Weak links

[Steve Davy]

http://ozreport.com/16.006
Forbes Flatlands - day three wrangles

Davis Straub - 2012/01/08 01:25:48 UTC

Spoke briefly with Scott Barrett, the winner of day 2, on the launch situation. Seems that he got let off down wind in zero sink, when we were pretty clear that the tug pilots were required to tow everyone to 2,000' (maximum), upwind (north) of the launch area within 2 KM of the launch area. He landed, went to the back of the line, and then had to struggle with other pilots moving in front of him claiming weak link breaks, when perhaps that was not the full truth.

Scott was towed up again to over a dust devil and the line went slack at 300'. He was able to climb out from there, but now was late and started the race after 3 PM (the last start time), at 1000' AGL. He still made goal.

The issue of weak link breaks was discussed in a small committee today. The point is that pilots who have weak link breaks are slotted in behind the first four pilots (those on the dollies). If you just land for other reasons, you go to the end of the line. As there is not a good way for the launch crew to know who actually had a real weak link break, a new system will proposed tomorrow.

If you get off below 1,000' AGL for any reason you will be slotted in behind the sixth pilot after you land. Above that, you'll go to the end of the line. If you say that you got off at less than 1,000' AGL, get slotted in, and then when your track log is examined and it is found that you were above 1,000' AGL, you will receive a 30% penalty. Or perhaps another penalty like having to launch last (or is it first?).

[Zack C]

Lockout, tug (only) weak link blows, bridle wraps on the tow ring. Now NONE of the releases in the system is protected from overload.

Good point, I hadn't considered that, and I should have given how much we've discussed this stuff.

Bobby Bailey - who has no clue as to what a weak link is - built a light breakaway into the tow mast because he felt that Dragonfly drivers too stupid to put a weak link on their end of the towline deserved to live.

Of course, Dragonflies have built-in weak links...

Zack

[Tad Eareckson]

The issue of weak link breaks was discussed in a small committee today.

- Hey Bob, you listening? This is EXACTLY the sort of small committee you could really use on your Training Manual Team! Think how BEAUTIFULLY they'd get along with everyone else and how quickly they'd be willing to compromise.

Maybe you could have specialized divisions on your Training Manual Team.

- 130 Pound Greenspot Division...
-- optimal position for 130 pound Greenspotters to cut back in line
-- best wheels, gloves, helmets to use with 130 pound Greenspot
-- how to:
--- best land back on the cart when your 130 pound Greenspot blows the instant you lift off from it
--- minimize damage and injury when 130 pound Greenspot blows ten feet off the cart
--- most quickly replace a VG side downtube when 130 pound Greenspot blows ten feet off the cart
--- stay hydrated while carrying your glider back the length of the runway when your 130 pound Greenspot blows at a hundred feet
--- best hook a thermal when your 130 pound Greenspot blows at two hundred feet
-- best times of day to avoid the thermal turbulence which results in dangerous 130 pound Greenspot failure
-- how to:
--- identify the extent of wear on 130 pound Greenspot which makes it dangerously understrength
--- tie and install 130 pound Greenspot such that the knot is eliminated from the equation and your towline is maxed to 520 pounds
-- why 130 pound Greenspot:
--- simply works well and relatively predictably for the enormous range of conditions and applications in towing
--- works a hell of a lot better than all the other bullshit Jim Rooney has seen out there
-- how to best pitch up and roll the glider in a lockout to utilize 130 pound Greenspot as an instant hands free release
-- the best strength of 130 pound Greenspot to use for a:
--- 200 pound glider
--- 350 pound glider
-- how much altitude is typically required for recovery after 130 pound Greenspot has increased the safety of the towing operation - PERIOD - or your tug driver has fixed whatever was going on back there by making a good decision in the interest of your safety and giving you the rope
-- why:
--- anything stronger than a single loop of 130 pound Greenspot makes the tug driver's job insanely dangerous - unless he's towing a tandem
--- it's simply not reasonable to expect the tug driver to keep his weak link strong enough to hold beyond the point at which your 130 pound Greenspot blows
--- premature releases and towline failures are extremely dangerous but 130 pound Greenspot failures only increase the safety of the towing operation - PERIOD
--- anyone who discusses aerotow weak links in terms of Gs is a dangerous nut case who needs to be ridiculed and ostracized
- Aerotow Release Division...
-- how to:
--- fight a lockout with one hand while reaching for your release with the other
--- how to climb up the basetube to get to your release lever on the right downtube after you've locked out to the left
-- how many times you should hit your lever or pull your loop before going to your backup release
-- why it's physically impossible for the bottom end of a two point bridle to tie itself to a tow ring
-- how to grasp the downtube while squeezing the lever to ensure that the lever mounting doesn't spin outboard on the release lever
-- the unforeseeable dangers of complex release mechanisms
-- ten reasons why straight pin mechanisms are unacceptably dangerous
-- how to best grasp a Bailey Release barrel to pry it open when it's maxing out a loop of 130 pound Greenspot.
-- why:
--- one point bridles must be an absolute minimum of two feet in length
--- you should NEVER - under ANY circumstances - launch with a release actuator in your teeth the way all the Russians do
- Hang Check Division...
-- why it's critical that you remember to buckle your chin strap while doing a hang check
-- how to:
--- remember to do another hang check after you've unhooked to get your cell phone
--- pull yourself up into the control frame after launching unhooked
--- fly the glider while standing in the control from after launching unhooked
--- hang from the basetube with one hand and throw your parachute with the other after launching unhooked and discovering that pulling yourself up into the control frame isn't anywhere near as easy as you thought it would be
--- fly the glider with your elbows pressed to your sides after you've launched without your leg loops
--- best execute a standup landing after launching without your leg loops
-- the twenty reasons it's unacceptably dangerous to allow your suspension to go tight during and/or five to ten minutes before launch
-- why it's critical that everyone on launch crew remains totally focused at all times on cycles at the front of the ramp

