It will take few days before to read everything. It's close to be an encyclopaedia in 12 Vol !
Thanks.
If you don't mind, maybe you will accept to answer some specific questions you surely did before.
Nothing would make me happier. Well, nothing I can imagine actually happening any time soon would make me happier.
I'm convinced with your "protow" release...
Just for the record... I DESPISE the term "pro tow". There's NOTHING professional about it. It's a dangerous compromise of an ideal towing system and there's no amount of skill or experience that can compensate for it. I don't have much of a problem with people towing that way on appropriate (higher performance) gliders and have towed that way myself and would do so again - but I refer to it as one point.
...with straight pin and small and thick bridle. I will do one.
Don't do the bridle yet.
With it, do you use weaklinks on the both side too in a "1 point" and "2 points" use ?
1. Your glider MUST BE weak link protected at all times no matter what happens.
2. And what's on the tug doesn't count because you:
- can't trust those bastards; and
- never know what the front end of the towline is going to tie itself to after it comes loose.
3. Actually, it's not so much the glider that needs to be protected. What you REALLY need the weak link for is to make sure that none of your releases are overloaded.
4. The front end weak link MUST be stronger than the back end weak link because it's always inconvenient and sometimes deadly to leave a hang glider with the towline.
5. If you put appropriate Tost sailplane weak links at both ends of the towline you're covered. You won't be able to overload your glider or any of your releases (if your bridle/release system is properly configured).
6. If you properly incorporate weak links into your bridle/release you:
- don't need a (heavy) Tost weak link on the back end of the towline
- ensure that you'll be using the appropriate weak link(s) for your glider
- can configure your bridle / release / weak link system to virtually eliminate the problem of a bridle wrapping at the tow ring
Bridles...
- The primary / two point bridle MUST BE long and therefore MUST BE long enough to be capable of wrapping at the tow ring.
- As you now know, the secondary / one point bridle can and should be made short and fat enough so that it's incapable of wrapping when one end is released.
Several years ago I figured out that you could make very effective weak links by stitching two elements together - the number of stitches determining the strength. I called them "Shear Links" because the two elements shear apart at failure.
I then figured out that such a Shear Link could also be a secondary / one point bridle and called it a "Bridle Link".
You can see how Bridle Links are constructed, installed, configured in:
http://www.flickr.com/photos/aerotowrelease/sets/72057594141352219/
http://www.flickr.com/photos/aerotowrelease/8318603266/
http://www.flickr.com/photos/aerotowrelease/8306152861/
And Zack is using one of them in the photo in his last post on this thread.
Bridle Links have excellent tolerances, don't wear out or degrade, will not wrap, and are cheap and easy to make. There's no good reason not to use them.
With it, do you use weaklinks on the both side too in a "1 point" and "2 points" use ?
If you don't have a weak link on the end of the towline and you have a bridle long enough to wrap you MUST have weak links above and below the tow ring.
Do you use a specific rope friction-proof as a bridle ? or is it useless ?
Friction isn't an issue with respect to bridle material except that you NEVER want to have fabric moving on fabric. You need a smooth metal tow ring (carabiner) for your primary bridle and a thimble...
http://www.flickr.com/photos/aerotowrelease/8312737353/
...for the secondary bridle (Bridle Link) to shift and feed through. (You can also see the thimble in Zack's photo if you look real hard.)
The primary bridle - and all the material between you and the tug - MUST be low stretch so the tow can be best controlled and you don't lose an eye when something blows - as did one of my acquaintances (Mike Robertson - 1986).
Bridles are predisposed to wrapping if they:
- are thin and flexible - the way Davis makes them;
- increase in mass, thickness, and/or stiffness towards the ends - the way Davis makes them; and/or
- have other irregularities in the half you're trying to feed through.
So you want the bridle to be low stretch, braided (not twisted), thick, stiff, and uniform or smoothly and gradually tapering.
You seem to be really confident with weak link you selected.
Yes. Just as confident as the sailplane manufacturers who designate specific weak link ratings for their birds.
...I'm still scared to have weaklinks on my shoulders as it could blow with V-bridle...
GOOD! You should be. That's one of the scariest things I can think of in hang glider towing.
...in tandem...
And solo.
It should also be pretty scary NOT having a weak link below the tow ring and thus having your secondary releases (and glider) potentially exposed to virtually unlimited towline tension - but Americans have always been known for their bravery (if not their intelligence).
...(even if they are well calculate as they could be weakened by friction if you don't change them every flight).
Two solutions...
- Put an appropriate - preferably Tost - weak link on your end of the towline.
- Configure your system so that your secondary weak links aren't subjected to friction, abrasion, abuse, degradation.
About the WORST thing you can do is put a string loop weak link directly on one of your harness's tow loops - so, naturally, hang gliding being hang gliding, that's exactly how damn near everybody does it.
If you go with Option 2 you pick up a REAL SIGNIFICANT safety advantage.
