I thought you may have meant more from Jim. I've been meaning to write something since I tested the weak-links ourselves... that was over a year ago. I will try. Thanks for the prod
Hey Mark...
What was the purpose of all that weak link testing? What we're you supposed to do with the numbers you got?
130 pound Greenspot has a huge track record so why start looking into reinventing the wheel when we've got a proven system that works?
What did you think about the Zack Marzec fatality? Do you agree that...
IMHO aerotowing is relatively safe compared with foot launching. I would certainly like to make it safer. What we would all like to know is what could we do to make it safer.
We have no agreement that a stronger weaklink would make it safer.
...we have no agreement that a stronger weak link would make it safer?
Was all of your testing done on lighter/safer fishing line because you were finding that Rooney Links were putting too much stress on the gliders and allowing them to pitch up too high and to get too deep into lockouts?
Here's the entirety of your participation in the Zack Marzec discussions:
You can't see anything about him on his FB profile if you aren't his friend. I looked.
I never met him but it was nice to put a face to a name. Very tragic
I'da thunk that a hang glider towing professional such as yourself with enough of a burning interest in the focal points of our safe towing systems to have actually tested them to determine their actual breaking strengths would've had a bit more to say on that one.
Or did your testing reveal that breaking strengths really have no bearing on the safety of a tow and it's really just a matter of individual preferences - like sail colors?
We tried to simulate how the rope is pulled while on aero-tow.
My experience in weak links breaking during lock out is that it does not happen very fast. The line is pulling and pulling and pulling and then it snaps. It takes about two or three seconds. I have induced a lockout purposely and not on purpose several times with the tandem glider and students above me in the harness. It may seem like it's very fast but if you analyze the whole thing from start to finish it takes a few seconds.
So what you're saying is that...
Bill Bryden - 2000/02
Dennis Pagen informed me several years ago about an aerotow lockout that he experienced. One moment he was correcting a bit of alignment with the tug and the next moment he was nearly upside down. He was stunned at the rapidity. I have heard similar stories from two other aerotow pilots.
...while the lockout itself might happen blindingly fast...
The world is a whole lot different in the driver's seat.
It's just so damn easy to sit back at the keyboard and explain theoretical situations and reactions.
Actually doing it, well that's just a whole other thing.
One of the most interesting parts of doing "Lockout training" with people is watching reality hit them square in the face.
All their wonderful theories get blown right out the window... "DAMN! That happens FAST!"... probably the #1 reaction.
I keep thinking... that just surprised them. Like really surprised them.
Not just newbies btw... the near universal reaction is "Damn that happens fast!" (Because... it does!)
Yet, so many preach that *they* will of course do the "right thing" in the time of pressure... yet so many are surprised... aka, their theories were off... their mental image of how it would be and how they would react were wrong... yet... they would risk their lives on these incorrect theories?
It all sounds so good... when you're sitting on the couch.
Everyone's natural instinct on tow is to fight.
You're wrestling that F'er and you will win! You have to have spirit boy! Stay on the ball!
Well damn if that just ain't 100% contrary to hitting that release isn't it?
Have a think about this one as well... if you lock out... if you get to the point where you've lost authority over your glider... you're betting on the fact that you're 100% on your game? You're in that situation because you probably weren't 100% on it... yet, you're going to bet your life that your reaction will be correct? REALLY?
Better you than me.
But, by all means... please continue.
I thought we'd already solved the world's problems... but apparently not.
Do let me know when you've got all this sorted.
Thanks
...the weak link blow doesn't. So a lockout would tend to look something like this:
Yeah, that's pretty consistent with my experience. About two or three seconds between when things go to hell and the Rooney Link blows.
And two or three seconds is plenty of time to blow a release - assuming that you're one of the 0.3 percent of towers who fly with blowable releases - and beat the Rooney Link.
But if you're low and you lock out - whether you beat the Rooney Link, lose an extra second while the Rooney Link is getting what it needs to blow, or lose an extra two thirds of a second on top of that for a two G weak link to blow - you're probably fucked. Whatever happens or doesn't it's probably not going to make any difference.
We agree so far? Good.
So our only good survival strategy is not to get into a low level lockout.
