a new one again..
I try to finish a doc on 2 points AT with lot of good things translated from yours..
I hesitate to write a small chapter about "tension" to help to understand that tension is not equal to danger and could help in some circunstances, that a lack of tension could be problematic, that
There is very little correlation between tow line tension and the severity of outcomes
, and then that a stronger wl should be use..
Would you help me to list situations in which the tension increase without being an imminent danger:
-cart start without any help, cause the friction on the ground (weight, wheels, ground), the surface wing facing the wind, tug start power
-jolts, mismanagment of the tension at the 2 ends of the line
-increasing the angle of attack to climb at the right alignment
-incipient lock-out at high angle of attack before correcting it
-acceleration and sink of the tug
what else ?..
maybe interesting to talk about "load factor" for a banked glider with a strong wl to encourage not to fly with bent downtubes..
Figure with different forces and how they play in a lockout situation (D. Pagen)
Tow line tension? Surely you mean 'pressure'. Whatever were you learned (:
Re: Tow line Tension
Posted: 2012/03/13 17:55:01 UTC
by Tad Eareckson
I wonder if idiot hang gliding people who scuba dive have tension gauges on their air tanks.
I try to finish a doc on 2 points AT with lot of good things translated from yours..
Thanks much. Happy to see the potential for increased circulation.
I hesitate to write a small chapter about "tension" to help to understand...
People ACTUALLY ON THE END OF THE LINE instinctively know this. It's when they're trying to "THINK" on the ground that they go for Hewett Links and gentle takeoffs with low gauge settings.
Would you help me to list situations...
Zack C - 2011/03/04 05:29:28 UTC
As for platform launching, I was nervous about it when I started doing it. It looked iffy, like things could get bad fast. I've since logged around a hundred platform launches and have seen hundreds more. Never once was there any issue. I now feel platform launching is the safest way to get a hang glider into the air (in the widest range of conditions). You get away from the ground very quickly and don't launch until you have plenty of airspeed and excellent control.
Two things I'm sure of - death and taxes.
And one of the factors that goes into the first thing...
When you lose tow tension your angle of attack goes way up.
And if your angle of attack was way too high to begin with, your hang glider may not ever again be of any use to you or anyone else.
Jack Axaopoulos - 2009/07/04 12:13:01 UTC
Bullshit.
a) only the pilot can let the angle of attack increase when you lose tension. Thats 100% on the pilot. You are simply wrong and misleading again.
b) "And if your angle of attack was way too high to begin with..." Which should never be the case or youre making a pilot error. Again, you are misleading people.
This is the problem I have with you. You attempt to fallaciously attribute pilot errors to issues of mechanical towing devices or other things.
Sorry... but if you suddenly lose power, your nose just doesnt pop
Michael Bradford - 2009/07/04 13:00:24 UTC
Rock Spring, Georgia
SG,
A glider under tow is a powered aircraft. String powered. When climbing under power, the angle of attack is relevant to the climb path, not the horizon. And if the tow force is subtracted instantly, the angle of attack is instantly translated, whether or not there is pilot input. A classic Departure Stall can easily, almost instantly result. Pitch and power are not independent forces.
If you are in the middle of a climbing correction when the "power" fails, failure to immediately lower the angle of attack can yield an immediate deep stall.
Really sick of this bombastic, grandstanding, arguing style I come to my own forum each day and get pissed off. Time to end this.
That's OK, brain dead douchebag, we'll continue here where were trying to attract - rather than eliminate - intelligent life forms.
We're string powered aircraft and we need to start thinking and acting like powered aircraft.
Powered aircraft use all the power they can muster to get off the runway every time they wanna get airborne and maintain full power until they're way the hell up away from the stuff that can hurt them.
Back in the Seventies and briefly into the Eighties gliders were towed with a bridle splitting the tension between the hang point and basetube. This made them very roll unstable but, with good pilots, drivers, and releases, high tension was valued - as long as it didn't get ridiculous (which it frequently did when someone desperate to get airborne recruited some total idiot with an overpowered waterski boat to haul him up) - and the lockout wasn't the greatest danger.
