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

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, that's a very good hypothesis, could well be right, it certainly
fits the facts as well as the conclusion we reached did. Fit an angle of
attack indicator to a tow-plane and go and try it.

At 20:21 20 February 2014, kirk.stant wrote:
On Thursday, February 20, 2014 1:21:58 PM UTC-6, Steve Leonard wrote:
=20
Time to start working on a secondary pull system (sorry, Kirk. No
explos=
ive bolts or missles. Would be more fun, though.) using attitude and
eleva=
tor positon. Or maybe attitude and pitch rate. Need to keep it as
simple
=
(fewest inputs and software) as possible. I do like the idea of initial
te=
sts of set values to turn on a light in the cockpit for the pilot to see
th=
at the automatic system will have operated. Got any reasons not to start
a=
t 10 degrees nose down pitch attitude and half way to max nose up
elevator
=
travel?

No pyrotechnics? How are we going to grow the sport without pyrotechnics
(a=
nd a TV reality show...).

How about:

1. Tow gliders vertically with helicopters (It's been done..)
2. Have the towplane push the glider with a reverse towbar setup.
3. Mount the glider on top of the towplane - space-shuttle/747 style.
4. Two words: Electromagnetic catapults.
5. Automatic BRS on towplane triggered by sudden pitch-down.
6. Custom design towplane made from 2 Pawnee fuselages, F-82 style; would
m=
ake it easy to mount tow hook near CG on center wing.
7. "Tail-gunner" facing backwards in towplane with both hands on tow
releas=
e. Better not **** that guy off before you launch!
8. Use F8F Bearcats for towplanes - they would climb so steeply that if
the=
glider kited, it would only level off the towplane (and then the
glider's
=
wings would come off as you accelerated through glider's Vne - Better
relea=
se quick!).
9. Use webcam on tail of towplane to track glider and release him when he
g=
ets out of position (displacement, rate, or combination of both). As
added=
incentive, use bluetooth to set off smoke bomb in glider cockpit if
releas=
e is triggered.
10. Take all glider pilots up in a two-seat towplane (with a briefed
studen=
t and instructor in the glider) and at a safe altitude demonstrate what
an
=
upset looks and feels like from both ends of the string.

I like #8, myself, but I think #10 would work pretty darn good.

Kirk
66
Tuggie

On 21/02/2014 06:21, Steve Leonard wrote:

Not to be to "chicken or egg" here, but, I don't think the horizontal
tail of the towplane stalled. I think the glider provided an upward
force, creating a nose down pitching moment far greater than the
elevator could counter (obviously, right?).

Mmm. ...and how would that differ from a stalled tailplane? Isn't it
the same as an accelerated (1g) wing stall?

We know that this event does not happen often, but when it does, it
often has catastrophic results. I don't think there is a practical
way to attach the rope to the CG of the towplane. So, we are left
with training (which we have seen does not eliminate the problem) or
some sort of automatic system (since it has been documented that it
is unlikely a pilot can react fast enough to be able to save his or
her own life if it goes really bad).

Experience shows that training NEVER eliminates problems but can reduce
a problem's frequency to acceptable levels. Kiting is already a very
rare event as another poster (Chris himself, IIRC) showed and this is
largely due to training.

Experience also shows that automation may eliminate a problem but also
produces failure cases (which must, in any case, be trained for).
Further, as Air France's A330 showed, automation almost always means
that pilots aren't as good at dealing with the problem as they would be
if they knew their training was the only thing stopping the accident.

No. In this case, well-trained, alert glider and tug pilots are the
cost-effective solution to the problem. The automated release is pie in
the sky.

GC


Time to start working on a secondary pull system (sorry, Kirk. No
explosive bolts or missles. Would be more fun, though.) using
attitude and elevator positon. Or maybe attitude and pitch rate.
Need to keep it as simple (fewest inputs and software) as possible.
I do like the idea of initial tests of set values to turn on a light
in the cockpit for the pilot to see that the automatic system will
have operated. Got any reasons not to start at 10 degrees nose down
pitch attitude and half way to max nose up elevator travel?

Steve Leonard

On 21/02/2014 11:16, son_of_flubber wrote:

.... snips
3)What happens in rotor? Is it possible to stall the horizontal
stabilizer of the tow plane? Perhaps it would be good to
automatically released in severe rotor, especially if my AGL and
distance to a landable spot were within predefined limits. Someday I
think I might stay on tow in rotor longer than I should. A mode 3
alarm might provide timely and objective advice to the pilot in
rotor. The device could confidently detect inverted flight on tow
and auto-release immediately.

4)If you had this kind of sensor and computation power in a glider,
it could detect and warn of things like 'imminent spin on turn to
final' and other mistakes. Once you had the hardware platform
installed a lot of useful safety features could be added.

Are you an Airbus engineer?

GC

On Thursday, February 20, 2014 1:31:56 PM UTC-7, Martin Gregorie wrote:

Back to some sort of bridle from the wingtips so any pulling vector is

through the CG (or close).



I'm sure that would work well in the air, but isn't there a potential

problem during the landing roll-out? With no tension on the tow rope it

seems to me that you've got a U-shaped loop of rope dragging on the

ground behind the tow plane which would provide considerable drag on a

grass field if it isn't recently mown. Would this also be a problem at

the start of the take-off roll?

Well, you could make the bridle in two pieces that connect at the release, and come apart when the glider is released; you would now have a long towrope trailing one wingtip and a short one trailing the other.

