Weak links

[Tad Eareckson]

No, I can salvage a little dignity but am still pretty screwed on this one.

I've been jumping all over Donnell for making neat little vector diagrams that have nothing to do with reality and have, albeit to a lesser extent, committed the same sin.

I got the steady state stuff right (I think) but I didn't take inertia and lag time into account.

This is pretty much the opposite of what Donnell did. He assumed the glider/pilot system was a rigid unit. The pilot is cast iron with its body and head hollowed out to save weight and arms locked and hands welded to the basetube so it can't pendulum and won't react to application of / changes in tow tension. Thus the Lake Bridle, Koch two stage, and one point aero spell violent pitch ups and instant death.

Let's try this...

When you accelerate things they weigh more and, unless you're accelerating them straight up - à la Saturn V - they weigh more in a different direction - à la telling the guy on the flight deck it's OK to push the button for the steam catapult.

So when you rapidly accelerate the glider by pulling mostly forward, say, 150 pounds at and only at the hang point, Sir Isaac says that the 200 pound pilot is gonna be saying "wait a minute" and will stay behind and the suspension will feeling more than 200 until he's hanging vertically again. And the glider's gonna take that into consideration when it's deciding how it wants to trim.

I have a lot of material I need to review. The delete, lock, and ban buttons would've been so much easier.

P.S. What happened to the glider and pilot after that very first tuck?

[MikeLake]

The delete, lock, and ban buttons woulda been so much easier.

Na, leave that easy option for those who paint themselves into a corner and don't even know how to open a f***ing window.

P.S. What happened to the glider and pilot after that very first tuck?

Glider scrap.
Poor fellow, a vegetable for a while then spent the rest of his life as someone else.

[Tad Eareckson]

Na, leave that easy option for those who paint themselves into a corner and don't even know how to open a f***ing window.

No need to "LEAVE" that option. We both know who they are and that option is poised and waiting.

Poor fellow, a vegetable for a while then spent the rest of his life as someone else.

Wow. Had hoped that the penalty had been a lot lighter and more temporary.

And we still have assholes all over these flight parks telling people to use the "backup" releases on their shoulders WHEN the primaries on their keels fail.

I stood there at Ridgely next to a Target trainer while Sunny told a student that the primary was out of commission and to just do the barrel release. And the anchor point on that glider was WAY fore of the hang point.

And we still have assholes deliberately releasing from the bottom first so the bridle will stream out of their way from the keel and they won't have to stow it.

I'm feeling stupid for not being able to predict a tuck from pulling off the hang point (and I'm still surprised that the result could be that serious) - HOWEVER...

I would NEVER have configured myself that way or so advised anyone else.

Why/When was this done? Pre or post Brooks Bridle?

This single line setup was abandoned after the very first tuck.

What an odd culture you have over there. You didn't try it again a few more times with a different winch, stretchier towline, a lighter weak link, a bigger hook knife... just to make sure?

[MikeLake]

Sunny told a student that the primary was out of commission ...

Sorry, a concept I don't understand.
Release/out of commission, no I don't get it.

Why/when was this done? Pre or post Brooks Bridle?

If I can remember (from over 30 years ago, so I'm doing my best here), this heart bolt only method was first proposed by a pilot called Bart Doets from the Netherlands. I think he is still active (unless there are 2xHG pilots from the Netherlands called Bart).
These were the frame towing days.
He concluded (with some justification) that it was better to be pulling from the top of "A" frame instead of the bottom, arguing that pulling from the bottom perpetuates a lockout whereas pulling from the top, to some degree, resists a lockout.

The likely pitfalls were pointed out in Wings! by those who were active at the time and the accident confirmed their theories.

The watchers all knew this was wrong (or at least thought they did) but these were pioneering days, lots of suck it and see.
This was all pre Brooks when 'lockout' was THE challenge.

I was a watcher.
This was a fixed line system (that didn't help). The glider started to 'nod' and after about 3 or 4 'nods' it was upside-down. There seemed nothing particularly violent until the tuck.
Come to think of it I can't guarantee the tow point was not a short way in front of the hang point, but I believe the outcome would have been the same whatever.
I think there have been at least 2 other fatalities using this tow method in Europe (Germany I think).

And we still have assholes deliberately releasing from the bottom first so the bridle will stream out of their way from the keel and they won't have to stow it.

Towing from the top line only is an unbelievably dangerous situation, transferring to this mode due to some bottom line failure or hook up is likely to be even more dangerous.

