http://www.kitestrings.org/post11558.html#p11558
--01--
Right at the beginning of the second to last decade of the previous century Dr. Lionel D. Hewett, since incorporating a sane release system in his towing configuration was real low on his list of priorities, declared that what had previously been indisputably determined to be the statistically most catastrophic failure of a towing operation, even in the area of ultra lockout prone frame-only connections, to be the glider's best hope for long term survival. Put a loop of No. 18 braided nylon twine between your Center of Mass bridle and the tow ring and there'll be no fucking way you'll be able to get into any serious trouble. Go to 16 if you want any greater ridiculously wide safety margins.
And this shit sandwich went global in the 1981 version of a nanosecond minus a significant whisper of opposition from the hang gliding establishment - which included sailplane people.
And the one thing upon which you can safely bet your bottom dollar in hang gliding is that whenever the hang gliding establishment incorporates a totally insane hypothesis or procedure it'll immediately start working overtime to degrade it even further. Hence the Bailey-Moyes 130 pound Greenspot Standard Aerotow Weak Link.
And Yours Truly was drinking the Kool-Aid (2005/08/30 13:00:13 UTC) until about half a dozen years into Highland Aerosports' seventeen season existence. Brain started kicking in then it REALLY started kicking in. I wasn't the first to get it by any means. Mike Lake - for example - got it back in the Stone Age before the advent of pilot connection towing. And comp pilots were sneaking extremely Fallible Weak Links into the launch line during the 1999 US Nationals at Quest at the end of April (a month before Ridgely opened up with a display of Davis Links going off like popcorn (including my first effort in smooth air on their first day)). But when I got it I had the relatively new power of the Internet at my disposal for research, communication, visibility. And in my humble opinion the crusade I launched on my old club forum was a major historical event in the (d)evolution of this sport. Somebody cite something to counter the claim.
So I've gone through damn near all of the relevant CHGA forum traffic and created an archive - everything in one place, consolidated, chronologically ordered, in context, properly attributed, efficiently formatted.
38 participants listed in order of appearance:
Discussion Entry Time Stamp - Posts
---
2005/03/05 00:37:37 UTC - 006 - Lauren Tjaden
2005/03/05 02:24:13 UTC - 015 - Hugh McElrath
2005/03/05 16:44:12 UTC - 143 - Tad Eareckson
2005/03/05 17:11:22 UTC - 064 - Brian Vant-Hull
2005/03/05 18:20:47 UTC - 001 - Paul Adamez
2005/03/08 03:41:20 UTC - 046 - Jim Rooney
2005/03/11 02:43:09 UTC - 003 - Steve Kinsley
2005/08/25 13:18:56 UTC - 005 - Scott Wilkinson
2005/08/25 13:29:58 UTC - 018 - Matthew Graham
2005/08/25 13:36:00 UTC - 011 - Chris McKee
2005/08/25 13:51:22 UTC - 002 - Linda Baskerville
2005/08/25 14:25:17 UTC - 001 - Dave Rice
2005/08/25 16:53:03 UTC - 007 - Cragin Shelton
2005/08/26 14:28:42 UTC - 001 - Daniel Broxterman
2005/08/26 17:55:48 UTC - 001 - Rance Rupp
2005/08/26 18:40:26 UTC - 034 - Marc Fink
2005/08/27 02:11:56 UTC - 001 - John Simon
2005/08/31 00:33:01 UTC - 004 - Dan Tomlinson
2007/05/16 23:15:19 UTC - 009 - Danny Brotto
2007/05/21 18:44:42 UTC - 001 - Mike Lee
2007/05/25 12:03:13 UTC - 002 - John Claytor
2007/05/30 03:31:24 UTC - 001 - Kurt Hirrlinger
2007/06/03 00:47:16 UTC - 007 - Jim Rowan
2007/07/17 13:33:25 UTC - 028 - Gary Devan
2007/07/23 22:56:56 UTC - 006 - Bacil Dickert
2008/07/22 04:32:22 UTC - 002 - Paul Tjaden
2008/10/28 02:03:57 UTC - 005 - Kirk Lewis
2008/10/28 02:09:26 UTC - 005 - Kevin Carter
2008/10/30 04:33:48 UTC - 001 - Mark Cavanaugh
2008/10/30 20:38:14 UTC - 001 - Tim Hinkel
2008/11/03 19:29:05 UTC - 035 - Janni Papakrivos
2008/11/11 20:18:07 UTC - 002 - David Bodner
2008/11/15 13:42:14 UTC - 001 - Jeff Eggers
2008/11/16 23:36:25 UTC - 003 - Shawn Ray
2008/11/23 07:36:09 UTC - 002 - David Churchill
2008/11/26 01:33:33 UTC - 002 - Gene Towns
2008/11/30 19:24:09 UTC - 001 - Carlos Weill
2008/12/09 01:25:18 UTC - 001 - Allen Sparks
Note that about two years and eight months prior to my 2007/05/16 12:53:34 UTC launch of the first Tad-O-Link thread the FAA has pulled hang gliders in under sailplane AT weak link regulations and that u$hPa will sit on that intelligence until three and a half years after the beginning of my three month suspension from the CHGA rag for telling the douchebags sabotaging the thread to go fuck themselves.
Source threads with number of archived posts:
http://www.chgpa.org/forums/viewtopic.php?f=2&t=229
007 - Quest Friday, shoulder towing
http://www.chgpa.org/forums/viewtopic.php?f=2&t=233
011 - AT releases
http://www.chgpa.org/forums/viewtopic.php?f=2&t=939
032 - Weak link breaks?
http://www.chgpa.org/forums/viewtopic.php?f=2&t=966
003 - inertia
http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467
126 - weak links
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3035
001 - Tad's Barrel Release and maybe an alternative
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3380
001 - Lauren and Paul in Zapata
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3391
006 - More on Zapata and weak link
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3600
246 - Weak link question
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3648
001 - Oh no! more on weak links
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3659
011 - New Lookout Release
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3661
002 - Flying the 914 Dragonfly
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3665
030 - I'm outta here
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3671
010 - Forum Rules and Etiquette
Archived in their entireties:
- Quest Friday, shoulder towing
- AT releases
- Weak link breaks?
- inertia
- weak links
- More on Zapata and weak link
- Weak link question
- Flying the 914 Dragonfly
- I'm outta here
- Forum Rules and Etiquette
At this point:
http://www.chgpa.org/forums/viewtopic.php?f=2&t=3035
Tad's Barrel Release and maybe an alternative
Jim Rooney - 2008/02/25 02:59:11 UTC
gleefully announces that he's put me on his ignore list. Same deal:
http://www.hanggliding.org/viewtopic.php?t=14230
pro tow set-up
So anything he's said about Yours Truly subsequent to that point is based on the record prior to it. So when he makes statements in later contexts he's either actually (pretending to be) basing them on that record or lying about having me blocked.Jim Rooney - 2009/11/03 06:16:56 UTC
God I love the ignore list
Following CHGA threads:
- Weak link question
- I'm outta here
- Forum Rules and Etiquette
are all locked. So it's not just Yours Truly they want silenced and forgotten. They don't want ANYBODY discussing those issues. So we'll just give them a little extra exposure over here. I'm locking this topic but only because it's intended to be an archive. We can discuss it at our "Weak links" thread and/or elsewhere on the forum.
---
http://www.chgpa.org/forums/viewtopic.php?f=2&t=229
Quest Friday, shoulder towing
Lauren Tjaden - 2005/03/05 00:37:37 UTC
Today I experienced a lovely flight, a little 40 minute number to 3100, flown after 3 PM, when the thermals had lost some of their sharp edges. I was brave enough and smart enough not to run when other pilots came in on my tail. Once I got scared enough I let another pilot take my thermal, but I at least stayed on the outside of the circle and came back in after he got higher than I was, instead of punishing myself by marching off to another area in a huff. When it's blue, you gotta give up your pride! Actually I am just learning a bit about how to fly politely in company.
Landing was interesting with many pilots plummeting from the sky at the same moment, complicated by a small, tempting -- but ultimately unworkable -- thermal, 3-4 hundred feet over the LZ. Ah, that is what the tug plane is for; you can always try again if it is too challenging and you are in danger pushing it.
After landing, it was time to confront my third challenge for the last two weeks. The challenges were: (number 1) I had to go XC at least once, (number 2) try to get my 4, and (number 3, the one that I hadn't done) tow off my shoulders. It is amazing what a woosie I am. Worry worry worry but I was damned if I was going to put it off.
Zach (Woodall) and Paul explained that I couldn't jam the bar out in front of me like I do when I launch regularly; that I might pop up and stall my glider (and fall to the ground and writhe in pain and then die), but that I must allow myself to be pulled though the control frame a bit and then hold my arms rigid.
Zach kept saying, no, more forward, no, more than that, when I asked if my body was forward enough. Finally I just said, OK, I am launching. He said later my pitch was perfect but I was petrified for a couple of seconds wondering if I got it right.
The tow was uneventful but the bar pressure was lots more, and I already fly with half VG so I don't feel I can increase it. It was harder to follow the plane when I got high on it. Zach pointed out later I could just stay a little low. Actually I think it will be fine since I am strong, but it will be more difficult to tow in midday conditions, because of the bar pressure. But I sure liked the clean configuration and it is much less drag. Really so much less crap hanging off my down tube.
So Paul just told me he has 3 more goals for my next 2 weeks. COOL! It is very constructive for me to have these things to aim for.
Come see us soon.
Love
Lauren
Hugh McElrath - 2005/03/05 02:24:13 UTC
Lauren,
I just read something in the USHGA mag about towing configurations and they mentioned greater risk of a lockout when towing from the shoulders. What do the folks down there say?
Lauren Tjaden - 2005/03/05 13:25:42 UTC
My understand is that since all the tow forces are on you (when towing from the shoulders), not you and your glider combined, that in a lockout it might be more difficult to recover since your shoulders will be pulled in the direction of the plane more strongly (someone please correct me if I am wrong, since I have limited experience with this, to say the least). Also, the bar position is further back so you have less leverage to push it back into position than if it was further ahead of you.
On the plus side, you?have less drag and less hassle in the air stowing your tow bridle.
I also feel it may be easier to pin off in case of a lockout because you have a bailey (for me, two of them, one on each side) and they are much closer to your center of gravity. Reaching that handle way out to the side can be challenging in a hard turn. The bailey is right there.
I would welcome hearing more expert opinions, as well.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=233Hugh McElrath - 2005/03/05 16:10:16 UTC
Hmmm... thanks for the thoughtful reply. Since I don't use a bicycle brake handle but a loop around my palm, I have even less problem pinning off than with a bailey (which I have for backup). That may actually be the tie-breaker for me: right now, I can pin off without removing my hand from its position on the base tube. Towing from the shoulders I would have to find one of two bailey's possibly with a gloved hand (have to look down with the chin guard of my helmet in the way, too). Roger the hassle of retrieving the tow bridle and the drag of the release. Decisions, decisions...
AT releases
Tad Eareckson - 2005/03/05 16:44:12 UTC
Damn, Hugh stole a lot of my thunder before I could post but...
The two point release I developed the better part of four years ago blows you off tow with stored energy, is actuated with minimal force by sliding your hand inboard along the basetube a couple of inches, and is lighter and magnitudes cleaner than any other two point system out there. It restores virtually all of the full point of performance that Rob Kells estimates the external cable housing crap sucks out of your faired downtube and the transmission element can't bind in such housing. It is also, as far as anyone has yet been able to determine, one hundred percent reliable.
Yeah, the modern crop of fast, low pitch pressure gliders makes the one point/shoulders only/pro tow option very attractive and it's nice not having to reel in and stuff all that trailing bridle upon getting to altitude. I use and feel reasonably comfortable with it myself when taking demo hops - especially after getting the first hundred feet below me.
And the aerotow launch itself seems to have proved itself so insanely safe that I was starting to think that maybe things weren't all that critical until someone provided a lot of evidence to the contrary last summer.
The more difficult it is to effect a release the more people are gonna die.
Attention Eagle people:
If you're willing to invest in a couple of extra zipper pulls you don't have to leave your sail unzipped.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=229Hugh McElrath - 2005/03/05 17:02:56 UTC
Thanks, Tad. I was too green to fully appreciate your system when you showed it to me a couple of years ago. Now I'm more interested. Do I have to fabricate this myself from parts or are you in business?
Quest Friday, shoulder towing
Brian Vant-Hull - 2005/03/05 17:11:22 UTC
You have the secondary release in conventional towing anyway (yes, I've used it), and not that much more to stow, though I may be wrong. I guess for competition you may worry about a little extra drag, but otherwise why bother with the extra safety issues?
http://www.chgpa.org/forums/viewtopic.php?f=2&t=233Paul Adamez - 2005/03/05 18:20:47 UTC
My biggest concern with the V bridle is if my Spinniker release fails and I use my secondary and the bridle gets hung up on the caribiner on the end of the tow line. Now I am being towed straight from the hang loops, or keel, with no way of releasing, in a very bad tow configuration. Not good.
I've been giving thought about going with the Pro Tow, especially with all the discussion on the OZ Report, but am concerned too about any increased lock out tendencies with this method. With the Pro Tow I may be more apt to release sooner if I get too out of wack and not try to wrestle with the situation, which may be a good thing.
AT releases
Tad Eareckson - 2005/03/06 19:33:17 UTC
Oh joy of joys! Finally the prospect of doubling the population of this system.
Yeah, I welcome with open arms anyone - individual, park, manufacturer - to plagiarize this rig and keep all that R&D from going the way of Beta tape and, yeah, I'd be happy to be in the business if anyone would rather avoid the hassle him-/herself.
I have extensive documentation on components, loads, and specs and have written (and several times rewritten) an article. Kolie and Pauls Adamez and Gerhardt have been very kind to do some photo shoots but I keep finding things I should have set up better and really ought to go out with a tripod and sacrifice part of a day before going to press.
Re the first Paul's concerns...
The spinnaker shackle doesn't fail in its function. If a reasonable pull is applied to the spring loaded latch the gate opens. (Caveat - I have found that a hang up of the weak link on the notch at the gate may occur upon a low tension release but it doesn't last long after a little tension is restored.) It's the activation and transmission elements that fail. Problems I've seen and/or had reported include improper adjustment of cable play, insufficient throw capability of the mounted brake lever assembly, and binding of cable and housing (the sort of problem that used to render a lot of ballistic parachutes inert). Although the loop activated flavor appears to be a pretty reasonable second-best, Sunny related that Highland has seen so many failures that they no longer sell them (your mileage may vary).
The leech line based transmission, evolutionary variations of which I've been using since 1994, does not fail and is extremely efficient in delivering the force to where it's needed.
Yeah, the scenario Paul described involving a two point system in which the primary fails and the bridle wraps could be a real nightmare - especially if the trim point is way forward on your keel (like mine). There was a group of tow pilots who hadn't thought things through more than the initial step members of which were deliberately releasing at the bottom end of the bridle so that it would stream better out of the way during free flight. When step two chanced along one of them had his glider fail under negative loading and was lucky to just get majorly injured.
But in the course of conventional setups and operation this, statistically, just isn't on the screen - especially if you're using proper equipment and technique.
Bridle wraps are rare and almost nonexistent if:
- the ends are cleanly spliced or tapered and it's of a fairly stiff, inelastic, and substantial material
- weak links aren't stupidly long
- releases are initiated under low tension
The wisdom I scored from Sunny regarding the last point is... At wave off, climb, dive to slacken the tow line, and release. The tow ring (carabiner) slowly falls away while the bridle gently feeds through it. (Also eliminates that annoying stall one experiences otherwise and the shackle doesn't hammer itself.)
Further along - let's make this a worst case lockout scenario - there's a weak link at the top of the bridle which will now be experiencing something along the lines of a double load and a tug driver with a lever on that end which may do you some good.
And, again, the technology has existed for over a decade such that no one should even be worrying about a primary release failure.
And there's very little reason that we should have to let go of the steering wheel to try grab something at a bad time either.
I also note in the 2005/02/21 installment of the Oz Report a reference to failure of the secondary bridle to feed through the end of the primary after a wrap. I've been using a painfully obvious remedy to that problem - which also prevents those components of your equipment from sawing each other apart - for over a decade as well. It involves a stainless steel sail thimble.
Hugh McElrath - 2005/03/06 23:02:06 UTC
OK, Tad, you've blown me away with too much information - but the part about loop-type releases having a higher failure rate sure got my attention. What is the failure mode? Won't release or release uncommanded? I've had the latter, just learned to make damn sure the shackle is all the way on the gate. Let's get together at Ridgely or in town and work on replicating your rig - or making a Mark II...
Brian Vant-Hull - 2005/03/06 23:35:59 UTC
I believe the problem is not with the method of pulling the release, but the way the gate itself was configured with these models - the tow line would end up pulling on the hinge and there was thus no force to pull the gate open. There's a couple of ways to mitigate this problem by changing the way the gate is suspended, but the problem is *not* with the loop pull itself.
There's a line that connects the gate to the glider. If this line attaches exactly opposite to the hinge, there's a good chance the tow line will naturally pull against the hinge. If this is happening it's imperative to reroute the attachment line.
I had problems with my pull loop release until I had the attachment line rerouted. At some point Ralph flew my glider and was scared silly when it didn't release, but unfortunately I don't remember if this was before or after I rerouted the line.
There may have been other problems associated with not having extra force from the lever effect of the bicycle release. Sunny or Adam may know.
Tad Eareckson - 2005/03/07 14:15:12 UTC
You really didn't expect me to shut up after a paragraph or two, did ya?
Release uncommanded is an annoyance, won't release is the potentially deadly problem that puts the loop style on the Banned In Ridgely list. The complaint I heard from Sunny was that the shackle wasn't opening. The problem that you (Hugh) described in the former category is a byproduct of both styles and another issue which disappears with a leech line setup.
With that detail on the checklist, I wouldn't sweat your copy - if it works, it works. I kinda like it when stood alongside the bicycle brake jobs. Checked one out as thoroughly as I could on the ground and the best I could speculate was that the cable will, by definition, be subjected to two changes in direction and the resulting binding resistance. Its counterpart often gets away with one turn and, as Brian says, benefits from something on the order of a four to one force magnification courtesy of the lever mechanical advantage.
I can, however, with a little effort imagine scenarios in which the loop contributes to a control problem or broken wrist.
I've long been puzzled by reports of gates failing to open after the latch has cleared (e.g. Ralph's 2000/08/26 malfunction (yes, prior to modification)). The hypothesis is that our weak links, with their diameters magnitudes smaller than the lines for which the Wichard Quick Release Shackle 2673 was designed, focus their tension force directly on the center of the pivot point and there isn't enough offset to start to swing the gate.
I've never been able to duplicate this failure on the ground (or in the air). If I pull a loop of 130 pound braided Dacron directly in line it opens. If I immobilize the shackle upside down (gate up), cram a loop of dental floss inside the pivot cutout on both sides of the gate end, and pull the line aft 140 degrees and parallel to the fixed arm... it opens - easily and immediately.
A couple of seasons ago Les Taff informed me that the offset drilling mutilation one often sees is not perpetrated to accommodate opening but to keep the weak link from getting chewed up by the couple of sharp edges of the pivot cutout. Apparently some copies are more problematic than others - I've never had a problem with the ones I've used. And if I did I'd address the issue with a file.
Another idea with respect to Paul's double failure scenario. In the event of a primary malfunction under best case scenario options (i.e., at wave off) I might give a thought to diving then pushing out and rolling (to minimize the danger of the resulting stall) to try to pop the weak link before I started using up other options. Opinions?
I don't have any great Mark II concepts. After release I'd like to rid myself of about eight inches of taut leech line standing up against the breeze but the last few years of thinking about it haven't yielded anything very worthwhile.
I took a look at some U2 (right?) diagrams and the basetube looks like it would be easy to work with.
Brian Vant-Hull - 2005/03/07 14:33:14 UTC
I don't know where "banned from Ridgely" comes from, since several of us have been using the pull loop system for years. After I rerouted the attachment line I never had another release problem, and that was years ago. I can understand they wouldn't sell them - though I think with modification they are fine (preferable in my book for instant pull access).
I rather like the "drilling mutilation" solution: the attachment line rerouting is a little too subtle for my taste, but I don't have the tools or perhaps even the skill to drill through a small section of curved metal without the bit skating all over. Someday I'll probably have it done.
