In general, a little experimentation lets you find a system that provides the safety margin your life depends on, but doesn't break needlessly.
Why do we need to experiment? I'm pretty sure we have enough data right here in your scholarly publications and off of the web.
Now let's see, what are we trying to accomplish with a weak link?
The most popular weak link is the readily available 205 leech line.
It must be popular.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3600
Weak link question
Jim Rooney - 2008/11/24 05:18:15 UTC
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.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467
weak 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. You're not the only one on the line. I didn't ask to be a test pilot. I can live with your inconvenience.
http://ozreport.com/12.081
Weaklinks - the HGFA rules
Davis Straub - 2008/04/22 14:47:00 UTC
Here is the requirement from the 2007 Worlds local rules (which I wrote) for weaklinks:
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.
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.
Most importantly, it must be popular with the shitheads who drive the tugs and control the competitions. Screw what a million comp pilots want. Since when do THEY get to make decisions about when to stay on and get off tow?
130 pound Greenspot wins the popularity contest hands down. That translates to 260 pounds one point or 226 two. 1.30 Gs for a 200 pound one pointer or 0.75 Gs for a 350 pound two pointer. Yeah, I know that makes no sense whatsoever. But the category is popularity - so what are you gonna do?
The ideal breaking strength of a weak link is from 100% to 120% of the total flying weight.
We want the breaking strength to be ideal.
The weak link at the pilot's end should break at 75 to 80% of the combined pilot and glider weight.
And we want it about 32.5 percent more ideal for aero than for surface.
For aerotowing operations, a weak link breaking strength equal to 80 to 100% of the total flying weight--the weight of the pilot and glider--is a reasonable starting point.
But we probably wanna make aero 12.5 percent less ideal once every five years or so.
One big problem is the difficulty of regulating tow pressures in gusts. This is what caused lockouts in the past. The proper use of weak links reduces this problem.
For static towing we want the weak link to regulate tow pressures in gusts 'cause if we get gusted the pressure's gonna go up and we're ALMOST CERTAIN to lock out and die. So how 'bout fifteen percent? So if normal tow pressure is 130 psi the weak link should blow at 150 psi? Sound good?
Structural failure under tow is a thing of the past due to our systems to limit the tow force (weak links and pressure gauges).
Structural failure? Do we really wanna be using weak links to be protecting against structural failure? That sounds SO sailplane. And sailplanes are such different beasts - they use releases that work and the glider doesn't roll completely out of control while you're trying to get to the lever. Oh well, six G gliders - 1.2 G weak links? Think that'll do it? I'd think that you COULD go a bit higher but 1.2 is the top figure I can find in Towing Aloft so we better not push our luck. We sure don't wanna bring back structural failure - or the bamboo and duct tape gliders that were structurally failing.
A weak link is a very simple device--typically a loop of line--that is intended to break in the event towline tensions exceed a safe or desired threshold.
DUDE! Who could POSSIBLY argue against safe or desired thresholds!
So all we gotta do is determine a safe threshold and then we'll know what to desire!
In recent years, two serious lockout accidents occurred with surface based towing: one resulting in a fatality and the other a very serious injury. In both of these events the line tension was being monitored directly and it never exceeded 120-130 pounds, well below the breaking point for the weak links!
And Steve Elliot got killed on aero at what was probably 125 pounds so it's pretty clear that we should probably go down to 110.
Also keep in mind that it is better to break weak links than bones.
Of course in some circles broken bones are ALSO considered symptoms of unsafe thresholds so we better knock it down to a hundred.
Weak links very clearly will provide protection from excessive angles of attack, high bank turns and the like for this form of towing.
Well yeah, OF COURSE we CLEARLY need a weak link to provide protection from excessive angles of attack, high bank turns, and the like for fixed line length towing...
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.
Dennis Pagen - 2005/01
I rocketed up well above the tug, while the very experienced tug pilot, Neal Harris, said he was also lifted more than he had ever been in his heavy trike. I pulled in all the way, but could see that I wasn't going to come down unless something changed. I hung on and resisted the tendency to roll to the side with as strong a roll input as I could, given that the bar was at my knees. I didn't want to release, because I was so close to the ground and I knew that the glider would be in a compromised attitude. In addition, there were hangars and trees on the left, which is the way the glider was tending.
...even when such protection is likely to kill us three seconds after it kicks in. You'd think that as popular as this 130 pound Greenspot is it would do the trick but it just doesn't seem all that reliable - probably need to go way lighter.
