KGARS - Kiting Glider Automatic Relase System

On Tuesday, May 19, 2020 at 10:56:50 AM UTC-7, wrote:
On Tuesday, May 19, 2020 at 1:14:22 PM UTC-4, wrote:
I’d suggest we get input from tow pilots who’ve actually experienced an upset. I suspect tow rope angle is not likely to help, but tow plane pitch change and elevator position are likely inputs that can be measured and provide reasonable value. But it’s just a guess. Asking someone who’s been there makes a lot of sense.

Increased towrope angle and increase in tension precede pitch change. Measuring and controlling from these inputs would seem to me to be better than controlling off pitch change, which is an output, and elevator position which is a following output.
FWIW
UH

It is true that increasing tow rope angle precedes a towplane upset, it is not exclusive to upsets. That is why I suggested putting a load cell on the tow release to measure the force on the tow rope which is a better indicator of a kiting event.

Tom

It is true that increasing tow rope angle precedes a towplane upset, it
is
=
not exclusive to upsets. That is why I suggested putting a load cell on
the=
tow release to measure the force on the tow rope which is a better
indicat=
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would be
good... Don't we have them now.. they are called Weak-Links. All you
need to do is correctly calculate the maximum tension that you could allow.


As a starting point.. A 350kg Glider with a 35:1 L/D ratio just requires
10kg of pull to keep it flying. So factor in a safety margin to allow for
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs to
be made for safe aero-tow.

At 11:21 20 May 2020, Sci Fi wrote:
As a starting point.. A 350kg Glider with a 35:1 L/D ratio just requires
10kg of pull to keep it flying. So factor in a safety margin to allow
for
turbulence, of say 10x, and what you need is a 150kg Weak-Link.

In addition to drag, during a normal tow, the rope needs to pull the glider

uphill! Typically (6knots climb rate at 60 knots airspeed) that requires
10%
of the weight of the glider - 35kg in your example.

So total steady-state 'pull' would be 45kg, and your safety factor makes
for
a 450kg weak link. Just what is routinely used in the UK! YMMV.
J.

Le mercredi 20 mai 2020 13:30:05 UTC+2, Sci Fi a écritÂ*:

It is true that increasing tow rope angle precedes a towplane upset, it
is
=
not exclusive to upsets. That is why I suggested putting a load cell on
the=
tow release to measure the force on the tow rope which is a better
indicat=
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would be
good... Don't we have them now.. they are called Weak-Links. All you
need to do is correctly calculate the maximum tension that you could allow.


As a starting point.. A 350kg Glider with a 35:1 L/D ratio just requires
10kg of pull to keep it flying. So factor in a safety margin to allow for
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs to
be made for safe aero-tow.

The weakest one from Tost is 300 kg (green) and is usually used in Europe for aerotow.
Anything lower would be less then the static thrust of the towplane. That would be the safest configuration of all, beacause you wouldn't even leave the ground.

On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset, it
is
=
not exclusive to upsets. That is why I suggested putting a load cell on
the=
tow release to measure the force on the tow rope which is a better
indicat=
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would be
good... Don't we have them now.. they are called Weak-Links. All you
need to do is correctly calculate the maximum tension that you could allow.


As a starting point.. A 350kg Glider with a 35:1 L/D ratio just requires
10kg of pull to keep it flying. So factor in a safety margin to allow for
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs to
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: the decision would not be based on a static load level, it would be based on the input of several sensors using a technique called state estimation. An upset state or event is characterized by a rapidly increasing load on the tow rope, a rapidly increasing pitch down attitude of the towplane, and a decreasing towplane airspeed. Note: a weak link is not a sensor.

Tom

At 15:11 20 May 2020, 2G wrote:
On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset,
it
is
=3D
not exclusive to upsets. That is why I suggested putting a load cell
on
the=3D
tow release to measure the force on the tow rope which is a better
indicat=3D
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would
b=
e
good... Don't we have them now.. they are called Weak-Links. All
you
need to do is correctly calculate the maximum tension that you could
allo=
w.
=20
=20
As a starting point.. A 350kg Glider with a 35:1 L/D ratio just
requires
10kg of pull to keep it flying. So factor in a safety margin to allow
fo=
r
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This
is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs
t=
o
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: the
decision
=
would not be based on a static load level, it would be based on the input
o=
f several sensors using a technique called state estimation. An upset
state=
or event is characterized by a rapidly increasing load on the tow rope,
a
=
rapidly increasing pitch down attitude of the towplane, and a decreasing
to=
wplane airspeed. Note: a weak link is not a sensor.