Manned Kiting
The Basic Handbook of Tow Launched Hang Gliding
Daniel F. Poynter
1974
"The greatest dangers are a rope break or a premature release." - Richard Johnson
The greatest dangers were rope breaks and premature releases.
So...
Harry Robb - 1975/09
Polyethylene or polypropylene, 12 strand, braided 3/8 inch line, 500 feet in length is used in competition. Lines for novice flyers should be about 150 feet long, and increased in length as experience is gained. According to the Kiting Handbook by Dan Poynter, this size line has a tensile strength of 2025 pounds. Each end of the tow line is normally provided with a stainless steel screw-pin shackle with an approximate 3/16 inch shank which fits in the slot of the safety release hook. The screw pin of the shackle is inserted through a loop of the tow line at least two or three feet, providing sufficient friction to prevent disengagement. Although some flyers use only the loop of the tow line in the safety release, this practice is not recommended as it greatly accelerates the abrasion and fraying of the line. Once the line shows very many single strand breaks, its tensile strength is greatly decreased and should be discarded. No flight should ever be made with a knot in the tow line. Aside from the abrasion caused by the knot rubbing on itself, the tensile strength is decreased by as much as fifty percent. Lines require constant inspection - prior to the first flight of every day by every flyer. In a tournament, the Lineman Starter can inspect some portions of the line on each flight, and the Safety Inspector will inspect the entire line slowly, foot-by-foot, two or three times daily. The tow line is a life line and must be treated with utmost respect.
...people who knew what they were doing didn't have rope breaks or premature releases.
Then Donnell Hewett came along at the beginning of the Eighties with one half decent idea and...
Now I've heard the argument that "Weak links always break at the worst possible time, when the glider is climbing hard in a near stall situation," and that "More people have been injured because of a weak link than saved by one." Well, I for one have been saved by a weak link and would not even consider towing without one.
...a couple hundred others that were total shit, eliminated all the science, common sense, and quality equipment, and turned hang gliding towing into a lunatic religious cult in which shitheads like Tracy Tillman, Peter Birren, Steve Wendt, Adam Elchin, Davis Straub, and Jim Rooney thrive very well and a lot of people listening to them get mangled and killed.
And that's why we have Kite Strings where we're trying to unlearn all the crap and start doing things right again instead of (or, if you're lucky, in addition to) going out flying and having fun.
When we teach somebody to launch off a slope we get him to:
- use two guys to hold the wings level
- watch the ribbons for a few seconds to see if anything nasty is about to happen
- RUN LIKE HELL with the wings level everything he's got to really accelerate his bird into the air
- maintain speed until he's well clear of anything that he can get turned into that will hurt him
When a competent aerotow operation launches a glider we do pretty much the same thing:
- use launch dolly to hold the wings level
- watch the ribbons for a few seconds to see if anything nasty is about to happen
- floor the tug and keep the glider locked on the dolly so the wings stay level until we're accelerated to a crisp enough airspeed to very safely get the bird into the air
- maintain speed until we're well clear of anything that we can get turned into that will hurt us - not that we'll have a choice if we want to stay behind the tug
Where we get into into the most trouble is by listening to total dickheads like:
Jerry Forburger - 1990/10
High line tensions reduce the pilot's ability to control the glider and we all know that the killer "lockout" is caused by high towline tension.
Dennis Pagen - 1993/04
A weak link is perhaps the most important safety device in the whole operation. It is intended to limit the ultimate forces in a towing situation and obviously must be very reliable.
If you find yourself breaking weak links repeatedly, try using lighter tow forces initially. Also keep in mind that it is better to break weak links than bones. In general, a little experimentation lets you find a system that provides the safety margin your life depends on, but doesn't break needlessly.
A weak link and release system must be incorporated at both ends of the towline. The weak link at the pilot's end should break at 75 to 80 percent of the combined pilot and glider weight.