- Notice that Rohan Holtkamp's name is appearing on the lists of finishers?

Rohan is half of Dynamic Flight. That's Dynamic Flight as in:
http://www.dynamicflight.com.au/WeakLinks.html
Notice that Rohan isn't doing shit to address this insane 130 pound Greenspot issue that's continuing unabated into a third decade now.

[Tad Eareckson]

Of course, Dragonflies have built-in weak links...

So Bobby made the tow mast a weak link 'cause the more non essential things you have breaking at and beyond the back end of the Dragonfly the safer it is for its driver...

http://ozreport.com/5.126
Flytec Dragonfly

USAFlytec - 2001/07/14

Steve Kroop - Russell Brown - Bob Lane - Jim Prahl - Campbell Bowen

The tail section of the Dragonfly is designed so that it can accept in-line as well as lateral loads. Furthermore the mast extension, which is part of the tow system, is designed to break away in the event of excessive in-line or lateral loads. The force required to cause a breakaway is roughly equivalent to the force required to break the double weaklink used on the tail bridle. More simply put, the mast would break away long before any structural damage to the aircraft would occur.

...and who gives a rat's ass about the glider.

And then these morons...

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

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

On the tow plane we use 1-1/2 loops (3 strands) of 130# line. The weak link is placed in the top of a V-bridal which would yield a maximum nominal towline tension of around 780#. However, due to the fact the knots (two are required since there are three strands) are not "buried" the maximum towline tension is greatly reduced. I do not know the exact tow line tension required to break this weak link but the value is somewhat moot since the weak link is not too strong so as to cause any damage to the tow plane and it is not too weak to leave the glider pilot with the towline.

...decided that they needed the weak link, not to protect the tug, but to protect the breakaway deliberately built in to be the same strength as the weak link they had carefully determined was the perfect rating for tandem gliders (without, of course, a freaking clue as to its actual breaking strength) and thus guaranteed that damn near all solo gliders flying sane weak links and all tandem gliders PERIOD would end up with the rope.

So you're NEVER gonna hear about a tow mast snapping off.

If the tow mast DID snap off I'd GUESS that you'd be very unlikely to get a wrap, something ugly would happen when the tow mast got to the tow ring, and one way or another you'd be clear of the towline. But since tow masts - for all intents and purposes - DON'T blow before the triple strand (and the triple strand, in fact, frequently blows before the double strand on the solo glider)...

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!

No, Dragonflies DON'T have built in weak links.
And given Towing Aloft's publication date that was UNDOUBTEDLY a four strander.

[Zack C]

If the tow mast DID snap off I'd GUESS that you'd be very unlikely to get a wrap, something ugly would happen when the tow mast got to the tow ring, and one way or another you'd be clear of the towline. But since tow masts - for all intents and purposes - DON'T blow before the triple strand (and the triple strand, in fact, frequently blows before the double strand on the solo glider)...

I'm pretty confused at this point, but I've never really examined the bridle connection or release of a Dragonfly. I assumed the tow mast was the thing sticking up above the rudder the top end of the bridle attaches to, with the other end of the bridle attaching to the release (via the weak link). Thus, if the weak link/release end of the bridle wrapped at the tow ring, the mast would see the full tow tension and would break before either plane was in danger of a structural failure. I figured the tow plane in the Towing Aloft scenario must not have been a Dragonfly, but of course, trikes don't have bridles so it pretty much has to be one.

What am I missing?

Zack

[Tad Eareckson]

- Yeah, the tow mast extends above the rudder to a height which puts the bridle apex / tow ring on the thrust line.

