At 15:11 20 May 2020, 2G wrote:
On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset,
it
is
=3D
not exclusive to upsets. That is why I suggested putting a load cell
on
the=3D
tow release to measure the force on the tow rope which is a better
indicat=3D
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would
b=
e
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
allo=
w.
=20
=20
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
fo=
r
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
t=
o
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: the
decision
=
would not be based on a static load level, it would be based on the input
o=
f several sensors using a technique called state estimation. An upset
state=
or event is characterized by a rapidly increasing load on the tow rope,
a
=
rapidly increasing pitch down attitude of the towplane, and a decreasing
to=
wplane airspeed. Note: a weak link is not a sensor.

Tom

Sorry Tom, but I was brought up in the Horse-drawn era, where some very
elegant and simple solutions were found for problems. We engineered
systems in the most uncomplicated ways, because there were no 'Apps' or
'Actuators' or Hydraulics to make things complicated.
What could be simpler than a 'Weak-Link' of 150 kg breaking strain..?
Maybe the BGA needs to amend the rules to state that for aero-tows the
weak-link needs to be 1/3 the breaking strain of that used for winch
launches.
Glider owners would then need to have two lead ropes, one for winching with
a white or blue link. and the other with a green Tost link.