The United States Hang Gliding and Paragliding Association, Inc. - 2013/01/23
12. Standard Operating Procedure
10. Towing/Aerotowing Administration
09. Aerotow Pilot Appointment (ATP)
-B. Aerotow Equipment Guidelines
04. The actual strength of the weak link used by the hang glider pilot must be appropriate for the operation and have a breaking strength between 80% and 200% MCOW (max. cert. operating weight) of the glider, in terms of direct towline tension.
What's "DIRECT" towline tension? How does it differ from INDIRECT towline tension?
No sane person has directly routed towline tension to a glider since the early Eighties. Fifty to a hundred percent of the towline tension is ALWAYS routed through the pilot/harness and suspension to the glider with anything that isn't going to the keel at or a bit forward of the hang point.
And when you start deviating from that model just a little bit...
The United States Hang Gliding and Paragliding Association, Inc. - 2013/01/23
12. Standard Operating Procedure
10. Towing/Aerotowing Administration
09. Aerotow Pilot Appointment (ATP)
-B. Aerotow Equipment Guidelines
04. A weak link must be placed at both ends of the tow line. The weak link at the glider end must have a breaking strength that will break before the towline tension exceeds twice the weight of the hang glider pilot and glider combination. The weak link at the tow plane end of the towline should break with a towline tension approximately 100 lbs. greater than the glider end. Weak links must be used in accordance with 12 CFR 91.309(a)(3). The USHPA recommends that a nominal 1G (combined operating weight of the glider and pilot) weak link be used, when placed at one end of a hang glider pilot's V-bridle; or about 1.5-2G if placed at the apex of the tow bridle or directly in-line with the tow rope. The actual strength of the weak link used by the hang glider pilot must be appropriate for the operation and have a breaking strength between 80% and 200% MCOW (max. cert. operating weight) of the glider, in terms of direct towline tension. The weak link used at the tow plane end of the towline must be stronger, but not more than 25% stronger, than the strength of the weak link used at the glider end of the towline.
You state that:
Weak links must be used in accordance with 12 CFR 91.309(a)(3).
And CFR 91.309(a)(3) states that:
A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight.
You also state that:
Dr. Lionel D. Hewitt, professor of physics and developer of the 2-to-1 center-of-mass Skyting bridle for surface towing, is well respected for his knowledge of towing, bridles, and weak links. His position on weak link strength for aerotowing of hang gliders seems to be consistent with ours.
His position on weak link strength for aerotowing of hang gliders seems to be...
The sole purpose and function of this weaklink is to limit the towline tension to a manageable level, i.e. a level such that the pilot can still maintain control of the aircraft in the event that the weaklink breaks.
The appropriate strength of a weaklink depends upon pilot skill. A skillful pilot can maintain control when a stronger weaklink breaks whereas a less skillful pilot cannot. As a general rule, a beginning pilot should limit his towline tension to .5-g and an experienced pilot to 1-g. Only highly experienced pilots qualified to perform aerobatics while on tow should use a 2-g or stronger weaklink while being pulled forward (such as when aerotowing).
The appropriate strength of a weaklink depends upon the type of towing system used. Different strength weaklinks should be used for foot-launched ground towing, platform towing, aerotowing, boat towing, etc. As a general rule, forward pulling systems such as aerotowing, foot-launch ground towing, etc. should use 1-g weaklinks or less. Consistently downward pulling systems such as platform launch can go as high as 2-g's.
Last year, at LMFP I saw an incident in aerotow that resulted in a very significant impact with the ground on the chest and face. Resulted in a jaw broken in several places and IIRC some tears in the shoulder.
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.
Why is the devil always in the fine print, and incidentally in the things people *don't* say.
Yes, go read that incident report.
Please note that the weaklink *saved* her ass. She still piled into the earth despite the weaklink helping her... for the same reason it had to help... lack of towing ability. She sat on the cart, like so many people insist on doing, and took to the air at Mach 5.
That never goes well.
Yet people insist on doing it.
...no aerotowing ability - and total shit for aerotowing instruction
Your weak link comments are dead on. I have been reading the weak link discussion in the Oz Report with quiet amusement. Quiet, because weak links seem to be one of those hot button issues that brings out the argumentative nature of HG pilots and also invokes the "not designed here" mentality and I really did not want to get drawn into a debate. Amusement, because I find it odd that there was so much ink devoted to reinventing the wheel. Collectively I would say that there have been well over a 100,000 tows in the various US flight parks using the same strength weak link with tens of thousands of these tows being in competition. Yes I know some of these have been with strong links but only the best of the best aerotow pilots are doing this.
Steve Kroop is in total lockstep with Jim Rooney...
It always amazes to hear know it all pilots arguing with the professional pilots.
I mean seriously, this is our job.
We do more tows in a day than they do in a month (year for most).
We *might* have an idea of how this stuff works.
They *might* do well to listen.
Not that they will, mind you... cuz they *know*.
I mean seriously... ridgerodent's going to inform me as to what Kroop has to say on this? Seriously? Steve's a good friend of mine. I've worked at Quest with him. We've had this discussion ... IN PERSON. And many other ones that get misunderstood by the general public. It's laughable.
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.
...by US Naval Academy graduate and current USHGA Accident Reporting Committee Chairman Mitch Shipley.
And yes, get behind me with a "strong link" and I will not tow you.
...refuses to tow anybody with anything other than a pre-tied loop of 130 pound Greenspot standard aerotow weak link which blows under a direct load of...
Sorry, yes it's early... Just under... As you've said many times... 130 breaks at100 right?
...100 pounds or for a two point glider 174 pounds towline - 0.58 Gs for a 300 pound glider.
Are you seeing any problems with these FAA regs?
