I recently did a complete restring job on my wing, so I thought I would share my thoughts on the experience for the benifit of anyone else thinking of trying it.
First off, although it has the potential to go horribly wrong and leave you with a tangled mess, in fact it all went off fairly smoothly. Obviously, with 222 lines to replace you need to be systematic and organised about it, but otherwise it doesn't present any particular problems.
The whole thing took a couple of days, but I didn't have an ideal setup in terms of space, I was all alone and I took my time. The second half only took half a day and I reckon you should be able to do it all in a day, or even less if you have things layed out optimally. Still, suggestion number one (obvious, this one):
1) Leave yourself plently of time, with the possibility to overrun if needed.
It would be a bad idea to try this in a space that it too constrained. Not neccessarily impossible, but making it much harder. The ideal would be a gymnasium, but I did it in a friends house with a large living room. Ideally you need enough space to spread out half the wing and be able to pull the lines out flat (like you are preparing the wing for launch). After a while I laid the wing over the back of a couple of sofas, and this arrangement worked quite nicely. The idea is that you just have the lines that you are working on on the spine of the back, which puts them at a reasonable working height. You can tuck the lines that you are going to work on behind the sofas and the ones you have already done along the front. The ones you are working on are the only ones stretched out in front of the wing.
2) Get as much space as you can.
Everyone who I have spoken to about this said that they stripped the lines off the side they were working on before starting on putting the new lines on. I think this is an error. If you leave the old lines in place then you can compare the old and new side by side as you build them up. This virtually eliminates the possibility of big errors. When you get to the bottom line you can pull the whole tree out straight and compare it with the old tree. It is pretty normal that the new tree is a few cm longer than the old one, but it usually has an almost identical shape and is very obviously correct.
3) Leave the old lines on until you have compared them with the new and satisfied yourself that they are substantially the same.
I started out unthreading the old lines, but I discovered that this is a very slow process and would probably add several hours to the overall operation. I then had a rethink about why I wanted the old lines intact, and I couldn't think of a good reason. What was I going to do, resell them to somebody on e-bay? If ever I break a line I'm not going to replace it with an old one which is weaker and has shrunk substatially. If I do a temporary repair it can be with a higher gauge line cut to the correct length. Any permanent repair is going to involve a newly made line. So from then on I cut the old lines off once I had checked them aginst the new ones. If anybody can come up with a reason why I will come to regret this descision then I would be interested to hear it. The only problem is that it introduces the possibility of error; you might cut the new line off rather than the old one. If this does happen it isn't the end of the world as you can get another line made to replace the single one you cut, however it is worth using some kind of system to reduce this possibility as much as possible. More on this later. One further point, if you are going to unthread the lines then you need to make sure that you don't insert the new line through the hole in the old line when you attach it to the glider. This is easily done and will leave you with the choice of dissassembling what you have just done or cutting the old line anyway.
4) Cut the old lines off unless you have a really really good reason for wanting them intact.
You need to be methodical. For each riser I isolated the lines and layed them along the floor, removed the shackel, labeled the old lines (more on this later), attached the new lines, put them into the shackel, cut off the old lines, attached the shackel to the riser (without twists if possible), moved the glider until the next set of lines was over the backs of the sofas and then stored the newly added lines out of the way along the floor. Thus the risk of tangles was reduced and there were only one set of lines in the work area at any one time.
5) Be methodical.
Prior to starting work I had a first run through at identifying the lines in the bundle that was delivered. This was not entirely straightforward as the labeling left a little bit to be desired. For a start not all lines were labeled with their width, and I found the lengths a little difficult to read (they were hand written). There is a real problem/danger when there are several lines that differ only by their width. It is very easy to mistake 125.5 by 0.6 for 125.5 by 0.5 for example, particularly when the latter is just labeled 125.5, and I spent a bit of time deducing which lines were which and improving the labeling. Then you need to lay the lines out around your workspace. Here I had a problem since there wasn't anywhere to put the lines nearby the work area, so I had to make do with laying them over the bed in the bedroom and draipsed over various chairs around the place. This had a strong slowing effect on proceedings as every time I needed a new line I had a little walk to go and get it. I didn't try to lay the lines out in the order I would need them as I reckoned that that would take even longer than just searching for them as needed. I did however lay the remainder back each time in the order that I had used them, so the second half was much easier than the first.
6) Identify the lines before starting work.
7) Lay them out as close to the work area as possible.
Don't forget that kevlar tangles at the slightest provocation - don't give it any.9) Be very careful with lines that are the same length but different widths, it's very easy to get the wrong one.
When I had done half the wing I took it outside to try inflating it. This lets you check one half against the other and adds to your confidence that you haven't gone wildly wrong. If you have any doubts about things like which shackel the stab line goes onto then now is a good time to resolve them as you have the old side to compare with.
10) Do a trail inflation when you have done one side to compare it with the old setup.
The process of knotting the lines together is pretty easy. Align the loops of the upper lines that you are linking to a lower line, then pass the loop at one end of the lower line through all of them. Now through this loop pass the other end of the lower line and pull all the way through. You must be careful not to create a Cow Hitch (here and here are both wrong). If you do then you must capsize it so that the knot if more symetrical (see jaymzwing's description here for some good photos). This also applies to the knot made directly onto the tape loops on the wing.
11) Make sure that the knots are correctly seated.
When you have finished, it goes without saying that you should do loads of inflations and then little bunny hops before doing a test flight in stillish air. I'm not going to say what I did; suffice to say that I got away with it.
There was one further trick that I found very useful, which was to label the old lines. My initial impetus for this was because I thought I would recover the old lines and I wanted to know which was which. Well, OK, in fact the real real impetus was that I needed to write a program to print the lables out and that would be a useful delaying tactic to avoid the dread day when I would start untying my glider's lines. Anyway, once I had started putting labels on the old lines I discovered that it had a couple of benifits. Firstly, when you are going to replace a line you can read the details of the new line from the label on the old line. This removes the danger of making a mistake when refering to the line diagram. I started doing this, but quickly found that reading the label was a lot less error prone. Putting the labels on the lines was very quick. I printed them out in such a way that I could put sticky tape half on/half off one side, cut down between the labels leaving only a bit of paper between each one, then run along the lines tearing them off one by one and sticking them onto the lines. The whole operation only took a couple of minutes per riser and easily saved more time than that, as well as being less error prone. The second advantage was that when it came to cut the old lines off I made a point of always pulling the knot open until the label came up against the loop. This made sure that I was pulling on the right line (the old one) since the new lines didn't have labels on.
12) Label the old lines.
The next post describes the line label printing stuff I have written, in case anybody wants to do the same thing.
All in all, if you feel like restringing your glider yourself, my advice would be to go ahead. Just be aware that it's a long job. If you're looking for an excuse to pay someone else to do it for you, look no further. It's a long job, you might as well let the pros do it.
As for me, I'm glad I did it myself, but I really don't know if I would do it again. Maybe.
Jonty
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