Weak links

[Tad Eareckson]

http://groups.yahoo.com/group/skysailingtowing/message/4606
Weaklinks and aerotowing (ONLY)

Davis Straub - 2005/02/09 06:13:39 UTC
Cathedral City, California

A few statements to try to pin this down.

Oh good. Davis is gonna make a few statements to pin down the weak link issue. Then we'll finally all get it.

1. Weaklinks do nothing for us with regard to lockouts. Neither prevention nor releasing (breaking) when fully locked out.

Sure they do, Davis...

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Marc Fink - 2011/08/28 21:11:09 UTC

I once locked out on an early laminarST aerotowing. went past vertical and past 45 degrees to the line of pull-- and the load forces were increasing dramatically. The weaklink blew and the glider stalled--needed every bit of the 250 ft agl to speed up and pull out. I'm alive because I didn't use a stronger one.

Ya just gotta be at 250 feet or better for them to work properly.

Your release needs to be activated when in this situation.

MY release has already been actuated.

http://www.hanggliding.org/viewtopic.php?t=21033
barrels release without any tension except weight of rope..

Bart Weghorst - 2011/02/25 19:06:26 UTC

I've had it once where the pin had bent inside the barrel from excessive tow force. My weaklink was still intact. The tug pilot's weaklink broke so I had the rope. I had to use two hands to get the pin out of the barrel.
No stress because I was high.

How the fuck are you planning on releasing the bent pin shit you use and sell? Assuming, of course...

http://www.chgpa.org/forums/viewtopic.php?f=2&t=3391
More on Zapata and weak link

Paul Tjaden - 2008/07/22 04:32:22 UTC

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.

...you can even get to it before everything's already over.

http://ozreport.com/9.032
The Worlds - weaklinks

Rohan Holtkamp - 2005/02/07

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 of Robin's death if you doubt this in any way.

From the article above:

You should also now be able to understand that the towline forces in a lockout need not be very high. They only need to be sufficiently high to cancel out the effect of a maximum pilot weight shift/yaw in order to cause a continuation and worsening of the situation. Lockouts can and do both occur and continue without ever exceeding normal tow tensions. As a result A WEAK LINK OFFERS LITTLE PROTECTION FROM A LOCKOUT.

The biggest fallacy in towing is that a weak link will protect you from a lockout. For ground towing this is wrong. The tow line force required to break the weak link is roughly 2-3 times the force required to sustain a lockout - I have seen this demonstrated on numerous occasions. As a result you could potentially continue a lockout all the way to the ground without ever breaking the weak link. If you have ever seen a child's kite lock out and arc into the ground you should intuitively understand this.

2. Weaklinks are only of value to the hang glider pilot if you come off the cart prematurely and hit the ground hard with your glider and dig in.

Are they of any value whatsoever to the hang glider itself...

Tost Flugzeuggerätebau

Weak links protect your aircraft against overloading.

...to keep it from getting overloaded?

They are supposed to break then.

Really Davis?

http://ozreport.com/13.003
Forbes, day three, task three

Davis Straub - 2009/01/05 12:09:11 UTC

I read the accident report and Steve did not fly off the cart. His left wing started going down (this indicates that the wing is stalled and that the angle of the glider on the cart is too high) and Steve didn't initiate any actions to correct the problem.

The left wing went down further with the other wing rising, still no corrective action on Steve's part. His left wing contacted the ground and the glider "cartwheeled" in. The glider did not suffer any damage but Steve was fatally wounded.

This is an accident that didn't have to happen. All tow pilots need to check their angle on the cart. I have been raising the rear cradle on all the carts that I have used here. Pilots are responsible for checking their tow angle by getting on the cart and letting go of the base bar. If the base tube is in front of the trim position they need to raise the back cradle.

Pilots can also pull in when the cart starts to raise the keel above the cradle. But this is a trickier maneuver.

- Of how much value to THAT pilot was the weak link when he came off the cart prematurely?

http://groups.yahoo.com/group/skysailingtowing/message/4633
Weaklinks and aerotowing (ONLY)

Steve Kroop - 2005/02/10 04:50:59 UTC

Weak links are there to protect the equipment not the glider pilot. Anyone who believes otherwise is setting them selves up for disaster.

Oh well, at least the equipment came out smelling like a rose.

http://groups.yahoo.com/group/skysailingtowing/message/6726
Weaklinks

Peter Birren - 2008/10/27 23:41:49 UTC

I know about this type of accident (Davis's) because it happened to me, breaking four ribs and my larynx... and I was aerotowing using a dolly. The shit happened so fast there was no room for thought much less action. But I wasn't dragged because the weaklink did its job and broke immediately on impact.

Oh well, at least the weak link did it's job and he wasn't dragged.

Is 130 pound Greenspot a great weak link material or what!

- What's the G rating of this weak link that's supposed to break and only be of value to the hang glider pilot if he comes off the cart prematurely and hits the ground hard and his glider digs in?

3. The tug pilot has a weaklink and it is supposed to break under the load of you plowing in.

Really? Is that what it's supposed to do?

http://ozreport.com/forum/viewtopic.php?t=553
Weak Links vs Strong, but foolproof release?

Justin Needham - 2005/02/09 23:03:22 UTC

Re your comment "why weaklinks". I had a scary incident back in the early 90's where a doubled up weakink (unbeknown to me) caused a bad accident.

