On Wednesday, May 20, 2020 at 7:30:05 AM UTC-4, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset, it
is
=
not exclusive to upsets. That is why I suggested putting a load cell on
the=
tow release to measure the force on the tow rope which is a better
indicat=
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would be
good... Don't we have them now.. they are called Weak-Links. All you
need to do is correctly calculate the maximum tension that you could allow.


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. This is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs to
be made for safe aero-tow.

SiFi - if you check your POH under 'Weak Link', you will find a mfg recommended weak link breaking strength for winch launch AND one for aero-tow. They may be different, depending on the glider.
We must get away from this 80%-200% 'rule'! There is an FAR out there that states that if the glider has an approved POH at the time of certification, whatever is in this book takes precedence over the FARs.
So if we were to start using stronger (i.e. thicker) ropes like our European brethren do, instead of one from the aviation department of your local hardware store AND outfit it with the proper weak link, we may actually kill tow birds with one stone: reduce or eliminate rope breaks due to wear and tear and increase safety by having the proper weak link installed, which may actually break in a kiting event.

Uli
'AS'