Kite Strings

In ATGuidelines

Yawing

A glider can be yawed at a surprisingly large angle away from the tug and still in good shape as long as it remains level. The glider pilot should stay level and ready to release but allow the tow line to yaw the glider back into alignment.

In Mousetraps ~29/#02/A/c
You list this as an Emergency situation

Yaw

The glider heading has diverged more than twenty degrees from the tow.

but wrote no procedure then..

Do you consider 20° Yaw as an incipient lockout ? or an issue cause :

Mousetraps ~03/#02/B/b/i

A two point bridle, by definition, positions the tow ring upwind of the nose wires but is capable of wrapping. Its top end can, if the glider has yawed an extreme degree off line, foul with a nose wire after separation from the release mechanism (although this may have never happened in actual practice).

____________

In Mousetraps ~29/#02/A/b/i

Limit

The glider rolls past 45 degrees.

45° seems to me a lot as an advice..

- I started writing Mousetraps as documentation for myself and anybody else (such as yourself) to be able to duplicate the equipment I had developed.

- I then expanded it to include an aerotowing procedures manual before Gregg Ludwig asked me for help - doing the same thing - on revising the USHGA procedures.

- Until well along in the previous decade I was still suffering a lot from Deference To Experts Syndrome.

- As per what I said at:

http://www.kitestrings.org/post1299.html#p1299

I used what I considered at the time to be the best sources available.

- Upon review of my source materials it appears that I probably screwed up with respect to:

The glider heading has diverged more than twenty degrees from the tow.

I think that should have read:

The glider has diverged more than twenty degrees from the track of the tow.

in which case it would be neither an issue of glider yaw nor a problem for it. It could only but probably wouldn't be a problem for the tug which would pull his tail sideways. And unless he were low and headed for the trees it would be a self correcting problem. And a Dragonfly has so much rudder authority I doubt he'd notice anything wrong anyway.

...but wrote no procedure...

- You're right. I missed that. The intent was - with the original/existing wording - that you release before your bridle got too close to the leading nose wire.

- However, if it's a matter of being off track it's the tug's potential problem and he should wave you off if he feels threatened or blow you off if he IS threatened.

- This:

The glider fails respond to a roll correction within a second.

from USHGA Aerotowing Guidelines documents is crap. In - I'd say - most situations in which the glider isn't responding releasing is the LAST thing you wanna do.

Do you consider 20 degrees yaw as an incipient lockout ?

Not at all.

- Towed gliders are roll unstable as hell but they're yaw (and pitch) stable.

- The only yaw problems on aerotow I know about occur when and for a short time after the glider lifts off the cart in a strong crosswind. If you just hold the glider level it starts auto correcting immediately and the tug auto corrects when it gets airborne.

...or an issue 'cause...

But, yeah you definitely don't wanna get so far out of whack that your bridle comes in contact with a nose wire. But to my knowledge the only times that's happened with a tight towline have been in surface towing when some moron has decided to crab in a strong crosswind to stay over the runway and in line with the truck.

45 degrees seems to me a lot...

That's also crap from USHGA Aerotowing Guidelines. In a lockout the glider may already be dead, in a tip stall letting go could be suicide or murder or make no difference.

On rethinking emergency go / no go decisions... Trying to specify parameters for making calls is a dangerous waste of time.

- There are too many variables - airspeed, turbulence, altitude, ground obstructions, gradient, glider responsiveness, bridle configuration, line tension, driver responses - to be able to predict a call.

- People aren't crashing or dying 'cause they don't know whether or stay on or get off. People crash and die 'cause they:
-- don't use ribbons and launch into crap which will slam them in no matter how good their equipment, skills, and reflexes are;
-- can't stay on tow 'cause their weak links, towlines, releases, or drivers drivers suck;
-- can't get off tow 'cause their releases suck;
-- have crap tension management 'cause their drivers suck.

Any freakin' ten year old kid standing along the runway who's never seen a glider before can tell when something bad will happen:
- no matter what if:
-- the glider comes off tow
-- the glider doesn't come off tow two seconds ago
-- the pilot takes a hand off the basetube
-- tension is increased, maintained, or decreased

If only we could get drivers and flight park operators up to that level.

If you're gonna look at procedures - emergency and otherwise - stay with the Guidelines. That's the more recent document and it's pretty solid.

P.S. Some day when I'm feeling less negligent I'll try to get everything updated and consistent.

Thanks

The glider has diverged more than twenty degrees from the track of the tow.

With track of tow you mean the tow line or the tug heading ?

