Martini

A docile (no fun) canopy for $2000 to replace a super-fun and wingsuit-friendly canopy that costs $3-400? Too much crack around here and it's not the nylon kind. Sometimes you eat the bear..............

Any canopy can be used for wingsuiting. Sometimes you eat the bear..............

Never heard that one…..ever. Have you ever done a hop-n-pop with feet forward, fun to see the PC and initial deployment in front of you. Yeah, I know, flame away. Sometimes you eat the bear..............

Fortunately the fantasy appears to be harmless. Not necessarily the case with theism. Sometimes you eat the bear..............

One of the best and most beautiful wingsuit vids I've seen in years. And a Birdman video, who'da thunk. Sometimes you eat the bear..............

Because, just like everything else in skydiving, it is fun. Too dangerous for you, stay on the ground. Sometimes you eat the bear..............

You believe in a fantasy. Sometimes you eat the bear..............

Probably true if lightly loaded, I like mine loaded higher and accept the more limited flare power at low airspeeds. Sometimes you eat the bear..............

He responded to my canopy for sale as well. Because I despise these people and have the time I plan to screw with him for my own pleasure. Sometimes you eat the bear..............

The recovery arc of a canopy is only equal upwind/downwind if in a stable airmass. If there is considerable wind gradient, that is a change in relative velocity with altitude, then upwind and downwind behavior can vary significantly. A hook starting at 750 feet could easily go through a 20 mph gradient without time to stabilize in the "new" airmass. Sometimes you eat the bear..............

You haven't mentioned how many jumps are on the current line set, you do say that you know that it is out of trim. A domed or pocketed slider will not give you a canopy that is in trim. There are a ton of old Sabres out there with original linesets that would be fine if relined, they sit unused because they open badly. The canopy, if in good flying condition, is worth at most $600, investing $300 might not be a good plan. All canopies will eventually need lines replaced though and at some point every canopy will need to be retired. Your rigger should be able to help you make a decision. Sometimes you eat the bear..............

This issue has been discussed many times here. All of my Sabres have been great openers. Some people have had very bad experiences with Sabres. Packing is an issue. Line trim is an issue. The 170 is a notorious bad boy, possibly/not because it uses the same slider as a 107. I have a Sabre that I put a larger slider on to improve the openings, it opens even better with the original slider and......a new line set. Since you know it's out of trim I'd start with a new line set. Or, if you're feeling really brave, stretch the lines according to Brian Germain's method. I use it, others consider the technique to be dangerous. That's a separate issue. See how much fun this is? Sometimes you eat the bear..............

You can't "never mind the wind". If you're flying downwind and add a little brake you may go further than flying hands up. Using the same amount of brake in a headwind may shorten your glide. Even if you quantify the extra glide distance in still air on half brakes you'll find the data useless. Gliding is too complicated for such simple assumptions. How much is half brakes anyway? Is your brake pull calibrated so that it is exactly repeatable? Did the trim on your canopy change in the last 50 jumps? Are you gliding up/downwind and at what velocity? Air temp? Altitude? Humidity? Different jumpsuit=different drag? Gain/lose some weight? Is there some rising or sinking air that will have an effect? And a bunch of other influences. Just so you know, my instincts are to want the same information that you are looking for, I finally gave up trying to get it. Pick a method that suits you, get some data and understand that it will never be any more than an approximation. And a pretty useless one at that. I have a standing offer for anyone who wants to ground launch a skydiving canopy on a cliff above my house. You'll only need a glide of 2.5:1 to make a "safe" landing area. The offer is that I'll show you the exit point and I call 911 when you launch. No takers so far. Sometimes you eat the bear..............

I'm afraid you've been misinformed. Skydiving is full of rules and regulations that USPA uses to keep the FAA happy. BASE jumping isn't controlled by the FAA so there aren't any regulations for BASE. You can go ahead and get a wingsuit and a BASE rig and jump. Proximity flying is perfectly legal and there are tons of legal mountains to jump off. Best of luck! Sometimes you eat the bear..............

Amazing how many suckers there are out there! Sometimes you eat the bear..............

Maybe you could suggest a flower arrangement? Sometimes you eat the bear..............

While you are considering which system to choose you might also consider what kind of flowers you like. Sometimes you eat the bear..............

The lines are calculated using a very complex algorithm devised by Robert Pecnik. The formula is for sale but only to very experienced BASE jumpers and at a very high price. Sometimes you eat the bear..............

