Hey Guys,
Once again, a couple more thoughts from Paul. The lockout Lauren mentioned was precipitated by my attempt to pull on more VG while on tow. I have done this before but this time the line wouldn't cleat properly and while I was fighting it, I got clobbered and rolled hard right in a split second. There was a very large noise and jerk as the relatively heavy weak link at the tug broke giving me the rope. I recovered quickly from the wing over and flew back to the field to drop the line and then re-launched after changing to a normal weak link. I have never had a lockout situation happen so quickly and dramatically and had no chance to release as I have always thought I could do. Had the tugs link not broken, things could have gotten very ugly very fast. I still don't like weak links breaking when they shouldn't, but the one I was using was way too strong.
Regarding flying in Zapata: I don't think either of us really realized what is involved. To fly in Zapata, you must accept that you are willing to fly over incredibly desolate terrain with LZ situations ranging from lots of tiny oil and natural gas drilling patches with pipes and tanks all around them to possibilities of landing on roadways where the ditches are extra wide. There are some small pastures but many are covered thickly with cactus. You probably aren't going to die out there but to say that retrieves are inconvenient doesn't begin to tell the story. Yesterday, I was faced with drifting out over a sea of mesquite and cactus at about 800' agl while climbing at about 50 fpm. From my low altitude I could see no LZ's ahead. Many would have gone on and risked landing in that crap. I chose to dive back into the wind and land at the last available LZ and the pick up from there was a huge hassle compared to what most of us know. There are places along the routes north where one must be willing to fly over very large distances of unlandable terrain with only your faith in your skills and fate keep you safe. Could I do it? Yeah....I suppose. Is the potential risk and almost guaranteed hassle worth it? Not to me. I have great respect for the guys that do this but it's just not my thing. Give me a nice competition over this stuff anytime.
Paul
More on Zapata and weak link
Moderator: CHGPA BOD
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Tad Eareckson
- Posts: 304
- Joined: Wed Feb 09, 2005 8:50 am
Sorry Janni, I gotta step out of character and go with the majority on this one. Records and numbers are really cool but wasn't sounding like much fun. No place for the faint of heart? Hell, isn't that pretty close to the locale of "No Country For Old Men"?
Anyway...
Paul,
I'm pretty sure I gave you a couple of 12 stitch White/Orange bridle links - possibly the next step down but definitely no higher.
I'm REALLY sorry if I neglected to state or failed to make clear at the time that you can pretty much count on getting a couple of hundred feet of Spectra if things get out of kilter enough. But even if the other end of the tow line were completely devoid of weak links things would only have gotten another 20 pounds and millisecond or two worth of ugly - assuming Russell had a double loop of Greenspot up front.
The double loop incorporated in the relatively long Dragonfly bridle blows at close to 400 pounds of tow line tension and the White/Orange fails very close to 420 - so what you felt was about what you woulda got - minus about a fat house cat.
There are, however, five 35 pound increments available below what you were using - 385, 350, 315, 280, and 245. That gets you below what a single loop of Greenspot on a one point bridle would do - 280 - if it were reliable - which, as we all know all too well, it ain't.
If you're interested in dumbing down from what you were and up from what you are using - pick a number and I'll be happy to send you a couple. Otherwise I'd recommend just using a double loop. That'll dial you down to about one and a third Gs.
Anyway...
Paul,
I'm pretty sure I gave you a couple of 12 stitch White/Orange bridle links - possibly the next step down but definitely no higher.
I'm REALLY sorry if I neglected to state or failed to make clear at the time that you can pretty much count on getting a couple of hundred feet of Spectra if things get out of kilter enough. But even if the other end of the tow line were completely devoid of weak links things would only have gotten another 20 pounds and millisecond or two worth of ugly - assuming Russell had a double loop of Greenspot up front.
The double loop incorporated in the relatively long Dragonfly bridle blows at close to 400 pounds of tow line tension and the White/Orange fails very close to 420 - so what you felt was about what you woulda got - minus about a fat house cat.
There are, however, five 35 pound increments available below what you were using - 385, 350, 315, 280, and 245. That gets you below what a single loop of Greenspot on a one point bridle would do - 280 - if it were reliable - which, as we all know all too well, it ain't.
If you're interested in dumbing down from what you were and up from what you are using - pick a number and I'll be happy to send you a couple. Otherwise I'd recommend just using a double loop. That'll dial you down to about one and a third Gs.
-
Tad Eareckson
- Posts: 304
- Joined: Wed Feb 09, 2005 8:50 am
From skysailingtowing, 2005/02/08 18:30...