I meant such that the towline is more than twenty degrees laterally from straight aft of the tug - which would normally be more than twenty degrees laterally from the heading of the tug. However...

When Ridgely started up in 1999 and I was towing a lot behind Chad's Dragonfly I was bothered for a long time that I was seeing a lot of the left side of the plane almost all of the time. I eventually remembered to talk to him about it and found out that the Dragonfly yawed a lot with power and he just didn't feel like holding rudder pressure the whole tow to trim it out.

It was rather weird because, with the Dragonfly's propellor rotating counterclockwise (as viewed from behind), it was yawing opposite to what was predicted by the aviation texts. I kicked things around with Brian Vant-Hull for a while but we never did figure out what was going on.

So anyway... The heading of the tug isn't necessarily the track of the tow. In that case when I was lined up perfectly with the track I was way off to the left of the heading. But it doesn't really matter because the glider's misalignment from the heading is helping the Dragonfly align its heading with the track - i.e., it's doing some of the job Chad isn't with his rudder.

The glider has diverged more than twenty degrees from the track of the tow.

and

the towline is more than twenty degrees laterally from straight aft of the tug

are not really the same:
the towline can diverge from the tow's track but what about the glider with the towline?
and the glider can diverge from the towline but what about the total angle with tow's track?

Let's put the towline twenty degrees to the right of straight aft of the tug and assume that he uses his rudder to counter whatever power related issues cause him to yaw (such that heading and track are the same), the towline stays tight, the planes stay level and level with each other, and we're not about to plow into any trees.

Those two conditions are the same - except that reason for the misalignment could also be that the tug had diverged from the track. But that's history at this point.

The glider heading can be aligned with the towline or to the right or left of it.

As long as everyone stays level these are all self correcting issues.

The glider (due to its sweep) is yaw stable and will align with the towline if it isn't already. And when it's aligned with the towline it doesn't have any more problems than it would if it were surface towing in a strong left crosswind, way to the right of the runway, and pointed at the truck.

The tug may be getting his tail pulled hard right and yawed to the left of heading but... So what? He's got a new heading (track) now and there either aren't any trees or he's above them.

I don't hear about yaw/heading issues with aerotowing and I've never heard a reliable report of a glider getting a bridle contact with a nose wire when the towline has been kept tight.

The only time I've ever had a yaw issue myself was when Ridgely was towing at about their crosswind limit. I was a bit nervous about the takeoff and Sunny told me to just keep the glider level (i.e., not to try to "fix" the "problem"). I came off the cart and went sideways to the right fast and far, held the glider level, tracked along the runway, and waited for the Dragonfly to lift off. When it did it yawed hard left, end of problem, and away we went.

ATGuideline

Actuation Sequence(..)
Should the glider pilot experience a primary release failure he should respond as follows.
(..)
Weak Link
If locking out at a safe altitude altitude take no action and allow the weak link to fail.

Why asking to take no action rather than push out in the turn ?

Because...
- Any time you release from the bottom (or top) you risk a bridle wrap.
- The higher the tension the greater the risk of a wrap.
- In a lockout the tension can get high fast.
- If your trim point (on the keel) is:
-- back near the hang point you've got a somewhat serious problem
-- a foot in front of the hang point there's a real good chance you'll need your parachute and some new spars
- Parachutes don't always work the way people hope they will.
- If you're high and blow the weak link there's zero possibility of anything bad happening.

euh...
not sure you answered my question or not sure I understood your answer...
In this situation (no more primary release and safe altitude) blowing a wl will be at the same tension what ever you do (wl will blow at its blowing load no more no less). My question: why don't force the wl to blow earlier by pushing out during the turn of the lock-out (increasing G) rather than do nothing and wait ..until the nose heading the ground at small angle of attack ?..

Oops. I didn't really read your question before answering it. Sorry.

My thinking (which could be wrong) was that you could still be climbing as the lockout progresses and the stall after the blow if you did nothing - or, better yet, continued to fight the lockout - would be less severe and require less recovery altitude. (The tension would be the same but the bank wouldn't necessarily be as steep.)

It would also give the tug more opportunity to dump you but then you'd probably have to land after descending to a safe altitude to put the towline where it wouldn't get lost.

But anyway...
- None of this is critical one way or another. Do whatever feels good.
- There's no excuse - and never has been - for going up with a two point release that has any possibility of failing.

If someone were bored enough it would be interesting to go up in smooth air with a camera running and a GPS receiver recording and compare the results of gradual and abrupt lockouts with a one and a half G weak link.