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Shrunk Lines.


Steve
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For a long time I’ve been thinking that some of my skills were deteriorating. I used to have a certain smugness that I could always launch in zero wind regardless but for a long time I’ve been struggling more and more. I realised one morning recently that after an hour of failing to launch my wet wing in zero wind that perhaps my skills needed a revisit and a shed-load of ground handling time … or that maybe there was something up with my wing.

Like everyone, line stretching is something that I’d heard about and I’d put it on the list of things to do ‘one day’ along with washing the wing (never going to happen) and polishing those scratches out of my Land Rover (never going to happen). But I did a few hours of reading and it was clear that my launch issues were quite possibly being caused by shrunk line outers. My wing has seen year-round use for nearly five years and although tested and fine for porosity, line strength, etc. it has never had a line stretch.

I remedied this last week and it took just over an hour - which was quite relaxing and easy. It also gave me the opportunity to look closely at the wing, more closely than during a normal routine check. What happened truly amazed me, although it’s pretty obvious now that this shouldn’t have been neglected in the first place.

I didn’t touch the A and B lines for obvious reasons. I started with the D lines and straight away stretched the first line by over two inches. I could feel the stretch as I did it and I measured it against the opposite line before stretching that one too for the same amount. The D lines all stretched similarly. The C lines stretched slightly less but still by between one and two inches. This made me think how seriously out of trim my wing was and for how long I’d been flying it like this.

The proof came yesterday when I flew the wing. Or should I say when I flew my NEW wing. It came up so willingly that I thought something was wrong. It was hanging to the left but one step corrected it and it sat overhead as I took gentle paces forward instead of the usual forward force required to keep it there. The amount of A riser input needed was much reduced and the entire launch was a joy.

In flight the wing behaved and handled much better. I’d noticed that there wasn’t much difference between trim extents previously but now it made a difference and the turns were much more effective. Landing too was a joy. I guess the pressure in the wing is now what it was meant to be and what a difference it makes.

So me paying little to no attention to line stretching has now been replaced with a keen interest in it. As my flying usually involves damp or sodden grass I will be doing this every few months from now on. To those who have been doing this regularly as part of routine maintenance I feel ashamed but enlightened, for those that haven't I recommend you give it a try.

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I don't know if there's a standard way of doing it but I attached my risers to a concrete parasol base and laid it out upside down so the C and D lines were easy to get to. Then I used my hands and gently pulled/leaned back until the base lifted up. I've read about using a pulley and a 25 kg weight or scales but this worked fine for me. You can feel the stretch, it's a bit odd the first time but it's only the sheath stretching, not the line itself. I held the line for about 10-15 seconds and then compared it to its opposite.

I started on the D lines in the middle and worked out, always working in pairs - holding both pairs but stretching only one at a time and comparing both after stretching before moving on (by pairs I mean each left and right line not the two next to each other). It was very straight forward. Make sure you don't pull the tab, all the pulling must go down the line to the riser (to state the bleeding' obvious).

The other obvious thing is to double-check and make sure both pairs are exactly the same length after stretching. I read somewhere that after half an inch of line length error a wing is out of certification, whether this is true or not I don't know but judging by the difference it made I'd guess it is.

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IMG_1289.JPG.d7e877e24d8a1486e85f0f6beeb

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Thanks for taking the time to write that up. :-)

Very useful. I have to be honest and say that I thought the line shrinking thing was a thing of the past as the tec had moved on so much. Clearly not!

SW :D

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You're both welcome.

To be clear, it's not the lines that are shrinking which is why unsheathed lines don't shrink. It's the outer sheath that shrinks and shortens the length and that's what gets stretched back. The line can't stretch, it can only snap as far as I know.

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  • 1 month later...

Just as an update to this, I've had several flights in varying conditions since stretching the lines and the difference has been substantial. It's especially noticeable in low or zero wind launches, and even landings. Last night I mentioned this (again) to a friend who is flying an original Revolution with a zillion hours on it which has had innumerable soakings over the years and he had no interest in checking his lines. His flying skills have adapted to the wing as the lines have shrunk, like mine did, but you really have to try it to believe the difference it makes. His 'if it ain't broke ...' attitude means he won't get the massive rewards of improving his wings performance.

If your wing is used in damp conditions (this is the UK!) and the lines get wet the dry out, the outers will shrink. Therefore your wing will be out of trim on the C and D lines (the A and B lines are under enough constant tension to ensure they are restretched under normal use).

I still get surprised by the difference, there was a dribble of wind last night and I prepared to work my arse off with the A lines and running but it was as easy as it could have been.

https://youtu.be/rw6Q2263v7M

It only takes an hour and it gives you the chance to look your wing over more than you normally might.

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This reminded me I still haven't looked at this on mine.

Damn it.

I've just at the end of a week in a windy Cornwall and not flying,when I had all the time in the world to look at this. Now all packed up ready to go homeward, tomorrow. Might get a chance when I get home at the weekend. Be very interested to see if I get a similar stretch.

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