>
Sorry, but I simply cannot stay out of this lively discussion on weaklinks. Concerning that topic, I am firmly convinced of the following points:
1. Every towing system, without exception, contains a weaklink. It may be a string or mechanical device deliberately inserted into the towline, the towline itself, the release mechanism, the flying wires of the glider, the pilot's harness (when body towing), or some other component of the pilot-glider-tug system. But something eventually is going to be the first thing to break. That thing is the weaklink.
2. Of all of these options, the ONLY PROVEN ACCEPTABLY SAFE weaklink is a string deliberately inserted into the towline which consistently breaks at a known and specified tension.
3. The sole purpose and function of this weaklink is to limit the towline tension to a manageable level, i.e. a level such that the pilot can still maintain control of the aircraft in the event that the weaklink breaks.
4. The appropriate strength of a weaklink depends upon pilot skill. A skillful pilot can maintain control when a stronger weaklink breaks whereas a less skillful pilot cannot. As a general rule, a beginning pilot should limit his towline tension to .5-g and an experienced pilot to 1-g. Only highly experienced pilots qualified to perform aerobatics while on tow should use a 2-g or stronger weaklink while being pulled forward (such as when aerotowing).
5. The appropriate strength of a weaklink depends upon the type of towing system used. Different strength weaklinks should be used for foot-launched ground towing, platform towing, aerotowing, boat towing, etc. As a general rule, forward pulling systems such as aerotowing, foot-launch ground towing, etc. should use 1-g weaklinks or less. Consistently downward pulling systems such as platform launch can go as high as 2-g's.
6. The appropriate strength of a weaklink does not depend upon weather conditions or the flight attitude of the glider (turbulence, wind gradient, lockouts, etc.). It is impossible to design a weaklink to release the pilot when he loses flight control because there is no correlation between towline tension and flight control. (A pilot may be in perfect control under high tension but out of control under low tension.) A weak link can only be designed to release the glider under the worst possible conditions before the towing forces exceed the limits of safe recovery when the weaklink breaks.
7. The appropriate strength of a weaklink should always be tested on the ground, not in the air. For example, if a weaklink is tested on the ground to consistently break at 1-g, then you can be certain it will do the same thing in flight. Therefore, if this ground-tested weaklink keeps breaking inconveniently while aerotowing, you can be certain that the problem is not the strength of the weaklink. The problem is with something else concerning the towing system, the flying technique, or the flight conditions. For example, if there is enough thermal activity that the tug and glider enter different air causing the towline to go slack, then there is also sufficient difference in the air to cause the towline to tighten and the tension to increase rapidly. Unless there is sufficient stretch in the towline to allow a skilled pilot time to compensate for this rapid increase in tension, it will quickly increase beyond the weaklink breaking point even while the pilot is in perfect control. If the problem is a lack of stretch of towline, the system needs changing. If the problem is flying technique, the pilot needs more training. If the problem is excessive air turbulence, flight operations need to be suspended. Simply switching to a stronger weaklink does not make this situation better, it simply makes things more dangerous when that weaklink does not break and when (not if) it does break.
Donnell Hewett
Department of Physics
Texas A&M University-Kingsville
<
The author of that post - for the benefit of anyone who doesn't know already - was the guy who figured out about a quarter century ago that you don't configure a hang gliding tow bridle to anchor on the three corners of the control frame triangle and in so doing got himself censored out of Hang Gliding magazine and bagged a doctorate in physics.
Nevertheless - I gotta take issue with a few items, minor and major.
-
Point 1
Excellent. No problem there. I would just amend it to state that I'm pretty comfortable stating that the next thing to go in the absence of weak links and possibly any fabric between tug and glider is gonna be the Dragonfly's tow mast (extending from the rudder post).
Point 2
Yeah, the ends of the tow line are really excellent places to install weak links and that's where USHGA requires them. We ignore that directive but, what the hell, incorporation in bridles can safely substitute IF done right.
The weak link doesn't have to be a string. The metal inserts of the Tost system and the stitching of the shear links do the job better.
Point 3
Yeah on the manageable level, nah on the caveat (more later). Here's where sailplanes, the FAA, and Dynamic Flight get it right and damn near everyone everyone else starts getting it wrong.
Point 4
Think about it.
A single loop of Greenspot on the end of my two point bridle gives me 0.76 Gs at best - and 0.39 Gs at worst. I can and have done some pretty cool aerobatics on tow within that limitation. I've also busted off of tow straight and level in glassy air.
