Tow Plane Upsets......

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. 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.

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.

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, “slipped back in the seat pulling back on the stick and going vertical.” I took a stab at the release to no avail, the 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.

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) The second time the pull of my tail to the right and nose to the left was a bit more violent…..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….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’t seem at all concerned……I shall withhold my comments at this point.

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.

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….next I will need approval to put a cushion on the seat or to have an inspection after washing the airplane.

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. In my case I would also like to see a more accessible release handle…would (or should) an STC be required for this? This would 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.

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….fly well….the life you save might be your tow pilot.

Walt Connelly

Hi Walt I am a tow pilot but don't have nearly as many tows. I do have a lot of total time and an A&P/IA.

I've given it a lot of thought and research. I won't tow with anything but a Tost tow hook for the exact reasons of your difficulty releasing. Of the three Pawnee's I tow with the releases are within easy reach from a normal seating position. I am adding a Tost hook to my personal Cub for tow pilot training . I intend to put the tow release within easy reach of my left hand near the throttle. There's a lot of leeway on where to put the release. An STC isn't really needed as installing a tow hook system is outlined in AC 43-13.

Just some of my thoughts. Hope they help.

Walt,

Our Pawnees have Tost releases. Schweizer hooks were removed about 30 years ago after an upset accident. The release cable is within a few inches reach of the throttle lever.

The release cable runs along the floor near the flap handle to a pulley attached to the floor that turns the cable 90 degrees upwards and then it attaches to the bottom of the instrument panel directly in front of the throttle quadrant. Reach forward and pull the cable, the glider is gone.

Release handles mounted to the floor are an accident waiting to happen, as are Schweizer hooks. As you have now experienced!

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.
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.

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.

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, “slipped back in the seat pulling back on the stick
and going vertical.� I took a stab at the release to no avail, the
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.

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)
The second time the pull of my tail to the right and nose to the left
was a bit more violent…..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….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’t seem at all concerned……I shall withhold my comments at this
point.

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.

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….next I
will need approval to put a cushion on the seat or to have an inspection
after washing the airplane.

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.
In my case I would also like to see a more accessible release
handle…would (or should) an STC be required for this? This would 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.

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….fly well….the life you save
might be your tow pilot.

Walt Connelly




--
Walt Connelly

Walt, I "feel your pain". It has been long reported that a Schweizer hook is difficult if not impossible to release under abnormal situations such as yours. A lot of tow pilots claim if that if the stick hits a stop, pull the release now! Another item I've always been acutely aware is the co-location of the flap handle and the release handle. Do you in a stressful time have the ability to grab the release NOW! Perhaps a Tee handle on a heavy cord in your lap would be quicker and provide more leverage. I like Dave's comment in favor of switching to Tost releases

It seems to require a dead towpilot before a club gets rid of Schweitzer
tow
hooks.

A manual release system will never be suitable to stop the rapid pitch up caused in this situation. It happens too fast for a manual (actually a sensory-brain-muscle-manual) system, however good the manual system on the tug.

Glider CofG winch hooks are not really suitable for aero-towing, are they? Some of these gliders can't be controlled in pitch once the kiting starts. I have seen people leave their shoulder starts loose on areotowing, and that means the pilot can slide backwards - with hand held on the stick, so that moves too - on pitch-up. (Always use tight shoulder straps on launching, please).

I have lost two acquaintances, both gliding "greats" in such tug upsets. I would say banning the use of aero-towing using a CofG winch hook would be the safest bet to save lives, until an automatic system is available.I suspect this is something EASA and the FAA would sort very quickly ( the banning bit, not the automatic system). Sensors to measure pitch, rate rate of the tug, and also tug/rope angle and angular rate,suitably processed and actioned automatically could allow immediate release BEFORE the critical situation is reached - if we feel that we must continue to launch by aero-tow using CofG hooks.

A rule of nose hooks or "compromise" hooks only, meanwhile, would probably reduce the risk towards zero.

I have posted what follows on a previous occasion but, given the posts in
this thread, I think it bears repeating.

