At 11:21 20 May 2020, Sci Fi wrote:
As a starting point.. A 350kg Glider with a 35:1 L/D ratio just requires
10kg of pull to keep it flying. So factor in a safety margin to allow
for
turbulence, of say 10x, and what you need is a 150kg Weak-Link.

In addition to drag, during a normal tow, the rope needs to pull the glider

uphill! Typically (6knots climb rate at 60 knots airspeed) that requires
10%
of the weight of the glider - 35kg in your example.

So total steady-state 'pull' would be 45kg, and your safety factor makes
for
a 450kg weak link. Just what is routinely used in the UK! YMMV.
J.