15 years ago
Hi everybody!!
Paragliding lines shrink with the use.
- Does anyone have a proper technique to stretch the lines?
- And about how many hours of flight we should do this?
I started looking for these data in the web, but I didn’t find yet a description of the method to do it.
Locally, some guys do the following:
- They fix both risers to a hook and apply 15kgs with dynamometer (or they hang a 15kgs item through pulleys) to the twins extremes of the cascade (I mean the lines to the left and right sides of the wing, for they should be identical), where the cascade is attached to the intrados. They apply the force with gloves in both hands, just before the attachment loop. They check that after the pull BOTH twins lines are identical in length. They never stretch the commands cascade (obviously).
- Timing used for this operation is about 200 hours of flight.
Personally I never did this, and to me it is not logical to apply the same weight to whatever diameter of lines… along the cascade the diameters are changing!!
Another issue is the number of cycles of load… the lines closer to the risers receive many cycles in one stretching operation (on the other hand, those are the thicker lines of the cascade…)
Comments and critics are welcome!!
Faso
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My freestyle glider - 7 years old with only around 20hrs of solid flying no water landings.
Attached photo showing results before & after being stretched.
Whilst flying I'd noticed the middle brake lines were tight when flying. So brake pressure began in the middle first when applying the brakes. Not good.
I measured all lines with pro equiptment and lazer. Lines were upto 30mm or so out and brakes were longer-yes longer! After stretching I'd made around 10 to 15mm difference but generally still over manufactures tollarance 10mm.
After stretching with a 20kg load all line groups - except the brake lines.
Test flight with excellent results and the middle brake line is looking normal again.
When flying it before and after I didn't find it made any difference to its flying launch or character. It's still a great wing.
Hi Faso,
The link shrinking happens often if you dry your lines too fast, not so much because they have been wet. Same with clothes. If you take your wet clothes from the machine and hang them up or throw them in the tumble-dryer.
If you have had your glider wet, never put it in a hot room. Kiting your glider is one of the best ways to dry it, or hang it in the shadow. If you are to fly your glider wet/moist, never do any manouvers that will expose your glider to g-forces as it might stretch the risers.
Signs of line shrinking is that you have to guide your glider higher up on launch in weak conditions before releasing the risers, and that especially on groundhandling the glider tends to go into parachute stall easily. You should always inspect and compare the riser lengths if you have problems with your glider. Look especially to the B-riser as it tends to get stretched more than the rest due to the high load.
Note, it is the housing of the lines that shrink, not the lines. This is not a common problem on unsheated lines. On normal flight the A and B line sets will be stretched due to the load of the pilot, so it is only the C and D line sets that needs to be stretched (if you care you can do the brake lines as well)
I've bought a fish-spring-weight 0-25 kilos as the main-lines will be stretched with 20kg's and the intermediate and top lines will be stretched with 10kg's. This is recomandations I got from Flight Design and from Swing. Check your manual, call your dealer or mail your brands producer. It's been stated that todays lines are pre-stretched, but if the housing shrinks, what good does it do?
I fix the risers to a three, car etc. And start stretching from the top line. BE CAREFUL to stretch the line, NOT the line attachment point as it will rip. Be sure you are inside the line loop facing you and not pull against the sewing of the loop. Pull until 10kg's keep it for some seconds, as you mention the intermediate lines will be stretched twice, no problems, you don't need to stretch them individually as they are stretched through the top lines, then you move down to the main lines and stretch them with 20kg's.
When you are finished you will be amazed on how much easier your glider will launch, and how much better it stays over your head without going parachutal.
Of course, you should be sure of that it is the lines that is the problem, and not the cloth due to high porosity.
Vertical greetings -Luis "Mickey" Fonseca- ;)
"In paragliding acrobatics it's not the speed that kills you, but the lack of it..."