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

Dan, that might work if the towplane's attitude was constant. However, during a kiting event, the towplane is being pitched nose down, so the hitch would not likely get activated, as the hitch to surrounding structure angle may not change. I wish it could be that simple, but it isn't. See the previous post about a kiting even where the glider was still in sight in the mirror, even though the towplane was significantly nose down.

Steve

Per Steve's comment that the only energy for the glider comes from the towplane engine I have a comment which is in many ways a request for enlightenment.
I had a kiting incident at Moriarty in my 27. All worked out OK, other than fright, mostly because I got off quickly, just as the kite began. How it began is not very clear at all, and much of this is later rationalization I fear, best I can come up with. Skilled glider pilots who watched failed to come up with much, if anything, that helps.
Tow began normally. Within first few seconds, both still on the ground, the tow plane bobbled a bit -- nothing that much given that this was Moriarty on a nice strong thermal day. When I hit the place where the bobble happened the 27 popped into the air a few feet.
My explanation is that I made moves that exaggerated what followed. Anybody with better ideas please join in.
I pushed forward on the stick, the glider began to react, as I flew out of whatever it was caused the bobble, the glider sank fast towards the concrete, so I (rationalizing) assume I moved the stick back to ease the bump.
The glider bounced off the concrete, not that hard but bounced. The one thing I believe I truly remember is that there was a bit of a snake in the rope -- ie some slack.
The tow plane was of course accelerating. So (rationalizing) as the glider bounces up I have at best neutral stick, maybe a bit aft still, and the slack comes out of the rope and the glider at this point began the early stage of a winch launch.
I know that I did two things quickly -- one was hit the release, the other was to get the nose down. Once at flying speed, at maybe 30 feet (I don't have any real guesses from the observers), I moved to the right to use the taxiway. Then, when the tow plane came in sight going like stink out of my way down the runway, I moved back and landed on the runway.
Not a scratch, including to the tow plane's prop. Good towing Mike Stogner..
My point is that there can be a hell of a lot of energy in the rope if for some reason it gains a bit of slack and is then turned into an elastic band.. For some strange reason weak links sometimes do not bust when they might be expected to ...






On Sunday, February 9, 2014 3:27:23 PM UTC-7, 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.

On 2/21/2014 3:23 PM, wrote:
Per Steve's comment that the only energy for the glider comes from the
towplane engine I have a comment which is in many ways a request for
enlightenment.
Snip...
I pushed forward on the stick, the glider began to react, as I
flew out of whatever it was caused the bobble, the glider sank fast towards
the concrete, so I (rationalizing) assume I moved the stick back to ease
the bump. The glider bounced off the concrete, not that hard but bounced.
The one thing I believe I truly remember is that there was a bit of a snake
in the rope -- ie some slack. The tow plane was of course accelerating. So
(rationalizing) as the glider bounces up I have at best neutral stick,
maybe a bit aft still, and the slack comes out of the rope and the glider
at this point began the early stage of a winch launch. I know that I did
two things quickly -- one was hit the release, the other was to get the
nose down.
Snip...
My point is that there can
be a hell of a lot of energy in the rope if for some reason it gains a bit
of slack and is then turned into an elastic band. For some strange reason
weak links sometimes do not bust when they might be expected to ...

Ropes indeed can store significant strain energy. Compared to poly ropes,
nylon rope is akin to a rubber band. Is anyone in the U.S. still using nylon
towropes behind their tugs? Real fun for beginning students and instructors...!

As to how that energy got into the rope...I'm with Steve.

Your written assessment sounds entirely plausible to me. Good job dealing with
your unwanted surprise.

Bob W.

"Dan Marotta" wrote:

I just had a flash (brain fart) of an automatic release system. You
mechanical guys could probably make something like this work. Please bear
with me...

How about simply inverting a Schweizer release and mounting it on a sturdy
hinge. Then, in addition to the normal release rope, which the tuggie
should be able to release in any attutude, add a second release cable fixed
at the under side of the release, and forward of the hinge, such that, if
the hinge is rotated upward (as in kiting) the fixed cable draws tight and
releases the rope? The length of the fixed cable could be set to open the
release at a preset angle.

Seems simple enough. Please show me the error of my ways.