Tad Eareckson - 2005/03/08 00:00:06 UTC
Naw, the "Banned In Ridgely" comment was just a reiteration of my earlier mention that it's no longer available at the counter. And, yeah, it's next in my preference line below what I have and above the brake lever. If one is accepting the aerodynamic penalties of a two point system anyway I think it's nuts not to have the option of having a finger on the trigger when the cart starts to roll. If the cable routing turn radii are sufficient and the bottom end of the housing is properly secured I don't see a problem.
Although there doesn't seem to be any data to back up my paranoia I keep envisioning the downstream end of the latter mechanism protruding from an eye socket. Also seems like somebody is eventually gonna find a way to snag something real important. And it doesn't exactly scream "streamlining".
I must part paths with you on my feelings about the drilling however - I really, really hate it. Rotates the load 90 degrees from the way it was designed to operate and dumps it all on the latch which wasn't envisioned to take anything. And I'm wondering if it might have an adverse enough effect on required trigger tension that you really need that brake lever mechanical advantage at the upper range of things.
Before doing anything irreversible allow me to run a tensioner between the fixed arm of the shackle and the glider's nose. If your attachment line rerouting is addressing any problems, I believe the tensioner will do it better and bestow a couple of other advantages as well.
Also, although, as I said, I've never had a problem, I just took a couple of small files to a couple of spinnaker shackles and rounded out some sharp edges around the pivot cutout and hinge pin riveted faces. It took a few minutes and reduced the threat level to the weak link from no way to no freakin' way - without marring the finish of those beautiful pieces of hardware. Possibly more labor intensive than clamping one under a drill press but not much and with infinitely more satisfactory results.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=229Hugh McElrath - 2005/03/08 00:57:50 UTC
Duh... I've never thought of doing maneuvers before releasing - just keep flying straight and level and pop the release. I don't normally stall - just keep the nose at the same AOA (don't let it pop up) and enjoy the relaxation of letting the glider fly at its own speed instead of being dragged faster than it wants to go.
Quest Friday, shoulder towing
http://www.chgpa.org/forums/viewtopic.php?f=2&t=233Jim Rooney - 2005/03/08 03:41:20 UTC
There's a bit of a distinction to note here. One that is not mentioned in the USHGA article.
There are two ways to use a 3 point towing system. The top towpoint can either be on the keel or on your carabiner. The differnece between these is important.
The method described in the magazine is a keel mount. Since the tow forces act both on the CG and the glider, your gliders nose gets pulled through turns. You can also reduce pitch preassure by moving the tow point further up the keel.
Towing off the carabiner is very different in that all tow forces act on the CG. The important distinction here is that it will "feel" like towing off the keel, but it acts like towing off the shoulders.
It feels like towing off the keel because your bar position is similar and the tow force is split between you and your hang strap. This is different from keel towing since the other half of that tow force is not acting on the glider.
The comment in the magazine is that the pro tow method makes lockouts harder to correct. This is in no small part due to the tow forces in a keel tow setup are trying to pull your nose out of a lockout.
This is not true in a carabiner tow setup.
The difference between the carabiner tow and a two point shoulder tow is that the tow force is no longer split. You get it all. This changes your bar position and you feel all the tow force. This is not pitch preassure, just pulling preassure. The difference in how your glider flies is none. All tow forces are still routed through the CG.
Something of note between the keel tow and carabiner tow... in the rare event of becoming stuck on the top towpoint only (primary fails to release, secondary releases the shoulders but not the bridal), the carabiner tow will still be pulling of the CG if you're towing off the carabiner, the keel tow will be trying to tumble you.
In the end, it's all a matter of tradeoffs. None of the systems are failsafe and each has its stronger and weaker points.
$.02USD
AT releases
Tad Eareckson - 2005/03/08 12:56:13 UTC
I would strongly recommend the climb, dive, release procedure at all waves off.
There's nothing that pops the nose up at release - it's been popped since you left the cart. That may not be real apparent on the glider you're driving but take a side view of a tug with glider in tow next time you're sinking past such a combination.
If you release under tension the AOA changes instantly - and your pitch attitude has to be reduced to regain it. Either you pull in or do nothing and wait for the glider to work on the problem.
"Popping the release" subjects the spinnaker shackle to a bit of abuse and the bridle to a little extra friction and wear but also sends the bridle, which is supposed to keep going up with you, whipping towards equipment which is about to descend with somebody else.
Give the gentle option a try - it's pretty neat watching the slow feed through the floating carabiner. And I would be amazed if a wrap ever developed when the tow line is slackened.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=939Steve Kinsley - 2005/03/11 02:43:09 UTC
Winter boredom and the Oz report resulted in my invention of "the squid"AT shoulder release. This is a two ring (or 3 -- haven't decided which is better) where the final loop runs thru a grommet and you hold it in your teeth. Want off? Open your mouth. When you are 100 ft up and presumably out of danger you slide a barrel (the body of the squid) over the loop which crimps it at the grommet and you have a standard barrel release. I can hold on with my teeth all the way and not use the slider/keeper but gotta be sure I have fresh polident.
Tried it at Manquin and down in Fla. Seems to work fine. (flew with a standard barrel on the other side just in case) Also gets a lot of laughs. Show it to you.
Weak link breaks?
Scott Wilkinson - 2005/08/25 13:18:56 UTC
Being a new AT pilot who hasn't experienced a weak link break yet...I'm curious about what types of scenarios can cause this? Obviously a lockout can cause one...but I'm wondering more about breaks right off the cart. This seems to happen a lot (maybe not?) and I don't understand how/why?
Any illumination is appreciated!
Matthew Graham - 2005/08/25 13:29:58 UTC
Talk to the sailplane people about this. They have scenarios for what to do if a weak link breaks at various altitudes. I've never seen anything taught on this subject at any of the tow parks. They might. I just haven't seen it. Anyway, you should have a plan of action for a weak link break:
on the cart
just after coming out of the cart
at an altitude of up to 30
from 30-60'
60-100'
above 100'
and so on
Once above a few hundred feet you can do a regular approach.
The plan may vary according to conditions. So think about it and go over it in your head as you are waiting in line to be towed.
You should also have a plan of action on what to do if you are given the rope.
Chris McKee - 2005/08/25 13:36:00 UTC
Additional to Matthews List ...
Weak link break at 50 feet with tow cart still attached ....
Answer: Roll on landing to keep cart behind you
BTDT
Linda Baskerville - 2005/08/25 13:51:22 UTC
Having trained with Sunny, I can tell you that they work the weak link break into your training - i.e., Sunny pulls the release on you at various points.
Basically, you have to have your anticipated escape mode in mind at all times as you tow up - I repeat my mantra (literally) as I am being towed up, of where I can land if the weak link breaks so that I don't have to think about it to make a decision on short notice, but will be able to respond immediately. At Ridgely, (towing west) it would be " straight ahead straight ahead straight ahead" , then as I see the altitude increase enough it switches to "RC field RC field RC field RC field RC field" and then lastly as the altitude becomes enough it is "windsock windsock windsock " until I feel I am out of the "emergency" adrenaline response altitude and in normal approach zone.
At Blue Sky (towing south) it would be much the same thing although you could substitute Soybeans (to the right) for RC field.
I'm sure with enough experience, I won't have to repeat my mantra on tow, as it will perhaps become instinctive.
Some regular sources of weak link breaks are: getting into the prop wash of the tug, and also skyrocketing out of the cart, and also hitting an abrupt thermal lift. I'm sure there are plenty of others - like various cart acroBATics.....
Scott Wilkinson - 2005/08/25 14:08:57 UTC
Thanks all for the great responses! Some really excellent points I'll commit to memory and work on.
That's great Sunny works with you on simulated breaks at Ridgely---not something we do at Blue Sky, so that's good! In addition to your mantras on where to land Linda, I'm always thinking (if it breaks) "pull in, pull in, pull in, pull in!"
Being a "large and tall" pilot (6' and 225lbs) on a big glider, I don't get pushed around as much by thermals...but then again, I'm pushing the weak link that much closer to its breaking point (since everyone tends to use the same test-strength line for the link).
Dave Rice - 2005/08/25 14:25:17 UTC
I've only had one weak link break while aerotowing and it happened while I was still very low and over the runway. I was happy that I automatically pulled in as soon as I heard the snap and got slow. I'm glad that my reaction was to dive** at the ground even though it was really close to it. I was able to maintain manuevering speed and landed without incident.
**When I say "dive" I'm talking about the Falcon version of diving which I think is more a function of the pilot trying to go fast than of the glider actually getting its nose pointed at the ground. If I had pulled in as much as I did with a higher performance glider my results would probably have been different. Sometimes it's really nice to fly a Falcon.
Brian Vant-Hull - 2005/08/25 14:32:50 UTC
If you think you're too low out of the launch cart and pop the nose to get up to position, that will do it: sudden slow down of the glider. Try to correct smoothly, which is not to say do slow corrections; just don't jerk the bar.
Cragin Shelton - 2005/08/25 16:53:03 UTC
Scott,
I, like others, had weak-link break training at both Highland and Blue Sky. Sunny, Chad, Steve, and Tex have all been involved.
One very important item in the training, and a direct response to your note above... it is NOT obvious that a lockout will cause a break. Holding that assumption gets a lot of pilots in trouble, because they fight their way through trying to correct a lock out too long; they figure if it gets too bad, the weak link will break and they will be off tow in time to correct their flight attitude.
The truth is that most lockout conditions will NOT break the weak link. Weak links fail when subject to sharp forces / sudden changes in tension. Many lock outs occur smoothly as the pilot and glider move out of safe position and the HG attitude goes widely off the toe line direction. Therefore, a pilot on tow must always be ready to hit the release as a lockout is approaching. Do not wait for the weak link to "save" you.
If you have not done so, get a copy of Towing Aloft by Pagen and Briden, and read about both weak links and lockouts in that book.
Scott Wilkinson - 2005/08/25 17:59:20 UTC
Good points Cragin, and yes---I've already deeply internalized the concept of releasing long before things get bad. (If anything, I'm more likely to release prematurely if things even kinda, sorta start to get bad---there's never a problem with that if you're above 200 feet!)
Of course, I'm sorry to say I've already had an unforgettable demonstration of what can go wrong without a wink link (in Holly's accident) and without releasing.
Out of curiousity---when you "trained" for this at Blue Sky, do you just mean it was discussed verbally? Or did Tex do "random releases" during tandems with you flying? (Seems like a hard thing to train for on your own.)
Cragin Shelton - 2005/08/26 06:58:52 UTC
discussion only.
Because of my size, I never had any tandems at Blue Sky. All my tandems were either many years ago at Kitty Hawk, or over at Highland
And the weak link discussions at Blue Sky included both truck and AT situations.
yea.. it is difficult to "surprise" yourself with a simulated break
Jim Rooney - 2005/08/26 11:46:12 UTC
Weaklink breaks are standard curriculum at nearly every tow park I've been to. At Highland, once we start doing pattern tows, the student never hits the release. We hit it and we hit it when they're not expecting it.
Ok, on with the first question....
Weaklink breaks happen for any number of reasons and one will catch you off guard at some point. Be ready and pull in.
One of the more interesting and poinient ones is the smooth air break. Towing up in smooth air, in position and you have a good weaklink... just towing along straight and level, nice and smooth... when the weaklink breaks. There's no appearent reason. No rough air, no rough glider inputs... it just breaks.
I see a lot of people break weaklinks by coming out of the cart too fast (staying in too long). They generally vault up into the sky and experience some quick loads from pitching up to catch the tug or pulling in not to zoom past it and the weaklink breaks.
The other common one, which is sometimes experienced at the same time as vaulting into the sky is smashing through the tugs wake. Sometimes the wake is unavoidable, but being on the cart excessively long increases your chances of hitting it.
Disclaimer:
Coming out too slow sucks too. I'm not recommending it.
A good cart exit should be like sliding out of it... it should just dissapear. If you sink after exiting, that's too slow. If you pop out, that's too fast. Flavor to taste.
Craigin makes a good point about weaklinks and lockouts. You can't rely on the weaklink to break. The way I teach things is that if your weaklink breaks, you didn't recognise the lockout fast enough and didn't hit the release fast enough.
Daniel Broxterman - 2005/08/26 14:28:42 UTC
While we're on this topic...at Wallaby in April the launch crew put a 2nd weak link in my system between the bridle and the Bailey. I fly with a two point, Wallaby-style release, with a single Bailey secondary. As I recall, here's the scenario they had in mind:
Pilot releases with primary, bridle catches on the tow line or release mechanism. If pilot becomes extremely out of position, the additional weak link would probably breaks prior to pilot finding and Bailey.
Does anyone else use two weak links, one on each release point?
Brian Vant-Hull - 2005/08/26 14:46:48 UTC
I also use two weak links, but in 8 years of use have never replaced that second one. I wonder if this second one has ever actually broken for anyone?
As to Batman's reply to Scott, while a new tow pilot has less experience with pulling off a flare, I don't see why an experienced tow pilot won't learn to perfect a flare. I do think it's harder to flare on a training hill due to less speed, so you may put a sharper edge on that particular technique. But learning to setup is arguably more important. And yet launch runs are important too! Do it all!
I used to be much better at going back to the training hill...
Chris McKee - 2005/08/26 15:15:44 UTC
An experienced HG pilot of any type should be able to flare, land equally as well. I just dont' like the statement that training hills are poor substitutes for landing practice. It is blatantly wrong and very misleading.
Rance Rupp - 2005/08/26 17:55:48 UTC
From what I've seen, folks that use a TH for 'flight' training (as opposed to L/L practice only) tend to fly slower on the approach just to savor the air time. That tends to 'teach' them to have a slower approach for their landing and that is a bad idea. Like Chris said, for experienced pilots, flares are flares, no matter where you are.
Chris, If you are talking about the whole landing, then I have to disagree with you about landing practice on TH's. I do believe that they are good for the launch and the flare. However, a landing also includes setup, approach (dbf or otherwise), downwind flying (sometimes), and flying through gradient. These are simply not doable at a 100' TH.
PS: Chris, I know you are familiar with all the other aspects of a landing, the latter clarification is more directed to the newcomers.
Chris McKee - 2005/08/26 18:17:47 UTC
Rance -
What I was referring to was the post that Scott made on one of the other threads that Training hills are poor substitutes for landing practice. It might be semantics, but "approach (dbf or otherwise), downwind flying (sometimes), and flying through gradient" are part of the flying phase. In my vernacular, landing is the phase where you are established on final, correcting for turbulence and approaching the flare. If anything, training hills tend to reinforce that more than any tow park due to the fact that usually tow parks have HUGE LZs that aren't surrounded by trees or hills thereby causing a gradient. Having received my H2 by flying Taylor's Hill 90% of the time, you are under turbulent gradient conditions most of the time. Especially when a spot is involved, the minute you take off you are mentally setting up your downwind & base then rolling final into thermals cooking off in the LZ and the forcing yourself to pop a picture perfect flare to avoid faceplanting into a load of fresh cow crap. If that isn't good landing practice than our foot-launch instructors must be miracle workers because most of the pilots they have graduated have done quite well on their first mountain flights.
Matthew Graham - 2005/08/26 18:28:54 UTC
Landings
Hi Rance,
My impression as an Observer is just the opposite. Hang 2s with lots of training hill landings really burn it in and nail their landings. I think this may be because they're nervous during first flights at altitude and fly really fast in general. The challenge is to get them to recognize best glide, best manuevarblility speed and min sink. Tow park have a better grasp of flying speeds but they tend to to come in slower on approach. Not too slow... just slower.
Tow pilots are definitely more comfortable with their approach patterns. However, they sometimes get nailed by the gradient. Thus, I always recommend both forms of instruction to new pilots. Why just do one or the other or get fixated on one form of instruction or flying.
Again, these are just my impressions.
Marc Fink - 2005/08/26 18:40:26 UTC
More Voodoo JuJu and other Superstitions
This arguement is beginning to sound suspiciously alot like the mountain launch arguement. How are the basic physics (not the environment) of landing a glider altered depending on where you fly?
Chris McKee - 2005/08/26 19:38:37 UTC
No one said anything about the physics of flying being different, only the difference in levels of learning depending on how you learned to fly either foot or tow. Nothing is set in stone, but in general, tow students come out as a H2 with much better pattern work, but not as defined landing skills. Foot launch students are usually better at landing due to the fact that we do it so many more times at a training hill and the focus is more geared towards the landing phase. As the pilots become more experienced with both types of flying, they become better balanced in all phases. I thought my flying was fine being a foot launch pilot, but my pattern work has become much better now that I've spent the last 3 summers towing.
Brian Vant-Hull - 2005/08/26 20:45:51 UTC
The physics ain't different, just the environment. ALOT different in both cases.
Marc Fink - 2005/08/26 20:52:35 UTC
Oh I see!
Thanks for that clarification.
I read "training hills are poor substitutes for landing practice"...and I thought they meant training hills were a poor place for landing practice. Silly me for misunderstanding that!
Still, I'm wondering if what was really meant was "high ground clearance is the best training for altitude approaches?"
Linda Baskerville - 2005/08/27 01:38:46 UTC
training hills and approaches
I had never thought of the training hill at Taylors as a place for DBF; perhaps that is a shortcoming in my training there. But at Taylor's, because you are relatively close to the ground (50' or so?), the experience I had, and the concept I developed, was to simply do up to a 90 degree turn (possibly a 180 if the ridge lift was adequate to give me the clearance) to land at a spot, or into the wind if it was cross. This parallels my idea of a final leg of a DBF.
At Taylor's as soon as I've launched, I'm not burning off altitude to position myself for a landing, I am coming down to land; my choices are so limited by low altitude, I do not have the option of choosing to come in with a lefthand turn or a right hand turn over the landing area to improve my approach or avoid rotor off of trees, I am committed to landing.
A DBF, to my mind, is how to approach a landing from high(er) altitude: getting the altitude right, the angles right, the length of the each leg right. Would a Taylors landing really be the equivalent in miniature(unless you were popped up to about 300 feet?) I've always thought of most training hill landings as simply being on final leg (with the possible exception of Oregon Ridge launches which really can afford you enough altitude from the top on a good day to pull off a DBF).
If I were to do a training hill style "DBF" as you describe above with one or two 90 degree turns at or below 50', when I'm coming into land at Ridgely, I think they'd haul me off the field and burn my glider, and then ban me from the flight park because the altitude is too low to be safely pulling off turns. It seems to me that Pagin references making that last turn onto final for a DBF from somewhere around 50' AGL (glider performance , and wind, and LZ conditions notwithstanding).
I'm trying to figure my way through this - it is an interesting question.
Maybe it is all simply semantics?
John Simon - 2005/08/27 02:11:56 UTC
Yikes!!! This is a nearly perferct XC!! Glad to hear your back in the
game Paul! Wish I would made it Thur. but had a few things that would not
allow it. I'll be trying again soon though. Great flight... congrats!!!!
Scott Wilkinson - 2005/08/27 04:16:12 UTC
I don't know Chris---this sounds like a seriously misinformed statement to me!I can't speak for Ridgely, but Steve Wendt's students are generally extremely good at landing, period. ("Landing" meaning the upwind/downwind staging area, figure 8s, DBFs---everything right down to the flare.)
If anyone thinks doing "landing practice" by 10 super-low flights in a day down a training hill beats 10 different approaches and landings from 800' in a day, then I'm completely dumbfounded!
I agree with Matthew---better to do it all. But if I had to pick one or the other, I wouldn't train for high-altitude flights and landings exclusively on a training hill. (Just my preference---I know others have done it very successfully, and I'm not bashing them!)
I rarely see anyone float down slowly at Blue Sky---I sure as heck was scorchin' through my approaches 7 times today! And they weren't all the same---I was mixing it up, moving the spot, practicing different approaches, etc.
Hugh McElrath - 2005/08/27 12:59:33 UTC
Jim,
While we are on the subject of towing and when to preemptively release: I think it was you who articulated the rule of three: if you have three oscillations and they are getting bigger or even not dampening out, hit the release.
Jim Rooney - 2005/08/27 18:48:08 UTC
Ding Dong
Yup, that was me. Something I picked up from Bo. He calls it "ringing the bell". (think of someone's body swinging back and forth as they occilate). If you ring the bell once, you can still fix it. If you ring the bell twice, it's time to get on it or get off the line. If you ring it three times, you best be off the line.
