Kite Strings

Glad to have you with us, Mike.

Tad, my confusion stemmed from the fact that I didn't realize you were talking about a perfect world (where everyone uses sane releases). I think I got you now. Weak links are for releases, releases are the same for all pilots/gliders, so weak links should be also.

Interestingly, this takes us back to where this whole discussion began, when I said pretty much all of us were using ~600 lb weak links for surface towing. You were slightly critical of this approach:

Tad Eareckson wrote:It sounds like you're using one-size-fits-all jobs instead of optimizing them for the glider.

Tad Eareckson wrote:Which would imply that everyone you've observed towing with HHPA...all fly gliders with the same maximum certified operating weights.

I responded:

Zack C wrote:...if you buy my original definition of when a weak link should blow (when tow line tension is well above what should be experienced during a tow but below what would break the glider by a safe margin), you have a pretty wide acceptable breaking strength range.

Given your above post, I would now think you wouldn't have any problems with our surface tow weak links. I still believe the acceptable breaking range of weak links is quite large, though I would modify my statement above a bit to account for release overloading. So yeah, I don't see a problem with the one-size-fits-all approach, so long as that size is appropriate.

But that said, I still think 600 lbs is pushing it. I've had 600 lb weak links break and it makes me very uncomfortable being anywhere near that tension. It makes me feel like the glider could break at any moment. Even though we've done a bazillion tows without ever having a structural failure, I guess I'll always be paranoid. But I see no problem using a 400 lb weak link to address that fear.

Interesting point about the hook-in weight range not being an indication of load capacity. If I ever meet up with Steve Pearson again I'll try to find out if he has any idea just how much line tension gliders can take.

Another thing I've always wondered: we always talk about G loading as a scalar, but how does the direction of the tow force affect the glider's load capacity? Surely 600 lbs pulling straight down isn't going to affect the glider the same way as 600 lbs pulling forward (or backward in the case of the tug).

Zack

Tad,

We were discussing our tug weak link on the Releases thread, but I'm going to continue that discussing here since it's more relevant to this topic.

I noticed last weekend our tug had six strands of 130 lb Greenspot instead of four of 205 leech as Gregg reported. I wrote him about this and he said that's what we used to use and that it should be changed. But I was wondering if you knew how much force six strands of 130 can take. I imagine it's much less than 600 lbs...

Zack

Mike,

And here's how the discussion went in the American theocracy - nothing dramatized, actual names.

From:

Manned Kiting
The Basic Handbook of Tow Launched Hang Gliding
Daniel F. Poynter
1974

The tow line should be about 125 feet long and made of 2000+ lb. material such as 3/8" polypropylene.

Often a flyer who appears to be in a hopeless position at 6', recovers and continues to fly.

The boat should not fly him wide open because a burst of speed may be needed to pick him up at one point.

A knot was not removed from the tow rope and on the second flight, it failed. The kite looped and folded around the pilot.

"The greatest dangers are a rope break or a premature release." - Richard Johnson

Broken ropes have put many kite flyers in the hospital and a few in the ground.

Donnell Hewett - 1980/12

Skyting requires the use of an infallible weak link to place an absolute upper limit to the towline tension in the unlikely event that everything else fails.

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. I want to know without a doubt (1) when I am pushing too hard, and (2) what will break when I push too hard, and (3) that no other damage need result because I push too hard.

Furthermore, I will not use a mechanical weak link no matter how elaborate or expensive because there is always the possibility that it may fail to operate properly. In skyting we use a simple and inexpensive strand of nylon fishing line which breaks at the desired tension limit. There is no possible way for it to jam and fail to release when the maximum tension is exceeded. Sure, it may get weaker through aging or wear and break too soon, but it cannot get stronger and fail to break. If it does break too soon, so what? We simply replace it with a fresh one.