Pilots must use weaklinks provided by the meet organizers and in a manner approved by the meet organizers. All weaklinks will be checked and use of inappropriate weaklinks will require the pilot to go to the end of the launch line to change the weaklink.
Weaklinks will consist of a single loop of Cortland 130 lb Greenspot braided Dacron Tolling line and should be placed at one end of a shoulder bridle.
I've heard it a million times before from comp pilots insisting on towing with even doubled up weaklinks (some want no weaklink). I tell them the same thing I'm telling you... suck it up.
You will only ever need full throttle for the first 50ft of a tandem tow. Don't ever pull a solo at full throttle... they will not be able to climb with you. You can tow them at 28mph and you'll still leave them in the dust... they just won't be able to climb with you... weaklinks will go left and right.
I was not the only one breaking weaklinks as it seemed for a while every third pilot was having this problem. You've got to get the keel cradle set right.
Our towline is our engine and its tension - assuming we can and do fly competently - is the primary thing keeping us safe.
And our safety is always somewhat and sometimes totally dependent upon the guy at the other end managing that tension.
- Cut the tension completely and abruptly we're ALWAYS gonna lose airspeed and often stall - especially if we're dealing with turbulence at the time - and start going down at some rate or another.
- If the tension is low we may not get into the air at a safe speed and we'll have a slow, dangerous climb through the kill zone.
- Dial in just the right tension - which we can and do easily do using a payout winch - and:
Zack C - 2011/03/04 05:29:28 UTC
You get away from the ground very quickly and don't launch until you have plenty of airspeed and excellent control.
- Since, to stay safe, tugs need to fly a little faster and thus deliver a little more tension than gliders - especially at takeoff - are completely happy with we've got to be extra careful to stay in position and control things smoothly so we don't start oscillating. And if we don't stay tracking reasonably well behind the tug our tension will go up more and can start aggravating the situation.
Note: The towline tension in aerotow is less than what's used for platform but it's pulling straight forward so its all forward thrust and there's usually more of it and no downward vector jacking up the effective weight of the glider.
So there's an ideal towline tension (for aero or surface) and we - as glider pilots - don't really need to know what it is. We'll get a feel for the right amount of thrust on tow just as we get a feel for the right amount of airspeed in free flight - and:
- nobody needs to be looking at a tension gauge or airspeed indicator to know what it is
- it's a lot better to be a good bit above ideal tension than a little bit below
- a halfway competent pilot can handle a good bit of extra tension/airspeed without much problem
You can install an engine that's inappropriately powerful for the particular plane and if you use it to go beyond VNE and engage in other forms of unauthorized fun that will have unpleasant consequences.
So if you had a plane with such an engine it wouldn't be a bad idea to install a governor to reduce the likelihood of the plane being torn apart.
A payout winch on a truck is analogous to a governor and the weak link is out of the equation unless something goes wrong with the payout winch.
You can't use a payout winch for aerotowing. (Well, you could, but there would be so many downsides that it would be completely stupid.) You tow at a fixed minimum airspeed (that which is necessary to keep the tug from falling out of the sky) and fly on a relatively short low stretch towline. So you need a weak link for a tits up situation to keep the glider from getting overloaded.
A payout winch will, regardless of what the glider's doing, either maintain constant predetermined tension - usually - or allow low tension to climb and stabilize at the predetermined tension. That's a pretty good way to do things.
A weak link - on the other hand - determines a maximum allowable tension but functions by instantly dropping the glider for maximum allowable to zero and irretrievable tension. That's just about always gonna be an ugly situation...
Wills Wing / Blue Sky / Steve Wendt / Ryan Voight Productions - 2007/03
NEVER CUT THE POWER...
Reduce Gradually
Increase Gradually
...and you better be pretty high when you get yourself into it.
When you select a weak link rating - say 1.5 Gs like I do - you're saying, "I'm never gonna be in a situation in which I need 1.6 Gs to stay alive." So when you use a 1.5 G weak link you better make damn sure you never let yourself get into a situation in which you need 1.6 Gs to stay alive.
