Weak links

General discussion about the sport of hang gliding
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

TowMeUp.Com - 2012/04/27

If you happen to tow with us on one of our towboats, you would notice we almost always have a pair of links tied from 250 pound test line and another from 300 pound test line. The smaller links break at around 264 pounds and are used by almost all solo pilots.
That's a bit odd Stuart. 'Cause earlier on this page you say:
One weaklink does not work for all pilots.
Most reliable sources believe that a weaklink should be sized so that it breaks at 75% to 100% of the inflight load.
Light pilots need weaklinks that break with a lower force than heavy solo or tandem pilots.
So I don't think it's unreasonable to assume that you're towing flying weights from 150 to 250 pounds on the same 264 pound weak link.

So that means a G range from a little over one G for the big guys to one and three quarters for the wee folk.

Are your bottom end reliable sources OK with you going over double - a full G over - what they believe a weak link should be sized to for the women and children? I always thought those were the ones who got FIRST pick of the lifeboats.

This is really most confusing.
The larger link breaks at around 384 pounds and is used for tandems.
Who gives a fuck about the tandems? We'll probably hafta sacrifice a student but at least you'll get taken out at the same time.
The links are all the same length when tied which we use to tell if a link has had a transient overload applied. Lets say on the previous tow the pilot had an overload situation occur that dramatically stretched the link, but didn't cause it to blow out. This will be obvious when the next pilot is hooked up for the tow, as the overloaded link will be an inch or 2 longer than the others. We simply cut it off, use the other link for the tow, and replace the link when the drogue is rewound for the next tow.
- Sounds like crap. I haven't seen that testing Dacron.

- So what you're saying is that when the glider's pulling to almost the limit of what you've deemed maximum safe tow tension nobody on the surface or glider is having any problems or even noticing anything going on. (Big surprise.)
Leader Lines are typically short lengths of spectra with sewn eyes on both ends. Typically they are connected between the apex of the drogue chute and the weaklink clip in link. Leader lines serve 2 functions. Primarily they are used to add space between the drogue chute and the pilot. In the event that tow tension is reduced in flight, the drogue chute will inflate. The use of a leader line ensures this happens well in front to the pilot, rather than in the pilots face. We typically use a leader line of lower breaking strength than the towline and use it as a "backup" weaklink for those applications where a pilot elects not to use any type of safety link. Our sewn leader lines are available in 6 - 8 foot lengths in the following breaking strengths. 825 Lb., and 1800 Lb breaking strengths.
For those APPLICATIONS where a pilot elects not to use any type of safety link?

You mean "applications" like towing paragliders?

"Applications" where a pilot ELECTS not to use any type of safety link?

So what kind of irresponsible asshole ELECTS to tow some other irresponsible asshole who's too stupid to use ANY safety link?

Oh, right. You DO use a safety link - an 825 or 1800 pound length of Spectra. Reasonable compromises with the seventy-five to a hundred percent limit most reliable sources believe to be appropriate.

So let's do the math for those applications where a pilot elects not to use any type of safety link.

Three and a third to five and a half Gs. Sounds like a plan to me!

Let's not even bother with the eighteen hundred pound stuff. We went off the deep end a long time ago.

Why don't you just put everyone up at one and a half to two Gs and stop writing all this lunatic crap?

P.S.
We are big fans of testing and virtually all of the products on this site are tested to failure to ensure they perform as designed.
How'd your releases do at 825 and 1800 pounds?

Moron.
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

http://ozreport.com/forum/viewtopic.php?t=15716
weak links
Davis Straub - 2009/04/19 16:20:50 UTC

We have tested the Cortland Greensport line many times. Many times.

Anyone else is of course encouraged to do so also.
Davis Straub - 2009/04/19 19:32:23 UTC

Tree branch, spectra line, your body.
Davis Straub - 2009/04/21 16:27:15 UTC

210 (hook in weight) + 71 (glider weight) = 281 (total)
weaklink = 200 lbs (approximately) Halved = 400 lbs.
400/281 = 1.42 (approximately)
If the weaklink was 180 lbs then 360/281 = 1.28
Davis Straub - 2009/04/22 23:08:34 UTC

281 lbs here (total with glider and 212 hook in weight). If the Greenspot is about 180 - 200 pounds which as I recall is what we found at Quest Air (not 125 lbs), well you can see the numbers above.