Caution: For tension controlled towing, a weak link cannot be counted on to break during a lockout, high bank angle, high angle of attack, etc.
A weak link that breaks between 100 to 120 percent of the total flying system weight is generally recommended.
This just seems so backwards to me. The highly popular and recommended 0.8 to 1.0 aerotow weak links are obviously WAY too strong to serve the primary purposes of providing protection from excessive angles of attack, high bank turns, and the like...
A weak link is the focal point of a safe towing system.
...and 1.0 to 1.2 is so nonfunctional in tension controlled towing that those systems essentially have no focal point whatsoever.
I'm thinking we should go 0.6 to 0.8 for aero and 0.4 to 0.6 for payout.
But then we've got this sort of problem...
If you find yourself breaking weak links repeatedly, try using lighter tow forces initially. Remember, the glider and reel have inertia that is lowered once they start moving.
and...
With a tension controlled tow, weak links might break but more regularly will not. The reason should be obvious: a good control system will attempt to maintain a constant tension and not allow forces to climb high enough to break the weak link.
Maybe we should use bad control systems which do crappy jobs of maintaining constant tensions and thus will maybe spin with hardly any resistance at launch and lock up during lockouts so that forces to climb high enough to break the weak link.
A weak link is required that will not break needlessly in response to moderate thermals, or pilot inputs...
WHOA! We DON'T want weak links which break needlessly in response to moderate thermals or pilot inputs? That can't be right. That goes against EVERYTHING 130 pound Greenspot and our fine flight park operators, tug drivers, instructors, and competition organizers stand for.
http://vimeo.com/17472550
password - red
http://farm8.staticflickr.com/7258/13851486814_77efdf1004_o.png
This is most confusing.
Well, as long as they blow in REALLY GOOD thermals I guess we can maybe tolerate them holding in moderate thermals. Definitely don't want them holding in the good stuff. Who knows what could happen? Hypothermia, hypoxia, thermals crowded with swirling, midair-prone gliders, people leaving the airport and getting lost hundreds of miles downwind... Creeps me out just thinking about it.
But...
Soon after lift-off the trike tug and I were hit by the mother of all thermals. Since I was much lighter, I rocketed up well above the tug, while the very experienced tug pilot, Neal Harris, said he was also lifted more than he had ever been in his heavy trike. I pulled in all the way, but could see that I wasn't going to come down unless something changed. I hung on and resisted the tendency to roll to the side with as strong a roll input as I could, given that the bar was at my knees. I didn't want to release, because I was so close to the ground and I knew that the glider would be in a compromised attitude.
...are you ABSOLUTELY POSITIVE that it's a really great idea to have weak links blowing in response to really good thermals?
...yet will break at a low enough point to avoid disaster or excessive pilot panic.
In recent years, two serious lockout accidents occurred with surface based towing: one resulting in a fatality and the other a very serious injury. In both of these events the line tension was being monitored directly and it never exceeded 120-130 pounds, well below the breaking point for the weak links!
OK, we DEFINITELY gotta keep the weak links under half a G. Non negotiable.
For aerotowing operations, a weak link breaking strength equal to 80 to 100 percent of the total flying weight--the weight of the pilot and glider--is a reasonable starting point.
I don't think so. Didn't we JUST establish that half a G is plenty enough lock out and kill pilots? And it's almost a no brainer that excessive pilot panic was involved in at least one of those. WAY too high dudes.
For surface based towing, there is a debate on the recommended breaking strength for weak links.
I simply can't understand why there should be.
- If there's a RECOMMENDED breaking strength why would anyone but a total moron debate the issue?
By the late 1980s, all the current towing systems--aerotowing, reel-in winch, and static line--were essentially perfected.
- All of these systems were PERFECTED a decade ago. Why would ANYONE question or mess with perfection?
Since almost all modern surface based towing (static line, payout winch, and stationary winch) are tension controlled systems, the weak link selection is partially dependent upon the towline tensions used.
Well yeah. OBVIOUSLY. Let's do the math.
The RECOMMENDED weak link strength range for surface towing is 1.0 to 1.2 Gs and, obviously, the weak link at the top end is twenty percent more likely to lock you out and kill you than the one at the bottom.
And we all know that it's safe to assume that pretty much all gliders fly at 250 pounds. So 250 pounds for a safe weak link and 300 for a dangerous one.
If we set the:
- tow tension - sorry - PRESSURE to a nice safe 125 pounds we should use a nice safe 250 pound weak link
- pressure to a dangerous 150 pounds we should also use a dangerous 300 pound weak link
It would make no sense whatsoever to use a dangerous pressure with a safe weak link or vice versa.