A Swift pilot who had been towing on the same site had been doubling weaklinks to prevent early breakage, but not advising the flex wing pilots of his actions. We had all been clipping into the same line. My launch on this occasion was in medium length grass where the tug had slow acceleration. The tug pilot was inexperienced. The winds were pretty much zero. On my "all out", I guess a gentle thermal tailwind hit me from behind as I began to run. This was enough to prevent me from getting airborne. I ran a very long way till I could no longer keep up with the groundspeed. The glider wasn't taking my weight, and I was then forced to push out to try and avoid hitting the ground. Unfortunately even in deep ground effect mush, there was still not enough lift. The control frame hit down, followed immediately by the nose of the glider and then everything went crazy.

At this point, a normal weaklink would have broken instantly and I'd have been left embarrassed but (probably) healthy in a heap down the runway. On this occasion, the doubled link wouldn't break. I was accelerated along the ground, with a flattened control frame, with my face in the dirt and absolutely no ability to release since my arms were being flailed about. All I clearly recall, is shouting "stop stop stop" since I could do nothing else. I was in severe danger of breaking my neck, since my head was being caught up in all this as I did 20MPH+ across the ground.

The tug pilot was inexperienced, and for those few seconds was concentrating on getting airborne, not on looking at me. (Mistake number 2) After ploughing a furrow for ~ 75 meters, while my glider disintegrated about me, the tug pilot got the message and finally stopped.

Why didn't I use a trolley you ask? Well there was no trolley on site, and perhaps I was relying on my normal perfectly adequate nil wind launch technique a little too much. (Potential mistake number 3). It didn't seem an undue risk under the circumstances at the time, - we all take calculated risks every time we fly. Unfortunately this risk had no safety valve.

I guess Justin just didn't plow in hard enough enough for the tug pilot's weak link to work properly. Or maybe, like Justin, the tug pilot was using one of those DOUBLED weak links to prevent early breakage. What MORONS!!!

So what G rating weak link SHOULD the tug pilot be using to break when the glider plows in?

It is also supposed to break under the load of catching the tow rope on a tree or fence or whatever.

Yeah, sure it is.

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!

- Wouldn't it be a good idea to put it on the end of the towline - rather than on the end of the bridle - so the driver doesn't have to wait for the towline to blow after the weak link blows?

- So as long as you've got a proper weak link there's really no danger to flying low over trees or fences or whatever.

- What's the proper G rating for a weak link which makes it safe to fly low over trees or fences or whatever?

4. The hang glider pilot's weaklink is supposed to be weaker than the tug pilot's weaklink to give the tug pilot an extra margin of safety.

Right. It's supposed to be weaker than the tug's weak link in case the tug's weak link is strong enough for him to have his control compromised by the glider. As was the case with...

Dick Reynolds - 1992/11
Rising Fawn, Georgia

Four months have passed since my crash. Fortunately, I've regained control of the old brain, and would like to take this opportunity to pass on my experience in hopes that the rest of you might avoid a similar predicament.

Lookout Mountain Flight Park had acquired a new Moyes aerotug and I was the pilot - claiming 200 plus tows to date. At 11:00 AM on May 17, 1992 I had decided to take two more tows and then call it quits for the day.

The conditions on this particular morning were very light - great for towing. Takeoff went smoothly, with the glider then the tug lifting off, thus increasing my angle of climb. My airspeed was four mph above stall. I took my eyes off the indicator to watch the hang glider's progress when the engine abruptly seized. I can distinctly remember taking my hand off the throttle to wave the hang glider off, and it was at that point that I fully realized there was no time! I pulled the release and pushed the stick forward.

All this occurred somewhere around fifty feet. The combination of high nose angle plus the pull exerted by the climbing hang glider brought me to a screeching halt, so to speak. I believe my response time was less than a second, but this still me just hanging with very little elevator authority. The nose fell through the horizon to 30 degrees negative and the ground rapidly rushed toward me. I attempted to pull up at approximately 25 to 30 feet, with no response. My feet, butt, and gear impacted simultaneously.

I consider myself fortunate in that my friends were there to immobilize me. The doctors tell me that I'll be walking in a year or so, but that I shouldn't plan on winning any foot races.

...Dick Reynolds.

Has absolutely nothing to do with...

http://ozreport.com/10.124
Weaklink Break

Davis Straub - 2006/06/15

The tug's weaklink breaks as I come off the cart. (Highland Aerosports)

On the second day of the ECC competition just as I came off the cart the tow line went slack when it came detached from the tug (but not from me). You can see what happened then as Jim Rooney filmed it.

http://ozreport.com/data/Weaklink/

Flying a foot or so off the ground on the base tube pushing out was pretty interesting, all with a good ending.

...the glider not getting 250 feet of spectra draped over his basetube just off the runway.

5. There are situations where breaking a weaklink can be dangerous to the hang glider pilot, say towing east out of Quest and just coming up to the trees. Or towing downwind.

NO!!!

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Jim Rooney - 2011/08/26 02:44:10 UTC

The "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.

I've always heard that the "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.

Sounds like...

http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467
weak links

Jim Rooney - 2007/08/01 19:49:30 UTC

It's more of this crappy argument that being on tow is somehow safer than being off tow.

...more of this crappy argument that being on tow is somehow safer than being off tow.

6. Weaklinks need to be strong enough to not break in circumstances where they would put the pilot in trouble, but weak enough to break to help get the pilot out of worse trouble.

DUDE!!! This sounds like a job for a Navier-Stokes equation!

How strong should aerotow weaklinks be?

Well ferchrisake!

http://ozreport.com/12.081
Weaklinks - the HGFA rules

Davis Straub - 2008/04/22 14:47:00 UTC

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.