- We've lost the ability to tow beginners on really safe half G weak links.
- If we tow any glider with a max certified operating weight of 218 pounds or up we've gotta Wrap and Tie the 130 pound Greenspot to bring it up from 100 to 260 pounds. And what with Mark Knight and Jim Rooney telling everyone...
The knots do not matter so much for just one tow to how they break or the breaking strengths.
...that the manner of tying the fishing line doesn't have much bearing on the breaking strength and Davis Straub, who's always established the pretied loop of 130 pound Greenspot as the only thing acceptable at USHGA sanctioned competitions, carefully analyzing the discussions 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.
The sailplane guys have been doing this for a long time, and there are many hang glider pilots and quite a few tug pilots who don't understand what the sailplane guys have learned over the years.
Name ONE THING it took the sailplane guys a matter of years to learn (preferably something with more substance to it than Russell Brown's using the Wrap and Tie Method to get a loop of 130 pound Greenspot to blow at 260 pounds).
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.
What we have covered in this article is practical information and knowledge gleaned from the real world of aerotowing, developed over decades and hundreds of thousands of tows by experts in the field. This information has practical external validity. Hopefully, someone will develop methods and technology that work better than what we are using as standard practice today. Like the methods and technology used today, it is unlikely that the new technology will be dictated onto us as a de jure standard. Rather, to become a de facto standard, that new technology will need to be made available in the marketplace, proven in the real world, and then embraced by our sport.
So is that how proper weak links for sailplane models were determined?
When Schempp-Hirth specifies a Tost 4 600 decaNewton weak link for its Nimbus 2C...
I would like to add, however, that at least my reading of accident reports suggest that a fatal glider accident is more likely when the towline fails prematurely. For that reason, I like to stay near the stronger end of the FAR 80 to 200 percent range.
Actually, reading the Pilot's Operating Handbook for several German gliders, I note the weak link for aerotow is specified as an exact figure. For example, the weak link for both aero tow and winch for my Nimbus 2C is specified as 600 KG (1323 Lbs) or a blue Tost weak link. The tolerance is plus or minus ten percent. The US Airworthiness Certificate specifies that the Nimbus 2C is to be flown as specified in the Pilot's Operating Handbook. Considering the possible flying weights, this ranges between 95 and 160 percent which is a narrower range than specified in the FARs.
Makes me wonder if we should be using Tost weak links instead of old bits of rope.
...is it because they had experts take it up for hundreds of thousands of tows over the course of decades to determine that that strength best met their expectation of breaking as early as possible in lockout situations but being strong and reliable enough to avoid frequent breaks from turbulence?
Dr. Trisa Tilletti - 2012/06
One standard weak link design for sailplanes is to just use the tow rope itself as the weak link, as long as it has a breaking strength between 80% and 200% of the MCOW of the glider, per FAR 91.309(a)(3). The de facto standard is to use 1/4", 5/16", or 3/8" hollow braid polypropylene rope, commonly with breaking strengths of about 1000 lbs., 1500 lbs., and 2000 lbs., respectively.
So how do you know what the breaking strengths are?
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.
Weren't they determined under lab conditions which cannot completely include all the factors and variability that exist in the big, real world? Don't you hafta put them up in really turbulent conditions to get useful assessments of their breaking strengths - such as...
The lockout Lauren mentioned was precipitated by my attempt to pull on more VG while on tow. I have done this before but this time the line wouldn't cleat properly and while I was fighting it, I got clobbered and rolled hard right in a split second. There was a very large noise and jerk as the relatively heavy weak link at the tug broke giving me the rope.
..."relatively heavy"?
Dr. Trisa Tilletti - 2012/06
Any of those three rope diameters would be legal for us to use as a weak link for our Blanik, with a MCOW of 1100 lbs., but, practically, we feel that 1500 lbs. is best.
So upon what are your FEELINGS based?
Dr. Trisa Tilletti - 2012/06
You and I have flown sailplanes for almost as long as we have flown hang gliders. We own two sailplanes and have two airplanes that we use for towing full-size sailplanes. In all the time that we have flown and towed sailplanes, we have not experienced or even seen a sailplane weak link break.
Did you fly the thousand, fifteen hundred, and two thousand to the points of not breaking and like the way the fifteen hundred didn't break best? What kinds of glider responses and/or sensations did you experience when the various polypro weights didn't break?
I checked some of the references you gave in your article...
Dr. Trisa Tilletti - 2012/06
Dr. Lionel D. Hewitt, professor of physics and developer of the 2-to-1 center-of-mass Skyting bridle for surface towing, is well respected for his knowledge of towing, bridles, and weak links.
The appropriate strength of a weaklink should always be tested on the ground, not in the air. For example, if a weaklink is tested on the ground to consistently break at 1-g, then you can be certain it will do the same thing in flight.
Dr. Trisa Tilletti - 2012/06
It works out to be a ratio of about 0.575 to 1 for a typical 3-point bridle. This ratio is dependent on the length of the V-bridle and the angle it makes relative to the towline, which is explained in the Pagen/Bryden book Towing Aloft.
Towing Aloft - 1998/01
It is imperative that you make and test your own weak links on a test rig to know at what point they break. You should make and test at least 10 weak links. They will all break at slightly different points, but measure them and find the average. Also compare several of the highest and several of the lowest breaking values to the average. If they differ by more than 10% you do not have a reliable and predictable weak link system. The hazard of having a link breaking at a much higher tensions is obvious.
Safety Tip: The only way to insure safe, consistent weak links is to test each batch of new weak link material with the same equipment (release, rings, bridles, etc) for breaking strength.
