Does anyone use a tug tow hook that releases automatically whenglider kites?

On Monday, February 10, 2014 8:55:46 AM UTC-6, son_of_flubber wrote:

Are you saying that high performance gliders are incapable of kiting, or that the pilot of a high performance glider will never pull back on the stick at launch in ground effect?

If you do some research on kiting, you will find a good article in the BGA magazine about it.

To be pedantic, Kiting is defined as an uncontrollable pitchup and rise of the glider on tow - once it starts it happens so fast that it yanks the towplane tail up faster than the tow pilot can release. Most glass ships (due to wingloading, elevator authority, etc) appear to not be susceptible to this problem. Older light wingloading gliders are.

What the G-103 did in this accident is not kiting (technically), but just flying too high on tow (and totally the glider PIC's error) - the tow pilot should have released as soon as he reached the aft stop on the elevator. But with a Schweizer tow hook, that is damn near impossible unless it has the inverted mod.

There is also a long discussion somewhere (RAS, BGA?) about automatic releases, and the consensus was that it would be difficult to implement. Personally, I would imagine that a release triggered by hitting the aft stick stop might work, but it gets complicated on the ground, while landing, etc. Hugh potential for dropping ropes all over the place! It would have to sense the presence of a glider (tension on the rope) and the stick full aft and the towplane being airborne - then probably have to be a pyrotechnic guillotine to be reliable. Yeah, good luck getting a 337 for that past the FAA!

If a pilot pulls back on the stick that hard during launch when I'm towing, and I survive the crash, I am going to beat the **** out of him and his instructor(s) with a broken Pawnee wing strut. I've had a student pitch up in a 2-33 (solo) to do a soft release (argghhh!) and pull my Pawnee's tail up (during a pattern tow, no less). He released just before I did. He got seriously talked to after landing.

Yes, glider pilots can kill tow pilots. As a glider pilot you should think of that every time you get hooked up for a tow. And fly your tow like a damn Blue Angel!

Kirk
66

By the way, you can also give your towpilot a thrill by pulling way off to the side - and if he is stupid enough to keep full rudder in and try to fight you, you can stall his vertical stab/rudder - and off he goes into Mr Toad's wild ride as his plane loses all yaw stability all at once!

Unless I'm told the glider is going to box the wake, I pretty much keep my feet off the rudders and let the glider point me wherever he wants...

On Monday, February 10, 2014 1:35:29 PM UTC-5, Don Johnstone wrote:
At 17:47 10 February 2014, Eric Bick 1DB wrote: What about release? Any unintended= consequences? I can maybe see the weak link rubbing up against the wheel w= ell doors. Also, our club has a PW-6 with chin hook.. POH says - "Flying under the towi= ng airplane downwash is not recommended since the towing cable rubs the fus= elage front part." Not sure low tow is the be-all, end-all answer. Eric Bick I think you will find the recommended procedure is to move up to high tow for release, ask the Aussies, they are the experts on this. I do use low tow but always move to high tow for the release.

I have something over 11000 tow done in low tow and release from that position all the time. Properly done, the rope goes away straight out and does not end up above the sailplane. If does end up above, the pilot was too low when releasing.
UH

On Sunday, February 9, 2014 5:27:23 PM UTC-5, son_of_flubber wrote:
This topic was buried in a drifting degenerate thread. I'm wondering if anyone knows more about the tow hook innovation mentioned below by UH.



On Saturday, February 8, 2014 9:31:13 AM UTC-5, son_of_flubber wrote:



Why does the pilot need to pull the release if the glider kites? Why is the release for a deadly tow position not fully automatic? Is a simple purely mechanical, totally foolproof and 100% automatic release not possible? As the guy in the glider, I would be fine with a 100% automatic release. If I kite, release me immediately.





On Sunday, February 9, 2014 5:05:52 PM UTC-5, wrote:



There was a design and prototype of a release like this created many years ago and published, I believe, in Soaring magazine. I know if no one that has adopted this which makes it fairly clear that this is not perceived as a huge problem.



A Brit made such a device and the design was circulated around. Externally, it was shaped something like a Tost release, but the tow ring would slip out when the rope angle increased to X degrees.

Tried to post this yesterday bit it didn't appear. For some reason my
(rare) posts to ras often don't appear. I will also post it on uras and
ask someone to post it on for me. Apologies if that results in
repetition.

