missing release

[SamKellner]

Hello Hawks,

It was a super tow to cloud base ~2500'. As the tow vehicle neared the end of the runway, I glanced down to visually locate the release pin line.

Maybe two seconds later, I felt a normal thump of release and the tow line fell away. WTF ? Mind controlled release ?

Here's what was left attached when I landed, as compared to an identical release.

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Rants

[SamKellner]

Tad,

This ain't one of them bent pin releases. And it aint one of them streight pin releases.

It's a bent pin that was streightened release..............

I thought this would topic would spark your interest.

No the release was not connected to the tow line. When the pin was pulled out of the 3rd loop, ~+-.062 sec. after the weak link performed as designed, there was nothing to keep the tow line attached to that part of the release. If it made it to the ground without becoming detached, I'd be surprised. It just became FOD.

Have you heard of "topping off the tow"?.

[SamKellner]

Tad,

About "topping off the tow".

A couple of days after I had flown with the guys at Hearne, yet unaware of my release malfunction, Zack asked a question on another forum, about exagerrated tow forces he experienced, at the end of the tow.

We might need to get Zack in on this conversation.

[SamKellner]

I don't have a whole lot of truck tows and the highest I ever got was only a bit over fifteen hundred feet.

Yeah, I was surprised at the tension Zack guessed he was feeling near the top of tows. Granted, he's probably often lifting a lot more line than I did but I woulda thunk the drivers would be pretty good at backing off on the brake pressure to compensate a bit.

But, what the hell, it's not a safety issue and probably doesn't make any appreciable difference in the efficiency of the tow.

You didn't have a "release malfunction" - in the sense that it did exactly what it was designed to and you were instantly / cleanly / completely separated from tow... But:

1. I've never before heard of a configuration that automatically costs you one release mechanism per weak link failure - in hang gliding, paragliding, or sailplaning.

2. I'd have thunk that the reason you had decided to release at that point was 'cause that you were no longer climbing and that the reason you were no longer climbing was 'cause the tension had dropped to the point of uselessness.

3. Despite all the total rot taught by the morons running the flight parks and published in works of fantasy like Skyting and Towing Aloft, a weak link has one function and one function only - to blow before the glider does in a really rare and extremely ugly situation in which the people have almost certainly totally lost control of the tow a long time ago. Weak links which fail in routine circumstances are expensive and dangerous.

I'll ping Zack and let him know about this discussion.

Thanks.

Tad, Zack must be out flying. He drives also and can clue us in on the procedure at both ends.

1500' is a better tow than we get on our local airfield. Our winch is a POS. We are trying to buy a proven modle. With a good winch we might get 1000' max. ~3000ft runway.

There's some about tow forces I do not understand, at least unable to discuss in correct terminology.

The force that took my release did not feel excessive. It did not even feel unsafe. It did seem to have a threshold effect. Something I'd like to know more about as a PL pilot. It might be a safety issue without a weak link.
But, it's called "topping off the tow", for a reason.

Right, the pictures do not show the 3-loops. I thought sure the loop of smallest diameter line would have been the "weak link". That should make a nice quote

However, when I purchased these 5 releases ~11yr ago, the maker did say the weak link was indeed the part that failed on my tow, the only one that protected me with a weak link break. ie #1. That's my last new one and I'm gonna need a spare.

Not sure of their top-off procedures but Zack will probably say the pressure is increased at the end of the tow. Vehicle slows. I'm thinking the force comes from somewhere and not really line weight or line drag.

ie#2. I was climbing. No vario, but still climbing good. The tension never dropped. It felt like it accelerated to weak link failure. It was real breezy that day. That might be a factor? Glad in my case no loss of control. Actually I almost fell asleep on the ride up.

ie#3. Yes, to blow before the glider does! I'm not sure if it is possible to over fly the tow vehicle while still climbing with tight line. That kinda sounds like perpetual motion

Where's Zack? Are we talking about the same thing. The more experienced PL pros are probably laughing at my ignorance. When I become a pro, I hope I never get too important to talk to students with questions.

[Bob Kuczewski]

Hi Tad and Sam,

It looks like you guys are swapping information and no one is getting thrashed or insulted. ... You guys are really disappointing Davis and SG.

P.S. I'm not seeing a way to get the photo up - may be a problem with my antique browser. But Bob can probably stick it in later if I send it to him.

I'll be happy to insert the picture if you send it to me. But rather than give you a fish, how about if I give you a fishing lesson?

Here's the basic procedure for inserting a picture from your own computer ...

At the bottom of your posting page, there's a tabbed box that looks like this:

upload001.png (8.77 KiB) Viewed 8859 times

If you click on the "Upload attachment" tab, it will look like this:

upload002.png (8.4 KiB) Viewed 8859 times

If you click on the "Browse..." button, it should bring up a navigation box that will let you find pictures on your own computer. Find the file you want to upload, and then press the "Open" button. That will load the file name into the "Filename:" text area. Then you can press "Add the file" and it will be added as an attachment at the end of your post.