Has anyone ever heard of an accident anywhere at any time in the history of center of mass towing precipitated by aerobatics at altitude?
And how come the FAA doesn't correlate sailplane pilot proficiency with weak link strength? And as far as I'm concerned a 0.5 G weak link shouldn't be anywhere near a tow line regardless of who's on the ends.
There's also a weak link in pilot competency and it ain't his ability to perform aerobatics - it's his ability to terminate the tow before the need to recover from a wingover is exacted. Up high that proficiency doesn't much matter - one can pick things up as one goes along. But down low one can't learn anything while trying to fly through topsoil.
Point 5
I think this is totally backwards.
Downward pulling systems are generally tension controlled, i.e. in the normal course of events it's impossible for the weak link to be subjected to much more than an ambient preset load. Those folk tend not to break them.
Aerotowing is speed controlled, there ain't hardly nuthin' to dampen tension fluctuations, and in good air those fluctuations can and tend to be huge while remaining well within the range of recoverability. We break them all the time.
Point 6
Rat own - 'cept for the implication of the last sentence. If one still has an intact glider and enough altitude one is always well within the limits of safe recovery.
Point 7
Again - If the weak link fails before the glider breaks it's done its job.
At the other end of the scale... Unnecessary weak link breaks tend to be pains in the ass at best and dangerous at worst.
-
Saturday I asked Sunny how many weak link breaks had occurred in the history of Highland Aerosports which were both desired and necessary - desired because the bubble had been lost and necessary because there was insufficient opportunity for the pilot to react. Got the answer I expected - ZERO. That adds up to a lot of needless and expensive pain in the ass over the course of nine and a half seasons.
And that's precisely the same number of occasions I've heard of anyone ever anywhere having a problem due to a weak link that was too strong.
As I've said before... A weak link should be thought of almost exactly the same as a parachute - you always wanna have one but you NEVER wanna have to use it. And if its use is required it's almost invariably as a consequence of pilot error.
Now lemme think... CHGA-MHGA sorta sites - within the periphery of Manquin, Daniels, North Fork Mountain, Cumberland, Breezewood, McConnellsburg, Ridgely - the number of deliberate parachute deployments we've had for nonaerobatic flights since the days of bamboo have been - what - ZERO?
Paul's of 2008/07/20 is the ONLY AT weak link break I've EVER heard of ANYWHERE that was both desired and necessary and even in that scenario there were pilot choices made that probably contributed to the severity of the lockout.
Whenever one takes a hand off the basetube - to actuate a release, punch a button on an instrument, change a VG setting, or reach for a downtube for examples - one compromises one's control of the aircraft. Paul already had Items 3 and 1 working against him and both of those were options.
Just to be clear on this - these are not criticisms. If you're weak link protected and out of striking distance from the ground there's not a lot that can happen to you as long as you've got some measure of tow line tension. When Steve, Hugh, or I are towing one point we have to reach for the release after we get to safe altitude and I frequently go to the VG lever on tow (and I've put myself on my ear before cranking from off to on but have never popped off as a result).
And he got severely hammered at the precise moment Murphy said he would.
So you've got an extremely high AT time pilot flying in world record thermal conditions with two or three things going wrong at the same time and you get a probable once in a lifetime weak link break. Yeah, that sounds about right.
Again - I disagree that that 420 pound / 1.4 G weak link was too strong. It was 180 pounds / 0.6 Gs below the USHGA/FAA limit. The reason he got the Spectra was 'cause the weak link on the tug end was only up to the task enough for Karen to take full advantage of her weak link range allowance. To make it up to the limit for the heaviest solo glider it needs to be able to handle an additional 300 pounds of tow line tension.
But I decided that if I were ever gonna break another weak link it wouldn't be because the one on the glider end wasn't up to snuff. I don't have any control over what goes on the front end but I'd rather take the one in several hundred chance of getting the rope over the course of a long towing career than put up with the bullshit I've experienced before and that's what I continue to recommend to others.
Going out on a limb time...
With a finger or set of incisors on the trigger the lockout that can't be terminated well before a 0.8 G weak link fails has yet to be invented. Yet the culture - as a whole - clings like a barnacle to the mistaken belief that, regardless of one's weight, a single loop of 130 pound Greenspot is the mandatory component to ensure that one doesn't put a dent in the runway and ignores the technology that actually does accomplish that goal.
And it's entirely possible to be low and in trouble in situations in which one REALLY would rather the weak link held.