A properly designed weak link must be strong enough to permit a good rate of climb without breaking, and it must be weak enough to break before the glider gets out of control, stalls, or collapses. Since our glider flies level with a 50 pound pull, climbs at about 500 fpm with a 130 pound pull, and retains sufficient control to prevent stalling if a weak link breaks at 200 pounds pull, we selected that value. Of course, a pilot could deliberately produce a stalled break at 200 lbs, just as he can stall a glider in free flight. But if he is trying to limit his climb rate and the forces exceed the break limit, the glider simply drops its nose to the free flight attitude and continues flying. If the weak link breaks (or should the towline break) at less than the 200 pound value, the effect is even less dramatic and controlled flight is still present.

Most people are amazed at how small a string is needed for the weak link of a tow system. In fact, many people upon seeing it in operation for the first time make a comment something like "Don't you need something a little stronger than that? It's going to break!" But, of course, that's the whole point, it's supposed to break. And in order to break at about 200 lbs, it needs to be a single strand (loop) of No. 21 or 24 size nylon cord or a double strand (loop) of No. 12 or 15 size. For our glider we have found through trial and error that a loop of No. 18 braided nylon twine is ideal. A single strand of this twine is rated at 140 lb breaking strength, so a double strength loop should break at 280 pounds. In practice, we have found that because of the knots, it actually breaks at about 200 lbs when tied in a loop and attached to the towline.

Although we suspect that the same weak link would work well with other gliders, we have not had the opportunity to run tests on other gliders to verify this suspicion. Until such tests can be run, we strongly recommend that considerable caution be exercised in determining the correct weak link for any other glider. One should start with a line that definitely breaks too soon, gradually increasing the strength until a point is reached where the glider is able to climb at a good rate without breaking the weak link, but where no stall occurs when the weak link does break.

Obviously, more work needs to be done in this area, but even so, we have found our current system to be quite satisfactory and able to provide the necessary tension limiting and regulation needed for safe and enjoyable flight under tow.

WORK? Not just WORK but MORE WORK? Get real dude - we're pretty wiped already just from skimming those paragraphs. And if it seems to have worked for a few flights for a 150 pound Hang One physics professor on a 50 pound Sandpiper second generation Rogallo it's obviously good enough for people who can't handle grade school arithmetic. Any objections? Two hundred pounds it is then.

"Well, only tested with two flights. On the first flight it operated perfectly, and on the second something jammed up on a ring and the guy was killed."

How did it do on the third?

http://www.hanggliding.org/viewtopic.php?t=16384
Tow Release Malfunction

Mike Lake - 2010/03/29 20:05:42 UTC

The cool guy in the video had plenty of time but Murphy says that this might not always be the case. Make no mistake this was 50% of a fatality.

http://www.sahga.com/forum3/viewtopic.php?f=1&t=2125
Shane Smith has passed away

John Lowery - 2011/01/16 03:19 UTC
Tucson

This is just heartbreaking. Shane Smith passed away today in a hang gliding accident while scooter towing at Phoenix Regional Airport.

http://www.hanggliding.org/viewtopic.php?t=21033
barrels release without any tension except weight of rope..

Bart Weghorst - 2011/02/25 19:06:26 UTC
Cowboy Up Hang Gliding, Jackson Hole

Most of the time. But I've had it once where the pin had bent inside the barrel from excessive tow force. My weaklink was still intact. The tug pilot's weaklink broke so I had the rope. I had to use two hands to get the pin out of the barrel.
No stress because I was high.

And here we go again. Anybody wanna start a pool on the date?

"Score that release as 'average' then"

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.

http://www.hanggliding.org/viewtopic.php?t=16384
Tow Release Malfunction

bisleybob - 2010/03/26 19:08:27 UTC

now imagine a release that can never in no way jam up

Jim Rooney - 2010/03/26 20:54:43 UTC

Dude, quit bogarting that stuff ;)
How's it go? Never say never.