"kirk.stant" wrote in message
...
On Friday, February 21, 2014 11:41:20 AM UTC-6, Steve Leonard wrote:

Kirk, I don't think we want to consider a bridle from the tips. This
would require HUGE spar changes, as you could easily impart 500 lbs aft
force at both wing tips. This will pretty likely fold the wings aft and
make for a very high speed, although only vertical and down capable, tug.
Maybe the missle you were hoping to use? :-)

I know that - I was really just throwing out some hare-brained ideas to see
what would stick.

My solution is a lot simpler:

1. Near term: Replace ALL Schweizer tow hooks on tow planes with Tost hooks
(so you can at least release if you get upset high enough), then provide
very specific training to ALL glider pilots on the cause an effect of a tug
upset, to include a demo ride in a towplane at the receiving end. And treat
all aerotows of gliders with CG hooks as potential kiting accidents and
brief accordingly.

2. Long term: some sort of sensor controlled automatic release on tug to
eliminate problem, assuming our respective government aviation agencies will
agree to their installation. Make it mandatory so the numbers are high
enough to drop the price down to something affordable. And remember, it has
to not only apply to fixed tow hooks, but also to retractable tow ropes (now
how do you measure the forces?).

I still prefer the Bearcat towplane option. Kite away!

Kirk
66

We had a Schweizer tow hook on one of our tugs years ago, and it made
me suspicious about its performance under load. I decided to test it
by fixing the end of the tow rope round a tree and setting the tug on
full throttle. It was absolutley impossible to release at the tug end,
no matter how hard I pulled on the release cable.

We don't use them any more.

Steve Leonard wrote:

On Thursday, February 20, 2014 5:48:43 PM UTC-6, Colin Wray wrote:
Most people posting here do not understand the word "instantaneous". Chris
Rollings, and the CofG hook exponents, are the only people who get it.

Glad to see you chose my post to respond to when you decide to imply that most of us (myself included) don't know what "instantaneous" means, Colin. I work a lot with electrical guys and your idea of "instantaneous" is an eternity to them. Half a second? That is a lifetime in the world of electrical system responses. I work with regulations and know about human reaction times. I know that the event being discussed will go from start to disaster in less than typical event to recognition to reaction time. Even for someone who is expecting it and knows exactly when it starts.

I understand the dynamics of it at least as well as you do. Maybe better. I know that cambered wing sections can generate higher C/L max than symmetric sections. I know what a C/L versus Alpha curve is. I know its slope. I can tell you what it takes in terms of AOA change to go from 1 g to minus 1 g. I know that a wing that is 5 times the size of the tail on the towplane, and attached to the towplane via the tow rope roughly 20 times further back from the towplane aerodynamic center than the tail will be able to produce more than 30 times the pitching moment to the towplane than the tail on the towplane can. I know that if the glider does this, there is NO way the towplane pilot can do anything to stop it. Again, I don't think the tail on the towplane stalls. I think the glider effectively becomes the "tail" of the tug, and it can and does overpower anything the elevator might do.

I agree that a system based on angular displacement of the rope likely won't work, as the relative angle between the two planes doesn't change much and you can slowly go higher than this and not cause a problem to the tug. Longer ropes can damp the response, but not eliminate it. I read what Chris wrote, and I get it. I get it that you can do this and not break a proper strength rope. You have once again assumed that because someone is proposing an automatic system to try and minimize (notice, I know I can NOT prevent it) the impact, you assumed that "he doesn't get it".

Design thoughts. When is a towplane nose down? In an upset or on descent. If the towplane is in its descent, where is the elevator? It certainly won't be more than half way to full nose up! It might be a quarter to half way up during a normal tow, but the nose will not be below the horizon. And if a kiting event starts, the towpilot will no doubt start pulling back. What I have proposed is a starting point for evaluation of an automatic system to MINIMIZE the risk to the tuggie in the event of kiting. I strongly suspect that 10 degrees nose down is too much, as the tug will already have gone negative load factor, and the event must be stopped before then. But, I am proposing a starting point.

Have you got a better proposal for a starting point for a system to MINIMIZE the risk to the tuggie? In case you are wondering, autothrottle won't Minimize it. :-)

End of rant.

Steve Leonard

Steve, I bow to your vatly superior knowledge of aerodynamics, and I
can now see that you really do 'get it'. (Sorry). I was basing my
comments on little more than my involvement in two of these episodes.

I guess that in real kiting accidents, where the rope remains
reasonably tight throughout, there will be a measurable time before it
becomes unrecoverable. My upset as the tug pilot featured a slack rope
which snapped tight, so any kiting must have been akin to a sling shot
for the glider.

