Weak link - single or reserve?

[Tom Nau]

Hi All,

Our commercial operation (more like a club) is starting to do winch
launches. I just bought a Tost weak link for my glider from W&W. Are
most people using a "single" weak link or a "single and a reserve"
weak link? Thanks.

Tom Nau

[Bert Willing[_2_]]

Using a single weak link is a bad idea because the lifetime of a weak link
under load is limited (i.e. after x launches it has a good chance to fail
under much less than the nominal rupture load).

Bert

"Tom Nau" > wrote in message
...
> Hi All,
>
> Our commercial operation (more like a club) is starting to do winch
> launches. I just bought a Tost weak link for my glider from W&W. Are
> most people using a "single" weak link or a "single and a reserve"
> weak link? Thanks.
>
> Tom Nau

[Bill Daniels]

"Tom Nau" > wrote in message
...
> Hi All,
>
> Our commercial operation (more like a club) is starting to do winch
> launches. I just bought a Tost weak link for my glider from W&W. Are
> most people using a "single" weak link or a "single and a reserve"
> weak link? Thanks.
>
> Tom Nau

I think the reality is that it's about 50-50.

IMHO, I like the Tost reserve link system. Highly stressed metal does
fatigue so a single weak link will get weaker with each launch until it
eventually breaks under normal loads. The reserve link with the slotted
hole provides a second, reserve link to take the loads should the primary
fail at less than its rated strength. Using a reserve link avoids
unnecessary weak link failures.

There are "gotchas" though. Someone has to make very sure that two links of
the same type aren't accidently used. If that happens, you have effectively
doubled the weak link strength.

You also have to inspect the double link before each launch to see if the
primary failed on the previous launch. But then, you should be doing that
anyway to insure that you are using the right link color for the glider
being launched.

My suggestion is to choose a paint color signicicantly different that the
regular Tost weak link colors - say hot pink or day-glo. Then, dip one end
of the slotted links in the paint as soon as you get them so anyone can tell
at a glance that "two-tone" links are the slotted kind.

Bill Daniels

[Marc Ramsey[_2_]]

Tom Nau wrote:
> Our commercial operation (more like a club) is starting to do winch
> launches. I just bought a Tost weak link for my glider from W&W. Are
> most people using a "single" weak link or a "single and a reserve"
> weak link? Thanks.

Where is this operation?

Marc

[Tom Nau]

On Jan 17, 10:23*am, Marc Ramsey > wrote:
> Tom Nau wrote:
> > Our commercial operation (more like a club) is starting to do winch
> > launches. *I just bought a Tost weak link for my glider from W&W. *Are
> > most people using a "single" weak link or a "single and a reserve"
> > weak link? * Thanks.
>
> Where is this operation?
>
> Marc

We normally fly out of Boerne Stage Airfield, 15 nm NW of San
Antonio. But we are doing winch launch training at Hondo, TX about 45
miles east of Uvalde.

Tom

[Jesper Thomsen]

"Tom Nau" > wrote in message
...
> Hi All,
>
> Our commercial operation (more like a club) is starting to do winch
> launches. I just bought a Tost weak link for my glider from W&W. Are
> most people using a "single" weak link or a "single and a reserve"
> weak link? Thanks.
>
> Tom Nau
>

In Denmark where winch launching is about 90% of all starts, we also used
backup weak links for a while, but they've almost all disappeared again.

Experience shows that the second weak link is not strong enough to stand up
to the forces that appear when the primary weak link breaks (for whatever
reason). The Net result is that you break two weak links instead of just
one, and you don't get any added security or resilience for the price of the
second weak link.

Plus you add the unnecessary complexity of having to check that the two weak
links are different and that either didn't break during the last launch,
plus you're dragging two weak links through stones, dust, mud, grass etc.
instead of just one.

/J

[Andreas Maurer]

Hi Bert,

On Thu, 17 Jan 2008 16:39:01 +0100, "Bert Willing"
> wrote:

>Using a single weak link is a bad idea because the lifetime of a weak link
>under load is limited (i.e. after x launches it has a good chance to fail
>under much less than the nominal rupture load).


At least for my club I cannot confirm that - we have weak links (blue,
red and brown) that are several years old.

I'm pretty sure that the life expectancy depends on the type of ground
- weak links that impact tarmac after release are more prone to fail
than ones that hit comparably soft grass.

Usually the weak link on our aero tow rope fail pretty early due to
bending when they hit the (grass-) runway at 60 kts.


Bye
Andreas

[Martin Gregorie[_1_]]

Tom Nau wrote:
> Hi All,
>
> Our commercial operation (more like a club) is starting to do winch
> launches. I just bought a Tost weak link for my glider from W&W. Are
> most people using a "single" weak link or a "single and a reserve"
> weak link? Thanks.
>
The club I fly at does a lot of winching. We don't use a secondary link,
but we do use about 2m of steel cable (the 'strop') between the weak
link and the rings. This cable is inside brightly colored plastic garden
hosepipe, which is colour coded to match the weak link, so the club has
a set of strops at the launch point, each used with the one type of weak
link.