They should be all consist of a single loop of Cortland 130 pound Greenspot braided Dacron Tolling line and should be placed at one end of a shoulder bridle.

The lowest figure I've seen is that they should break at 85 kg (187 pounds) of tension. The range discussed at the Worlds was 85-115 kg (187 lbs to 253 lbs).

Did any of those shitheads bother discussing the flying weights of the gliders? Just kidding.

Any chance of an 85 kilogram weak link breaking in a situation which could be dangerous to the hang glider pilot, say towing east out of Quest and just coming up to the trees? Or towing downwind?

Any chance of an 85 kilogram weak link NOT breaking to help get the pilot out of worse trouble, say in a lockout in which all he's got to get him off tow is a piece o' shit Davis Pro Tow Mini Barrel Release?

Donnell Howell mentions (using hookin weight of 100 kg and glider weight of 36 kg):
1/2 G (inexperienced pilot): 68 kg (150 lbs)
1 G (experienced pilot): 136 kg (300 lbs)
2 G (very experienced aerobatic pilot): 270 kg (600 lbs)

- Hewett - you moron.

- I thought all gliders were supposed to weigh 260 pounds so a loop of 130 pound Greenspot on the end of a bridle would put them at a perfect 1.0 Gs.

- So obviously we can predict that an inexperienced pilot won't be able to stall or lock out with a half G weak link, a very experienced aerobatic pilot will be able to recover from a whipstall in twenty feet or less, and a regular Joe should fly at one G 'cause that's a good rule of thumb - and an easy number to remember.

Looks like we have a rather wide range here.

Nah. It's all pure, unadulterated, totally clueless bullshit.

At Quest and Wallaby 130 pound test line in a loop with a fisherman's knot is used.

Well they're the pros who really know what they're doing so we should just ignore the fact that none of these assholes is saying anything about flying weight and get with the program. That way if we fail to maintain the correct tow position (centered, with the wheels of the tug on the horizon), the weak link will break before we can get into too much trouble. Sounds like a plan to me!

That is two strands minus the weakness due to the knot (225 lbs).

Yeah? So how come most folk who ACTUALLY TEST this stuff find that it actually blows around 130?

If I put it on my Pro-Tow, then the tension on it is reduced by the cosine of the angle (results is =>300 lbs).

Bullshit.

- If you put it on:
-- a bridle end the tension INCREASES as a consequence of the apex angle
-- your "Pro-Tow" the angle is so freaking acute that the load increase is so negligible that it's not worth mentioning

- Don't you even bother pretending to begin to understand anything about weak link loading 'cause in THIS:
http://ozreport.com/forum/viewtopic.php?t=15716
thread you don't have the slightest freaking clue...

http://ozreport.com/forum/viewtopic.php?t=15716
weak links

Davis Straub - 2009/04/22 12:07:12 UTC

Pro tow?

So. It would be the same with a V-bridle.

...what the hell I'm talking about - asshole.

I've been flying with two of these (four strands) for the last year (and never replaced the "strong links") so approximately 600 lbs.

- You tested to get that figure, right?

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.

- So how well does your Pro Tow Mini Barrel Release work under twelve hundred pounds of tow tension?

- Which was worse? Immediately locking out and slamming in?

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Jim Rooney - 2011/08/31 09:25:57 UTC

Oh how many times I have to hear this stuff.
I've had these exact same arguments for years and years and years.
Nothing about them changes except the new faces spouting them.

It's the same as arguing with the rookie suffering from intermediate syndrome.
They've already made up their mind and only hear that which supports their opinion.

Only later, when we're visiting them in the hospital can they begin to hear what we've told them all along.

Or having Rooney visiting you in the hospital and beginning to hear what he was telling you all along?

It appears that Tracy is using a loop of 130 lbs test line just like Wallaby and Quest with some kind of knot, which I can't figure out. They did extensive tests at the Worlds and by far the fisherman knots were the most consistent and least reduction.

- That's odd. In just about all the tests I've done the loop fails on one of the strands at the point at which it exits the bridle eye - so the Fisherman's Knot is completely irrelevant.

- The LEAST reduction?

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Davis Straub - 2011/08/26 14:04:52 UTC

We had six weaklink breaks in a row at Zapata this year.

Wouldn't you want the MOST reduction to make them safer?

So I will have to find out just how strong the weaklinks are on the Dragonflies at Quest.

Yeah.

http://ozreport.com/forum/viewtopic.php?t=24534
It's a wrap

Lauren Tjaden - 2011/08/01 02:01:06 UTC

In general, the weak link on the glider end will break before the one on the plane. However, my glider's main weak link was wrapped in a huge bunch around the 'biner, therefore it did not break. I also had a secondary weak link on my shoulder (which does not take as much force), but the plane's link broke first. Really, it was just half a second (or less) until the break, and the backups worked as they should.

I just thought it was very interesting the way the line wrapped and thought it was a good reminder for all pilots who aerotow to keep their weak links short.

Also, a tandem weak link is doubled, due to the much greater tow forces on it due to its much greater weight. Technically the tow plane's weak link will break sooner than the tandem's will. Of course what happens in reality is not exactly what happens in principle -- though it WAS what happened in this case.

Had the plane's weak link not broken, I would have been left towing from my shoulders, which would have been okay. I could have released from my barrel release on my shoulders or Paul could have given me the rope. Had all else failed, I could have used my hook knife.

For whomever asked about the function of a weak link, it is to release the glider and plane from each other when the tow forces become greater than desirable -- whether that is due to a lockout or a malfunction of equipment or whatever. This can save a glider, a tow pilot, or more often, a hang glider pilot who does not get off of tow when he or she gets too far out of whack.