If one is locking out but still climbing it might be advisable to stick around long enough to gain the altitude required to get the glider level again.
If one is stalling tow line tension is one's friend.
P.S.
On the afternoon of 2008/02/02 Carlos was at a grand behind a Ridgely tug when he got hammered and locked out to the left. He fell in that direction so far that he was unable to reach the bicycle brake lever mounted on his starboard downtube and somehow managed to get the rope despite the fact that his bridle was fitted with a single loop of Greenspot and the Dragonfly was packing a double. So... the death and taxes thing.
P.P.S.
With respect to the ubiquitous brake lever actuated releases the way they are almost always configured, doesn't that one incident pretty much make hash out of the following?
PART 104 - PILOT PROFICIENCY SYSTEM
11. USHPA HANG GLIDING AERO TOW RATINGS
02. USHPA Aero Vehicle Requirements
F. A release must be placed at the hang glider end of the tow line within easy reach of the pilot...
>
Sorry, but I simply cannot stay out of this lively discussion on weaklinks. Concerning that topic, I am firmly convinced of the following points:
1. Every towing system, without exception, contains a weaklink. It may be a string or mechanical device deliberately inserted into the towline, the towline itself, the release mechanism, the flying wires of the glider, the pilot's harness (when body towing), or some other component of the pilot-glider-tug system. But something eventually is going to be the first thing to break. That thing is the weaklink.
2. Of all of these options, the ONLY PROVEN ACCEPTABLY SAFE weaklink is a string deliberately inserted into the towline which consistently breaks at a known and specified tension.
3. The sole purpose and function of this weaklink is to limit the towline tension to a manageable level, i.e. a level such that the pilot can still maintain control of the aircraft in the event that the weaklink breaks.
4. The appropriate strength of a weaklink depends upon pilot skill. A skillful pilot can maintain control when a stronger weaklink breaks whereas a less skillful pilot cannot. As a general rule, a beginning pilot should limit his towline tension to .5-g and an experienced pilot to 1-g. Only highly experienced pilots qualified to perform aerobatics while on tow should use a 2-g or stronger weaklink while being pulled forward (such as when aerotowing).
5. The appropriate strength of a weaklink depends upon the type of towing system used. Different strength weaklinks should be used for foot-launched ground towing, platform towing, aerotowing, boat towing, etc. As a general rule, forward pulling systems such as aerotowing, foot-launch ground towing, etc. should use 1-g weaklinks or less. Consistently downward pulling systems such as platform launch can go as high as 2-g's.
6. The appropriate strength of a weaklink does not depend upon weather conditions or the flight attitude of the glider (turbulence, wind gradient, lockouts, etc.). It is impossible to design a weaklink to release the pilot when he loses flight control because there is no correlation between towline tension and flight control. (A pilot may be in perfect control under high tension but out of control under low tension.) A weak link can only be designed to release the glider under the worst possible conditions before the towing forces exceed the limits of safe recovery when the weaklink breaks.
7. The appropriate strength of a weaklink should always be tested on the ground, not in the air. For example, if a weaklink is tested on the ground to consistently break at 1-g, then you can be certain it will do the same thing in flight. Therefore, if this ground-tested weaklink keeps breaking inconveniently while aerotowing, you can be certain that the problem is not the strength of the weaklink. The problem is with something else concerning the towing system, the flying technique, or the flight conditions. For example, if there is enough thermal activity that the tug and glider enter different air causing the towline to go slack, then there is also sufficient difference in the air to cause the towline to tighten and the tension to increase rapidly. Unless there is sufficient stretch in the towline to allow a skilled pilot time to compensate for this rapid increase in tension, it will quickly increase beyond the weaklink breaking point even while the pilot is in perfect control. If the problem is a lack of stretch of towline, the system needs changing. If the problem is flying technique, the pilot needs more training. If the problem is excessive air turbulence, flight operations need to be suspended. Simply switching to a stronger weaklink does not make this situation better, it simply makes things more dangerous when that weaklink does not break and when (not if) it does break.
Donnell Hewett
Department of Physics
Texas A&M University-Kingsville
<
The author of that post - for the benefit of anyone who doesn't know already - was the guy who figured out about a quarter century ago that you don't configure a hang gliding tow bridle to anchor on the three corners of the control frame triangle and in so doing got himself censored out of Hang Gliding magazine and bagged a doctorate in physics.
Nevertheless - I gotta take issue with a few items, minor and major.
