http://ozreport.com/forum/viewtopic.php?t=25174
Build Your Own Weak-link Tester
Steve Davy - 2011/09/14 07:59:23 UTC
http://www.towmeup.com/linkbreaker.html
THERE IS A HUGE MISCONCEPTION IN THE PILOT COMMUNITY RELATED TO HOW STRONG A TIED WEAKLINK ACTUALLY IS IN PRACTISE! KNOWING WHAT LOAD YOUR WEAKLINKS WILL WITHSTAND BEFORE THEY BLOW OUT IS CRITICAL TO FLIGHT SAFETY. A WEAKLINK THAT BLOWS OUT PREMATURELY CAN IN MANY CASES BE WORSE THAN USING NO WEAK LINK AT ALL!
Gee Stuart, do ya think?
Jim Rooney - 2011/09/14 09:34:20 UTC
Not really sure where you're quoting from, but your link doesn't follow your quote.
Did you try searching for a chunk of the text from the first sentence or just looking around the site a little bit?
The very first sentence from your link...
A weaklink is an absolutely essential element for the safe operation of any towing system and must be used for all tows to ensure the safety of the towing operation.
Doesn't really line up with your quote.
You're right. Stuart's something of an asshole (don't worry, nothing of your caliber) - as evidenced by a good bit of everything so far quoted and this:
Most reliable sources believe that a weaklink should be sized so that it breaks at 75% to 100% of the inflight load.
also from his site.
And here's somebody who's got it a lot righter than most:
http://www.paraglidingforum.com/viewtopic.php?t=28697
Weak links why do we use them. in paragliding.
Ake Larsson - 2010/02/13 16:31:31 UTC
In the my part of the world (flatland Sweden) where you have to tow to get some airtime no one uses weaklinks, I belive it is the same in Finland. Even most of the beginner training is done on tow in Sweden and whitout a weaklink. Play the %, a weaklink might save you one serious accident in a hundred years but will give you a lot of smaller accidents when it breakes.
So Stuart - and Jim... If the fucking weak link is so goddam absolutely ESSENTIAL for the safe operation of any towing system, how come we're not hearing about people dropping like flies at all these operations that aren't using them.
Testing's great, but your conclusions are wrong.
What conclusions? All he did was quote something.
How about instead of trying to stir the pot, you try maybe having a conversation?
How 'bout instead of ignoring questions you don't like and/or can't answer you plead ignorance and/or stupidity?
Dawson - 2011/09/14 09:40:33 UTC
Or, the simple method is to tie a loop of rope to the rafters in your garage/shed/hangar/neighbors lounge room, hook your harness to the rope, but with a weak-link between your karabiner and the rope ( maybe use a steel ring on the rope ). Climb into the harness and check your height - you should adjust the rope so that you are hanging just an inch or so above the floor.
A good weaklink will not break with you hanging there, but will break if you just bounce your weight on the weaklink a little, i.e., it's got to be a little bit over 1G.
Good, Dawson, let's do it that way.
- We don't hafta install the weak link on and engage it with the material and hardware that'll be used in flight 'cause what possible bearing could that have on anything?
- We can ignore the mass of the glider itself 'cause that's pretty trivial - only 45 percent of the minimum hook-in weight of a U2 145 for example.
- We'll use an International Standard Little Bounce so our results are consistent and repeatable.
- And we'll get a weak link a little bit over one G - regardless of whether it's on the end of a towline or two or one point bridle.
- And, of course, one G is what we should all be shooting for because it's RECOMMENDED and a GOOD RULE OF THUMB for preventing gliders from getting into too much trouble.
Jim Gaar - 2011/09/14 13:05:23 UTC
There's just no one single solution.
No, of course not. Hang gliding isn't like sailplaning where you just use a weak link 1.3 to 1.4 times the maximum certificated operating weight. This is hang gliding where you might rip your wings off or lock out.
Based on my experience with AT and PL launches...
Oh good. Another bozo who wouldn't know what a number was if one bit him in the ass is gonna give us his OPINION based on his EXPERIENCE.
...the weaklink will break at different points, times, moments, situations no matter the type, size, length, whatever.
Did you try 1.5? Did you try using a weak link to protect the glider from overloading?
I've had the same type weaklink break at any number of situations whether it was less then 1 g or more, knotted or doubled, whatever.
Really?
- What was the G rating range of the weak links you test flew?
- How did you determine the breaking strengths of these weak links? I'm guessing the Dawson Method 'cause I'm not hearing you raise any questions about the validity of his technique. Or maybe you used the Quest method of declaring a single loop of 130 pound Greenspot to be 260 pounds, about the average wing load of a single pilot on a typical glider, and a double loop, of course, being twice that.