I rarely break weak links -- in fact, I believe the last one was some two years ago, and I have never broken one on a tandem (probably because I am light and also because I change them whenever they show any signs of wear). They are a good thing to have, though!!

So does Quest.

Bill Moyes lost eleven spectra ropes in the first two days of the Worlds because the pilot's weaklink was stronger than the plane's weaklink.

Bullshit.

Bill Moyes lost eleven spectra ropes in the first two days of the Worlds because the tug's weaklink was lighter than the glider's weaklink.

Bill Moyes lost eleven spectra ropes in the first two days of the Worlds because he's too fuckin' stupid to use equipment capable of doing the job it's supposed to be doing.

I had heard that the plane's weaklink was 115-135 pounds.

Bill Moyes lost eleven spectra ropes in the first two days of the Worlds because he's using a weak link incapable of towing a 270 pound glider at one G.

The ones on the Dragonfly were on V-bridles at the end of the V-bridle, and the ones on trikes were on three ring circuses.

End result: A very wide range of possible weak link values here depending on pilot skills and weight.

End result: A bunch of total assholes without the slightest clue what they're doing trying to run operations way over their pay grades.

Competition:

Pilots need to be able to go to the front of the line (if they are ready to launch) if they have a weaklink break.

Pilots who have weaklink breaks aren't pilots and need to stay the fuck out of the way of people who come to the line ready to fly.

Otherwise you'll have "strong links."

- What's a "strong link"? Can you express that in Gs? Just kidding?

- If a 200 pound little girl glider flies the same loop of 130 pound Greenspot that a 350 pound big dude glider is she flying a "strong link"?

- Like the doubled Greenspot YOU fly? So you can get up on on task while the people who fly under the "rules" you and your scumbag friends dictate are replacing downtubes and and getting back in line. I hope your surgeon shows up with a hangover because of the bender he went on to deal with the stress of all the medical malpractice and wrongful death lawsuits.

Sailplane experience

I have it. I don't see any reason to get it for hang glider aerotowing.

Were your sailplane instructors as fuckin' clueless about the function of a weak link as your hang gliding instructors?

What don't I discuss here: The tow line type - spectra or poly, the length of the tow line, the type of release mechanism and bridle.

You haven't begun to scratch the surface of other stuff you never will have any business whatsoever discussing.

[Tad Eareckson]

http://www.youtube.com/watch?v=jvK1ONl1CqE

Failed launch

mrcirrus - 2006/11/22

Failed to recover quickly in a very gusty wind on ridge site. No serious injuries.

jsd23

What a horrible height to lose the cable.

alpacaj

If he had been quicker putting the nose down, he might have been alright. (Always be prepared for cable break, that's why you hold the release during the launch.)

Conan1ts

I don't hold the release switch during takeoff (because I don't want to release the cable accidentally, for example after rotation), but my left hand is always prepared for it.)

chrisrobsoar

The glider is FBC an ASW 15 (FCB is a Pegase flown from Portmoak). The ASW 15 has the CoG hook offset to the left making sideways launches the norm; during a nasty low launch failure when low the right wing drops first.

It is very difficult to judge how far to lower the nose with very low launch failures, too little (so too slow) the glider stalls at the round-out, too much and you just fly into the ground (and do not operate the airbrake until you are on the ground).

pyewackett3822

Hello Conan,

If you are based in the UK the BGA have issued a directive that we keep our hand on the release throughout the launch. It's not really an 'and or' option.

Conan1ts

I'm from Hamburg, Germany. I guess there is no such advice for us. But it's interesting that you have to do that in the UK.

hrford

If a wing drops during the ground run and causes a ground loop and your hand isn't on the release, you'd probably find it difficult to reach for it as your glider is starting to rotate sideways quickly. Directives or not, I'd rather have my hand ON the release.

[Tad Eareckson]

http://www.paraglidingforum.com/viewtopic.php?t=44952
In flight adjustable weak link.

Nigel Thomas (EnVeeTee) - 2012/01/29 10:57:58 UTC
South Coast UK

http://www.paraglidingforum.com/viewtopic.php?t=28697
Weak links why do we use them. in paragliding.

Forum Moderators - 2010/02/24 22:02:46 UTC

Tad Eareckson

We, the Moderators, feel that weak links are an important topic. In our view Tad Eareckson's posts have discouraged others from taking part in this discussion, so, after several warnings, he has been banned. His most recent post, after this topic was locked, is here:

http://www.paraglidingforum.com/viewtopic.php?t=30195
moderation

We are happy to lift the ban if we come to the view that Tad has further positive contributions to make - please contact us by PM or by email if you feel that this is the case.

I knew if you motherfuckers just banned me long enough one of the bagwing crowd would eventually recover enough to bring up another lunatic idea about weak links. Didn't even take a whole two years. Great job, guys!

Our computer controlled, pilot operated stationary winch is taking shape. We are about to start tow force trials in the field some time next week.

Might not be a bad idea to have a human with half a brain or better down there anyway.

Looking forward; has anyone come across (or is there such a thing as) an adjustable weak link which can be adjusted by the pilot whilst under tow?

Gawd I hope not.

One of the greatest safety issues concerning me is a malfunction of the winch whilst the pilot is close to the ground with insufficient height to deal with any emergency. Particularly, authority over the winch being lost, resulting in max tow force followed by a line/weak link break while the pilot is only fifty or a hundred feet high - (tow stall situation?).

