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

At 14:14 20 February 2014, Hans Heydra wrote:
Hi Guys
Just read through the last 66posts on this page. After what happened here
in South Africa this week I though something needs to be done. I was
thinking along the lines of a tilt switch. Whilst noodeling I cam across
a
UK company see...
http://www.leveldevelopments.com/pro...tilt-switches/
and what they did for another company.
http://www.leveldevelopments.com/cas...ghting-system/
This really stood out....
**The final sensor was a custom solution comprising a three axis
accelerometer and 3 axis tilt sensor. The tilt sensor used a customized
filter algorithm to ensure the dynamics of the vehicle in use did not
cause
false alarms.**

This system can be tested a low initial cost with a light on the tug
pilots
dashboard every time it is triggered to iron out false alarms.

Only thing you need is a tilt switch. With a safety ON and OFF.
Basically before the tug the pilot turns "ON" the tilt switch switch then
proceeds with the tug. If the tug is pulled into a **30 degree dive the
tilt switch is activated and drops the rope automatically through a yet
to
be worked out system.(Could be explosive, pneumatic or some other method)
Once the glider pilot has released (under normal gliding conditions) the
switch is turned "OFF" by the tug pilot so it will not be deposited over
some farm field when the tuggie dives back to the field at **30 degrees.

**30 degrees is an example could be 25, 35, 40 Tests would have to be
done.



To repeat one point, our tests left us convinced that the tail-plane on the
tow-plane stalled quite early on in the kiting event, it would need some
tests to check exactly how early. It might be that the nose down angle
would have to be quite small, something that could happen in turbulence
perhaps.

On Thursday, February 20, 2014 9:36:03 AM UTC-5, Chris Rollings wrote:


To repeat one point, our tests left us convinced that the tail-plane on the

tow-plane stalled quite early on in the kiting event, it would need some

tests to check exactly how early. It might be that the nose down angle

would have to be quite small, something that could happen in turbulence

perhaps.


That's a pretty interesting (and gut wrenching to this tow pilot) point Chris.

Stall warning flipper on the horizontal? Feasible?

-Evan Ludeman / T8

The more I think about it I think we are going down the wrong path. Move the tow-hook to the CG of the towplane and the problem pretty much goes away.

Back to some sort of bridle from the wingtips so any pulling vector is through the CG (or close).

Or an "outrigger" on each side of fuselage sticking out far enough for the bridle to clear the tail, again installed close to the CG. That might be an easier structural solution, but the geometry would make the outriggers pretty long!

Kirk
66

Just looking to properly understand and maybe differently explain the dynamics of the situation, Chris. What you described before was:

"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"."

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?). Once the glider has pitched the plane sufficiently nose down, the wing of the towplane is actually pushing DOWN (even though the pilot is pulling the nose up), hench the negative g felt in the towplane. The glider wing on its long moment arm can produce a far greater pitching moment than the horizontal tail on its short moment arm. The towplane transitions from steady, upright, one g flight, to negative g doward arcing flight because the glider changes the angle of attack of the wing of the towplane from positive to negative.

Your pictures taken later show this is likely. The glider has a large pitch change before it starts its vertical displacement. Similarly, the towplane will get a large pitch change nose down before it starts to deviate from its climbing or level flight path. And it will happen so rapidly, the pilot will not be able to tell if it happened because he pulled back and the tail stalled, or because the glider created such a large nose down pitching moment. I strongly suspect the results would be the same if the towpilot did nothing to try and keep the nose up in the CG hook kiting event. Glider pitches towplane, towplane responds due to lift vector changing magnitude initially, then direction.

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).

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 Thursday, February 20, 2014 1:21:58 PM UTC-6, Steve Leonard wrote:

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?

No pyrotechnics? How are we going to grow the sport without pyrotechnics (and 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 make it easy to mount tow hook near CG on center wing.
7. "Tail-gunner" facing backwards in towplane with both hands on tow release. 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 release quick!).
9. Use webcam on tail of towplane to track glider and release him when he gets out of position (displacement, rate, or combination of both). As added incentive, use bluetooth to set off smoke bomb in glider cockpit if release is triggered.
10. Take all glider pilots up in a two-seat towplane (with a briefed student 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

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

Steve Leonard wrote:

Just looking to properly understand and maybe differently explain the dynamics of the situation, Chris. What you described before was:

"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"."

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?). Once the glider has pitched the plane sufficiently nose down, the wing of the towplane is actually pushing DOWN (even though the pilot is pulling the nose up), hench the negative g felt in the towplane. The glider wing on its long moment arm can produce a far greater pitching moment than the horizontal tail on its short moment arm. The towplane transitions from steady, upright, one g flight, to negative g doward arcing flight because the glider changes the angle of attack of the wing of the towplane from positive to negative.

Your pictures taken later show this is likely. The glider has a large pitch change before it starts its vertical displacement. Similarly, the towplane will get a large pitch change nose down before it starts to deviate from its climbing or level flight path. And it will happen so rapidly, the pilot will not be able to tell if it happened because he pulled back and the tail stalled, or because the glider created such a large nose down pitching moment. I strongly suspect the results would be the same if the towpilot did nothing to try and keep the nose up in the CG hook kiting event. Glider pitches towplane, towplane responds due to lift vector changing magnitude initially, then direction.

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).

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

Most people posting here do not understand the word "instantaneous".
Chris Rollings, and the CofG hook exponents, are the only people who
get it.

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 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.

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