Emergency Procedures

[Tad Eareckson]

Please..

Oops. I tried and AOL said the file was too big. I'll jump through some hoops and get the relevant stuff to you in some form shortly.

they did it, really !!?

Yeah, John Williamson - who's a good friend of Bill Moyes and goes back to near the beginnings of the Dragonfly, towing, and hang gliding - told me he had one behind him, noting that the weak link doesn't always blow when things start getting weird (the way Wallaby and Towing Aloft tell you it will). Davis also reports experiencing one.

why ?

My best shot at an answer...

When you push out you're slowing and thus increasing towline tension. Thus you have more of a forward artificial gravity vector and the glider will pitch up and maintain airspeed - assuming the tug has the power to maintain the tension and not stall himself.

I thought the speed of the turn changed that.

As the lockout progresses - yes, the back end of the towline will start feeling some crosswind. But I don't think you're going to find many gliders staying on tow into lockouts long enough to get too sideways before somebody releases or a weak link blows.

But of course if the tug doesn't have or use the power or dive to compensate and a weak link blows things tend to get very ugly very fast. That was the issue that killed the tandem glider I mentioned in my previous reply to you - Bill Bennett and Mike Del Signore, 1996/07/25. And it also claimed Arlan Birkett and Jeremiah Thompson, 2005/09/03. Similar effect when you do that, lock out, and are forced to release - Jamie Alexander and Frank Spears, 1998/10/25.

If the glider...

I'm afraid I'm lost here. If knew all the variables I might have a shot at struggling through the equation.

force of drag
velocity squared
coefficient of drag

Think I'm OK on those.

atmospheric pressure
angle of attack

How am I doing on those?

[Tad Eareckson]

Hang Gliding - 1996/10

The following article is excerpted in part from the new book, Towing Aloft by the authors (due out this fall).

LOCKOUTS AND WEAKLINKS
Dennis Pagen and Bill Bryden

Towing has come a long way since I had my first experience being pulled from the basetube on a short rope by a car, without the benefit of a tension gauge or a forward release. This practice might seem radical, but it was the norm in the 1970's. Today, proper bridles, weak links and towline tension regulators all serve to limit and properly distribute tow forces. With these systems and safe procedures we have greatly reduced the two big towing heavies: structural failure and lockouts.

However -- with a capital H -- we have not totally eliminated lockout problems. The reason seems to be in part education. A few slip-ups here and there concerning procedures and equipment have lead to unhappy happenstances. In the interest of keeping all tow pilots well informed, we offer these insights concerning weak links and lockouts.

Let's start with a few myths that are commonly believed religiously:

1) Lockouts will not occur if I maintain a low tow force.

2) Lockouts don't happen when aerotowing.

3) Lockouts won't happen if I use the proper weak link.

There are other myths that abound in the towing nether world, but these serve to illustrate our points. Think about them as you continue to read and see how the logic applies to disprove each of the assumptions.

LOCKOUTS

We have all seen lockouts. When a child's kite starts to spin around the kite string it is locking out. A glider on tow would perform a similar windmill action around a towline once it is locked out, except that the surface gets in the way (see Figure 1). At least one pilot has locked out while up high on aerotow and ended up upside down before he released.

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.

Lockouts occur progressively, which means they start small and get big -- sometimes real fast. Turning away from the towline is what begins the lockout situation. This turning can be initiated by turbulence, a stall, or miscontrol by the pilot (over-control of an oscillation or not following a turning tug).

At the start of a lockout situation the pilot can effectively eliminate the problem by making the proper corrective roll control. However, strong turbulence, shorter towlines, steeper towline angles and higher tow forces make the process occur more quickly -- sometimes faster than the pilot can react. Since a true lockout means that the pilot can no longer correct the roll, we call a situation that can be corrected an incipient or potential lockout.