I've had two bridle wraps (sloppy bridle design - my fault) under normal tension during regular planned releases. The jolt when the bridle ties itself to the tow ring is freaking UNREAL - they had to use pliers to untie one of them back at the flight line.
My primary weak link (at the top) was about 272 pounds. The secondary weak link (at the bottom) was about 320. It didn't have a PRAYER - it just VAPORIZED. So configured like that you have an almost one hundred percent guaranteed secondary emergency auto release. The tandem pilots at Ridgely reached the same conclusion.
I'm comfortable enough with my tolerances to say give it a twenty percent margin. If you're not then you can go up to a hundred percent (double on the bottom what you're using on the top). But the narrower you make it the lower the probability that you're ever going to need to go to a secondary release.
In the event of a snag I would be towed by the keel. And in this configuration I don't understand how a weak link there would instantly blow, as a normal tow tension is 15kg...
No way. You'd need more than that to roll it on a paved runway at five miles an hour. Where did you get that number from?
...far lower than the strength of the wl, except maybe by the 'jerk' of re-tension ?
YOU CANNOT AFFORD TO RISK BEING TOWED BY THE KEEL FOR EVEN A SECOND. People have INSTANTLY had their keels broken, been tucked and had their gliders broken under negative loading, and tumbled.
You don't have any mass up there. When the top end of the bridle wraps there's a big pilot with a lot of mass and inertia and a weak link at the bottom end is almost certain to blow. That's very unlikely to happen if you wrap the bottom end. Here's what Rohan Holtkamp says on the issue:
http://ozreport.com/forum/viewtopic.php?t=11591
Where to put the weaklink - the HGFA rules
Rohan Holtkamp - 2008/04/21
Once again history has shown us that this thread-through system can hook up and the hang glider remains being towed by the keel only, with the bridle well out of reach of even a hook knife. I know of just one pilot to survive this type of hook-up, took him some twelve months to walk again though.
I towed my Wills Wing HPAT 158 - VG full on, flying weight 145 kg - behind a 914 Dragonfly and measured 57 kg tow tension - 70 with the turbocharger kicked in. And when you release without pulling in the glider decelerates very abruptly and the tug does just the opposite.
So, in a "2 points" you use 4 wl, one on the apex, one on the primary release and 2 on shoulders at each end of the bridle. Is that right ?
That was right before I developed the Shear Links. Now I have a Ribbon Bridle so there's a primary Shear Link built into the top, a secondary built into the bottom, and a Bridle Link between my shoulder releases.
But the Ribbon Bridle is insanely labor intensive and I won't ever do another one.
Zack's using what I would recommend and use for myself - a sliced hollow braid Dyneema line with a string loop weak link at the top end and a Bridle Link between the shoulder releases.
Which one you will advise to change every flight?
If you're using a one G or better weak link at the top and not chewing it up with a spinnaker shackle you may not EVER need to change it. Inspect it every now and then to make sure it isn't getting fuzzed. And you'll never need to replace a Bridle Link unless it blows.
May you give me the equation to calculate the 1G weaklink with a sixty degree angle, please ?
You have a North Wing T2. Its maximum certified flying weight is 235 kg. Split that in half - 117.5. Multiply by 1.15. You want a 135 kg weak link at the top end of the bridle.
(The 1.15 you get from the secant of half the apex angle.)
Could you explain me that...
As discussed above, twenty percent is just an arbitrary minimum based upon my weak link tolerances with which I feel comfortable.
How do you manage the different weight of passengers.
Ignore them. You're ONLY concerned with the MAXIMUM CERTIFIED FLYING WEIGHT of your glider. For example...
- North Wing says that you can safely fly the T2 fully loaded at 235 kg.
- The HGMA (and/or DHV) has certified that glider to something in the neighborhood of six Gs positive loading but three Gs for sure / no sweat.
- As totally freaking clueless as USHGA is on weak links they - and the FAA - have a regulation which allows that fully loaded glider to be aerotowed using a two G weak link.
- With the glider doing its normal one G you can add two Gs of tow tension and the glider will only feel three Gs.
- If you're also pulling a hard turn on tow you could add a half a G's worth of stress to the glider but...
- Three and a half Gs isn't going to break your glider.
- If you're pulling a hard turn away from the tug on aerotow you're not going to be on aerotow much longer no matter what you're using for a weak link.
- If you were towing with the glider under its maximum certified flying weight you COULD go to a weak link over a like number of kilograms over two Gs and maintain the same safety margin.
- But one and a half Gs is a good enough figure for a weak link that's very unlikely to blow when you're halfway under control or have a reasonable shot at getting it back and is about what the sailplane manufacturers and most people who know what they're doing shoot for.
Do I have to change the 4 wl every flights ?
No. See above.
Or which margin you would accept as you seem to accept some: you usually prefer 1.5G wl and tell me ok for 1G.
I don't know what you're using for a tug or what its limitations are. Bobby Bailey doesn't have a clue what a weak link is and thus the back end of the Dragonfly is poorly and dangerously designed. The tow mast is designed to snap off when the tow tension gets to around 200 kg. If you can go to 1.5 without too much risk of getting the towline go to 1.5. If you can't get the tug capacity to over a G then there's not much point.