When off the tow my 30 year old 2 point setup allowed for the belly cord to be disconnected so the rest of the contraption would wind up against the keel. I had a system in place where if this accidentally happened during the tow the line would automatically release.
(Note: This is not because I'm a brilliant designer or innovator or anything else. I watched someone tuck, didn't like what I saw, didn't want that happening to me, so I implemented a solution, simple.)
During my 23 year absence this 2 point setup (remnants of which are still in use today) morphed into something else and this safety feature was forgotten, abandoned or not understood.
I know of one fatality that I am sure would not have happened had that safety feature been in place. (*more on this).

I was fairly well stunned with the recent exchange at OZ speculating as to the likely outcome of this bottom line failure/hook-up.
No need to speculate all been done, tested and people killed or injured.
You would think with global commutations and a 30+ year history these lessons would by now all be common knowledge.
I really did attempt to get some sort of information exchange going to share this type of basic stuff.

*A knot came undone on the belly cord so all the load was suddenly transferred to the keel. THE KEEL FAILED and the pilot was killed.
A maintained, certified, 6g, 5th generation glider!
Readers! Where is the top attachment point on your set-up anything OUTSIDE of the sleeved area?

[Zack C]

But beyond establishing values what other experimentation was going on...?

What I meant by that was that besides testing different materials, they tested various numbers of strands, the effects of knots in the middle of strands, and the effects of various materials connected to the weak link.

...how and under what circumstances are we defining "prematurely"?

If it broke before they were subjectively worried about the glider breaking.

Did anybody point out that you could put a higher G weak link on smaller gliders 'cause they're proportionally stronger?

I don't think anyone realized that.

Were the people who - for whatever reason, legitimate or il - NAILED six hundred pounds for surface using 130 pound Greenspot for aero?
..
If surface and aero are entirely separate factions were the surfacers saying anything to the AT crowd?

Once aerotow operations started I think everyone forgot about surface towing. I don't know what they were using originally but when I moved here everyone was using 130 lb. Like I once did (and just about everyone else still does), I'm sure they viewed aerotowing differently from surface towing.

Gawd - that's not even anywhere close to placard.

15 degrees...

It was a figure I sloppily pulled out of my head and put down without checking.

That's what I'm saying...do we have any idea what kind of positive load will break a glider? How can we know if we've never tested a glider to failure? That's what I want to ask Steve about. I hear people quote 6-10 Gs or something but I have no idea where they're getting this.

If a donkey's pulling a heavy cart uphill in a strong headwind he's gonna come in second against a donkey not pulling a cart.

Yeah, it's intuitively obvious, but you know my feelings on intuition. It's always nice when your model reinforces common sense.

...ALL the glider is feeling is what's coming through the hang point.

For the pilot weight and tow force, sure, but what about the glider weight?

Nobody has a problem with it - UNLESS/UNTIL the glider gets turned away a bit too much.

Presumably because the driver won't be able to respond to tension increases as fast as a payout winch, and short of going in reverse there's an upper limit to how far the driver can reduce tension. If this is the case I see your point, though I don't know how dangerous it's proven in practice.

So what's stopping drivers from dialing down hydraulic pressure as the tow progresses?

We don't have a tension gauge. Drivers have no idea what the line tension is. Even pilots have a hard time telling...it's easy to confuse a higher climb rate with higher tension. And the amount of line spooled will vary depending on vehicle speed and wind, so it's very hard to guess what the pressure should be. If you set it too low the glider will stop climbing. Radios are the only practical way I see to address this.

Gregg is equipping his boat with a line tension gauge. He's also been talking about having a gauge on the pilot end of the tow line. I'm very interested in what kind of readings he gets.

You NEVER take your eyes off the GAUGE!!!

In practice, all the stationary winch towing I'm aware of in the States is scooter towing, usually used for training purposes. The instructor keeps eye contact with the student at all times. For this reason these winches often don't even have tension gauges.

I don't quite understand how the automatic tension regulation thing works for stationary winches, but I'll have a talk about it with our UK peeps.

Zack

[Tad Eareckson]

Mike,

Sorry, a concept I don't understand.

Gawd. Not even a CONCEPT of release failure. What a backwards country. Spend half an hour at ANY US aerotow park and get a clue about our background noise or, as you call it, "occupational hazards".

Two point aerotow...

