Weak link - single or reserve?

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

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

"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

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

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

"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

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

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 |

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 |

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