-
Point 1
Excellent. No problem there. I would just amend it to state that I'm pretty comfortable stating that the next thing to go in the absence of weak links and possibly any fabric between tug and glider is gonna be the Dragonfly's tow mast (extending from the rudder post).
Point 2
Yeah, the ends of the tow line are really excellent places to install weak links and that's where USHGA requires them. We ignore that directive but, what the hell, incorporation in bridles can safely substitute IF done right.
The weak link doesn't have to be a string. The metal inserts of the Tost system and the stitching of the shear links do the job better.
Point 3
Yeah on the manageable level, nah on the caveat (more later). Here's where sailplanes, the FAA, and Dynamic Flight get it right and damn near everyone everyone else starts getting it wrong.
Point 4
Think about it.
A single loop of Greenspot on the end of my two point bridle gives me 0.76 Gs at best - and 0.39 Gs at worst. I can and have done some pretty cool aerobatics on tow within that limitation. I've also busted off of tow straight and level in glassy air.
Has anyone ever heard of an accident anywhere at any time in the history of center of mass towing precipitated by aerobatics at altitude?
And how come the FAA doesn't correlate sailplane pilot proficiency with weak link strength? And as far as I'm concerned a 0.5 G weak link shouldn't be anywhere near a tow line regardless of who's on the ends.
There's also a weak link in pilot competency and it ain't his ability to perform aerobatics - it's his ability to terminate the tow before the need to recover from a wingover is exacted. Up high that proficiency doesn't much matter - one can pick things up as one goes along. But down low one can't learn anything while trying to fly through topsoil.
Point 5
I think this is totally backwards.
Downward pulling systems are generally tension controlled, i.e. in the normal course of events it's impossible for the weak link to be subjected to much more than an ambient preset load. Those folk tend not to break them.
Aerotowing is speed controlled, there ain't hardly nuthin' to dampen tension fluctuations, and in good air those fluctuations can and tend to be huge while remaining well within the range of recoverability. We break them all the time.
Point 6
Rat own - 'cept for the implication of the last sentence. If one still has an intact glider and enough altitude one is always well within the limits of safe recovery.
Point 7
Again - If the weak link fails before the glider breaks it's done its job.
At the other end of the scale... Unnecessary weak link breaks tend to be pains in the ass at best and dangerous at worst.
-
Saturday I asked Sunny how many weak link breaks had occurred in the history of Highland Aerosports which were both desired and necessary - desired because the bubble had been lost and necessary because there was insufficient opportunity for the pilot to react. Got the answer I expected - ZERO. That adds up to a lot of needless and expensive pain in the ass over the course of nine and a half seasons.
And that's precisely the same number of occasions I've heard of anyone ever anywhere having a problem due to a weak link that was too strong.
As I've said before... A weak link should be thought of almost exactly the same as a parachute - you always wanna have one but you NEVER wanna have to use it. And if its use is required it's almost invariably as a consequence of pilot error.
Now lemme think... CHGA-MHGA sorta sites - within the periphery of Manquin, Daniels, North Fork Mountain, Cumberland, Breezewood, McConnellsburg, Ridgely - the number of deliberate parachute deployments we've had for nonaerobatic flights since the days of bamboo have been - what - ZERO?
Paul's of 2008/07/20 is the ONLY AT weak link break I've EVER heard of ANYWHERE that was both desired and necessary and even in that scenario there were pilot choices made that probably contributed to the severity of the lockout.
Whenever one takes a hand off the basetube - to actuate a release, punch a button on an instrument, change a VG setting, or reach for a downtube for examples - one compromises one's control of the aircraft. Paul already had Items 3 and 1 working against him and both of those were options.
Just to be clear on this - these are not criticisms. If you're weak link protected and out of striking distance from the ground there's not a lot that can happen to you as long as you've got some measure of tow line tension. When Steve, Hugh, or I are towing one point we have to reach for the release after we get to safe altitude and I frequently go to the VG lever on tow (and I've put myself on my ear before cranking from off to on but have never popped off as a result).
And he got severely hammered at the precise moment Murphy said he would.
So you've got an extremely high AT time pilot flying in world record thermal conditions with two or three things going wrong at the same time and you get a probable once in a lifetime weak link break. Yeah, that sounds about right.
Again - I disagree that that 420 pound / 1.4 G weak link was too strong. It was 180 pounds / 0.6 Gs below the USHGA/FAA limit. The reason he got the Spectra was 'cause the weak link on the tug end was only up to the task enough for Karen to take full advantage of her weak link range allowance. To make it up to the limit for the heaviest solo glider it needs to be able to handle an additional 300 pounds of tow line tension.