I'll let the forces on the V-bridle be divided by 2 and leave it at that.
Dallas Willis - 2009/04/23 20:33:25 UTC

Tad is right about the force not being split in half. The tow force on the tow rope is directly ahead towards the tug. Then the force is split into two sections of your bridle. Let's assume pro-tow. The force felt on the weak link or the bridle in the angled direction towards the tow rope is greater than half the total force on the tow rope. Not by much but it is greater. In words, you have to make a force vector diagram and use cosine (SOH CAH TOA, so Cosine of an angle = length of adjacent / length of hypotenuse).

I've attached a couple diagrams (yeah I know they suck) that should show this. I chose a 60 degree angle just for kicks but you can adjust this and the force "units" to your liking. But in this example with a tow line force of 100, each bridle sees 57.7 units of force in their angled direction (and thus on the weaklink) or about 15 percent more than "half". For a tow force of 200 units the bridle would see 115.5 units of force (again about 15 percent and that number should keep for all values of the tow force and a 60 degree angle).

Change the angle to 30 degrees and you end up with 51.8 units of force for a 100 unit tow line, or 103.5 units for a 200 unit tow line so about 3.5 percent.
Davis Straub - 2009/04/24 03:23:41 UTC

Let's also be clear, that the Greenspot weaklink works fine and that as least as far as pro-tow go it meets your criteria and mine.
Davis Straub - 2009/04/26 22:05:31 UTC

Tad doesn't agree, but the rest of us no doubt do, that we are in a partnership with the tug pilot, and that he needs to be protected also, and therefore our weaklink has to be less than his.
http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Davis Straub - 2011/08/26 14:04:52 UTC

We had six weaklink breaks in a row at Zapata this year. Russell Brown (tug pilot, tug owner, Quest Air owner) said go ahead and double up (four strands of Cortland Greenspot).
I'll check my weaklinks once again, to see if they are about 1.5 G.
Davis Straub - 2011/04/26 22:15:56 UTC

Yup, at least 175 pounds- single loop of Cortland Greenspot 130 pounds test.

That was one end of the loop in a barrel release where the edges are a bit sharper than where I normally connect the weaklink loop with cloth loops at both ends.

I was jumping a bit so it is more than 175 pounds. Maybe 200+.

1.25g at 175 pounds.

1.42 at 200 pounds. So it is likely more than that.
http://www.youtube.com/watch?v=TaVg_bzK3Aw


http://ozreport.com/forum/viewtopic.php?t=24534
It's a wrap
Davis Straub - 2011/07/30 19:51:54 UTC

I'm very happy with the way Quest Air (Bobby Bailey designed) does it now.
Paul Tjaden - 2011/07/30 15:33:54 UTC

Quest Air has been involved in perfecting aerotowing for nearly twenty years...
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

http://blog.4herrings.com/2011/08/11/zapata-world-record-encampment-wre-2011-parte-dos/
Zapata World Record Encampment (WRE) 2011- Parte Dos | Cloud Base addict
BJ Herring - 2011/08/11

Zapata World Record Encampment

Stalwart of the WRE and friend Pete Lehmann let his knee have an affair with the runway. Needless to say it was short and dirty and needed antibiotics as the bone made contact.

Image

Weak links were going like hotcakes so we doubled them up. On my Atos, I had my only break right as one hand let go of the cart so I held on like crazy to the other side and skidded to a stop.