Tom

Sorry Tom, but I was brought up in the Horse-drawn era, where some very
elegant and simple solutions were found for problems. We engineered
systems in the most uncomplicated ways, because there were no 'Apps' or
'Actuators' or Hydraulics to make things complicated.
What could be simpler than a 'Weak-Link' of 150 kg breaking strain..?
Maybe the BGA needs to amend the rules to state that for aero-tows the
weak-link needs to be 1/3 the breaking strain of that used for winch
launches.
Glider owners would then need to have two lead ropes, one for winching with
a white or blue link. and the other with a green Tost link.

Naming no names but it's quite a hard pull off soft grass (aka Sod) for a
K21 with two
large people and a Pawnee! And surely the device should be "Kiting Off
Upwards
Automatic release System"?
- KOUGARS.


At 15:45 20 May 2020, Sci Fi wrote:
At 15:11 20 May 2020, 2G wrote:
On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset
it
is
=3D
not exclusive to upsets. That is why I suggested putting a load cel
on
the=3D
tow release to measure the force on the tow rope which is a better
indicat=3D
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload
would
b=
e
good... Don't we have them now.. they are called Weak-Links. Al
you
need to do is correctly calculate the maximum tension that you could
allo=
w.
=20
=20
As a starting point.. A 350kg Glider with a 35:1 L/D ratio jus
requires
10kg of pull to keep it flying. So factor in a safety margin to allow
fo=
r
turbulence, of say 10x, and what you need is a 150kg Weak-Link. Thi
is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link
needs
t=
o
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: th
decision
=
would not be based on a static load level, it would be based on the
input
o=
f several sensors using a technique called state estimation. An upset
state=
or event is characterized by a rapidly increasing load on the tow rope
a
=
rapidly increasing pitch down attitude of the towplane, and a decreasing
to=
wplane airspeed. Note: a weak link is not a sensor.

Tom

Sorry Tom, but I was brought up in the Horse-drawn era, where some ver
elegant and simple solutions were found for problems. We engineere
systems in the most uncomplicated ways, because there were no 'Apps' o
'Actuators' or Hydraulics to make things complicated.
What could be simpler than a 'Weak-Link' of 150 kg breaking strain..?
Maybe the BGA needs to amend the rules to state that for aero-tows th
weak-link needs to be 1/3 the breaking strain of that used for winc
launches.
Glider owners would then need to have two lead ropes, one for winching
wit
a white or blue link. and the other with a green Tost link.

Once I started thinking about kiting accidents as a total energy transfer that robbed the towplane of airspeed, it definitely changed how I felt about the opportunity for release and recovery. Below a few hundred feed, it may not matter if the release happens after you have lost flying speed.

I've often felt that the 80%-200% rule for weak links was faulty. At least for protecting the tow pilot.

At least one element of a kiting accident is the transfer of energy from the towplane to the glider. In the simplest form, we want to restrict the gliders ability to strip the towplane of flying energy. This should be the job of the weak link. F=MA provides some guidance here. We have a pretty light towplane with a Cessna 150/150. Probably in the 700kg range with fuel and a pilot.

If a kiting accident decelerates the towplane 6kts every second. That's maybe 2-3 seconds from the start of the incident to complete loss of flying airspeed.

Go metric so the units are easier and round a bit. 3m/s^2 of acceleration. F=MA. F=700kg*3m/s^2 = 2100N.

That's about 214kg of force. ~471pounds. That's not far off of 80% of gross of a 1-26. But way less than 80% of say a 2-33.

But the issue is that weak links seem to be built around protecting the glider, when maybe they should be around protecting the tow pilot. Regardless of whether the tow pilot is hauling a light 1-26 aloft or a ballasted open class glider, it's the force required to stop the towplane from flying that is what worries me.