But I decided that if I were ever gonna break another weak link it wouldn't be because the one on the glider end wasn't up to snuff. I don't have any control over what goes on the front end but I'd rather take the one in several hundred chance of getting the rope over the course of a long towing career than put up with the bullshit I've experienced before and that's what I continue to recommend to others.
Going out on a limb time...
With a finger or set of incisors on the trigger the lockout that can't be terminated well before a 0.8 G weak link fails has yet to be invented. Yet the culture - as a whole - clings like a barnacle to the mistaken belief that, regardless of one's weight, a single loop of 130 pound Greenspot is the mandatory component to ensure that one doesn't put a dent in the runway and ignores the technology that actually does accomplish that goal.
And it's entirely possible to be low and in trouble in situations in which one REALLY would rather the weak link held.
If one is locking out but still climbing it might be advisable to stick around long enough to gain the altitude required to get the glider level again.
If one is stalling tow line tension is one's friend.
P.S.
On the afternoon of 2008/02/02 Carlos was at a grand behind a Ridgely tug when he got hammered and locked out to the left. He fell in that direction so far that he was unable to reach the bicycle brake lever mounted on his starboard downtube and somehow managed to get the rope despite the fact that his bridle was fitted with a single loop of Greenspot and the Dragonfly was packing a double. So... the death and taxes thing.
P.P.S.
With respect to the ubiquitous brake lever actuated releases the way they are almost always configured, doesn't that one incident pretty much make hash out of the following?
PART 104 - PILOT PROFICIENCY SYSTEM
11. USHPA HANG GLIDING AERO TOW RATINGS
02. USHPA Aero Vehicle Requirements
F. A release must be placed at the hang glider end of the tow line within easy reach of the pilot...
-
Flying Lobster
- Posts: 1042
- Joined: Fri Feb 25, 2005 4:17 pm
Re: More on Zapata and weak link
Hewett's point 7 is about the best analysis of towing and the relationship to weak links that I have ever read anywhere.
marc
marc
Great Googly-moo!
Re: More on Zapata and weak link
With respect to the ubiquitous brake lever actuated releases the way they are almost always configured, doesn't that one incident pretty much make hash out of the following?
PART 104 - PILOT PROFICIENCY SYSTEM
11. USHPA HANG GLIDING AERO TOW RATINGS
02. USHPA Aero Vehicle Requirements
F. A release must be placed at the hang glider end of the tow line within easy reach of the pilot...
*****
I mount the brake lever on the base tube near one corner-- I can easily pull the handle with two fingers without letting go of the base tube. I have a round comfort bar base tube. However, I've also mounted the brake lever on the new flat WW speed bar base tubes and it works just the same.
Matthew
PART 104 - PILOT PROFICIENCY SYSTEM
11. USHPA HANG GLIDING AERO TOW RATINGS
02. USHPA Aero Vehicle Requirements
F. A release must be placed at the hang glider end of the tow line within easy reach of the pilot...
*****
I mount the brake lever on the base tube near one corner-- I can easily pull the handle with two fingers without letting go of the base tube. I have a round comfort bar base tube. However, I've also mounted the brake lever on the new flat WW speed bar base tubes and it works just the same.
Matthew
-
Tad Eareckson
- Posts: 304
- Joined: Wed Feb 09, 2005 8:50 am
Marc,
My heroes in this sport are the folk who with enough brains to step back from the crowd, look at what it's doing, and say waydaminute. Donnell Hewett is way up there on my list. I've got a pretty high regard for what Peter Birren has done as well.
But I get the feeling that neither of these individuals has spent much time around a high volume Dragonfly operation and consequently don't have a good feel for where we're actually having problems and where we ain't - despite what looks good on paper.
A little more on the issues addressed in Point 7 with respect to Dragonfly towing in general and Ridgely in particular...
-
1. Weak Link Strength
Yeah, weak link strength should always be tested on the ground. One big problem was that nobody ever did that for many years. It was just accepted that a single loop of 130 pound Greenspot tied with a Fisherman's Knot and installed on a bridle with a Double Lark's Head blew at (130*2=) 260 pounds and - obviously - a double loop would hold to 520. Then, finally somebody (me) actually tested them on the ground and said nope - 140 and 200.
So what that means is that nobody much heavier than Karen - and more recently my small but growing band of shear link rebels - is actually flying the 1 G or better weak link that Doctor Hewett uses in his example.