Actually (shame on us) we only use a 144kg tested wl on the apex...
That's pretty light. Why were you using that rating?
Hang glider people DO get away with light weak links all the time with usually nothing more than a bunch of minor crashes and a lot of clogged launch lines. But every once in a while...
...(and one more stronger on the tug side (maybe 50% stronger as I don't exactly remember (I know it's bad))...
Please find out for me. And please find out WHY they're using that rating.
If it IS fifty percent stronger that will only get you up to 0.92 Gs max loaded. I'd fly that if I couldn't do any better but I wouldn't be real happy about it.
...no different one and no more elsewhere..
If you had good secondary releases you could probably get away with doing that by relying on the tug's weak link (assuming it's on the end of the towline and not just on one end of a bridle. You can probably still get away with it as it is but I wouldn't go up on it - especially given that the fixes are so easy.
What is your opinion on a release in the apex of a V-bridle rather than the 2 releases system ?
They're junk. It's not that it's a bad idea to have the release there but unless you put a lot of cable crap in the air there's no way to actuate it with your hands on the basetube.
The people who configure and advocate for having the release there are all idiots. Peter Birren comes to mind immediately:
http://groups.yahoo.com/group/skysailingtowing/message/6726
Weaklinks
Peter Birren - 2008/10/27 23:41:49 UTC
Imagine if you will, just coming off the cart and center punching a thermal which takes you instantly straight up while the tug is still on the ground. Know what happens? VERY high towline forces and an over-the-top lockout. You'll have both hands on the basetube pulling it well past your knees but the glider doesn't come down and still the weaklink doesn't break (.8 G). So you pull whatever release you have but the one hand still on the basetube isn't enough to hold the nose down and you pop up and over into an unplanned semi-loop. Been there, done that... at maybe 200 feet agl.
The ONLY good way to do a two point aero configuration is to have the release mechanism on the keel and the actuator in hand on the basetube.
I understood you are against carabiners.
Not in the least. They DO introduce a possibility for snagging something but I'd guess the hazard is about a billionth of a typical standup landing.
- If you're towing one point and have a faired basetube connect the carabiner to the bridle gate up to eliminate the possibility of it snagging.
- If you have a round basetube connect it with the gate up anyway.
- You can reduce stress/wear on your releases and virtually eliminate the possibility of a bridle wrap by climbing a bit just before release and then diving just prior to and during release. If you do that don't do it to the extent that you overfly the carabiner afterwards.
- Don't ever allow a slack line situation to develop.
About snagging event, which difference you see with a small carabiner and a standard ring ?
I actually don't see any difference 'cause all I've ever towed with was a standard aluminum nonlocking oval carabiner. But I think all this business about special carabiners, round rings, and homemade teardrop rings is a bunch of crap - none of these idiots are looking at the bridle design and I know for sure that's the big issue. And with a good weak link system and emergency secondary release the big issue is a total non issue anyway (except if your bridle separates from the tow ring before the tug lands and you lose it).
Does the 'top of a bottle' cut (the one which protect the wl on the apex below the ring) protect against a snag ?
I doubt it has any bearing one way or the other on the snag issue but I might be worried about it chewing up the bridle a little upon release. (Are you operating off of grass or pavement (or both)?) If I were using a weak link which stayed on the back end of the towline I'd go with Tost.
...and front wires against carabiner ?
This business about wires, bridles, releases, carabiners, and wires is bunch of totally imaginary bullshit invented by idiots who've never been around aerotowing and/or can't read, think, or look at pictures.
We have HUGE aerotow operations over here which pull off zillions of tows with really crappy tug and glider drivers, instructors, equipment, and procedures. The carabiner NEVER gets near the wires unless there's a major slack line event. And major slack line events are rare as hens' teeth and totally avoidable if both pilots are awake. And if you get into a major slack line event all bets are off anyway and the carabiner might not be terribly high on your list of things to worry about.
I have to organize a comp in my flatland and we need a quick system to catch bridle of each pilot..
Use a carabiner and only fly pilots with enough common sense to avoid flying into thunderstorms.
...(sorry for the win-win consideration).
No problem. We're moving fast in the right direction and I'm very happy. Just do me and yourself a big favor and don't ever talk to any of those assholes again. (And I can give you a really long list of other assholes never to talk to as well.)
I'd like to accept your help to work on setting an easy primary release as VG system but I need more time than actually..
Keep looking at my photos and forget the stuff inside the basetube - that's a lot of work and isn't really important. The rest is pretty easy.
...look at my drawing too, is that right ?
Yeah, all those numbers are fine. BUT...
- Don't even THINK about "a snag with the under bridle part". You can't afford to have that happen much more than a sidewire failure.
- There's no such thing as "a snag with the small V-bridle" - we can totally design that out of the equation.
Thanks again for participating and keep the questions coming. That's the primary raison d'etre for this forum.