A spinnaker shackle up top somewhere. Lotsa people anchor it at the carabiner but, especially for lower performance gliders, it tends to go on the keel - ideally far enough fore to trim the glider to the speed of the tug. Then you have a cable going down to a lever or loop on the down or basetube. These things are absolute junk and fail all the time in too many ways to describe in under an hour.

But that's OK 'cause you have one or - if you're less stupid - two shoulder mounted "very very reliable" bent pin releases that work most of the time as long as you don't have any "pressure" on them.

So you hit the lever for the spinnaker shackle / top / primary release and, if you're lucky, it lets go of the top of the primary / two point bridle.

Then the bridle will probably feed through the ring (carabiner) on the end of the towline and you're good to go.

If the primary bridle ties itself to the tow ring - which, using "standard" junk bridles, is a not uncommon occurrence under normal tow tensions (Sunny says one in a hundred for tandem) and a really not uncommon occurrence at high tension, you try to pry open one of your very very reliable bent pin releases and hope that the secondary (shoulder to shoulder) bridle feeds through the eye splice at the bottom of the primary bridle without jamming - the way it did to kill Shane Smith a bit less than two months ago. If that happens and you're less stupid you then try to pry open the other very very reliable bent pin release - now with four times the initial "pressure" on it - and, one way or another, your problems will be over.

But these "secondary" releases are being used more often as BACKUP releases for WHEN (not if) the primary fails. Six seasons ago I had the pleasure of watching Sunny try to sell Jim Lawrence a Quest release he could not make function right out of the plastic bag.

And they have one on a trainer that they KNOW DOES NOT WORK. Sunny's telling this student not to even bother trying, just to use the very very reliable bent pin release at the bottom - not as a secondary, not as a backup, but as an ONLY. And if the bottom fails to clear the tow ring he's instantly towing one point entirely from the keel a foot or so in front of the hang point with NOTHING he can do about it - in or beyond the half second in which it'll make any difference. And you think that experimental heart bolt tow was dramatic?

(That was probably way more explanation than Mike needed but it's there if anybody else ever comes along confused.)

...this heart bolt only method was first proposed by a pilot called Bart Doets from the Netherlands...

Same guy. There's a 1985/04 Wings! article of his reprinted in the 1985/07 issue of Skyting. I've always recognized him as someone with a brain but he pissed me off a while back by giving me some shit while I was trying to convince some of the Oz Report morons that checking one's connection status JUST PRIOR TO LAUNCH would not necessarily lead to a catastrophic and irreversible breakdown of western civilization.

The watchers all knew this was wrong (or at least thought they did) but these were pioneering days, lots of suck it and see.

The Wright Brothers went to Kitty Hawk 'cause there were high steady winds. The place also has lotsa sand. They experimented at low altitudes over soft surfaces flying at low groundspeeds and used short tethers and nobody got hurt. I have a sneaking suspicion that if you had handed them a hang glider and harness (and maybe a few spare downtubes) with no accompanying information whatsoever they would've figured out how to properly fly and tow it in about twenty minutes.

Come to think of it I can't guarantee the tow point was not a short way in front of the hang point...

Keep working with that 'cause the more I think about my "inertia" explanation the less I like it. Even if you accelerate the glider quickly from the hang point and leave the pilot behind the fore/aft stuff is still balanced - he's only swinging and pulling backwards as a response to the increased pull / acceleration forward. They cancel each other out. The glider should pitch up.

The glider started to 'nod' and after about 3 or 4 'nods' it was upside-down.

I think that there was a positive feedback sorta thing going on.
- He's towing fixed line surface.
- The tow angle is increasing.
- The anchor point is a couple of inches in front of the hang point.
- At the beginning - at a low tow angle the effect of the anchor point is negligible 'cause there's a negligible downward vector at the anchor point.
- As the altitude / tow angle increases the towline is pulling more perpendicularly to the keel and trying to pitch him down.
- He compensates by pushing out while the tow angle continues to increase.
- And the more successful he is at getting the nose up the more effective the towline is gonna be at shoving it back down again.
- They argue about it a couple of times but there really wasn't any doubt about who was gonna win this one.

I think he'd have been OK with the towline going to the hang point.

I think there have been at least 2 other fatalities using this tow method in Europe (Germany I think).

Skyting - 1983/11

Peter Roth
Neu-Isenburg

Since towing became legal in Germany on 5 May 1982, we have had three towing fatalities.

One was due to a lockout using a one-point (heart bolt attached) towing bridle.

That's not much, but he says "lockout" - not tuck. And since he was a Skyting Bridle user he DOES know the difference...