As much as I didn't like it, a few of the yanks between me and the Dragonfly were like an accidental wheelie on a dirt bike (2 stroke) and would have broken the single links for sure.
http://ozreport.com/12.081
Weaklinks - the HGFA rules
Davis Straub - 2008/04/22 14:47:00 UTC

At the 2008 Forbes Flatlands Greenspot for the first time was used as the standard weaklink material (thanks in large part to the efforts of Bobby Bailey). We applaud these efforts to improve the safety of aerotowing by using a better weaklink material.
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

Continuing from a discussion that got underway at about:

http://www.kitestrings.org/post2163.html#p2163

http://ozreport.com/forum/viewtopic.php?t=9945
Launched unhooked
George Stebbins - 2007/10/26 16:05:20 UTC

The weak link is NOT there to prevent the glider from being overstressed on tow.
BULLSHIT. That's what it's there for and that's ALL that it's there for - asshole.
OK, it serves that function too...
Fuck you.
...but its main purpose is to release if you get too far off-line or some other issue causes the forces to become stronger than you, the pilot, can control.
Try real hard to pull your head out of your ass, George.

- The device whose main purpose is to RELEASE you if you get too far off-line or some other issue causes the forces to become stronger than you, the pilot, can control is called - oddly enough - a RELEASE. It - like every other component of your tow system - has ONE PURPOSE and ONE PURPOSE *ONLY*.

http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467
weak links
Danny Brotto - 2007/05/16 23:15:19 UTC

Weak links are not a secondary release system...
- Try to learn the difference between a WEAK LINK and a RELEASE.

- That might be a tough assignment for you 'cause if you're spending any time at Quest it's highly unlikely that you've ever seen a release that can be counted on to function as a release.

- But fuck you anyway 'cause you've had as much opportunity as Antoine has to look at my photos and read my documentation - and you get to do it in your first language.

- I got news for ya, dickhead... If you've got a weak link capable of surviving long enough to accelerate the dolly and get you airborne you've got a weak link WAY heavier than you need to get you far enough off line and totally cancel out your control authority enough to kill you several times over.
The forces become too strong for the pilot to overcome LONG BEFORE the glider gets overstressed.
Yeah George. That's exactly right. So pick a G rating which will preclude that from happening.
Does the weak link always do its job?
Yeah, it ALWAYS will. If you've got a weak link which blows at 225 pounds towline tension it'll blow at 225 pounds towline tension. If you've got a weak link which blows at 450 pounds towline tension it'll blow at 450 pounds towline tension. Either of those weak links will blow before the glider is overstressed by the tow and may blow:
- in time to keep you from slamming into the runway
- just before you slam into the runway
- right after you slam into the runway
Nope.
Fuck you.
On the other hand, making it too weak is a danger too.
- Really George? I don't think I've ever heard that before in hang or para gliding. If that could possibly be true surely somewhere in the world you'd be able to find a national organization or government agency which specifies a minimum rating. Can you cite me anything?

- Any chance of getting that expressed in Gs?

- At how many Gs do you fly George? Lemme guess... One? 'Cause whenever a Quest Air douchebag hands a loop of 130 pound Greenspot to anyone he tells him it puts him at about one G and that's a good rule of thumb?
The key is to minimize risks.
And you do that by keeping your head safely stuffed up your ass and pulling it out only for brief periods to swallow whatever crap some dickhead like Russell Brown, Steve Kroop, Bo Hagewood, or Paul or Lauren feeds you.
A reasonable weak link does that.
A REASONABLE weak link... Is that anything like a...
Always use an appropriate weak link with a finished length of 1.5 inches or less.
Wills Wing APPROPRIATE weak link? Anything under an inch and a half finished length?
It will seldom (but not never) break when it shouldn't.
How very considerate of it. What's a G figure at which we can be assured that nothing bad will happen because of the failure?
It will usually (but not always) break when it should.
Dickhead.
Different forms of towing use different strengths.
Yeah. Dickhead towing uses 130 pound Greenspot. Non dickhead towing shoots for one and a half Gs.
And tandems need stronger ones regardless, because the tow forces are higher.
But since all solo gliders weigh the same then they can all use the same weak link.
There are some folks who tow with very strong weak links.
- Who?
- How strong?
They are asking for trouble, IMO.
- Can you name anyone who's gotten any?

