At 17:41 17 February 2014, SF wrote:
If this was an industrial control problem. I would try two things.
1: Mount a Tost CG release on the tow plane upside down and at an angle
whe=
re the upwards angle of the tow rope would initiate a back release. The
an=
gle required, reliability, tendency for unintended operation,and whether
or=
not this would actually work, to be determined by testing. Based on
somet=
hing like this that was attempted and reported on here earlier, I have a
lo=
w confidence in this scheme working out.

We actually tried exactly that as our first attempt (can't remember now if
it was a Tost or Ottfur Hook we used, but they are much the same anyway).
It didn't work because, as I said, the "kiting" departure is caused by the
upward component of the pull on the rope, not the upward angle. If a light
weight single seat glider is flying in steady flight behind the tow-plane
at about 60 knots the tension in the rope is only a few 10's of pounds. If
the glider is pitched 45 degrees nose up the tension in the rope is about
700 - 900 lbs. In the first case, the glider being high enough that the
rope angle is 30 degrees upwards is easily containable by the tow-pilot, in
the second case he is pitched 70 degrees nose down in less than 2 seconds.

2: Using a TOST release, add an electric solenoid activation device
somewhe=
re in the cable run to the release. The solenoid could be activated by a
"=
full back stick" limit switch and a short time delay circuit on the tow
pla=
ne, the normal manual pull handle in the cockpit, or a switch on the
stick.=

"...A short time delay circuit...." The whole sequence from everything
normal, to tow-plane 70 degrees nose down and destined to lose about 400
feet, takes less than 3 seconds.

On most tail-draggers (= many/most tow-planes currently in use), it's
normal to bring the stick fully back shortly after touch-down, be tedious
to have to go and find the rope after every tow.

Again, testing would have to be done to confirm that this scheme would
ac=
tually work.
I have no idea how any of this could be accomplished given it's an
airplane=
and the FAA is involved. Their requirements are baffling to someone
that
=
does not live in that world.

Ultimately, taking the human element out of the equation could prove
imposs=
ible. The cure being worse that the disease is also a real possibility
due=
to unintended consequences. However we have always done it this way,
isn't=
a good answer either. =20