The pilot released his line, the drag chute opened, seeing this the winch operator assumed that all attachments were away and pulled on full power to regain the rope. At this time the rope was still connected to the keel. Just as the pilot tried to release manually, full power to the keel jerked the glider into a vertical dive. The pilot was thrown into the sail. At this instant, the bolt holding the crosstubes together sheared off and the glider folded up, spiraling in a vertical dive. The pilot could not throw his parachute. When he finally managed to get it out, it did not open properly. He then managed to grab the lines and jerk at them frantically until it finally opened. All this happened a lot quicker than it took to write it down here. The pilot released at 200 meters, the chute finally opened at 20-30 meters slowing him down to a soft landing, unhurt. Since I am that pilot, I'm now celebrating my birthday twice a year.

When off the tow my 30 year old 2 point setup allowed for the belly cord to be disconnected so the rest of the contraption would wind up against the keel.

The Step-Up Bridle? Gawd, I have trouble figuring that one out from the illustrations. I've been able to do it - ONCE - so I know it works, but I've never been able to muster the effort since.

I watched someone tuck, didn't like what I saw, didn't want that happening to me, so I implemented a solution, simple.

Again, how odd. Over here we just teach the pilot how to stay out of a situation in which he can tuck and have him use a lighter weak link which he can break at will just by pushing out. Our instructors are so much better than yours so we don't really have any need of this sort of "solution" bullshit.

I was fairly well stunned with the recent exchange at OZ speculating as to the likely outcome of this bottom line failure/hook-up.

I don't think any of these assholes on the Davis and Jack Shows have anything left with which to stun me - although, I have to admit, Antoine and the people discussing his proposals were making a real good stabs at it. Kinda makes you wonder a bit about the quality of the instruction they're getting at the flight parks, don't it? Really makes you wonder about ALL of them when people are saying some of this unbelievable shit and nobody's jumping on it.

You would think with global commutations and a 30+ year history these lessons would by now all be common knowledge.

Not when you have people with attention spans and memories not extending beyond three partial sentences with lotsa LOLs in them and everybody listening to Head Trauma Rooney telling them how he personally invented hang gliding from scratch nine years ago.

I really did attempt to get some sort of information exchange going to share this type of basic stuff.

Try sending people here. That's our primary mission.

Readers! Where is the top attachment point on your set-up anything OUTSIDE of the sleeved area?

Good point - and something I haven't properly considered before. On my own glider for AT - yes. In a worst case scenario I could hit that point with about three hundred perpendicular pounds. I don't know what that would do to 7075 that far out front.

Zack,

...I'm sure they viewed aerotowing differently from surface towing.

Touché. They hit upon a pretty good solution but they really didn't understand the physics of what was going on and couldn't extrapolate to a somewhat different environment. Like Nate The Artist Wreyford says, "Who gives a shit?"

I hear people quote 6-10 Gs or something but I have no idea where they're getting this.

I think six is a safe translation from HGMA certification. But I've seen photos of what the glider looks like when it's being tested. After you've seen that kind of distortion you really don't worry about what anything remotely beyond what you can do to it shy of badly blown extreme aerobatics.

Yeah, it's intuitively obvious, but you know my feelings on intuition.

That isn't intuition - that's stripped down bare bones physics. You:
- are lifting a weight - just like an elevator
- are fighting drag - just like a bicycle
- have a fixed power availability - lotsa horsies or one donkey
- are using that power to generate thrust - off the air or the hillside
- can forget everything else

For the pilot weight and tow force, sure, but what about the glider weight?

Yeah, the glider has to lift itself but...

Let's make this one point aero or platform towing off your hips to keep things simple.

Everybody's feeling the same vectors - gravity and tow. And if you're in a turn in a cloud you don't have any better idea where down really is than the glider does.

Under tow if you ask the parachute in your container or the outboard sprog in your port wingtip which way down is and how big the planet is they're gonna give you the same answers.

Or, now that I think about it, make it a Gray Treefrog. I had to spend about twenty minutes trying to chase one out of my double surface at Currituck one time. Put him ANYWHERE in your harness or wing and he feels the same forces.

If this is the case I see your point, though I don't know how dangerous it's proven in practice.

Read the 1999/12/11 Debbie Young fatality in my FAA document.

http://www.energykitesystems.net/Lift/hgh/TadEareckson/index.html

Note how our illustrious Accident Review Committee Chairman and Towing Aloft coauthor never once brings up the issue of the cost of a payout winch versus the value of her life.

