Surface towing for teaching

[Steve Davy]

Technical properties of synthetic fibres:
http://www.barry.ca/publication/rt-technical-properties-of-synthetic-fibres-oct-08.pdf

Animated knots - ropes overview:
http://www.animatedknots.com/rope1.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

Animated knots - ropes materials:
http://www.animatedknots.com/rope2.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

Animated knots - ropes properties:
http://www.animatedknots.com/rope3.php?LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

[Steve Davy]

Polyethylene lines such as Spectra and Dyneema are reported to have very low coefficient of friction, and knots tend to slip because of this.

I'm wondering if Polyethylene would be just the ticket for a four-string release.

[Tad Eareckson]

Why don't you consult with some of the few people...

http://ozreport.com/forum/viewtopic.php?t=31052
Poll on weaklinks

Jim Rooney - 2013/03/03 19:37:19 UTC

My response is short because I've been saying it for years... and yes, I'm a bit sick of it.
This is a very old horse and has been beaten to death time and time again... by a very vocal minority.

See, most people are happy with how we do things. This isn't an issue for them. They just come out and fly. Thing's aren't perfect, but that's life... and life ain't perfect. You do what you can with what you've got and you move on.

But then there's a crowd that "knows better". To them, we're all morons that can't see "the truth".
(Holy god, the names I've been called.)

I have little time for these people.

It saddens me to know that the rantings of the fanatic fringe mask the few people who are actually working on things. The fanaticism makes it extremely hard to have a conversation about these things as they always degrade into arguments. So I save the actual conversations for when I'm talking with people in person.

A fun saying that I picked up... Some people listen with the intent of understanding. Others with the intent of responding.
I like that.

...who are actually working on things? You could find out the best way to address your issues and I could find out who they are and the projected date of the next release release. (Should be any day now - the last one was about 22 years ago.)

But seriously folks...

It's a double edged sword.

Both the friction and stiffness of the material are freakin' HUGE factors in stepping:
- down the load transmitted to the release pin
- up the minimum actuation tension

Lower the coefficient of friction you'll need to add a loop to achieve the same load to actuation ratio and you'll end up with a similar required minimum actuation tension.

I'd say use whatever you feel like as long as it's:
- low stretch
- UV resistant

And make sure that the min required tension isn't something that will contribute significantly to the severity of a lockout headache.

[Steve Davy]

I talked with Pat about Lin's little adventure and what's been done to avoid a repeat.

When asked if a guillotine had been installed he expressed that he didn't like/trust the added complexity. And that his fix was to go with a two string that can't be configured incorrectly.

He has gone to a two string and added that it now has a stainless pin (rather than a plastic coated cable) engaging a spectra line loop. Said he tested it at 370lbs and estimated the pull to actuate at 15lbs.

About the auto release basically he just doesn't trust folks he's towing to release in a lockout or if the winch "runs out of gas" and the towline gets pulled back due to the retrieval line. He also told me that Rob McKenzie gave him the idea of using an auto release.

PS Pat uses a Koch two stage himself.

[Tad Eareckson]

I talked with Pat about Lin's little adventure and what's been done to avoid a repeat.

Ban GoPro cameras?

When asked if a guillotine had been installed he expressed that he didn't like/trust the added complexity.

Simplicity good! Complexity BAD! A guillotine might work when you don't want it to or not work when you do want it to. Then where would you be? Much better to run around asking if anyone has a Swiss army knife while your student works on getting his parachute out of the container.

And that his fix was to go with a two string that can't be configured incorrectly.

Much simpler and cheaper than implementing a prelaunch check procedure policy.

He has gone to a two string and added that it now has a stainless pin (rather than a plastic coated cable) engaging a spectra line loop. Said he tested it at 370lbs and estimated the pull to actuate at 15lbs.

What was the glider doing while he was pulling it?

About the auto release basically he just doesn't trust folks he's towing to release in a lockout or if the winch "runs out of gas" and the towline gets pulled back due to the retrieval line.

- None of the...

http://ozreport.com/forum/viewtopic.php?t=31052
Poll on weaklinks

Jim Rooney - 2013/03/05 01:32:20 UTC

Btw, it's nothing to do with you "counting" on the weaklink breaking... Its about me not trusting you to hit the release.
If it were only about what you want, then you could use what you like.
You want the strongest weaklink you can have.
I want you to have the weakest one practical.. I don't care how much it inconveniences you.
I don't trust you as a rule. You Trust you , but I don't and shouldn't.

...really excellent instructors and drivers trust the people they're towing to release at the proper time in an emergency situation...

Joe Gregor - 2004/09

There is no evidence that the pilot made an attempt to release from tow prior to the weak link break, the gate was found closed on the Wallaby-style tow release.

Ya give state of the art equipment to do the right thing at the right time and the best instruction imaginable and they always wanna...

