Tracy
Let's start with the definition of practical. A good definition of practical [ref 8] is: "of, relating to, governed by, or acquired through practice or action, rather than theory, speculation, or ideals."
Yeah Tracy...
Larry West - 2012/02/20 14:49:54 UTC
He was connecting his paraglider tow bridle to his harness (Z5) shoulder loops and I thought that was weird, and asked him about it. He told me "that's how I towed all week" so I asked him if he was going to tow with it over or under his basetube and he replied "I did both and it doesn't make any difference." This scared me, so I asked him how much theory Mark taught, and my buddy said "None. We just flew a lot." I laughed and said "That's cool, but they had you take a written test, didn't they?" and he got mad (he was already stressing) and said "Larry, we just flew and those guys said I was flying like a Hang 3.", at which point I just walked away and waited for something bad to happen... which it did five minutes later.
Let's skip all that tedious weak link theory and get these birds into the air using what we use 'cause we've always done it that way.
Lisa
Even though the FAA does not specify the technology of weak link construction, there are practical, accepted standard methods of constructing and attaching weak links for sailplanes and hang gliders.
Yeah Doctor USHPA-Towing-Committee-Chair Colletti?
- Here's what USHPA says about attaching weak links for hang gliders:
A weak link must be placed at both ends of the tow line.
You don't do this and NOBODY does this. And over three years ago I handed you assholes really good revisions of the SOPs and Guidelines which would allow for safe configurations using weak links installed on bridles. And you pissed all over them and me.
And if you can't revise documentation to specify safe, no cost practices then you can go fuck yourself.
- There are also practical, accepted standard methods of constructing and attaching barrel releases which are totally moronic.
Tracy
That's because there are two types of standards, de jure and de facto [ref 9].
De jure standards are those dictated by law, like the FAA's requirement for weak link strength or created by a standards organization, like ASTM standards for construction of light sport aircraft. Neither the FAA nor ASTM has a de jure standard for weak link construction. About all that the FAA has to say about it is: "Tow ropes and weak links are assembled using a tow ring that is appropriate for the operation" [ref 7].
Similarly, ASTM standards state: "The rated ultimate strength of the weak links to be used in the towing cable shall be established and shown to be suitable in operation" [ref 10].
You mean like putting them on a test rig and finding out they blow at about half the loading that you and your shitheaded buddies have been assuming they do?
De facto standards are those that are market driven and have received wide acceptance by the industry.
Yeah dickhead...
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.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467
weak links
Jim Rooney - 2007/07/22 22:30:28 UTC
I've heard it a million times before from comp pilots insisting on towing with even doubled up weaklinks (some want no weaklink). I tell them the same thing I'm telling you... suck it up.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3600
Weak link question
Jim Rooney - 2008/11/24 05:18:15 UTC
I've personally refused to tow a flight park owner over this very issue. I didn't want to clash, but I wasn't towing him. Yup, he wanted to tow with a doubled up weaklink. He eventually towed (behind me) with a single and sorry to disappoint any drama mongers, we're still friends. And lone gun crazy Rooney? Ten other tow pilots turned him down that day for the same reason.
Jim Rooney - 2007/07/19 14:50:52 UTC
And yes, get behind me with a "strong link" and I will not tow you.
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.
MARKET driven.
De facto standards result from many organizations adopting the use of them. When it comes to weak links, the FAA lets the industry and marketplace develop, sell, and use what works--meaning that which is practical and "appropriate to the operation" [ref 7].
Yeah.
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.
Not that they will, mind you... cuz they *know*.
Stuff that WORKS. Kinda like flying your glider into a tree WORKS really well to stop it. So let's make that the de facto and de jure standard.
Lisa
I get it--it's like de jure and de facto standards for hang gliders.
Yeah Lisa, I was pretty sure you would. It's really wonderful to see just how well you and Tracy understand each other's thinking and logic.
Sailplane weak links rarely fail inadvertently--
Yeah? So how often do they fail advertently?
...that's not so much the case for hang gliding weak links.
Yeah.
http://www.hanggliding.org/viewtopic.php?t=11497
Aerotow release options?
Adi Branch - 2009/07/02 12:50:02 UTC
I have to chirp in on this.. I know I'm a noob and all that, but Tad seems to be talking sense to me. From what I can gather the US has some quite different (dated?) ways of doing things which it appears are not used here in the UK, and some of the reasons I've heard cited for not using these methods relate directly to accidents in the US.
For instance, the idea of tying your own weak link is absolute nuts to me, as is using a bit of string for the job! Over here it's aluminium only (sailplane style link) and if I turned up with a bit of tied string, I'd be shown the exit road.
I dunno... Maybe I'm missing something, but if someone (who appears to be knowledgeable in his field) is suggesting some aspects of towing methods are unsafe (to which as an outsider I agree with him), then why are there criticisms and not constructive arguments or additional input to rectify these issues?
Go figure. (Not that there's anything wrong with using a good tied bit of string. But if you so fuckin' stupid as to use it for twenty years without ever once TESTING it - or even LISTENING to the people who HAVE...)
To help people understand why this is so, I think that it would be good to describe and compare de facto standard sailplane weak link designs with hang glider weak link designs.