I went to the funeral of one of two guys who needed a couple of Gs to stay alive and didn't after the weak link blew - but tug had no ability to give them anything at that point anyway and if the weak link hadn't blown there'd have been one more crashed plane and funeral.
When people know what they're doing and do it we don't have problems with high tension and/or low level lockouts. The reasons we have dolly launched aerotow crashes in descending order of my best guess as to frequency...
- Davis Links
- insufficiently trained glider pilots
- tug drivers making good decisions in the interests of the safety of the glider pilots
- conditions: thermals, dust devils, gusts, crosswinds - and failure to check
- dollies: design, stability, adjustment
If you wanna throw in other flavors of towing we can add...
- foot launch
- inadequate tension
- excessive tension at the wrong time
These wonderful releases that we spend so much time and energy developing and tweaking...
If people are doing everything right they tend not to make much difference. But when somebody goes up with some piece of shit he bought from Matt and makes a mistake or has something happen to him he gets killed. And we're human, we make mistakes, we have shit happen to us, and we train new people who aren't as perfect as we are - so they're worth the effort.
maybe interesting to talk about "load factor" for a banked glider with a strong wl to encourage not to fly with bent downtubes..
Better talk with somebody else so I don't have to admit how much I flew with straightened downtubes. Not saying that it's a great idea but...
- I know a lot of a lot of people do it.
- Incidents of in-flight downtube failures are close to nonexistent.
- I think it's a low priority threat and we'd get a lot more bang for our buck getting people to adhere to the preflight procedure for load testing sidewires.
I'll get to the lockout vector diagram issue in my next post here.
P.S. Sorry, I know this is way more information than you needed but maybe somebody else...
Re: Tow line Tension
Posted: 2012/03/16 12:46:19 UTC
by deltaman
gliders were towed with a bridle splitting the tension between the hang point and basetube.
I saw that before on the web but don't refind. a pic ?
LOCKOUTS AND WEAKLINKS
Dennis Pagen and Bill Bryden
It is important for all pilots to understand the cause of a lockout. First, a working definition is in order. A lockout is a progressively increasing turn to the side away from the towline which the pilot's weight shift cannot overcome. Note the italics. They are the key words or phrases.
From this, could we say that there is NO precise and invariable towline tension value to set the no return point of a lock-out ? this towline tension value varies with the position of the glider too.
Does an AT incipient lockout that increase to the point of a lockout with low tension (< greenspot 130lb) occur at a dramatical banked situation if the pilot doesn't pull on its basebar to hold some authority on his glider by reducing the towline tension?
for the time being. That should be required reading for anyone who hooks up behind anything anyway. (My first couple of tows were at the tail end of that era.)
From this...
A lockout is a progressively increasing turn to the side away from the towline which the pilot's weight shift cannot overcome.
YOU DON'T HAVE TO BE ON TOW FOR THAT TO HAPPEN.
Just the goddam AIR can do that to you. It can totally overwhelm your control authority and send you any direction at any roll attitude it wants. I was damn near killed flying the dunes one time when a thermal just exploded, rolled me seventy degrees to the left while I had everything I owned resisting, aimed me back towards the steep face of the dune, and dumped me out the back with a twenty mile per hour tailwind. I was along for the ride and sure I was dead until I bottomed out of the stall with my face a few feet from the dune, rocketed up the face, and cleared the top with about five feet to spare.
So if something like that can happen in free flight there's no weak link that can prevent it from happening on tow.
On tow we are roll UNSTABLE and the fucking tow bridle is hooked up to our control system. The tension going to both ends of a two point bridle affects the glider's pitch, roll, and yaw. And it doesn't take much tension from the side to neutralize a lot or all of what we can do with our arms - especially when it's conspiring with the air to screw us over. It's INHERENTLY DANGEROUS and we need to stay on our toes and work our butts off to keep the goddam glider pointed straight at the other end of the towline ALL the time 'cause the worse things get the worse they're gonna get.