Whilst I was Chief Instructor at Booker Gliding Club, we conducted two
series of test on the phenomenon variously referred to as “Kiting�,
“Winch Launching behind the Tow-Plane� and “Sling-Shot Accident�,
one in 1978 and one in 1982; my memory of them is quite vivid.
Â*
Airplanes used were, for the first series, a Beagle Terrier (a side by
side, two place, high wing, tail-dragger), fitted with an Ottfur Glider
hook for towing (very similar to the Tost hook, dissimilar to the Schweizer
hook) with a 160 hp Lycoming engine; for the second series of tests a
PA18-180 with a Schweitzer hook was used. Gliders used were a Schleicher
Ka 8b and ASK 13. Tow rope initially used was a heavy (4000 lb breaking
strain) rope with a thinner rope weak link at the glider end (nominally 900
lb, but a well worn specimen could break at as little as 200 – 300 lbs
– laboratory tests, not opinion), the second series of test used the same
heavy duty rope with “Mity� links at each end, 1100 lbs at the
Tow-Plane end and 900 lbs at the Glider end – these links use metal shear
pins, one under load and a second unloaded, which takes over if the first
one fails. This eliminates failure due to fatigue and means that the links
always fail at close to their nominal load even after some time in service
– again laboratory tested, not just subjective opinion. Rope length was
around 180 feet in all cases.
Â*
I was the Glider Pilot on all tests; Tow-Plane Pilot was Verdun Luck (then
my deputy Chief Instructor) for the first series of tests and Brian
Spreckley (then Manager of Booker GC) for the second. The object of the
tests was to try to reproduce the “Kiting� under controlled
circumstances, with a view to developing a Tow-Plane release mechanism that
would automatically release the glider if it got dangerously high above the
Tow-Plane. All tests were conducted at about 4000 feet agl.
Â*
First test: Terrier Tow-Plane and ASK 13 on nose-hook. At about 4000 feet
I took the glider progressively higher above the tow-plane, eventually
reached about 100 feet above tow-plane (i.e. rope angle more than 45
degrees above horizontal). At about this point, the tow pilot, who had
been using progressively more back stick, ran out of back stick and the
Tow-Plane began to pitch nose down but not excessively violently. I
released at that point. It took a very positive control input on my part
to achieve the displacement, we both felt it was something unlikely to
occur accidentally, even with an inexperienced glider pilot, and there was
plenty of time for either party to release if it did occur.
Â*
Second test: Terrier Tow-Plane and ASK 13 on C of G hook. I pitched the
glider about 25 – 30 degrees nose up – the weak link broke immediately!
Tow pilot reported a sharp jerk, but no significant change to flight
path.
Â*
Third test: Terrier Tow-Plane, K 8b on C of G hook. I pitched the glider
about 25 degrees nose up. The glider continued to pitch up fairly rapidly
(as at the start of a winch launch) and substantial forward movement of the
stick only slightly slowed the rate of pitch. The glider achieved about 45
degrees nose up, speed increased rapidly from 55 knots to about 75 knots
and the glider was pulled back towards level flight (again as at the top of
a winch launch). I released at that point. The entire sequence of events
occupied a VERY short period of time (subsequently measured as 2 - 3
seconds). The Tow Pilot reported a marked deceleration and start of
pitching down which he attempted to contain by moving the stick back; this
was followed immediately by a very rapid pitch down accompanied by
significant negative “G�. The tow-plane finished up about 70 degrees
nose down and took about 400 feet to recover to level flight. We both
found the experience alarming, even undertaken deliberately at 4000 feet.
Our conclusion was that the combination of the initial pitch down and the
upward deflection of the elevator caused the horizontal stabilizer/elevator
combination to stall and the abrupt removal of the down-force it provided
caused the subsequent very rapid pitch-down and negative “G�.
Â*
Our first conclusion was that, in the event of this sequence occurring
accidentally as a result of an inadvertent pitch up by the glider pilot,
there was effectively no chance that either the glider pilot or tow-pilot
would recognise the problem and pull the release in the available time.
Â*
Attempts to produce a tow-plane hook that would release automatically were
unsuccessful for reasons that became apparent later.
Â*
These tests were repeated a few years later with a PA18 – 180 as the
tow-plane, Brian Spreckley flying it. The third test described above was
repeated and photographed from a chase plane using a 35 mm motor drive
camera on automatic (this took a frame every half second – video
camcorders of small size were not readily available then). The photo
sequence started with the glider in a slightly low normal tow position and
starting to pitch up, the second frame has the glider about 30 degrees nose
up and about 20 feet higher than previously in the third frame it is about
45 degrees nose up and has gained another 30 feet or so, the tow-plane is
already starting to pitch down, in the fourth frame the glider is about 100
feet higher than its original position and the climb is starting to
shallow, the tow-plane is about 50 degrees nose down, the final frame shows
the tow-plane about 70 degrees nose down and the glider almost back in
level flight , almost directly above it (that was about the point that I
pulled the release).
Â*
Sufficiently alarmed by events, Brian Spreckley had been trying to pull the
release in the tow-plane earlier and found that it would not operate until
my releasing at the glider end removed the tension from the rope.
Subsequent tests on the ground showed that the Schweizer hook fitted to the
tow-plane, whilst perfectly satisfactory under normal loads, was jammed
solid by the frictional loads when subject to a pull of around 700 lbs with
a slight upwards component – not something that a normal pre-flight check
would reveal.
Â*
We solved that problem on our tow-planes by replacing the bolt that the
hook latches onto with a small roller bearing. So far as I know, no one in
the UK has tested the Schweizer hook as fitted to a glider, but I would not
be surprised if it exhibited the same characteristics at high loads.
Â*
The photo sequence also showed that at no time was the glider at an angle
greater than 30 degrees above the tow-plane’s centre-line. However, of
course once the glider has pitched up, the wings generate considerable
extra lift and that extra lift provides extra load on the rope. With a
large, heavy glider it is easy to exceed weak link breaking strains and
with a lightweight machine the tension can easily rise to 700 lbs or so.
With that much load on the rope, quite a small upward angle provides enough
of a vertical component to produce the results described.
Â*
That of course is the reason that attempts to produce a hook that released
if a certain angle was exceeded were unsuccessful. The, quite small, angle
between the rope and the fuselage centreline needed to trigger the
“Kiting� when the glider is pitched significantly nose-up is not much
greater than the amount of out of position commonly experienced in
turbulent conditions. We did build an experimental hook and tried it, but,
set to an angle that prevented “Kiting� it occasionally dumped an
innocent glider in turbulence, and set to an angle that prevented that, it
didn’t prevent the “Kiting�. What was needed was a hook that
responded to the vertical component of the load, not the angle at which it
was applied, and that problem we decided was beyond us (at least in a form
robust and fool-proof enough to be attached to the rear end of a
tow-plane).
Â*
Our conclusions for preventing “Kiting� we
Â*
Don’t aerotow gliders, especially lightweight, low wing-loading gliders,
on C of G hooks intended for winch launching (I think the JAR 22
requirement for nose hooks to be fitted to new gliders for aerotowing was
at least in part a result of these tests).
Â*
Don’t use short ropes. The speed at which things happen varies directly
with the length of the rope.
Â*
Don’t let inexperienced pilots fly at anywhere near aft C of G.
Â*
Don’t let inexperienced pilots fly solo in turbulent conditions.
Â*
Replace or modify all Schweizer hooks fitted to tow planes. (So far as I
know there are none on gliders in the UK, so that question never arose).
Â*
We did also modify our PA18’s so that instead of the release cable ending
at a floor-mounted lever, it went round a pulley where that lever used to
be, and then all the way up the side of the cockpit, anchored at the roof.
This meant that grabbing any point on the wire and pulling it in any
direction could operate the release; considerably easier than finding a
floor mounted lever when being subject to about minus two “G�. We
never regarded this modification as being likely to prevent a worst-case
scenario, because, as stated earlier, it was the opinion of all involved,
that in a real “Kiting� incident, there was no realistic hope that
either pilot would respond in time.