Mike Lake - 2011/03/02 01:11:45 UTC

Looking at a spring gauge and slowing down or speeding up a vehicle according to what the glider might be doing is a very unsatisfactory tow method effectively thrown out here (UK) almost immediately.

I am amazed that this type of towing is still practiced today and even more amazed that in some instances the 'tension controller' is also trying to drive the vehicle at the same time.

Drivers have no idea what the line tension is.

Still seems that driver oughta be able to crank a knob a quarter turn to the left when the glider in the mirror shrinks to three quarters of an inch without doing too much damage.

For this reason these winches often don't even have tension gauges.

http://www.paraglidingforum.com/viewtopic.php?t=28697
Weak links why do we use them. in paragliding.

Ake Larsson - 2010/02/13 16:31:31 UTC

In the my part of the world (flatland Sweden) where you have to tow (paragliders) to get some airtime no one uses weaklinks. I believe it is the same in Finland. Even most of the beginner training is done on tow in Sweden and without a weaklink. Play the percentages, a weaklink might save you one serious accident in a hundred years but will give you a lot of smaller accidents that occur when it breaks.

Steve Uzochukwu - 2010/02/13 22:03:55 UTC

Are you using payout winches, static winches, or both?

Both, but mostly static.

What do you do about tension regulation to prevent too much force being applied to the tow line?

A good tow tech that knows what he is doing.

This is the main reason this forum is called "Kite Strings". Ten-year-old kids and common sense tow operators - minus weak links and gauges (and, in the former case, pilots) - do better jobs of getting kites safely into and out of the air than aerotow parks and US surface tow operations do.

Asterisk. It's still stupid not to use a two G weak link - you eliminate ALL the unwanted crap and still save the once a century guy. Even the European bagwingers can't seem to get over Donnell's mind-set that it's gotta be under a G or nothing.

I don't quite understand how the automatic tension regulation thing works for stationary winches, but I'll have a talk about it with our UK peeps.

Lemme give it a shot. You pull the glider in at pretty much whatever you want but if it gets slammed by a gust or starts locking out and turning away there's a clutch or some hydraulics that prevent the tension from going too nuts without abruptly dumping you like a weak link or (à la Shane) hook knife will.

[MikeLake]

(That was probably way more explanation than Mike needed but it's there if anybody else ever comes along confused.)

No not at all I like detail and I am learning all the time.

...this heart bolt only method was first proposed by a pilot called Bart Doets from the Netherlands...

Found it! October '79. Pre Brooks.
http://www.british-hang-gliding-history.com/magazines/wings/no-57/no-57.pdf

Keep working with that 'cause the more I think about my "inertia" explanation the less I like it. Even if you accelerate the glider quickly from the hang point and leave the pilot behind the fore/aft stuff is still balanced - he's only swinging and pulling backwards as a response to the increased pull / acceleration forward. They cancel each other out. The glider should pitch up.

Not off the hook yet I'm afraid.

Take the extreme. The pilot and glider are stationary and the pilot is anchored to a handy nearby very tall tower.
A 45 degree 200lbs pull is applied to the glider at the hang point.
Where is the glider going to go?

Now instead of being anchored to that handy nearby very tall tower, take a very very very fat KFC munching heavyweight pilot.
Where is the glider going to go?

Normal size pilot?
OR ... does it depend on if the pilot is holding on tight to the base bar?

I think he'd have been OK with the towline going to the hang point.

Going over the memory of this I disagree I think the glider was stalled (to some degree) and, as the nose dropped the tension increased and pulled the glider around the pilot. I don't think the glider's positive pitching attributers ever got a chance to contribute to a recovery. This is the key.

The Step-Up Bridle? Gawd, I have trouble figuring that one out from the illustrations. I've been able to do it - ONCE - so I know it works, but I've never been able to muster the effort since.

Obsolete, not worth the effort, although it did tick most of the safety boxes.

Really makes you wonder about ALL of them when people are saying some of this unbelievable shit and nobody's jumping on it.

Learning from my recent experience on Oz I would say there were many readers who were decidedly uncomfortable. Not particularly with what I had to say but the wholly transparent attempts made to 'silence' me.
'That' thread was the busiest for some time and I am sure not everyone was waiting to see if the stubborn Englishman would put his foot firmly in his own mouth.
My posts were obviously not welcome, I really think by a minority.
Who is going to support or even engage in a dialog under such circumstances?