Manned Kiting
The Basic Handbook of Tow Launched Hang Gliding
Daniel F. Poynter
1974

"The greatest dangers are a rope break or a premature release." - Richard Johnson

Bull's-eye, dude.

I'm looking for a weak link which will fail at a low tow force whilst the pilot is near the ground, then as altitude is gained and more tow force applied, the strength of the link can be increased?

Right.

BHPA - 2009/12/15

Weak links

A weak link is a simple device intended to prevent excessive tow tensions ever being applied.

There are countless ways that excessive tow tensions can be generated: these are easily visualised with fixed line vehicle towing, but even with constant tension winches, malfunctions, mistakes and mishaps can lead to excessive loads.

Excessive tow tensions, when towing modern paragliders, result in the pilot being significantly in front of the canopy. If a line break or release (deliberate or accidental) was to occur in this situation there is a significant danger of the canopy surging forward and tucking, or of the pilot penduluming backward, or of some other fairly horrible uncontrolled dangerous event occurring - all of which would be even more hazardous if it happened near the ground. Excessive tow tension when towing hang gliders can lead to dangerously steep climb angles which would result in very severe problems if a line break or release was to occur. A weak link prevents excessive tensions ever being applied.

What you REALLY WANT near the ground is a light weak link which will blow before your glider can experience enough tow tension to stand it on its tail.

Quest Air

A good rule of thumb for the optimum strength is one G.

A good rule of thumb for the optimum strength is one G. No freakin' way a glider can stand on its tail if you're using a one G weak link 'cause that's a really good rule of thumb.

TowMeUp.com

Most reliable sources believe that a weaklink should be sized so that it breaks at 75% to 100% of the inflight load.

Oh hell, maybe use 0.75 just to be on the safe side of what most reliable sources believe.

I think I have devised such a link but was wondering if the community had any ideas.

Good idea! See what ideas the community has! Then pick whatever lunatic bullshit best matches your existing understanding of the issue. Whatever it is, you're sure to find something real close.

Cheers

Mario Mohl - 2012/01/29 16:19:22 UTC
Mexico

I'm looking for a weak link which will fail at a low tow force whilst the pilot is near the ground...

This is exactly what will get you hurt, as you have yourself stated in your post !!

No way, dude! Not in the UK! BHPA weak links are only capable of making the tow safer. Read the specs, ferchrisake.

Use a tow assist to help the wing deal with possible speed/force variations. Avoid the stall and let the pilot release when he is at enough altitude.

Another option for testing purposes is to specifically limit either the max force or the max speed, while testing the other.

Wanna specify a G rating? Just kidding.

Nigel Thomas - 2012/01/29 17:23:40 UTC

Cheers Mario and Steve for your comments.

Where are Steve's comments? If Steve is who I think he is - Steve Uzochukwu - stay the hell away from him. The guy's an asshole.

It would seem the weak link idea is a non starter.

My hopes for your long term survival just got a lot better.

I think a better idea is to have a completely separate and independent radio link to the winch, which will have one sole purpose - to shut the winch down. This way, as the pilot experiences and issue, the winch can be stopped on command.

How 'bout having somebody with some common sense who has a clue what he's looking at down there?

This only adds about 120 Euro to the overall cost, so not a big deal.

What would it cost do do something halfway sane instead? You wanna instantly cut tension to zero during the tow? Instead of sending a radio signal to the OTHER end of the towline can you think of some kind of device you could use at YOUR end of the towline which you could use to do the job? And no, an in flight adjustable weak link is not an acceptable answer.

Thanks again for your comments.

Mario Mohl - 2012/01/29 17:36:06 UTC

Nothing against having this but shutting the winch down could be equivalent to a line / link break. The tow assist is still the safer way.

- Wanna specify a minimum line / link rating? Just kidding.

- Any chance whatsoever that he might want / need something equivalent to a line / link break to happen at a time of his choosing while simultaneously wanting / needing both hands on the controls?

I've had line digs happen at low altitude, suddenly the payout turns into a static line, tow assist allows the wing to ride out the yank and the pilot to release at a better time.

That can't POSSIBLY be right.

http://groups.yahoo.com/group/hhpa/message/11119
Question

Henry Wise - 2010/09/16 15:42:30 UTC

As far as the weak link's concerned - it's there for protection in case the winch locks up (been known to happen, all be it rarely).

The weak link is there for protection in case the winch locks up. And there's no freakin' way you could POSSIBLY be in a situation when the winch locks up in which you wouldn't want the weak link to blow instantly.

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Jim Rooney - 2011/08/26 02:44:10 UTC

The "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.

The purpose of a weaklink is to increase the safety of the towing operation. PERIOD. So you bloody well better be ready when it does.

Nigel Thomas - 2012/01/29 19:37:14 UTC

I can close the winch down in a number of ways, shut off, ramped reduction of torque and so on, it's under my control.

I so admire and envy your confidence.

Jiri Stipek - 2012/01/29 21:17:58 UTC
Melbourne

I can see two problems with the in flight adjustable weak link concept:

1) Do you REALLY want the weak link break easily close to the ground? From my experience, this is the most common source of injuries during towing.

Jim Rooney - 2011/08/26 02:44:10 UTC

The "purpose" of a weaklink is to increase the safety of the towing operation. PERIOD.

- Bullshit.

Jim Rooney - 2011/08/31 09:25:57 UTC

"light" weaklink issues?
"I had to land"... boo hoo.
Oh, I thought of an other one... I smashed into the earth after my weaklink let go cuz I fly as badly as I tow, and I'm only still here cuz my weaklink didn't let me pile in harder.