At 10:06 24 April 2017, Peter Whitehead wrote:
A manual release system will never be suitable to stop the rapid pitch up
c=
aused in this situation. It happens too fast for a manual (actually a
senso=
ry-brain-muscle-manual) system, however good the manual system on the
tug.

Glider CofG winch hooks are not really suitable for aero-towing, are
they?
=
Some of these gliders can't be controlled in pitch once the kiting
starts.
=
I have seen people leave their shoulder starts loose on areotowing, and
tha=
t means the pilot can slide backwards - with hand held on the stick, so
tha=
t moves too - on pitch-up. (Always use tight shoulder straps on
launching,
=
please).=20

I have lost two acquaintances, both gliding "greats" in such tug upsets.
I
=
would say banning the use of aero-towing using a CofG winch hook would be
t=
he safest bet to save lives, until an automatic system is available.I
suspe=
ct this is something EASA and the FAA would sort very quickly ( the
banning=
bit, not the automatic system). Sensors to measure pitch, rate rate of
the=
tug, and also tug/rope angle and angular rate,suitably processed and
actio=
ned automatically could allow immediate release BEFORE the critical
situati=
on is reached - if we feel that we must continue to launch by aero-tow
usin=
g CofG hooks.=20

A rule of nose hooks or "compromise" hooks only, meanwhile, would
probably
=
reduce the risk towards zero.

Originally Posted by Charles Longley

Hi Walt I am a tow pilot but don't have nearly as many tows. I do have a lot of total time and an A&P/IA.

I've given it a lot of thought and research. I won't tow with anything but a Tost tow hook for the exact reasons of your difficulty releasing. Of the three Pawnee's I tow with the releases are within easy reach from a normal seating position. I am adding a Tost hook to my personal Cub for tow pilot training . I intend to put the tow release within easy reach of my left hand near the throttle. There's a lot of leeway on where to put the release. An STC isn't really needed as installing a tow hook system is outlined in AC 43-13.

Just some of my thoughts. Hope they help.

Thank you Charles.....this is the kind of response I am looking for especially from an A&P/IA.

Walt

In Australia we do low tow only with the aim of reducing tug upsets. It intuitively 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 much more time to react.
It's also much harder to lose sight of the tug, it's right there in your field 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.
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.

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.

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, “slipped back in the seat pulling back on the stick
and going vertical.� I took a stab at the release to no avail, the
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.

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)
The second time the pull of my tail to the right and nose to the left
was a bit more violent…..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….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’t seem at all concerned……I shall withhold my comments at this
point.

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.

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….next I
will need approval to put a cushion on the seat or to have an inspection
after washing the airplane.

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.
In my case I would also like to see a more accessible release
handle…would (or should) an STC be required for this? This would 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.

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….fly well….the life you save
might be your tow pilot.

Walt Connelly




--
Walt Connelly