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Wing Man
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PostPosted: Wed Aug 03, 2011 1:35 pm    Post subject: VG broke in Flight. Equipment failure Reply with quote #1   
H i Guys,

So I was up at indian Valley this past weekend and had a shocking little experience. 5 seconds after launch I felt ,what was like a brick, hit my glider. Quickly, I thought of my hang lines but put that out of my head because I ALWAYS do a proper hang check and do the visual check myself.

So, the first corrective decision was to get the hell away from the mountain. So, I go to pull on the VG... which just pulls and pulls with no resistance. Ah Ha! problem found! Now I am thinking of my preflight and I always check all the pulley connections and the ropes that connect the pulley box to the cross bar. This is what starts sticking out in my mind. That part is usually pulled tight and then rests on top of the screw that has a Phillis head for that hinge that connects at the two cross bars. This has always drawn a concern to me because I imagine it causing wear and then eventually breaking through the rope. So every time I preflight I move it to the out side of the screw head. In doing so I am able to check the knot and make sure that it is secure.

When I got to the LZ I checked and it was this rope connection to the cross bars that came undone.

Talking with Wills Wing I was told that they have never heard of this coming undone before and most likely, since the glider has 30hrs on it, the knot was not fully seated and the tails that finnish of the Bowline knot were not long enough and while the knot was seating it slipped past the tails allowing it to undo its self.

So, I have been doing a little google research and want to share the correct fix with everyone. in the hopes that it will not happen to someone else.

Here is a link to a site for climbing knots. Here, on the Bowline page, it talks about the slip of the knot and how rock climbers do an additional line wrap through to combat this problem. They call it the Yosemite tie-off. check it out. I plan to do this as well as a back up rope for this connection when I do my repair later today.

http://www.animatedknots.com/bowline/index.php?Categ=climbing&LogoImage=LogoGrog.jpg&Website=www.animatedknots.com

Now, all of this was a major concern to me when I saw my L/D was at 3.2. For those of you that have been to Indian Valley, you know that this is a very bad situation if you cant get up. The bail out LZ would have probably been out of rang at this L/D. However, and luckily, on my way in I caught a nice little thermal and climbed it to 9400 before I set off east into the valley and to a new could being born. From there, it was a 1:1 to the valley floor and I was safe. But the though of that VG chord breaking in an aggressive 1200' up at 3/4 VG setting on my way to cloud base before the cloud suck hit, entered my mind at the base of the cloud climb. I couldn't imagine what would have happened! I would hope the wing would not have folded from the shock load. Those high G loads while pulling wing tip maneuvers don't need any other complications.

So, go check that connection and add a back up rope! I don't want to know what my parachute looks like when its inflated!
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AIRTHUG
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PostPosted: Wed Aug 03, 2011 1:48 pm    Post subject: Reply with quote #2   
Also sounds like a good 'reality check' in leaving yourself options.... IE might not make LZ without VG... might not escape cloud suck without VG...

Sounds like pretty narrow safety tolerances, IMO...

Not saying I don't do similar things.... just saying this is a good reality check to step back and think about the things we take for granted, like VG thumbsup

Thanks for sharing!

And I concur, with only 30 hrs it's pretty unlikely that spectra chord was worn enough to break... spectra is known to be difficult when it comes to holding knots...

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pjwings
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PostPosted: Wed Aug 03, 2011 2:09 pm    Post subject: Reply with quote #3   
Hey, thanks for the link. animatedknots.com is a cool site. I'll check mine out today!
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CHassan
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PostPosted: Wed Aug 03, 2011 2:33 pm    Post subject: Reply with quote #4   
Didn't I read that bowlines are temporary knots and that you should not be used on that line? Thought it was a WW tb.
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Wing Man
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PostPosted: Wed Aug 03, 2011 2:45 pm    Post subject: Reply with quote #5   
I spoke with Steve at WW and he told me they use a bowline.

The site does say that these knots need to be kept under tension and vibration and slacking of the rope will cause them to untie. Anyone keep that part under tension all the time? Notice how they say the knot should have 12 times the circumference for the length of the loose end (the tail). NO ONE has that stock from the factory. Plus that would bind in our pulleys .

When I worked in the Fire Department and did rescue we would use the Bowline. It is considered a rescue knot, but tension is kept on the line and we tie half hitches for safety.

I will be using the Yosemite tie-off and half hitches AND a back up line from now on. thumbsup
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PredatorJoe
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PostPosted: Wed Aug 03, 2011 2:49 pm    Post subject: Reply with quote #6   
CHassan wrote:
Didn't I read that bowlines are temporary knots and that you should not be used on that line? Thought it was a WW tb.

