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.