weak links

[Tad Eareckson]

Obviously didn't proof that one very well either.

[Tad Eareckson]

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 spar with John a bit more 'cause he's got 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 an indirect consequence.

Anecdotaly, 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]

The Calf Path
1895
Sam Walter Foss
1858-1911
Public Domain


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.

--

Thanks again, Garrison.

[Tad Eareckson]

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 tow line 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;
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.

[Flying Lobster]

I'm sorry, I can't resist--but it finally dawned on me, you are truly "the missing link!"

marc

[brianvh]

Can't you see this has become Tad's personal blog? You're, like, totally destroying the experience.

[Tad Eareckson]

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 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?

[brianvh]

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.

[CraginS]

[quote="Tad Eareckson"]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?[/quote]

Bill Bennet

[Tad Eareckson]

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.

Naw, 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's got 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.

[Flying Lobster]

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?

marc

[Tad Eareckson]

>
Cragin Shelton <cragins>
2001/08/08 09:03:01
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.
<

Paragraphs 5 and last sentence of Paragraph 8 - Solid.

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 it's 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 comforable 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]

Sacred Cow in crosshairs...

Some AT related excerpts from Towing Aloft...

Page 54

A 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 53

A 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.

Page 60

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.

Discussion/Assault...

Maybe it is the focal point but it shouldn't be. You've actually got 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 793

Since 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.

Page 795

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.

Three of those four sentences tell you most of what you need to know about weak links.

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.

[Batman]

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]

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 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.

[deveil]

Dough!

[deveil]

(tadd, the intention, to be sure, was to put a smile on your face, as well as any one else.)

[mcelrah]

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?

Hugh

[Tad Eareckson]

Naw, 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 got 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've only got 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've got indications that reliability starts going to hell. Go with Tost for the heavy stuff.

[mcelrah]

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... - Hugh

[Matthew]

see--

http://www.towmeup.com/bridle1.html

[Tad Eareckson]

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 planted on the steering wheel. On a paraglider you've got 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've got 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.

[deveil]

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.

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.

[Flying Lobster]

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... - Hugh

Dave Prentice. Aerotowing a paraglider has nothing to do with other conventional methods of towing paragliders.

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.

marc

[jimrooney]

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.

Please re-title this thread "Tadd's Blog"