Turbulence and slack line can certainly impart higher forces on a line than is required for steady state towing and climbing.

Has anyone ever explored the idea of a short bungee as a shock absorber? Something to slow the shock load, but allow the weak link to be more appropriately sized to the towplane?

I have thankfully never had anyone kite behind me in the towplane. I have been yanked all over the place by students in a 2-33 though. Low and inside on a turn and they decide that's the time to correct. Woof, there goes 5kts of airspeed in a heartbeat when my pitch attitude hasn't changed.

I've also had people get very high on tow because of a thermal or they went wide on a turn and that extra speed resulted in extra altitude. When it happens slowly and the energy isn't really coming from me in the towplane, it's not that noticeable. Even with the glider 40ft high, the pitch force if they aren't climbing is negligible.

I'm glad to see so many people pouring some thought into this problem. It's scary to have to acknowledge that my life is entirely in the hands of the person I'm towing for the first minute or so of the tow. A simple fix like shock absorbers and appropriate weak link rules sure would be nice versus automation and complexity and those failure modes that come with that.

Morgan


On Wednesday, May 20, 2020 at 8:45:06 AM UTC-7, Sci Fi wrote:
At 15:11 20 May 2020, 2G wrote:
On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset,
it
is
=3D
not exclusive to upsets. That is why I suggested putting a load cell
on
the=3D
tow release to measure the force on the tow rope which is a better
indicat=3D
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would
b=
e
good... Don't we have them now.. they are called Weak-Links. All
you
need to do is correctly calculate the maximum tension that you could
allo=
w.
=20
=20
As a starting point.. A 350kg Glider with a 35:1 L/D ratio just
requires
10kg of pull to keep it flying. So factor in a safety margin to allow
fo=
r
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This
is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs
t=
o
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: the
decision
=
would not be based on a static load level, it would be based on the input
o=
f several sensors using a technique called state estimation. An upset
state=
or event is characterized by a rapidly increasing load on the tow rope,
a
=
rapidly increasing pitch down attitude of the towplane, and a decreasing
to=
wplane airspeed. Note: a weak link is not a sensor.

Tom

Sorry Tom, but I was brought up in the Horse-drawn era, where some very
elegant and simple solutions were found for problems. We engineered
systems in the most uncomplicated ways, because there were no 'Apps' or
'Actuators' or Hydraulics to make things complicated.
What could be simpler than a 'Weak-Link' of 150 kg breaking strain..?
Maybe the BGA needs to amend the rules to state that for aero-tows the
weak-link needs to be 1/3 the breaking strain of that used for winch
launches.
Glider owners would then need to have two lead ropes, one for winching with
a white or blue link. and the other with a green Tost link.

On Wednesday, May 20, 2020 at 9:45:59 AM UTC-7, Morgan wrote:
Once I started thinking about kiting accidents as a total energy transfer that robbed the towplane of airspeed, it definitely changed how I felt about the opportunity for release and recovery. Below a few hundred feed, it may not matter if the release happens after you have lost flying speed.

I've often felt that the 80%-200% rule for weak links was faulty. At least for protecting the tow pilot.

At least one element of a kiting accident is the transfer of energy from the towplane to the glider. In the simplest form, we want to restrict the gliders ability to strip the towplane of flying energy. This should be the job of the weak link. F=MA provides some guidance here. We have a pretty light towplane with a Cessna 150/150. Probably in the 700kg range with fuel and a pilot.

If a kiting accident decelerates the towplane 6kts every second. That's maybe 2-3 seconds from the start of the incident to complete loss of flying airspeed.

Go metric so the units are easier and round a bit. 3m/s^2 of acceleration. F=MA. F=700kg*3m/s^2 = 2100N.

That's about 214kg of force. ~471pounds. That's not far off of 80% of gross of a 1-26. But way less than 80% of say a 2-33.

But the issue is that weak links seem to be built around protecting the glider, when maybe they should be around protecting the tow pilot. Regardless of whether the tow pilot is hauling a light 1-26 aloft or a ballasted open class glider, it's the force required to stop the towplane from flying that is what worries me.

Turbulence and slack line can certainly impart higher forces on a line than is required for steady state towing and climbing.

