Blanik Weak Link for Winch Launch???

Hi Gary

We use 2.51 or 2.75mm Spring Steel single strand cable, in grade C temper.
This gives 1860 to 2070MPA breaking strain, which is theoretically significantly
more than the blue link.

Full spec is:
2.51 mm
1860/2070 MPA
Code: 46 /0264/1862 1 / A
Din 17222 Grade C

Tests have been done on knotted wire and the reason for the situation found.
Quite simply , the first knot in the wire lowers the strength to around 900KG at
the knot - which is where it breaks. Since we always knot the wire to our
parachute, the weak link is superfluous, but we keep it for insurance.

The single strand spring steel is very resistant to wear in our rough gravel
strip, and is very easy to repair. We get about 1000 launches on a cable before
it work hardens to the point where the increasing frequency of cable failures
prompts replacement.

Speed on the launch is fairly simple, let the L13 fly itself off the ground at
around 75-80Km/h.
Hold attitude steady as the speed increases to around 100Km/h and altitude goes
up to around 100'. Rotate smoothly into steep climb, knowing that you have
enough energy to recover from a break. Speed generally touches 110-120km/h
before slowing to a climb out at a target speed of 95-100Km/h, with half flaps.
We stow the flaps if speed exceeds 100 because the force required at higher
speeds is too high.

This gives best results on our winch, which I suspect is a little underpowered
for the Blanik. Standard procedure on the winch is to smoothly roll on full
power in four seconds and hold it until the last seconds of the launch. (when
you hear the winch stop labouring, you know it is time to start backing off the
power, or you will overspeed)

Maximum height tends to be achieved when the transition to steep climb is early
in the launch, so a headwind makes a big difference.

Hope this helps.
Bruce