The other big problem is... The more you move up the scale from Karen - 200 - to me - 320 pounds - the less you can rely on that weak link to retain that 140 pound integrity. The peak loading that occurs when the dolly starts rolling can degrade the damned thing to 72 pounds by the time you get airborne. So - actually - no, you can't be certain it will do in flight what it did on the test rig. Just about all of us can be pretty much certain it won't.
2. Towing System
Our towing system is not the cause of any weak link breaks. If you hook up behind a Ridgely tug using a bridle assembly they've sold you every significant portion of the tow system between Dragonfly and glider is low stretch Spectra. You start throwing nylon into the mix you start slowing your climb, burning more gas, and introducing the possibility of something recoiling into your face.
3. Flying Technique
The flying technique of NOBODY is bad enough to justify a weak link break.
4. Flight Conditions
The more the flight conditions suck on tow the more you want to be able to stay on tow long enough to make it to a workable altitude. If the weak link blows before you get to the point of no return (a la Janni 2008/07/19) it wasn't strong enough. And if an adequate weak link blows before you can actuate your release you need to do some serious thinking about your response capability. It should not be a "when (not if)" situation. It is something that the average pilot should never experience.
And I totally disagree with the statement that - within the 0.8 to 2.0 G range - switching to a stronger weak link makes a tow more dangerous. All it means is that one is very likely to experience a more interesting wingover at failure.
In actual practice it's the under strength weak links that make things more dangerous. On this point Paul was in agreement a couple of months ago. And, as far as I know, Doctor Hewett has never had anything to say with respect to this end of the spectrum.
Towing up behind a Dragonfly is a lot safer than landing and a helluva lot safer than landing in the air which it has just powered through.
-
A little more dissection...
Point 3
"The sole purpose and function..." Notice that that paragraph makes no reference to preventing one from slamming in in the course of a low level lockout. And in nothing else of his I've seen is that popular fallacy reinforced.
Point 4
A 1 G weak link is probably OK. 1.4 Gs marks the center of the safety range. The only excuse for towing 2 Gs is 'cause you don't have anything lower 'cause by the time you're stressing a 1.4 G weak link you're so far gone that there's no freakin' way you're gonna get the tow back even if you are John Heiney.
If Doctor Hewett is right on all this stuff than the FAA and USHGA are wrong.
The best analysis of towing and the relationship to weak links that I have ever read anywhere is:
http://www.dynamicflight.com.au/Reading/WeakLinks.html
and what they say is in accordance with the FAA and USHGA and significantly at odds with the skysailingtowing post. If you or anyone can punch any holes in what Dynamic Flight's page I'd really like to know what they are.
A few more data points with respect to sub 1 G weak links...
On 2008/06/02 Lauren popped one high enough to get her away from launch but too low to turn back and land and spent a lot of valuable ECC Round 2 time carrying her glider back from the west end of the runway.
Later that competition I watched a Dragonfly blast off from the flight line with only an empty carabiner on the end of the tow line.
Bob Buchanan recently experienced ten consecutive weak link breaks attempting to get his Exxtacy to 2500 feet.
Bob Koshmaryk recently got dust devilled so bad on launch that his Discus was dragging a tip and his weak link didn't break. He was able to fly out of the situation successfully.
Matthew,
The bicycle brake lever is - along with curved pin barrel releases - amongst the worst ideas ever to be inflicted on the arena of aerotowing. It's just so much more draggy crap than is necessary to do the job.
However... If I were forced to use one - yes - I'd put it on the basetube where I could keep a finger or two on it at least long enough to get to safe altitude.
Although it's something you'd prefer not to have in front of or below your face or chest when you pancake in I think it looks a lot more dangerous than it is.
Marc's got a scary story about a bridle snagging on a basetube mounted instrument and having his positive pitch range dangerously limited for almost too much time. Although I would definitely have concerns about that sort of thing I'd say that they are totally overridden by the plus side of being positive of the ability to release in nothing more than decision and reaction time.
My heroes in this sport are the folk who with enough brains to step back from the crowd, look at what it's doing, and say waydaminute. Donnell Hewett is way up there on my list. I've got a pretty high regard for what Peter Birren has done as well.
But I get the feeling that neither of these individuals has spent much time around a high volume Dragonfly operation and consequently don't have a good feel for where we're actually having problems and where we ain't - despite what looks good on paper.
A little more on the issues addressed in Point 7 with respect to Dragonfly towing in general and Ridgely in particular...