Hugh McElrath - 2005/08/28 12:13:43 UTC
Bah! Landing in fields is for pussies; real men land in trees!
Tad Eareckson - 2005/08/30 13:00:13 UTC
I see no reason to incorporate two weak links in a two point release system. I use three - and have been pushing for multiple weak links for five years.
Weak Link 1 is regular strength, is installed at the top end of the primary bridle, and makes things work like the primary release.
Weak Link 2 is a bit under double strength, joins the bottom end of the primary bridle and the Ronstan sailmaker's thimble, and provides protection in the event of a primary bridle wrap. The thimble keeps the primary and secondary bridles from sawing each other apart and prevents those two elements from functioning as a locking mechanism at the time separation is really desirable.
Weak Link 3 is regular strength, is installed at the port end of the secondary bridle and engaged by the pin of the port secondary release, and helps keep you alive WHEN your cable activated primary release fails or your primary bridle wraps. Also, if the primary release mechanism of your two point system is back home in the closet and/or you decide to tow one point...
I see no reason to fly with only one shoulder mounted release. If you dispense with the thimble or tow one point you REALLY ought to have two of them. If you incorporate the thimble or tow one point you REALLY ought to have two of them (see Steve Kinsley's 2005/08/26 post (don't quite understand that one - did the weak link lasso the eye of the parachute pin?)).
I've been thinking that all secondary bridles are way too long. Gonna start experimenting with 110 mm next Ridgely trip. Should reduce the wrap potential at that junction from no freaking way to incredibly no freaking way.
The barrel release I make incorporates a straight parachute pin and is lighter, stronger, and more efficient than the standard curved pin job with none of the latter's propensity to open as a result of contact with the basetube.
The weirdo contraption on Steve's right ought to be mandatory equipment for the one point aerotow crowd. It'll probably take a while but someone's gonna die 'cause he or she wasn't using it. I've taken his concept and trimmed things down to a little over the mass of a photon.
We have the most reliable, safest, strongest, lightest, cleanest stuff out there, I doubt there's any room for significant improvement, and it's too bad no one else is taking much advantage of it.
Dan Tomlinson - 2005/08/31 00:33:01 UTC
Tad's post is difficult to read but I've seen his work. His release mechanism is elegent in it's simplicity and effectiveness.
Marc Fink - 2005/08/31 10:02:15 UTC
One reason Tad's stuff hasn't caught on is that he usually writes from the "You all are stupid" or "You all are going to die" point of view.
He's a pretty sharp guy and makes interesting stuff. It would be a great help to the rest of us if he posted pictures of his handiwork--pretty hard to visualize his verbal discriptions. Does he actually produces these for sale to the flying public? I would also suggest he send out a few units to prominent individuals in the towing community for stress testing.
Scott Wilkinson - 2005/08/31 11:47:53 UTC
Tad's point of view is irrelevant to me---there's no intelligent reason to ignore his work if it is superior to what we're all currently using. (The sport would never improve if everyone thought "if it ain't broke, don't fix it".)
http://www.chgpa.org/forums/viewtopic.php?f=2&t=966Jim Rooney - 2005/08/31 23:46:25 UTC
As with many changes in avaition, change is approached with a bit of skepticism. Rightfully so. There's something to be said for "tried and true" methods... by strapping on somehting new, you become a test pilot. The unknown and unforseen become your greatest risk factors. It's up to each of us to individually asses the risks/rewards for ourselves.
That said, I think I can speak a bit about Tadd's releases. I use both Tadd's and the traditional barrel release systems on a daily basis. Neither to me is superior to the other. They are extremely similar (both simple barrel releases). Tadd's are less prone to accidental release (read: nearly impossible)... this holds true for the basetube release scenario. This is both good and bad. What helps in one respect is a downside in an other. The question is how easily do you like your release to release? A traditional barrel is easier (think: while wearing gloves). Personally I don't find it to be an issue, but like I said, to each his own.
They are also easier to rig incorrectly and are thus more prone to the release failure where they hang up on the eye side of the pin. Granted, it's a bit of a trick to get it wrong, but it can happen and it is easier. It's an obvious thing when you know what to look for (but then, so is hooking into your glider right?).
At the end of the day, I like both release styles... they're just a bit different.
I think Scott has a good point. Tadd's oppinion is irrelevent (so is mine for that matter). The way I'd put it is that the only oppinion that matters is your own... after all, it's your butt in the sling.
$.02USD
inertia
Tad Eareckson - 2005/09/01 02:40:15 UTC
This is gonna be way too long - delete it.
Unless you're Dan. Thanks for the plug, Dan. Now you can delete it.
Yeah, I do need to get an article out on the Oz Report. I've written and revised one dozens of times and have had help from Kolie and Pauls Adamez and Gerhardt with photo sessions but I keep seeing things I need to set up better. Built a model which will illustrate components better than on the real deal but haven't gotten around to the camera work yet.
The documentation has always been available upon request and I do have photos of the glider mounted components which'll do until I'm ready for prime time.
The system itself has, however, been on display every time I've made it to Ridgely over the last four seasons and just about every poor slob who has failed to see me coming soon enough to escape has had a piece of my tedious evangelistic spiel. I apologize for allowing you to slip through the cracks, Marc.
The system has been scrutinized by the big guns from the Florida flight parks, Dennis, and some top notch competitors. The only negative feedback I've had has been from individuals whose only clue was that it didn't look like the big ugly chunk of metal with which they were marginally familiar.
This stuff needs more testing about as much as global warming needs more confirmation study. It gets tested more brutally than anything it's gonna see in the air long before it gets more than five feet off the downstairs carpet. By the time it leaves the the runway all that's left are minor adjustment and design tweaks. The secondary release system has been going up on Ridgely tandem flights for a couple of years. I'd have my equipment evaluated by someone who understands glider releases better than I do but I don't think that person exists. Sorry if that sounds arrogant but I've paid major dues and my AT, truck, and balloon equipment is top notch.
Although Scott's last comment really doesn't need expanding on but... If Bin Laden has provided a cure for AIDS and your white cell count was really low this morning...
My point of view (which was indicated in my post) is not "You're all gonna die" but "You're not dying fast enough" - i.e., there's so much in the way of redundant layers of protection that we can use shoddy equipment and get away with it most of the time.
You can build a city ten feet below sea level smack in the middle of Hurricane Alley, spend a couple centuries destroying the buffer zone, and mostly get away with that. I haven't had any need for a seat belt since I was three years old (and didn't have one).
We're launching off of carts behind highly experienced tug pilots at airports with windsocks and ribbons all over with releases and weak links at both ends of the string. Somewhat contrary to the bumper sticker shit doesn't happen - except in a wee tiny percentage of tows...
A year ago I went way out of my way primarily to share with the Manquin folk the technology I've spent an obscene amount of time developing on and off over the course of the past decade or so. The feedback I received was something on the order of "I guess it's adequate for use at this flight park but it's gonna take five extra minutes to replace a left downtube."
Eight months after my visit there was a catastrophic accident which probably could have been totally prevented and, at the minimum, greatly mitigated by 120 millimeters of Dacron fishing line. Let's call it a penny's worth. It doesn't cost anything, it doesn't weigh anything, it doesn't slow you down, it's not ugly, and, incorporated at the end of a secondary bridle, it'll last forever. What's the downside?! (Notice how I refrained from the caps lock key during that last sentence.)
One aspect of my system is really cool but expensive and not terribly critical. Other aspects can be incorporated independently, cost little or virtually nothing, and provide big performance and safety boosts.
Also, Steve had announced his "squid" release at winter's end. It wasn't available at your local WalMart at the time but, if the weak link might have left a trace of unpleasantness, that mechanism would have definitely cleaned things up completely.
I'm not shooting at Daniel but it's extremely frustrating to continue watching the occasional bit of death and destruction here and in Chicago and on the other side of the world when the technology to prevent it has been around for a long time.
I have some polio vaccine, it won't help with smallpox and AIDS, but it doesn't cost much and for nothing I'll show ya how to whip up some of your own in the kitchen.
A glider in line for a full installation recently left a fly-in in a couple of Hefty Bags so I have lots of extra components lying around and the summer's just about over. Any takers?
Hugh McElrath - 2005/09/01 03:11:32 UTC
Hey, Thad, Steve Wendt says my glider will be fixed in a couple of weeks, so it's still a candidate for early installation of your system.
http://www.chgpa.org/forums/viewtopic.php?f=2&t=2467Tad Eareckson - 2005/09/02 14:12:36 UTC
Yeah, sorry Hugh, didn't catch your announcement in the Pulpit Teams post before sending. I'll slap the RESERVED stickers back on the parts.
I'm wondering if the curved pin release is, in fact, easier to actuate 'cause the barrel has 143% of the diameter or my straight pin job is easier 'cause the barrel's over twice as long. I've never seen any evidence that there's any difficultly in opening either one (assuming one can get one's hand there at the right time). And since I never fly without them I most assuredly had thunk gloves during the design process. I can make the barrel any diameter I want but there's nothing wrong with the current model.
Given the choice between sticking something in the airflow (and, after release, my sternum) long and trim versus short and fat, I'll go with the former(never seen a Willow Ptarmigan diving on a Gyrfalcon).
I also get lighter and stronger. Both will function under a 200 pound load but after the test on the curved pin you'll have to stitch in a new one.
With a bit of extra effort the straight pin release can be connected to the bridle or weak link in locking mechanism mode but if one is that stupid my feeling is that that individual should either leave the sport, gene pool, or both.
And as of a week ago we know of one more curved pin failure than straight (1:0).
Not that this really matters anyway. If you fly with a proper two point system the likelihood that you will ever have to use a secondary in a critical situation is something around zero and if you're flying one point you should have a squid trigger in your teeth.
With respect to the full two point system... The conventional cable based system is not "tried and true" - it is "tried and unreliable". I hear of failures just about every time I go out. My system has NEVER malfunctioned on the bench or in the air and I have yet to see the scenario in which it can be made to. I suggest that old designs need to be approached with more skepticism than new.
And the stored energy version of my leechline lanyard based system is not "new". It's been around for over four years. In terms of hang glider evolutionary scale that's freakin' ancient. And the first evolutionary stage of this thing first went aloft eleven years ago Sunday. And there's never been a failure involving any of those. Is that long enough?
When I clip into a hot-off-the-press new topless supership demo for the first time I am not the test pilot. I'm just some jerk checking out a superior, proven, certified design.
Finally (for the time being anyway), nobody's opinion, including that of the pilot on the cart, is worth a rat's ass.
This system is not built on opinion. It's built with respect to stuff like physics, engineering, aerodynamics, mechanics, load testing, worst case scenario capability, and logic.
Weight is a bad thing, strength is a good thing.
Abrasion is a bad thing.
A 3/64 inch leechline lanyard running inside a faired downtube causes less parasitic drag than a cable housing four times that diameter velcroed to the out side.
A straight pin exerts less lateral force and experiences less stress in a barrel than a curved one.
No one ever died as a result of having a weak link.
A pilot having a finger (or pair of incisors) on the trigger has a greater chance of survival than one who has to hunt, peck, and pull.
A pilot using a release system with no history or capability of failure has a greater chance of survival than one using a system in which failures are routine.
Flying decisions need to be made on the basis of numbers. With a rosy future opening up in the field of intelligent design education there's plenty of room elsewhere for opinion.
weak links
Tad Eareckson - 2007/05/16 12:53:34 UTC
Got bored towards the end of last season and started doing a lot of archive searches along the lines of "weak link broke" with respect aerotowing to see if any of the little bits of string served any function more useful than do the sacred back up suspension straps and hook knives.
Short answer - no.
In more depth... Most of them happen for no reason whatsoever or 'cause somebody approached the tow line with a piece of fuzz. The minuscule percentage of breaks desired should not have been necessary.
Also did enough research in the tow discussion group archives to now be one of about half a dozen pilots of the hang glider flavor who understands what a weak link is (after all these years working on these systems).
News flashes...
The allegedly overstrength weak links of Mike/Bill and Robin had nothing to do with their accidents.
and
Holly had a weak link and it worked fine.
The sole purpose of a weak link is to keep the planes at the ends of tow line from breaking up. None of the tugs sustained any damage and all three gliders were in great shape all the way to the ground.
A really flimsy weak link can easily transmit enough tension override your control authority enough to slam you into the runway and stay intact all the way to that point. And you can use that same weak link to put the tug out of control.
A weak link may fail in a lockout but there's supposed to be a pilot controlling the aircraft who should have released long before things got to that point. If you're low and waiting for that safety feature to kick in you're playing Russian roulette - kinda like waiting for the air bag to inflate instead of hitting the brakes.
Let's pretend we're sailplanes and have to fly under government standards. The FAA says we gotta have either a tow line (see Holly above) or weak links at both ends of one that fail at between eighty and two hundred percent of payload (the weight of the stuff at the back end of the tow line). Expressed another way that's about 1.40 plus or minus .43 Gs. (The USHGA AT Guidelines specify the same top end but, consistent with the junk we use, say nothing about the bottom.)
Right now if a Karen/Ayesha sort of person approaches a flight line and asks for a weak link she gets a little loop which, when installed on a two point Spectra bridle fails when the tow line tension hits about 240 pounds.
If I make the same request I get the same piece of string and end up off the bottom end of what the FAA defines as the safe range - as does anyone else who suits up, clips in, steps on the bathroom scales, and sees a number larger than 305 on the left side of the needle. What I really want is something that blows when the line tension hits 620.
So the situation is that we're using chintzy weak links as compensation for chintzy releases that we can't get to in time and may not work even if we do (see Robin above) and gumming up flight lines for relaunches during prime time with one of the Dragonflies out of commission.
We should be breaking weak links at about the same frequency as do sailplanes and that we throw parachutes - never. And if a weak link is broken it should be because someone really screwed up.
Placement...
Weak links don't belong on the end of the bridle. All two point bridles can wrap. Every one point bridle I've ever seen 'cept for the ones I've made is way too long and can wrap. Bridles are most likely to wrap when released under high loading, i.e., when it's likely to be the least convenient and the highest loading possible is at weak link failure.
If you have a weak link at the top end of your two point bridle and/or one between your aerotow (shoulder) loop and an end of your secondary/one point bridle (as, insanely, is recommended in the USHGA Guidelines) you have one or two "maybe links".
The fact that Holly had no secondary weak link was inexcusable (that's cultural - not individual). If she had been using a two point bridle and it had wrapped she would have been in exactly the same position - towing one point and using 5 G weak link.
Weak links belong on the ends of the tow line. You can pick up a safety advantage by supplementing them with links on the bridle(s) but... this is way too long already.
Here's a quote from "Towing Aloft" (Page 349)...
"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!"
Lesson learned - Rather than reconfigure to a system that actually works when you really need it, just keep on doing things the same way and maybe you'll keep on getting lucky.
Chris McKee - 2007/05/16 14:57:36 UTC
I'm not positive, but I believe that Holly forgot to put in a weak link. The story I heard was Tex released the rope. You might doublecheck that, but I think that was part of the problem with Holly's incident.
Tad Eareckson - 2007/05/16 22:30:55 UTC
Thanks for the response, Chris.
I stand partially corrected. I checked back and although there were a couple of early reports that the tow line broke, the later and most reliable one from Steve stated that Tex let go. I plead guilty to locking in to first impressions and am glad to have learned that the tug pilot took appropriate and timely action.
I have to modify Holly's accident category a bit but my point still stands - if the tug landed and the glider was intact before it hit the ground, the weak link was not a legitimate factor.
What is consistent with all the reports is that her primary/two point bridle didn't make it to launch. One of the points I'm trying to make is that, even if it had, she was gambling that it wouldn't wrap and, if it did, she wouldn't be needing a weak link at her end of the line. She needed to have at least one on one end of her secondary bridle.
A couple more quotes from "Towing Aloft"... Page:
045338The towline release is a critically important piece of equipment. It is the device that frees you from the towline and it must be failure-proof.Anybody else see a major disconnect (or, actually, lack thereof)? That was at the beginning of 1998 but we're still using the same crap.The most common release emergency is when your release doesn't work.
Here's a quote in reference to 2005/06/08 at Ridgely...
I think the Russian roulette analogy is a bit generous. I don't think you're gonna be lucky an average of five outta six times. We need to have pilot control of these situations. In accordance with USHGA Guidelines, you need to release immediately at low altitude if:Yesterday I was LUCKY that my weak link broke on my first launch (the next two pilots after me broke theirs at the same place, a thermal breaking off at the end of the field).
- you're
-- pointing more than 20 degrees away from the tug;
-- rolled past 45 degrees; and/or
- your oscillations are getting worse.
Danny Brotto - 2007/05/16 23:15:19 UTC
Weak links are not a secondary release system...
... they help and hurt under various circumstances.
http://www.dynamicflight.com.au/Reading/WeakLinks.html
Marc Fink - 2007/05/17 14:06:06 UTC
"Captain, there's a black hole dead ahead and its drawing us in.."
"Scotty...full reverse on warp thrusters..get us out of here now!"
Tad Eareckson - 2007/05/17 23:03:32 UTC
Thanks very much for that link, Danny. I feel so much less alone now. Wish I had known about this James Freeman person before I duplicated a lot of the typing he had done two years prior.
Still needs some evolution though. A small percentage of the AT crowd has figured out that the weak link belongs on the end of the tow line, but I only know of one other individual (Marco Vento in Portugal) who has figured out that a weak link is not a cheap piece of knotted string.
He's using Tost sailplane weak links which I had checked out but shied off from 'cause, while you can get inserts for whatever failure point you want, the base structure is really overbuilt for the range in which we're interested.
I subsequently developed a color coded system based upon two leechline elements stitched together, the number of stitches determining the strength rating, with a tolerances within plus or minus twenty percent. My predictions are that these things will last forever - will not wear out or degrade with use - and undesired (i.e., all) weak link breaks will become a thing of the past.
They will probably be adopted at Ridgely - we're currently working out a few options. A 400 pound weak link will keep solo gliders from 250 pounds up within specs and leave tandems no worse off than they are now. We can temporarily pop something on the end of the heavy stuff for the Karen/Ayesha sort of person.
If/when this stuff flies although you'll still be able to use your little loop of Greenspot, there will hopefully be a penalty for having your fuzz give up the ghost immediately or shortly after the Dragonfly gets loud. If you would prefer to be in charge of the decision as to when to terminate the tow, lose the fishing line and make sure the bridle eye is big enough to clear the spinnaker shackle if you're still using that crap.
This new technology is an adaptation of a concept I developed for integration with my primary and secondary bridles and started using last season. About a month ago I got slapped really hard and was able continue on behind the tug. No way I'd have survived that with a conventional weak link. It's a really good feeling to know you're not riding up on the brink of disaster the whole time.
Marc Fink - 2007/05/18 14:16:20 UTC
Tad--I've said it in the past--I really admire anyone that seeks to improve safety in towing (becuase it is necessary)--but I really don't have the slightest idea what the frig you are talking about!
You toss around load limiting figures without any real asociation to breaking strengths and desired load limitations. Just because a weaklink on liftoff breaks doesn't mean it has failed to do what it's supposed to do. If you go out and get slammed in turbulence on lift-off and the weaklink breaks--the failure is not in the weaklink--but in the pilot's judgement for going at that time in those conditions and/or not responding quickly enough to unload the pressures. Them's the breaks, so to speak.
You have a predilication for using scare tactics and pure speculation in some of your accident interpretations. You seem to expect that people to accept your equipment and ideas based on your convictions before they're proven.
Please get in touch with Peter Birren and get some info on development and implementation of safety systems. When you have a safe system based on meaningful quantitative test results--then present it in a positive way. I promise I'll be the first to adapt when and if it passes muster.
Jim Rooney - 2007/05/19 01:43:49 UTC
yeah, but speculation and 'conviction' are so much more fun
Glad to see you recognised the black hole just before it sucked you in... too bad it's too late to avoid it... enjoy your pointless debate
Tad Eareckson - 2007/05/19 12:09:20 UTC
Marc, the archives are littered with examples of you not having the slightest idea what the frig people are talking about.
If you bother to read my previous posts in this thread and run some grade school arithmetic you will note that I haven't tossed around any figures. Those are FAA and USHGA figures.