Dr. Trisa Tilletti - 2012/06
A third practical, but less common and more expensive, de facto standard for sailplanes is use of a metal TOST weak link. This weak link design is more commonly used in Europe than in the U.S., and is more commonly used for winch towing. The TOST weak link is a small strip of metal precisely fabricated to break at a specific load, within a tolerance of plus/minus 5%.
Like our type-approved equipment, also our weak links are manufactured according to the EASA-approved production methods. Each batch is tested on computerized test equipment and the results are documented. This guarantees consistent high quality and traceability.
How come all the references you cited who refer to the issue take the polar opposite position and state in no uncertain terms that lab testing of weak links is the way and the ONLY way to determine/predict in-flight breaking strengths and is critical to the safety of ANY tow operation?
You couldn't find any OTHER total fucking assholes - even in hang gliding with loads of other scum like Davis, Rooney, Cragin, Bo, Steve Kroop, Paul and Lauren easily available - to support your position that lab testing is really of no practical value?
The WT style of weak link performs very consistently, likely due to the extra weak link loops snugging down onto the bridle and not shifting around, and because the knot used to make it is separated far from the pulling pressures. Basically, it removes the knot from the actual weak link loop that is used, so it behaves much like a continuous loop of line without a knot in it.
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.
No external validity whatsoever. In the big real world that sucker holds very consistently to 260 pounds because the knot used to make it is separated far from the pulling pressures so it behaves much like a continuous loop of line without a knot in it.
But in lab conditions - which cannot completely include all the factors and variability that exist in the big, real world - it blows at slightly half of what it does on tow.
This article was peer-reviewed and approved for publication by the USHPA Towing Committee.
You and your Towing Committee totally NAILED IT! My admiration for y'all would be impossible to express in mere words. Hard to imagine where this sport would be without people like you with backgrounds in formal research and understanding of real world issues. Keep up the great work!
The United States Hang Gliding and Paragliding Association, Inc. - 2012/06
12. Standard Operating Procedure
02. Pilot Proficiency System
12. Hang Gliding Aerotow Ratings
-C. USHPA Aerotow Equipment Guidelines
04. Weak links must be used in accordance with 14 CAR 91.309(a)(3). USHPA recommends that a nominal 1G (combined operating weight of the glider and pilot) weak link be used, when placed at one end of a hang glider pilot's V-bridle; or about 1.5-2G if placed at the apex of the tow bridle or directly in-line with the tow rope. The actual strength of the weak link used by the hang glider pilot must be appropriate for the operation and have a breaking strength between 80% and 200% MCOW (max. cert. operating weight) of the glider, in terms of direct towline tension. The weak link used at the tow plane end of the towline must be stronger, but not more than 25% stronger, than the strength of the weak link used at the glider end of the towline.
Weak links must be used in accordance with 14 CFR 91.309(a)(3).
Well duh! It's been an FAA regulation ever since 2004/07/27 - close to eight years at this point. So what happened in the course of the seven months prior...
The United States Hang Gliding and Paragliding Association, Inc. - 2011/11
12. Standard Operating Procedure
02. Pilot Proficiency System
12. Hang Gliding Aerotow Ratings
-C. USHPA Aerotow Equipment Guidelines
04. A weak link must be placed at both ends of the tow line. The weak link at the glider end must have a breaking strength that will break before the towline tension exceeds twice the weight of the hang glider pilot and glider combination. The weak link at the tow plane end of the towline should break with a towline tension approximately 100lbs. greater than the glider end.
...to motivate you to include that information in the SOPs? Prior to that and ever since Donnell Hewett enlightened everyone in the early Eighties there's never been a minimum requirement for weak link strength - and certainly not a minimum which, for all intents and purposes, is considerably higher than the 1985/07 USHGA/FAA maximum (85 or under percent of flying weight / not to exceed 200 pounds) allowance.
Was the problem that...
Dr. Trisa Tilletti - 2012/06
Dr. Lionel D. Hewitt, professor of physics and developer of the 2-to-1 center-of-mass Skyting bridle for surface towing, is well respected for his knowledge of towing, bridles, and weak links [ref 4]. His position on weak link strength for aerotowing of hang gliders seems to be consistent with ours. He has acknowledged that we especially need to avoid inadvertent weak link breaks while aerotowing, because much of aerotowing takes place over unlandable terrain.
...there were a lot of people going down in unlandable terrain? Funny, I don't recall reading about a lot of such incident reports in the magazine or on the aerotow parks' websites or forums - the Davis, Jack, and Peter Shows and TUGS. Even if there IS such an incident every now and then...
Doc's body wasn't moving and we were shitting our pants until he started talking confused. The first thing I saw was his eye bleeding and swollen the size of an 8 ball. There was sand and dirt inside. Looked like he lost it at first until he could open it a little bit.
...is it really worth beefing up the weak link to take care of them? If we did that...
When I got there her nose was lacerated and her lip was bleeding (yeah, she had a full face helmet) and the dolly's left wheel was missing.
The radiography showed acute multiple fractures around the top and head of the humerus. Her nose didn't break but she may have hairline fractures to the septum. She had a hard time remembering the date, day, names of her kids, number of kids, and other basic things...
The dolly had hit a huge hole and she went left shoulder into the ground at 25+ mph.
Anyone that's flown at the Florida Ridge knows there are some serious craters out there.
...on the Florida Ridge runway.
USHPA recommends that a nominal 1G (combined operating weight of the glider and pilot) weak link be used, when placed at one end of a hang glider pilot's V-bridle; or about 1.5-2G if placed at the apex of the tow bridle or directly in-line with the tow rope.
Recommended breaking load of a weak link is 1g. - i.e. the combined weight of pilot, harness and glider (dependant on pilot weight - usually approximately 90 to 100 kg for solo operations; or approximately. 175 kg for tandem operations).
