Tow Plane Upsets......

A large proportion of the tow-plane upsets, including most of the fatals,
happen very shortly after take-off, before there is an opportunity to get
into low tow. Also, descending into the prop-wash can be a trigger to the
momentary loss of control that leads to the upset, if the glider is on a C
of G hook.

At 12:05 24 April 2017, wrote:
In Australia we do low tow only with the aim of reducing tug upsets. It
int=
uitively makes sense to me that kiting upsets are much more likely and
much=
worse than 'diving' upsets (do these even happen?), and low tow offers
muc=
h more time to react.
It's also much harder to lose sight of the tug, it's right there in your
fi=
eld of view.

On Monday, 24 April 2017 01:43:12 UTC+1, 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

On Monday, April 24, 2017 at 3:45:05 PM UTC+3, Chris Rollings wrote:
A large proportion of the tow-plane upsets, including most of the fatals,
happen very shortly after take-off, before there is an opportunity to get
into low tow. Also, descending into the prop-wash can be a trigger to the
momentary loss of control that leads to the upset, if the glider is on a C
of G hook.

Do these upsets *only* happen with a C of G hook?

I've done a fair bit of flying in a C of G hook Janus, including on days with wave and pretty bad rotor. Never had a problem.

Does an upset really happen because the glider pilot simply flies out of position? It seems unlikely to me. You need not only to be high but also with significant pull on the rope. All the times I've gotten high it's because the towplane suddenly ran into sink (of at least out of lift), and the result has been a slack rope, not the tight rope required for an upset. Simply maintaining station (even though high) until the slack starts to come out, and then descending back into position with a constant amount of bowing (i.e. low tension but not slack as such).

Without having actually been there myself, I suspect that upsets may be caused not by being out of position, but by having a slack rope suddenly come tight. With a C of G hook this causes a reasonably large nose up pitching moment which may not be able to be countered by the elevator. The glider can get significant angle of attack and lift and upwards and (as the angle increases) backwards acceleration. If you're towing at 68 knots (or more) with a stall speed of 40 knots then you can generate 3 G of acceleration. With 3 G of acceleration you've only got to get to 10 degrees nose up to tension the rope to half the glider's weight, 20 degrees nose up to put a full 1 G of force onto the rope, and 30 degrees for 1.5 times the glider's weight in tension.

The glider being out of position is most likely the very quick *result* of the glider going into winch launch mode, not the cause of it.

I can't see that low tow would make any significant difference to this. Slack being taken out violently (but not quite enough to break the rope) will have exactly the same effect as in high tow.

"Time to get to low tow"?!?!
You're doing it wrong.

Towplane and glider start rolling, glider lifts off and stays a few feet off the ground in ground effect, towplane lifts off and climbs out, when sight picture looks correct, glider starts climbing.
The propwash is not really a factor since it has not quite come together yet with normal ropes, maybe felt a bit on rather short ropes. By the time the turbulence has come together, it's over the glider.

BTW, I am not an AandP or IA, just an ex CFIG, long time glider pilot with some power time.

As to a release with a roller, any roller is better than a sliding surface, although keeping it rolling while operating on grass or dirt may be an issue.
On a sliding type release, at least make sure the edges of the hook where it goes into the release are smooth, not mushroomed out. A flat file now and then to smooth it out helps this.
Also some lube on release cable guide rollers, inside guide tubes and release pivots helps out a bit.