-- It's only possible to get injured as a result of the weak link breaking easily close to the ground if you're a shit pilot.
-- And shit pilots really need the weak link to break easily close to the ground to prevent them from piling in harder.

- I'm having a little trouble understanding why if, in your experience, the most common source of injuries during towing are weak links breaking easily close to the ground, you're not ensuring that people don't use weak links which break easily close to the ground. Seems like a total no brainer of a fix to me.

2) This seems to be a serious deviation from one of the golden rules of aviation (and paragliding especially, I dare to say); KISS. Any added complication is likely to bring more problems than it solves.

Yeah? It seems to me that one hundred percent of the people who adhere to this golden rule of aviation never have done or will do shit to advance aviation a fraction of a millimeter.

Nigel Thomas - 2012/01/30 11:10:46 UTC

Jiri, thanks for your post. I have established this is NOT the way to go - thanks for your input.

Good move, Envy. Shit-can all your ideas and just go with the flow because they MIGHT bring more problems than they solve and you'd be in flagrant violation of one of the golden rules of aviation.

[Tad Eareckson]

http://www.youtube.com/watch?v=OsEie-e4Ljc
Aerotow Quick Link Break on Takeoff
kartingjj - 2012/01/09
dead
0:00 - Aerotow takeoff quick link break
01-0805

0:10 - Line snaps
02-1103

0:17 - Now
11-1609

0:18 - Pull In !
21-1715

0:19 - Maybe land on feet???
23-1823

0:20 - NO, Too much propwash !
27-2211

0:23 - Straight ahead on wheels is dusty, but just fine.
28-2218

29-2315

30-2404

kartingjj - 2012/01/10 19:55

Had a weak link break on takeoff (good training). Immediately stuffed the bar and stayed straight ahead despite a slight crosswind.

Thought I would foot land, but felt the prop wash hit the wing and reverted to a wheel landing with a slide.

Aerotow Quick Link Break on Takeoff

Aerotow Quick Link... Yeah, I like that term for 130 pound Greenspot. That one lasted almost six seconds from the time your cart budged forward. Think what an awesome low level lockout protector that would've been!!! If only you had had a low level lockout. Oh well, sooner or later...

Had a weak link break on takeoff (good training).

Dude!!! Fer sure! And I always fly without wheels and land in narrow dry riverbeds with large rocks strewn all over the place so I'll get really good at landing without wheels in narrow dry riverbeds with large rocks strewn all over the place.

And I'm absolutely POSITIVE that if you keep flying those Aerotow Quick Links that you'll be FANTASTIC at pulling in, sliding in, and rolling to a stop - and maybe replacing downtubes.

And...

Aerotow Incident
http://www.youtube.com/watch?v=vb4nUTAJXTk
Allen Sparks - 2009/11/27
dead

Look how good Sparky is!!! When his Aerotow Quick Link Breaks on Takeoff at just about the same point he hardly uses the wheels AT ALL! (He doesn't really like wheels anyway.

http://www.chgpa.org/forums/viewtopic.php?f=2&t=3173
somewhat predictable accident at Highland

Allen Sparks - 2008/04/19 01:38:55 UTC
Evergreen, Colorado

We don't really have much LZ terrain that is wheel-friendly around here. So I am wheel-less for the time being, until I decide to do something else. I can tell you that it makes me take my landings even more seriously.

There's not much wheel friendly terrain in Colorado (other than the places he actually flies) and he tends to take his landings less seriously when he uses them.)

But hey... Sparky's Aerotow Quick Link lasted about a second longer that yours did so he had somewhat of an unfair advantage over you.

And, really, the way you pulled that one off... That was just beautiful!

Of course you might start finding your thermalling skills starting to suck. Ditto for the other assholes behind you. But, as we all WELL know, in aviation everything's a tradeoff!

http://www.hanggliding.org/viewtopic.php?t=14230
pro tow set-up

Jim Rooney - 2009/11/10 17:19:54 UTC

Ah, back to civil discussion.

(Now that Tad's been kicked off The Jack Show and can no longer gut you little motherfuckers whenever you say anything stunningly moronic - which is just about constantly.)

Something to note about leaving carts....
There is a drastic difference when being pulled by a 582 or a 914/912.

People have a tendency to leave the cart too soon when behind a 582. With the big tugs however, the problem is the opposite. This is especially obvious when you take someone that tows behind 582s and put them behind a 914.

It doesn't sound like a problem at first... more speed is good right? As with all things, yes but .... "to a point". See what happens behind a 914 if you use 582 technique is this....

You accelerate very rapidly of course and gain a lot of speed. I call it leaving the cart at Mach 5. No problem yet (well, there's a small one, but we'll get to that). As you leave the cart, the tug is already a good bit above you, so you ease off the bar pressure (you've got a ton at this point) and this is just about the same time you slam into the prop wash. Your weaklink lets go.

After a couple weaklink breaks in this manner, you start to wonder if Tad's right about these "weak" weaklinks. Nevermind that it's a technique problem not an equipment problem. Nevermind that using a stronglink greatly increases the chances that you will hurt yourself in a very bad way.

See, weaklinks don't care about speed. They care about load. Going Mach5 and easing off the pitch, even a little bit, greatly increases your load... remember that whole bit about windspeed being an exponential factor?

So there you are with in a highly loaded situation, and then you shockload the system by hitting the propwash. Not good.

Your weaklink is doing exactly what it should do.

But ya think there's any way to get these Aerotow Quick Links to hold long enough to give a little more breathing room to set up for standup landings? Ten seconds would probably be all you'd really need.