And we seem to be pretty good at doing that because non pilot induced low level lockouts are extremely rare - they're almost always preventable by monitoring for thermals and dust devils.
And we note that when low level lockouts DO occur they're:
- virtually always happening to gliders:
-- "protected" by Rooney Links
-- "equipped" with releases that stink on ice
- seldom survivable (although Roy Messing did manage to cling to life for four days following his impact)
We still in agreement? Good.
So wouldn't it make sense to use a weak link a bit stronger than Bryan Bowker's or Zack Marzec's Rooney Link? Hard to imagine worse outcomes for either flight so I don't think we have all that much to lose.
I noticed that the test strengths of the line for the weak links you tested and found suitable were:
130 - 160 - 200 - 205 - 250 - 300
That's an average of 208 pounds or 60 percent over a Rooney Link - the low figure in the spread.
And the weak link line you've decided is appropriate for you is 200 pounds - is 54 percent over Rooney.
The line range you selected surprised me a bit for a couple of reasons...
- This shit was worked out by the time Jim Keen-Intellect Rooney arrived through...
It was already worked out by the time I arrived.
The reason it sticks?
Trail and error.
...trail and error. And whenever someone comes along with the "new" idea of a stronger weak link...
Every now and then someone comes along with the "new" idea of a stronger weaklink. Eventually, they scare themselves with it and wind up back with one that has a very proven track record. I mean really... no exaggeration... hundreds of thousands of tows.
Say what you will, but if you want to argue with *that* much history, well, you better have one hell of an argument... which you don't.
It amuses me how many people want to be test pilots.
It amuses me even more that people...
A) Don't realize that "test pilot" is exactly what they're signing up for and B) actually testing something is a far more involved process than "I think I just try out my theory and see what happens".
Allow me to repeat... hundreds of thousands of tows.
Sure, there's other stuff out there too. Some of it even has a number of tows behind it... but hundreds of thousands is a very large number.
That's not "religion" my friend.
The shit works. It works in reality and it works consistently. It's not perfect, but Joe-Blow's pet theories have a very high bar to reach before they are given credence.
...he eventually scares himself with it and winds up back with one that has a very proven track record - I mean really... no exaggeration... hundreds of thousands of tows. Allow me to repeat... hundreds of thousands of tows.
- Jim Keen-Intellect Rooney has been a strong and uncompromising stalwart of...
Nonsense.
It's completely about convenience.
People like to argue about it and in their arguments, they dig up rationalizations of it not being about convenience, but sorry... it very much is about convenience.
Take if from the other angle... if it were about safety... if you are truly concerned about your safety... why are you towing? Why are the people that are arguing about weaklinks towing?
The answer of course is that it's not actually about "safety".
Jim Rooney - 2013/03/05 21:40:02 UTC
You want MORE.
I want you to have less.
This is the fundamental disagreement.
You're afraid of breaking off with a high AOA? Good... tow with a WEAKER weaklink... you won't be able to achieve a high AOA. Problem solved.
...safety over convenience.
So what's going on here?
Your range is 130 to 300. 215 in the middle, 40 percent to the extremes.
What I would've expected was something more along the lines of 130 - which was derived through trail and error - in the middle with a comparable low and high of 80 and 180. But instead we've shifted the middle up 65 percent.
What really concerns me is that you're caving to the blathering and lunacy of a bunch of Tad Clones and...
You know, after all this discussion I'm now convinced that it is a very good idea to treat the weaklink as a release, that that is exactly what we do when we have a weaklink on one side of a pro tow bridle. That that is exactly what has happened to me in a number of situations and that the whole business about a weaklink only for the glider not breaking isn't really the case nor a good idea for hang gliding.
I'm happy to have a relatively weak weaklink, and have never had a serious problem with the Greenspot 130, just an inconvenience now and then.
...severely compromising the safety of pilots at BOTH ends of the string...
See, you don't get to hook up to my plane with whatever you please. Not only am I on the other end of that rope... and you have zero say in my safety margins... I have no desire what so ever to have a pilot smashing himself into the earth on my watch. So yeah, if you show up with some non-standard gear, I won't be towing you. Love it or leave it. I don't care.