In Figure 2 we illustrate what takes place in a lockout. In (a) we see a glider in front view located to one side of the towline. The tow force is shown by the arrow TF and the total pilot and glider weight is the arrow W. The size of the arrows depicts the strength of the force and the direction shows the force direction. The other force working on the glider is the resultant, R, which is the sum of all the lift and drag on the glider. For the most part, R remains perpendicular to the glider's wing surface, W points downward and TF always points along the towline. The combination of TF and W is shown as the arrow CF.

When the pilot is to one side of the towline with wings level, misalignment of the forces R and CF works to pull the glider back into alignment with the towline, as shown by the arrow (see (a)). However, if the pilot is off to one side with the wings rolled as at (b), the misalignment of R and CF induces the glider to slip the other way -- away from the towline -- to make the problem worse. This is known as a positive feedback situation, and despite the seemingly cozy new-age turn, "positive," is an engineer's worst nightmare. Positive feedback sends things out of control and a lockout is a precise example.

But the pilot in (b) can still correct since he has room to move to the high side of the control bar and level the wings. However, if he doesn't respond soon enough with enough force, the situation quickly deteriorates to that of (c) and (d). Here we see all the forces (except weight) have increased and the bank angle steepens. The glider is accelerating to the side and downward in a slip, and its natural yaw stability rotates the nose toward the ground.

To make matters worse, the angle at which the pilot finds himself means that he must swivel against the force of gravity and against increased towline forces. In addition, in order to effect roll control the pilot must move past the point where the towline lines up with the hang point as Figure 3 shows.

Once the glider gets turned to the point where the tow rope, bridle or pilot's body contacts the cables or upright, no more roll control input is possible. At his point a true lockout begins and the only way out is to release from the towline or reduce all pressure at the tow rig so the glider becomes a free-flying aircraft once again.

WEAK LINKS AND LOCKOUTS

To understand the role weak links play in a lockout situation look at Figure 1 and see how the towline forces increase as the lockout progresses. In this case a weak link would supposedly break at some point, letting the pilot escape. However, there are tow problems with this assumption.

First, with a payout winch, a hydraulically controlled reel-in winch, or even a static line with a pressure gauge and experienced driver, tow force is limited to below the weak link breaking strength in most cases. So a lockout can progress without breaking the weak link, since as long as some tow force exists, a lockout can occur. Granted, a tow force-limiting system will reduce the frequency of lockouts, but it will not totally eliminate them.

It should be apparent from the preceding that lockouts can occur during aerotowing. The low angle of the towline (almost horizontal) and tow force was thought to eliminate lockout possibilities, but the lack of towline pressure regulation brings them back. Lockouts may be less likely to occur when aerotowing, but at least three of them have occurred just this past summer.

The second problem is that, even if a weak link breaks as planned, the lockout may have progressed to the point where you in an unrecoverable position close to the ground. Do not depend on weak links to save you from the dire consequences of a lockout.

LOCKOUT DEFENSE

In order to prevent lockouts all tow pilots must understand their cause and have a plan of prevention. This plan should entail limits as to how much sideways force on the glider is allowed before release is mandatory. These limits will be different for each type of tow system, glider and pilot. The plan should also include a method for practicing emergency releases. One of the biggest problems is the tendency of pilots to try to fly out rather than release.

Our best defense plan against lockouts is:

1) Stay focused and maintain your position aligned with the towline.

2) Keep your wings level as much as possible.

3) Input aggressive and timely roll control the instant a wing gets lifted. However, do not over-control. On aerotow the input often requires a side control that is released after a second or two. On surface tow this may be longer. During our personal experience with an incipient lockout on static-line tow, it required six seconds or more of hard side control for the glider to react. Pulling in to lower the nose helps the glider respond.

4) When you feel that a lockout situation is getting worse, despite maximum control input, release. Don't wait to become a statistic.

Next month we'll cover weak links.
---
Figure 1: A 360 degree lockout.
Ground level for surface towing

Figure 2: Forces in a lockout.
Towline
R
TF
W
CF
(a) Glider moves
(b) Glider motion
(c) Nose rotates down
(d) Nose rotates down

Figure 3: Roll corrections on tow.
No roll input. Pilot's body is in line with towline and hang point.
Roll input since pilot has moved beyond alignment point.