What's the deal guys?

Are you used to a 582 and just staying on the cart too long behind what obviously must be a 914 and then easing out at Mach 5?

No, that can't be quiet right. Both of you come off the cart after five second rolls and, hell, Sparky's not even holding onto his. And neither of the tugs have left the ground.

Maybe the system is getting shockloaded when you hit the propwash. Yeah, I think that's the problem. I mean on JJ's launch, what with all the dust, you can actually SEE the propwash. And, sure enough, the instant JJ slams into it is the instant his Aerotow Quick Link is shockloaded and does EXACTLY WHAT IT SHOULD DO - EXACTLY as Jim says it will.

http://ozreport.com/forum/viewtopic.php?t=24846
Is this a joke ?

Jim Rooney - 2011/08/25 04:55:25 UTC

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.

Jim Rooney - 2011/08/25 21:40:25 UTC

First, I sent Steve a bunch of info offline. Hopefully it clears things up a bit for him.
Unfortunately, he's stumbled onto some of Tad's old rantings and got suckered in. So most of this was just the same old story of debunking Tad's lunacy... again .

See, the thing is... "we", the people that work at and run aerotow parks, have a long track record.
This stuff isn't new, and has been slowly refined over decades.
We have done quite literally hundreds of thousands of tows.
We know what we're doing.

Yep. When professional pilots like Jim who run the aerotow parks and have long track records tell you how this stuff works you *might* do well to listen. This stuff's pretty irrefutable.

After a couple weaklink breaks in this manner, you might start to wonder if Tad's right about these "weak" weaklinks, but using a stronglink greatly increases the chances that you will hurt yourself in a very bad way. And God only knows what would've happened if you had tried to FLY through that deadly propwash - instead of landing in it.

So if ya wanna get up, I'm afraid I don't have much in the way of ideas.

No wait!!! Here's a thought...

Try flying AROUND the propwash right after you lift off the dolly. Sounds like a plan. Give it a shot and get back to me with how it went.

Assholes.

[deltaman]

Bottom Weaklink load
The load you have with the jerk after an upper wrap don't vary with the glider you fly.
but the bottom wl load (0.97G in 1 point) vary with the glider you fly.
So, different bottom wl have to blow under the same situation.
So with "normal" tension before wrapping, do you have an idea of the range of loads of a jerk (kg) ?

[Tad Eareckson]

The load you have with the jerk after an upper wrap don't vary with the glider you fly.

Yeah, it will.

Everybody's heard this story before, but...

- I once asked Sunny at Ridgely what the tension between their 914 Dragonflies and the gliders was.

- He said he was getting tired of having to tell people he had no idea when they asked that question and asked me to develop something to measure it.

- I developed a Shear Link principle device (which I describe in Mousetraps) which recorded the maximum tension on a tow - which, we found on a normal tow, occurred right at the beginning when the glider was accelerated from a dead stop.

- And I later rigged a hydraulic cylinder and gauge (also described in Mousetraps) so you could observe tension real time.

- I got numbers for my glider - Wills Wing HPAT 158 at my 320 pound flying weight - for normal tow and with the turbocharger kicked in - 125 and 155 pounds respectively.

- But for about two years before those useless goddam bastards kicked me out Sunny could never seem to be bothered to take me up for a short tandem hop to get some numbers - like he asked me to in the first place.

- With those numbers I could've extrapolated using the mass and glide ratios and gotten a good idea what was going on with other gliders, but so much for scientific curiosity within the Flight Park Mafia.

But, anyway, just on theory...

- There's a mass times velocity squared thing going on with a wrap.

- So even if you rigged the experiment between two spacecraft in orbit in the vacuum of space:
-- there'd be a jolt;
-- the more massive ("heavier") the "glider" the greater the jolt; but
-- the speed at which the tug was moving away relative to the glider would be the really big issue.

- Back down in the atmosphere at 2500 feet you've also got major aerodynamic drag issues.

- Between top end release and wrap the tow tension goes from - using my glider - 125 pounds to zero.

- Upon top end release my glider's pitch attitude starts adjusting down but my angle of attack spikes way up (which is another way of saying that my airspeed drops abruptly) and the tug's angle of attack drops abruptly and he accelerates away.

- So when the top end wraps...
-- A more massive (heavier) glider will yield a stronger jolt.
-- And the glider's acting as a drag chute.
-- So the more drag it generates the faster it decelerates and the more of a jolt is yielded.
-- And the jolt will be maximized with a big, low lift to drag ratio glider and minimized with a little high performance glider.

So with "normal" tension before wrapping, do you have an idea of the range of loads of a jerk (kg) ?

No. But...

- With my glider it's gonna be 125 pounds plus A LOT.

- As anybody who's towed about once or more knows, if you blow the release without first accelerating the glider, the degrees of tug acceleration and glider deceleration are dramatic.

- I've had two wraps - predictably due to bridle design issues - under normal tension lined up with the tug just fine. I can't give you kilograms but as you watch the wrap and wait for the jolt that's gonna come a tenth of a second later you wince in anticipation. There's no doubt whatsoever as to what's about to happen to your bottom end weak link.

But let me just reiterate...

Don't expect anything good to happen after a bottom end wrap unless you release instantly thereafter. There's very little mass behind the top end weak link and the glider will very happily react to a vector of the full tow tension applied at that point by nosing down and further minimizing the jolt. And if your primary release actuator doesn't have the desired effect and the tug driver is asleep at the switch the next thing you should be pulling is your parachute deployment bag handle.

