You measured them before use for 2 seasons use as well to see they were the same to begin with? I'm not disagreeing with your theory, but your tests are lacking a bit of control.

No idea really ... but I have experience with a different shortening line. I have BWS Noise kites, and there's a line on bridle between front and rear lines that pulls through a ring. This dyneema line will shrink by 10% of its length over time. To me, seems counter intuitive...lines should stretch under pressure, no? But have now seen it on multiple kites and with multiple new lines...for sure it shrinks. In that example, I think it is something to do with the friction in that ring it goes through...generates heat or something?

Anyways, "shrinkage is real". We know all about that, kiting in Canada in winter.

... I agree with original poster, lines shrink and I have no real explanation of why except the theory that when lines are constructed, the weave is kind of loose relative to the final product as we know it and by working them, they just go back to the pre-stretched state.

The lines are stretched, made nice and tight with some manufactures putting some coating on them then sewn to the work of art we see before us. But over time by loading and unloading them ie flying the kite, the coating or what ever the stuff is wears off and they go back to the pre-manufactured state purely by just using them. I worked out roughly 2 percent or so, and in kite trimming terms is a lot. The more work the lines get, the more they shrink, which is the reason the front lines seem to go quicker than the steering.

I wanted to find out for myself so I measured all my bars one day (with tape measure) and noticed a direct correlation of shrinkage to age of use.

My control was a new un-used bar, then differing ages of use with 1 week, 1 month, 6 months, 12 months and 2 years.

Biggest difference I found was about 300 mm and they definitely got shorter the older the bar was,,,,,and of course the floppier the lines felt too.

Further to my experiments, I wondered if bridle lines did the same so I got the bridle measurements from manufacturer and then compared 2 kites (same model and size) with one kite that was 8 months old kite and the other 1 month old.

The older one (8 months) had all the inner components of the bridle roughly 1 to 2 cm shorter with the newer kite measuring exact to original measurements. The shorter bits were balanced from left to right side btw. Rough as guts pic:


Interesting the older kite flys fine, just not quite the same as the new one. You can only see it from a distance but the LE kind of flattens out a touch when under load, kind of like as if a 5th line is a touch short.

Anyway, just something I noticed!

Cheers,

Robbie

sir ROWDY said..
You measured them before use for 2 seasons use as well to see they were the same to begin with? I'm not disagreeing with your theory, but your tests are lacking a bit of control.

That's a pretty fair call.... I just assumed that the manufacturer would make all same model bar and lines sets identical give or take very minimal amounts.

dafish said..
that is a pretty massive difference for only one season....which leads me to believe the newest generation and the second could not have been the same size to begin with. I would think that the lines would shrink unevenly, different favorite rotations and loops, jumping more favorably to one side etc. But the shrinkage would have been limited to 100 mm more or less. How many days did you put on the first bar? Really curious about this one.

The first bar must have done at least 200 sessions and maybe as much as 300 over 2 seasons The rear lines are uneven length and were adjusted when I calibrated the bar - about 50mm /1 knot difference. The chicken loop line also needed to be adjusted to accommodate correct front line calibration

What is the water temp at your local spot? This could contribute to shrinking in length

Who cares wether they shrink or stretch, just every 6 months check and correct them.

Lines are manufactured and stretched, then coated. The coating acts as a stabiliser and helps them stay at their stretched rate.
The issue becomes apparent if the coating de-stabilses. The easiest way to do this is with temperature.
North investigated this problem 2 years ago because of stretching issues and complaints within Australia. They found that about 83 degrees was the the crucial temp.
The issue that we have in Australia is temps in cars on a hot day can easily exceed this, in euroland 25 degs outside means a car temp of about 60 so line shrinkage is much less of an issue, but here 40 degs outside is about 85 in car, so lines destabilise and start reverting to their pre stretched rate.
Centre lines tend to stay stretched as they are under a constant load (while being flown)

So along with kids, animals and kites, don't leave your bar in a car on a hot day!

what an interesting thread.

ProductLinear Temperature Expansion Coefficient
- α -(10-6 m/(m K))*) (10-6 in/(in R))*)
Polyethylene (PE) 200 111
Polyethylene (PE) - High Molecular Weight 108 60
Polyethylene terephthalate (PET) 59 .433
Polyphenylene - glass fiber-reinforced 35 .820

Just get ozone lines and be done with it.