Has anyone ever explored the idea of a short bungee as a shock absorber? Something to slow the shock load, but allow the weak link to be more appropriately sized to the towplane?

I have thankfully never had anyone kite behind me in the towplane. I have been yanked all over the place by students in a 2-33 though. Low and inside on a turn and they decide that's the time to correct. Woof, there goes 5kts of airspeed in a heartbeat when my pitch attitude hasn't changed.

I've also had people get very high on tow because of a thermal or they went wide on a turn and that extra speed resulted in extra altitude. When it happens slowly and the energy isn't really coming from me in the towplane, it's not that noticeable. Even with the glider 40ft high, the pitch force if they aren't climbing is negligible.

I'm glad to see so many people pouring some thought into this problem. It's scary to have to acknowledge that my life is entirely in the hands of the person I'm towing for the first minute or so of the tow. A simple fix like shock absorbers and appropriate weak link rules sure would be nice versus automation and complexity and those failure modes that come with that.

Morgan


On Wednesday, May 20, 2020 at 8:45:06 AM UTC-7, Sci Fi wrote:
At 15:11 20 May 2020, 2G wrote:
On Wednesday, May 20, 2020 at 4:30:05 AM UTC-7, Sci Fi wrote:

It is true that increasing tow rope angle precedes a towplane upset,
it
is
=3D
not exclusive to upsets. That is why I suggested putting a load cell
on
the=3D
tow release to measure the force on the tow rope which is a better
indicat=3D
or of a kiting event.

Tom

Tom, if you made the load cell rupture when it sensed an overload would
b=
e
good... Don't we have them now.. they are called Weak-Links. All
you
need to do is correctly calculate the maximum tension that you could
allo=
w.
=20
=20
As a starting point.. A 350kg Glider with a 35:1 L/D ratio just
requires
10kg of pull to keep it flying. So factor in a safety margin to allow
fo=
r
turbulence, of say 10x, and what you need is a 150kg Weak-Link. This
is
much less than the lowest (White.) Link made so far. But as you know
those links are designed for Winch (Kiting.) Launches. Our Link needs
t=
o
be made for safe aero-tow.

I simplified the criteria in the spirit of understandability: the
decision
=
would not be based on a static load level, it would be based on the input
o=
f several sensors using a technique called state estimation. An upset
state=
or event is characterized by a rapidly increasing load on the tow rope,
a
=
rapidly increasing pitch down attitude of the towplane, and a decreasing
to=
wplane airspeed. Note: a weak link is not a sensor.

Tom

Sorry Tom, but I was brought up in the Horse-drawn era, where some very
elegant and simple solutions were found for problems. We engineered
systems in the most uncomplicated ways, because there were no 'Apps' or
'Actuators' or Hydraulics to make things complicated.
What could be simpler than a 'Weak-Link' of 150 kg breaking strain..?
Maybe the BGA needs to amend the rules to state that for aero-tows the
weak-link needs to be 1/3 the breaking strain of that used for winch
launches.
Glider owners would then need to have two lead ropes, one for winching with
a white or blue link. and the other with a green Tost link.

I am a firm believer of the KISS principal: Keep It Simple, Stupid. If a bungie shock absorber and a weaker weak link worked, fine. But it seems to me that we have had 80 years to perfect the weak link and it just hasn't happened. Since then we have had a progression in computer technology from zero to self-driving vehicles. Thus it seems natural to me to apply this technology to this problem.

Tom

I am a firm believer of the KISS principal: Keep It Simple, Stupid. If a bungie shock absorber and a weaker weak link worked, fine. But it seems to me that we have had 80 years to perfect the weak link and it just hasn't happened. Since then we have had a progression in computer technology from zero to self-driving vehicles. Thus it seems natural to me to apply this technology to this problem.

Tom

Bungie isn't really much a of a shock absorber, the exponential nature of the spring force isn't the best here. Combine that (or a spring) with an actual shock absorber and autorelease when the shock is compressed enough, you can set the limit of stolen energy via the tow-rope to pretty much anything within a certain time.

As a software engineer who's done plenty of embedded stuff also, I would much prefer an analog solution.