I suspect that is not quite true, as the glider's wings
in the 5000ft winch launch have to lift a longer and
therefore heavier length of cable into the air. However
the weak link remains the same and still protects the
glider. What allowed these very high launches to be
achieved was the combination of a very long (3000 metre)
winch run and the advent of modern lightweight synthetic
UHMWPE cable.

Derek Copeland


At 02:42 01 December 2006, News wrote:
Eric,

the forces are all the same.

there is no difference in forces strengths launching
to 1000ft or to 5000ft
the applying forces just last longer thats all.

I did hundreds of take offs on the winch.
I wish we would have good winches in Australia.
Here we only have historical rubbish standing around.

Chris



'Eric Greenwell' wrote in message
news:GBu1h.4529$WB4.3254@trndny04...
Gerhard Wesp wrote:
That sounds a bit frightening - 3500 fpm! What are
the stresses on the
glider to get that kind of climb rate? How far away
is disaster if the
pilot twitches a bit on the controls or hits some
wind shear or a
thermal?

Hmmm, if they are using weak links, I don't see a
problem.

Stress (=force) is related to acceleration, not to
speed. You can go
straight up at 1000000 fpm with the same force as
at 10 fpm. Just takes
you a bit longer to reach the speed.

Of course, the net force on the glider is zero, otherwise
it would
accelerate, but the individual forces are much greater
and vary during
the launch. We've all seen the wings curve up and
stay that way as the
pilot rotates into the climb on a winch launch, indicating
much more
lift is being generated to counteract the pull of
the cable.

Surely the cable tension must be greater to provide
a 3500 fpm launch
instead of a 1000 fpm launch? I'm curious about the
amount of tension
needed to provide a 1000 pound glider that 3500 fpm
climb.

--
Eric Greenwell - Washington State, USA
Change 'netto' to 'net' to email me directly

'Transponders in Sailplanes' on the Soaring Safety
Foundation website
www.soaringsafety.org/prevention/articles.html

'A Guide to Self-launching Sailplane Operation' at
www.motorglider.org