- But I've NEVER seen a weak link on a Dragonfly any place other than above the tow ring. Usually it's at a clip at the top of the tow mast (Towing Aloft drawing, Page 291) but Ridgely figured out that it was easier to replace the weak link (usually after a glider flew away with the towline) if they put a couple of feet of bridle extension on the clip.

- Yeah, IF you fixed the bridle to the top of the tow mast and engaged the bottom end of the bridle to the Schweizer type release below the rudder with a weak link you WOULD be weak link protected at all times but you'd get your nose jerked up if you got a wrap and the tow mast held - and that's not an unimaginable scenario by any means.

The smart thing to do would be to put a 350 pound weak link on the bottom and a 300 on the top - but that ain't never gonna happen.

[Zack C]

Thanks, that clarified a lot, but I don't see why if the mast broke you'd be clear of the line. Seems like the big chunk of metal would fail to clear the tow ring and the planes would remain connected with all the tension directed to the tug's release.

The smart thing to do would be to put a 350 pound weak link on the bottom and a 300 on the top - but that ain't never gonna happen.

Isn't the tow mast going to break well before the 300 lb top weak link (going by it breaking around the same tension as four strands of Greenspot, which is ~200 lbs)?

Zack

[Tad Eareckson]

Seems like the big chunk of metal would fail to clear the tow ring and the planes would remain connected with all the tension directed to the tug's release.

- I think the chances are really good it's gonna clear - definitely not smoothly but it's just a stick being pulled by one end and the tow ring diameter is WAY more than adequate.

- Those bridles are REALLY LONG. And there's a helluva lot of acceleration of the tug and helluva lot of deceleration of the glider on a release and ten times as much upon a weak link - or tow mast - failure. The jolt would be horrendous. Something's gonna blow.

Isn't the tow mast going to break well before the 300 lb top weak link (going by it breaking around the same tension as four strands of Greenspot, which is ~200 lbs)?

Yes. And when they get tired of snapping tow masts they'll beef them up to do the job adequately. (They actually won't of course - but that's the dream anyway.)

[Tad Eareckson]

Lauren Tjaden - 2005/01/11 00:33:44 UTC

I took the day off from riding and headed to Quest early with Paul. Jim Rooney stayed up early in lift he reported as "everywhere", but by the time we managed to launch conditions had deteriorated.

Paul flew first, and then a pilot trying Ron's rigid wing. I was next.

But I got complacent. The string was too long on my launch dolly, and I paid no attention to it. When I launched, I never did get pressure on my fingers indicating that I should let go of the rope.

And, of course, there was absolutely no freakin' way you could've sensed that you had twice as much airspeed as you really needed to get safely airborne.

Question: When you're launching out of the slot at Woodstock and don't have a dolly hold-down through which to feel tension, how do you know when to ease out on the bar?

I finally realized that I had been on the cart forever and released. Bad news. Rocketed straight up.

Who'da thunk.

My weak link broke like a defendant in a Perry Mason trial, and I plummeted to the ground in an ugly fashion.

Pretty ugly, huh? What was the breaking strength of that weak link and at how many Gs did it put you? Just kidding.

Thankfully didn't break Griffin or hurt myself.

Pretty lucky, huh?

http://groups.yahoo.com/group/TTTFlymail/message/11545
Cart stuck incidents

Keith Skiles - 2011/06/02 19:50:13 UTC

I witnessed the one at Lookout. It was pretty ugly. Low angle of attack, too much speed and flew off the cart like a rocket until the weak link broke, she stalled and it turned back towards the ground.

Any possibility you can detect a PATTERN here, Lauren? Just kidding.

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

Jim Rooney - 2011/09/02 19:41:27 UTC

Please note that the weaklink *saved* her ass. She still piled into the earth despite the weaklink helping her... for the same reason it had to help... lack of towing ability. She sat on the cart, like so many people insist on doing, and took to the air at Mach 5.

Did your dear friend explain to you how - because of your lack of towing ability, insistence on sitting on the cart, and Mach 5 takeoff - it was necessary for your weak link to *save* your ass by piling you and Griffin into the earth in an ugly fashion?

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

Paul Tjaden - 2011/07/30 15:33:54 UTC

Quest Air has been involved in perfecting aerotowing for nearly twenty years...

Yeah Paul, sure ya have. It's actually incredible to see just how far you and your colleagues and predecessors have come since the early Nineties when nobody had a clue what the fuck he was doing or talking about.

P.S. Damn. I messed up on the click and missed posting that response seven years to the second later by a second.

[Tad Eareckson]

I think the chances are really good it's gonna clear - definitely not smoothly but it's just a stick being pulled by one end and the tow ring diameter is WAY more than adequate.

On further consideration...

The chances are about zero it's gonna clear.

It would if it were being pulled slowly but it's not gonna be being pulled slowly. It won't be lined up anything close to properly when it gets to the ring and the effect will be like hitting - or catching on - a brick wall at twice the separation speed of the two planes. The weak link WILL blow.