Weaklinks
Why is there a difference? Do aero and surface towed gliders break at different loads?Peter Birren - 2005/02/08 19:22:49 UTC
I wrote mostly of "general" weaklink use in towing, not aerotow-specific though I knew that's what you were asking specifically about.
And if you use a payout winch then neither of those issues matters.So, yes, overtowing is when either the driver mistakenly goes too fast OR does not slow down when weather conspires to create a sudden increase in tension.
- How much slower do you think the tug can go without stalling?You're correct that it isn't a major problem with AT, but the potential exists for what can appear to be an overtow - say if the tug slows, towline goes slack, glider is mushed, tug regains speed... the quick application of force to the glider could approach "severe".
- If the towline goes really slack the glider's really asking for it by sticking around.
- Do you wanna put a number on "severe"? What's "severe" for a glider certified to six Gs or over?
- So he was doing better BEFORE his weak link blew than AFTER?This scenario is IMO what happened with Mike Haas at Cushing Field last year. His weaklink broke at a low altitude and he rolled off the stall.
- Just how "severe" do you think the quick application of force can be to someone using 130 pound Greenspot and flying two point?
Sure they should, Peter. Everybody keeps telling us they SHOULD - or WILL.They should work for lockouts...
The "pilot" tends to do that a whole lot more effectively if he doesn't hafta let go of the basetube while he's fighting the roll....but due to the nature of the beast won't work until the tension point is hit, meaning the pilot is in full lockout and the glider is producing more than the weaklink strength in lifting power. Prior to getting to the point of breaking the weaklink, the pilot should have released.
Of course you'll also eliminate the glider if it's standing on its tail and going up like a rocket - like it was for Eric Aasletten and Dennis Pagen. But that's OK 'cause USHGA stopped recognizing that category of tow fatality thirty years ago.Are you looking for a sure cure for lockouts? Simple: add a pitch limiting line from the glider's nose to the Apex release (closed bridle with release between bridle and towline). Each roll/yaw that takes a pilot away from the tow force direction produces a change in pitch between glider and towline. Limit that pitch and you'll eliminate full-blown lockouts.
I got a better idea, Peter. Don't pile it in on launch. And use the weak link to protect the glider from being overloaded - like they do in REAL aviation.While it may seem to be a holdover, there's still that nagging problem of piling in at launch. If this is the only immediate benefit of a weaklink, then it definitely has a place in the bridle/towline system.
Ever think about taking up another hobby? Or at least limiting yourself to brain dead easy platform launches?I've blown aerotow and static line launches...
That's NOT its job, Peter....where the weaklink did its job perfectly each time.
Tost Flugzeuggerätebau
Weak links protect your aircraft against overloading.
It's the job of the pilot and driver to prevent blown launches in the first place and - if that requirement proves too taxing for the people involved in the operation - it's the job of the pilot to use his RELEASE to abort. But of course the way you've got your releases configured...Dynamic Flight - 2005
The purpose of a weak link is solely to prevent the tow force from increasing to a point that the glider can be stressed close to or beyond its structural limits.
...you can only actuate them when you don't really need to.Al Hernandez - 2010
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.
And thus the world is a better place. By the way, Peter... Sometime in the next three and a half years you're gonna pile in an ANOTHER aerotow launch - off a dolly somehow - and your gonna break four ribs and your larynx. Are ya SURE ya don't wanna take up another hobby? Or maybe dumb down your weak link a little more?I'm happy to say that after each of these I walked away and was able to use the glider again (after some repairs).
- Whereas a straight pin barrel release would've been completely useless in those circumstances.I also have gotten in near-lockout situations, recognized what was developing, and released before it got any worse. (But then I'm using a release that is totally independent of the tow force :-)
- If you were using a one G weak link the tow force woulda been 275 pounds max. That would require a five pound pull for a keel mounted barrel. BFD. And you probably weren't a whole helluva lot over normal tow tension anyway.
http://groups.yahoo.com/group/skysailingtowing/message/6726
Weaklinks
AND I get to keep BOTH hands on the basetube - so I get to skip the unplanned semi-loop thing.Peter Birren - 2008/10/27 23:41:49 UTC
So you pull whatever release you have but the one hand still on the basetube isn't enough to hold the nose down and you pop up and over into an unplanned semi-loop.