Are they still recommending one G? Wouldn't that be problematic for our guys at the Worlds? Wouldn't having to shift over from a 1.5 recommendation here to a 1.0 there tend to throw them off their game? I mean, how would YOU like it if you were flying your Blanik and...
Dr. Trisa Tilletti - 2012/06
Any of those three rope diameters would be legal for us to use as a weak link for our Blanik, with a MCOW of 1100 lbs., but, practically, we feel that 1500 lbs. is best.
...somebody suddenly recommended a weak link that, practically, you didn't feel was best?
Has anybody looked at the equipment damage costs we will inevitably incur as a consequence of...
Dr. Trisa Tilletti - 2012/06
There has been a trend lately for some tandem operators to go with about a 400 lb. weak link on both the tandem glider and tug V-bridles, rather than 520 lbs., to help protect the equipment from large stresses. If tandem operators think that, practically, a 520 lb. double loop weak link is too much for a tandem, it is way too much for a solo pilot.
Solo hang glider pilots should not place a 520 lb. double loop weak link on their V-bridle, unless they get specific approval from the tow operator. It could be hard on the equipment and could be illegal if the tug is using a weaker weak link.
I know personally of another incident that occurred this year in a tandem (not at Quest, not with me). A pilot with limited tandem experience took up a tandem passenger behind a tug pilot with limited midday experience. The hang gliding pilot had difficulty controlling the glider's pitch due to bad flying on the tug pilot's part. He should have released earlier, but didn't.
By the time the glider released the tandem had been stressed pretty hard. The tandem pilot safely landed the tandem. Afterwards, while examining the glider to ensure that it had not been overstressed, it fell apart on the ground. Very lucky it was not a double fatality.
The pilot will report this in a timely fashion but it is not my place to reveal details. The weak link did not break.
Being stuck to the plane is not always good.
...being stuck to the plane for the extra half to three quarter Gs USHPA is recommending?
Thought I already answered that one... instead of quoting myself (have a look back if you don't believe me), I'll just reiterate it.
I don't advocate anything.
I use what we use at the flight parks. It's time tested and proven... and works a hell of a lot better than all the other bullshit I've seen out there.
130lb greenspot (greenspun?) cortland fishing line.
In stock at Quest, Highland, Eastern Shore, Kitty Hawk Kites, Florida Ridge, and I'm pretty sure Wallaby, Lookout and Morningside.
Not sure what Tracy up at Cloud Nine uses, but I'll put bets on the same.
I've personally refused to tow a flight park owner over this very issue. I didn't want to clash, but I wasn't towing him. Yup, he wanted to tow with a doubled up weaklink. He eventually towed (behind me) with a single and sorry to disappoint any drama mongers, we're still friends. And lone gun crazy Rooney? Ten other tow pilots turned him down that day for the same reason.
In the old threads there was a lot of info from a guy named Tad. Tad had a very strong opinion on weak link strength and it was a lot higher than most folks care for. I'd focus carefully on what folks who tow a lot have to say. Or Jim Rooney who is an excellent tug pilot. I tow with the "park provided" weak links. I think they are 130 pound Greenspot.
- Was there some kind of vote or poll on this? Or was it just three or four USHPA shits in conjunction with the lawyer...
Steve Davy - 2012/05/31 11:17:01 UTC
Take look at the June issue of the USHPA magazine. You'll find thirteen poorly written and confusing pages of weak link mumbo jumbo written by Drs. Lisa Colletti and Tracy Tillman.
Also included in the article- five photos, four bar graphs and eighteen references.
I suspect the article is an attempt to provide flight park operators and USHPA with justification and ammunition in a legal case filed against them.
...trying to preempt a civil suit or criminal negligence charge by deluding the public into believing that the aerotow industry has been operating in compliance with FAA aerotowing regulations ever since they first went into effect?
I don't need to tell you...
Dr. Trisa Tilletti - 2012/06
Unlike the FAA's relatively clear-cut legal rules, the practical aspects of weak link technology and application are not so clear-cut. For some people, talking about weak links is more like talking about religion, politics, or global warming--they can get very emotional about it and have difficulty discussing it logically, rationally, or with civility.
PS... you got to be careful mentioning weak link strengths around the forum, it can spark a civil war
Brendon McKenna - 2009/06/26 13:20:41 UTC
Hey Martin,
I have seen the odd discussion about weaklinks here on this list... LOL We definitely don't want to go there!
...the weak link issue can be a pretty hot topic - especially when the battle lines always split between Dragonflyers / Aussie Methodists / Westboro Baptists / global warming deniers / Teabaggers on the one hand and people with rudimentary or better grasps on reality on the other.
And what's the rationale for this 1.5 to 2.0 G USHPA recommendation?
What we have covered in this article is practical information and knowledge gleaned from the real world of aerotowing, developed over decades and hundreds of thousands of tows by experts in the field.
Did you compare hundreds of thousands of tows at 1.5 to 2.0 Gs by experts in the field to hundreds of thousands of tows at whatever the fuck a Pre-Tied loop of 130 pound Greenspot gives whatever the fuck glider it's tied to by experts in the field and look at how well expectations of breaking as early as possible in lockout situations but being strong and reliable enough to avoid frequent breaks from turbulence were met? Is there someplace I can take a look at that data myself? If we now have good data on this weak link performance can we upgrade our expectations to statements of facts?
We're using the same weak link for all solo gliders - as we always have. That means that different weight gliders will be flying at different G ratings. Wouldn't it be a fairly simple matter to find out what weight gliders are having the safest and most successful tows and then optimize all gliders for whatever G rating that turns out to be? Has anyone done that?