I've been flying at Ridgely since its first weekend of operation. I've seen and heard of a lot of weak link breaks at takeoff but none of them has involved somebody getting slammed at that point so hard and fast that his glider was in danger of failing and he didn't have time to get to a release either ('specially if that anybody is Steve or me). John Dullahan hit the classic worst case scenario about a year ago with a release actuator mounted in the worst possible location and still did what he needed to.
Define "proven". Is the equipment you use "proven"? By whom? What standards? Where's the documentation? What muster did it pass? Do you have a clue as to the tow line tension required to break your weak link? Do you have a clue as to how much tension you're normally dealing with behind a tug?
You're not using your equipment because it passed muster. You're using it 'cause a long time ago somebody at the only shop in town tossed together a half baked idea and sold lotsa them.
Where do you come off with the assumption that I DON'T "have a safe system based on meaningful quantitative test results"? I've offered several times on this server in the past couple of years to provide documentation to whomever wants it. It's up to 117 pages now. I don't recall any requests from you (or Jim, for that matter). The late Reverend Falwell made much more powerful arguments preaching from and to points of ignorance.
You still in the Skysailingtowing group? Did you bother to read my posts or download the file I put up last winter (he asks rhetorically)?
It appears that Peter Birren is the only one who did.
And yeah, I've read Peter's stuff and corresponded with him. I got turned onto the closed bridle way of doing things by him. His system takes care of some vulnerabilities inherent in our opening bridles but you gotta reach for the lanyard and I can make a pretty good case that in the real world my system is safer. We've both perfected things as good as they're gonna get in our respective fields and we're not gonna learn anything more from each other.
By the way - I don't do speculation and convictions. I do accident reports and physics. If you have evidence to the contrary please cite it.
Marc Fink - 2007/05/19 12:58:31 UTC
Tad--you have in fact made many erroneous statements concerning accidents--mostly to back up your convictions of the faulty nature of towing. The simple fact is that hundreds of thousands of tows using weaklinks in their present configuration successfully bely your contentions that we're all crazy for towing that way.
Simply put, your statements are irresponsible and are based on your personal interpretations.
I am a tow operator--as well as a "towee." I also do aerotow tandems. Using greenline or similar line, which generally tests at 125 lbs +- 50 lbs is widely accepted because it simply works well and relatively predicatably for the enormous range of conditions and applications in towing. If this weren't true, then accident rates would be much higher and these kinds of weaklinks would have been abandoned along time ago.
A 400lb load limit for a solo tow is absurd. You claim in-depth knoweldge of what you're doing--but do you know what kind of stitching your using, what kind of tack, and how it affects the integrity of the join you're doing?
Last year's jihad was against releases--now you're going after weaklinks.
Everyone supports you making efforts to improve things--but in the process you trash the present methods as somehow being an accident waiting to happen. You might not actually say it--but the implication is that both the operators and towed pilots are being irresponsible for using faulty equipment and practices.
Do pilots need to constantly review their tow systems? yes. Do weaklinks--being the weakest link in the system, after all--need to be carefully inspected and frequently changed? yes. Do we need to constantly try to improve things? yes. Do we need to scare the daylights out of pilots with doomsday scenarios and suggest punative action for using widely accepted practices before something better comes along? Definitely not.
My apologies to the list for waking this sleeping giant.
Tad Eareckson - 2007/05/19 21:29:05 UTC
Marc, let's take the weak link you described - 125 +/-50 - and put it on the end of a one point bridle. Its top end is 175 which doesn't happen until the tow line hits twice that which is 350. That makes it a (350/300=) 1.17 G weak link.
I'm talking about a 400 pound weak link THAT GOES ON THE END OF THE TOW LINE where it benefits from no force split and is thus a (400/300=) 1.33 G weak link.
So you and I are talking about a tow line tension difference of fifty pounds or a third of a G.
And I'm still 200 pounds or two thirds of a G below the limit specified by USHGA and the FAA. (If you have a problem with that figure take it up with your Regional Director - not me.)
Let's look at the bottom end - same glider, same bridle. 75 times two is 150 pounds which is half a G and .30 below what the FAA says is safe to tow a glider under their jurisdiction. And it gets worse if you put it on the end of a two point bridle.
I see you still haven't bothered to look at my documentation which answers the questions about my weak links but they don't deviate more than 21 percent up or down. You seem to be quite content with a tolerance of 39 percent. (I also note that you continue to be content to throw out broad accusations without citing any evidence.)
If hundreds of thousands of tows have been completed successfully then tens of thousands of attempts haven't.
Here's some stuff off the wire from the local crowd (none of which coursed from my pen)...NEVER TRUST A WEAK LINK!
Expect two things from your weak link:
(1) It will break unexpectedly at the most inopportune time, with no warning adn no indicaiton of a flight problem.
(2) It will hold strong and fast whenever you move into a lockout.Then I switched to the falcon and the birds were singing in tune again. Until the brand new weak link vaporized at about 1000 feet for no apparent reason.At 840 feet I noticed the tug was high and rising so I pushed out a bit to catch up. Broke the weaklink and stalled since I was so nose-high.First try was a notably short flight, with a weak link break moments after lifting from the launch cart. The wind had shifted, so I had a down-wind landing, rolling in. I succeeded in dragging a knee instead of a toe on one side, so I earned a nice strawberry scrape.I got five launches with three full flights on the US. Two weak link breaks. Both were non-issues.Got to Ridgley after 12, late as usual and was one of the last to launch. Broke a weak link. From now on I use a new weak link every time since they're giving us dental floss now.Kristen attached me to the plane and I rose briefly in the air. Pop! My weak link broke. (...The bad part is that sometimes the links just break, for no particular reason.)Just a quick story with good educational value for other tow pilots. Yesterday I was the second of 3 off cart weak link breaks behind a 914 tug. Turbo was kicking in too quick says Bo.I bent one this year when I had a weak link break right off the cart...I had a weak link break at maybe 50 feet. I thought I was going to have to land in the soybeans -- the very tall soybeans -- when I looked at my angle. But, my glider stalled quite dramatically almost instantly (hard not to stall when you have a break), and dove towards the ground (a bit disconcerting from so low)....I hit enough turbulence to break my weak link. #%*&!Steve had a weak link break on his first launch just after leaving the cart and rode it in on the asphault.A second later, we are horrified to see her weak link has broken. We know she has been well prepared, but we want her first flight to be perfect....but at 400 feet my pussy-##s weak link broke.I had a late start due to a weak link break.Being a "large and tall" pilot (6' and 225lbs) on a big glider, I don't get pushed around as much by thermals...but then again, I'm pushing the weak link that much closer to its breaking point (since everyone tends to use the same test-strength line for the link).I've only had one weak link break while aerotowing and it happened while I was still very low and over the runway. I was happy that I automatically pulled in as soon as I heard the snap and got slow.One of the more interesting and poinient ones is the smooth air break. Towing up in smooth air, in position and you have a good weaklink... just towing along straight and level, nice and smooth... when the weaklink breaks. There's no appearent reason. No rough air, no rough glider inputs... it just breaks.Broke the weak link at 100' this time. The tow was a little rowdy, but not that bad. Don't know what caused the break.This time the link broke at 900'. Damn.Broke the weak link at 1000'. And it was a fairly mellow tow.I was in line early but had a green tow pilot. My weak link broke after an extremely fast 350 feet.Anyway, on my first tow, Tex entered a thermal at just over 1100 AGL, and I failed to track properly behind him. I got turned away from him (not badly) and as I was about to get back into position the weak link broke at 1200 AGL.I could feel a huge gust hit right as I came off the cart. Uh oh. I was right behind the tug at maybe 100 feet when my link broke. (Kev said yesterday the weak link might have also broken because of the very powerful tug, which throttled back yesterday.)And, somehow, after all these years, I've never heard anyone say, "Thank gawd my weak link broke! My crossbar was about to go!"My weak link broke for no obvious reason at ~2,000' as Zack was pulling me in a wide turn to get back into a thermal he had found earlier.
We're too close to and often off the bottom end on this crap. This stuff doesn't happen to sailplanes and they couldn't afford it. We've just accepted it 'cause we think that's the way it's gotta be.
This isn't about trying to make everyone think that he's gonna die 'cause his weak link popped at twenty feet. This is about trying to put the decision regarding termination of the tow in the hands of the pilot - where it belongs.
Tad Eareckson - 2007/05/19 23:00:28 UTC
Make that forty percent.
Chris McKee - 2007/05/20 02:53:35 UTC
One thing in all of these quips that you cut/paste from our posts that you haven't mentioned is that not all of these weaklink breaks are from brand new weaklinks. A couple of those posts were mine and I don't tie a new weaklink every time I fly. Usually I go 10 or more tows before I decide to retye it or it breaks and I have to anyway. I always check my weaklink visually, but if it breaks, I pull in and make my decision on where to land. If you are getting into a lockout and blaming it on a weaklink, than your decision ability is flawed in the first place. If you get out of position on tow, it should be the pilots decision to use his release and go around for a second time than blame a lockout on the weaklink NOT breaking.
I agree with Marc (scary!) Last year we listened to rant after rant about the releases. Are we going to have to revisit this new topic each week until that vein in someones head begins to pulse rapidly and they decide to beat you silly with a broken downtube?
In all seriousness, we all care about safety ... and none of us will beat you with a downtube, but we will all fantasize about it if you keep this up!
Tad Eareckson - 2007/05/20 15:57:51 UTC
When I make the decision to sacrifice a day and pump into the atmosphere the CO2 it takes to get to the bridge and beyond, I don't want to stand around cooking in my harness while the soaring window evaporates - even on the rare occasions when there's more than one tug running - 'cause people with unreliable weak links get connected to the tow line in front of me - and then go back in line in front of me with my lift ticket subsidizing the expenses.
I've been to Ridgely twice this season and have twice been subjected to same already from gliders within a couple of positions of my place. Both times the pilots were using antique weak links which had been near or off the bottom end of the scale even on their first flights.
Someone with a weak link below a .8 G capacity on the end of his bridle is not prepared to fly. I don't even want him near the tow line while I'm stuffing battens if he's affected the length the line will be by the time I cross the taxiway.
Selfishly - I wouldn't even want him paying Highland for the extra tows 'cause I want him up there marking thermals for me. (I need all the help I can get - all the sailplanes are gone and the vultures have been absolutely negligent so far this year.)
Chris, neither you nor anybody else is forced to read anything with my name on it - you don't even have to delete it from your mailbox anymore. But the only time your decision to fly with a questionable weak link (and all of them are questionable now) doesn't have a negative effect on everyone else is when it pops and you claw your way up anyway.
The last two sentences of your first paragraph are a reiteration of what I and the author of the link referenced by Danny have been saying.
Marc's statement about the reliability of Greenspot weak links is nonsense.
The bottom end of a Falcon 140 is less than half of a Talon 150. And they and everything in between get the same string?
Weak link ratings are not selected as a function of the range of conditions. They exist solely to protect the airframe. As you said Chris, they do and can not ensure your control or protect you from a lockout.
You're not going to be seeing much of an effect in terms of accident rates as a result of shoddy weak links. You will see a higher per day rate of landings and takeoffs. We see them.
The statement that things are just great 'cause if they weren't we'd have done something better is like saying that the water couldn't possibly be hot 'cause all those frogs would've jumped out by now if it were.
I was, by the way, well aware of the fact that you and lotsa people don't bother changing their weak links when they should but that's irrelevant 'cause -
A. That happens to be the temperature of the water; and
B. We all know from personal experience (yours truly included) that you can have a brand new loop of Greenspot break straight and level fifty feet up in glassy air for no reason whatsoever.
There just aren't any AT weak link breaks in situations in which our six G airframes are being threatened. A weak link goes 'cause a tug is climbing too fast? Was a cross spar about to blow? And Lauren doesn't even weigh anything. This is bullshit.
Here's what I'm proposing - and I've shifted to another flavor implementation since starting this thread.
You find out how much you and your stuff weighs. If need be you step on the bathroom scales out at the flight line.
When you get your preflight check you say "250 pounds."
The launch person hands you a Gray/Blue 360 pound shear link with a tow ring incorporated in its aft eye which puts you at right about the middle (1.44) of the FAA's .8-2.0 G range and everybody's ass is covered.
You can see what one of these things looks like at:
http://www.flickr.com/photos/aerotowrelease/
As for me, 310 pounds, I'm gonna sign the waiver and use 600 pound/2 G shear link with an error could spill me a hundred pounds into the red zone 'cause I'm not worried about my glider breaking up. (Actually, that probably won't happen 'cause the Dragonfly tail may be a limiting factor.)
You run your bridle through the tow ring and connect the bridle to your release.
You get to launch and the launch person unclips the previous shear link from the carabiner and replaces it with you.
This weak link will only fail when you want it to which, as you pointed out, Chris, will only be well into a lockout and long after you should have tested the functionality of your release.
If it does fail, which should happen at a frequency less than that at which your parachute is deployed, you are requested to secure the back half of the shear link before releasing and stowing your two point bridle.
So, Chris, if you're absolutely positive that there is no room for or possibility of any improvement in these systems, just click on by. Otherwise, critique what I'm saying.
I really do appreciate efforts to correct me when I've made an error like the Holly/tow line thing. (I'm still waiting for Marc to provide a single quotation supporting his accusations.)
Brian Vant-Hull - 2007/05/20 17:25:27 UTCGee, Tad, I've used my hook knife and been glad I had it.Tad Eareckson - 2007/05/16 12:53:34 UTC
Got bored towards the end of last season and started doing a lot of archive searches along the lines of "weak link broke" with respect aerotowing to see if any of the little bits of string served any function more useful than do the sacred back up suspension straps and hook knives.
Don't feel qualified to comment on weak links. What follows is pure gut opinion and therefore not subject to argument. Have to admit I don't know of a case where someone was clearly saved by one. I popped 5 in a row once while trying to learn how to tow a K2. Really don't know whether the breaks saved me or not, but clearly I wasn't handling it smoothly and could have been getting myself in trouble. Whether or not it's true I always feel comforted by the thought that something is designed to pop before the forces get too large, and feel better with something weaker rather than stronger. Pure untested psychology.
I think you'd want them breaking every now and then just so you know they CAN break. Is 1 break every 50 tows an acceptable number? I think right now we're hitting about 1 in 20.
Tad Eareckson - 2007/05/20 23:16:27 UTC
Hi Brian,
I didn't state that very well. I do still have a hook knife available above my parachute container but, since I'm never flying near bodies of water more formidable than the upper reaches of the Choptank and Tuckahoe I find myself asking myself why with increasing frequency lately. Could come in handy in a tree but that ain't likely flying from Ridgely either - even for me.
If I ever heard of your hook knife incident I've forgotten - unless it involved falling out of a tree at High Rock. Can you fill me in?
If you used your hook knife as a means of leaving a tow line behind please REALLY fill me in 'cause my contention is that the only way that can happen is if your release and bridle system REALLY sucks to begin with.
There are a set of USHGA AT Guidelines which REQUIRE you to have a hook knife but RECOMMEND that you have a secondary release. Major priorities crisis.
A little aside - I don't think you can learn to tow a K2.
Here's the deal about weak links. I don't think you get it. Don't feel bad. I JUST got it within the past few weeks - months after reading a post on the towing list from somebody who gets it. The guy on the link Danny cited gets it.
THE WEAK LINK IS NOT THERE TO SAVE ANYONE. THE WEAK LINK IS ONLY THERE TO SAVE THE PLANE.
The RELEASE is there to save you (and I commend you for being a member of the minority of pilots who appreciate the importance of having a hand on the actuator at all times).
You only need to have the weak link go a bit before the cross spar (I'm ignoring the tug for the purpose of this discussion). We've never been anywhere close to that.
Even a flimsy weak link at the bottom end of the acceptable range (.8 Gs) can hold enough to put and keep you in a lockout. In a lockout you - by definition - have NO control of the glider. The only way to regain enough control to live, if you're anywhere near the ground, is to release.
The weak link might go soon enough to let you live, or it might not go until after you're dead. You can't afford to wait and find out.
Your confidence must be in your abilities to make a correct and fast decision to release and physically implement it. Steve and I can handle the latter requirement by relaxing our jaw muscles.
We're asking the weak link to function as an emergency release to save the pilot. It cannot do that. We've dumbed them down so much that if you get waked by a migrating Monarch you're blown off tow.
I've been doing some testing lately and it's looking like the maximum tension the tow line/weak link/glider normally experiences happens while Bob is running next to you saying, "Have a good flight!" And I have an educated guess that says that the standard weak link experiences some degradation during this acceleration and in the course of the flight - even before it gets chewed up by the notch on the end of the spinnaker shackle gate.
In the weak link I've developed the critical element is isolated and protected and, in theory, will not degrade and will last forever. It either survives unscathed or it explodes at pretty close to the point you ask it to.
We don't want them breaking at a rate of 1:20 or 1:50. We want them to break at the rate sailplane weak links break - never. If we can't control the glider we should have released long before they break. (I'm gonna use your one in twenty guesstimate until somebody comes along with something better.)
If we want to be sure they break we don't want to test them in the air. We want to verify that on the kitchen table using the 776 pound capacity tester I built last winter. But I've done that already on a range from zilch up to 636 pounds. They work.
Marc Fink - 2007/05/21 01:19:31 UTC
You've aerotowed your kitchen table? Awesome!
Chris McKee - 2007/05/21 01:50:59 UTC
I've got a topless table ... glide ratio sucks though
Brian Vant-Hull - 2007/05/21 14:52:18 UTC
If the maximum force truly is largest right when the tug starts to pull you (and this seems eminently reasonable during a normal flight), and a lockout never approaches this force (don't know if this is true), then your contention that our weak links are entirely too weak rings true.
How have you been testing the forces? Could you (hehe) do us a favor and test it during a lockout?
I used my hook knife to get free of the glider while in the tree at HR.
I really like the idea of a mouth actuated release for the first 30 seconds of tow...been too lazy to put it into practice.
Marc Fink - 2007/05/21 17:05:41 UTC
Ain't no device going to mitigate the fact towing in turbulence is riskier and takes more piloting skill. Changing your breaking pressures is only going to shift the bar on the decision set that the pilot must make in those split seconds during initial tow. Tad is correct in one statement--the weaklink does protect the plane, especially during roll-out and liftoff. Upping the load limit means more trust will be placed in the towed pilot in doing the right thing. keeping the line under higher pressure at initial lift-off, IMO, will increase the probability of lock-outs over the broad range of pilots and conditions, while increasing the risk to the tug as well.
When Tad succeeds in convincing one single very experienced commercial aerotow tug pilot that his system is better and safer, then I'll start taking his ideas seriously. Tow operators are the ones who really have it on the line, so to speak, and if and when a better idea comes along they will adapt if it improves the safety or efficiency of their operations. Untill then, your still a test pilot.
Dan Tomlinson - 2007/05/21 18:18:18 UTC
risk management
People who calculate risks and returns often use a quantitative technique. They multiply the expected probablility of an event times the "value" of its consequence. The premise is that if the consequence is relative modest you can tolerate a realitively higher probability. In our sport unfortunately the consequences can be extreme, therefore it is prudent to lower the probability of a serious consequencal event as much as possible. While I am sure it has happened I have yet to see a serious outcome from a premature weakling break. On the other hand a weak link that doesn't function when it should can amd oftem has led to a catastrophic result. It seems that the lesson is to err conservatively, better to break too early than too late.
Last year Tad carefully looked over my harness while sitting under the canopy with nothing else to do. he found a significantly frayed line that could have resulted in a serious accident for me. I was at first reluctant to listen to him since he always seems to be such an alarmist, but upon inspection confirmed that he was right. I took two lessons away that day, one preflight your harness as well as your glider, and two don't discount someone's observations based upon your own preconceived notions.
Mike Lee - 2007/05/21 18:44:42 UTC
links
A funny thing occured to me while flying this weekend......
I can't recall a weak link breaking on launch or climb-out
in the mountains......
Flying both affords me the chance to relax my brain......LOL
Hope to see ya'll soon
'Til then, mike
Tad Eareckson - 2007/05/22 02:13:19 UTC
Marc,
Thank you for contributing something halfway responsible to the conversation - for a change. It would be nice if you acknowledged a few things with respect to your previous posts which you made without bothering to read and/or take the time to understand what was being discussed but I'll take what I can get.
However...
First off, since USHGA specifies an upper - 2.0 Gs - but, for some bizarre reason, not a lower weak link limit, can we agree that at some point there is a safety compromise by using and excessively feeble weak link?