Bent pin releases are indeed very very reliable. But 100%? Nope. It's exceptionally rare, but they jam. All mechanical things do.

If they were perfection, everyone would be using them. They're not. As with all things, they are a tradeoff. Having that big ole chunk of metal on my sternum as I depart a launch dolly, just a couple feet off the ground, is not my idea of a good situation to be in.

What do they call them again? "Chest Crushers"?

So, good? Yes.
Perfect? No.

You say "average", we say "very very reliable". Tomatoes, tomahtoes.

And somehow that nice round, best guessed number stuck.

How odd. Precisely what that nice round pin that twenty years ago Bobby grabbed off the table a few feet away does when you put it inside a nice straight scrap of tubing. A round peg in a square hole - literally.

How could ANYONE in the early '80s do anything other than make a best guess?

By understanding what the German big glider boys had been doing since the early '20s?

How is any value likely to be relevant 30 years on?

The Brooks Bridle seems to have held up pretty well over the same period. Would've let Shane go back home happy 46 days ago.

Why 'never to be exceeded'.

It's a RULE. In a civilized society you hafta have RULES. Without rules we revert to the jungle. If it says "never to be exceeded" you don't exceed it. You exceed it you're one step down the slippery slope leading to chest crushers, necrophilia, cannibalism, and medical marijuana.

And you Tad might now be flying with your buddies giving them a never ending stream of abuse because they insist on using sh** rig releases.

I might have been flying a little while longer. But eventually I would've ended up the same way over very very reliable bent pin releases.

Zack,

Glad to have you with us, Mike.

Major honor and privilege actually. We owe Mike and a few of his crowd BIG TIME. And we need to lean on him to get down as much of that sort of history as possible.

Given your above post, I would now think you wouldn't have any problems with our surface tow weak links.

As you noted, I didn't have a significant problem with them then. And if they hadn't banned me I'd have already gone back and told them they were actually doing things better than I was thinking at the time.

But I really doubt that anybody really understood WHY what they were doing was pretty optimal and I notice that nobody engaged me to justify it. If you can't explain something all it is is another dime a dozen hang gliding OPINION. Yeah, that's the way the Houston guys do it. In Austin everybody goes three hundred. Tomatoes, tomahtoes.

I still believe the acceptable breaking range of weak links is quite large...

As do I and have so said many times.

But that said, I still think 600 lbs is pushing it. I've had 600 lb weak links break and it makes me very uncomfortable being anywhere near that tension.

Just 'cause you HAVE six hundred pounds doesn't mean you have to USE six hundred pounds. Just 'cause you HAVE a Porsche 911 Turbo doesn't mean you have to stomp it to the floor every time you go to the grocery store. The afterburners on your F-18 are there for if or when you NEED them.

If you don't wanna do six hundred pounds everybody has at least one piece of equipment he can use to stop doing six hundred pounds. And you also have a radio so it needn't be all or nothing.

But if you ever get into a Dennis Pagen or Arlan Birkett / Jeremiah Thompson situation I one hundred percent guarantee you your gonna be EXTREMELY uncomfortable NOT having all of those six hundred pounds at your disposal - even if the majority of them are still being held in reserve.

Even though we've done a bazillion tows without ever having a structural failure, I guess I'll always be paranoid. But I see no problem using a 400 lb weak link to address that fear.

If you're towing in fear of the difference between four and six hundred pound weak links you should be scared shitless of what happens between the time you release and land in thermal conditions. Do you do moderate aerobatics? If not start doing some wangs on the way down after the lift has switched off. Get a feel for what the glider can do no sweat. And remember that there's no regulation that requires that you have to just hang around doing nothing while the tension builds up to that point.

If I ever meet up with Steve Pearson again I'll try to find out if he has any idea just how much line tension gliders can take.