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 20:32 10 February 2014, Karl Striedieck wrote:
On Sunday, February 9, 2014 5:27:23 PM UTC-5, son_of_flubber wrote:
This topic was buried in a drifting degenerate thread. I'm wondering
if
=
anyone knows more about the tow hook innovation mentioned below by UH.
=20
=20
=20
On Saturday, February 8, 2014 9:31:13 AM UTC-5, son_of_flubber wrote:
=20
=20
=20
Why does the pilot need to pull the release if the glider kites? Why
is=
the release for a deadly tow position not fully automatic? Is a simple
pur=
ely mechanical, totally foolproof and 100% automatic release not
possible?
=
As the guy in the glider, I would be fine with a 100% automatic release.
If=
I kite, release me immediately.
=20
=20
=20
=20
=20
On Sunday, February 9, 2014 5:05:52 PM UTC-5,
wrote=
:=20
=20
=20
=20
There was a design and prototype of a release like this created many
ye=
ars ago and published, I believe, in Soaring magazine. I know if no one
tha=
t has adopted this which makes it fairly clear that this is not perceived
a=
s a huge problem.
=20


A Brit made such a device and the design was circulated around.
Externally,=
it was shaped something like a Tost release, but the tow ring would slip
o=
ut when the rope angle increased to X degrees.

From our experiments, being in low tow would only increase the available
time in which to release by less than 1 second. More to the point, in my
opinion, descending through the turbulent prop wash shortly after take-off
could quite easily trigger the momentary loss of control that would
precipitate the kiting event.

At 18:35 10 February 2014, Don Johnstone wrote:
At 17:47 10 February 2014, Eric Bick 1DB wrote:

What about release? Any
unintended=
consequences? I can maybe see the weak link rubbing up against the
wheel
w=
ell doors.

Also, our club has a PW-6 with chin hook. POH says - "Flying under the
towi=
ng airplane downwash is not recommended since the towing cable rubs the
fus=
elage front part."

Not sure low tow is the be-all, end-all answer.

Eric Bick

I think you will find the recommended procedure is to move up to high to
for release, ask the Aussies, they are the experts on this. I do use lo
tow but always move to high tow for the release.

On Tuesday, February 11, 2014 3:56:33 AM UTC-5, Chris Rollings wrote:

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).

Thank you Mr. Rollings for your pioneering work with tow hooks and thank you for responding to my question.

(And thanks to all the people who deployed the internet and made conversations like this one possible. Wow.)

On Tuesday, February 11, 2014 12:56:33 AM UTC-8, Chris Rollings wrote:
Tried to post this yesterday bit it didn't appear. For some reason my
(rare) posts to ras often don't appear....

There you go, messing up a perfectly good Internet discussion with actual data and relevant experience.

But seriously, thanks for posting about this. Your investigation supports my general working thesis that for every problem there exists a solution that is simple, obvious, and wrong.

Bob K.

On Tuesday, February 11, 2014 3:56:33 AM UTC-5, Chris Rollings wrote:

What was needed was a hook that
responded to the vertical component of the load, not the angle at which it
was applied...

This statement defines the starting point, not the ending point.

How about a weather proof calibrated mechanical device placed between the Tost release hook and the tug that pulls the Tost release lever when the vertical component exceeds a limit? There is a well-proven mechanism that does something like that on my downhill ski bindings. A rocket-scientist is not required.

Is it a matter of the FAA and insurance underwriters making any change to the status quo cost-prohibitive? What sort of gauntlet does one need to run?

On Tuesday, February 11, 2014 12:41:48 PM UTC-6, son_of_flubber wrote:

How about a weather proof calibrated mechanical device placed between the Tost release hook and the tug that pulls the Tost release lever when the vertical component exceeds a limit? There is a well-proven mechanism that does something like that on my downhill ski bindings. A rocket-scientist is not required.

Well, if you think it is that big a problem and it can't be addressed through better (more threatening) training, then how about an optical device on the towplane that tracks the glider and 1. warns the tow pilot and glider pilot when the glider is moving out of the safe tow envelope, and 2. fires a guillotine on the tow rope when the glider reaches the limit. Add a flashing light on the tow plane to warn the glider pilot that he is about to be dumped.

Or, just teach the glider pilot to NEVER lose sight of the towplane, and to immediately release if he does.

Is it a matter of the FAA and insurance underwriters making any change to the status quo cost-prohibitive? What sort of gauntlet does one need to run?

Bwahahahaha!!!!

ROTFLMFAO!

Gasp, sigh, that just really made my day!

Cheers,

Kirk
66

Chris Rollings wrote:

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�.

I was the pilot of a tug involved in exactly the scenario described by
Chris above. The culprit was a K6 using a belly hook, and the only
reason I am here to tell the tale is that it occurred at 400ft. It was
actually a dual tow with the K6 on the short rope and a K13 on the
long rope in low-tow position. The K6 had recovered from some earlier
excursions, but all seemed to be going well before it happened.

The "up-ending" was instantaneous, there was no way to have reached
any type of release before the rope broke, and in any case I can
assure you that when descending vertically on full throttle at 400ft,
your first reaction it to close the throttle.

Our CFI in the K13 said he hadn't seen the underside of a PA18 in plan
form quite so close before.

In those days we used to store spare ropes and things behind the rear
seat of the PA18, and my situation was not improved by the whole lot
coming forward and landing on my head and all over the cockpit.

A good friend of mine later died towing a K6 with a PA18, which
incident quite probably was the trigger for Chris' investigations.