The point is to have a weaklink that doesn't break when you don't want it to...
Did you try 1.5 Gs?
Good luck with that.
Did you try 1.5 Gs?
The best defense is always to be ready and aware. The last thing I say to folks I am launching off carts and platforms is, "Be ready for an early release or weaklink break." It should be on your personal checklist as well.
Well, yeah. OBVIOUSLY. There's just no freakin' way we can get a weak link which doesn't break when we don't want it to and to protect ourselves from the weak link whose PURPOSE...
is to increase the safety of the towing operation. PERIOD.
...we've ALWAYS gotta be ready for it increasing the safety of the towing operation. PERIOD.
http://www.hanggliding.org/viewtopic.php?t=13689
eating dirt
Jim Gaar - 2009/09/18 19:23:44 UTC
Hell I've literally shoved the control frame out in front of me to avoid a whack when it got a little ahead of me in a light DW landing, similar to when I've had to slide it in on my belly (did that once after a weaklink brake coming off a launch cart.
Great job of reacting to your weak link increasing the safety of your towing operation, Jim. There's just no beating you professionals.
Tow me up. I'll find my way down
Don't you hafta find your way up first, asshole?
Which, in part reads...
A popular misconception uses a very common 135 pound test green spot trolling line. In fact the myths associated with this product are so strong we no longer carry it. If you wish to obtain some, it can be easily found at any decent fishing store as Dacron Trolling Line made by the Green Spot company. Here's how the myth goes - Look at the knot tied link shown in the picture above. Many, many pilots believe that if you take a 135 pound weaklink line and tie it in a loop that it will break at 270 pounds. The logic is that there are 2 parallel load paths sharing the load, each one capable of withstanding 135 pounds. They miss the fact that any properly tied weaklink will ALWAYS fail at the knot. The line is pulled tighter and tighter at the knot and should break right at the knot every time. Depending on the knot used the line will break at 40-60% of its rated strength. Typically a weaklink tied with a double grapevine will break at slightly over the rated strength of the line. The only way to tell for sure is to break test it with a calibrated tester. There have been many inadvertant weak link breaks caused simply because pilots ASSUMED that the link was stronger than it was. This has led to the asinine belief that if one loop is good 2, 3, or 4 is even better.
In use the weaklink material will stretch well over 60% in length before it fails at the knot. Adding a multitude of loops makes it impossible to spread the load evenly, and the link will likely bind up causing it to fail in an often unpredictable and unrepeatable manner. To ensure consistent breaking strengths, stacking equal length weaklinks works, using a single appropriate strength link is the best, and multiple wraps should never be used.
- It's 130 pound.
- It's Greenspot.
- It's made by the Cortland Line Company.
- That's not the myth. The myth is that if you ISOLATE the Fisherman's Knot in the center of the Double Lark's Head with which it's installed on the bridle "it's hidden from the main tension in the link and excluded altogether from the equation" and will thus blow at 260 pounds.
- Another port of the myth is that the Double Lark's Head itself isn't really a knot and will thus have no bearing on the equation (despite the fact that it's virtually always at one of the two points the Greenspot exits the Double Lark's Head that the failure occurs).
- Another part of the myth - and the REALLY asinine belief - is that it doesn't matter whether it's on the end of the towline or of a bridle - it will still blow at 260 pounds towline tension.
- Yet another part of the myth is that all solo gliders weigh 260 pounds.
- And still another part of the myth - and a completely asinine belief - is that "A good rule of thumb for the optimum strength is one G".
- NOBODY in hang gliding uses the words "stronger" and "better" in the same sentence when they're talking about weak links.
- Dacron doesn't stretch sixty percent before blowing. More like a quarter of that.
Jim Gaar - 2011/09/14 14:42:18 UTC
Really good site though!
Ya think so, Jim?
http://www.paraglidingforum.com/viewtopic.php?t=28697
Weak links why do we use them. in paragliding.
Stuart Caruk - 2010/02/11 20:26:44 UTC
Sometimes Tad goers to far, but many of his observations are spot on.
Been there, done that.
For moi, old news and boring...
Yeah Jim. Obviously. You've got this stuff DOWN.
Jim Rooney - 2011/09/14 17:20:14 UTC
Ditto.
Yeah Jim. Ditto. And you also aren't saying anything about the Dawson Method. And that means you're ALSO totally cool with it.
Here we are again Ridgerodent.
You seem to fail to understand that we've been at this a very very long time.
Yep. Just like the cults who for hundreds of years dutifully sacrifice virgins to volcanos each night to ensure the Sun God reappears in the eastern sky the next morning. They've been doing it for a very very long time, they're very very good at it, and it ALWAYS WORKS.
Some of us do this for a living...