Yes? Good.
Now, can we determine a value for that lower limit? The FAA sez 0.8. Any objections to that figure? No? Good. Zero point eight it is.
OK Marc, listen good. THE WEAK LINK ABSOLUTELY DOES NOT PROTECT THE GLIDER AT ROLLOUT AND LIFTOFF. That's the one point of the flight at which it is the least part of the safety equation. IT ABSOLUTELY DOES NOT PREVENT A LOCKOUT. It can limit the extent of a lockout up high but down low you're in deep shit unless you're climbing.
No weak link can enhance your control of the glider in turbulence. You will be totally out of control, i.e., LOCKED OUT, before its strength becomes a factor.
The weak link keeps the glider from breaking up in the air. It may accidentally function to prevent the glider from slamming into the ground but provides no guarantee. If you start trying to ask it to perform a dual function you compromise its ability to get you SAFELY clear of the ground and up high enough to stand a reasonable chance of finding lift.
Like James Freeman said - "None of this is rocket science. It is basic physics combined with elementary mechanics."
There are only two things you have to consider with respect to a weak link - what strength and where to put it.
If you listen to PETER BIRREN (http://www.birrendesign.com/LKAero.html) (Marc) or me, you put the weak link BETWEEN THE TOW LINE AND THE BRIDLE. That way you don't have to worry about the bridle wrapping at the tow ring (carabiner) if the weak link fails. He suggests a quadruple loop of 130 pound Greenspot which, assuming a quadruple loop is twice as strong as a double loop of the stuff I tested, translates to FOUR HUNDRED AND FOUR POUNDS (Marc).
I interpret your second paragraph to mean that you will never, under any circumstances, review the data and attempt to understand the science yourself? You'll just follow the lead of someone with enough brains to do it for you? Fine. I'd just prefer not to hear anymore about equipment that passes muster when your definition of that is just a matter of what most of the rest of the sheep are doing.
Dan,
Thanks for crediting me with the catch but I think the most I saved you from was some awkwardness and discomfort. The stuff that kept you connected to the glider was OK.
Brian,
Thanks very much for the positive contribution to the discussion. Nice to be talking to someone for whom physics is not a totally alien and irrelevant concept. I knew there was intelligent life out there somewhere. Eternal gratitude for taking the first step in rescuing the conversation from the gutter to which, I feared, the Usual Suspects would once again manage to drag and leave it.
Last fall I developed a device based on the strength per stitch principle in which there are graduated sequences of stitches. You install it between the tow line and the glider. When the tug rolls sequences fail up to the holding point and the pilot can see (thanks, Sunny, for the idea of putting it on the proper end of the tow line) what is or isn't happening when. The gauge goes back down with the tug where it is retrieved and examined.
Only have a few tests to date but I myself went up behind it on my last outing and got something with which I'm pretty happy (dolly tires properly inflated, conditions and glider weight and configuration (full VG) recorded). Max load of about 160-175 pounds occurred at launch and was not exceeded in flight.
Recently I adapted a hydraulic cylinder and one and two point bridle/release configurations so's you can get constant readings in flight. (Hint: If you try this at home don't stare at the gauge too long or you'll have a real hard time finding the tug when you finally look up.)
With the 914's turbocharger kicked in (like they do for tandem) I got about 155 pounds. I'm calling the normal solo power setting 125 but I had trouble holding steady early in the flight and will need to go back up to get something with which I am really satisfied. A little pitch input translates to a lot of needle swing.
I'm guessing, at this point, that the in flight tension is only a function of engine setting, i.e., solo and tandem will be the same but the latter will be going up slower.
If you want more extensive info on the gauges lemme know and I can send you a PDF (149 K) (there's a schematic of the max tension recorder).
I once asked Sunny if they train students using induced lockouts but he pointed out that if you brought the bridle in contact with a nose wire and the top end wrapped you could have real serious structural problems real fast (oh, yeah).
However...
If you pop one of my links on the end of the tow line... I'd have absolutely no problem doing that at altitude and it could be a useful training tool.
We wouldn't be learning anything about tow tension though. As of a week ago we know about what steady state is, we know that the graph is going up as we roll away from the tug, and we know about where conventional weak links fail.
We could, however, experiment with different weak link strengths and get a subjective feel of the glider at failure.
I'm delighted to hear that you're interested in joining the Steve/Tad/Eastern Europe fraternity of folk who can release without doing anything.
Steve's three-strings are effective and free but the grommet/webbing interface needs work. My four strings are stronger and more versatile but are labor intensive and go out as part of a full secondary assembly (barrel release on the port side).
Take a look at the pitchurs -
http://www.flickr.com/photos/aerotowrelease/
and lemme know if you have further interest. I really like the confidence it gives me and I feel extremely bulletproof while I'm putting a safe distance between me and the grass.
Tad Eareckson - 2007/05/22 04:43:29 UTC
Gotta extract foot from mouth. Peter sez four strands - not loops. So a double loop of 130 at 200 pounds.
For me - 310 pounds - a "larger pilot" - a double loop of 150, extrapolates to 230 pounds. .74 Gs. Off the bottom end of what we all just agreed was the safe lower limit so I don't feel so bad.
I, for the purpose of this discussion, want to be smack dab in the middle of the safe range - 1.4 Gs so I do, in fact want 434 pounds which is between quadruple loops of 130 and 150.
Another correction - Shoulda read - less than half of the top end of a Talon 150.
Tad Eareckson - 2007/05/22 05:01:53 UTC
Here's part of a report from Joe in the 2004/09 issue of Hang Gliding.It's a real good bet that he was using a loop of the same understrength crap that "we" all swear by on the top end of his two point bridle. It didn't do anything to prevent or limit the extent of the lockout enough to keep him alive.Joe Gregor - 2004/09
Highly experienced mountain pilot aerotowing a newly-purchased glider experienced a lockout at low altitude. Witness reports indicate that the glider began oscillating immediately after leaving the launch dolly. The weak link broke after the glider entered a lockout attitude. Once free, the glider was reportedly too low (50-65' AGL, estimated) to recover from the unusual attitude and impacted the ground in a steep dive. The pilot suffered fatal injuries due to blunt trauma. 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.
Chris McKee - 2007/05/22 10:56:56 UTC
Tad -
I'm confused. How can you blame the weaklink in your posted accident report when it clearly says the pilot did not make an attempt to use his release? Maybe I'm missing something, but wouldn't that be pilot error? If you are in lockout, than you as the pilot have made a bad decision in not getting off tow! Yes the weak link broke, but that wasn't the cause of the accident. The cause of the accident was getting into lockout in the first place. The broken weaklink was just a secondary order of effect. Most pilots are obstinate in thinking they can fly themselves out of a pilot induced ocillation, when in fact it would be MUCH safer to release before the PIO gets to the point of lockout. The stronger weaklink that you suggest would just complicate the matter worse in this situation. You'd just do your replication of a "Gayla Bat-Kite" and fly it straight into the ground. Short & simple - The weaklink did what it was supposed to do ... the pilot didn't.
Marc Fink - 2007/05/22 12:14:47 UTC
Was going to say the same thing--in addition to the pilot being unfamiliar with aerotowing and flying a new glider.
Put plainly, Tad, please explain how greater resistance to breaking a weaklink makes a lockout any less likely.
Tad Eareckson - 2007/05/22 13:08:50 UTC
Chris, Marc,
EXACTLY!!
That was pilot error.
If you are in lockout, then you as the pilot made a bad decision in not getting off tow!
Who said I was blaming the weak link?
The weak link didn't make any difference. It was a single loop of 130, it could have been ten thousand pound steel carabiner, the results would have been exactly the same.
(I don't think he was being obstinate or cocky - I think he was too scared to take his hand off the basetube and, according to Bill Moyes, shouldn't have had to but I don't want to digress right now.)
Chris - The guy died. How could a stronger weak link have made things worse?
Dan (Tomlinson) still thinks that dumbing down the weak link makes things safer. Read the title of Danny (Brotto)'s post -
"Weak links are not a secondary release system..."
(That's DOCTOR Freeman, by the way, I realize now I had taken note of him before as a result of an Oz Report reference.)
If the glider gets crooked low to the ground you need to do whatever it takes to get it straight. When we're free flying we have a reflexive weight shift response. When we're on tow we may need to supplement that action with a reflexive action with respect to a release actuator.
When we understand that dumbing down the weak link doesn't make us safer then we can start using them in the middle of the safe range - 1.4 Gs - rather than off the bottom end of it.
Chris McKee - 2007/05/22 13:24:03 UTC
I give up ... What exactly is your point in this whole thread? And what relevance did the accident report have to with this thread? Your logic train has derailed and I'm jumping off before it goes over the cliff. Fly how you want, with what equipment you want, blah blah blah. When you start showing empirical data with proven and qualitative results instead of clouding the issue with conjecture, misquotes, and speculation maybe I will be more inclined to listen, but right now it just seems you are grasping at straws and I have no clue what the point in all of this is.
By the way, sailplanes weigh considerably more than hang gliders, yet take off in the same conditions. One could extrapolate that the effect of the turbulence we feel in a HG would be significantly less than the sailplane experiences do to much more inherent stability. You also have moving control surfaces, longer wingspan, etc when make towing a much more controlled experience than HG. I think there are WAY to many variables that you are not including in your simple analysis when trying to compare towing a hang glider vice towing a sailplane. Apples do NOT = Oranges under most circumstances unless you are calling them both fruit.
P.S. Neither Apples nor Oranges have a good glide ration.
Brian Vant-Hull - 2007/05/22 15:30:50 UTC
I think Tad is saying the following:
1. The initial force when the tug begins to accelerate the glider is greater than the force experienced during a lockout.
2. Hence any weak link that would protect you from a lockout would have broken before you get off the ground.
3. Hence we are wasting our time with weak links that keep breaking on us.
The only problem I see is if this reasoning is correct why do weak links keep breaking in the air? If assertion #1 is incorrect then we definitely do not want links that never break.
So explain why weak links break in the air instead of at the initial pull and I'll be satisfied. But it truly needs to be a good explanation.
Tad Eareckson - 2007/05/22 22:25:33 UTC
OK (sigh), back down into the gutter...
Chris,
I'm not the least bit surprised that you have no clue. Lemme tell you what I told Marc a few posts ago. You have yet to request the documentation I first offered to make available to anyone on the list a couple of weeks shy of two years ago. It's loaded with data.
And, oh yeah Chris, what's the data on the stuff you're currently using?
My points are (listen carefully now)...
1. One size does not fit all (Marc), especially if that size is off the bottom end of the reliability range.
2. We can use high quality weak links in the middle of the safety range and totally eliminate any weak link break which does not involve a pilot who has really fucked up IF we don't continue to behave as a large herd of stupid sheep (fat chance).
With respect to sailplanes...
Last fall I consulted with a sailplane pilot who is also an AT release designer and learned that sail planes are, as you speculate, no brainers to control on tow.
First of all, the upper weak link limits are not mine. They are set by the FAA and the USHGA Towing Committee to cover the planes under their jurisdictions.
And last night we unanimously decided to adopt the FAA's lower limit as our own.
But since hang gliders are a relative bitch to control AND certified to withstand higher loadings...
SHOULDN'T WE BE MOVING THE WEAK LINK RATINGS FOR THESE ORANGES EVEN FARTHER IN THE DIRECTION I AM RECOMMENDING?
Now, back out for some more air...
Brian,
Three is fine, One and Two are not exactly what I'm saying. The rollout and steady state tensions are reasonably low and not that far apart but, yeah, I think that's plenty enough to do it. I'd feel more comfortable saying that we need a .8 G minimum and that minimum will lock out the asses of you and the horse you rode in on.
Here's what I think is going on with respect to conventional weak links - to answer your question with my best guess.
First of all - those are steady state numbers. I'm only interested in low numbers 'cause thermals and position irregularities can take you up to and beyond what the weak link will handle. I was flying one point and extremely poorly (all over the sky) and overshooting pitch inputs most of the time. You can REALLY swing the needle pulling that last trick.
The Greenspot is pretty marginal to begin with. And two knots are involved. A Fisherman's Knot joins the ends and the resultant loop is installed at the eye of the bridle with a Double Lark's Head.
Knots involve rather sharp bends in the line and, under loading, the fibers on the outside of the bend are subjected to more stress than those on the inside.
I think that what's happening is that the weak link is degrading in the course of the tow. You lose some outside fibers when you start to roll and little surges and corrections keep snapping away until... SHIT!
That's the best I have.
This just in from Portugal...Too bad ya hafta hit the western edge of Eurasia to find a pocket of enlightenment relatively free of the fundamentalist nut cases striving to make sure we never crawl out of the dark ages.Subj: Re: [Tow] Re: Bridles and Releases
Date: 2007/05/22 11:35:22 UTC
From: marco_vento ~~ at ~~ yahoo.com
To: skysailingtowing ~~ at ~~ yahoogroups.com
6248
Tad (is this your name?):
We have been using the TOST weak links in association with either KOCH double release (for dolly launch and for foot launch) or MOYES release (for dolly launch or launch on wheels). The great point is the reliability and precision of these weak links. The weak side is the mass, but the pilot side, when the link breaks, is lighter - the protection box keeps attatched to the cable when the link breaks.
We are quite happy with it, although they are expensive, no false breaks occur anymore. The links are available in a wide range of calibrated break loads as well.
Please send us photos and info on your weak links - we are very much interested in it. Please also inform us how we could acquire some samples.
By the way, all my friends call me Vento - it's my family name but it means wind. Quite appropriate, isn't it? Please call me like that as weel:-)
Greetings
Vento
Tad Eareckson - 2007/05/24 12:18:38 UTC
Hellooo? tap tap tap This thing on? cricketchirp cricketchirp cricketchirp
OK, nobody's listening anymore but just for the record...
Here's something Kevin wrote a year and a half ago when he was under the impression that I was defending a release that was inherently prone to premature release (but was, in fact, improperly adjusted).
http://www.chgpa.org/forums/viewtopic.php?f=2&t=1079
$15 pacifiersNow I'm guessing that even a curved pin barrel doesn't suck enough to be responsible for all that carnage so... Lessee, what else could... Oh, yeah.Kevin Carter - 2005/09/24 21:49:39 UTC
One pilot in the Texas Open had three premature releases in a row with glider damage on all three and different degrees of pilot injury. I myself have had a low level release that caused minor injury.
When you are discussing the acceptable risk of a premature release.....take the blinders off man. It is a real risk that should be minimized and not taken lightly.
So now that we have an easy, obvious solution dumped in our laps what should we do? Grab the pitch forks and torches and head for the infidel.
After screaming for "empirical data with proven and qualitative results" Chris has stormed out of the room and slammed the door behind him. And he now has absolutely no more interest in that very data I've had available years now than he ever has or will.
That data now includes reports on the results of 179 tests of weak links of various flavors and configurations, most of which took an hour or two to set up.
But hey, Chris is a Great Pilot and thus already knows everything worth knowing. And the most important thing is that it's not worth even considering unless everybody's doing it that way already.
Marc will not have demonstrably inferior and dangerous equipment pried from his cold dead fingers until the good stuff "passes muster". You could show him in a heartbeat performance tests which would instantly get the "Case Closed" stamp but what he really means is also, "What are the rest of the sheep doing?"
So he retreats from his promise to "be the first to adapt when and if it passes muster". Now he's gonna be the second to adopt it after it passes the muster of a tug pilot.
A TUG PILOT! Jim is a "very experienced commercial aerotow tug pilot" whose ability to evaluate these systems is also limited to the sheep thing. I know several "very experienced commercial aerotow tug pilots" who have absolutely no interest in or understanding of the stuff that goes on the glider.
With a brain half the size of that of a Turkey Vulture you have a thousand times the processing power to fly a lot more superbly than any of us ever will at either end of the tow line.
And just what does aerotowing have to do with anything?
Too bad Les isn't around anymore. And try running my stuff by Campbell.
Tow park operators? Steve Wendt is a tow park operator. The reason Holly didn't have a weak link when she slammed into the ground was because Steve couldn't have been less interested in the technology I had made a trip to share with him eight months prior.
Marc, it's a freakin' WEAK LINK. Only one of two things can happen.
If it breaks for no reason you're now (no) worse off than the One-Size-Fits-All Miracle Links with which you're currently so enamored.
If you think that a stitch of dental floss holds triple digits, rather than something in the ballpark of 18 pounds, so what? You're a superb tow pilot with the most reliable release system on the planet and you're totally confident that you can get off before you lock out. Besides, you have a weak link at the other end of the towline so the worst that could happen would be that you get stuck with the rope.
So exactly what is it that so frightens you?
Take a hint from Vento. He's a pilot, so he knows everything already, but also a mechanical engineer, so he doesn't. He's the only other hang glider person I know of anywhere using a quality weak link system. And, of course, he has totally eliminated premature failures from his operation.
Danny Brotto - 2007/05/24 21:58:44 UTC
Less pull...
Some things to think about...
Depending on set-up, the weak link does not experience the full load provided by the line to the tug. In a bridle like I use (only towing off the shoulders) the load is split between the 2 bridle connect points (where they attach to the harness.) So if the tug pulls at 100 lbs, the weak link only sees only a portion of those pounds; somewhere between 50 and 100 lbs. The exact amount can be calculated based on the span of the harness connect points and the length of the bridle; it's a 2-D statics problem that a first year mechanical engineer should be able to solve. The short of it however is that the weak link experiences less load than the pull force being presented to the glider. In practice, a weak kinl is not as weak as the simple straight-line breaking strength.
In the more traditional 3 point bridle (harness shoulders and keel connection) the load is shared among 3 points. This is a little more complicated 3D static problem but the point is again that the weak link experiences less load than the pull force presented to the glider.
We set gliders with strong tow pitch pressures up with a keel-forward bridle connect position. While can alleviates pitch tow forces on the pilot to almost nonexistent, it concentrates pressures to the keel/release and onto the weak-link assembly. I would fully expect that gliders set up with 3 point bridles for light tow force pitch pressure to break weak links more readily than the norm.
With the various tow bridle set-ups, a consistent "calibrated" location for a weak-link is in the tow line. The problem here is that we would see weak breakage as the tow rope caught things dragging thru the grass and what not. And then there's the additional variable of the tow line material. Spectra does not stretch much and does not have much “give”. This presents a different dynamic load than polypro that yields with stretch.
Marc Fink - 2007/05/25 00:26:39 UTC
Excellent points, Danny. We tow with an elastic polypro system in Maine--which I personally don't like cause I hate the "rubber band effect" (especially on tandems)--but others like the "forgiving nature" of the energy absorbtion.
There's yet a third variable missing from the discussion so far which I think is crucial and gets to the core of this discussion.
That is the drag of the glider itself through the air, which, depending upon many variables, can rapidly increase or decrease the pressures on the tow system.
And I say tow system--because I don't believe that you can look at this problem through one of isolation of just one component and expect that adjusting that one component can adjust for failings in other aspects of the system.
I suspect he'll kill me for mentioning it--but Larry Huffman has never broken a weaklink in 11 years of aerotowing. Is he lucky, beating the odds somehow, or only goes and tows in perfect calm conditions? I think not. Rather, he recognizes that safe towing is not a question of where you keep the tug or glider as an absolute priority--but that the overall safety of the tow has to do with towline pressure management. Thus, the pilot needs to anticipate what will happen to the pressure on the line and take whatever corrective action is necessary to correct a potential overbuild of pressure. It takes alot of skill to be able to respond with the right degree at the right time to prevent oscillations in tow pressures. These typically happen when transitioning spots of lift/turbulence where most likely the rising and falling of the tug and glider will be out of synch and therefore the proper input needs to be in anticipation of that lag.
I'm hardly an expert on towing and I tend to do my fare share of wandering around under tow, and occassionally break a weaklink (less than a dozen, ground towing since 1989 and aerotowing since 1996) when I just can't keep things in line when going through an especially strong thermal--which is just as well since I probably should have released anyway to work it--but how often do we find ourselves hanging on to the bitter end of the tow even though the tug pilot has dragged us through the core several times??
I've towed at alot of different airtow parks--and I see alot of pilots do things that contribute to marginalizing the safety of their tows beyond just the string and bridle they are attached to. Proper setup of the gear, attachment points, and angle of the harness can make a big difference in the pilot's ability to make smooth control imputs while under tow.