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

Ryan Voight - 2009/11/03 20:51:52 UTC

My whole point is that people tend to "hang on" too long trying to save things, rather than recognize a bad situation and release (one way or another), go back, and reset.

I'm not saying wait until you're so locked out you're passed 90 degrees bank and then pitch up to break the weaklink and do half a loop into the ground. I'm saying get the hell off way before that, and if you can't let go you CAN pop the weaklink pretty easy... they're weak after all

I'm done with this thread. Went from a good discussion RE: one barrel or two, and became a "the sky is falling and towing is death" tyrade. If you don't want to tow, don't... let other's do what they want. Live and let live my friend.

..."hang on" too long trying to save things, rather than recognizing bad situations and releasing (one way or another), going back, and resetting.

- So how come Lin's autorelease didn't kick in when the towline was pulling back? Oh right...

1:09
http://vimeo.com/68791399


He disengages it before the towline starts pulling back. Pat's right. You just can't trust these people.

He also told me that Rob McKenzie gave him the idea of using an auto release.

- Rubbish. Let's give credit where credit is due...

Doug Hildreth - 1991/03

1990/03/29 - Brad Anderson - 24 - Novice - Flight Designs Javelin - McMinnville, Oregon - head injury, ruptured thoracic aorta

"Strong novice" pilot with truck tow experience and instructors present launched and rose to fifty feet over truck. Pushed out hard enough to release and continued to push out after release. Whip stalled and dove into the ground. Died instantly.

1990/07/05 - Eric Aasletten - 24 - Intermediate - UP Axis - Hobbs, New Mexico - head

Towing competition in midday thermal conditions. Normal launch sequence to fifty feet where apparent thermal caused glider to go into extreme nose-high attitude, accidentally releasing tow line. Hammerhead stall with head first crash onto runway. Helmet broke. Died immediately.

These guys were the REAL pioneers of the autorelease / pitch and lockout protector mechanism.

- So how much of a dent has the autorelease / pitch and lockout protector put in Mission's fatality rate? I'd guess they were killing maybe seven or eight students a year without it and are now down to about one or two? Has he got any good videos of this thing doing its job? Maybe he could publish an article in the magazine about its effectiveness and push to make its use mandatory in all surface towing operations.

PS Pat uses a Koch two stage himself.

Seems to have in increased tolerance for added complexity when his own ass is on the line. So how does he configure it in conjunction with his autorelease? Or does he not use one because he's been at an around all this plenty long enough to understand what's what and who's who?

[Steve Davy]

Shit!

Pat told me it was Joe Greblo that gave him the idea not Rob McKenzie. I tend to get those two mixed up for some reason.

[Tad Eareckson]

http://www.ushawks.org/forum/viewtopic.php?f=23&t=811
FTHI

Bob Kuczewski - 2011/10/25 06:28:43 UTC

Joe knows far more about hang gliding than I probably ever will.

Yeah. He does.

[Steve Davy]

http://www.youtube.com/watch?v=4lWVrOQN428


Tad, Mike, Zack anybody

Can you think of any good reason why Edward could not or should not have attached at the harness mains rather than the shoulder loops?

Also once the first stage is released is it a disadvantage to be towing from the shoulder loops?

[MikeLake]

http://www.youtube.com/watch?v=4lWVrOQN428


Tad, Mike, Zack anybody

Can you think of any good reason why Edward could not or should not have attached at the harness mains rather than the shoulder loops?

Also once the first stage is released is it a disadvantage to be towing from the shoulder loops?

Attaching anywhere around about the chest area is fine as far as the flying experience is concerned once everything is under load and the pilot is prone.
I would guess attaching to just the shoulder straps would result in some harness 'slop' when the pilot isn't prone and in my case with my harness this method would route half the force through a 1" plastic clip. I wouldn't be too comfortable with that!
I can see these disadvantages as compared to just fixing loops to something substantial just under the armpits.

[Tad Eareckson]

I can't be of much help on this one 'cause:
- I can barely remember surface towing
- I didn't do much of it
- most of what I did was platform

But...

- We're just talking about moving the effective attachment point a few inches.

- At low tow angles with the pilot prone the thrust line is about the same and it would be better to be towing off your shoulders (à la one point aero) but not that much.

- The higher the tow angle the more you'd prefer to have the attachment moving back and lining up with harness mains but I'm sure it's not that big of a fuckin' deal.

- Trade-off thing - like so much in aeronautical engineering (strength/weight, performance/handling...).

- Of course all the staging does is allow the towline to "pass through" the basetube - and the farther forward the attachment the longer you can delay the transition.

- The one inch plastic clip is probably a Fastex nylon clip and they're a lot more persistent than one tends to believe by looking at them. Pretty simple matter to test it to safely over what the weak link allows or replace it with something more substantial if it flunks.