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

On Wednesday, February 19, 2014 7:36:56 PM UTC-5, Steve Leonard wrote:
Chris has hit the nail on the head with his testing and reporting. When it goes wrong, it goes wrong fast. Faster than you can possibly react. We can try all we want to teach how to not do it, but it will sometimes happen. Why not come up with a system that will minimize the risk to the towpilot? I think we have concluded that for now, we cannot eliminate it without creating other significant problems. If we are considering an automatic system, why wait to full nose up elevator and nose down 20 degrees? As Chris said, if you are there, you are probably doomed. If the nose is down 10 degrees (or maybe even 5?) and the elevator is half way to full up, something is wrong. Would you agree? On tow, elevator is up, nose is up. On descent, elevator is down, nose is down. Why not develop and test a parallel releasing system that has inputs from a gyro for pitch attitude and a simple sensor for elevator position? Test at safe altitude, as Chris and company did. I know this is not going to prevent kiting, but if we can reduce the risk when it happens and maybe not even add bad failure modes, it should be well worth the effort. Just my thoughts. Steve Leonard

The least expensive improvement that many operations can make immediately is to adopt the use of longer tow ropes.The effect of pilot error is drastically reduced by this one simple change. Many places I fly as guest use ropes that are marginally short as matter of standard practice.
We try not to use ropes shorter than 200 ft.
UH

On Wednesday, February 19, 2014 8:08:24 PM UTC-6, wrote:
The least expensive improvement that many operations can make immediately is to adopt the use of longer tow ropes. The effect of pilot error is drastically reduced by this one simple change. Many places I fly as guest use ropes that are marginally short as matter of standard practice. We try not to use ropes shorter than 200 ft. UH

Same practice at Sunflower Gliderport. (my home base)

Steve

At 02:08 20 February 2014, wrote:
On Wednesday, February 19, 2014 7:36:56 PM UTC-5, Steve Leonard wrote:
Chris has hit the nail on the head with his testing and reporting. When
i=
t goes wrong, it goes wrong fast. Faster than you can possibly react. We
ca=
n try all we want to teach how to not do it, but it will sometimes
happen.
=
Why not come up with a system that will minimize the risk to the
towpilot?
=
I think we have concluded that for now, we cannot eliminate it without
crea=
ting other significant problems. If we are considering an automatic
system,=
why wait to full nose up elevator and nose down 20 degrees? As Chris
said,=
if you are there, you are probably doomed. If the nose is down 10
degrees
=
(or maybe even 5?) and the elevator is half way to full up, something is
wr=
ong. Would you agree? On tow, elevator is up, nose is up. On descent,
eleva=
tor is down, nose is down. Why not develop and test a parallel releasing
sy=
stem that has inputs from a gyro for pitch attitude and a simple sensor
for=
elevator position? Test at safe altitude, as Chris and company did. I
know=
this is not going to prevent kiting, but if we can reduce the risk when
it=
happens and maybe not even add bad failure modes, it should be well
worth
=
the effort. Just my thoughts. Steve Leonard

The least expensive improvement that many operations can make immediately
i=
s to adopt the use of longer tow ropes.The effect of pilot error is
drastic=
ally reduced by this one simple change. Many places I fly as guest use
rop=
es that are marginally short as matter of standard practice.
We try not to use ropes shorter than 200 ft.
UH


The tests I described were done with ropes about 180 feet long, I think it
would probably need ropes of 400 feet or more to give sufficient time for
there to be even a chance of releasing in time if a kiting event started.
There are practical reasons for not using ropes that long at most sites.

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.

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 Thu, 20 Feb 2014 09:55:38 -0800, kirk.stant wrote:

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).

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?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

At 14:36 20 February 2014, 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.

Which is why I suggested speed camera technology to detect a faster than
normal rapid climb of the glider in relation to the tug. Measuring the
height or even the angle is just not going to give the system time to work.
Detecting the rapid vertical acceleration early will do that. Even if the
pilot in the glider detects the early acceleration, inertia probably means
that he will be unable to correct in time.