Zack,
Really sorry to have played my part in mixing up the various threads here.
There is such a crossover and I'm fairly well lost.

Tension control on a static, sorry stationary winch is really just like on a payout winch except the drum is powered.
Once the tension reaches a preset level a clutch slips and it matters not if the drum at the time (due to wind speed) is winding in, stopped or even paying out.
We have a technique here called (surprise surprise) kiting. This is when the upper winds are strong.
The winchman reduces tension a bit and the line pays out, just like a payout winch.
This line is then wound in and the pilot gains height. The process is then repeated.
A bit like step towing but without the (risky) procedure of a down wind leg with a trailing wire.

Another brutally simple method of tension control is when the pull on the drum reaches a preset tension (a spring on a tilting drum) it physically pulls back the throttle lever.

[Zack C]

They hit upon a pretty good solution but they really didn't understand the physics of what was going on and couldn't extrapolate to a somewhat different environment.

Where they (and just about everyone else) failed is in their belief that there's a direct correlation between line tension in speed controlled towing and danger, or line tension and the desirability of being off tow. But I think they understood tension controlled towing well enough.

Really sorry to have played my part in mixing up the various threads here.
There is such a crossover and I'm fairly well lost.

No worries...Tad and I were doing it before you came here. The threads may be hitting multiple topics, but their flow is logical.

Thanks for the explanations. You guys seem to be way ahead of us with regards to foot launch and stationary/static winch towing. (Also liked your 'the English excel at queuing' statement. One of our English guys described his experience with UK winch operations and they sounded like paragons of efficiency. I wonder how many people here even know what a 'queue' is...)

Zack

[Tad Eareckson]

Wings! - 1979/10

Bart Doets
Van Hoornstraat 17
Hilversum, Holland

There has been a lot of writing in Wings! about tow launching. Though living in flat Holland, most of our pilots are only remotely interested, since tow launching has been officially prohibited above fifty metres - any hang gliding is forbidden above a hundred metres. This is mostly because the people who make airplane laws are mostly airplane pilots, and they doubt the aerodynamic stability of our kites. And, in fact, we cannot yet say bluntly they are mistaken.

Still, I have some hope that one day we will tow launch happily in this country - if, before that day, no volcanic eruption will create a hill of several hundred metres in one of our polders. Until either of these, we will soar our twenty-metre dunes.

As you see, any creative ideas of mine on tow launching aren't worth trying out at fifty metres. But maybe one of your readers may give his opinion on the following.

The two main risk factors in tow launching are lock out and too high angle of attack. Against lock out, as far as I know, nobody has developed any alternative towing system except trying existing methods and concluding that lock out happened more or less often.

To fix the maximum angle of attack, most commonly, a two- or three-point bridle is used. In Wings! No. 6 Paul Baker states the three-point bridle would mean risks regarding pitch and yaw stability. (Page 30.) He hangs on to the two-point system and states this enables control of pitch near the ground. I find this doubtful, and I will explain why.

The top leg of the bridle, fixed at the top of the control frame, may be seen as the main towing line since its attachment point is quite exactly also the centre of drag and lift. So all we need further is a security on pitch stability that does not negatively affect yaw stability. . . The bottom leg of the V-bridge is considered to fit this means.

I think it does not. It fixes the MINIMUM angle of attack all right - but it does not prohibit a pilot to push out, slacken the bottom line, and stall - or break his kite due to overloading. On the other hand, as long as the bottom line is tense, it will FAVOUR LOCK OUT. Given a deviation from the towing path, a tensed bottom line will pull the control bar closer to the towing path while you would want it on the other side, to correct the deviation.

For pitch as well as yaw stability a second line on the king post seems aerodynamically all right - only I don't like the idea of what happens if its release fails, or the line gets stuck in the wires . . . Wouldn't get high either. Next comes my suggestion, which I hope will be criticized or accepted thoughtfully - I expect it to be rejected because it seems so simple.

Let's stick to the main towing point at the top of the control frame. My only towing experience until now taught that, at the top of the line, just this attachment enabled easy control of the kite, even when the boat turned a wide 180.

I suggest to make a second attachment, which may be just a releasable eyelet that the one bridle line runs through, on the forward part of the keel, at a point preferably worked out by some hang gliding mathematician. For an idea, let's say twenty centimetres (eight inch) in front of the top of the control frame.