Based on everybody's sailplane experience it seems that you have the best success with weak links that never break so is there some reason we wouldn't do well with two, three, four G weak links?
Sounds to me like there's not really much in the way of testing involved anyway. Whenever an operation wants to implement a different piece of fishing line...
Morningside decided that they were happy with 200lb weaklink. They changed their tug's link and they don't just pass the stuff out either. If you'd like to know more about it... go ask them.
Dr. Trisa Tilletti - 2012/06
Any of those three rope diameters would be legal for us to use as a weak link for our Blanik, with a MCOW of 1100 lbs., but, practically, we feel that 1500 lbs. is best.
...they just decide they're happy with it.
Is this recommendation supposed to be related to safety somehow? I didn't get the impression from your article that aerotowing hang gliders was particularly dangerous in any event. A heavy weak can be expected to blow a little later in a lockout situation and a light weak link will break a little more frequently from turbulence. Either way - big fucking deal. It's really just a matter of convenience.
Lockouts can be totally eliminated by using tandem instruction to train students to stay inside the Cone of Safety. And even if you're stupid enough to get into a lockout...
My whole point is that people tend to "hang on" too long trying to save things, rather than recognize a bad situation and release (one way or another), go back, and reset.
I'm not saying wait until you're so locked out you're passed 90 degrees bank and then pitch up to break the weaklink and do half a loop into the ground. I'm saying get the hell off way before that.
If properly used, there is a minimum of three ways to release from the towline. Do not depend on any of these ways by themselves and fly with a back up. The first release is the primary release which under certain situations may fail, second, is the secondary release that works most of the time, if all is set up correctly, and third, the weak link which will break under the right load. You should also fly with a hook knife that will allow you to cut the line if need be.
...PLENTY of safe options for terminating a dangerous situation - or...
Weak links must be used in accordance with 14 CAR 91.309(a)(3). USHPA recommends that a nominal 1G (combined operating weight of the glider and pilot) weak link be used, when placed at one end of a hang glider pilot's V-bridle; or about 1.5-2G if placed at the apex of the tow bridle or directly in-line with the tow rope. The actual strength of the weak link used by the hang glider pilot must be appropriate for the operation and have a breaking strength between 80% and 200% MCOW (max. cert. operating weight) of the glider, in terms of direct towline tension. The weak link used at the tow plane end of the towline must be stronger, but not more than 25% stronger, than the strength of the weak link used at the glider end of the towline.
...SOP on weak links, especially when THIS:
A release must be placed at the hang glider end of the tow line within easy reach of the pilot. This release shall be operational with zero tow line force up to twice the rated breaking strength of the weak link.
...is everything the SOPs have to say on the glider's release - and nobody makes the slightest pretense of compliance.
Speaking of which...
I'm SO looking forward to your next Higher Education article on aerotowing. It's just gotta be on glider end releases and, given that you needed fourteen pages to discuss a loop of fishing line, I'm guessing the release article will hafta be spaced over at least a half a dozen editions. When should we expect the first installment?
So we hav results from ten lab tests:
- 128.8 - 143.8 - 143.6 - 123.2 - 128.6 - 138.0 - 142.2 - 125.6 - 112.2 - 140.8
Average:
- 132.7
The high figure is 143.8 - 11.1 pounds / 07.7 percent over the average.
The low figure is 112.2 - 20.5 pounds / 15.4 percent below the average.
So in order to get these figures up and more consistent around the proper nominal value of 260 pounds...
Dr. Trisa Tilletti - 2012/06
So, the typical weak link used for aerotowing most hang gliders, made as a single loop from 130 lb. line, will have a nominal 1G breaking strength of 260 lbs. and be legal for both the very small, light glider and the heavier, larger glider--assuming there is no reduction in strength of the weak link due to a knot in the line.
And these are extreme cases. When we look at gliders and pilots of more average size, the standard 260 lb. weak link placed on the end of the V-bridle is FAA-legal for most gliders and pilots, and closer to the USHPA nominal 1G recommendation.
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.
...the one we need to use for compliance with FAA aerotowing regulations we need to use some or all the factors and variability that exist in the big, real world. So what do you think those are, Trisa? Engine vibration, wind, sunlight, radio waves, pollen, shock loading...?
Gimme just one factor that we can test under lab conditions that'll up the breaking strength 3 or 4 of the 96 percent increase we need to get from tested to NOMINAL...
adjective
1 (of a role or status) existing in name only : Thailand retained nominal independence under Japanese military occupation.
...ratings.
Dr. Trisa Tilletti - 2012/06
This article was peer-reviewed and approved for publication by the USHPA Towing Committee.
Got that part of your article dead on - motherfuckers.
The sailplane guys have been doing this for a long time, and there are many hang glider pilots and quite a few tug pilots who don't understand what the sailplane guys have learned over the years.
And here's what the sailplane guys have been doing with respect to weak links since the beginning of time:
Dr. Trisa Tilletti - 2012/06
I'll start with a legal review. The FAA has mandated requirements for weak links in FAR 91.309(a)(3) [ref 1] for civil aircraft towing sailplanes, ultralight gliders, and hang gliders in the US. It states:
(3) The towline used has a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not more than twice this operating weight. However, the towline used may have a breaking strength more than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle if--
(i) A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight.
and
(ii) A safety link is installed at the point of attachment of the towline to the towing aircraft with a breaking strength greater, but not more than 25 percent greater, than that of the safety link of the towed glider or unpowered ultralight vehicle end of the towline and not greater than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle.
And they don't seem to have...
Dr. Trisa Tilletti - 2012/06
Unlike the FAA's relatively clear-cut legal rules, the practical aspects of weak link technology and application are not so clear-cut. For some people, talking about weak links is more like talking about religion, politics, or global warming--they can get very emotional about it and have difficulty discussing it logically, rationally, or with civility.