Mostly 'cause you're too fucking stupid to be able to do anything else.
...and have been discussing these issues before you even started flying hang gliders.
No you haven't, shithead. He started flying hang gliders when they were still being towed from the frame, several years before there was any trace of practical aerotowing, over a decade before the Dragonfly arrived as a presence on the scene, and well over two decades before you began rearing your ugly stupid head in the sport.
We've been through all this crap loads of times...
Why bother? You had the perfect primary release...
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3107
I have a tandem rating!!!
Lauren Tjaden - 2008/03/23 22:20:15 UTC
When Jim got me locked out to the right, I couldn't keep the pitch of the glider with one hand for more than a second (the pressure was a zillion pounds, more or less), but the F'ing release slid around when I tried to hit it.
...the perfect backup release...
The barrel release wouldn't work because we had too much pressure on it.
...and the perfect weak link...
http://groups.yahoo.com/group/hhpa/message/11155
Question
Shane Nestle - 2010/09/17 22:17:50 UTC
So far I've only had negative experiences with weak links. One broke while aerotowing just as I was coming off the cart. Flared immediately and put my feet down only to find the cart still directly below me. My leg went through the two front parallel bars forcing me to let the glider drop onto the control frame in order to prevent my leg from being snapped.
...for twenty years.
...yet you seem to think you're going to somehow educate us...
WAY too easy. But I'll probably be using that one a lot in the near and not so near future.
...because you've read some shit on the internet?
Versus the absolute shit that you dickheads put on the internet.
zzzzzzzzz
No Jim. Keep talking. Every time you open your mouth I just get stacks of the coolest ammunition.
William Olive - 2011/09/14 21:51:55 UTC
This has been done to death.
http://ozreport.com/forum/viewtopic.php?t=12512
Weak Links
David Williamson - 2008/07/04 21:39:42 UTC
Has this subject ever been discussed on the Oz Report before? Well today I went aerotowing for the first time in six years and the first time on a topless glider. I took the first tow of the day and was on a 2X30kg weaklink...
Why? What were you trying to accomplish with that particular piece of string?
...which snapped before the tug had even pulled me one step forward.
Well then...
The "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.
Sounds like Rooney was ABSOLUTELY RIGHT all along. Who'da thunk?
My lazy technique of holding the tug back as long as possible and letting it catapult me off my feet did not help, but this has always been fine in more commercially orientated situations where the weak link may have been stronger.
Ooh! Sounds dangerous! You might have actually gotten airborne with that approach. And with a dangerous pop start to boot.
Then I take the first step to the run, and I am now running 25 mph, I am thinking, oooOOOOH SH#T, hope I don't have to run that far, hoping the HG gets lift so I don't have to run no more... My F-A running down the runway like a rocket. There is no wind, I have the right angle of attack, the HG is up, but still not enough lift for the pilot.
I can't reach my CUT line 'cause I have both hands on the downtubes, and if I let go of the Coke bottle grip I will crash.
I feel like pushing the HG into the air, or jumping up so it can lift, but I do not - that would make my situation worse.
I feel I am about to fall into the asphalt face first and crash, I am at my run limit, and feel I can not take another step. Still the glider is not lifting me.
Instead of a nice, smooth, controlled running launch gradually transitioning you into flight.
Later in the day I launched with a doubled up weaklink of 4X30kg and , after I came up too quickly through the prop-wash, I ended up in a stable lock-out to the left and was given the line by the vastly experienced tug pilot...
- If he was go goddam vastly experienced why wasn't he using a dolly to launch you?
- If he was go goddam vastly experienced why did he let you get behind him with a weak link on the first flight which wouldn't even allow you to move in the course of an otherwise safe foot launch?
- Why are you foot launching for aerotow and even bothering to bring up weak links as factors in your safety?
...who was being dragged back towards stalling speed. The weaklink did not break. I summise that, as two stands are too weak, and four strands are too strong, the range of safe and useful weaklink strengths is quite narrow in an aerotow situation.
Great. So we've determined that three strands of 30 kg is strong enough to get you going if you don't hold back too much for a lazy launch and yet light enough to break before you - or the tug - can get into too much trouble. So even if you have a shit tug driver who won't do your job for you when there's no freakin' way you can take a hand off the bar to get to your Koch Release you should still be OK.
And there's obviously no point in including a single word in this idiot twenty post thread about the weak link having a function to prevent the glider from being overloaded.
And, back to you Billo...
I can put you on board with the Dawson Method as well?
And, of course, having read that thread from start to finish, we're all totally cool with 130 pound Greenspot for everyone forever, right?
Damn, I wish we'd stop beating this topic to death, just listen to Rooney and the rest of you professionals and experts, and get with the program.