150 pounds pressure and a 250 pound weak link on a tension controlled system? Totally wacko. If you start out with a higher pressure you need to max out at a higher pressure. You just do. Should be obvious.
In any case, remember: aerotowing requires a much lighter weak link than surface towing. Also, most ultralight sailplanes use a direct hookup (without a bridle), so all the towline force will be taken by the weak link. Finally, be aware that a low separation from the tow line is more of an emergency with an ultralight sailplane than a hang glider or paraglider because of landing area requirements. Thus, more care should be given to weak link selection so as to minimize premature breaks, and still maintain a low upper breaking limit.
OK, gotta take all this into consideration to reach our magic number.
- Aerotowing REQUIRES a much lighter weak link than surface towing. It's in the book so we've got that restriction. And it just makes perfect sense. Everybody knows that the danger for an aerotowed glider rolled away from a tug at 0.9 Gs is comparable to that for a static towed glider rolled away from a truck at 1.1 Gs. These gliders remember the tension they had when they were under control and are thus better able to cope with the extreme when it hits.
- But we wanna minimize premature breaks - so we want a heavy weak link.
- And we also wanna maintain a low upper breaking limit - so we want our heavy weak link to be light as well.
Lemme feed this into the spreadsheet. No, that might crash the computer. Maybe we could get a schematic of this thing. Too bad M.C. Escher ain't around no more.
Caution: For aerotowing tandem, weak links SHOULD BE LIGHTER than for surface towing tandem.
80 percent or less for tandem.
And we need to use lighter weak links for tandems because they're more likely to lock out and completely invulnerable to whipstalling if they blow something. So we can go as low as we want and thereby make things as safe as we want.
Weak links often break near the beginning of a tow, when the glider is still low and the resulting release is typically uncomfortable for the pilot.
Too heavy a weak link - you're automatically gonna lock out and die. Too light and the worst you can experience is discomfort. Don't gotta be a rocket scientist to know how this information is gonna influence the equation.
"It is infinitely better to have a weak link break too soon rather than too late."
-- Towing Proverb
Especially if it's in the Proverbs. I'll bet if we checked the Book of Revelation we could get some really good guidance on this. Maybe Leviticus if that doesn't pan out.
A good friend of ours, Michael Robertson, the inventor of the High Perspective training wheels you see on virtually every student training glider, was blinded in one eye by a ring on the end of a tow rope. Michael was simply observing the operation from the front of the boat when the weak link broke during the platform launch.
And we don't wanna have something like that happen again. So we should use much lighter weak links so when they blow the polypro isn't storing as much energy. Wish we knew how many pounds were involved in that one.
You want to have plenty of airspeed to help carry you away from the dolly should a premature release or weak link break occur just after launching.
I dunno... Maybe we should jack it back up a little.
Flying at a speed similar to best glide provides more margin for corrective action and avoids a low altitude stall should the weak link break...
Yeah, jack it back up a bit. Getting run over by the cart and and low altitude stalls are only minor annoyances, but still...
The increased airspeed improves your ability to manage gusts and crosswinds. It also provides more time and room to land if the weak link breaks or the release disengages. However, higher release airspeeds will exaggerate poor technique and make launches more violent as well as increase the potential for weak link breaks or even mild whip stalls after launch.
Well, as long as they're just MILD whipstalls... And we probably don't hafta even worry about those if we keep the glider low, slow, and safe for a little while coming off the truck or cart. Let's bump it back down to something safer.
If the weak link breaks or release disengages with the pilot well forward of the canopy, the glider will surge forward more violently.
No! Up! Up! Up!
The result will be too high an angle of attack, which in turn causes loads on the canopy to rise and increase the risk of lockout or canopy collapse if the weak link breaks.
Up!
Obstacles upwind can create turbulence. This may interfere with safe launching or landing if the release disengages or weak link breaks before enough altitude has been achieved to reach a clear area.
Up!
The weak link may likely fail at any moment and having the extra speed can reduce the high potential of a stall or surge when it lets go.
Up!
A weak link break or slight roll during nose release can be traumatic and damaging to people and things. There are many schools of thought about launch tensions, speeds and techniques.
Up!
Tow forces required to get the glider and pilot moving through the water and up were rather high, potentially beyond the breaking point of the weak link.
Up!
When gliders are returning and landing on solid ground, do not be tempted to avoid the use of appropriate flotation. A weak link break or premature release could easily precipitate a landing in the drink.