I spose you _could_ call it a temporary knot since it's intended to be relatively easy to untie. but when tied and seated properly, it should never come un-done on its own. that knot has been used for many years on hang gliders and we also use it on the VG.

i believe ww is using un-jacketed spectra which is somewhat slippery. maybe this contributed to it coming untied? almost all of the spectra i've seen used on hg has a jacket which does provide significant more friction than bare spectra.
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NMERider
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PostPosted: Wed Aug 03, 2011 2:57 pm    Post subject: Reply with quote #7   
CHassan wrote:
Didn't I read that bowlines are temporary knots and that you should not be used on that line? Thought it was a WW tb.
The word 'bowline' is only mentioned twice on all of WW's website: http://www.google.com/search?q=site%3Awillswing.com+bowline and not in an adverse way. All the knots on my 450-hour old inner VG system on my T2C are ordinary bowlines. I have never seen a bowline slip or fail on Spectra rope. I'm glad Wingman wasn't hurt by this event.
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PredatorJoe
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PostPosted: Wed Aug 03, 2011 2:57 pm    Post subject: Reply with quote #8   
wingman,

based on this experience, maybe you wanna add to the 'heart rate while flying' thread Laughing
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NMERider
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PostPosted: Wed Aug 03, 2011 3:04 pm    Post subject: Reply with quote #9   
PredatorJoe wrote:
wingman,

based on this experience, maybe you wanna add to the 'heart rate while flying' thread Laughing
Don't forget the anal probe for pucker factor after chriswvv wipes it clean and replaces the batteries. mosh
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CHassan
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PostPosted: Wed Aug 03, 2011 3:20 pm    Post subject: Reply with quote #10   
My bad....... Tb2005620a says square knots were used and should be changed to a fisherman' knot.
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NMERider
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PostPosted: Wed Aug 03, 2011 3:50 pm    Post subject: Reply with quote #11   
CHassan wrote:
My bad....... Tb2005620a says square knots were used and should be changed to a fisherman' knot.
Thanks for the clarification. http://www.willswing.com/tech_bulletins/pdf/TB20050620a.pdf

Wingman and others do bring up the valid point about being aware of our glider's limits in case of VG failure.
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psuguru
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PostPosted: Wed Aug 03, 2011 4:30 pm    Post subject: Fisherman's knot Reply with quote #12   
I have an Airtime Pod-lite harness that uses a length of rope to each shoulder strap from a ring attached to the base of the hang strap inside the pod. I read of an incident where this rope failed due to the shock load of an emergency parachute deployment. The pilot came out of the harness and fell to his death.
I decided to replace mine (!) and chose 6mm Marlow Excel D12, a Dyneema plait. I reckon I'd have at least a 19G capability with a 50% loading factor.
Knotting this stuff is a nightmare. I started off using a bowline at each shoulder, but it would untie itself in front of my eyes. Eventually, I ran the rope through each shoulder loop and tied the ends together using a triple fisherman's knot. This seemed to be the number of turns required to stop the stuff untying. After a couple of hours use the knot compacted itself, so much so that, when I wanted to untie it, I had to use a hammer. The knot is big, about the size of a pistol grip.
The stuff in the WW technical note seems very similar, I'd be very wary about using a single-loop fisherman's knot.
As an aside, this method seems a bit crude. Was it beyond the ken of man to arrange a wire strop?

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PostPosted: Wed Aug 03, 2011 4:35 pm    Post subject: Reply with quote #13   
If you can bear to sit through a boring extended sledder at about the 8 minute mark my VG cord "snaps" as well. Sounded like a brick hit the glider like you described. Scared the piss outta me.

http://www.vimeo.com/15808347

Talking to Paul Voight, he said that he has seen this happen due to the pilot attempting to fold the wings up after forgeting to uncleat the VG cord from the base bar. This puts tremendous pressure on the VG cord and I believe he said he has seen that knot come undone or the line break up around the pulleys somewhere around the keel. When he saw my knot had come undone in the actual downtube he was surprised.

I told him I was guilty of forgeting to uncleat it remember trying to fold the wings and things being a bit tight. Embarassed

Have you ever accidently forgotten to uncleat your VG? This could be a possible reason.

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SKYSHARK
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PostPosted: Wed Aug 03, 2011 5:22 pm    Post subject: Reply with quote #14   
theres always the figure 8 knot that can be used. if you dont know how to tie a figure 8 on a bite be sure to look it up and follow carefully. Its the standard knot for securing the rope to your harness in rock climbing. Bowlines have been known to slip and for that reason are NEVER used while rock climbing.
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dave hopkins
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PostPosted: Wed Aug 03, 2011 5:40 pm    Post subject: Re: VG broke in Flight. Equipment failure Reply with quote #15   
Wing Man wrote:
H i Guys,

So I was up at indian Valley this past weekend and had a shocking little experience. 5 seconds after launch I felt ,what was like a brick, hit my glider. Quickly, I thought of my hang lines but put that out of my head because I ALWAYS do a proper hang check and do the visual check myself.