You don't need to. The glider doesn't know the difference between flavors of pounds delivered to its hang point. They can come as a consequence of pilot weight, pilot weight multiplied by a centrifugal factor, and/or tow tension. You have at least eighteen hundred pounds in your pocket and you can spend it however you want. And if you have a six hundred pound weak link, hook in at two hundred, and pick up an extra G in a hard turn away from tow you still have half of your spending money in reserve.

Another thing I've always wondered: we always talk about G loading as a scalar, but how does the direction of the tow force affect the glider's load capacity? Surely 600 lbs pulling straight down isn't going to affect the glider the same way as 600 lbs pulling forward...

The glider doesn't know anything about up, down, forward, or backwards. All it knows is the resultant of the vectors it's feeling at its hang point. If you're pulling straight down it's gonna think it has an eight hundred pound pilot. If you're pulling straight ahead it's gonna think it has a 632 pound pilot and the earth has shifted 71.6 degrees forward from where you're looking and will adjust it's trim (pitch up) correspondingly. If you're pulling straight aft... Never mind, you really don't wanna let yourself get into a situation to demonstrate what happens.

...(or backward in the case of the tug).

You can't worry about the tug. Even that ratty little loop of 130 that wouldn't even let you follow him through a normal easy turn on 2010/11/27 can kill him (or you) in other circumstances. That's why HE has a release he doesn't have to reach for. He's ALWAYS gonna be better off without us but we're the reason he even exists and we're paying him to get us going. If he's counting on a weak link of any rating to keep him safe he doesn't know what he's doing or talking about and shouldn't be up there.

I noticed last weekend our tug had six strands of 130 lb Greenspot instead of four of 205 leech as Gregg reported.

That's a stupid way to do things. I'm not crazy about double loops and TRIPLES? You're begging to trash your predictability. I could test it but I'm not sure what that would prove 'cause the strands all have to be loaded evenly. I'd go with my Shear Link. That's close to the top of the range of what I can do but still inside enough to make me comfortable. Tost doesn't hit close to six hundred but Ken Hammond could undoubtedly provide an insert that hits real close to whatever number you give him.

Keeping the line tension to within limits is a job of the tow equipment and not the weak-link (talking about ground towing), but I can see how this thinking might evolve with a fixed line tow setup with no automatic line tensioning system.

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.
Perhaps a weak-link is your only real hope in that situation and I guess a straw to grab at is better than nothing.

THE first and possibly THE most significant tow innovations (certainly ranking alongside body towing) were the various ground tow setups with automatic line tensioning devices (payout winch, slipping clutches etc.)
Anyone setting up a tow group should make this the first thing on their shopping list and much of the perceived use for that multi purpose tool called a weak-link will evaporate.

In the early '80s we were given a demo of a fixed line tow system complete with spring gauge, spaghetti bridles, rings, string and chunks of metal at longbow tensions positioned in front of the pilot's face.
The release was some kind of boat shackle that required about same continual tugging to actually release as it does for me to untangle my mobile phone charger.
After release the line had to unthread itself from various rings before the glider was actually free from a rather pathetic tow launch.

This was utter, utter crap, the whole setup and we (rather unkindly) laughed.
I am shocked to see so many elements of this system still in existence today.

This is not a 'high horse' statement, something I have recently been accused of. I'm a conservative Englishman, we generally don't do high horse.
Sh** is sh** and that was sh** of the highest order.

This post shows the difficulty in trying to discuss the various elements of a tow setup in isolation. Weak-links, releases, line tensions, limiting devices, lockouts, under/over, the role of the winch operator and Murphy's law all go to make up a system and are all, to some degree, intertwined.

Tad Eareckson wrote:But I really doubt that anybody really understood WHY what they were doing was pretty optimal and I notice that nobody engaged me to justify it.

I disagree. I think no one engaged you because they didn't read your posts (too many paragraphs) or didn't want to take the time to respond. Our first generation of towers experimented with weak links a lot (including actually measuring their breaking points). The vast majority of them settled on what we use today because it would protect the glider but not break prematurely.