I see alot of gliders, mostly high performance ones, take off with their AOA set too high in the dolly. This encourages an early liftoff before safe airspeed and increases drag and the likelyhood of an unintended wing up early on. In some cases pilots simply let the glider go off the cart as soon as it starts lifting, rather than holding on while building airspeed and adjusting a lower AOA. The extra speed will increase stability and control, as well as allow the towed glider to rise up to a safe "holding" altitude to let the tug rise up to the same level and at the same time reduce line pressure.
Things happen so fast in the first few seconds of a tow that I'm not sure the average pilot could respond with the correct decision fast enough to take away the necessity of a weaklink--one that might occcassionally break seemingly unpredicatably too early.
My opinion is that if you feel that somehow the system is at fault for repeated weaklink breaks or other mishaps during your tows--then a reassessment of all the equipment and processes--including the most important one--your brain--is in order.
marc
Disclaimer: these are just my opinions based on my experience and observations--always ask your professional tow operator what is best for you given your equipment, experience and conditions.
Tad Eareckson - 2007/05/25 03:20:40 UTC
Thanks Danny,
Since the shoulder attachment points are so close together (about nine inches) and the bridles that span them are invariably too long, I cheat a little and just divide by two. For what I'm calling a two point bridle (pilot and glider) the attachment points are, by definition, widely separated, I recommend and assume a bridle length which yields a 60 degree apex angle. I divide by two, blow the dust off a little trig, and multiply each end by 1.15.
I am strongly recommending a weak link which goes between the bridle and the tow line. In the both the Tost and my weak link the critical element is isolated and protected. I'm hoping mine will be able to withstand a virtually unlimited number of landings in the gentle environment of the Ridgely strip.
Its rating will not degrade until/unless the base material is badly worn and I'll be disappointed if it doesn't withstand hundreds of cycles.
If I understood Tom Lanning right, the Australians use a high stretch tow line and a very low rated weak link. He says it takes some getting used to but definitely has some merits worth considering. I think I'll stay with Spectra 'cause I can't imagine the alternative does anything for one's fuel economy.
Marc,
More power to Larry but...
Let's define him as 250 pounds and towing off the shoulders. Put a loop of Greenspot on one end of his Spectra bridle and he has a 1.12 G weak link.
I'm 310 pounds. Put an identical loop on the top end of my point bridle and I have a 0.79 G weak link - just off the bottom end.
If you're sitting pretty straight behind the tug in glassy air with a brand new weak link and the thing pops for no reason whatsoever then skill has nothing to do with it. This happens all the time. And world class pilots rain out of the sky at competitions all the time. This happens 'cause their weak links are cheap understrength crap, not because they're deficient in the skill department.
You have selected a G rating for yourself. You have selected it on the sole basis of the material being what everybody else uses regardless of his weight. You tell me what you weigh, in what configuration you're towing, and what kind of bridle (material and material diameter) and I'll tell you what that rating is (when your string is very new, anyway).
Mike Haas, the subject of the accident report I quoted, assuming he was within the hook-in range of his glider, was using a weak link of between 1.11 and 0.79 Gs, i.e., at the low end at best and a little off the low end of the safe range at worst.
HIS RELATIVELY FLIMSY WEAK LINK DIDN'T AND COULDN'T HELP HIM.
You're still thinking of the weak link as an emergency release. It's not! It can't be! You need to reread the link Danny referenced. (Don't worry - it took me years to understand this.)
The only emergency releases that can be counted on are the ones controlled by the pilot (odd how Chris got so furious when we were agreeing on that point). Shit never happens so fast that the pilot can't react faster than the weak link. If the pilot can't make a decision faster than the weak link can kick in he shouldn't connect to the tow line. If he does and shit happens... Shit happens.
I have been flying with a high quality 1.12 G weak link (hmmm... that's exactly what my hypothetical Larry uses) since last season. I'd go a lot higher but the one at the tug end ain't that good. It feels so much better being confident that I'm not on the ragged bottom edge anymore.
http://groups.yahoo.com/group/skysailingtowing/message/6251
Re: [Tow] Re: Bridles and ReleasesMarco Vento - 2007/05/24 16:15:32 UTC
Dear Tad:
I've seen the photos, quite clever I might say!
If you want to give a look at our operation see:
http://www.youtube.com/watch?v=K72Ql7Lnb1Q
dead
We use 1500 N and 2000 Newton weak-links. I am very interested in testing your links. Could you send some (let's say 2 of each?) to my adress (work adress):
M. A. Vento
Linde Sogas
Est. Nacional num. 1 km 38,4 Cheganças
Alenquer - Portugal
2580-381
Please tell me the costs and how could I pay you. (Bank transfer, credit card, ??)
Best regards
Vento
Tad Eareckson - 2007/05/25 10:14:07 UTC
P.S. Marc, just as you have arbitrarily determined that you're gonna tow at X.XX Gs, Hypothetical Larry will be at 1.12, and I'm gonna be dumped off the bottom of the scale, you've also put a new student at the bottom end of a Falcon 140 at 1.50.
So this isn't really about keeping everybody safe by staying within a hair's breadth of involuntarily popping off tow, is it?
John Claytor - 2007/05/25 12:03:13 UTC
Richmond
here is some raw statistics: I am about 215, loaded up harness 40 and fly a glider that weighs 85, 340 pounds total. I use the same weak link material as every body else, towing off of the shoulders with a weak link on both sides, equaling four starnds.
I break a weak link about once every two years. a little frayed is better in my way of thinking because I like my weak links weak.
If you are in the moderate range and breaking weak links all of the time, I am sorr friend but the evidence would point to technique, not inferior link material. If you are breaking these all of the time, you probably owe your health and safety to the system thay you may feel is failing.
Here is a concept:
When you are preparing to tow, sit on the cart on the runway ready in the position you are going to begin your role in. Now instruct the tug pilot to give you nothing less that full throttle. tell the person launching (who is really here to check your gear and communicate to the tug) not to push you into the role. Now the weak link will take its highest load during the flight and you are barely rolling on terra firma.
If it breaks you are safe. Just push out if you are rolling faster than you like. If it doesn't break than you are likely not to load up the link any more during the entire flight.
Actually I like the weak link a little frayed. And all of us should be ready for the weak link break during every second of every tow. Its part of the launch.
Tad Eareckson - 2007/05/29 23:04:08 UTC
Semi recovered from a punishing but rewarding weekend. Great day at Ridgely Saturday - even I could stay up long enough to get hypothermic and nauseous. Next two days were eaten up by a distant wedding and a lot of driving. Apologies to all my adoring fans for the prolonged absence.
Hi John,
The respect I have for anyone with enough brains and independence to say, "There's gotta be a better way of doing this." and start snooping around a West Marine store is equaled only by my contempt for folk whose immutable engineering standard is, "This is the way everybody's always done it." Thus the following flame pains me a bit, but...
For starters, the fact that you have weak links on both ends of your one point bridle is not relevant to the discussion. It doesn't hurt anything but, unless your bridle is excessively long (by which I mean anything over seven inches), it isn't helping anything either. What's pertinent to this discussion is that you have one end of your bridle retained by two strands.
One can't tell from the data you've presented that you've ever actually made it up to twenty feet before your weak link pops.
OK, I'm assuming that you tow a lot more frequently than once every two years and that what you meant was that the overwhelming proportion of your tows are successful? But you should be having zero breaks in a two year period no matter how much you tow. I'm taking a wild guess that that one average break does nothing to enhance your safety?
Also, when - not if, but when - that weak link gives up the ghost I want you to pay for the full tow and go to the back of the line so you're encouraged to use a better system and won't keep the next twenty gliders waiting.
I myself have had 224 tows of any kind dating back to 1980/11/14. Of those my ascent was limited by a dozen weak link breaks. Two of those were consequences of lockouts at altitude where safety wasn't much of an issue. In both cases I elected to allow the break - I could and should have released but had neither been instructed nor figured out that that was the proper course of action. (It is not known whether either of those lockouts was preventable).
So now we're down to ten relevant breaks - all of which were completely unnecessary and undesired. All of those constituted pains in the ass of various degrees and at least one cost me a really good flying day.
Last season I started developing the concept of stitching based weak links and incorporated it in my bridles. I ain't never gonna have no more weak link breaks.
I didn't start this thread 'cause I was, am, or will be "breaking these all of the time". I'm writing this 'cause everyone else is. As a consequence my lift ticket is too expensive, the wait for a cart is too long, and my flight park is operating inefficiently. To date I owe NOTHING to weak links - the "standard" version owes me big time.
In all of my research to date I know of ZERO weak link breaks which have prevented AT accidents and challenge everyone to provide a blemish to that record.
When I take over as Supreme Dictator of Planet Earth, the first thing I'm gonna do (after, of course, summarily executing all the single occupancy Hummer drivers) is mandate a 0.8 G lower limit for weak links (I'll probably raise that number later). You're struggling to hold onto the bottom end with new weak links and the fuzz is definitely gonna put you out of specs - so be forewarned.
I never said that ability to survive the roll qualifies a weak link for any part of the tow. It most assuredly does not. I need something slightly south of 175 pounds to get me - 310 pounds - moving and I sure don't want to be hovering around that figure. I need 248 pounds to get to the bottom of specs.
But, for arguments sake, let's say that a fuzzy loop of 130 pound Cortland is the ideal weak link for you. Are you gonna give a new loop of the same string to a 162 pound Falcon 140? Like Marc does?
Finally, how 'bout this... Lose your parachute pins and tweak your velcro so you automatically deploy when you hit three Gs positive. It's analogous. Like the idea?
I'm the freakin' pilot. I don't want some goddam lousy piece of shoestring telling me when it's time to get off tow. I will be the one to make that decision.
Hope you will be showing up for the ECC again this year. If you do, could you bring that side pull snap shackle release you developed? I'd like to see and play with it 'cause I think it would be quite compatible with the form of the shear link I'm using in conjunction with my own rig. A spinnaker shackle doesn't cut it, figuratively, 'cause it does, literally.
Although I couldn't disagree with your positions more I really do appreciate your positive contributions to the discussion.
John Claytor - 2007/05/30 00:39:57 UTC
You are right about the multitude of gliders that are subjected to the same system, and I can clearly see that one size probably doesn't fit all.
The snap shackle system I built never failed, and never had to be fixed or repaired during the time that I used it. The hardware is designed to release without any sharp or forged edges meeting the line upon release. if you have a spare shackle of that sort, bring it. I probably have a few in my sailing gear...
The release that I made (with the snap shackle), I gave it away to a pilot named Todd. He needed it to learn how to aerotow. The $150 for the Wallaby Ranch style releases hurts the flying budget... BTW the snap shackle is less than half of the cost of the spinnaker shackle, and the snap shackle ($22) is the most costly component of the rig.
I do have a story where a trike pilot towed me at Quest---Weak link worked---Everybody warned me about the trike pilot's style---Really glad to be here.
I'll save the details for the poker table next week.
Marc Fink - 2007/05/30 02:52:19 UTC
Tad, I'm truly dismayed at the prospect of you showing up at the ECC's--flying in that in environment is stressful enough without having someone walking around preaching imminent death to someone who aerotows with present systems.
If you don't think you can control your impulse to denigrate others for using something other than what you personally approve of, I'd just as soon not show up.
You gonna be a good and leave it alone during the comp?
Kurt Hirrlinger - 2007/05/30 03:31:24 UTC
weak links
What situations are the current weak links designed to resolve
Is it possible to apply an automatic release to HG
Tad Eareckson - 2007/05/31 01:03:19 UTC
And speaking of contempt for folk whose immutable engineering standard is, "This is the way everybody's always done it." - Heeeeere's MARC!!
If you had had education in reading and arithmetic enough to be able to follow this thread you would have understood from Post 1 that it's not about imminent death and what meets my personal approval. It's about getting gliders to altitude reliably on good days and based on accepted aviation standards.
It is indeed unfortunate that when, in an earlier post, you abdicated your "thought" processes to unspecified tug pilots you did not relinquish your posting rights along with them.
Just as Chris, obviously at this point, does not represent the unified voices of all on the list server, you most assuredly do not speak for the mass of the ECC participants - they're not ALL morons.
Equipment I have noted present at competitions past has included spinnaker shackles, twin and straight pin barrel releases, and redundant weak links. Those are all technologies introduced by yours truly. (I'll back off to "independently developed" on the first one if anyone can cite a reference prior to 1994/09/04).
At last year's competition Dennis Pagen said, "I agree." and went up with a pair of my barrels. The current and recently deposed Ridgely XC record holders fly with my design. PK was very happy recently after his maiden tow with the set he acquired from me at the end of last season. I suspect that Bob Lane's design I recently saw referenced in the Oz Report owes something to the secondary bridle assembly I sent down to Kevin a year prior.
Saturday night Sunny stated that the points I've made in this discussion sound solid and declared his intention to start flying with the shear link I provided.
(I hope everyone notices how Marc always slinks back under his rock without responding to questions like "By what standards is the equipment you use proven?")
John,
Yeah, I was afraid I remembered that you said you had given your release away. Believe you had incorporated a Ronstan snap shackle but I can't recall which one. Can you take a look at:
http://www.apsltd.com/Tree/d270000/e267100.asp
and see if you can find a match?
I look forward to the account of the trike tow and will keep an open mind but you gotta convince me that the weak link failure was necessary and would have occurred before I would have hit a vowel in whatever expletive I would have been uttering at the time.
By the way, I can provide you with a weak link of any strength up from the equivalent of a 123 pound loop of string that will maintain its integrity until your tow line tension hits that rating (245 pounds).
Tim (Kurt),
The current weak links are "designed" to pop for no reason whatsoever when you'd much prefer to be continuing up to a workable altitude and hold on to the death when your hands are frozen onto the basetube.
People think they're designing them to prevent lockouts. They're not and can't.
They should be designed as a failsafe to protect the glider up high - only the release can reliably protect the pilot down low.
Yeah, I think an automatic release would be doable but I also think you'd have to incorporate gyros and spend a lot of tow ten packs. As it is we have people with releases at both ends of the tow line and that should (but, yeah, doesn't always) work.
I think that if you want to spend money the best bang for the buck would be in the development of a computer simulator called "Lockout!" It's the area in which proficiency is most critical and the opportunity to practice is extremely rare.
Jim Rooney - 2007/05/31 13:27:30 UTC
Wow... this thread is still going?
Hahahahaha... as if this is shocking?
Guys, take all your equations and stuff them. We all know bumbelbees don't fly right?
Any tug pilot will tell you that this is all bunk. Weaklinks don't "protect" you from lockout, but I'll be damned if I listen to someone tell me that they don't break during lockout.
Try to get behind me without a weaklink... try... I will not tow you.
Cragin Shelton - 2007/05/31 18:07:25 UTC
Thread Advice
Weaklink - a bundle of threads tied in a loop.
Is this thread weak enough?
Here's a reading suggestion for at least some of the folks who have been playing in or reading this thread.
You can decide for yourselves who really needs to read it.
http://tinyurl.com/2ltzsw
Hugh McElrath - 2007/06/01 01:57:11 UTC
It is with great trepidation and against my better judgment that i enter this thread - but since when have I ever listened to my better judgment? In all the discussion about weak links, I think what has gotten lost is the idea of a primary release that can be actuated without removing a hand from the basetube - particularly in a panic situation approaching a lockout. I am quite happy with the one I have with a loop of line that goes around the palm - just slide the hand inboard 1/2 to 1 inch. I have accepted samples of Tad's and Steve's mouth-release prototypes, but confess I have yet to tow with them - primarily because I want the inventor to assist me in rigging it the first time. Also, last year I was still getting used to towing the U2 without a strap-on fin and didn't want any extra novelties. I seem to be pretty solid towing the U2 (finally) and will bring the samples. If I'm not in too much of a hurry during the comp, I'll be willing to try an alternate tow release. - Hugh
Tad Eareckson - 2007/06/01 12:27:40 UTC
Jim,
People like me have to use equations so that people like you will have something to fly.
I'm quite sure that you know that bumblebees don't fly but the equation crowd figured out that they catch the tip vortices on the backstroke.
The strength and performance of the design of that pair of barrel releases I wasted four hours making for you last fall was verified using equations.
And to waste a little more time (somebody who hasn't bothered to listen the first dozen times is highly unlikely to bother paying attention the thirteenth)...
Weak links do not necessarily break during lockout. Sometimes the glider slams into the ground first. A weak link will always break if the ground doesn't get there first.
I'd like you to provide a single QUOTE from this thread in which ANYONE suggested eliminating a weak link. Something a little more specific than the "You said..." vague accusations of which you and Marc are so fond.
By the way...
The best weak link protected two point gliders you tow are the ones using bridle systems I've designed and assembled. If the bridle wraps at the carabiner after failure of the primary weak link, the secondary at the bottom end blows instantly.
If your Dragonfly weak link pops and the lower bridle component wraps - you're out of ammo (see my first post).
Cragin,
A weak link does not have to and assuredly should not be "a bundle of threads tied in a loop" that you can "NEVER TRUST".
You can't make friends with or influence Jerry Falwell 'cause he don't need no stinking data, evidence, formulae, logic, common sense... He already knows The Truth.
Marc,
Look Marc! An ECC competitor who thinks a safety enhancement might be worth looking into.
Hugh,
In your case (two point) it's not really an alternate - just a supplement.
Since you're still towing in that configuration I'm starting to question my decision to talk you out of going with my full installation.
Look forward to seeing you.
Tad Eareckson - 2007/06/02 23:23:19 UTC
Correction -
With respect to the report:Although there can be a couple of ways to interpret that passage a very careful reading reveals what Daniel Broxterman meant.Yesterday I was LUCKY that my weak link broke on my first launch...
I had assumed that he was about to die but after an inquiry at Ridgely last weekend understood that getting involuntarily deposited back on the ground set him up to take advantage of a later lift cycle. The pop off was due not to the low level lockout onset I had envisioned but rather to some moderate turbulence and shouldn't have happened.
So move that one from the category of "Potentially Catastrophic" to the one which would normally have been "Moderately Annoying".
Jim Rowan - 2007/06/03 00:47:16 UTC
Why don't you give it a rest, Tad. You moved past the "Moderately Annoying" category several posts ago.
Tad Eareckson - 2007/06/03 10:41:24 UTC
Like I said before earlier...
Nobody's forcing anybody to read this thread. So if you don't have anything positive to contribute - and, based upon your previous posts, I couldn't possibly imagine that you could - ...
Tad Eareckson - 2007/06/03 14:52:18 UTC
'Nuther correction...
For "positive" in my previous post, swap "intelligent".
(In never proofread these things carefully enough.)
Tad Eareckson - 2007/06/03 20:06:46 UTC
Obviously didn't proof that one very well either.
Tad Eareckson - 2007/06/10 19:20:33 UTC
More corrections... Noticed redundancies in my first response to John and in my message to JR telling him to go fuck himself. Also found a "now" which should have been a "no".
Jim, thank you for illustrating more graphically and extensively than I could have possibly dreamt the point I was trying to make to Marc about just who is and isn't qualified to evaluate safety equipment.
I found quite noble your declaration about refusing to tow anyone not using a weak link, as bizarrely inappropriate and irrelevant to the discussion as was that comment.
Just curious though... Would you tow a new solo student using a two point bridle and a primary release mechanism you knew to be incapable of functioning?
Seems to me the latter scenario would be way more problematic but, hey, what do I know...
Darkened the ECC with my presence for a little evangelizing and free flying Thursday and Friday.
One of my first orders of business was to get an account of John Claytor's trike incident. Correct me if I'm wrong, John, but here's my shot at a summary...
Trike goes up like a rocket - fast and steep, glider starts oscillating, John's too busy trying to keep things under control to feel great about taking a hand off the wheel to actuate the release, weak link mercifully pops leaving him low and slow over Injun country with about one well executed survivable landing option.
My take...
I share - along with Bill Moyes and John Williamson - the conviction that if you have to move your hand to get to a release actuator you're inviting opportunities for trouble. There are systems available for one and two point systems that have no downsides other than expense.
I'd have liked to have sparred with John a bit more 'cause he has interesting ideas but time was limited and distractions were numerous.
Thursday evening I hit poor Victor with my spiel. Victor is an engineer, thinks and tinkers outside of the box, and is one of my favorite glider folk and there isn't much upon which we disagree but we butted heads a bit on this issue.