So, the first corrective decision was to get the hell away from the mountain. So, I go to pull on the VG... which just pulls and pulls with no resistance. Ah Ha! problem found! Now I am thinking of my preflight and I always check all the pulley connections and the ropes that connect the pulley box to the cross bar. This is what starts sticking out in my mind. That part is usually pulled tight and then rests on top of the screw that has a Phillis head for that hinge that connects at the two cross bars. This has always drawn a concern to me because I imagine it causing wear and then eventually breaking through the rope. So every time I preflight I move it to the out side of the screw head. In doing so I am able to check the knot and make sure that it is secure.

When I got to the LZ I checked and it was this rope connection to the cross bars that came undone.

Talking with Wills Wing I was told that they have never heard of this coming undone before and most likely, since the glider has 30hrs on it, the knot was not fully seated and the tails that finnish of the Bowline knot were not long enough and while the knot was seating it slipped past the tails allowing it to undo its self.

So, I have been doing a little google research and want to share the correct fix with everyone. in the hopes that it will not happen to someone else.

Here is a link to a site for climbing knots. Here, on the Bowline page, it talks about the slip of the knot and how rock climbers do an additional line wrap through to combat this problem. They call it the Yosemite tie-off. check it out. I plan to do this as well as a back up rope for this connection when I do my repair later today.

http://www.animatedknots.com/bowline/index.php?Categ=climbing&LogoImage=LogoGrog.jpg Website=www.animatedknots.com

Now, all of this was a major concern to me when I saw my L/D was at 3.2. For those of you that have been to Indian Valley, you know that this is a very bad situation if you cant get up. The bail out LZ would have probably been out of rang at this L/D. However, and luckily, on my way in I caught a nice little thermal and climbed it to 9400 before I set off east into the valley and to a new could being born. From there, it was a 1:1 to the valley floor and I was safe. But the though of that VG chord breaking in an aggressive 1200' up at 3/4 VG setting on my way to cloud base before the cloud suck hit, entered my mind at the base of the cloud climb. I couldn't imagine what would have happened! I would hope the wing would not have folded from the shock load. Those high G loads while pulling wing tip maneuvers don't need any other complications.

So, go check that connection and add a back up rope! I don't want to know what my parachute looks like when its inflated!


Several Combats have suffered a similar problem . Only its a screw that backs out. Pilots have had it pop at full VG and the glider survived. That's with carbon X-bars.

Dave
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dc82467
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PostPosted: Wed Aug 03, 2011 7:31 pm    Post subject: Reply with quote #16   
CHassan wrote:
My bad....... Tb2005620a says square knots were used and should be changed to a fisherman' knot.


Ditto

Double(or triple) fishermens Knot is the strongest and cleanest way to tie a loop in round cord, including slick spectra/kevlar type cords. As with all knots tie and dress corectly. Sloppy Knots are weaker. For flat webbing like for an emergency hang strap go with the simple watermans knot with 3-4" tails. I have experienced many a great fall at both ends of a climbing rope with both of these.
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Wing Man
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PostPosted: Wed Aug 03, 2011 10:45 pm    Post subject: Reply with quote #17   
excellent comments by all Thanks you.

What do you guys think of replacing it with Parachute chord? you know the thick stuff. I think it is called something like 580?
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PostPosted: Thu Aug 04, 2011 8:06 am    Post subject: Reply with quote #18   
I would use Spectra and stick with the bowline with an adequate tail. Also stick with WW recommendations.

Then I would stick with an improved pre-flight! I switched over to the 24:1 ratio, otherwise called "the T2 envy" pull. Cool

PS I have 150' of yellow Spectra. Send me an address and I'll cut you off some.
I also use a few drops of superglue to harden the ends. This keeps the ends real clean and also provides "a little more" insurance against a self untie.

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Davedebogusone
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PostPosted: Thu Aug 04, 2011 9:41 am    Post subject: Reply with quote #19   
I had one jam full on before, that wast fun either Shocked
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fakeDecoy
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PostPosted: Thu Aug 04, 2011 10:04 am    Post subject: Reply with quote #20   
Davedebogusone wrote:
I had one jam full on before, that wast fun either Shocked


Ha, I did that once on a T2C that was already flying scary bad out of spec. I pulled full VG with it wrapped around my hand and I accidentally tied a good knot in it.

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