[deltaman]

- So when the top end wraps...
(...)
-- So the more drag it generates the faster it decelerates and the more of a jolt is yielded.

I'm ok

-- A more massive (heavier) glider will yield a stronger jolt.

not sure to understand why mass is involved as I thought we were agree to say that a wl have nothing to do with the weight of the pilot+glider.

- Upon top end release my glider's pitch attitude starts adjusting down but my angle of attack spikes way up (which is another way of saying that my airspeed drops abruptly) and the tug's angle of attack drops abruptly and he accelerates away.

and this pitch attitude adjustment prepare the glider to fly faster at the point of re-tension with less drag, reducing the tension of the jolt..

There's no doubt whatsoever as to what's about to happen to your bottom end weak link.

I need to prepare a 2 points bridle system for solo gliders but don't know the load of the main wl the pilots will use..
I thought I don't care if you were right saying with 1G of total flying weight capacity the jolt is enough to blow the secondary wl. All gliders are capable to support hook-in weight around 100kg, so it is 120-130kg minimum as a mawimum weight load. With a bridlelink n°7 (#115kg), I'd like to be sure it will blow after a wrap that occured under a "normal" tension.
(I'm sure pilots won't use more than 115/1.2 for the principal wl.)

Aerotowing teaching
Do you think there is no useful passive security in AT for teaching other than tandem ? cause asking a student to release at the right moment when he is 100% stressed is not a 100% reliable method.. For example a friend, who is a trike teacher told me this story. He teached an aircraft pilot used to manage radio. When he asked him to make a communication during the take off as he was used to do with his own plane he stopped it without realizing he was so focused on his steering..

The idea of a pitch limiter relative to the tow line is attractive and could be helpful for the first flights in calm air. Yes it is not at all suitable when the glider is at low airspeed, below the tug position and want to push to climb but the lock-out is even more feared for a student and probably with more chance to occur...

[Tad Eareckson]

not sure to understand why mass is involved as I thought we were agree to say that a wl have nothing to do with the weight of the pilot+glider.

Tost Flugzeuggerätebau

Weak links protect your aircraft against overloading.

Mass has nothing to do with our decision regarding the strength of our weak link but it's most assuredly a factor in what will break our weak link.

and this pitch attitude adjustment prepare the glider to fly faster at the point of re-tension with less drag, reducing the tension of the jolt..

Not much.

- My free flying glider feels a force of gravity pulling its mass straight down at 320 pounds and trims in pitch accordingly.

- My glider being towed by a Dragonfly feels that vector force pulling straight down plus the tow force vector pulling straight ahead at 125 pounds.

- My towed glider now thinks that Earth has just increased its mass by seven percent and moved forward 21.3 degrees and it speeds up as if it's taken on 23.5 pounds of ballast and pitches up 21.3 degrees to trim.

- When you release the top end of the bridle the tow tension instantly goes to zero and the glider starts dropping its nose to normal pitch and slowing to normal airspeed for as long as it takes for maybe seven feet of bridle to feed through the tow ring as the tug accelerates away.

- When the end of the bridle ties itself to the tow ring there's a very powerful instantaneous jolt. The glider starts to adjust to the jolt by pitching back up and accelerating but the secondary weak link blows before much inertia has been overcome.

- If the secondary weak link (and everything else) held, the glider would adjust during the surge while the tug was decelerating and everything would return to normal tow (except you'd be in one point mode).

And let me emphasize that when we design a two point system for the secondary weak link to blow in the event of a wrap we're not using it primarily as a weak link. We're not using it primarily to protect anything from overload - we're using it to increase the reliability of our release system.

All gliders are capable to support hook-in weight around 100kg...

They're not just capable of supporting a hundred kilograms - they're EASILY capable of supporting it while the glider's pulling out of a loop at three Gs.

I'm sure pilots won't use more than 115/1.2 for the principal wl.

That maximum would keep just about any solo glider over one G with a fair margin but most people could stand to go a good bit higher.

You could use Sevens for the Bridle Links. I'd probably go with Tens as a minimum myself because I like the Strength Stitching at both ends and Ten is as low as you can go and have that - but it's not much of an issue either way.

And if you're making the Primary Bridles as the one you showed in the photos, I don't think you could induce a wrap on a bet anyway.

[deltaman]

The tow line tension IS the drag of the glider (plus a small percentage of its weight). That's why the weight is not a big issue. Right ?

and from that we can emphasize that a glider that want to be towed in 1 point should have enough speed capacity to follow the tug and be sure that its drag at this speed don't generate too much effort to reach the right pitch..

[Tad Eareckson]

The tow line tension IS the drag of the glider...

When the speeds of the two planes are the same and constant - yes.

But in turbulence the tension will be fluctuating and when the needle's on the upswing part of what it's registering is the mass - and thus inertia - of the glider.

...(plus a small percentage of its weight).

If the tug wants to maintain the same climb rate when the glider is more heavily loaded he'll have to fly faster and the glider will be developing more drag holding the angle of attack he needs to stay in position (level with the tug) and there will be more towline tension counteracting the drag.

That's why the weight is not a big issue. Right?

See above. And feel free to go to another source - I'm somewhere near (short of, at, beyond) the limit of my understanding of the issues.

and from that we can emphasize that a glider that want to be towed in 1 point should have enough speed capacity to follow the tug and be sure that its drag at this speed don't generate too much effort to reach the right pitch..

Same glider, same rate of climb, heavier pilot (or more ballast).

More tension, more out of position (pulled through the control frame) the pilot, more muscle needed to hold the glider level with the tug, less ability to exploit the glider's upper speed range.