Weak links

[Tad Eareckson]

http://ozreport.com/forum/viewtopic.php?t=24096
Leakey, Tx and Pack Saddle video clip of flight

Al Hernandez - 2011/06/25 06:01:41 UTC

Martin and I, arrived at Leakey at 10:45 am, the sky was a blue color, with few disappearing clouds in the area, winds 8mph to 14mph and not too much lift on Friday. Our intentions were to have fun on the Leakey payout winch and give it a test run and to our surprise the winch worked as we expected to. As we arrived Sam Kellner was the first up climbed to about 800 ft, flew around for a bit and came in and land it... Another pilot went up on a Genesis Pac Air Glider and had an okay flight, came in for a wheel landing on the grass.

Martin Apopot on his first flight got up to about 700 ft sled run, flying a falcon 145 single surface glider, good flight & safe landing.

Martin A. had two 800 ft sled runs after that.

On one of his not counted flight, Martin broke a weaklink at low altitude, causing an 80 ft free flight on his glider, the right wing was up, and flew way off to the right side of the runway, the glider flew over the airport fence, over the trees and house, for a little while, He managed to get his Falcon in control and landed safely back on runway... WHAT A RUSH ! what can I say S#it Happens.

We said good bye to Sam and the crew and Martin and I, headed out to Pack Saddle...

Continued at:
http://www.kitestrings.org/post464.html#p464

[Tad Eareckson]

DHV - 1999/02/23

Airworthiness advisory

Towing winch Wesselmann II DHV 05-0006-92

For several winch tows of the type Wesselmann II, when measuring the pulling force in line feed operation (strong wind, gusts), a considerable overstepping of the permitted regulating values was identified. This led to uncontrolled failure of the weak links in the line and in one case to pilot injury.

In agreement with the holder of the type certification Ingo Rohardt, Banzgraben 35, 22459 Hamburg, Tel: +49 (0)40 5521270 the DHV has decided on the following safety measures:

All winch tows of the model type Wesselmann II must have the pulling force regulating system modified by the holder of the type certification.

This airworthiness instruction came into force when published in the News for Paragliders and Hang Gliders (NfGH). The safety measure must be carried out before the next periodic maintenance check.

Gmund, 23. February 1999

Martin Jursa, DHV/OeAeC Technical Dept.

Oh perish the thought that anyone should be permitted to considerably overstep the values you're permitting.
So:
- were any of the gliders having any problems BEFORE the weak links blew? If so, it seems a bit odd that nobody was releasing.
- the pilot wouldn't have been injured if the weak link hadn't blown.
- was the real problem that the winch was holding too much tension - or that your stupid weak links weren't holding enough?

[Tad Eareckson]

Dave Broyles - 1990/11

I talked to a lot of pilots at Hobbs, and the consensus was that in the course of Eric Aasletten's accident, had a weak link break occurred instead of the manual or auto release that apparently did occur, the outcome would have been the same. Under the circumstances the one thing that would have given Eric a fighting chance to survive was to have remained on the towline. The pilot must always take full responsibility for his own safety.

The weak link breaking strength should be between 100% and 150% of the combined weight of the glider and pilot (the gross load) being towed, but each pilot should be totally responsible for his own weak link.

- It's absolute bullshit that a towed pilot is FULLY responsible for his own safety. The driver is responsible for providing and regulating tension providing and making sure that everything from the tow ring forward - line, front end weak link, winch, truck, tug, engine, fuel, oil, gauges, tires - are capable of delivering it properly and reliably.

HOWEVER...

- Despite what assholes like Jim Rooney "think", and get away with dictating...

And yes, get behind me with a "strong link" and I will not tow you.

...and doing...

Whatever's going on back there, I can fix it by giving you the rope.

...many aspects of the tow ACTUALLY *ARE* the pilot's FULL and SOLE responsibility:
- staying in position when he can
- releasing when he can't, must, wants
- using - as Dave says - a safe weak link

Despite the kind of rot written by assholes like Pagen and Bryden...

In the case of lockouts or turbulence, the weak link breaks as designed and should not be increased in strength.

...weak links that break in lockouts and turbulence are DANGEROUS.

http://ozreport.com/9.011
2005 Worlds

Davis Straub - 2005/01/13

Tom Lanning had four launches, and two broken weaklinks and a broken base tube. He made it just outside the start circle.

(A weak link that will break in a survivable stage of a lockout will also break in turbulence and you can die BECAUSE a weak link breaks in turbulence.)

Recognizing but throwing out of the equation the statistically insignificant freak exceptions to the rule...