[Tad Eareckson]

Bringing everybody up to date...

- The previous post was the article I had previously transcribed from the magazine. There's a similar discussion starting on Page 360 in "The excellent book, Towing Aloft, by Dennis Pagen and Bill Bryden" which came out fourteen months after the magazine issue - not "this fall".

- Antoine sent me a link to something I could use to send big files but I figured out how to spare the internet by taking partial screen shots of the two relevant illustrations and save and send them as little PDF files - 82 and 45 kilobytes. If anyone else wants to see them lemme know.

- Got a note from Antoine shortly thereafter which I didn't see till late yesterday...

deltaman - 2012/02/24 14:56 UTC

thanks++
but in Fig. 3 "Roll corrections on tow", he is wrong. I think you know that: You shouldn't move your shoulders away to the center, and only use your feet to make a correction. By shifting the end of the towline with your body you create a yaw torque in the opposite of what you wanna do.. (taming the beast)

I don't think he's wrong on that.

I never thought about what I was doing on aerotow (or any other flavor)... I just flew the glider by feel - just like in free flight but with less movement and more muscle and fear. And - barring a couple of lockouts - the glider did what I wanted it too. And I stayed behind the tug as well as the next guy in the nasty air I craved for what it would do after the tow was over.

"Taming the Beast" is a reference to the lockout discussion from Dynamic Flight - James Freeman and Rohan Holtkamp:

http://www.dynamicflight.com.au/Lockouts.html

That's a lot better information than you'll find in most places in hang gliding and a lot of it's intelligent and well thought out but a fair chunk is crap. I may get bored enough to do a full dissection sometime but, for now, as to the relevant passage...

To further complicate matters under tow there is a completely new element introduced - this is yaw. In free flight yaw plays a minor albeit important role. The yaw force that a pilot can apply is quite limited. Even if you might not recognise it the act of leading with your hips when applying a weight shift input in prone also applies a yaw force to the glider - to shift your hips right you must push with your left hand and pull with your right. But now consider this. What would happen if you attached the tow rope to the bottom left A frame corner? The glider would go spearing off to the right of course. Now consider what happens under tow if you put both hands on this same point and braced your arms. You are now redirecting a significant part of the tow force to the left hand side of the glider and producing a big yaw. The magnitude of this yaw is potentially far more than can be applied in free flight.

The yaw force that a pilot can apply is quite limited.

I think that the yaw achieved by a pilot applying force is all or virtually all wishful thinking.

Even if you might not recognise it the act of leading with your hips when applying a weight shift input in prone also applies a yaw force to the glider - to shift your hips right you must push with your left hand and pull with your right.

- I don't think about my hips when I'm trying to turn a glider - they're just back there somewhere.

- When I turn right I'm using BOTH hands to push the bar to the left. This increases tension on the right sidewire and decreases it on the left and rolls the glider. There's no torque being applied to rotate the glider around its vertical axis.

- I'm also pushing out on the bar to pitch the nose of to coordinate the turn and bring the glider around.

What would happen if you attached the tow rope to the bottom left A frame corner?

I dunno. Let's ask Harold Austin. (1991/06/09. Would've been fine on a Koch two stage.)

Now consider what happens under tow if you put both hands on this same point and braced your arms. You are now redirecting a significant part of the tow force to the left hand side of the glider and producing a big yaw. The magnitude of this yaw is potentially far more than can be applied in free flight.

- And if I aim for the side off a barn with my hands in the normal positions and lock my arms back I'm probably not going to have a good afternoon either.

- So what does this have to do with normal control movement and effort under tow?

- Name somebody stupid enough to try to brace an arm against 125 pounds of towline tension while the glider yaws out of control.

- The control frame corners are only about five feet apart, the downtubes angle in above it, your shoulders width is about a foot and a half so your centerpoint can't get closer than nine inches to a downtube, nobody goes anywhere near to maxing out at a downtube anyway.