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Jim Rooney - 2011/08/31 09:25:57 UTC

Only later, when we're visiting them in the hospital can they begin to hear what we've told them all along.
- Ever run into your little piece o' shit buddy when you're visiting them in the hospital?

http://groups.yahoo.com/group/TTTFlymail/message/11545
Cart stuck incidents
Keith Skiles - 2011/06/02 19:50:13 UTC

I witnessed the one at Lookout. It was pretty ugly. Low angle of attack, too much speed and flew off the cart like a rocket until the weak link broke, she stalled and it turned back towards the ground.
- Did you and/or your little piece o' shit buddy visit HER in the hospital?

- Fuck you're goddam idiot OPINION, George.

http://ozreport.com/forum/viewtopic.php?t=12512
Weak Links
George Stebbins - 2008/07/13 21:01:44 UTC

I've always been happy with the Quest Air links...
Yeah George. Everybody always is - regardless of his or her flying weight. And anybody who ISN'T very happy with Quest Air links...

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Jim Rooney - 2011/08/26 06:04:23 UTC

Take this weaklink nonsense.
What do I "advocate"?
I don't advocate shit... I *USE* 130 test lb, greenspun cortland braided fishing line.
It is industry standard.
It is what *WE* use.

If someone's got a problem with it... we've got over ONE HUNDRED THOUSAND TANDEM TOWS and COUNTLESS solo tows that argue otherwise. So they can politely get stuffed.
...can politely get stuffed.
...and only once did one break when it annoyed me seriously, and for no apparent reason.
BULLSHIT. It blew for one reason and one reason only and there was nothing the least bit mysterious about it. It blew because it was overloaded. And it was overloaded at NORMAL tow tension. Now take that data, think about it real hard for a couple of weeks, and see what you can come up with. Asshole.
(Just as I crossed the treeline. I had to whip a 180 before I ran out of altitude to do so. Then I had an interesting landing, not really having room to turn back into the wind...)
And then you went right back up with the exact same Quest Air link because you've always been happy with them and you're too fuckin' stupid to be able to visualize a scenario a little bit worse than that in which you could get your fuckin' neck broken.
I've had enough links break when they should to think mine is ok...
Thinking isn't really your thing, George. Leave it to people who've had a little practice.
deltaman
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Re: Weak links

Post by deltaman »

I miss opportunity to be aerotowed in my mountains but 2 months ago we spent 4 days teaching AT to 12 pilots in 2 points. All had 190kg weaklink (220kg on tug side).
One of them oscillate and start to lockout. I said by radio : (time to) release, he did it (JoeStreet release), but 1ms too late.. the weaklink was just blowed.
and no unexpected wl failure in 90 AT.
I'm confident in this way to think wl..
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

This is really great.

A 190 kilogram (419 pound) weak link translates to 185 percent of what a Davis Link can do on the best of days and about three and a third times...

http://www.youtube.com/watch?v=TaVg_bzK3Aw


...what it can be expected to do.

Let's call the glider 135 kilograms. So then we're talking about a 1.4 G weak link. This is the first account I've EVER had of an aerotowed hang glider blowing something in that neighborhood.

For the record, can you tell us...
- glider model and size
- estimated glider flying weight
- separation altitude
- altitude lost during recovery
- any control issues observed with and/or reported by the tug

Also...

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Jim Rooney - 2011/08/31 09:25:57 UTC

Only later, when we're visiting them in the hospital can they begin to hear what we've told them all along.
Any reports from the pilot of what Jim told him during the hospital visit.
...(JoeStreet release)...
Anybody who tries to sell any of these guys some piece of crap from Wallaby, Quest, or Lookout is probably gonna get it shoved down his throat - where it belongs.
deltaman
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Re: Weak links

Post by deltaman »