A safe and competent pilot ALWAYS flies with but NEVER throws (or loses from his container) a safe, mass appropriate parachute.

Likewise...

A safe and competent pilot ALWAYS flies with but NEVER blows a safe, mass appropriate weak link.

But we allow evil total douchebags...

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:

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.

...who don't stand a snowball's chance in hell of ever understanding what a weak link is to MANDATE dangerous, mass inappropriate weak links (and recommend installing them where they can be taken out of the equation altogether).

Additionally...

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

Davis Straub - 2005/02/09 06:13:39 UTC

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. Otherwise you'll have "strong links."

...evil total douchebags REWARD dangerous and incompetent diver drivers for using dangerous weak links by moving them to the front of the line and giving them "free" tows - at the expense of the dollars and soaring window opportunities of safe and competent pilots - and...

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.

...FURTHER PUNISH safe and competent pilots by moving them to the back of the line.

So here are a set of recommended rules for running a fair, safe, competent, and efficient aerotow operation...
---
- All gliders must be protected by a weak link which will fail at a towline tension equivalent to from 1.3 to 2.0 times the maximum certified flying weight.

- A table of gliders and appropriate weak links is available at launch.

- The flight park will provide free string material and free use of Tost weak links such that all glider models and sizes will be covered.

- Gliders flying two point must have appropriate weak links above and below the tow ring or use a Tost weak link at the end of the towline.

- Any glider who blows a weak link for any reason at any altitude will be charged for the tow, assessed a fine of thirty dollars, and wait for the line to clear of all other gliders - including relights. (Yes, even if you lock out violently, you can still easily beat the weak link.)

- If the tug blows the weak link the glider will be entitled to five free tows or a hundred dollar refund - at the sole discretion of the glider.
---
Ends of weak link problems, issues, discussions.

[Tad Eareckson]

Associated Press - 2011/07/17
Hollywood, Maryland

Maryland State Police are identifying a man killed when a glider crashed into trees near Saint Mary's County Regional Airport in southern Maryland.

Police announced Sunday that 55-year-old James Michael Dayton of Mechanicsville was killed Friday when the glider he was riding in crashed into trees near the airport in Hollywood.

Authorities say the pilot was 53-year-old Nicholas John Mirales of Prince Frederick. Mirales was in critical condition when he was flown from the crash scene.

A National Transportation Safety Board spokesman says the Slingsby 49B glider crashed shortly after takeoff when it became disconnected from its towing plane. The NTSB is expected to release a preliminary report of the accident within ten days of the crash.

But don't worry kids. Hang gliders aren't ANYTHING like SAILPLANES. Blowing the weak link on a hang glider is always a GOOD thing!

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.

Jim Rooney - 2007/07/19 14:50:52 UTC

And yes, get behind me with a "strong link" and I will not tow you.

And, of course...

Jim Rooney - 2007/08/01 13:47:23 UTC

Whatever's going on back there, I can fix it by giving you the rope.

Towing Aloft - 1998/01

Pro Tip: Always thank the tug pilot for intentionally releasing you, even if you feel you could have ridden it out. He should be given a vote of confidence that he made a good decision in the interest of your safety.

Always thank the asshole on the Dragonfly for intentionally releasing you, even if you feel you could have ridden it out. He should be given a vote of confidence that he made a good decision in the interest of your safety - even if he's already oozing with toxic levels of confidence while you're lying on the runway in a crumpled heap of what used to be your glider.

38°18'55.55" N 076°33'02.02" W

[deltaman]

Hang Gliding Competition - Flytec 2010
http://www.youtube.com/watch?v=pVeuqk6mQjk#t=2m6s
deltaplane sully-sur-loire video1.mp4
http://www.youtube.com/watch?v=4wK5QXoR7jI#t=6m20s (no wheels)
deltaplane sully sur loire video2
http://www.youtube.com/watch?v=1_DJ8c8kqOw#t=1m13s (no VG, Greenspot 130lb on 1 point bridle)
http://www.youtube.com/watch?v=1_DJ8c8kqOw#t=2m9s (80kg wl on the line)
http://www.youtube.com/watch?v=1_DJ8c8kqOw#t=3m20s (80kg wl on 1 point bridle, heavy pilot)
http://www.youtube.com/watch?v=1_DJ8c8kqOw#t=9m3s (break (old) rope (not a stretch one))
deltaplane sully sur loire video3
http://www.youtube.com/watch?v=-dg3UqSOGNg#t=5m14s (Greenspot 130lb on 1 point bridle, dolly take off with no help)

2:06
http://www.youtube.com/watch?v=pVeuqk6mQjk

6:20
http://www.youtube.com/watch?v=4wK5QXoR7jI

1:13 - 2:09 - 3:20 - 9:03
http://www.youtube.com/watch?v=1_DJ8c8kqOw

5:14
http://www.youtube.com/watch?v=-dg3UqSOGNg

[Tad Eareckson]

C'mon Antoine, post us one where the weak link DOESN'T blow at takeoff.