-
1. Weak Link Strength
Yeah, weak link strength should always be tested on the ground. One big problem was that nobody ever did that for many years. It was just accepted that a single loop of 130 pound Greenspot tied with a Fisherman's Knot and installed on a bridle with a Double Lark's Head blew at (130*2=) 260 pounds and - obviously - a double loop would hold to 520. Then, finally somebody (me) actually tested them on the ground and said nope - 140 and 200.
So what that means is that nobody much heavier than Karen - and more recently my small but growing band of shear link rebels - is actually flying the 1 G or better weak link that Doctor Hewett uses in his example.
The other big problem is... The more you move up the scale from Karen - 200 - to me - 320 pounds - the less you can rely on that weak link to retain that 140 pound integrity. The peak loading that occurs when the dolly starts rolling can degrade the damned thing to 72 pounds by the time you get airborne. So - actually - no, you can't be certain it will do in flight what it did on the test rig. Just about all of us can be pretty much certain it won't.
2. Towing System
Our towing system is not the cause of any weak link breaks. If you hook up behind a Ridgely tug using a bridle assembly they've sold you every significant portion of the tow system between Dragonfly and glider is low stretch Spectra. You start throwing nylon into the mix you start slowing your climb, burning more gas, and introducing the possibility of something recoiling into your face.
3. Flying Technique
The flying technique of NOBODY is bad enough to justify a weak link break.
4. Flight Conditions
The more the flight conditions suck on tow the more you want to be able to stay on tow long enough to make it to a workable altitude. If the weak link blows before you get to the point of no return (a la Janni 2008/07/19) it wasn't strong enough. And if an adequate weak link blows before you can actuate your release you need to do some serious thinking about your response capability. It should not be a "when (not if)" situation. It is something that the average pilot should never experience.
And I totally disagree with the statement that - within the 0.8 to 2.0 G range - switching to a stronger weak link makes a tow more dangerous. All it means is that one is very likely to experience a more interesting wingover at failure.
In actual practice it's the under strength weak links that make things more dangerous. On this point Paul was in agreement a couple of months ago. And, as far as I know, Doctor Hewett has never had anything to say with respect to this end of the spectrum.
Towing up behind a Dragonfly is a lot safer than landing and a helluva lot safer than landing in the air which it has just powered through.
-
A little more dissection...
Point 3
"The sole purpose and function..." Notice that that paragraph makes no reference to preventing one from slamming in in the course of a low level lockout. And in nothing else of his I've seen is that popular fallacy reinforced.
Point 4
A 1 G weak link is probably OK. 1.4 Gs marks the center of the safety range. The only excuse for towing 2 Gs is 'cause you don't have anything lower 'cause by the time you're stressing a 1.4 G weak link you're so far gone that there's no freakin' way you're gonna get the tow back even if you are John Heiney.
If Doctor Hewett is right on all this stuff than the FAA and USHGA are wrong.
The best analysis of towing and the relationship to weak links that I have ever read anywhere is:
http://www.dynamicflight.com.au/Reading/WeakLinks.html
and what they say is in accordance with the FAA and USHGA and significantly at odds with the skysailingtowing post. If you or anyone can punch any holes in what Dynamic Flight's page I'd really like to know what they are.
A few more data points with respect to sub 1 G weak links...
On 2008/06/02 Lauren popped one high enough to get her away from launch but too low to turn back and land and spent a lot of valuable ECC Round 2 time carrying her glider back from the west end of the runway.
Later that competition I watched a Dragonfly blast off from the flight line with only an empty carabiner on the end of the tow line.
Bob Buchanan recently experienced ten consecutive weak link breaks attempting to get his Exxtacy to 2500 feet.
Bob Koshmaryk recently got dust devilled so bad on launch that his Discus was dragging a tip and his weak link didn't break. He was able to fly out of the situation successfully.
Matthew,
The bicycle brake lever is - along with curved pin barrel releases - amongst the worst ideas ever to be inflicted on the arena of aerotowing. It's just so much more draggy crap than is necessary to do the job.
However... If I were forced to use one - yes - I'd put it on the basetube where I could keep a finger or two on it at least long enough to get to safe altitude.
Although it's something you'd prefer not to have in front of or below your face or chest when you pancake in I think it looks a lot more dangerous than it is.
Marc's got a scary story about a bridle snagging on a basetube mounted instrument and having his positive pitch range dangerously limited for almost too much time. Although I would definitely have concerns about that sort of thing I'd say that they are totally overridden by the plus side of being positive of the ability to release in nothing more than decision and reaction time.