...solely to spare a few selfish, inconsiderate, reckless individuals a little bit of inconvenience every now and then.
It's good to have more data points, but weak link tests should be conducted with the weak links installed on the same materials used in flight (i.e., a bridle, not a quick link). As far as I can recall, every weak link break I've had occurred at the bridle.
I found it interesting that Mark is using four strands of 160 on the tug. From what I've read (such as this...
Furthermore the mast extension, which is part of the tow system, is designed to break away in the event of excessive inline or lateral loads. The force required to cause a breakaway of the mast is roughly equivalent to the force required to break the double weaklink used on the tail bridle. More simply put, the mast of the DF would break away long before any structural damage to the aircraft would occur.
That's why we use 3strand at the tug's end. Using 4 strand can rip things off (it's happened).
I'd expect the tow mast to break before a weak link of that strength.
I have a feeling they've finally done the math and found out that it's a lot more expensive and more of a hassle to kill a tandem aerotow instructor than to snap one of those damnable tow mast breakaways.
Davis Straub - 2013/07/04 13:47:57 UTC
His tug's weaklink is 330 pounds (see chart above) also on half the load...
Due to the large bridle apex angle at the tug, the tug weak link will see more than half the towline tension (15% more at 60 degrees).
We've FINALLY GOT these sonsabitches. They're totally imploding and they don't have any options not to.
Gonna be interesting when USHGA and the flight parks continue to sell the excellent book, Towing Aloft, by Dennis Pagen and Bill Bryden and students and other readers find that much of the crap between the covers bears no semblence whatsoever to what they're seeing on the flight line.
Mark Knight and Jim Rooney put the loops through the wringer
...Jim Rooney who put the loops through the wringer it was only Mark Knight who had anything to say about:
- how:
-- he was using the test results to select a weak link for his own glider
-- the:
--- testing was conducted
--- weak link responds to loading and reloading
- the:
-- information from Stuart Caruk
-- significance of the knots used
- wear issues in normal use
No offense, dude, but I was REALLY hoping to hear a few comments from your colleague on this one. After all...
Jim, as I am starting to play with Elektra Tow (ET) at Quest Air (the battery powered "scooter" tow system you and Adam got me jazzed up about up at Highland) I've watched this thread closely. We all can learn.
Enjoy your posts, as always, and find your comments solid, based on hundreds of hours / tows of experience and backed up by a keen intellect/knowledge of the issues when it comes to most things in general and hang gliding AT/Towing in particular. Wanted to go on record in case anyone reading wanted to know one persons comments they should give weight to.
...Jim's the one:
- with the:
-- history of enjoyable posts and solid comments
-- keen intellect
-- knowledge of the issues when it comes to most things in general and hang gliding aerotowing in particular
- whose comments we should give the most weight
And I've never known Jim to shy away from a discussion involving weak links - at least until...
You've repeatedly assigned sentiments to me I never expressed, ignored my questions, and asked me questions I've already answered. I'm beginning to wonder if you're actually reading what I'm writing.
...dealing with what's actually being said by people with better than single digit IQs who don't have their noses stuck up his butt starts getting uncomfortable, difficult, embarrassing, humiliating.
For some reason that I can't fully comprehend there was a lot of discussion about weak links in the wake of the Zack Marzec unavoidable invisible dust devil fatality at Quest a bit over five months ago. And, before Davis was forced to lock down all the discussions to preserve the civility for which his forum is so respected, Jim Keen-Intellect Rooney had posted 43 times. And Mark Run-Of-The-Mill Knight had only posted 0 times. That's a ratio of over fifteen (maybe as much as twenty) to one.
So what's the deal here? I can only think that Jim is allowing you to take the lead in this to give the experience you'd need to fill some small fraction of his shoes should a tragedy like him being killed by an unavoidable invisible dust devil befall the world hang gliding community.
Damien Gates (Tex) - 2013/07/05 12:29:18 UTC
Brisbane
Love these tests, great value!
- Well, they would be if the tests were conducted with the weak link installed on something along the lines of a bridle - instead of a quick link. As it is about all we can do is look at the relative values and extrapolate from a proper test on one of the lines.
- Yeah, great value. It only took the Flight Park Mafia a little over two decades of forced one-size-fits-all 130 pound Greenspot hell to do something like this.