Tad Eareckson wrote:

Zack C wrote:I still believe the acceptable breaking range of weak links is quite large...

As do I and have so said many times.

I didn't mean to suggest otherwise...just musing that after all the discussion we've had, my mind really hasn't changed much on the subject of weak links, at least for surface towing. I'm just applying that mindset to aerotowing now.

Tad Eareckson wrote:Do you do moderate aerobatics?

No. I'm sure I'd be more comfortable with my wing if I did. 45 degree banks are about as extreme as I get.

Tad Eareckson wrote:The glider doesn't know the difference between flavors of pounds delivered to its hang point.

I know, but I didn't think we knew what force would break a glider. Where does your 1800 lbs come from?

Tad Eareckson wrote:The glider doesn't know anything about up, down, forward, or backwards. All it knows is the resultant of the vectors it's feeling at its hang point.

Yeah, I had to go back to the first appendix of Towing Aloft to get this. If I understand correctly, if you pull aft the glider/tug will pitch down, which is I'd guess why tugs climb slower when tugging.

But why the hang point?

MikeLake wrote:Keeping the line tension to within limits is a job of the tow equipment and not the weak-link...

Payout winches are the only tow systems I'm aware of that automatically regulate tension. Every stationary winch I've seen requires the winch operator to manually control tension (using a throttle and a tension gauge). Are there other automatic tension regulation devices? Over here stationary winch towing is mainly used for low altitude training.

MikeLake wrote: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.

Static line towing is not all that common here but I've seen it done and don't have a problem with it. Generally the rope is attached to a hydraulic cylinder at the back of the vehicle with a line running to a pressure gauge in the vehicle (calibrated to show line tension) and the driver just has to keep the gauge in the sweet spot by varying his speed. I don't see why controlling tension this way would be any different from manually controlling tension on a stationary winch (maybe that's your point...). As with any type of surface towing, it's a tension controlled form of towing and the weak link should never get anywhere near the breaking point. I actually think this method may be better at avoiding weak link breaks than payout winches. Payout winches don't actually keep a constant tension - they keep a constant torque on the drum and thus increase line tension as they spool out line. I've only broken 600 lb weak links on a payout winch.

MikeLake wrote:This post shows the difficulty in trying to discuss the various elements of a tow setup in isolation.

Which is why we're having a really hard time keeping threads on this forum organized. =)

Zack

Zack,

The static winches we use have automatic tension control via a fluid clutch arrangement. This will (and does) also payout comfortably on a good wind day.
There is also an arrangement that restricts the throttle lever as tensions go up to give feedback.
The winch-man's job is to (within bounds) simply smooth out the tow and he never takes his eyes off of the glider.
His reaction to an emergency, or more to the point the onset of an emergency, is instant and can be scaled.

The latter cannot be achieved with a fixed line system especially if the glider is not constantly and intently under observation.

I'm not sure if this tension control takes into account the variable drum size that effectively gets bigger as more line is wound on.

Oops, managed to skip over Mike's of 2011/03/02 in the course of addressing the recent deluge of activity here.

In the early '80s we were given a demo of a fixed line tow system complete with spring gauge, spaghetti bridles, rings, string and chunks of metal at longbow tensions positioned in front of the pilot's face.

This is Donnell and this is a BOOK. Skyting was such an unmitigated disaster that one doesn't even know where to begin to address it.

Donnell's "thinking" was that there was nothing safer than a glider in free flight and the goal of towing should thus be to simulate free flight as closely as possible and return the glider to it whenever ANYTHING was going wrong - or, just to be on the safe side, right.

Whenever towing is going textbook in smooth air the glider IS just thinking and behaving as if it's reacting to a heavier planet angled forward of where it normally is.

So - OBVIOUSLY - what we should be doing to simulate free flight is to make sure the position and gravitational pull of the planet remains unchanged and that it's acting proportionally on the pilot and glider at their centers of mass.

