Despite the alleged 'bildan tension spikes' from the automatic gearboxes
fittes to many current winches, in my experience weak link breaks during
the ground run are extremely rare. If you do get a very overpowered
launch, the weak link will normally break towards the end of the rotation
or early in the full climb. The best video example I can find on youtube
is:

http://www.youtube.com/watch?v=jvK1ONl1CqE

This launch was on a diesel powered winch (also favoured by bildan) where
you typically get a rather slow initial ground run acceleration, followed
by a sudden snatch into the air and often a considerable overspeed for
lighter gliders.

The video also shows what happens if you don't lower the nose quickly
enough after a launch failure. The pilot allows the glider to stall, after
which it never regains enough airspeed to round out. The glider (ASW15)
suffered a collapsed undercarriage and other minor damage, and the pilot a
bruised back. Fortunately nothing more serious, as it looks at one point as
if the glider might spin.

Otherwise weak links normally only break near the top of the launch, where
they are doing their job in protecting the airframe.

Derek Copeland


At 16:07 27 March 2009, MaD wrote:
On 27 Mrz., 12:00, John Roche-Kelly
wrote:
I think you may be missing the point here.
The weak link is to protect the glider airframe from exceeding maximum
loading ie towards the top of the launch, with the cable almost
vertical
and the wing loading at its maximum. Using these calculations to
determine
the best acceleration at the start of the launch is bad math(s).

Yes, yes, of course. I didn't mean to give the impression I would like
to be accelerated to the limits of the weak link - that would be
quite frightful. But bildan was throwing wrong figures about and
claiming (indirectly) the weak link limits the acceleration to safe
levels.

Marcel