- What value?
Dr. Trisa Tilletti - 2012/06
We could get into details of lab testing weak links and bridles, but this article is already getting long. That would be a good topic for an article in the future. Besides, with our backgrounds in formal research, you and I both know that lab tests may produce results with good internal validity, but are often weak in regard to external validity--meaning lab conditions cannot completely include all the factors and variability that exists in the big, real world.
With our backgrounds in formal research, you and I both know that lab tests may produce results with good internal validity, but are often weak in regard to external validity - meaning lab conditions cannot completely include all the factors and variability that exist in the big, real world.
I do want to highlight the fact that a weak link should never be associated (even indirectly) with saving you from lock out... It doesn't.
Oh right... you're preaching the sermon of the "purpose of a weaklink". Too bad reality is not so black and white.
What it does is possibly save your glider from failure because of the lockout you are in...
No. It doesn't POSSIBLY save your glider from failure because of the lockout. It DOES save your glider from failure because of the lockout - although it doesn't save your glider (or you) from failure because of hitting the runway during or after the lockout. A two G weak link WILL prevent structural failure of ANY certified/airworthy glider. You will not be able to break it up on tow.
OR getting dragged along the ground behind a tow vehicle.
Bullshit. You can specify a G rating - two, let's call it - that WILL prevent the glider from being broken up on tow. But until you can specify a G rating that'll:
- prevent a glider from being dragged
- limit the:
-- distance a glider can be dragged
-- degree to which the pilot's neck can be broken before the drag is terminated
DO NOT START DOWN THIS ROAD. If you wanna have a combination of pilot, driver, front and back end releases that both can't get a glider airborne and can't instantly abort a blown launch then - tough shit - you're gonna get a glider dragged and maybe the bozo on it killed.
DO NOT dumb down the weak link to try to minimize the consequences of this incompetent crap and increase the likelihood of somebody being killed when everything is being done right.
I realise these particular tests are directed to aerotow but it may also be applied to ground tow.
Yeah... If the purpose of a weak is to save your glider from FAILURE during a lockout it doesn't matter in which direction the string is pointed or what's on the other end of it.
You can enter and remain in a lock out without ever exceeding the strength of your weak link (1g).
Bullshit. If the purpose of the weak link is to increase the safety of the towing operation...
The "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.
...how's it gonna do that if it doesn't break? And we've all known since the advent of modern towing that...
Donnell Hewett - 1985/08
The system must include a weak link which will infallibly and automatically release the glider from tow whenever the tow line tension exceeds the limit for safe operation.
...a one G weak link will infallibly and automatically release the glider from tow whenever the tow line tension exceeds the limit for safe operation. And tell me how the tow line tension necessary to lock a glider out hasn't exceeded the limit for safe operation.
Do your homework, dude.
In aerotow it is not really the lockout breaking the weak link - rather the separation of the tow vehicle and glider increasing forces. That is the result of the lockout not the lockout itself per se.
We have no agreement that a stronger weaklink would make it safer.
There's a definite schism between the people who understand that the purpose of a weak link...
Tost Flugzeuggerätebau
Weak links protect your aircraft against overloading.
...protect your aircraft against overloading and the stupid pin bending pigfuckers who control this sport and want to use and sell it as a magic piece of fishing line that can out-think the pilot and make and execute all the proper decisions for him.
...at the expense of the inconvenience of a little lost airtime and a relight.
We definitely want it to break if you come off the cart and smack the ground.
It depends a lot on...
...which motherfucker is on the cart. And in your case I definitely wanted it to break because if it had held and dragged the glider it wouldn't have done a dead stop powerwhack and there'd have been virtually no hope whatsoever of you breaking your fucking neck slamming into it.
We don't want it to break too easily from just turbulence.
- But "WE" are totally cool with it breaking too easily...
Zack hit the lift a few seconds after I did. He was high and to the right of the tug and was out of my mirror when the weak ling broke. The load on the tug was not excessive as with a lockout, but I was not surprised when the weak link broke. I was still in the thermal when I caught sight of Zack again. I did not see the entry to the tumble, but I did see two revolutions of a forward tumble before kicking the tug around to land. The thermal was still active in the area that I had just launched from so I did a go round and landed on a runway 90 degrees cross to the direction we were towing in.