This system makes it easy for the pilot to check that the correct weak
link is used for his glider and the length and colour of the hosepipe
make the strop a bit easier to find after a break.

If you're all providing your own strops, which it sounds like you are,
it may be better to make up two strops, each with a single weak link,
than one with two weak links.

All the clubs I've flown at provide strops and weak links for their
members and visiting pilots.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

[Malcolm Austin]

At our club (Denbigh GC, UK) we changed the steel wire for a type of
polypropylene
rope. The shock absorbing properties of this have reduced the incidence of
weak link
breaks to almost zero.

The breaks that I have seen are usually at the bolt hole on the weak link,
on links
many months old.


"Martin Gregorie" > wrote in message
...
> Tom Nau wrote:
>> Hi All,
>>
>> Our commercial operation (more like a club) is starting to do winch
>> launches. I just bought a Tost weak link for my glider from W&W. Are
>> most people using a "single" weak link or a "single and a reserve"
>> weak link? Thanks.
>>
> The club I fly at does a lot of winching. We don't use a secondary link,
> but we do use about 2m of steel cable (the 'strop') between the weak link
> and the rings. This cable is inside brightly colored plastic garden
> hosepipe, which is colour coded to match the weak link, so the club has a
> set of strops at the launch point, each used with the one type of weak
> link.
>
> This system makes it easy for the pilot to check that the correct weak
> link is used for his glider and the length and colour of the hosepipe make
> the strop a bit easier to find after a break.
>
> If you're all providing your own strops, which it sounds like you are, it
> may be better to make up two strops, each with a single weak link, than
> one with two weak links.
>
> All the clubs I've flown at provide strops and weak links for their
> members and visiting pilots.
>
>
> --
> martin@ | Martin Gregorie
> gregorie. | Essex, UK
> org |

[Andreas Maurer]

On Fri, 18 Jan 2008 16:16:22 GMT, "Malcolm Austin"
> wrote:

>At our club (Denbigh GC, UK) we changed the steel wire for a type of
>polypropylene
>rope. The shock absorbing properties of this have reduced the incidence of
>weak link
>breaks to almost zero.

I know of a club that also used a polypropylene rope between aircraft
and weak link.
They stopped using that after this rope got entangled within the gear
of an ASK-21, leading to a severe ground loop immediately prior to
lift-off.

The stiffness of the steel wire prevents such an event.


Bye
Andreas

[Malcolm Austin]

Andreas,
I agree that would seem to be a problem for that location.
But I
have not seen it arise for the main winch rope. We do use a 15 metre length
of stiffer and thicker rope after the main winch rope which also might help
counteract that.

The cost and wear properties on our grass strip, plus the almost complete
lack of winch failures is a real plus. Even nicer is the handling side for
the winch man. It's 100% safer and we get no cut fingers. A repair
(splice) can be carried out in a few minutes with a pen knife and some tape
to cover the 3 ends of the rope. The section closest to the winch suffers
the
most wear, but this is easily and quickly replaced and minimal cost.Also
the guide rolls on the winch after about 8 months of use show zero wear.

I drive the winch every few weeks and after the 18 months of so of usage I
would hate to go back to steel. And as said before the amount of weak link
failures is virtually nil now.

Cheers,
Malcolm...


"Andreas Maurer" > wrote in message
...
> On Fri, 18 Jan 2008 16:16:22 GMT, "Malcolm Austin"
> > wrote:
>
>>At our club (Denbigh GC, UK) we changed the steel wire for a type of
>>polypropylene
>>rope. The shock absorbing properties of this have reduced the incidence
>>of
>>weak link
>>breaks to almost zero.
>
> I know of a club that also used a polypropylene rope between aircraft
> and weak link.
> They stopped using that after this rope got entangled within the gear
> of an ASK-21, leading to a severe ground loop immediately prior to
> lift-off.
>
> The stiffness of the steel wire prevents such an event.
>
>
> Bye
> Andreas

[Z Goudie]

At 15:48 18 January 2008, Andreas Maurer wrote:

>- weak links that impact tarmac after release are more
>prone to fail

Install weak links within an equivalent length of narrow
steel channel (with a hole at one end and a slot at
the other) as protection from wear/impact damage.

[Cats]

On Jan 18, 5:04*pm, Andreas Maurer > wrote:
> On Fri, 18 Jan 2008 16:16:22 GMT, "Malcolm Austin"
>
> > wrote:
> >At our club (Denbigh GC, UK) *we changed the steel wire for a type of
> >polypropylene
> >rope. *The shock absorbing properties of this have reduced the incidence of
> >weak link
> >breaks to almost zero.
>
> I know of a club that also used a polypropylene rope between aircraft
> and weak link.
> They stopped using that after this rope got entangled within the gear
> of an ASK-21, leading to a severe ground loop immediately prior to
> lift-off.
>
> The stiffness of the steel wire prevents such an event.