- glider model and size
ICARO MastR Medium 13.77 or Large 14.88 m²
- estimated glider flying weight
#120kg
- separation altitude
This pilot was the one with less experience with his glider and no much flight this year. He had tandem flights and a test before and had to release prevently.
So this time he started an incipient oscillation that became worst. I thought he will release by himself but have to tell him when he was waiting a little bit too long. He was maybe at #50m. He actuated but the wl broke first. The pilot didn't know that as he discovered on the ground that the wl was blown.
- altitude lost during recovery
VG: 1/3
nothing particularly impresive..
maybe #5-10m and a turn engaged 90° from tug track that he let continued backwind and landed well on the wheel, VG on, 90° side wind. (from what I remember)
Young AT pilots lose the common sense for the management of a good landing after being stressed by an incident.
- any control issues observed with and/or reported by the tug
Our tug pilot was Samir Elari, multiple world, european and french champion by microlight, he is instructor and a glider, balloon, paramotor and hangglider pilot too. So not the worst of us..
We told and explain him the load break of wl and he accepted that.
One time, juste after a slack line he reports a big jolt with no wl break but nothing he felt dangerous for him or his tug and the AT goes on..
And nothing special about the wl break when the pilot locked out.
Steve Davy
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Re: Weak links

Post by Steve Davy »

http://ozreport.com/forum/viewtopic.php?t=9945
Launched unhooked
George Stebbins - 2007/10/26 16:05:20 UTC

The weak link is NOT there to prevent the glider from being overstressed on tow.
I wonder what the response was to that statement?

http://ozreport.com/forum/viewtopic.php?t=27494
The exciting bits
Jim Gaar - 2012/04/27 03:34:28 UTC

We adapt and fly on, lesson learned each time.
Weak-links break! They are supposed to...we are ready for that. It's what we do.
I did not see any protest to Jim's comments.
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

#120kg
So if that's the Medium it's loaded to max hook-in and towing at 1.58 Gs. If it's the Large it's towing at the same based on actual flying weight and 1.34 times its maximum certified operating weight.
The pilot didn't know that as he discovered on the ground that the wl was blown.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=1725
Towing at Quest
John Dullahan - 2006/02/07 03:20:14 UTC

With winds of 10-12 mph I waited for a few minutes for a lull before giving the takeoff signal. Liftoff from the cart was nice and level, but at about ten feet the right wing was suddenly and violently lifted (Paul said a strong thermal came through just as I left the cart and pilots had to hold down their gliders). Almost immediately the glider went into a lockout and the weak link broke just as I hit the release.
And I myself have had a weak link blow simultaneously with the actuation of a spinnaker shackle release.

I suspect that when a string loop weak link is loaded close to its capacity it's the movement across the opening gate that finishes it off. That explanation works a lot better with a spinnaker shackle - which chews up weak links in the best of circumstances - but maybe there's enough friction involved with the parachute pin to send it over the edge.

Really appreciate the data.

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Marc Fink - 2011/08/28 21:11:09 UTC

I once locked out on an early laminarST aerotowing. went past vertical and past 45 degrees to the line of pull-- and the load forces were increasing dramatically. The weaklink blew and the glider stalled--needed every bit of the 250 ft agl to speed up and pull out. I'm alive because I didn't use a stronger one.
It will be useful in silencing and/or humiliating total morons Marc and Paul and Lauren Tjaden who try to correlate altitude loss and lockout severity with weak link strength.
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Tad Eareckson
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Re: Weak links

Post by Tad Eareckson »

I wonder what the response was to that statement?
Nothing.

He made it in the course of an idiot Davis Show discussion triggered by Bille Floyd's unhooked tow launch.

http://ozreport.com/forum/viewtopic.php?t=9945
Launched unhooked
I did not see any protest to Jim's comments.
What did you expect?

http://www.ushawks.org/forum/viewtopic.php?f=2&t=1041
"Sharing" of Hang Gliding Information ?!?
Merlin - 2012/05/26 13:22:30 UTC

I confess to previously having a bit of an Oz Report habit, but the forced login thing has turned me off permanently, and I am in fact grateful. Frankly, the site had pretty much been reduced to a few dedicated sycophants in any case.

I've seen many times the destructive consequences of "control freaks". I would just look at it as the perfect opportunity to grow membership here, Bob.
Hey Merlin... Just how many Bob Show posts from prior to your 2012/03/25 registration date have you read?
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