At 22:23 21 February 2014, wrote:
Per Steve's comment that the only energy for the glider comes from the
towp=
lane engine I have a comment which is in many ways a request for
enlightenm=
ent.
I had a kiting incident at Moriarty in my 27. All worked out OK, other
tha=
n fright, mostly because I got off quickly, just as the kite began. How
it
=
began is not very clear at all, and much of this is later rationalization
I=
fear, best I can come up with. Skilled glider pilots who watched failed
t=
o come up with much, if anything, that helps.
Tow began normally. Within first few seconds, both still on the ground,
the=
tow plane bobbled a bit -- nothing that much given that this was
Moriarty
=
on a nice strong thermal day. When I hit the place where the bobble
happen=
ed the 27 popped into the air a few feet. =20
My explanation is that I made moves that exaggerated what followed.
Anybody=
with better ideas please join in.
I pushed forward on the stick, the glider began to react, as I flew out
of
=
whatever it was caused the bobble, the glider sank fast towards the
concret=
e, so I (rationalizing) assume I moved the stick back to ease the
bump.=20
The glider bounced off the concrete, not that hard but bounced. The one
th=
ing I believe I truly remember is that there was a bit of a snake in the
ro=
pe -- ie some slack.
The tow plane was of course accelerating. So (rationalizing) as the
glider
=
bounces up I have at best neutral stick, maybe a bit aft still, and the
sla=
ck comes out of the rope and the glider at this point began the early
stage=
of a winch launch. =20
I know that I did two things quickly -- one was hit the release, the
other
=
was to get the nose down. Once at flying speed, at maybe 30 feet (I
don't
=
have any real guesses from the observers), I moved to the right to use
the
=
taxiway. Then, when the tow plane came in sight going like stink out of
my
=
way down the runway, I moved back and landed on the runway.
Not a scratch, including to the tow plane's prop. Good towing Mike
Stogner=
..
My point is that there can be a hell of a lot of energy in the rope if
for
=
some reason it gains a bit of slack and is then turned into an elastic
band=
.. For some strange reason weak links sometimes do not bust when they
might
=
be expected to ...

A while ago there was a discussion as to whether it was a good idea to have
one's hand on the release during the early stages of an aerotow as we do
for winching. I believe that we may have found a good reason for doing so.
It is clear from what everyone has said that it is vital that the glider
releases BEFORE it takes over the control of pitch on the tug, or at the
very least before the tug is pitched nose down. Searching for the release
may take more time than the tug pilot has. In most, if not all these
incidents the glider pilot survives.

On that note I do not think it is of any importance whether the tailplane
on the tug stalls or the glider overcomes the available power of the
elevator, the mechanism is not important, the important thing is that the
tug is pitched nose down so far that considerable height is needed for
recovery.

On 22/02/2014 05:10, kirk.stant wrote:

My solution is a lot simpler:
....snips
I still prefer the Bearcat towplane option. Kite away!

I liked the Bearcat idea - in fact I like Kirk's whole approach to the
discussion. I put the idea to some old colleagues who flew Sea Furies
who also liked it.

Unfortunately, there is a simpler solution which has been implemented
and proved effective at zero cost but doesn't involve Bearcat
endorsements for tuggies. You don't get kiting if you fly low tow.

Australia's move to low tow was to prevent kiting in an era of low wing
loading gliders in a country with sharp-edged thermals. It's been an
effective solution and it's globally applicable even today. If kiting
is the problem Steve and others make it out to be, low tow will be
adopted immediately. If it's not, this whole discussion could just look
like a giant circle w..k.

Steve?

GC


Kirk 66

In article om GC writes:
On 22/02/2014 05:10, kirk.stant wrote:

My solution is a lot simpler:
...snips
I still prefer the Bearcat towplane option. Kite away!

I liked the Bearcat idea - in fact I like Kirk's whole approach to the
discussion. I put the idea to some old colleagues who flew Sea Furies
who also liked it.

Unfortunately, there is a simpler solution which has been implemented
and proved effective at zero cost but doesn't involve Bearcat
endorsements for tuggies. You don't get kiting if you fly low tow.

You don't get kiting if you fly normal "high" tow behind the towplane,
if you remain in control.

If you don't remain in control, starting from low tow is not going to
make a lot of difference.