...a lot of heated discussions or lunatic fourteen page magazine articles on weak links - I suspect because they:
Like our type-approved equipment, also our weak links are manufactured according to the EASA-approved production methods. Each batch is tested on computerized test equipment and the results are documented. This guarantees consistent high quality and traceability.
- lab test their weak links without giving flying fucks about external validity and completely including all the factors and variability that exist in the big, real world;
- use ACTUAL rather than NOMINAL mid range and manufacturer recommended ratings; and
Dr. Trisa Tilletti - 2012/06
You and I have flown sailplanes for almost as long as we have flown hang gliders. We own two sailplanes and have two airplanes that we use for towing full-size sailplanes. In all the time that we have flown and towed sailplanes, we have not experienced or even seen a sailplane weak link break.
- never break any.
So why do you think the FAA specifies a minimum so high that sailplane weak links never break?
Why is no one in sailplaning lobbying for enough of a reduction for them to...
Now I don't give a shit about breaking strength anymore. I really don't care what the numbers are. I just want my weaklink to break every once in a while.
...get breaks every once in a while?
If a sailplane weak link break can't possibly be anything more than the inconvenience our top USHGA tug pilots and aerotow instructors are constantly insisting is the case for sailplanes why does the FAA specify a minimum in the same terms they specify the maximum? Why are they regulating against inconvenience?
Or is it the case that there's something actually DANGEROUS about light or degraded sailplane weak links...
Tost Flugzeuggerätebau
- Use only the weak links stipulated in your aircraft TCDS or aircraft manual.
- Checking the cable preamble is mandatory according to SBO (German Gliding Operation Regulations); this includes the inspection of weak links.
- Replace the weak link immediately in the case of visible damage.
- We recommend that the weak link insert are replaced after 200 starts: AN INSERT EXCHANGED IN TIME IS ALWAYS SAFER AND CHEAPER THAN AN ABORTED LAUNCH.
I'm Tracy Tillman, on the USHPA BOD, on the Tow Committe, and I am an Aviation Safety Counselor on the FAA Safety Team (FAAST) for the Detroit FSDO area. As a rep of both the USHPA and FAA, I would like to help you, USHPA, and the FAA improve safety in flying, towing, and hang gliding.
The FAA gets a lot of letters of complaint from a lot of yahoos. For best effect, I suggest that you describe in your letter (and also post to the skysailingtowing group and share with the USHPA Tow Committee) your areas of expertise (if any) related to this issue, and list your qualifiications, logged hours, and currency in certain categories, such as:
1. hang glider pilot rating and logged hours
2. hang glider aerotow rating, logged hours, and logged number of tows
3. hang glider tug pilot rating, logged hours towing, and logged number of tows
4. hang glider aerotow administrator appointment date
5. hang glider aerotow supervisor appointment date
6. hang glider tanderm instructor rating, logged hours of aerotow tandem instruction, and logged number of instructional flights
7. airplane pilot license ratings and logged number of hours
8. airplane tow pilot endorsement date, logged number of hours towing with airplane, logged number of tows
9. sailplane tow pilot license ratings, logged number of hours, logged number of tows.
10. sailplane instructor license date, logged number of hours of instruction, logged number of instructional tows
11. any other flying or engineering-related credentials that you may have as evidence of your competence to make these claims.
(BTW, if you have an AT hang glider rating or above the you would/should have received the USHPA Aerotow Guidelines as part of your instruction from the person who taught you to aerotow and/or gave you your AT rating, and you should currently have access to them via the packet that is accessible to you on the USHPA web site, if your AT or higher AT-related ratings and appointments are current.)
It would also be good for the FAA and USHPA to know what kind of ultalight or sport plane tug and airplane you use for towing hang gliders and sailplanes with at your operation (if any), along with a general description of your towing operation or who you provide towing and instructional services for (if any).
Additionally, if you want to really present a convincing argument, you should also: (a) get other experts to co-sign your letter, such as those who have some or most of the aerotowing-related credentials listed above, who have been doing this for many years with many students, and who support your argument; and (b) present reliable data based on valid research showing that there is a significant difference in safety with the changes that you recommend. Supportive comments from aerotow experts along with convincing data can make a difference. Otherwise, it may seem as if your perception of "the sky is falling" may not be shared by most others who have a wealth of experience and who are deeply involved in aerotowing in the US.
This information would also be very helpful in convicing the USHPA and others to take your complaint seriously. Most of the individuals who serve on the USHPA Towing Committe have most of the credentials listed above, so it will be great for you to let them know about your similar credentials and depth of experience, too. If you do not have those credentials, it will be a simple matter for the USHPA Tow Committee to respond to the FAA to discount your complaint, so it will be very important for you to present this information in your letter to the FAA and to others now.
The best way to make change is to get involved, and join the Tow Committee at its meetings. That's what people who really care do to make change. Such is the nature of the great opportunities we have to make a difference in the US (although it means having to spend time, money, and effort, compared to the ease of just sitting in front of a computer.)
Good luck with your endeavor, and regards,
Dr. Tracy Tillman
USHPA Director, Region 7
FAA Detroit FSDO FAAST Aviation Safety Counselor
...maybe you could explain to us yahoos just what it is.
Zack Marzec (27), an H-4 Pilot with Aero Tow and Tandem Aero Tow proficiency as well as Advanced Instructor and Tandem Instructor appointments, and a USHPA member since 2009, suffered fatal injuries when when his glider tumbled during an aero tow launch. During the launch, at an altitude of 150 AGL, the pilot encountered an invisible bullet thermal which pitched the nose up, causing the weak link to break. Upon the breakage of the weak link, the glider whip stalled and then tumbled twice. The pilot and glider's leading edge hit the ground simultaneously. The pilot was utilizing his own pro-tow style tow harness, this own high performance glider with VG on, and was not wearing a full face helmet.