His position was that a flimsy weak link forces him to be extremely smooth on tow.
I countered that:
1. A weak link's function is not to punish one for being slightly human.
2. Virgin Greenspot loops pop all the time in glassy smooth air with the glider dead center, level, and stable for no reason whatsoever.
and neglected to amend that with:
3. It costs Highland Aerosports (and thus us) money and screws over the people in line.
A few minutes later Victor's Pulse was on the ground with a broken downtube. Woulda been perfect had it been someone I strongly disliked. (There was no line at that time of day.)
At a hundred feet in glassy smooth air with the glider dead center, level, and stable Victor's virgin Greenspot loop popped for no reason whatsoever.
The downtube, in fairness, died not as a direct result of the pop but a compromise of the landing to save some walking. There is no question, however, that the aluminum was trashed as an indirect consequence.
Anecdotally, there seemed to be lotsa pops during the competition and I heard of none desirable. The 2007 winner broke one in turbulence - I had been working on him but so far haven't gotten through.
Statistically insignificant but the two people flying competition (seventh place) and free who used shear links had no breaks. Sunny is using a 1.17 G bridle link for one point configuration, yours truly is using a shear link of about the same rating for two point.
On Friday Hugh graduated to one point towing and represented a fifty percent increase in local squid users. I noticed one somewhat disturbing yaw at about eight hundred feet and need to give him more trigger line slack (unrelated) but otherwise things went well. I wimped out on setting him up with a shear link 'cause I didn't want to hear about it if something bad had happened during a low level oscillation but next time he goes up after we next cross paths he'll be a full member of The Club.
Pat Halfhill checked out my systems, pronounced them way slick, and promised to post to this thread proclaiming me to be not a TOTAL asshole. He goes way back and it was very interesting talking to him. It seems that Steve is only the second reinventor of the squid concept. I had learned a year ago that the eastern Europeans had been using a bite controlled multi-string a decade and a half before and Pat informed me that Rob McKenzie had introduced a version for truck towing.
I'm going out on a limb and stating that the critical mass of gray matter exists and this shear link concept will displace the fuzzy fishing line crap. The implementation can take one of several paths.
First some background...
Last season one of the Ridgely Dragonflies had a mast which developed a crack in the mast at the bolt which anchors the top aft end of the tubing which defines the leading edge of the vertical stabilizer. As this crack formed at the aft half of the circumference I'm thinking that it has everything to do with flexing as a result of drag produced by rudder control actions and nothing to do with tow line tension.
The double loop of Greenspot that has always been incorporated in the Dragonflies' bridles limits tow line tension to about 400 pounds. A heavily loaded Talon 150 can take a 700 pound tension and remain within specs (2 Gs).
I, again, am recommending a 1.4 G universal standard 'cause that's smack dab in the middle of the safe range, thus allowing the widest range of tolerances, and is plenty enough to eliminate virtually all undesired breaks. That brings the top solo tension down to 500 pounds.
If we can boost the Dragonfly weak links we can bring the stuff on the gliders up with less fear of getting stuck with the rope. But weak link breaks at either end should be so rare that that should be an issue hardly worth considering.
The tandems are their own. They seem to do OK with the same double loop of Greenspot on the ends of their bridles. As things are they seldom, if ever, get the rope 'cause the tug bridles are relatively long (thus transmitting less tension) and the weak links are not subjected to wear.
It would be great for everyone to know his flying weight. Hop on the bathroom scales with the backpack, look up or weigh the glider, do the arithmetic. I can also get a way more accurate than necessary total on site with a hydraulic cylinder under a limb of one of the maples by the pavilion.
For anyone towing one point I can, for maybe fifteen bucks, provide an appropriate shear link. The lengths of whatever you have coming off your port and starboard AT loops (on your harness) must be equal. Identical twin barrel releases are common and easy.
For two point towees I could provide a bridle system similar to mine 'cept these things are tedious to punch out and it's not worth it for something that's gonna get chewed up by a spinnaker shackle. That leaves Tim Hinkel and the former John Claytor as the only other candidates. Sooo...
Plan B. I provide individual 1.4 G Tow Line Integrated Shear Links for around forty bucks apiece. Seems like a lot to replace something requiring a knot in a penny's worth of material but it's only about eighty percent of what a Tost assembly sets you back and if it lets you get up to altitude during prime time and maybe saves you a downtube ( especially if its one that goes on a Talon and gets folded after a pop coming out of the cart a la Denis Scheele - 2002/09/28 ) it starts sounding pretty good. For the time being if it fails for any reason not involving an Exacto knife I'll restitch the parts for the price of a report of what happened.
The recipient swaps his Greenspot for loop of 205 or 350 leechline which will survive a bit of spinnaker shackle abuse before it becomes an issue and takes any redundant weak links out of the system.
Upon the landing of the tug that just hauled you up, the glider launcher (e.g., Bob) removes your weak link from the carabiner and tosses it in a box after launching the next glider.
Hopefully this will become standard practice and you can trade your shear link to the flight park for a couple of tows and just request your color code as you near the front of the line.
P.S. I've been rereading some archives and I noted that Robin caught a lot of posthumous flak for using a doubled loop of Greenspot. Even if he was at the bottom end of the range of the smaller AirBorne C2 the worst he would have been doing was to have pushed the USHGA specs. The spinnaker shackle hang up was what killed him - and we've had those - up high anyway - at Ridgely.
Tad Eareckson - 2007/06/19 12:29:47 UTC
The Calf Path
1895
Sam Walter Foss
1858-1911
Public DomainThanks again, Garrison.I.
One day, through the primeval wood,
A calf walked home, as good calves should;
II.
But made a trail all bent askew,
A crooked trail as all calves do.
Since then three hundred years have fled,
And, I infer, the calf is dead.
But still he left behind his trail,
And thereby hangs my moral tale.
The trail was taken up next day,
By a lone dog that passed that way.
And then a wise bell-wether sheep,
Pursued the trail o'er vale and steep;
And drew the flock behind him too,
As good bell-wethers always do.
And from that day, o'er hill and glade.
Through those old woods a path was made.
III.
And many men wound in and out,
And dodged, and turned, and bent about;
And uttered words of righteous wrath,
Because 'twas such a crooked path.
But still they followed - do not laugh -
The first migrations of that calf.
And through this winding wood-way stalked,
Because he wobbled when he walked.
IV.
This forest path became a lane,
that bent, and turned, and turned again.
This crooked lane became a road,
Where many a poor horse with his load,
Toiled on beneath the burning sun,
And traveled some three miles in one.
And thus a century and a half,
They trod the footsteps of that calf.
V.
The years passed on in swiftness fleet,
The road became a village street;
And this, before men were aware,
A city's crowded thoroughfare;
And soon the central street was this,
Of a renowned metropolis;
And men two centuries and a half,
Trod in the footsteps of that calf.
VI.
Each day a hundred thousand rout,
Followed the zigzag calf about;
And o'er his crooked journey went,
The traffic of a continent.
A Hundred thousand men were led,
By one calf near three centuries dead.
They followed still his crooked way,
And lost one hundred years a day;
For thus such reverence is lent,
To well established precedent.
VII.
A moral lesson this might teach,
Were I ordained and called to preach;
For men are prone to go it blind,
Along the calf-paths of the mind;
And work away from sun to sun,
To do what other men have done.
They follow in the beaten track,
And out and in, and forth and back,
And still their devious course pursue,
To keep the path that others do.
They keep the path a sacred groove,
Along which all their lives they move.
But how the wise old wood gods laugh,
Who saw the first primeval calf!
Ah! many things this tale might teach -
But I am not ordained to preach.
Tad Eareckson - 2007/06/27 12:59:53 UTC
Had an interesting experience on Sunday afternoon.
Had a discussion with Christy shortly before going up about why anyone who tows two point REALLY needs a secondary weak link.
The tow was bumpy enough that I figured it would be OK to hit the button at 1600'. I was under a good bit of tension in the lower region of a column which would take me up the next twenty-four hundred at a very steady climb averaging 582 fpm and had a good news/bad news sorta event which commenced with the top end of my primary bridle solidly tying itself to the tow carabiner.
To help understand what I'll be talking about check the Primary and Secondary Shear Links photos at:
http://www.flickr.com/photos/aerotowrelease/
The bad news... while any two point bridle can wrap this flight was likely good evidence that my current design is more prone. The lack of a smooth taper was the issue in this case.
I have not recommended this bridle design to anyone using a spinnaker shackle as the primary release mechanism 'cause said hardware will chew up the eye of whatever is engaging it. 'Round these parts the only eligible candidates are Tim Hinkel and yours truly and the latter is currently the only one concerned.
On to the good...
I'm using 240 and 288 pound weak links at the top and bottom ends of my bridle respectively (and my secondary bridle is a 525 pound bridle link).
I'm now connected to the tug a skipped heartbeat longer than I had planned and my brain is going into barrel mode when the secondary weak link blows and I'm off and climbing.
Although it absolutely WILL fail after a primary gives up the ghost I really wasn't expecting the secondary to go under these circumstances. Guess the little jolt was enough to do the trick.
I watched the bright white bridle long enough to determine that it was still secured to the towline and got it and a report from Bob after a nice flight which took me to a max of 5396'.
Anyway, it was very rewarding to see that there is a good chance that that system will auto release in a more dangerous scenario.
Last season Victor, I found that afternoon, had a bridle wrap and secondary weak link failure.
Sunny, also that year, had a wrap with a tandem at release and was in instant one point mode. The combination of the tow line dropping relative to the glider and the harness being pulled forward caused the twin barrel releases to be dragged across the basetube. They opened simultaneously. Although both primary and secondary bridles were lost, that serendipitous auto-safety was kinda cool.
I was pleased to note that Victor had doubled his Greenspot but had to chew him out for maintaining a single loop on his secondary bridle. Although on a Spectra bridle a single fails at about 140 and a double 202, the geometry of the system adds some stress to a weak link on a secondary bridle and one can get killed pretty fast if:
- the trim point on the keel is forward;
- the bottom end goes first;
- the bridle wraps; and
- the primary weak link holds.
You can't go wrong having weak links of equal strength installed on the top end of your primary and on either/both end(s) of your secondary bridle.
That double loop on Spectra, by the way, is a much better one-size-fits-all option for two pointers than the single standard. It keeps everyone from two (Karen) to four hundred pounds within specs.
It didn't take Steve Padgett much convincing to put his primary bridle through the end of a 378 pound shear link. His previous flying day at Ridgely had earned him one successful tow to altitude for three efforts.
Hugh's two point tow on Saturday was safetied with the same link. Henceforth he is planning on towing one point using a 420 pound bridle link.
Steve Kinsley was set to go with the same bridle link but needed his one-of-a-kind one point system adjusted first. He'll be permanently on board after we get that taken care of.
I managed to blow most of PK's resistance to hell and believe he will shortly join the club of folk who want to be in charge of their separation altitudes.
Correction...
The crack was on the leading, not, as I believed, trailing face of the Dragonfly mast so my rudder drag fatigue hypothesis had to get tossed. So maybe tow stress is the culprit but I'd still like to see if it would hurt anything to up the front end weak link strength by about half.
Off topic...
As everyone with the ability to look sideways and/or down already knows - the farm that used to be across the road from the west end of the runway is being replaced by an industrial park. Just realized the pair of Kestrels we've always had nesting in the vicinity has been nowhere in evidence this year. A connection? Do ya think? Those beautiful little birds are getting wiped out from the eastern third of the country along with grasslands and everything that depends on them.
Marc Fink - 2007/06/28 11:45:55 UTC
I'm sorry, I can't resist--but it finally dawned on me, you are truly "the missing link!"
Brian Vant-Hull - 2007/06/28 18:14:35 UTC
Can't you see this has become Tad's personal blog? You're, like, totally destroying the experience.
Tad Eareckson - 2007/07/02 12:36:22 UTC
Hi Brian,
I was very happy to see your name linked to the previous post 'cause it had been four weeks since I had a respondent typically encumbered by the thought process. Then I clicked and got a toned down version of Marc/Chris/Jim/JR. Was kinda hoping that I was gonna get a comment on my response to your question of 2007/05/22.
So let's say it's a blog. Isn't that pretty much what constitutes the bulk of this forum? Folk reporting on flying experiences, incidents, hang gliding related points of interest?
I get occasional comments along the lines of "We're sick of it!" (Royal "We") but then I look at the ol' Views counter. What was it when you posted? About thirteen hundred? All time record for the forum maybe?
If you're not interested - don't click. How much bandwidth does the whole thing chew up? One small photograph?
Just about the whole freakin' planet is using weak links which are, at their best, about half as strong as they should be. Light bulbs have just switched on for half a dozen local pilots. That's worth the bandwidth. If something glows for someone cruising the archives many years from now - it's worth the bandwidth.
Dan (Tomlinson),
I was just rereading your 2007/05/21 18:18:18 UTC post and managed to focus on something this time.
You stated that weak links failing to kick in when needed have often led to catastrophic consequences. I know of no such incidents. Can you cite any?
Brian Vant-Hull - 2007/07/02 21:28:24 UTC
Tad - hey, I'm in the middle of the mind numbing task of combining a huge reference list and getting them all in the same style...can't handle any intellectual effort right now. Sorry, I know you were expecting great things of me.
Anyway, it's clear you've spent more time than any of us thinking about towing apparatus, and that has to be a good thing. Any reasonable person has to admit the weak link strength should scale with tow mass. The exact numbers required is quite a bit more subjective.
People are gonna lob grenades. If you lob them back you wipe out more than the person who threw it, and your prospective audience evaporates. Just look at the last page of this thread, and your posts right before the deafening silience.
I think in the last week or so you are finally (in very small steps) taking on the mantle of the long suffering prophet of a good idea, one who will quietly absorb the attacks and keep plodding away. If you stick with this approach it will eventually work. People erect churches to patiently suffering dead guys. Or if you don't like religion look at Jackie Robinson. But it takes patience and forebearance. If you lose the forebearance even for an instant it will take more patience to rebuild the audience.
And don't mind the grenades...it's part of the process.
Cragin Shelton - 2007/07/03 05:43:56 UTC
Weak Link Failure with Catastrophic ConseequencesBill BennetTad Eareckson wrote:Hi Brian,
>>SNIP<<
Dan (Tomlinson),
I was just rereading your post of 2007/05/21 and managed to focus on something this time.
You stated that weak links failing to kick in when needed have often led to catastrophic consequences. I know of no such incidents. Can you cite any?
Tad Eareckson - 2007/07/04 12:00:22 UTC
Hi Brian,
Thanks for the note.
You may be right about retaliatory grenades but I don't toss them until all efforts at rational discussion have failed. I decided that some bridges were in major need of incineration and have no regrets so far.
And I'm hoping that other readers are sharing some of my unhealthy delight at watching folk pump nine millimeter slugs into their feet.
Nah, not fond of religion. Push it to its "logical" conclusion and you get Crusaders, suicide bombers, and witch burning. Push logic, math, science and you get "Here's what's gonna happen if we do this."
Jackie had to start at an extremely low nadir. It's possible I have enough momentum going now to make an occasional charge into the bleachers but I'd rather have the 25+10=35 cops control the abusive drunks.
Yeah, things got pretty quiet - 'cept for yours truly of course - but I'm pretty sure that's 'cause no one wants to touch this with a ten foot pole. Yours truly isn't having much fun touching this with a ten foot pole either. I do, however, greatly enjoy the inputs and correspondence with folk with whom one can carry on a civilized conversation - about 6.3 relevant respondents to the point of your post.
I may or may not have had some audience evaporation but this keeps getting read. Even when it gets buried in the chronological order the numbers keep creeping up. I'd like to believe that the people who are reading and, perhaps, rereading are also thinking.
With respect to picking numbers...
Once one gets what James Freeman is saying in the link Danny posted things get real easy.
I'm gonna lose ten pounds to make the math easy and we're gonna say that the cross spar of my 300 pound glider buckles at six Gs (conservatively). I'm gonna be a wimp and require a two G safety margin. I put a 900 pound weak link on the end of the tow line and I pop at four Gs (one provided by the glider, three by the link). My glider is still intact and I'm perfectly happy.
But I don't need a three G weak link 'cause if the glider has loaded up to much more than two G's the tug is probably nowhere near where I'd normally expect to find it and I'd just as soon be off tow anyway.
But... I'M NOT PICKING THESE NUMBERS (much - see comments on USHGA below)! THESE ARE FAA AND USHGA NUMBERS!
I'm just saying use the number dead center in the middle of the safety range defined by these entities.
Elaboration...
USHGA has problems. One of them is the spelling of bridle. Here's another...
"(5) Inadvertent weak link breaks at low altitude can lead to accidents."
But they only specify the same two G upper limit that the FAA uses for sailplanes and say NOTHING about a lower limit.
So you can use the string off your tea bag as a weak link - 0.01 Gs let's call it. You will be perfectly safe until a dust devil comes along and sucks you off the cart.
As you start upping that number things will, at some point, start getting dangerous. You're going to see a lot of downtubes and an occasional arm get broken.
As you approach 0.8 Gs things start getting safer again 'cause your chances of getting to a hundred feet go way up.
If you use a weak link in the middle of that 0.8 to 2.0 range you're never going to have a weak link break.
Five months ago I was ordering a couple of Tost weak link assemblies from Wings and Wheels, a sailplane supply place in Lakewood, New York. Tim Mara apparently doesn't sell a whole lot of those 'cause folk on this side of the Atlantic generally use the tow line as the weak link. He had asked one of his customers for some feedback on the Tost links. The response was, "Well, we've never broken one."
I thought, "Yeah, they've never broken one. Bull's-eye!"
More with respect to weak link strength...
Chad, Sunny, and Adam all thought that the Greenspot loops WERE almost precisely in line with the strength I'm recommending for gliders around my weight.
The hypothesis was...
130 pound string, tie a Fisherman's Knot to form a loop, that weakens it, but you isolate the knot in the middle of a Double Lark's Head.
Single loop - 2 strands times 130 equals 260 pounds. Double - 520 pounds.
Sounds reasonable.
Then I broke out the bathroom scales (and later built a test rig). Nope.
Single - 140. Double - 200.
So all I'm saying is we should be doing what we thought we were doing.
Cragin,
Nope.
That glider hit the runway 'cause the release at the back end of the line wasn't actuated and the one at the front didn't work. The airframe didn't snap before impact so the weak link was not an issue.
I'm gonna go out on a limb here and state that it is physically impossible for a glider to need a weak link when it is within striking distance of the ground 'cause you there's no way for you to build up enough loading to stress the frame - even if you wanted to. (I stand ready to be shot down by an aerobatics pilot but let's at least think about this one.)
This recently in from Christy...
Bill (port) had the release actuator.
How 'bout we consider the ramifications of the Pilot In Command (Mike) not having access to the brake pedal.
Marc Fink - 2007/07/05 11:58:41 UTC
I remember Bill's accident and talked to a couple of people that were there at the time of the accident--and as I recall nobody had a vantage point good enough to make any conclusions as to the real cause of the accident and what really transpired. How can anyone who wasn't even there make any meaningful conclusions?
Tad Eareckson - 2007/07/06 12:50:20 UTCParagraphs 5 and last sentence of Paragraph 8 - Solid.Cragin Shelton - 2001/08/08 09:03:01 UTC
On Trusting Weak Links
Reading Joe's last item in the lockout thread prompts me to point out a consideration in the discussion:
NEVER TRUST A WEAK LINK!
Expect two things from your weak link:
(1) It will break unexpectedly at the most inopportune time, with no warning adn no indicaiton of a flight problem.
(2) It will hold strong and fast whenever you move into a lockout. You must never plan or expect on a weak link break. It may well not break when you fly with that attitude. As Joe said, if your situation is new to you and not right, get off tow!
I have never had an instructor use those words to me, but all towing instructors I have worked with have given that message in some form. Pagen & Bryden address it clearly in _Towing Aloft_.
This issue is critical for all tow pilots, but requires special emphasis for truck-towing, or any system that uses tension control. Any line, including the weak link, can hold together in much stronger forces pulled out along its linear axis with gradually increasing force, than whne subjected to a quick change in force. Weak links work best when popped. Tension systems, which include all pay-out winches, are designed to reduce the sudden changes in force. It is fairly easy for a glider on a payout winch with tension control to gently move into a lockout condition and never stress the weak link sufficiently to break.