- I just put the end of a tape measure in my right hand with my right arm in normal flying position and, with my left hand, pulled out tape until I was looking at 20 inches (in front of my nose). Locking my right arm to the right as I would for a hard left roll I pulled tape out until I was looking at 34 inches. So 14 inches off center is as far as I can get without climbing around on the control frame.

- And even in a really nasty lockout I've never had the slightest urge to climb around on the control frame.

- My wingspan is 34 feet and 5 inches.

- For you sane people I can can move 0.36 meters off center and my wingspan is 10.49 meters.

- And that offset is supposed to have some appreciable effect countering the glider's sweep based yaw stability and my roll control authority?

- Especially when I'm not bracing my left arm against the tow tension?

[deltaman]

Hi Tad,

I never thought about what I was doing on aerotow (..) And - barring a couple of lockouts - the glider did what I wanted it too.

- I don't think about my hips when I'm trying to turn a glider - they're just back there somewhere.

We are agree that it's not enough to establish a relationship of cause and effect. We could imagine that with awareness of your steering you possibly change it to use more hips than shoulders..

- When I turn right I'm using BOTH hands to push the bar to the left.

I don't, and more if it is a small banked turn, more again in AT. I open my outside hand and push, and pull with the other, moving my feets/hips.

I think we could illustrate this Yaw torque by looking at the way to drive a cart during the takeoff:

http://www.flickr.com/photos/psucvollibre/6788727990/


and here in an AT situation:

http://www.flickr.com/photos/psucvollibre/6934840635/

http://www.flickr.com/photos/psucvollibre/6788727952/


and by viewing lockout videos, I feel that it's not completely wrong

http://www.youtube.com/watch?v=F_n5B3-MIC4

http://www.youtube.com/watch?v=GdE5DyqfUCg

[Tad Eareckson]

I'm pretty sure you've had tons more aerotow experience than I have and I haven't been behind a tug or even under a glider for well over three years so I'm quite willing to defer on this.

We could imagine that with awareness of your steering you possibly change it to use more hips than shoulders.

Possibly, but, on or off tow, I'm focused on what the glider's doing and how it's responding and it's also possible that our inputs and movements are the same.

I don't...

I was just talking about the roll/lateral input. I also torque the bar (fore and aft) as you describe (but with both hands closed (I think)).

On the ground I was always fortunate enough to have the carts track straight on takeoff so I never had to do anything. But I would predict that the shoulders position would be a lot more important - especially early in the roll (at lower airspeeds).

...and by viewing lockout videos...

Both of those lockouts were set up by people (one tug and two gliders) just not controlling the situations. They may be illustrating some of that effect but I'd say that they've got problems that dwarf the issue we're discussing.

I feel that it's not completely wrong...

I think it's completely right. If you offset the line of thrust there WILL BE a yaw effect - it's just a matter of degree.

And you could experiment a little on a tight, low sweep glider in smooth air to get a good feel for how the glider responds. And I'll happily go with your findings.

Reminds me of a discussion that was going on early in Ridgely's operation. Some people were having problems with dolly tracking on takeoff and it was speculated that crown of the runway and differential front tire pressure might be issues.

The pressure hypothesis sounded great - made perfect sense. Then one morning Chad inflated one tire, flattened the other, and took off straight as an arrow.

Obviously there had to be a yaw effect - one side of the dolly was moving forward with less resistance than the other. But apparently it just wasn't significant enough to worry much about.

But keep the tires properly inflated anyway 'cause that sure can't hurt the situation and if shoulder position is having a positive or no negative effect...

[deltaman]

Fig 3 - Dennis Pagen
About roll correction

He is right for surface towing at high angle but I just have wanted to defend the relevance of the yaw torque for AT steering when the glider is not at a steepen angle and too much banked.

[deltaman]

1- Yaw torque, min 4:15
4:14
http://www.youtube.com/watch?v=pC1yrdDV4sI


2- AT 2 points benefits
I had not seen the importance of a properly adjusted trim in limiting oscillations by limiting the amount of movement between the pull action and the new neutral (trim) each time the glider is banked. When this pilot pull to take speed to help to correct and relax when he just turn the other way he starts to oscillate because he release the speed in the turn.. I think that this pilot (not much competent) could take advantage to be trimed more forward..