[deltaman]

WL & BEING DRAGGED

A weak link should break quickly in the event the glider impacts the ground to prevent further injury by being dragged by the tow vehicle.

Tad
This is a job for a release - not a weak link.
AND
On a grass strip you are WAY better off if your weak link holds and you are dragged than you are if your weak link breaks and your glider comes to a sudden stop.

It's hard to accept that.. How much tension we will need to drag a pilot and its glider on an AT strip ? With a 1.5G of maximum glider loading, how far the pilot will be dragged before the wl blows if the tug don't stop ?..
I understood the sudden stop but..

WL & WEIGHT
Please,
can you explain me how the weight (G) which is a vertical force is important to consider wl as the forces which are applyed on it are more "horizontal" with the force from the tug and on the other way the drag of the pilot+glider ?

[Tad Eareckson]

How much tension we will need to drag a pilot and its glider on an AT strip ?

There's no way to predict that. Nose up or down, soft versus hard ground, round versus faired basetube, wheels, type of wheels, weight of pilot and glider, how much of the pilot is on the ground...

With a 1.5G of maximum glider loading, how far the pilot will be dragged before the wl blows if the tug don't stop ?

If the glider does a power whack, à la Davis:

http://ozreport.com/pub/fingerlakesaccident.shtml

http://ozreport.com/pub/images/fingerlakesaccident2.jpg
http://ozreport.com/pub/images/fingerlakesaccident3.jpg


it's a pretty good bet that SOMETHING's going to break and the glider's going to stop immediately and stay stopped.

But if the nose stays up or doesn't dig in you could get dragged for a very long time. For me a 0.8 G weak link would be around 256 pounds which is about twice normal tow tension behind a 914 Dragonfly and I'm sure that's more than enough to drag me under many circumstances.

can you explain me how the weight (G) which is a vertical force is important to consider wl as the forces which are applyed on it are more "horizontal" with the force from the tug and on the other way the drag of the pilot+glider ?

- Yes, WEIGHT is a force which is force always pointing straight down.

- And ALL aircraft are designed to support their own weight plus that of whatever else is inside (or hanging from) them - (fuel, pilots, passengers, bombs, marijuana, all of the above...) - and pull hard turns and punch through turbulence without breaking apart.

- But once the plane is off the ground it can become difficult or impossible for it - or you - to tell which way down is without a horizon (real or artificial) to reference and tell how much things "weigh". The plane and you can become weightless or so heavy the blood can't stay in your brain and you black out. You can be upside down at the top of a loop, weighing what you normally do, and feeling that straight up is straight down.

- So, once airborne a G is only the same as weight with the plane in level flight at a constant speed and altitude.

- When I'm being towed up by a Dragonfly my glider and I are feeling the 320 pound force of gravity pulling straight down and the 125 pound tow tension pulling straight ahead.

- Draw a rectangle with 320 millimeter sides and a 125 millimeter top and bottom. If you're towing from left to right draw a diagonal from the upper left to lower right corner. If you measure it or do the math we feel like we weigh 343.5 pounds and are being pulled down 21.3 degrees forward of real down.

- So assuming I was at maximum hook-in weight for that glider I'm now 23.5 pounds over or pulling 1.07 Gs. Big Freaking Deal - I can go up to at least six.

- And if I'm a hundred pounds under maximum hook-in weight I can beef up my weak link an extra hundred pounds without the glider knowing or caring the difference.

- NOBODY ever needs to blow a weak link when he's pointed at the tug. If the force suddenly gets real high the glider will immediately dissipate the excess by accelerating and climbing. (Climbing too fast relative to the tug could become problematic in the near future but it's not an immediate problem. (And if it does you really don't want a weak link or Jim Rooney to help you solve it.))

- However... If you're turning away from the tug and using a Lookout "Release" the tow force can build up quickly and you're also pulling Gs from the turn so the glider can be feeling possibly three or more Gs with a one and a half G weak link and thinking that down is mostly where the tug is. THAT'S a good time for a weak link break - if you're high you're glider will stay together and allow you to recover and if not it won't make any difference - except to the tug.

