http://ozreport.com/forum/viewtopic.php?t=31052
Poll on weaklinks
JD Guillemette - 2013/03/12 00:32:50 UTC
Deltaman - 2013/03/12 00:05:16 UTC
Before to use math you have to test a loop (2 strands) of 130lb
Zack,
You agree that each leg of the bridle splits the tow force so each leg "sees" 1/2 the tow line force.
So the configuration of the weak link is eactly the same as the bridle, so each leg (or strand) of the weaklink will see 1/2 of that side of the bridles tow force.
1/2 of 1/2 is 1/4.
Now what I suspect what maybe happening here is that the method of weakllink attachment may not be allowing the two strands of weaklink to balance out.
Rubbish. What you SHOULD be suspecting is that it's physically impossible for a thread, string, cord, line, rope bending around a sharp curve to maintain anything close to the strength for which it's rated by testing it straight with the ends held fast in Chinese finger trap type devices.
The bridle slips through a metal ring so each leg of the bridle will alwyas be equal.
If the weaklink attachment binds and doesn't allow the two stands to "balance the load" one breaks, then the other in a cascade effect.
A loop of 130 installed on a typical spectra bridle blows at around 130 now matter how the hell you configure it.
I fly with standard pro tow...
I'll bet you're a lot better at holding the nose down than the late Zack Marzec was.
...with release on both sides.
So...
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3391
More on Zapata and weak link
Paul Tjaden - 2008/07/22 04:32:22 UTC
I have never had a lockout situation happen so quickly and dramatically and had no chance to release as I have always thought I could do.
...your chances to release in a lockout should be twice what Paul's were.
The bridle has one weaklink attached with double larks head knot.
Releases on both ends, weak link on one end. Good thinking.
I attached the weaklink to the relaease on my left (simple pin through the loop). The weak link can balance the load becasue it can slip around the pin in the release and so the laod is balanced.
A lot of people don't use the release on the weak link side of the bridle and istead the use another double larks head knot (or single, more on that) to attach to the webbing tab on the harness.
We refer to those people as idiots. Great job, Ridgely, turning them out at the rate you've managed to over the course of the past fourteen seasons.
This will not allow the loads on the two weaklink strands to equlaize and in actuality only one strand is loaded and the other is (in lack of a better word) standby.
Right. One strand is fully loaded while the other is totally slack and shares none of the load whatsoever.
so the one breaks, then the other. So what may look like two stands is only one, and so it breaks at the load of only one strand.
Rubbish. If that were true virtually no gliders so configured would survive dolly acceleration.
Now if a single larks head is used some people would suggest, and I agree, that the knot reduces the weaklink strength.
But perish the thought that we should put anything on a load tester and find out what's ACTUALLY going on - because any numbers so derived would have no external validity.
So by having a "non-binding" weaklink attachment you can greatly increase it's usable load.
Why would ANYONE want to INCREASE it's usable load? The weaker they are...
http://ozreport.com/forum/viewtopic.php?t=24994
No-knot weak links
William Olive - 2011/09/01 01:22:08 UTC
String links work. String links fail safe (ie anything that degrades them makes them weaker).
...the safer they are. If you increase the usable load they won't as clearly provide protection from excessive angles of attack, high bank turns, and the like for that form of towing.
This probably why I don't break many weaklinks.
Yeah JD, you don't break nearly as many weak links as those of us who've bench tested them and found them to blow at 130.
Zack C - 2013/03/12 00:42:04 UTC
William Olive - 2013/03/12 00:18:07 UTC
BTW, in my personal experience, I have had a WL break where the release rope has then wrapped around the tow rope ring. The release broke off before the tug end WL went, which meant that I had to buy a new release.
This is why, as I mentioned earlier, it's wise to have weak links on both shoulders.
Oops. In my previous post I was envisioning a two point tow. I forgot how dedicated all these assholes are to optimizing their one point "release ropes" for the same failure rates they're able to achieve for amateur tow configuration.
If you're towing two (three) point, release from the keel (whether due to a manual release or weak link break), and the bridle wraps on the tow ring, one of the shoulder weak links will most likely break (certainly if they're calibrated to be slightly stronger than half the top weak link's strength). If the shoulder bridle wraps after a shoulder release/weak link break, the weak link on the other shoulder will most likely break.
That said, shoulder bridles can be made short enough that wraps are impossible (this will require moving shoulder releases forward, which I find makes them easier to grab).
And, of course, the percentage of people reading this who'll modify their equipment to eliminate this failure mode will be ZERO. And, some years down the road, WHEN a one point bridle wrap has some really ugly results there will be the usual moronic discussion which will go on for twenty pages until Davis senses progress being made and locks it down.
Keel bridles will always be long enough to wrap, but the chance of this can be minimized by using a stiffer bridle material.
That's ridiculous.
http://ozreport.com/9.098
The thin 1500 pound aerotow bridle
Davis Straub - 2005/05/03
What do you need a 4000 pound bridle for?
Diver Bob Maloney came up with another invention. I unfortunately lost the pictures of his very slick bridles, but he has created two aerotow bridles from Spectra and Vectran lines in thicknesses used for shroud lines on parachutes. The Spectra lines are very thin but can handle 750 pounds. You put a weaklink on that that can handle 200 pounds (about). Why do you need a stronger bridle line? So far there is very little wear on the bridle line.
Bob uses Vectran for the three point bridle. The Vectran leg goes to the keel. Vectran is used because it can handle the heat generated when the Sepctra line on the shoulders is released and slides through the loop at the end of the Vectran.
Bob's aerotow shoulder-only bridles costs $8. The three point bridle costs $15. You'll also need to get a barrel release (
http://www.questairforce.com) and either the larger or smaller one with work fine. I use the larger one.
Bob Lane said that Quest Air sold over 40 of their bridles (and Bob sold 15 or 20) during the Nationals. The Quest Air bridles use thicker Spectra and are designed not to whip around and accidentally tie themselves to the carabineer. Bob says his bridles will not do this either.
It is great to see these safer, simpler, and easy to use aerotow bridles becoming popular.
Diver Bob Maloney says thin ones can't wrap and Davis says they're safer and simpler and easy to use. Why would any sane person use a thick bridle that's more dangerous and complex and hard to use?
JD Guillemette - 2013/03/12 00:48:46 UTC
And for the reasons mentioned above by Zack ... that is why I have a release on both sides. If my primary (right shoulder) wraps the tow line, either the weaklink breaks or I can release.
But I can see Zacks point that if my weaklink breaks (left side), and it wraps the tow line, I would have to release the right ... because I don't have a weaklink there.
- If you don't have a weak link there, what's limiting the load on that release and what makes you think you're gonna be able to blow it?
- Why the hell don't you just put a goddam weak link there, shut the fuck up, and go flying?
Good Point.
Idiot.
Zack C - 2013/03/12 01:12:26 UTC
JD,
The load tests that I've seen had one end of the weak link attached to a Spectra bridle (as in flight) and the other attached to a ring that allows the strands to be evenly loaded. In almost all cases, the weak link broke at one of the two places it exited the bridle. Weak links I've broken in flight have always broken at the bridle as well. The bridle attachment appears to be the weak point.
Tests were performed attaching the weak link to the bridle using single and double lark's heads in addition to the 'wrap and tie' method and no significant variance in breaking strength between these methods was found.
What do you expect us to believe? Your little post about actual bench test results here or the fourteen pages of crap by aerotow professionals published in the magazine last June?