And thus the whole goal of Skyting is to provide this simulation as ideally as possible - for under fifteen bucks - and to hell with what's actually going on with the glider and pilot. So as long as that spring gauge is holding steady on an agreed upon graduation, the driver can be absolutely certain that everything's just fine on the other end of the nylon towline.

And you use a Swiss Army Link just over normal tow tension to make sure that no one is allowed deviate very far from the theoretical ideal and the glider is thus unable to be towed too hard or fast, stall, or lock out before it has the gift of actual and pure free flight under actual and pure gravity restored to it - with no meddling decision making or input from the "pilot".

A freakin' ten-year-old Chinese kid flying a kite a couple of thousand years ago coulda done a better job with a bit of observation and common sense.

Donnell totally scrapped all kite flying and sailplane and conventional hang glider towing wisdom and technology of the day and, when presented with the vastly superior technology Mike and his crowd had independently developed around 1981-2, he just blew it off 'cause it didn't fit into his assumptions. Shane would NOT have died on a Brooks or Lake Bridle - and that crash was in no small part a legacy of Skyting.

On 1984/05/12 I kited up to a thousand feet out of Jockey's Ridge State Park in Nags Head from a stationary payout winch in a 30 mph west wind on that contraption Mike describes. Paul Gibney and I were both real concerned about the proximity of the Atlantic Ocean in that kinda wind. If that damned panic snap had wrapped on the corner of my control frame instead of just bashing the crap out of my helmet I'd very likely have been killed. Donnell had absolutely no business putting something like that into circulation.

The Skyting assembly is the patron saint of shit rigged releases and set the bar for all time. Ever since 1981 all you've had to do was as good or better than and you had a precedent for putting someone in the air with it.

Zack,

I disagree. I think no one engaged you because they didn't read your posts (too many paragraphs) or didn't want to take the time to respond.

HHPA ARTICLES OF ASSOCIATION

ARTICLE II - OBJECTIVES

2. To, encourage other people to become interested in this sport, and to inform and educate those who do become interested.

6. To promote safety in flying.

Kinda guts a couple of the stated objectives of the parent organization, don't it?

Our first generation of towers experimented with weak links a lot (including actually measuring their breaking points).

Great. Rather a novel approach in US hang gliding in which the standard practice is to assume and/or declare values. But beyond establishing values what other experimentation was going on and what was it supposed to be proving?

The vast majority of them settled on what we use today because it would protect the glider but not break prematurely.

- That's somewhat reasonable - but how and under what circumstances are we defining "prematurely"?

- Folk may hit on something that works well or even land on something that's a theoretical ideal - but you need to understand the theory to properly train people and run an airline.

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

- 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?

I didn't mean to suggest otherwise...

I know.

45 degree banks are about as extreme as I get.

Gawd - that's not even anywhere close to placard. Get into some boring ridge lift sometime and start getting to eighty. You can't get into much trouble as long as the glider's steeply rolled. If you stall the tip and just let yourself fall to the low side the glider fixes itself. Scare yourself a little and do pairs in reversing directions so you get equally comfortable left and right.

Where does your 1800 lbs come from?

It was a figure I sloppily pulled out of my head and put down without checking. I think I had been using it in some old battle about backup suspension 'cause it made the arithmetic easy. It's probably OK but just to be on the safe side make it fifteen hundred pounds - 250 hook-in at six Gs.

Yeah, I had to go back to the first appendix of Towing Aloft to get this.

Be very very careful with that book. There's some really good information in there and lotsa really really really bad stuff.

If I understand correctly, if you pull aft the glider/tug will pitch down...

Yeah, the plane's just trimming to the resultant of the vectors pulling on it.

This is where Donnell fucked up bigtime. This is why he predicted all kinds of death and destruction would result from the use of the Brooks and Lake Bridles. His neat little vector diagrams were predicting gliders pitching up and down radically when in fact they'd be doing the exact same thing as they were with his Skyting Bridle - minus the twenty peripheral ways to kill yourself.