If you want to insert it into your post, then use one of the "Place inline" buttons listed in the "POSTED ATTACHMENTS" area:

upload003.png (11.56 KiB) Viewed 8859 times

Just set your cursor where you want the image to appear and click on the "Place inline" button for the correct picture. Be careful, because I think it adds pictures to the list of attachments from the top (like a push-down stack).

There are some dimension limitations, so don't try to post really high resolution photos. There may also be a limit of something like 10 photos per post.

Give it a try and let me know if you have any trouble.

Bob K.

[SamKellner]

Bob,

You are the one that deserves a gold star. The Hawks forum is the best
Chattoryman paid you a nice compliment on another forum today, or at least I read it today, about helping him get back into the sport.

I'm glad to be a small part. For me, it's about continuing learning something new, to improve my skills and understanding.

Thanks,
Sam

[ZackC]

A couple of days after I had flown with the guys at Hearne, yet unaware of my release malfunction, Zack asked a question on another forum, about exagerrated tow forces he experienced, at the end of the tow.

We might need to get Zack in on this conversation.

Sorry, I wasn't paying attention to the regional Hawks forums.

Sam, this is the release incident you had at Hearne, correct? So it was caused by the weak link breaking? What was the material? How many strands/loops? Was the vehicle still moving when it broke?

The exaggerated tow forces I asked about (on the HHPA group) were experienced after the vehicle stopped. Normally when the vehicle stops tension drops to near zero, but when it's windy, the opposite happens...tension spikes significantly. I didn't understand why the payout winch wouldn't spool to prevent this, but Gregg's explanation was that the wind was not quite strong enough for the pull to overcome the static friction of the brake, resulting in higher tension than the brake pressure would indicate. I usually get off the line hella quick at this point 'cuz I dislike high tension, but I would imagine you could gain a good bit of altitude staying on the line.

If the drum stops turning the tension is gonna drop as the vehicle slows.

Not always, as described above.

Not sure of their top-off procedures but Zack will probably say the pressure is increased at the end of the tow. Vehicle slows.

No, we don't increase pressure at the end of the tow. Paying out line quickly at the beginning of the tow and then slowing the vehicle is a technique Towing Aloft describes as 'slingshoting'...some of our long-time guys are familiar with this technique and have used it but as a winch operator I always just maintain constant (air)speed and pressure throughout the tow. When being towed, I like the winch operator to reduce pressure later in the tow to try to keep tension somewhat constant.

I actually don't know what 'topping off the tow' means.

...I woulda thunk the drivers would be pretty good at backing off on the brake pressure to compensate a bit.

Most guys don't want pressure to be backed off. I'm the only one I know that radios for tension decreases during the tow...Jack's gotten so used to towing me I don't have to ask anymore.

But, what the hell, it's not a safety issue...

No, but it can cause weak links to break. (Even so, they are extremely rare in our group...I can't remember the last time we had one blow.)

Stu Caruk (http://www.towmeup.com) is probably a real good place to start for a winch. Ain't cheap but my guess is that the more you pay at the beginning the less you're gonna pay down a rather short road.

There was a discussion about winches on the org recently...this one also seemed popular.

The drag of the line - which increases as a consequence of its diameter - will cause the line to bow back and pull off the winch faster and, as is the case with the weight and sag, also pull less forward and more down and also cause the glider to trim more nose down.

I never thought about that. Line drag does not affect tension, correct? This is something we've (HHPA) debated in the past.

Thanks, but the problem is my 2003 Mozilla 1.3.1 browser.

I'm sure you have a good reason for not upgrading...

Zack

[SamKellner]

Tad,

Is that the release you are promoting?

[Bob Kuczewski]

Thanks for that information Tad. Since your current browser has trouble uploading images, I've taken the liberty of posting them here. Let me know if you'd like them integrated into your own post and I can do that as well. Here are the two images:

http://www.flickr.com/photos/aerotowrelease/3313497455/

3313497455_9dcefe478a_z.jpg (20.76 KiB) Viewed 8741 times

http://www.flickr.com/photos/aerotowrelease/2337501636/

2337501636_d4595c4883_z.jpg (22.55 KiB) Viewed 8741 times

[ZackC]

Comparing the line diameter to the pin width my best guess is 205 leechline (single loop).

If that's the case, I'm not surprised it broke. (Tad's measured these to break around 260 lbs.)

What are people using for launch tensions?

I don't know and I don't know if anyone does. The optimal pressure settings were found through experimentation. I'd love to know what the actual tensions are (not just at launch but through the whole tow), though I don't think it's all that important in the end.

Shouldn't be debating.

What's funny is the debate was about whether or not drag caused an increase in tension (at the glider). No one suggested it could cause a decrease.

The tension reaching the glider (and its weak link) is 150 pounds minus what's eaten up by those 250 parachutes.

I'm having a hard time wrapping my brain around this. I don't have a very intuitive grasp of physics (probably why I suck at engineering). I appreciate the explanation, though, and will continue to think about it. In the end I think it's a bit academic since other factors appear to affect tension a lot more.

And there should be a tow ring or thimble in the loop at the end of the tow line to keep form abrading the weak link.

We do use a quick link on the end of the line.

I don't pay to much attention to winch issues...

Be that as it may, there is a wealth of excellent information on this thread. Thanks.

Zack