Maybe another magazine article. (Should be plenty of space available 'cause you've already said everything you're going to on Zack Marzec in an obscure little corner of the website.)
It is an acceptable method, but not necessarily a de facto standard. It can be used to make, for example, a 390 lb. weak link from 130 lb. line for use on a tug. It requires the use of two knots, one at each end of the weak link to attach it to the bridle or ring, and it doesn't really work on a pilot V-bridle. A practical option would be to just make a 400 lb. WT loop from 200 lb. line.
And you're NOT saying "...as we do at Cloud 9" - as if any of you Dragonfly douchebags could conceive of anything remotely resembling independent or creative thinking.
Something to bear in mind... the tug's weaklink is three strand.
For clarity... A normal single loop weaklink would be considered two. A tandem double loop is considered four.
In the tandem setup, the "weaklink" in the system is at the tug end, not the glider.
Ya'll seem to be missing this.
...we knew that already. Ever since you stupid clones figured out that...
For tandems, either two loops (four strands) of the same line or one loop of a stronger line is usually used to compensate for nearly twice the wing loading. When attaching the weak link to the bridle, position the knot so that it's hidden from the main tension in the link and excluded altogether from the equation.
Steve Kroop - Russell Brown - Bob Lane - Jim Prahl - Campbell Bowen
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.
...if you design the tow mast breakaway to break away at the same tension your optimal weak link blows the tow mast breakaway will break away at the same tension your optimal weak link blows you've universally gone to triple strand tow mast breakaway protectors.
So now you're operating at what you're assuming is three quarters of what you were assuming was the optimal tandem weak link.
And the title of this month's load of crap is titled:
HIGHER EDUCATION - 2012/06
TIE A (BETTER) WEAK LINK
We're gonna tie it "better" so it breaks more "consistently"...
Many pilots don't really understand weak links. Simply, the ideal weak link used for aerotowing consists of a continuous loop of string or length of material, without a knot in it--especially not a frayed knot--because a knot weakens the string and weakens it inconsistently, resulting in inconsistent breaking strengths.
...by taking the knot out of the equation - but just on the back end. Knots have absolutely no effect on front end weak links.
And don't pretend you assholes are using different flavors of fishing line or varying your numbers of loops or bridle lengths to tweak max towline loads. THIS:
But in actual practice, especially at a busy flight park, the tug monkey has limited time to maintain his "Master" weak link at 100%, so it will degrade in strength until he finds time to replace it. Same is true for the busy tandem monkey, so it's a statistical game as to when the tug's weak link might eventually fail before the gilder's.
The rear monkey, keen on survival, is aware of this and is ready to accept it (the rope) when it happens.
The Tug Pilot is responsible for his weak link and must manage it accordingly. Same for the other end. They both must be prepared for the worst while hoping for better.
is the way you ALL operate. You're using a triple strand of 130 pound Greenspot - declared rating: 390 pounds - to protect your tow mast breakaway and NOTHING else. You don't even use a bottom end weak link...
Towing Aloft - 1998/01
I witnessed a tug pilot descend low over trees. His towline hit the trees and caught. His weak link broke but the bridle whipped around the towline and held it fast. The pilot was saved by the fact that the towline broke!
...to protect the tug itself.
So let's plug some numbers in...
Falcon 3 max certified operating weights:
- 235 - 145
- 571 - Tandem
Legals:
- 470 - max 145
- 457 - min Tandem
We'll give you the benefit of the doubt and use a long bridle for the tandem so the weak link is only feeling about half load and a short bridle for the baby glider so the weak link's feeling fifteen percent over half.
Towline:
- 678 - 145
- 780 - Tandem
Gs:
- 2.9 - 145
- 1.4 - Tandem
Don't insult my intelligence by trying to make the claim that you're staying legal - let alone anything approaching safe - towing all gliders, some way over twice as heavy as others - all day with the same piece of crap on the front end.
P.S. And if you want something REALITY based divide all the tensions by two.
Simply, the ideal weak link used for aerotowing consists of a continuous loop of string or length of material, without a knot in it--especially not a frayed knot--because a knot weakens the string and weakens it inconsistently, resulting in inconsistent breaking strengths.
So? Your expectation of weak link performance is that it...
We want our weak links to break as early as possible in lockout situations, but be strong and reliable enough to avoid frequent weak link breaks from turbulence. It is the same expectation of performance that we have for the weak links we use for towing sailplanes.
...breaks as early as possible in lockout situations but is strong and reliable enough to avoid frequent breaks from turbulence. How is it possible for it to meet your expectation UNLESS it has inconsistent breaking strengths?
Expecting to add to my long list of sled rides this year, I was surprised just how much thermal turbulance was out there on tow. At 2200 feet, I watched as the Tug rocketed up and my glider joined the space shuttle launch a few seconds later. I fell out of the thermal in a hard right turn and knew I had no chance to get back wings level. As I reached for my release, the weak link snapped (AS IT'S SUPPOSED TO) and suddenly I was off tow.
Chris's Pre-Tied standard aerotow weak link was strong and reliable enough not to break when he was climbing through turbulence but broke as early as possible - much faster than he could effect the easy reach for his release - when he was in a lockout situation - AS IT WAS SUPPOSED TO.