...when a glider is standing on its tail in a thermal blast.
- How come in the span of a third of a century of listening to you stupid pigfuckers who want the weak link to break as early as possible in a lockout or blown launch but don't want it breaking too easily from just turbulence specify a towline tension limit or G rating that hits that sweet spot?
...and your safety/life is entirely dependent upon whether or not you happen to have enough altitude to recover or you agree with his above post.
Everybody...
Note Rooney's CONSPICUOUS absence from this discussion. He's logged on and lurking but there's obviously a gag order on him.
---
Edit - 2013/07/05 16:10:30 UTC
Nah, as of 2013/07/05 15:48:58 UTC he's in there. But this'll work even better for us.
I do want to highlight the fact that a weak link should never be associated (even indirectly) with saving you from lock out... It doesn't.
I personally have in the distant past in Australia been saved repeatedly by weak links from a lockout (or during lockouts or during what appeared to be lockouts or during increased forces due to being out of whack behind a tug) by my weaklink breaking.
Your weak link, of course, being the sacred loop of 130 pound Greenspot and you were always at the precise altitude necessary for recovery with that standard. If the weak link had been ten pounds heavier you'd have needed ten feet more than you had and hang gliding around the world would've been reeling from the shock of such an untimely and tragic loss of such a valuable resource and all around wonderful human being.
Bullshit. Your lockouts were all high and if you'd been flying a two G weak link you wouldn't have noticed the difference. If you'd been low you'd have been dead and hang gliding would've had to dredge up and inflate the ego of some other stupid despicable asshole to take your place.
But I was referring to others who have disagreed with the above quoted statement, not to my own experience.
The dregs you and your asshole buddies have all brainwashed.
Damien Gates - 2013/07/05 13:14:30 UTC
Then they are wrong. My original point was also not to conflate the 'result' of the lockout with a lockout. I concede it may be semantics but believe it is important to frame the discussion correctly at all times...
On The Davis Show? Good freakin' luck.
...because of the...
...Hewett based...
...myth...
Lie.
...that a weaklink protects you from lockouts; it doesn't or you would never lock out.
For whomever asked about the function of a weak link, it is to release the glider and plane from each other when the tow forces become greater than desirable -- whether that is due to a lockout or a malfunction of equipment or whatever. This can save a glider, a tow pilot, or more often, a hang glider pilot who does not get off of tow when he or she gets too far out of whack.
...get too far out of whack.
It protects you from the result (some of them) of a lockout.
The simple fact is a tow force of less than 1g applied at a particular vector (via the tow line when you get off course and banked) is sufficient to overpower the ability of the pilot (forces they can apply to the wing) to overcome a lockout.
Even if you can bench press three hundred pounds?
As I stated: the weaklink did NOT save you from a lock out, that had already occurred, and was continuing. The weaklink broke because the lockout caused your glider to increase separation from the tow vehicle as you could not overcome the forces causing the lockout.
This separation would also occur if you get real high and continue to do so, perhaps the tug drops as well... Weaklink breaks... But you are not locked out, or when hitting the ground out of a cart... No lockout.
So I don't give much credence to something that someone doesn't agree with about what we do for some theoretical reason.
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.
As my friend likes to say... "Sure, it works in reality... but does it work in theory?"
Hahahahhaa... I like that one a lot
I am not saying the weaklink has not saved you from the predicaments you give as examples. They obviously did.
And you think by keeping Davis's ass alive they...
Pilots must use weaklinks provided by the meet organizers and in a manner approved by the meet organizers. All weaklinks will be checked and use of inappropriate weaklinks will require the pilot to go to the end of the launch line to change the weaklink.
Weaklinks will consist of a single loop of Cortland 130 lb Greenspot braided Dacron Tolling line and should be placed at one end of a shoulder bridle.
Ya wanna know the one weak link in the history of hang gliding that did the most to increase the safety of the towing operation - as well as towing operations the world over?