So, to repeat: Never trust a weak link. Be prepared to fly off tow in a surprise break at all times when attached, and be prepared to hit the release at all times in case of a surprise attitude change.
Paragraph 7 - Solid with respect to tension limiting systems. Since Greenspot is so monumentally unreliable anyway there's not much point in discussing popping.
Paragraphs 2 and 4 and first sentence of Paragraph 8 - Solid with respect to virtually the entire culture at the time but crap locally as of whenever it was last year that I noticed a real linear relationship between number of stitches and strength.
And I'm gonna predict that my weak links don't care about the speed at which stress is applied. Retains its integrity up to 239 pounds - explodes at 240.
(The author, by the way, had the opportunity to take a look at the advance which would have allowed him to spend more time thermalling and less straightening downtubes and waiting in line but was quite certain that what I had wasn't worth readjusting the focus of his vision.)
There is a major consistency problem with Paragraph 5 and the offering of the Bill Bennett/Mike Del Signore crash as an example of the use of an overstrength weak link having catastrophic consequences.
OK - Let's say that there was an overstrength weak link as alleged. Bill, Mike, Double Vision, harnesses, parachute - 500 pounds? Maybe less but close enough and an easy number.
To put that glider out of USHGA specs would have taken a 580 pound weak link on the top end of the two point bridle. In terms of Greenspot that's nearly five loops. (Yeah, I know - Bullshit! But let's go with it...)
Lockout. Number of survivors - Zero.
Now let's look at Mike Haas...
Single loop of Greenspot which, by now, everyone with an IQ equal to or greater than his Hang Rating agrees is - at best - hovering around the bottom end of the safe range.
Lockout. Same number of survivors.
Conclusion - Weak link G ratings were totally irrelevant.
On to the "inexperienced tug pilot who dumped power when he shouldn't have".
If you're doing your job on the back end of the string the tug pilot can't kill you. If you fuck up someone on the front end may be able to salvage your ass but that's gravy.
I once saw a masterful job of a winch operator very probably saving a life. Well... I didn't actually see it 'cause at the moment I was running for mine 'cause that lockout was due to terminate in about two seconds at the precise spot at which Ray Dunmyer and I were standing. Lawrence Battaile had popped off the beach with his right wing stalled and Jonnie Thompson gave it the gas and pulled him back and up. That was one situation in which the failure of a marginal weak link would not have made the day go better.
Let's try to kill a tow pilot. He's pretty safe on the ground so you need some sort of energy. You can get that with wind or occasionally hay and oats but you almost achieve that goal by setting fire to gasoline. You transmit that potentially lethal energy to the tow pilot by means of a string but your wily prey always has the option of severing his relationship with said cordage.
We know precisely what caused that accident - same thing that causes virtually all tow accidents. The glider stayed on tow too long - it hit the ground still connected to the tow line.
Too long may be defined as something on the order of a second or two after liftoff if the bridle is routed under dolly tubing but it's usually something of much more comfortable duration - as was the case in this situation.
There are several excellent and reasonably consistent eyewitness accounts of this accident. We know what happened. It would be nice to know why some of these things happened but that information is secondary.
I'll give it my best shot - They were too slow. Tried to milk it, started losing control, tip stalled. Shoulda pulled the basetube and pin then gotten back on the cart.
Anybody ever notice that out of zillions of opportunities at Ridgely we've never seen anything remotely resembling that scenario behind a Rotax 914?
Tad Eareckson - 2007/07/15 22:06:51 UTC
Sacred Cow in crosshairs...
Some AT related excerpts from Towing Aloft...
Page 54Page 53A weak link is the focal point of a safe towing system.
Speed controlled towing is when the speed of the device doing the towing is maintained at a reasonably constant value. Controls, such as the throttle, are used to keep the speed of the tow vehicle or tow winch operating at a constant speed. Towline tension can vary dramatically in response to thermals, sink, pilot corrections, etc. Aerotowing is clearly in this category as the tug needs to maintain a minimum speed to prevent stalling. Many of the early towing efforts of the '70s where the vehicle drove at a fixed speed would also fall into this category of towing. Weak links very clearly will provide protection from excessive angles of attack, high bank turns and the like for this category of towing.Page 60A weak link is required that will not break needlessly in response to moderate thermals, or pilot inputs, yet, will break at a low enough point to avoid disaster or excessive pilot panic.
For aerotowing operations, a weak link breaking strength equal to 80 to 100% of the total flying weight--the weight of the pilot and glider--is a reasonable starting point.Discussion/Assault...Three recent tandem aerotowing accidents have occurred--one fatal. The common thread in all three was a lockout and the use of a much too heavy weak link. Tandem gliders are much less responsive than smaller gliders and the pilot in command often has a less than ideal position on the control bar. The situation shouldn't be compromised by an over-strength weak link.
Maybe it is the focal point but it shouldn't be. You actually have two legitimate focal points and they can trade in positions of prominence over the course of the tow but Numero Uno is almost always the release actuator (this assumes that the mechanism engaged by it has a good chance of actually functioning). The basetube slides to the fore around the time you're saying bye-bye to the dolly in a normal flight and in the event you're low, banked, and climbing or getting pulled out of a bad situation by your driver.
With respect to the last sentence of the second paragraph...
Yeah, they'll ultimately provide that protection but you can easily be dead - or effectively so - before it kicks in. You can find yourself in some very creative combinations of attitudes while still connected to the tug courtesy of something quite understrength.
Page 53...
Depends on what you mean by disaster. Yeah, it absolutely can prevent a cross spar from buckling. But there is no way it can guarantee that you won't slam into the ground on a hitherto pristine glider or serve to maintain your emotional stability. They got pharmaceuticals for the latter issue but there always seems to be some caveat about driving and operating machinery on the label.
and...
Yeah, 0.8 to 1.0 Gs is a good starting point. The middle of 0.8 to 2.0 Gs is a really good finishing point.
And many of us, including Victor and yours truly, have demonstrated that the loop of 130 pound Miracle String described elsewhere in the chapter is reliable to no more than about 125 pounds of tow line tension - that translates to 0.4 Gs for the two aforementioned individuals. (Gee it's great towing up on a good day without having my heart in my throat the whole time as had always been the case previously.)
Page 60...
I'm guessing the fatal accident referenced was Bill and Mike. Nah. There isn't a weak link in the galaxy that's gonna save you from a low level tip stall.
I'm working on collecting and organizing information from that wreck (there are some missing pieces) but, for the time being, you can take my three sentence assessment from my previous post to the bank. That is EXACTLY what happened. We figured that out at the time but I had forgotten some of those discussions.
If anyone has any information that didn't come across the wire I would greatly appreciate knowing it.
Just looked into purchasing a set of Hang Gliding magazine DVDs but they're backordered till January (just how long does it take to burn those things anyway?). Would also appreciate a copy of the report of the 1996/07/25 accident.
Also, I'm still desperately seeking an account of a single incident in which a weak link break was a desirable component of an aerotow - meaning shit was happening so fast that the pilot had no reasonable opportunity to actuate a reliable release mechanism.
Let's take a look at...
Van Sickle's Modern Airmanship, Fifth Edition
1981
Page 793Page 795Since improper technique by the winch driver or carelessness on the part of the pilot can impart many g's load to the aircraft, the FAA requires that a weak link be used in the launching cable at the aircraft end. It should break with a pull of about twice the weight of the glider.Three of those four sentences tell you most of what you need to know about weak links.The tow hook on the airplane is made so that the tow pilot can release his end in an emergency, as can the sailplane pilot...As in other types of launching, a weak link is required if the towline's breaking strength is more than twice the weight of the sailplane being towed.
Note: That text states that (then) modern sailplanes can withstand 8 to 12 Gs so they're a bit stronger then hang gliders. Strike my previous reference.
Update...
I was really bothered by my 2007/06/24 bridle wrap and went back to the drawing board. The new design has been up four times and I'm very happy with everything about it except the enormous tedium of hand stitching three ten foot lengths of 3/32 inch line together. The result, however, incorporates shear links at both ends, is virtually totally uniform in thickness, and is so stiff it would by difficult to knot it to a carabiner by hand.
Off topic...
At least one Kestrel was able to withstand the bulldozing so far. The 06/24 morning fog was too thick to get a gender but a representative of the right species was making a lot of noise at the top of the AWOS tower. Also, speaking of falcons, look for Peregrines as you're crossing the last two bridges before Kent Island en route to Ridgely. They've been nesting on the Bay Bridge for decades but a pair managed to fledge an offspring on the Severn River Bridge this season.
Chris McKee - 2007/07/16 02:39:14 UTC
With all the space you're taking up on this website, maybe you should think about joining CHGPA so you can help pay for this service. I believe this is considered a benefit of membership dues within the club. At least kick in your yearly membership dues to support your use of this as your public forum! Just something to think about ... its the right thing to do.
Tad Eareckson - 2007/07/17 12:29:11 UTC
First off, yeah, Chris, I do know that you are quite sure that this is nothing more than an exercise in taking up space and unworthy of reading and responding to. I'm guessing that you got into no more depth in my previous post than noting its length but if you've made it this far in this one - I was wondering when you were gonna take a look at all that empirical data you were demanding in your previous.
Second, never in the nearly twelve year history of the various forms of the local glider list server/forum has it ever been related to CHG(P)A membership nor (someone correct me if I'm wrong) in any way supported by dues. It's mostly been fueled by the blood, sweat, and tears of volunteers such as Brian Hardwick, Dave Green, and Mark Cavanaugh (did I miss anyone?)
Third, you've posted half a dozen times on this thread and each of those has come with a pair of images. Those twelve little pictures have eaten up a bit less than twice as many ones and zeros as the combined text of all messages to date - including this one. So let's not get too self righteous about bandwidth and storage.
Fourth, I'm a member of two other groups (towing and tugs) and they're both free too.
Let's dispense with the numbers now...
Along the lines I wrote in a response to you five years ago - I was a CHGA member from around 1982 through 1999. Towards the end of that period I did a massive amount of work running Hangola and serving as Secretary for four years (I was actually listed as Secretary for a fifth but I won't count that as by the end of the span I had imploded and didn't do shit).
In the same general time frame I was realizing, as Ralph did some years later, that it was totally insane wasting a good chunk of one's life transcribing and editing digital information for paper format and distribution, I had also burned out on the whole mountain/driving/shuttling/hike-in/ridge soaring/site maintenance scene.
Then early in the 1999 season Highland Aerosports suddenly dropped out of the sky and landed way closer to my back yard than I could have possibly dreamt. (Now if only someone could find a way to grow a hundred foot dune at Sandy Point State Park...) At that time all of my eggs went into that basket and that's where I transferred my volunteer energies.
If al-Qaeda manages to nuke Ridgely I'm gonna have a real hard time generating the enthusiasm to roll to the ridges (not that there's anything wrong with that). The AT environment has always been where I've wanted to fly - since a decade and a half before that mode of getting airborne was halfway practical - and I'm now way too spoiled to entertain much thought of going back.
I perform a lot of little chores from which folk benefit - directly or in- - that don't get noticed much. When you hop on a launch dolly I'm probably the reason your tires don't flatten to the rims. There's a bit of glass and aluminum that the crew doesn't have to move from the picnic tables to the dumpster 'cause it ends up in my recycling bin (Erica finally gave up in frustration after several efforts at organizing recycling 'cause hang glider pilots - collectively - don't give a rat's ass). I've probably saved the airport thousands of dollars of electrical bill 'cause I'm one of about fifteen or twenty Americans who realizes that most light switches also have an "OFF" position.
I've ensured that there are - so far - half a dozen Ridgely flyers that are never gonna gum up a line while they try for a second (or third) time to get to release altitude.
The ratio of time I've spent developing, fabricating, testing, documenting, and illustrating tow equipment to my airtime is astronomical. (Marc is an excellent example of why only a small portion of these advances have been adopted on a very small scale - "It can't be any good, 'cause if it was - we'd be using it!")
Towing Aloft represents a lot of effort of compiling, illustrating, explaining glider towing issues. It's a valuable resource and I appreciate it. Dennis and Bill sell it, we buy it. A lot of the information is very good, it's riddled with mistakes, some of it is crap (some of the latter category comes better to light with nearly a decade of extra experience, some was clearly identifiably so while the ink was still wet).
So, Chris, I fork out a not inconsiderable penny for materials and equipment, lose a few assemblies to folk who never quite get around to reimbursement for so much as materials cost, do all this work, analysis, and correction and make it available for free (and, contrary to your assessment, lotsa people who aren't forced to actually read it), get rewarded with a lot of stupid abuse, and you're not happy unless I go even further into the red? If you're trying to make me squirm with a guilt trip you gotta do way better than that.
Update...
Saturday afternoon I was able to get my grimy little hands on the latest version of Tim Hinkle's two point release. As I've told him - I'm not a fan of slap-ons. I like to see (actually, not see) control cables INSIDE the tubing... But if you want a one anyway - this is a thing of beauty. Very simple, elegant, mechanically efficient, and it's gotta be brutally strong. If you're considering acquisition of a spinnaker shackle based assembly... Don't.
I had asked him to put an assembly together for me before I had seen this state of evolution. When I get one I can take home I'll get some photos up.
Gary Devan - 2007/07/17 13:33:25 UTC
Dough!
Gary Devan - 2007/07/17 13:57:19 UTC
(tadd, the intention, to be sure, was to put a smile on your face, as well as any one else.)
Hugh McElrath - 2007/07/17 14:08:02 UTC
Tad,
Let me know what I owe you for the release.
I direct your attention to the "Manquin Sunday" thread. (Should rightfully be on the PG side.) Would welcome your analysis of rigs for PG scooter/truck towing. Maybe the weaker weak link is appropriate here?
Tad Eareckson - 2007/07/17 16:40:10 UTC
Nah, that wasn't directed at you, Hugh. We just recently got you properly adjusted and on your way and I hadn't asked for reimbursement. A one point assembly, complete with a pair of those rather pricey Wichard Snap Shackles, that disappeared into the wilds of Spring Mills, Pennsylvania a year ago has me a bit pissed off however.
And I do appreciate you sticking through the adjustment issue and posting that nice little review. (I have thought and am thinking more about a magazine article.
Yeah, I had been reading the discussion between you and Matthew and, of course, my ears pricked up at the first mention of the term "release".
I tend to shy away from paragliding issues 'cause I only have the cranial capacity to be obsessive/compulsive in one field but if I sat down with someone who understood bag flying and towing issues I might be able to come up with something useful in the spillover realm.
I do, in my little collection of tow oddities, have a Keller/Koch two stage release. That flavor is best employed for hang glider stationary winch launching and step towing but the PG model is just the same piece of hardware configured for one stage. No reason whatsoever that the second stage of my release can't be ignored and you're welcome to take it for a spin.
It's also rather elegant but kinda overbuilt and I've come up with an equally good and infinitely less massive HG solution - pretty sure part of it would work for pipeless.
With respect to weak links...
"Uprating" is only part of what I'm pushing.
While I'll cling to my stand of 1.4 Gs like an octopus my concept can be used to reliably get you down to about half the tow line tension of what a loop of Greenspot on the end of a bridle is SUPPOSED to give you.
PG weak links? No problem. Anything from about 126 up to around 600 pounds. Much above that and I have indications that reliability starts going to hell. Go with Tost for the heavy stuff.
Hugh McElrath - 2007/07/17 18:18:33 UTC
Well, I did have some experience helping Dave [insert last name here], an experienced competition PG pilot and instructor, who was working with Bobby Bailey and his unique biplane Dragonfly to try and aerotow a paraglider down at Quest. They were experimenting with twice-as-long towrope and having the Dragonfly launch into a turn, so that the PG could turn inside and not have to go as fast. Dave was quadrupling the weaklink and it was still breaking quite consistently. A weak later, he posted that he had successfully towed to 3000+, but I have heard no more about PG aerotowing and I'm told Bobby removed the second set of wings from the Dragonfly...
Tad Eareckson - 2007/07/18 16:57:17 UTC
Sorry, Gary, I didn't catch that you had posted a second time before my clicked "Submit" for my previous. I did admire the creativity of the little image but no one really wants to admit that Homer is a caricature of us. Do me as Bart or Lisa next time. He's more of a hang glider personality and has actually been up tandem before, she's way more likely to make a doomed attempt to organize a recycling effort and kick butt at the science fair.
OK, I opened up my copy of Towing Aloft and familiarized myself enough with paragliders to dip a toe into the water. (Put the magnifying glass on the photo on Page 45 - two stage Keller/Koch being used as a one stage.)
And, yeah, I became acquainted with TowMeUp last winter. There's a lot of good information at that site.
The high speed trim assist and auto-release configuration both look pretty cool. The former is quite analogous to sliding your two point hang glider release attachment point fore on the keel.
The split bridle also gets good marks but I don't think that boat towing is an issue around here and that concept is essentially incompatible with the auto-release, although you could combine them at the expense of a small extra step of operation.
My tow line integrated shear link (http://www.flickr.com/photos/aerotowrelease/) would fit very comfortably onto the end of a paraglider tow line, 'cept you wouldn't need or want the larger thimble - pop it out and use the little RF2180 on both ends.
I prefer though, as with hang gliding, to leave the weak link with the glider so nothing either delicate or expensive need get dragged after release and if I were gonna put something together...
I'd be inclined just to use a couple of barrel releases with a bridle link between them. That would still cost the auto-release capability (although you could get it back my jumping through a couple more hoops) but leave you a split bridle and let you keep the weak link.
The barrels would have to be comfortably accessible in a worst case scenario - low tow line angle - yet be far fore enough to allow for attachment of the trim lines to the bridle halves. Might have to go to remote barrels (see the pictures again) if that geometry doesn't work.
On a hang glider you can actuate the primary release of a two point system with both hands firmly planted on the steering wheel. On a paraglider you have to move your hands with respect to the main structure of the aircraft to make it go where and how you want so that's a bit of a problem if you want to keep doing that and release.
I'm thinking it would be pretty easy though, to run a remote barrel lanyard up to your teeth so you can simultaneously control your flight and terminate the tow.
Pretty good way to configure a hang glider platform launch system too, eh what?
Again, I don't want to shoot my mouth off too much about PG issues but you have Towing Aloft recommending 0.75 G weak links and Hugh talking about quadrupled weak links popping with no consequences to the aircraft. I gotta extrapolate that the principles are the same. Use the release to release and the weak link to prevent the canopy from being overloaded.
Gary Devan - 2007/07/18 23:09:58 UTC
fair enough. more so even.
umh, while i'm still out here 'at the edge' . . . 'taking advantage of your good humour by being forward here. . . you've always been a creative writer - but it sometimes helps, when writing, to maybe 'breathe' more often. just a small thing.
Marc Fink - 2007/07/19 06:54:41 UTCDave Prentice. Aerotowing a paraglider has nothing to do with other conventional methods of towing paragliders.Hugh McElrath - 2007/07/17 18:18:33 UTC
Well, I did have some experience helping Dave [insert last name here]...
I've used and sold many "tow-me-up" bridles--but they can "stick" to an in-line weaklink occassionally by virtue of a thinner line binding on the thicker material. This can be easily shaken off with a little weighting--but it's enough to keep the towline with you if you're not careful. Nowadays, I recommend looking at the bridles made by Critterware.
The reason weaklinks break in paraglide towing at the start of the tow is almost always due to excessive tow force relative to a high angle of attack of the canopy (hence the "accelerator" which is intended to lower the angle of attack while under tension).
Bridles also need to perform reliably in reverse inflations.
As annoying as it may be to experience problems with weaklinks towing a hang glider--you can easily end up getting seriously hurt or killed with a towing malfunction while towing a paraglider.
DO NOT become a test pilot for paraglide towing equipment unless you are very experienced and willing to take the risks.
DO NOT become a test pilot for new or inexperienced tow systems/operators unless you are very experienced and willing to take the risks.
--01--Jim Rooney - 2007/07/19 14:50:52 UTC
Weak links don't always break in lockout situations... so lets make them stronger? Are you nuts?
I don't care if they're "Meant" to break in lockout. How the hell is it a bad thing if they do?
You're advocating making tow systems more dangerous for the sake of definitions. Here in reality, weak links work. They may not suit your definitions, but you're on crack if you think they're not doing people good.
And yes, get behind me with a "strong link" and I will not tow you.
I would much rather be off tow when I want to be on than on tow when I want/need to be off.
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