Starting to get more complicated, of course...

Kirk

Lots of good ideas, but some of the dynamics of a tug upset has been
missed. Chris Rollings mentioned the loads in the rope rapidly increasing
from c50lbs to over 700lbs as the glider assumes a winch launch attitude.
This load on the tug will RAPIDLY slow it down, thus losing flying speed.
So not only does the glider climb, the tug descends with rapidly falling
airspeed, and the elevator becoming ineffective. As the ug loses speed it
will pitch nose down anyway.

Chris also mentioned a very strong deceleration, and I can vouch for this
when a K6E kited behind me on a tow at Aboyne. The K6 pilot missed the
release toggle due to wearing gloves, and had already started his climbing
turn. He realised his mistake and releassed the rope, by which time I was
steeply nose down with little airspeed, albeit at 4000 feet! I was
effectively a passenger during the upset, but interestingly did not lose
sight of the glider in the tug mirror, showing the tail was NOT pulled up.
I have always been very wary of tugging gliders on belly hooks since!

Terry Slater

At 13:16 21 February 2014, kirk.stant wrote:
On Thursday, February 20, 2014 1:31:56 PM UTC-7, Martin Gregorie wrote:

Back to some sort of bridle from the wingtips so any pulling vector
is

through the CG (or close).



I'm sure that would work well in the air, but isn't there a potential

problem during the landing roll-out? With no tension on the tow rope it


seems to me that you've got a U-shaped loop of rope dragging on the

ground behind the tow plane which would provide considerable drag on a

grass field if it isn't recently mown. Would this also be a problem at

the start of the take-off roll?

Well, you could make the bridle in two pieces that connect at the
release,
and come apart when the glider is released; you would now have a long
towrope trailing one wingtip and a short one trailing the other.

Starting to get more complicated, of course...

Kirk

Terry, the dynamic of the towplane slowing was not lost on me. The only source for the kiting energy of the glider is the tug. Any climb rate for the glider above that being provided by the engine of the tug will come out of the tug in the form of lost airspeed. That is probably the first thing the towpilot will notice. But, the same loss of speed could occur as a result of the glider's powerful dive brakes openning, so that cannot be used as a trigger for an auto system. Also, slowing the tug will not make it pitch down, unless the slowing is to below the stall speed of the tug. It will make it start to drop, as lift is now less than weight. And, Terry, if you were nose down, your tail likely was pulled up. In an amount that kept the glider in your mirror. Your airpseed loss was the transfer of your kinetic energy to the increased kinetic and potential energy of the glider. The nose down was likely a combo of the glider pulling your tail up and possibly stalling of the wing of the tug. You effectively became a moving anchor point for the glider.

GC, stalled tail and accelerated stalls are not at all the same. Maybe you need some training? :-) My belief is that a kiting glider with a wing that is 3-5 times the size of the tugs tail can provide far greater tug pitch authority than the tail on the tug. You don't have to stall the tug's tail in order to produce more force with something else than it can produce.

You can test the stalled tail theory by flying the tug sans glider at tow speed. Push the stick rapidly forward to create the nose down pitch rate, then pull rapidly back to arrest it. If the stick back pull does not stop the nose down pitch, the tail was stalled. If it does, the tail is not stalled. This may not be the case for an aerobatic plane intentionally doing an outside snap.

As to "well trained glider pilots", ask Terry about the "well trained pilot" he was tugging who thought he pulled the release, so he started his climbing turn away. Well trained or not these things do happen. Not often, but they do happen. And when they happen at low altitude, the result is usually fatal. First step in training is to burn it into the heads of all glider pilots that on air tow, you don't even consider turning away from the towplane until you have seen the rope going away. Amazingly simple but forgotten more than most would imagine.

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? :-)

Mark, fairleads over the tail have issues, too, as boxing the wake will quickly show. But, maybe the air load and the pull of the rope in the other direction will sort of cancel, and not risk bending the fin? However, if there is restriction to up or down pull, you have lost the benefit.

As to other failure modes of an automatic system and the "need to train for them", well, don't we already train for rope breaks? If the system is designed well, it won't make a disconnect any more likely than it is now. And, it is not a change to the airframe, but only an additional means of operating the release. I tend to think that this would be much easier to certify, once you have shown sufficient reliability of the system by design, and that it does not substantially increase the risk of an unplanned seperation of the tug and the glider in practice.

So, with what we have available to us today, why are we afraid to try and design a system to reduce this risk?

Steve Leonard

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

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

At 18:10 21 February 2014, kirk.stant wrote:
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
wou=
ld 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
th=
e missle you were hoping to use? :-)

I know that - I was really just throwing out some hare-brained ideas to
see=
what would stick. =20

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
v=
ery 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
trea=
t all aerotows of gliders with CG hooks as potential kiting accidents and
b=
rief accordingly.






2. Long term: some sort of sensor controlled automatic release on tug to
el=
iminate problem, assuming our respective government aviation agencies
will
=
agree to their installation. Make it mandatory so the numbers are high
enou=
gh 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



I see no way to do this ,but,
put a pylon on the main spar and tow from the cofg ,shorten the vertical
stabiliser and add some area below the fus then protect the tail feathers
with
struts.
If I remember correctly ski boats went from a rope on the back to center
poles to give more maneuverability .
Try getting that past EASA or the FAA .