- What Steve Kinsley and the folk at Dynamic Flight...

http://www.dynamicflight.com.au/WeakLinks.html

...understand that the morons you usually find flying tugs and gliders don't is that in situation in which a Matt Taber victim is rolling away from the tug the forces are building up so fast that a loop of 130 pound Greenspot is only going to blow you off tow a millisecond faster than a 1.5 G weak link will.

Summary...

In a situation in which a weak link NEEDS to blow (which you should have released from a long time ago) all bets regarding weight and which way is down are off.

[deltaman]

In a situation in which a weak link NEEDS to blow (which you should have released from a long time ago) all bets regarding weight and which way is down are off.

really good..
So that's why you don't consider the weight of the pilot but only the breaking load of each glider

is there an easy way to demonstrate this ?:

If you're turning away from the tug and using a Lookout "Release" the tow force can build up quickly and you're also pulling Gs from the turn so the glider can be feeling possibly three or more Gs with a one and a half G weak link and thinking that down is mostly where the tug is

If you don't participate to the turn (without cadence it) to blow the wl, will it really blow 1 ms after the 130lb ?

If i've got a 200kg wl and have a lockout, I can have the tight towline perpendicular to my round basebar, steel or carbon speedbar.. Which force is needed from my basebar to break the wl ? It looks like the same distribution as V-bridle ?.. Is there a risk for my basebar to be broken ?

Thanks

[Tad Eareckson]

is there an easy way to demonstrate this ?:

Most of these things can be thought through and illustrated with vector diagrams a lot more easily (and - often - safely) than they can be demonstrated.
- A glider (or any plane) banked sixty degrees in a coordinated turn is pulling two Gs.
- Add the towline tension which is limited by a one and a half G weak link.

...will it really blow 1 ms after the 130lb ?

No, I made that up. But the point is that if you're locking out AND turning rapidly away from the tug the load will be building up very quickly and the difference between your situations at light versus heavy weak link failure probably won't be terribly significant, possibly not even detectable by a pilot or observer.

http://www.chgpa.org/forums/viewtopic.php?f=2&t=3648
Oh no! more on weak links

Carlos Weill - 2008/11/30 19:24:09 UTC

I tried to release but my body was off centered and could not reach the release. I kept trying and was close to 90 deg. All these happen very quickly, as anyone that has experienced a lock out would tell you. I heard a snap, and then just like the sound of a WWII plane just shut down hurdling to the ground, only the ball of fire was missing. The tug weak link broke off at 1000ft, in less than a second the glider was at 500ft.

- Carlos is flying a Quallaby release which, naturally, he can't get to when it matters.

- He's using a loop of 130 pound Greenspot (on the end of his two point bridle). He's small so let's be REAL generous and call this one G.

- But the goddam Dragonfly weak link STILL blows first so we know that he blew off in the course of a rapidly progressing SEVERE lockout at LESS THAN 130 pound Greenspot.

- If this happens at 450 feet he's dead.

- If this happens at 450 feet with an extra half G of weak link (120 additional pounds of towline tension) how much deader is he gonna be?

- In the lockout how much more time and roll will it take to put another 120 pounds of tension on the line?

(And note that you can be locking out and NOT turning rapidly away from the tug - in which case the weak link is very unlikely to do anything to help you get off tow (which is one reason we fly with releases).)

If i've got a 200kg wl and have a lockout, I can have the tight towline perpendicular to my round basebar, steel or carbon speedbar.. Which force is needed from my basebar to break the wl ? It looks like the same distribution as V-bridle ?.. Is there a risk for my basebar to be broken ?

- I'm still waiting to hear of an aerotow lockout in which anything besides the pilot's hands comes in contact with any part (tubes, wires) of the glider.

- And even if a heavily loaded line (tow or bridle) came in contact with the basetube it would be impossible to break it - or even bend it beyond what it would do when you pull back on it.

- The basetube likewise will have zero effect on the failure of the weak link. What WILL blow the weak link will be the lift generated by the glider.

- What WOULD happen to you is what happened to Shane Smith six months ago. The bar would be pulled back and the glider would pitch down or - depending upon how badly you were rolled - sideways.

It's good to think about all these worst case scenarios but I wouldn't worry about them overly much because:
- In real life they don't happen. We've got better stuff to give us nightmares.
- If they happen:
-- up high they probably won't matter much
-- down low you're gonna be dead in two to three seconds anyway so it doesn't really matter

Focus on not getting into worst case tow scenarios because a lot of them you won't be able to survive any better (or worse) than you can worst case free flight scenarios (which you should also focus on not getting into).