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

Chris Rollings wrote:

At 10:06 16 February 2014, Jonathon May wrote:
At 08:50 16 February 2014, Chris Rollings wrote:
At 01:21 16 February 2014, Don Johnstone wrote:
At 22:39 11 February 2014, kirk.stant wrote:


Or, just teach the glider pilot to NEVER lose sight of the towplane,
and
to=
immediately release if he does. =20

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 nee
to
r=
un?

One of the never to be breached rules of aerotowing for a glider pilot
i
the UK is "if at any time you loose sight of the tug for ANY reason yo
ar
to pull the release"
If you read Chris's article carefully you may deduce that in the wors
cas
scenario, the rapid vertical departure of the glider, by the time th
glider pilot realises he has lost sight of the tug, and attempts to pul
the release it is already far to late to make any significant differenc
t
what is going to happen.



"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."

It was this very scenario that killed a very good friend of mine who
was

very experienced tug pilot. There are some events that, paradoxically
require corrective action to commence before onset if they are to b
effective in time to change the outcome.

As for cheap solutions, I am firmly of the view that most wooden glider
with only CoG hooks should not be aerotowed, those with compromise
hook
should be aerotowed with extreme care.



I would add that, although I haven't done the same tests with any glas
gliders, I'm pretty sure that many of the light-weight Standard/15m type
would behave in the same way on a C of G hook. Std Cirrus would be a
prim
candidate, would somebody with access to one care to try it at saf
altitude and report the result?

What I find rather sad about the gliding movement is the lack o
willingness to go and get the facts. We have been aware of this proble
for over 35 years, I described flights tests that I carried out, to try
t
improve understanding and seek a solution. Has anyone else done the
same?


In my opinion more relevant has any one tried these departures from track

with the next generation tugs eurofox to name but one.
We are all used to boxing the wake of a Pawnee and I know the teams
introducing them into clubs are taking a steady measured introduction .
But I don't want to be known as the the guy that killed the tuggie
because
I
didn't know what was acceptable .
My apologies to all at YGC for washing in public but this thread stirred
my

concerns and I know that when I get to fly behind the fox I will get a
briefing
But as Chris said until you have tested and published the results no one
knows.
Jon




Jon, I share your concern about the new generation of light-weight
tow-planes, I strongly suspect they will be more vulnerable to upset
accidents. I think that carrying out test like the ones I described should
be a requirement before the authorities approve the type for towing. It
may be possible I'll get the chance to try it out behind a Eurofox later
this year, I'll publish the results here if I do.

Chris, as it happens I have also been in the glider during one of
these incidents, and once again I emphasise that it is all over in
fractions of a second, with absolutley no chance to take any sort of
corrective action.

It was not a light sailplane either - an ASH25 in fact - flown by its
owner with me taking no part in the rear cockpit. (I will try to be
more observant in future). The airbrakes had opened as we left the
ground, and although the tug pilot was shouting 'bremse' into his
radio it took quite some time for the translation to sink in, at which
point P1 slammed the brakes shut and quite possibly and inadvertantly
pulled back on the stick. Bang, all over, and one very annoyed and
very lucky tug pilot back on the ground. Maybe the time to translate
the message saved his life.

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 where the upwards angle of the tow rope would initiate a back release. The angle required, reliability, tendency for unintended operation,and whether or not this would actually work, to be determined by testing. Based on something like this that was attempted and reported on here earlier, I have a low confidence in this scheme working out.
2: Using a TOST release, add an electric solenoid activation device somewhere 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 plane, the normal manual pull handle in the cockpit, or a switch on the stick. Again, testing would have to be done to confirm that this scheme would actually 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 impossible. 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.

That might be the scenario to build an auto release. it would require an electronic gyro which any more is inexpensive and easy to implement along with the full back stick switch, if the Tow plane pitches down more than a certain amount (Maybe 20 degrees down pitch) and with full aft stick initiates and auto release.

Brian

Another fatality on Sunday in South Africa - with a Cessna glider tug crashing just on the initial part of the flight. Eye witnesses seem to have seen the glider (Ventus CM) kite and force the tow plane into the ground. A very experienced tow pilot and gliding instructor will be sorely missed by the gliding community.