If you're a competent tow pilot in smooth air it's no problem keeping the glider lined up properly and safely for the duration of the tow. But a thermal can instantly render your competence completely useless and you can get killed just as dead just as fast as somebody who's never been near a glider before. And it won't matter:
-a) what your towline tension is;
-b) whether it's a static or payout system;
-c) what you're using for a weak link;
-d) what you're using for a release;
-e) how good your reflexes are;
-f) how good your driver is;
-g) if the weak link stays happy with you rolled on your ear all the way to impact;
-h) if the weak link blows when you're banked one degree to the left;
The good news is that it takes something pretty extreme to do that to you and we can pretty easily avoid launching into something that nasty - but the point is that you can't make any predictions about what will or won't happen based tension or weak link strength.
...could we say that there is NO precise and invariable towline tension value to set the no return point of a lock-out ?
Absolutely. And no imprecise value either. A car going fifty miles per hour on a mountain road may be perfectly safe. Another car may be going five miles per hour, find some ice at the wrong time, and slowly slide off the edge of the cliff.
this towline tension value varies with the position of the glider too.
You can't make ANY predictions. You could be straight behind the tug and about to blow a one and a half G weak link or way the hell off to the lower left with a slack towline. You've got two planes capable of flying at different speeds in different directions in different parcels of air. Anything between zero pounds and weak link is a possibility for any relative positions.
Does an AT incipient lockout...
Yes. When you're in or going into a lockout tension is NEVER helping people get things back in line.
Lockouts are bad on aerotow because:
-a) the towline is short and thus there's a lot of transverse movement relative to the front end;
-b) the tug can't do much in the way slowing down to reduce tension;
-c) they progress so quickly that he never has any time to react anyway.
But the glider can stuff the bar, reduce the tension quickly and dramatically, and get under the high wing with a lot of airspeed and has a pretty good shot at getting things back under control if the air doesn't overwhelm him.
Re: Tow line Tension
Posted: 2012/03/19 17:33:27 UTC
by Tad Eareckson
deltaman - 2012/03/16
Does an AT incipient lockout that increase to the point of a lockout with low tension (< greenspot 130lb) occur at a dramatical banked situation if the pilot doesn't pull on its basebar to hold some authority on his glider by reducing the towline tension?
Wallaby Ranch - 2012/03/18
Welcome to Wallaby Ranch, the first and largest Aerotow Hang Gliding Flight Park in the World! We're the aerotowing (or "AT") professionals; no-one knows AT like we do; it's all we do, and we do it everyday, year-round. This primer will teach you the basics of AT theory and technique. Our instructors have fine-tuned this system over the course of many years, while teaching thousands of people how to aerotow hang gliders.
A weak link connects the V-pull to the release, providing a safe limit on the tow force. If you fail to maintain the correct tow position (centered, with the wheels of the tug on the horizon), the weak link will break before you can get into too much trouble.
I can't help think if I was close to the ground when lockout started, the three seconds that passed before it released the second time could be three seconds too late!
Sounds like Outback here has a lot better understanding of the basics of AT theory than you AT professional assholes have any hope of ever attaining.
Thanks for that last paragraph, Antoine. In watching that video I was so focused on what that piece of shit release wasn't doing that I wasn't noticing what an excellent illustration we had of what a load of shit our AT weak link theory is.
Re: Tow line Tension
Posted: 2012/03/20 03:07:43 UTC
by Tad Eareckson
Figure with different forces and how they play in a lockout situation (D. Pagen)
I'm confused by that illustration. It seems that the locked out glider is facing backwards.
But anyway...
If you want to include a good illustrated explanation of the forces and aerodynamics involved in a lockout... Fine, great. But...
Tad Eareckson - 2012/02/23 22:58:24 UTC
And, while it's good to understand the physics of what's going on, fortunately, we don't really have to.
It will be of no practical value whatsoever to a brand new student, a highly experienced tow pilot, or anyone in between in preventing, dealing with, or recovering from a lockout.