If the tug has just lifted off, being in low tow sounds a bit difficult,
but that would be a particularly hazardous time.


As for automatic methods to mitigate the problem, perhaps the solution
is not to modify tow planes, but to modify gliders. If the glider is
in a very high pitch attitude on tow, it might be a good time to automatically
release.

Another modification might be to attach the tow rope to the top of the glider.
This would cause the tow force to pitch the glider down.


Is this more of a problem when folks try to tow a slow glider like a 2-33 at
high speeds?


Alan

On 22/02/2014 16:17, Alan wrote:

...You don't get kiting if you fly normal "high" tow behind the towplane,
if you remain in control.

If you don't remain in control, starting from low tow is not going to
make a lot of difference.

Experience (tens of thousands of aerotows) shows there is an enormous
difference. The inadequate control and time to go from high tow to
kiting is orders of magnitude different from that required to go from
low tow to kiting. In fact, I've never heard of that ever happening.
Even with low time students. Kiting from high tow, however, is
apparently so common as to need a whole new system of electronic
whizzbangery and gallons of bandwidth to stop.

If the tug has just lifted off, being in low tow sounds a bit difficult,
but that would be a particularly hazardous time.

Yes. Liftoff is a time to be wary and we train accordingly.
Nevertheless, all I can say is that low tow has prevented kiting
accidents for many years. But don't take my word for it, keep this
ridiculous discussion going with another screwball idea for pivoting,
autoswivelling, pitch-sensing, stick-following nonsense.

If the issue is serious - as it was in Australia - flying low tow will
solve it. If it isn't - see my previous post.

GC



As for automatic methods to mitigate the problem, perhaps the solution
is not to modify tow planes, but to modify gliders. If the glider is
in a very high pitch attitude on tow, it might be a good time to automatically
release.

Another modification might be to attach the tow rope to the top of the glider.
This would cause the tow force to pitch the glider down.


Is this more of a problem when folks try to tow a slow glider like a 2-33 at
high speeds?

Alan

The time difference to go from low tow to kiting compared to high tow to
kiting is about 1 second - try it at safe altitude. As observed you can't
take-off in low tow so the highest risk time, just after take off when the
combination is accelerating, is exactly the same. The transition from
normal tow to low tow, early in the climb, puts the glider into the
turbulence of the prop-wash which may well cause the, less than one second,
loss of control which is all that is needed to start the kiting. Finally,
low tow on a glider with a C of G hook, leaves the rope wrapped around the
side of the cockpit, not really a good idea and C of G hooks are where the
danger lies.

The cheapest mechanical solution is, fit a nose hook to any glider that is
going to be aerotowed.

My best estimate of low level kiting fatal/serious accident frequency is of
the order of one in a million. "Tens of thousands of aerotows" is not a
big enough sample to draw conclusions.

At 07:58 22 February 2014, GC wrote:
On 22/02/2014 16:17, Alan wrote:

...You don't get kiting if you fly normal "high" tow behind the
towplane,
if you remain in control.

If you don't remain in control, starting from low tow is not going
to
make a lot of difference.

Experience (tens of thousands of aerotows) shows there is an enormous
difference. The inadequate control and time to go from high tow to
kiting is orders of magnitude different from that required to go from
low tow to kiting. In fact, I've never heard of that ever happening.
Even with low time students. Kiting from high tow, however, is
apparently so common as to need a whole new system of electronic
whizzbangery and gallons of bandwidth to stop.

If the tug has just lifted off, being in low tow sounds a bit
difficult,
but that would be a particularly hazardous time.

Yes. Liftoff is a time to be wary and we train accordingly.
Nevertheless, all I can say is that low tow has prevented kiting
accidents for many years. But don't take my word for it, keep this
ridiculous discussion going with another screwball idea for pivoting,
autoswivelling, pitch-sensing, stick-following nonsense.

If the issue is serious - as it was in Australia - flying low tow will
solve it. If it isn't - see my previous post.

GC



As for automatic methods to mitigate the problem, perhaps the
solution
is not to modify tow planes, but to modify gliders. If the glider is
in a very high pitch attitude on tow, it might be a good time to
automatically
release.

Another modification might be to attach the tow rope to the top of
the
glider.
This would cause the tow force to pitch the glider down.


Is this more of a problem when folks try to tow a slow glider like a
2-33 at
high speeds?

Alan