Tracy
One standard weak link design for sailplanes is to just use the tow rope itself as the weak link, as long as it has a breaking strength between 80% and 200% of the MCOW of the glider, per FAR 91.309(a)(3). The de facto standard is to use 1/4", 5/16", or 3/8" hollow braid polypropylene rope, commonly with breaking strengths of about 1000 lbs., 1500 lbs., and 2000 lbs., respectively [ref 11]. These tensile strengths can vary a bit, depending upon manufacturer of the rope. Any of those three rope diameters would be legal for us to use as a weak link for our Blanik, with a MCOW of 1100 lbs., but, practically, we feel that 1500 lbs. is best.
Oh.
- So you COULD have gone with gone with the one thousand - which would've been almost exactly the flying weight of the glider that USHGA recommends.
- But instead you went for 1.36 times the maximum certified operating weight of the glider - which pretty much EXACTLY what ALL sailplane manufacturers specify.
Most interesting.
Of the three diameters of polypro tow rope, only 1/4" tow rope would be legal for us to use as a weak link for our Alatus ultralight sailplane.
Lisa
1000 lbs. is at the maximum limit for our Alatus. Practically, it is better for us to add a lighter weak link at the end of the 1/4" tow rope for the Alatus.
Tracy
Adding a second, lighter weak link on to the towline is a very popular de facto standard weak link design for sailplanes. Here, a thicker row rope is used as the weak link for the tug and a short length of thinner row rope is attached to the glider end of the long tow rope as the weak link for the glider. The short length of thinner rope can be spliced directly into the thicker tow rope or attached to the end of the tow rope using hardware. Splices are used rather than knots, because knots significantly and inconsistently reduce the strength of the rope.
HOW inconsistently? What's your test data showing?
We prefer this weak link style for our Blanik as well as the Alatus. For the Blanik, we use 3/8" polypro as the towline...
http://ozreport.com/forum/viewtopic.php?t=1143
Death at Tocumwal
Gregg Ludwig - 2006/01/22 18:15:15 UTC
I just cannot understand why operators continue to use poly towlines (for aerotow ops) when spectra towlines are clearly superior. Poly is less expensive... but when considering the cost of a tow plane and HG and the advantages of spectra, a few dollars of savings is foolish.
...and 5/16" polypro as the weak link line added to the end of the towline. This way, the weak link for the glider is 1500 lbs. and the weak link for the tug is 2000 lbs., which is 25% greater than the weak link for the glider, but not more than twice the MCOW of the glider.
Gregg Ludwig - 2006/01/23 16:32:52 UTC
Towline elasticity produces a rubber band effect that results in ever changing towline forces that can also produce significant airspeed changes as well. Since Spectra does not offer elasticity (or very little) this effect does not occur and a safer tow results. Trikes normally tow with longer lines of 200-250 feet so the advantages of Spectra are even greater.
Lisa
Those approaches to weak link design are very practical and are widely used for sailplanes. It is important to realize that most sailplane operations use polypro for the tow rope rather than Spectra.
Oh. MOST sailplane operations use polypro for the tow rope rather than Spectra. Hard to imagine that all of them aren't.
Unlike Spectra, polypro has some stretch to it under load--and can stretch up to 20% before breaking.
Yeah?
Rodney Nicholson - 1986/11
Ontario Hang Gliding Association
In the third and most recent incident, the weak link broke shortly after launch and the end of the tow rope, with metal ring attached, whiplashed back and hit the spotter/winch operator in the eye. At present the chances appear ninety percent that he will lose the eye completely.
So what happens with all that stored energy AFTER breaking?
It acts like a shock absorber to soften impact loads, which helps to prevent damage to the structure and hardware of the tow plane and sailplane and helps to avoid unnecessary weak link breaks.
Steve Seibel - 2006/01/23 20:34:34 UTC
Obviously one of the dangers of an elastic towline is that when it breaks, it can spring back and hit the pilot with much force--I've heard of a (nylon?) towline actually breaking its way through the canopy and into the cockpit of a sailplane after it broke under a heavy load.
So I guess the stupid people using Spectra at their sailplane operations are getting a lot more damage to the structure and hardware of the tow plane and sailplane and experiencing a lot more unnecessary weak link breaks. Have you tried reasoning with them?
And LOOK AT THIS from Reference 11 - Wings and Wheels:
http://www.wingsandwheels.com/page30.htm
Ultra High Molecular Weight Polyethylene Braids
Spectra
Spectra rope has one of the highest strength to weight ratios of the performance fiber ropes available, and can be up to ten times lighter than an equivalent strength steel cable. Spectra fiber is made from a High Modulus Polyethylene (HMPE) that carries exceptional properties in relation to high strength, low stretch, low weight, and low friction. HMPE fiber is also considered the lightest of the high strength / high modulus fibers.
UHMW PE/Spectra 1000 Braided Cords exhibit superior abrasion and ultraviolet resistance. Spectra braids have very low elongation at break (4%-5%) and are used where extreme high strength and low elongation are required.
Pound for pound Spectra braids are the strongest braided cords available. In addition to the raw braid the above items can be pre-stretched and/or treated with various synthetic finishes.
Most popular for ground launching ultralight and hang gliders due to the low weight and high strength but increasing popularity for glider winch and auto launching.
Low stretch, very low elongation at break - just four to five percent, marketing to and popular with ultralights and hang gliders as well as sailplanes?!?!?!
And they're paying TWO AND A HALF TIMES as much for the 2000 pound Spectra as the vastly superior 2200 pound poly that you're using?
MY GOD!!! What is WRONG with these people?!?!?!