Up!
However, definitely avoid variances which increase the tension excessively and may break the weak link.
Up!
A weak link is an integral part of any towing system in order to prevent overloading and lockouts.
Down!
A weak link is a fuse that protects the equipment--your body!--on an overloaded circuit.
Down!
While aerotowing, the weak links break most often when the launch begins on a dolly or during a lockout or turbulence.
Ooh... Tough one. Up for the beginning of launch, down for a lockout, and down for turbulence. We DEFINITELY don't want gliders staying on tow in turbulence.
http://ozreport.com/13.238
Adam Parer on his tuck and tumble
Adam Parer - 2009/11/25
Due to the rough conditions weak links were breaking just about every other tow and the two tugs worked hard to eventually get everyone off the ground successfully.
Not for long anyway. It's OK if you blow the weak link every other tow and hafta recover, land, and relaunch in turbulence. MUCH safer that way.
Inadvertent weak link breaks slow a group operation down...
Up.
...and may compromise safety if they happen critically low.
Up.
Always use a weak link when towing--WEAK LINKS SAVE LIVES.
DOWN!!! FOR THE LOVE OF GOD - DOWN!!!!!
It is much better to be free of the line and dealing with a slipping, diving, or winging over glider than a lockout. Of course, your weak link should break before the lockout becomes too severe, but that assumes a properly applied weak link.
Down.
On a tow in New York, a new tow pilot got way to one side and began to lock out. The tug pilot didn't release and the glider pilot didn't react. The lockout proceeded very rapidly and went to the side so fast that the towline hooked on the trike wing. Both the trike and hang glider pilots were in danger of a serious accident when the weak link broke.
Down.
In that same year, with that same tug pilot, I was aerotowing on a turbulent day. At about 120 feet we were hit by something nasty that left the towline slack and me sitting well above and way to the right of the tug. I remember looking at it from the side.
WAY down.
Weak links are an essential part of the safe towing formula.
Downer and safer.
In general, a little experimentation lets you find a system that provides the safety margin your life depends on, but doesn't break needlessly.
Dude! I'm totally brickwalled by this.
120 to 130 pounds will CERTAINLY kill me in a lockout but the Dragonfly tows me at 125. And it takes about 170 just to get me started rolling on the cart.
A weak link is REQUIRED that will not break needlessly in response to moderate thermals or pilot inputs but the ever popular 130 pound Greenspot blows in glassy smooth air straight and level behind the tug.
And then there's THIS problem:
A weak link is required that will not break needlessly in response to moderate thermals...
In the case of lockouts or turbulence, the weak link breaks as designed and should not be increased in strength.
We REQUIRE it to NOT break needlessly in response to moderate thermals but are DESIGNING it TO break in turbulence.
Whoa! Tough orders everywhere you look! Maybe Watson can come up with something.
We especially thank Gerard Thevenot for teaching us to aerotow, Wallaby Ranch for refining our skills and Raven Hang Gliding for their helpful input. We also owe a debt of gratitude to Wayne Sayer, the Wallaby Ranch, and Raven Hang Gliding for proofreading the manuscript.
Individuals such as Donnell Hewett, Dave Broyles, Lars Linde, Mike Robertson, Brad Kushner, Malcolm Jones, David Glover, Greg McNamee, Jan Alda, Alan Chuculate and Bill Moyes have also offered specific information either through their writing or by personal communication.
How is it that you calculate group intelligence? Take the IQ of the stupidest person in the group - in this case, Bryden - and divide by the number of people in the group - maybe about twenty? I'm thinking deep into single digits.
Here's an idea...
Tost Flugzeuggerätebau
Weak links protect your aircraft against overloading.
http://www.dynamicflight.com.au/WeakLinks.html
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. Lockouts can and do occur without increasing tow tension up until the point where the glider is radically diverging from the direction of tow. At this point tension rises dramatically and something will give - preferably the weak link. Given that a certified glider will take 6 to 10 Gs positive a 1.5 G weak link as opposed to a standard 1 G weak link should not significantly increase the risk of structural failure. It will however significantly decrease the probability of an unwanted weak link break.
How 'bout instead of listening to the lunatic rantings of you fuckin' whack jobs we go with people who actually make sense?
How 'bout we use a goddam one and a half G weak link to keep the glider from getting overloaded and our hands and a release on the basetube to control it and protect against lockouts and stalls?
P.S. Do you assholes actually believe the crap you print in these books or do you just figure you can sell them for more if they weigh more?