Your weak link comments are dead on. I have been reading the weak link discussion in the OR with quiet amusement. Quiet, because weak links seem to be one of those hot button issues that brings out the argumentative nature of HG pilots and also invokes the "not designed here" mentality and I really did not want to get drawn into a debate. Amusement, because I find it odd that there was so much ink devoted to reinventing the wheel. Collectively I would say that there have been well over a 100,000 tows in the various US flight parks using the same strength weak link with tens of thousands of these tows being in competition. Yes I know some of these have been with strong links but only the best of the best aerotow pilots are doing this.
Why are you trying to reinvent the wheel when we've got a proven system that works?
The lockout Lauren mentioned was precipitated by my attempt to pull on more VG while on tow. I have done this before but this time the line wouldn't cleat properly and while I was fighting it, I got clobbered and rolled hard right in a split second. There was a very large noise and jerk as the relatively heavy weak link at the tug broke giving me the rope. I recovered quickly from the wingover and flew back to the field to drop the line and then relaunched after changing to a normal weak link. 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. Had the tug's link not broken, things could have gotten very ugly very fast. I still don't like weak links breaking when they shouldn't, but the one I was using was way too strong.
Sure, it has the consistency not to break in turbulence but not the inconsistency to break as early as possible in a lockout situation while Paul is discovering that his piece of shit bent pin barrel release gives him no chance to release as he always thought he could do.
Note that it was Russell Brown's relatively heavy tow mast breakaway protector with not one, but TWO exposed knots that broke inconsistently while Paul (and Russell) had no ability to release and saved the day - AS IT WAS SUPPOSED TO.
I really don't think your "better" Wrap and Tied weak link which break more consistently at 260 pounds...
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.
...is a good idea for hang gliding and I'm really surprised at and disappointed in Davis, Rooney, Paul, Lauren...
Zapata has delivered as promised, day after day with howling winds and good lift, where flights of over 100 miles (and much more) are possible.
Yesterday I chased Paul again. The tow rope weak link broke when Paul locked out and the weak link he got from Tad did not break. Russell said it was about the worst he has ever had his tail pulled around. Anyhow, I would advise against those weak links, though Tad's barrel releases do seem better able to release under stress. After Russell got a new rope and Paul recovered, he was late leaving and got trapped under some cirrus.
Now I don't give a shit about breaking strength anymore. I really don't care what the numbers are. I just want my weaklink to break every once in a while.
...Bart for not warning people about this dangerous position you're taking.
The sailplane guys have been doing this for a long time, and there are many hang glider pilots and quite a few tug pilots who don't understand what the sailplane guys have learned over the years.
And here's what the sailplane guys have been doing with respect to weak links since the beginning of time:
Dr. Trisa Tilletti - 2012/06
I'll start with a legal review. The FAA has mandated requirements for weak links in FAR 91.309(a)(3) [ref 1] for civil aircraft towing sailplanes, ultralight gliders, and hang gliders in the US. It states:
(3) The towline used has a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not more than twice this operating weight. However, the towline used may have a breaking strength more than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle if--
(i) A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight.
and
(ii) A safety link is installed at the point of attachment of the towline to the towing aircraft with a breaking strength greater, but not more than 25 percent greater, than that of the safety link of the towed glider or unpowered ultralight vehicle end of the towline and not greater than twice the maximum certificated operating weight of the glider or unpowered ultralight vehicle.
And they don't seem to have...
Dr. Trisa Tilletti - 2012/06
Unlike the FAA's relatively clear-cut legal rules, the practical aspects of weak link technology and application are not so clear-cut. For some people, talking about weak links is more like talking about religion, politics, or global warming--they can get very emotional about it and have difficulty discussing it logically, rationally, or with civility.
...a lot of difficulty discussing it logically, rationally, or with civility. To what do you attribute the difference?
- Are hang glider pilots inherently illogical, irrational, and/or uncivil?
- Does USHGA's instructional program totally suck?
- All of the above?
These are RELATIVELY clear-cut legal rules? Just what is it in them that you're finding ambiguous or confusing? Lemme know so's I can help you out with it.
WHAT "practical aspects of weak link technology and application"? You need something that breaks between eighty and two hundred percent of max certified operating weight on the back end and something up to 25 percent stronger on the front end. Want me to repeat that or say it slower?
And - when you're trying to get away with using a triple strand of 130 pound Greenspot on the Dragonfly bridle for staying legal with everything you tow - from a 165 pound min loaded Falcon 3 145 to a 571 pound max loaded Falcon 3 Tandem - don't pretend that you're concerned in the least about optimizing breaking strengths for safety or anything else.
And - when the FAA mandates the same 286 pound minimum for a T2 154 whether it's flying max loaded at 357 pounds / 0.8 Gs or min loaded 257 pounds / 1.1 Gs and you capitulated without a whisper of protest - don't pretend that you or anyone else is making the slightest effort to tweak weak links for lockout protection.
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.
Is that something the sailplane guys have learned over the years? That in order to comply with FAA aerotow weak link regulations you just use whatever value some asshole has declared to be the breaking strength and not lab test it because lab conditions cannot completely include all the factors and variability that exist in the big, real world?
Lemme quote a chunk of the relevant regulations for ya...
A safety link is installed at the point of attachment of the towline to the glider or unpowered ultralight vehicle with a breaking strength not less than 80 percent of the maximum certificated operating weight of the glider or unpowered ultralight vehicle and not greater than twice this operating weight.
It refers to the BREAKING STRENGTH and the BREAKING STRENGTH *ONLY*. There ARE NO other factors and variability that exist in the big, real world taken into consideration in these REGULATIONS - so we really don't need to be discussing them.
When the NTSB investigates a commercial sailplane crash that killed the pilot and tourist because the half G green Tost weak link dropped it back on the runway or the four G black Tost weak link snapped the wings off they don't wanna hear any crap about the other factors and variability that exist in the big, real world. They want heads on platters - where they belong.