[Tad Eareckson]

Well, have a
- not much competent pilot flying a
- not much competent primary release, a
- not much competent secondary bridle, and a
- not much competent secondary release.

It's a no brainer that he also has a
- not much competent weak link.

Therefore we know that he was trained and signed off by a
- not much competent instructor working at a
- not much competent school
and being towed at a
- not much competent aerotow operation by a
- not much competent tug driver.

The school is Kitty Hawk Kites at which I learned in 1980 and taught and towed (a little) in 1980 and 1982. The people under whom I directly worked were all
- not much competent douchebags
with the exception of Doug Rice:

http://www.youtube.com/watch?v=ls2QiDtSO7c
Rescue 911-Episode 415 "Hanging Hang Glider (Part 1)"
BeatleMoe - 2008/05/14
dead
http://www.youtube.com/watch?v=ZX_6UZ2UWEE
Rescue 911-Episode 415 "Hanging Hang Glider (Part 2)"
BeatleMoe - 2008/05/14
dead

who knew and could communicate his stuff pretty well ('cept - obviously - for the hook-in check issue) but was even more of a social retard than I am.

That tow site is Currituck County Airport and is the facility Kitty Hawk Kites uses for its string based operations. I first platform towed there in 1990 and first towed behind the Dragonfly 1991/08/02-04 during the promotion tour for the new tug. There was room for improvement but aerotowing was never safer. That was one of the coolest, funnest, happiest experiences of my flying career. Kinda glad I didn't know then what I know now.

Kitty Hawk Kites is authorized to operate in compliance with regulations established by the United States Hang and Paragliding Gliding Association so we know that we have a
- not much competent national organization.

The national organization is authorized to aerotow by the Federal Aviation Administration under the agreed upon regulations so we know we have a
- not much competent US public safety agency.

Kitty Hawk Kites is an Authorized Wills Wing Hang Glider Dealer and the primary responsibility of an Authorized Wills Wing Hang Glider Dealer is

A) Offering competent, safe instruction in the proper and safe use of hang gliding equipment.

so we know that we have a
- not much competent US based hang glider manufacturer.

Hopefully you will do much better with France than I did the United States (and I think there are some good indications that you will).

I had not seen the importance...

I think you may have something of a point but...

This guy is - or, hopefully, was - CLUELESS. I don't want to beat up too much on a noncombatant because of lack of skill or feel for a glider but he doesn't bother...
- centering his glider on the dolly.
- moving the left basetube bracket outboard

I can let him slide on some oscillation but he has all day on this tow to smooth things out and it never dawns on him to ease up on the input the tiniest bit. I almost blew lunch all over my keyboard on one of my viewings.

He makes hard corrections when there's nothing to correct.

- Sometimes he:
-- takes a nap when he REALLY needs to correct.
-- twists his body under the hang point when he needs to correct.
-- inputs for roll on the wrong side.

- When he needs to take way the fuck over three seconds ago he makes a pathetic little shift a couple of inches over - which is what finally locks the crap out of him with no help whatsoever from Mother Nature.

Trim point is the LEAST of this guy's problems. It was not safe to tow him even in smooth air.

And I don't see that he's holding anything significant in the way of bar pressure anyway.

Also...

- If you move the trim point a lot forward the glider still tows and maneuvers at the same airspeed - which is established by the tug's requirements. So the glider pilot is controlling the glider the same but with less effort.

- The glider pilot needs to be able to safely handle the glider at a reasonably wide range of airspeed because he will encounter a reasonably wide range range of airspeed.

- I don't like moving the trim point very far forward.

-- In my (somewhat limited) experience it's not a big deal to hold pressure with the trim point a good bit farther back than ideal - at least on tighter gliders.

-- In necessitates more crap in the airflow.

-- The farther forward the trim point the more and faster screwed you are if the bottom end of the bridle wraps.