Thanks Mark, It's great to get some insight into this subject. I didn't really expect that you had done a series of tensile tests on stretched lines but having an expert opinion of the mechanics is helpful. I would have expected that loading the shrunken lines into the elastic state would have been sufficient to "uncurl" them into extension. I have also seen and heard of canopies with serious trim issues after relatively few jumps, it's a great indicator of how heat sensitive Spectra is. Also nice to hear that alternative line types are available even for the Sabre, I'll look into it if I need new linesets. Happy New Year to you too. Paul Sometimes you eat the bear..............

I glad you're posting on this subject, right now it appears that you are the only one with scientific knowledge. I'd like to ask a few questions, I really have no agenda, naturally I'd like confirmation that the technique I've been using is sound but you have already stated that you are against line stretching and I'm quite open minded. Can you describe the amount of tensile loss as a function of stretching heat-shrunk lines? I know there are several variables but a general idea would be useful if you haven't graphed your testing. I've never subscribed to the theory that unloaded lines shrink, that would mean that they shrink just sitting on the shelf. Since paraglider lines also shrink but aren't subject to frictional heat, do you think that exposure to sunlight is causing shrinkage? I'm aware of the increased complexity of PG lines (sheathing, mixed materials etc). I have three Spectra-lined Sabres, one with nearly new lines, the others with decent but slightly out of trim lines. I don't know if non-Spectra linesets are available but in any case I'll be jumping the current linesets for a while. Do you believe that I'm putting myself at risk by stretching these lines to some degree? BTW these canopies have consistently butter-soft openings. I do own one HMA-lined canopy, it's my preferred line material. Unfortunately it's a smallish crossbraced canopy and not my favorite for wingsuiting which is what I generally do. No perfect solutions here barring purchase of another canopy, I like the Sabres too much to replace them, never mind the cost. Thanks for contributing here, we all benefit from more reason and less speculation. Sometimes you eat the bear..............

Your approach isn't stirring the pot, it's pretty much the norm. Things aren't really that black and white though. Lines going out of trim are like boiling the frog, it usually happens so slowly that you only realize the trim issue when the performance degrades to a clearly unacceptable level. By occasionally stretching the lines you may enjoy a much better overall performance. You may not care, that's fine it's your canopy. I believe stretching lines is a good plan so I do that. It's not just a case of taking horribly out of trim lines and resurrecting them to save a few bucks. But as you say, do whatever you like. Sometimes you eat the bear..............

Then I'm never using the technique again, radioactivity scares me. Sometimes you eat the bear..............

Two reasons. Stretching could result in breaking or at least thinning some of the fibers, in fact that seems very likely. Not all fibers are at the same stress level, the line is not perfectly homogenous to begin with and heat/shrinkage will most certainly not be uniform. Some degree of makeup may be a factor similar to steel with grains, crystallization, work hardening, micro tears etc. In other words shrinking and stretching might end up with material that has physical properties that differ from the original. Sometimes you eat the bear..............

Thanks for the thoughtful and well written post. In my first post I wrote that HMA and Vectran do not respond to stretching but you're right, there are many who can't distinguish Spectra from string cheese. The stretching I referred to was on a Sabre 120 (not 210) loaded at 1.6-1.7, it was deliberately done to clean up twisting openings. The lineset was not only out of trim lengthwise but more significantly was badly asymmetrical. The stretching adjustment had the desired effect and lasted about 100 jumps, I did it again to good effect but after that I had it relined. While use of this method probably should be something that is either taught or performed by a competent rigger some people seeking do it on their own would be good with a clear set of instructions and video specific to their canopy type. While I appreciate your point of view regarding potential pitfalls I would prefer not to disregard a tool that I, as well as others, have found to be useful. I have never attempted to give detailed instruction on this technique and wouldn't except with qualified people and on the same canopy type. I'll always be willing to discuss this topic though, thanks for contributing more depth to the subject. Sometimes you eat the bear..............

Too bad, you often post good stuff. I'm not sure why you, as well as others, have chosen an adversarial position on this topic. And I disagree, people can be influenced to change what they do. If John LeBlanc or Bill Booth supported this technique it would be the norm. If they came out against it the discussion would be over. I don't expect that either of them will publicize an opinion so it is up to us to discuss the subject and if possible study it to reach a sensible conclusion. But if you really don't care then that's OK too, I expect at this point most people don't care either. But this isn't like discussing an RDS that will only ever affect a few, if stretching was a generally accepted tool it could affect many. I didn't invent this process and I don't mean to deliberately promote it but I think that it merits discussion. I also believe that since I have used the technique and have given it some consideration that I have something to contribute here. Sometimes you eat the bear..............