The only way I understand Dennis's explanation is to do a slow, step by step review of the text and vector diagrams. If it's been more than five or ten minutes since I've done the review I have to do it again.
And just how valuable is a solid understanding of the forces and aerodynamics involved in a lockout in preventing one?
Bill Bryden - 2000/02
Dennis Pagen informed me several years ago about an aerotow lockout that he experienced. One moment he was correcting a bit of alignment with the tug and the next moment he was nearly upside down. He was stunned at the rapidity. I have heard similar stories from two other aerotow pilots.
Dennis can't prevent a lockout any better than I can and I can't prevent a lockout any better than some Jack or Davis Show halfwit with fair Hang Two flying skills - assuming we're all flying the same equipment.
But the good news is we're NOT all flying the same equipment and they're WAY more likely to get killed than I am.
Congratulations Dave Broyles and Dennis Pagen for the great articles on lockouts. This is a highly misunderstood aspect of towing and hopefully your articles will help prevent some serious accidents.
in a letter to the editor.
The only reason lockouts are misunderstood is because of all the deadly crap that Donnell Hewett wrote on the issue and its repetition and amplification by people like Dave Broyles and total assholes like Dennis Pagen and Bill Bryden. Those two frauds did NOTHING to help prevent any serious accidents - on the contrary they enabled and caused them and sold the public on the idea that they were just an inevitable cost of doing business.
In 1974 - although the hookup to the glider left something to be desired - the lockout was understood as well as it needed to be - then or now:
If the glider gets rolled too far away from the towline it's gonna crash.
This comes as no great surprise to a ten year kid with about two minutes of kite flying experience under his belt - regardless of whether he's watching one of his little ones or one of our big ones - and the defenses against lockouts ain't rocket science neither.
- Don't LET the glider get rolled too far away from the towline.
- If the glider DOES get rolled too far away from the towline get off the towline (utilize a mechanism that actually works).
Manned Kiting
The Basic Handbook of Tow Launched Hang Gliding
by Daniel F. Poynter
1974
"Never take your hands off the bar." - Tom Peghiny
- Maintain/Maximize control at all times.
Doug Hildreth - 1991/06
Pilot with some tow experience was towing on a new glider which was a little small for him. Good launch, but at about fifty feet the glider nosed up, stalled, and the pilot released by letting go of the basetube with right hand. Glider did a wingover to the left and crashed into a field next to the tow road. Amazingly, there were minimal injuries.
Comment: This scenario has been reported numerous times. Obviously, the primary problem is the lack of pilot skill and experience in avoiding low-level, post-launch, nose-high stalls. The emphasis by countless reporters that the pilot lets go of the glider with his right hand to activate the release seems to indicate that we need a better hands-on way to release.
I know, I know, "If they would just do it right. Our current system is really okay." I'm just telling you what's going on in the real world. They are not doing it right and it's up to us to fix the problem. Think about it.
Steve Kinsley - 1996/05/09 15:50
Personal opinion. While I don't know the circumstances of Frank's death and I am not an awesome tow type dude, I think tow releases, all of them, stink on ice. Reason: You need two hands to drive a hang glider. You 'specially need two hands if it starts to turn on tow. If you let go to release, the glider can almost instantly assume a radical attitude. We need a release that is held in the mouth. A clothespin. Open your mouth and you're off.
Get ten thousand tow pilots to understand the forces and aerodynamics involved in a lockout... You:
- have done NOTHING to increase the safety of towing.
- are mostly wasting your time anyway 'cause 9,995 of them are incapable of grasping any concept requiring anything better than fourth grade math and science skills and abilities.
Get ONE built-in, Joe Street, Four-String, or Remote Barrel release into circulation you've - at best - maybe saved someone's life and - at worst - planted a seed.
But we're gonna have to plant a good many seeds for anything to start happening 'cause the hang gliding establishment is gonna keep hitting anything we've got with its very substantial reserves of herbicides - on this continent anyway. For Europe I have a lot more hope.