Here is the link to the active thread on the AvCom site regarding this incident including the eye witness account. Registration on the site will be required to view the topic. http://www.avcom.co.za/phpBB3/viewto...p?f=9&t=130916

Whether an automatic release would have saved the plane and pilot can be speculated but its certainly worth investigating if it will save lives from being lost in this type of accident.

Clinton

Not an 'auto release', but some info from this document :

http://www.glidingmagazine.com/pdfs/...20Rollings.pdf

"That of course is the reason that attempts to produce a hook that released
if an certain angle was
exceeded were unsuccessful. The quite small angle 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 foolproof
enough to be attached to the rear end of a tow-plane)"

Solved by

"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 has tested the Schweitzer
hook as fitted to a glider,
but I would not be surprised if it exhibited the same characteristics at
high loads."
http://www.facebook.com/KranskopGliding

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

At 03:57 18 February 2014, Brian wrote:
That might be the scenario to build an auto release. it would require an
el=
ectronic gyro which any more is inexpensive and easy to implement along
wit=
h the full back stick switch, if the Tow plane pitches down more than a
cer=
tain amount (Maybe 20 degrees down pitch) and with full aft stick
initiates=
and auto release.

Brian


That might work but I suspect it would be impossible, in the real World, to
get a sufficiently high degree of reliability that we did not get more
accidents from innocent gliders be jettisoned at low altitudes than we
currently get from kiting accidents.

That didn't solve the Kiting problem, merely made it probable that the
release would still be able to be operated when the rope was under very
high tension. It remained the opinion of all involved that in a real,
accidental Kiting incident, there was effectively no chance that either
tow-pilot or glider pilot would re-act in time to release before it was too
late.

At 08:17 18 February 2014, Pieter Oosthuizen wrote:
Not an 'auto release', but some info from this document :

http://www.glidingmagazine.com/pdfs/...20Rollings.pdf

"That of course is the reason that attempts to produce a hook that
released
if an certain angle was
exceeded were unsuccessful. The quite small angle 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 foolproof
enough to be attached to the rear end of a tow-plane)"

Solved by

"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 has tested the Schweitzer
hook as fitted to a glider,
but I would not be surprised if it exhibited the same characteristics at
high loads."
http://www.facebook.com/KranskopGliding

Thanks Chris - appreciate your comments!

Apologies if I interpreted it incorrectly.

PO


At 10:30 18 February 2014, Chris Rollings wrote:
That didn't solve the Kiting problem, merely made it probable that the
release would still be able to be operated when the rope was under very
high tension. It remained the opinion of all involved that in a real,
accidental Kiting incident, there was effectively no chance that either
tow-pilot or glider pilot would re-act in time to release before it was
too
late.

At 08:17 18 February 2014, Pieter Oosthuizen wrote:
Not an 'auto release', but some info from this document :

http://www.glidingmagazine.com/pdfs/...20Rollings.pdf

"That of course is the reason that attempts to produce a hook that
released
if an certain angle was
exceeded were unsuccessful. The quite small angle 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 foolproof
enough to be attached to the rear end of a tow-plane)"

Solved by

"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 has tested the Schweitzer
hook as fitted to a glider,
but I would not be surprised if it exhibited the same characteristics at
high loads."
http://www.facebook.com/KranskopGliding

At 11:54 18 February 2014, Pieter Oosthuizen wrote:
Thanks Chris - appreciate your comments!

Apologies if I interpreted it incorrectly.

PO

I think Chris has made it pretty clear that the fitting of an automatic
system is not at this time a practical solution. I think he has also made
it pretty clear that once the sequence starts the result, as far as the tug
is concerned, is inevitable.

This is one of those situations where tug pilots are going to have to
decide what risks they are willing to take. I would support any tug pilot
who said that he would not tow a glider on a CoG or Compromise hook. On the
other hand I would not tell him he could not do it. There is also a
responsibility for those of us who teach aerotowing to really get across to
students the danger, to the tug pilot, of getting out of position. I am not
sure we have done this in the past, I know I have not been as pedantic as I
should in getting this point home.
Tug pilots do not always know the people they are towing so they are
perhaps not aware of the experience, or lack of it, of the pilot on the
back. In those circumstances the saviour should be the authoriser. We all
know that does not work. Perhaps tug pilots need to be more circumspect in
who they are prepared to tow.