That's partly why the strops our weak links are attached are inside
some kind of plastic tube. I have a feeling the BGA recommends this
but I can never find stuff on their website, so don't know if I'm
imagining that.

[Andreas Maurer[_1_]]

On Fri, 18 Jan 2008 16:13:36 -0800 (PST), Cats >
wrote:

>That's partly why the strops our weak links are attached are inside
>some kind of plastic tube. I have a feeling the BGA recommends this
>but I can never find stuff on their website, so don't know if I'm
>imagining that.

If you need some written arguments: The German SBO explicitly demands
a stiffened rope between glider and weak link.

See here (if you speak German):
http://www.daec.de/se/downfiles/sbo.pdf


Bye
Andreas

[nimbusgb]

On 19 Jan, 00:13, Cats > wrote:

>
> That's partly why the strops our weak links are attached are inside
> some kind of plastic tube. I have a feeling the BGA recommends this
> but I can never find stuff on their website, so don't know if I'm
> imagining that.

http://www.gliding.co.uk/forms/clubmanagement/winchops.pdf
and
http://www.gliding.co.uk/bgainfo/documents/safewinchguidance.pdf

Finding stuff on the site is a pain, especially since the search
facility is useless!

Ian M

[Cats]

On Jan 19, 3:46*am, nimbusgb > wrote:
> On 19 Jan, 00:13, Cats > wrote:
>
>
>
> > That's partly why the strops our weak links are attached are inside
> > some kind of plastic tube. *I have a feeling the BGA recommends this
> > but I can never find stuff on their website, so don't know if I'm
> > imagining that.
>
> http://www.gliding.co.uk/forms/clubmanagement/winchops.pdf
> andhttp://www.gliding.co.uk/bgainfo/documents/safewinchguidance.pdf
>
> Finding stuff on the site is a pain, especially since the search
> facility is useless!

Thanks. I knew it was in there somewhere!

[Gavin Short]

At 00:18 19 January 2008, Cats wrote:

>> The stiffness of the steel wire prevents such an event.
>
>That's partly why the strops our weak links are attached
>are inside
>some kind of plastic tube. I have a feeling the BGA
>recommends this
>but I can never find stuff on their website, so don't
>know if I'm
>imagining that.
>
>

From the BGA website

http://www.gliding.co.uk/forms/lawsandrules.pdf
Page 52, RP (Recommended Practice) 7



Gavin
Std Cirrus, CNN now G-SCNN, #173

[Ian]

On 18 Jan, 23:23, Z Goudie >
wrote:
> At 15:48 18 January 2008, Andreas Maurer wrote:
>
> >- weak links that impact tarmac after release are more
> >prone to fail
>
> Install weak links within an equivalent length of narrow
> steel channel (with a hole at one end and a slot at
> the other) as protection from wear/impact damage.

I thought that was part of the standard Tost kit.

Ian

[Tom Nau]

On Jan 18, 8:40*am, "Jesper Thomsen" > wrote:
> "Tom Nau" > wrote in message
>
> ...
>
> > Hi All,
>
> > Our commercial operation (more like a club) is starting to do winch
> > launches. *I just bought a Tost weak link for my glider from W&W. *Are
> > most people using a "single" weak link or a "single and a reserve"
> > weak link? * Thanks.
>
> > Tom Nau
>
> In Denmark where winch launching is about 90% of all starts, we also used
> backup weak links for a while, but they've almost all disappeared again.
>
> Experience shows that the second weak link is not strong enough to stand up
> to the forces that appear when the primary weak link breaks (for whatever
> reason). The Net result is that you break two weak links instead of just
> one, and you don't get any added security or resilience for the price of the
> second weak link.
>
> Plus you add the unnecessary complexity of having to check that the two weak
> links are different and that either didn't break during the last launch,
> plus you're dragging two weak links through stones, dust, mud, grass etc.
> instead of just one.
>
> /J

Thank you, everyone, for your input.

Tom Nau
San Antonio, Texas

[Z Goudie]

At 10:36 19 January 2008, Ian wrote:
I thought that was part of the standard Tost kit.

Use a SERIOUS piece of steel channel!

[Bill Daniels]

"Z Goudie" > wrote in message
...
> At 10:36 19 January 2008, Ian wrote:
> I thought that was part of the standard Tost kit.
>
> Use a SERIOUS piece of steel channel!
>
I'm pretty familiar with steel channel shapes and I don't know of one I'd
use for this purpose. The Tost stainless steel 'envelope' does a great job
of protecting the 'dogbone' weaklinks. It's unlikely you will wear one out
in less than 5 - 10 years. Get the official one - they're worth the money.

On this subject, the Tost winch line hardware is very, very good and well
thought out. Use it for a while before trying to experiment.

Bill D