How did you calculate that one G or less would blow you loose in the course of a blown launch and one and a half wouldn't. Oh, right - you said "should".One G or less should do it and is easy to figure out.
Whereas if you use a 0.8 G weak link you'll be WELL protected from full-blown lockouts.Material is readily available and presently being used. More than this and it becomes a "strong link" that may not break during a nose-in, and it may not break when that full-blown lockout is achieved.
- And then you'll just fly away without a care in the world.The weaklink will not prevent a lockout from happening, that's certain... and if you want one that will work quickly in a lockout, then it'll be too light for day-to-day towing in thermal conditions. If the pilot can recognize what's going on, it's possible to push out quickly and break the link... _IF_ the link is sized right.
- Like Mike Haas would have if he had pushed out quickly and broken his right sized weak link a little sooner.
- And the reason you wouldn't just continue to fight the lockout and release with both hands on the basetube?
- Oh, right. You can't.British Hang Gliding and Paragliding Association Technical Manual - 2003/04
On tow the Pilot in Command must have his hand actually on the release at all times. 'Near' the release is not close enough! When you have two hands completely full of locked-out glider, taking one off to go looking for the release guarantees that your situation is going to get worse before it gets better.
Actually, Peter, that goes counter to ANY thinking.This is not an intuitive move and goes counter to panic thinking.
But why wait until fully locked out? Why not release before it gets that far?
Does that answer your idiot question?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.
Do you ACTUALLY believe that's what's going on in the heads of people experiencing dangerous low level lockouts?Is the 3-5 cent weaklink string too expensive? Is this one launch so critical that the pilot is willing to stake his life on it?
http://www.ushawks.org/forum/viewtopic.php?f=17&t=649
missing release
Still not taking your meds?Peter Birren - 2011/08/29 18:59:08 UTC
Still not taking your meds?
Works to WHAT, Peter? Blow when he piles it in at launch? Blow before a full-blown lockout is achieved?http://groups.yahoo.com/group/skysailingtowing/message/4589
WeaklinksThen I'd suspect the material or the knot used to tie it. You fly a rigid with aerodynamic control, which is faster than a flex wing, so I imagine you'd be doing OK. You've certainly been towing for quite some time and know what to expect. Do you rely on weaklinks at the site or have you found what works for you (tested) and carry your own?Davis Straub - 2005/02/08 17:08:45 UTC
I've had problems when it is quite a bit more than a nuisance and I've been managing the tow force just fine, thank you.
ANYBODY who doesn't understand:Other pilots with plenty of towing experience may have grown complacent or are practicing poor form.
is a complacent idiot and practicing poor form.Manned Kiting
The Basic Handbook of Tow Launched Hang Gliding
Daniel F. Poynter
1974
"Never take your hands off the bar." - Tom Peghiny
"The greatest dangers are a rope break or a premature release." - Richard Johnson
http://ozreport.com/12.081You may be doing just fine, but that may only be fine in your mind. I'm not casting aspersions or accusing you of poor form, but stranger things have happened. If you're breaking weaklinks at nuisance times, something is wrong, either the weaklink, your setup or your towing style.
Weaklinks - the HGFA rules
Maybe it's the weak link - and all the idiot "theories" about its functions.Davis Straub - 2008/04/22 14:47:00 UTC
From section 3.4 of the 1999 Hang Gliding Federation of Australia Towing Manual:Here is the requirement from the 2007 Worlds local rules (which I wrote) for weaklinks:Recommended breaking load of a weak link is 1g. - i.e. the combined weight of pilot, harness and glider (dependent on pilot weight - usually approximately 90 to 100 kg for solo operations; or approximately 175 kg for tandem operations).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.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.
Nobody - outside of your your backwards little cult - uses closed bridles.Where is your weaklink? Are you using an opening or closed pro-tow?