This point, which would be the main towing point until released at a line angle of say 40 degrees, would need a severe pushing action by the pilot to climb, while it would be impossible for him to stall or overload. Besides, being well in front of the centre of drag, it will secure him pretty well against lock out. Above a certain height, it may be released to climb the full length of the line, towed by the top of the control frame, as maniable as any other bridle system.

Dear towing experts, please explain to me why this idea won't work; or either use it and refer to it as the Bart Bridle . . . . Thank you.

Mike Lake

The club purchased a static winch from Len and towing had arrived.

A meeting was arranged sometime later to discuss the way forward. It was well attended and many issues were discussed.

On the 26th September 1979 at the Fleece in Suffolk.

The club had one valuable member (Brian Barry? I can't remember) who had studied tethered flight in some detail. He had been appointed a tow technical adviser.

His name was Brian Pattenden.

During discussions he described his theory that some part of the tow force should go through THE PILOT.

You may wish to reread the above. What was being described was C of M towing. I believe this was a first, worldwide!

It was a radical suggestion at the time and was greeted with silence. However, the seeds had been sown.

Unfortunately, at the same meeting, when asked for his advice on safe towing his answer was 'DON'T DO IT'. This was not what several dozen flight starved pilots wanted to hear. His short reign as tow technical advisor came to an end.

Donnell Hewett - 1983/12

It's hard to say when skyting was born. It was conceived during the summer of 1980, developed during the fall, written up for publication in December 1980, first published in Hang Gliding in April 1981, rejected by the established hang gliding community almost immediately, self-published in SKYTING NO. 1 in October 1981, reintroduced to the hang gliding community in Whole Air in March/April 1982, and promoted through the Skyting Newsletter since June 1982. By this time interest was growing rapidly as pilots began to realize the advantages of towing with a system based upon the skyting philosophy and theory.

(Look at the dates on those things.)

Mike,

Not off the hook yet I'm afraid.

Actually... I think I'm smelling victory here.

Take the extreme. The pilot and glider are stationary and the pilot is anchored to a handy nearby very tall tower.
A 45 degree 200lbs pull is applied to the glider at the hang point.
Where is the glider going to go?

Nowhere. You have the pilot ANCHORED to the tower - let's say by his ankles. So you're gonna have a rather painful mess sagging down a bit from a line running forward and down at a 45 degree angle.

But I don't think you meant to ask that. So let's try it again without the shackles and assume no wind.

Now he's being being pulled off the tower and he's initially gonna fall off like a dead air cliff launch 'cept worse. But then the glider's gonna recover from the stall and start climbing (assuming the other end is tied to a truck which will keep moving fast enough to maintain that 200 pounds) until it trims out when the tow angle becomes what it would be throughout a platform tow - about 70 degrees. The better the L/D of the glider the higher the tow angle it can achieve and maintain.

Or maybe you mean that the "pilot" has been trained by Steve Wendt to assume that he's connected to the glider at the edges of cliffs and handy nearby very tall towers. We'll assume that the would-be pilot misses his grip on the basetube and falls away harmlessly to his death and the glider will stay level on its own indefinitely instead of temporarily.

It's gonna accelerate more quickly and the stall will be negligible. It'll climb faster at a higher pitch attitude and stabilize at a higher tow angle and, on a fixed length line, higher.

Now instead of being anchored to that handy nearby very tall tower, take a very very very fat KFC munching heavyweight pilot.
Where is the glider going to go?

Who cares? He's probably gonna die of a heart attack in the course of the flight anyway.
From the ground? Forward and up. Even your Bart Bridle test pilot did that for a while - with the attachment either at or fore of the hang point.

Normal size pilot?

Forward and up faster, at a higher pitch attitude, and to a higher tow angle.

OR ... does it depend on if the pilot is holding on tight to the base bar?

We have to throw out pilot input for the purposes of our experiment. Just watch how the glider trims and restrict the pilot to minor adjustments to keep the glider tracking properly. If you let him use lotsa muscle as he pleases all bets are off - especially if the girlfriend has just dumped him for his other girlfriend (who used to be his boyfriend before the operation).

Going over the memory of this I disagree I think the glider was stalled (to some degree) and, as the nose dropped the tension increased and pulled the glider around the pilot.

If the glider was stalled/mushing prior to the tuck... Again, all bets are off. A tuck on tow is a consequence of the glider being trimmed too fast. If there was a stall involved it had to be the pilot's doing.

And now that we know what a true Bart Bridle looks like...