And worse yet, he predicted and insisted - despite what was obviously going on - that the Skyting Bridle made the glider auto stabilizing in roll - UNLESS/UNTIL the bridle or pilot contacted a nose wire or downtube. So as long as that didn't happen a lockout wasn't a possibility. Then in the late summer of 1982 Tom Pendergraft planted the deadly "adverse yaw" seed and Donnell immediately pounced on it to explain why gliders were locking out just fine with nothing coming anywhere near anything on the glider.

So then the focus was all on insane schemes to eliminate "adverse yaw" instead of recognizing that if you pull a kite one way it's gonna roll the other and doing the engineering to allow you to release without interrupting or eliminating your control.

...which is I'd guess why tugs climb slower when tugging.

C'mon Zack. Don't get too analytical. 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.

But why the hang point?

Discounting control input (what you're doing with your hands), ALL the glider is feeling is what's coming through the hang point. OK, two point AT bridles often attach on the keel fore of the hang point. So you're effectively moving the hang point forward a bit when under tow to trim faster.

Static line towing is not all that common here but I've seen it done and don't have a problem with it.

Nobody has a problem with it - UNLESS/UNTIL the glider gets turned away a bit too much. Then people tend to have really huge problems with it really fast.

I don't see why controlling tension this way would be any different from manually controlling tension on a stationary winch...

See above.

As with any type of surface towing, it's a tension controlled form of towing...

No. It's speed controlled. You're using speed to (try to) regulate/adjust tension.

Payout winches don't actually keep a constant tension - they keep a constant torque on the drum and thus increase line tension as they spool out line.

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

Which is why we're having a really hard time keeping threads on this forum organized.

Yep.

Mike,

The static winches...

When we say static over here we mean "fixed line". We refer to a winch that stays in one place as "stationary".

...and he never takes his eyes off of the glider.

KEERIST. Don't you guys know ANYTHING? You NEVER take your eyes off the GAUGE!!! If the gauge is holding steady the glider couldn't POSSIBLY be having a problem! How many times do I have to repeat this?

If you can get the glider to pitch down by applying to the HANG POINT a tow force from any direction from straight ahead to straight down then I've written a lot of stuff that's gonna get me in a lot of trouble. I'm predicting that any pull with any forward component to it will result in a positive pitch reaction.

"I'm predicting that any pull with any forward component to it will result in a positive pitch reaction."

Absolutely and 100% agreed.

Except if the pilot is not moving at the same time (or the same rate) as the glider.
Imagine pulling from the heart bolt area on a gusty day and losing energy. The slick glider needs to fly. Follow this by a surge of energy and the lump of a pilot is left behind. The glider, doing its utmost to fly in a most positive pitching way, rotates around the pilot.
This is a bit like the old keel mounted power units that had the same effect in turbulence.

Now I must admit I'm not taking into account the pilot's reaction, if he has time to do anything. This single line setup was abandoned after the very first tuck.

This scenario IS compatible with what you say as aerodynamics mostly go out of the window when you stop flying.
So, you are well in the clear Tad and no need for even a bit of fudge.

If you can get the glider to pitch down by applying to the HANG POINT a tow force from any direction from straight ahead to straight down then I've written a lot of stuff that's gonna get me in a lot of trouble. I'm predicting that any pull with any forward component to it will result in a positive pitch reaction.

So please either make your anchor point an inch or two ahead of the hang point or throw out or fudge your data so I don't have to delete your posts, lock the topic, and ban you.

(I think I'm starting to get the hang of this Administrator thing. Davis, Jack... How am I doing?)

Tad Eareckson wrote:Discounting control input (what you're doing with your hands), ALL the glider is feeling is what's coming through the hang point....

Just as an interesting note.
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.