Yeah, Peter. That's what it produces when nothing's going on. Unfortunately, on any day worth getting out of bed for, there's always something going on.What are your expected tow forces? (aerotow produces 100-150 pounds)
How do you handle turbulence - smoothly or with quick inputs?
130 pound Greenspotters DON'T handle turbulence.Towing Aloft - 1998/01
In the case of lockouts or turbulence, the weak link breaks as designed and should not be increased in strength.
http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?
Jim Rooney - 2011/08/28 19:39:17 UTC
The frustration of a weaklink break is just that, frustration.
And it can be very frustrating for sure. Especially on a good day, which they tend to be. It seems to be a Murphy favourite. You'll be in a long tug line on a stellar day just itching to fly. The stars are all lining up when *bam*, out of nowhere your trip to happy XC land goes up in a flash. Now you've got to hike it all the way back to the back of the line and wait as the "perfect" window drifts on by.
I get it.
It can be a pisser.
Though whole purpose of 130 pound Greenspot is to make sure you can't get up more than two hours after sunrise or before sunset. That way nobody gets hurt.Davis Straub - 2011/08/26 14:04:52 UTC
We had six weaklink breaks in a row at Zapata this year.
Idiot.Do you like the idea of getting dragged in a blown launch?
What the fuck does that mean? A lockout - by definition - is something that can't be handled.How far into a lockout can you handle?
But not the glider's flying weight, as per hang gliding - or the glider's maximum certified flying weight, like in REAL aviation.The Reel Pilots tested many different strings before settling on 130 or 150 pound test braided dacron kite string depending on pilot body weight.
Well then, y'all should be just fine in a worst case scenario when...These translate to 235 and 260 pound breaking strengths in 4-strand setups, less than 1 G, and we haven't had an inadvertant weaklink break in a very long time, either static line or aerotowing. Any lighter and the string will break when encountering a strong thermal. At least that's been our experience.
...your life is dependent upon sustained thrust."The greatest dangers are a rope break or a premature release." - Richard Johnson
http://groups.yahoo.com/group/TTTFlymail/message/11545What is the big issue? Re-launching? Oh, the wasted time! Oh, the hassle! Oh, the embarrassment! These are sure preferrable to Oh Shit!
Cart stuck incidents
http://ozreport.com/forum/viewtopic.php?t=865Keith 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.
Tandem pilot and passenger death
And, by the way, Peter...Mike Van Kuiken - 2005/10/13 19:47:26 UTC
The weak link broke from the tow plane side. The towline was found underneath the wreck, and attached to the glider by the weaklink. The glider basically fell on the towline.
- Launching is time consuming, expensive, and dangerous.
- Relaunching is twice as time consuming, expensive, and dangerous.
Davis Straub - 2005/02/08 17:08:45 UTC
At the moment most competition pilots use "STRONG LINKS."
Jim Rooney - 2007/07/22 22:30:28 UTC
I've heard it a million times before from comp pilots insisting on towing with even doubled up weaklinks (some want no weaklink). I tell them the same thing I'm telling you... suck it up.
http://ozreport.com/9.032And Robin paid the price... is it worth it?
The Worlds - weaklinks
I'll do the math for ya, Peter. Rohan's saying that with a 176 pound weak link - about sixty pounds under your lightest - Robin would still have been screwed.Rohan Holtkamp - 2005/02/07
After viewing video evidence of the entire flight, even a 80kg weaklink would have made little difference. His actual weaklink did test to be stronger than 180kg, but that was not the primary cause of his accident. Release failure was, same as Mike Nooy's accident. A full lockout can be propagated with less than forty kg of tension. Read "Taming the beast" on our website and/or come have a look at the video if you doubt this in any way.
If you try hard enough you can rig a spinnaker shackle to become nonfunctional - just like you can with a Linknife. And, if you've got enough total morons running the operation, you can get in line with either one set to jam.He also paid the price by using the wrong release in the wrong place.
- Peter
(yet another e-mail where I didn't mention the L-word :-)
