly fish, asymmetric wingtip wrap, double wingtip wrap and bow tie. If you completely release the wind pressure on a foil kite it's just a piece of cloth in the air, but a tube kite will hold its shape and start to fall down. When the wind starts up again, the foil kite can take many different shapes as the wind pressure is put on a shape the kite was never designed for. I do know that for my C kite it twists a lot in the air, a lot more than my bridled kite. I also know that when I do a really hard downloop (less often on a kiteloop) on my foil kites almost always the wing tip near the water starts to fold completely inward, I guess there's no wind pressure to hold the foil in its proper shape.
I frickin "Origami'ed" a brand new (never used) 7.5m Best Kahoona (inflatable) yesterday. And I mean full on origami folded it in the air. I would love to know a police sketch artist to describe the still inflated shape it took while still up in the air and maintaining it's inflation with a fold in the leading edge. Something like a beach ball is what came to mind at first. I still think it was my fault as I loaded it hard on a turn I was cutting sharp for the spray. It was pretty fluky wind coming off of a shelter belt (trees planted to stop the wind for erosion and livestock protection) on a local lake here. I have inverted, taco'ed, bow-tied, and a few other wraps I have never heard any one else describe, but this one was straight up Origami. Essentially, the best description I could give you of it is that it had wrapped half of the trailing edge around the leading edge and both the tips (steering lines attachments) were somehow touching, I never launched it while swimming all the way across the bay trying, so it was stuck. I got to the kite and could not figure out how to unfold it, and I was scared it would blow if I did, so I deflated it in it's still folded shape.


But your statement is almost entirely correct, and it is also the very root of why most kiters think that a foil has less rigidity to it than an inflatable. My explanation deals ONLY with the situation of when the kites, both inflatable and foil, have wind flowing over them. When there is no wind due to turbulence or a complete lull (if moving it would have to be an apparent wind lull), then the rigid inflated structure of an inflatable IS more rigid. And that is the paradox. How can a foil stay up in lighter winds than an inflatable with more stability, yet higher winds favor inflatables for stability? It is due to flying skill with a focus on maintaining flow over the kite via the wind window, and to some degree, apparent wind generated by rider movement, in BOTH cases. Some credit must go to the mass stored in the leading edge of the inflated kite, and the mass somewhat more evenly distrubuted in the foil kite. Weight being forward in the leading edge of an inflatable would also be a factor, as well as the foil having more "neutral buoyancy" in the air (makes it come down slower).

The point is that when sitting on the ground, an inflatable takes partial shape (not a foil section except for a small amount at the struts), whereas a foil does not. No air flow = Inflatable more rigid. Air flow = foil more rigid.

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Re: I need convincing too:) Bar back lines!

Postby downunder » Thu May 03, 2018 4:43 am

Regis-de-giens wrote:
Wed Apr 25, 2018 8:23 pm
Considering the huge loading difference between a 60kg rider on a foil and a 100 kg freestyler, it is really not optimum to use a similar line combo. This is to me the limitation of bar standardisation. Pratical and economical for kite brands , but necessarilly dimensionned for the worst demanding style and heavier riders or obvious safety reasons . Hence FS option for thin rear lines 160kg (with appropriated warning) ... and that everyone can easily understand are still oversized for a non-racer lightweight foiler in low end ... in 1t years of kite I never changed any line and got no breaks ever.
Matteo V wrote:
Wed Apr 25, 2018 5:56 pm
foilholio wrote:
Wed Apr 25, 2018 1:33 pm
I do think elasticity is an issue as you go weaker, but then maybe a benefit for the more relaxed riding as it would smooth out gusts!
Rear line stretch will depower the kite in a gust. But it will also reduce response time for sheeting in as those rear lines stretch.
Elastic elongation depends on the ratio Force / diameter ^2. As a consequence on foilkites with most of the load going to the front lines , if you use same diameter for front and rear lines , you will get a higher elongation on front line in gust ... which will power-up the kite... during gusts => not great !
To me diameter shall be balanced with force repartition.

Side note : To limit wear during loops on my rear thin lines, the first 2.5 meters (near the bar) have higher diameters and then connnected by splices. And final connection to the kite is done by a dyneema loop of higher diameter to keep the thin line straight only.
Umm, looks like Matt got some opposition with his views? Dare to fix "1t years"? Be careful Regis, this are his words:
"And you think you are leading? You are way behind the crowd on extremely small diameter lines. But more over, you don't need them, because you don't race. And the actual benefit to smaller or extremely small diameter lines is minuscule. "
I wonder how come he did not 'crush' your refreshing post?

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Re: I need convincing too:) Bar back lines!

Postby Matteo V » Thu May 03, 2018 5:30 am

Here goes!
Regis-de-giens wrote:
Wed Apr 25, 2018 8:23 pm
Considering the huge loading difference between a 60kg rider on a foil and a 100 kg freestyler, it is really not optimum to use a similar line combo. This is to me the limitation of bar standardisation. Pratical and economical for kite brands , but necessarilly dimensionned for the worst demanding style and heavier riders or obvious safety reasons . Hence FS option for thin rear lines 160kg (with appropriated warning) ... and that everyone can easily understand are still oversized for a non-racer lightweight foiler in low end ... in 1t years of kite I never changed any line and got no breaks ever.
"it is really not optimum" - No disagreement from me. I kite on lines that are not optimum, unless they are worn a bit. But when they wear too much they are detrimental. Life span of lines is important. Again, I agree with this statement as "optimum" is something that is a very narrow definition, or rather, nothing is really optimum. Lifespan and low stretch vs gentle use and drag reduction is a line on a graph. Optimum for efficiency may leave out consideration for acceleration and range.

"....obvious safety reasons . Hence FS option for thin rear lines 160kg (with appropriated warning)"
- Yep, we have been over that and I still agree. That is what I pointed out when you (downunder) pointed out FS thin line set. Again, this gives us a warning for "less than safe" line thickness. And somewhere between the Ozone 200kg lines and FS 160kg lines is a point where saftey for jumping is a concern. At 200kg, there is at least one MFG that reccomends an interval of 100hrs replacement. So I agree with Regis-de-giens again.

"1t years of kite I never changed any line and got no breaks ever" - This is where I would love to know what lines he is using! But I suspect his conditions and style may help out with the lifespan. For me, kiting for 3months in the summer on the ocean beach is tough on my lines. I can replace 2 front line sets in those conditons. Much tougher than on the grassy launches in the Midwest, where I can go 2 years or more without replacing my lines. But I do wear lines even without sand abrasion as I loop a lot - multiple loops that actually have me sticking with a mid "Y" bar that releases onto both front lines. Not the safest, but I go through lines too fast with low "Y" bars that release onto a single front line.


So I just DO NOT disagree, nor is anything that Regis-de-giens has presented in contradiction or denial of my points or blatant reality. He is correct as he acknowledges the cost vs benefit that you (downunder) are denying, along with the obvious safety issues.

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Re: I need convincing too:) Bar back lines!

Postby foilholio » Thu May 03, 2018 1:51 pm

Lines can last a truly long time. I have never needed to replace lines for wear on any kites I have owned ever. I have had a line set with about 2000 hours on it. It is certainly a foil kite thing. Down wind launches and landings and never dragging the lines over the ground, i.e. walking up the lines as you wind them.


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