Eight inches in front of the hang point - the guesstimate for the zero to guesstimated 40 degree tow angle part of the flight - would be EXTREMELY dangerous. Even a rather small fraction of that would scare the crap out of me. If he hadn't gone to stage two mode before the tow stopped being fun I don't think we need to get too abstract to explain the tuck.

Obsolete...

Kinda depends on what you're comparing it to, doesn't it?

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

Jim Rooney - 2009/11/02 18:58:13 UTC

Oh yeah... an other fun fact for ya... ya know when it's far more likely to happen? During a lockout. When we're doing lockout training, the odds go from 1 in 1,000 to over 50/50.

'That' thread was the busiest for some time...

It's still pretty busy. It's sunk back to Page 5 now and has picked up over eleven hundred hits since lockdown a bit over a month ago. My own release thread has picked up about six times that since Jack locked it on 2009/07/04 and it's currently on Page 107. Kinda odd 'cause people were always telling me about my status on the Ignore List (all time champ by a huge margin) and how nobody was reading me.

Who is going to support or even engage in a dialog under such circumstances?

You're a guest in a country whose economy is dependent upon the continuous production and sale of shitrigged releases. What did you expect? Love it or leave it - ya pinko hippie queer.

P.S.
- Page 30 of Wings! No. 6 is the back cover. I couldn't find anything relevant in the issue.
- In Issue 57 there's a photo of a Robin Pattenden. Any chance that's "Brian" Pattenden?

Zack,

Where they (and just about everyone else) failed is in their belief that there's a direct correlation between line tension in speed controlled towing and danger, or line tension and the desirability of being off tow.

That's right out of Donnell. Then it got picked up and amplified by everyone and his dog and it's still making life hell today.

But I think they understood tension controlled towing well enough.

If you understand one flavor "well enough" you can translate it to another.

One of our English guys described his experience with UK winch operations and they sounded like paragons of efficiency.

I used to catch a lot of crap from those assholes at Ridgely if I delayed them three seconds flicking the switch on the vario I forgot about until I was on the launch pad. But they never had any problem whatsoever with "free" relaunches (in front of me) for their 130 pound Greenspot clones and zombies.

[MikeLake]

Tad.

Actually... I think I'm smelling victory here.

If the glider was stalled/mushing prior to the tuck... Again, all bets are off. A tuck on tow is a consequence of the glider being trimmed too fast. If there was a stall involved it had to be the pilot's doing.

I can't see how a (fast) trim would make a tuck anymore likely assuming the glider is flying and within the trim range of the few inches we are talking about.
Regardless, I AM taking into account what the pilot is doing and other factors that might accompany the experience.
We really should have rubber stamped the terms of this bet much earlier.

Take my first statement.

Pulling from nothing but the hang point, by this I mean a SINGLE line at just the heart bolt area is fine and offers the same roll stability (or a reduction in instability) as other configurations.
The trouble is a small surge can (and does) rotate the glider around the pilot. It's easy to visualise how this would happen.
On my early two point designs I always considered the bottom line to be there just to stop the glider tucking.

It's easy to visualise how this would happen.

Ok. Not that easy.

The requirement is outside of a textbook tow and involves line tension surges and the pilot's reaction to them, somewhere in there there will also be a mild stall.

I have experienced a 'nodding' with the Step Up Bridle, many times in mildly rough conditions and at high line angles.
The Step Up Bridle worked in such a way that I could simulate this top line only tow by relaxing my push out on the stirrup of my harness.

During a 'nod' I have felt a pitch down with the glider accelerating ahead of me followed by the reassuring tug of the belly line an instant later.
Had that belly line not been in place I am sure the glider would have gone over although I never took this to its conclusion (obviously).

It takes a particular combination of 'nods', surges, and pilot input to induce this but it did occur far too often and easily for a hang point only tow to be viable without a bottom line.

In a nutshell the Bart Bridle was not viable as it was far too easy to experience pitch issues, even with the glider behaving exactly as it should.

Towing from the body only made this problem redundant and the 'nodding' disappeared overnight.

In Issue 57 there's a photo of a Robin Pattenden. Any chance that's "Brian" Pattenden?

No. Brian, despite his insight and obvious knowledge never had a tow launched flight (along with nearly everyone else to be fair).
I believe he joined a commune sometime in '79-'80 and was never seen or heard from again.

Zack.

We had some textbook 'payout' flights Saturday using our static/stationary winch on a relatively short runway topping out at 2000 feet (the UK limit).
I meant to get some video of the winch in action for you, but I was enjoying myself so much I forgot.
Next time.