Tow Plane Upsets......

At 01:13 28 April 2017, firsys wrote:
On Sunday, April 23, 2017 at 8:43:12 PM UTC-4, Walt Connelly wrote:
I have been towing for about two and a half years and have logged over
6,500 tows. Having recently experienced a couple of rather violent
glider kiting incidents, one at about 300 feet AGL I decided to
investigate the experiences of other tow pilots in these
circumstances.=
=20
I have spent several hours reading posts about gliders kiting and
upsetting the tow plane, many of the posts deal with creating an
automatic release that will recognize the actions of the glider and
release without input from the tow pilot. Nice idea, some really
creative approaches and the bottom line is anything can be done if you
have enough money and can get the FAA to buy into it and give
approval.
=20
Lots of opinions and ideas as to why these things happen. Bottom line
is that they do happen, they have resulted in loss of tow pilot lives
and the causes are well known.=20
=20
Of my two most recent experiences one was with a 67 year old licensed
private pilot, glider only, no other pilot ratings who at 2000 feet
tried to release, =E2=80=9Cslipped back in the seat pulling back on the
s=
tick
and going vertical.=E2=80=9D I took a stab at the release to no avail,
t=
he
pressure was too great and I soon found myself at about 75 degrees nose
down at full power. The natural instinct at this point is to pull back
the power and try again to release. He managed to release before I
could try for a second time and I recovered. If this has to happen to
you, 2000 feet is a good place to be. My understanding is that this
was
his first tow in more than a year. Something to think about. =20
=20
My second experience in the same week was with a 15 year old student on
her 3rd solo pattern tow. At about 250 to 300 feet I started a turn
from the downwind drift to the right. I felt a tug on my tail pulling
my nose to the left. After a few seconds I tried again to turn to the
right knowing that she was behind me to the right. Could not see her,
no mirror on the right. (much easier if she was a little to the left)
=20
The second time the pull of my tail to the right and nose to the left
was a bit more violent=E2=80=A6..followed by a very hard tug of my
tail
=
UP and
to the right. We could not have been much more than 300 feet when I
found myself nose down and trying to release=E2=80=A6.again the
pressure
=
was too
much to overcome and I needed to retard the throttle. Before I could
make a second attempt at release I heard a loud BANG as the rope broke,
I regained control and recovered just above the trees. (glad that I
had
made a pit stop before I started towing). She made it back to the
field
and didn=E2=80=99t seem at all concerned=E2=80=A6=E2=80=A6I shall
withhol=
d my comments at this
point. =20
=20
I had to straighten out the Schweizer hook which was off to the right
about 30 degrees before I could make the last 8 tows of the day.
=20
While I have concerns with both of these pilots my major concern is
that
the difficulty of actuating the release when the glider kites is well
documented. To make matters worse, the release in the tug I was
flying,
although a bit more manually accessible than the other two I fly
requires that the pilot pull it back and push down to fully actuate the
release. Not an easy thing to do under the circumstances. The other
two release handles are down on the floor to the left and for someone
of
my height, sitting on a cushion and trying to grab the release is very
difficult. It would seem to me that an easy fix would be to simply
make
a longer handle curved up so one could both see and feel for it in an
emergency. A longer handle would also provide a bit more mechanical
advantage although having read many of the posts I am not sure this
would overcome the pressure on the Schweizer hook. Of course I hear
all
the noise about needing to apply for a 337 and get FAA
approval=E2=80=A6.=
next I
will need approval to put a cushion on the seat or to have an
inspection
after washing the airplane. =20
=20
So, the fixes appear to be going to a Tost hook or inverting the
Schweizer hook which I understand can be done with an available STC.
=20
In my case I would also like to see a more accessible release
handle=E2=80=A6would (or should) an STC be required for this? This
wou=
ld be
the short term fix I would like to see. If the handle was made from
the
same stock as the current device, just a foot or so longer it would
seem
that this should be able to be done without a long drawn out approval
process. =20
=20
I love flying, enjoy the gliderport environment and people but I am NOT
willing to give up my life. When the glider kites things happen very
fast. Unless your hand is on the handle (not feasible in my
circumstances) you will not be able to release before the pressure gets
too great. If it happens much lower than I experience it will be
lights
out. So remember my glider pilot friends=E2=80=A6.fly
well=E2=80=A6.the
=
life you save
might be your tow pilot.
=20
Walt Connelly
=20
=20
=20
=20
--=20
Walt Connelly

In his excellent and erudite post on aerotow upset testing, Chris
Rollings
said " the speed at which things happen is proportional to the length of
th=
e rope"
I think he intended to say INVERSELY proportional to the length.

John F


Directly proportional, if the rope is twice as long, the time the
divergence takes is also twice as long.

On Friday, April 28, 2017 at 12:00:58 PM UTC+3, Chris Rollings wrote:
At 01:13 28 April 2017, firsys wrote:
In his excellent and erudite post on aerotow upset testing, Chris
Rollings
said " the speed at which things happen is proportional to the length of
th=
e rope"
I think he intended to say INVERSELY proportional to the length.

Directly proportional, if the rope is twice as long, the time the
divergence takes is also twice as long.

The time is directly proportional to the rope length. The *speed* at which it happens is inversely proportional.

But I'm not convinced and angle achieved in divergence is even the primary factor. If the glider goes into "winch launch" mode then it's pulling backwards with a tension of its own weight or more. Winch launch weak links range from 500 - 1000 kg. How many tugs have the thrust to prevent being drastically slowed -- and stalled -- by that vs the normal 50 - 100 kg tension in the rope? None, I should think. Even if the rope is thousands of feet long very bad things are going to happen.