When that one very clearly provided protection from excessive angles of attack, high bank turns, and the like for that form of towing it scared people shitless enough to start questioning the wisdom of using a weak link which will very clearly provide protection from excessive angles of attack, high bank turns, and the like for that form of towing.
What I am trying to do is define the terms under which we correctly describe the maladies of towing.
Unfortunately, he's stumbled onto some of Tad's old rantings and got suckered in. So most of this was just the same old story of debunking Tad's lunacy... again .
See, the thing is... "we", the people that work at and run aerotow parks, have a long track record.
This stuff isn't new, and has been slowly refined over decades.
We have done quite literally hundreds of thousands of tows.
We know what we're doing.
To reinforce my point: for static line ground towing (car towing) you can lock out from altitude all the way to the ground and NEVER exceed a tow force of 1g (as we define it for weaklink strength). When I get more time (and off the iPad) I will reproduce the vector diagrams from a reliable (I believe) source.
Jim Rooney - 2011/08/25 21:40:25 UTC
Sure "there's always room for improvement", but you have to realize the depth of experience you're dealing with here.
There isn't going to be some "oh gee, why didn't I think of that?" moment. The obvious answers have already been explored... at length.
Anyway...
Weaklink material... exactly what Davis said.
It's no mystery.
It's only a mystery why people choose to reinvent the wheel when we've got a proven system that works.
I don't know if there is a disagreement or not given the way that you put things. We'll see.
Yeah Davis, keep watching to see which way the wind's blowing and stay "open minded" so you'll always have an out and quietly step up onto whatever bandwagon happens to be the most popular this month.
John Hesch - 2013/07/05 13:44:37 UTC
Zack C - 2013/07/05 04:00:41 UTC
It's good to have more data points, but weak link tests should be conducted with the weak links installed on the same materials used in flight (i.e., a bridle, not a quick link).
I did some weak link testing ten years ago to satisfy my own curiosity, since it seemed that everyone had their "special" string that was supposed to break at the "right" strength.
Yeah. And they're always very careful to not assign a consistent value to that special string so they can alter it a hundred pounds one way or the other to support whatever point they're trying to make at any given moment.
I was looking for consistency...
Consistency to support what objective?
...at the time and used a carabiner and quick-link...
Then you weren't really getting any consistency that would be of any value on the glider and in the air. (Not that consistency in weak link strengths is much of a big fucking deal the way everybody is always telling people and assuming - if you pick a good target and get within a hundred pounds of towline tension you'll be in pretty good shape.)
...similar to Jim's setup.
That WAS NOT *JIM'S* setup. That motherfucker never set up anything more sophisticated than a rope over a tree limb in his miserable existence.
It would be good to see the results of a test-repeat, using a bridle and barrel-release rather than hardware that is of a larger diameter.
The carabiner didn't make any difference. These things ALWAYS blow at the point at which one of the two strands exits the bridle. The bridle material and diameter, however, can have a MAJOR influence on the results.
I realize that the link usually breaks at the knot, but it would put that question-mark to rest.
It breaks at A knot. The trouble is that all these knot hider quacks fail to consider the (Double) Lark's Head by which the weak link is installed on the bridle as a knot.
Mike Lake - 2013/07/05 13:50:12 UTC
Damien Gates - 2013/07/05 13:14:30 UTC
Then they are wrong...
An excellent post. Thank you.
Two or three eternities ago I thought the upper ranks of this sport were surely packed with intelligent honest people with whom one could have rational conversations and reach rational conclusions and get problems fixed and stuff into - and out of - the air. Now I know that it's all packed with scum like Davis, Rooney, Jack, Bob, Peter, Trisa, Bo, Matt, Dennis...
Davis Straub - 2013/07/05 14:12:25 UTC
Hmmm?!
Has this been a semantic argument all along?
A number of times over the last twenty nine years I have been out of whack behind a tug and my weaklink has broken, which I greatly appreciated. I didn't feel that my glider was in danger of being over stressed. I would have pulled the barrel release but the weaklink broke before I could react.
Davis, there is little that would make me happier than to see you keep:
- towing
- getting out of whack behind tugs
- breaking Davis Links
- appreciating breaking Davis Links
- not feeling that your glider was in danger of being overstressed
- flying with barrel releases you're unable to blow before your Davis Links pop
