View Full Version : Re: KGARS - Kiting Glider Automatic Relase System
Karl Striedieck[_2_]
May 19th 20, 03:06 AM
Richard Green of the Wycombe Test Group, High Wycombe, Bucks. UK designed and tested an auto release and offered to sell me one back in 1980. His long hand letter to me said that he was "an old age pensioner" so maybe he and his BGA certified release are something of history.
The engineering blue print of it is 3X2 feet in size, but a side view is on a normal size sheet of paper which I'd be happy to send to anyone. A Schweizer release is attached to the device which essentially operates when the angle up exceeds a certain limit.
He said the club made over 1000 tows with it and there were no "spurious releases."
Karl Striedieck
On Monday, May 18, 2020 at 7:06:34 PM UTC-7, Karl Striedieck wrote:
> Richard Green of the Wycombe Test Group, High Wycombe, Bucks. UK designed and tested an auto release and offered to sell me one back in 1980. His long hand letter to me said that he was "an old age pensioner" so maybe he and his BGA certified release are something of history.
>
> The engineering blue print of it is 3X2 feet in size, but a side view is on a normal size sheet of paper which I'd be happy to send to anyone. A Schweizer release is attached to the device which essentially operates when the angle up exceeds a certain limit.
>
> He said the club made over 1000 tows with it and there were no "spurious releases."
>
> Karl Striedieck
The question is has it every been tested in an actual towplane upset event? One other poster here thinks that there won't be much of an angle of the towrope to the towplane.
On Monday, May 18, 2020 at 7:06:34 PM UTC-7, Karl Striedieck wrote:
> Richard Green of the Wycombe Test Group, High Wycombe, Bucks. UK designed and tested an auto release and offered to sell me one back in 1980. His long hand letter to me said that he was "an old age pensioner" so maybe he and his BGA certified release are something of history.
>
> The engineering blue print of it is 3X2 feet in size, but a side view is on a normal size sheet of paper which I'd be happy to send to anyone. A Schweizer release is attached to the device which essentially operates when the angle up exceeds a certain limit.
>
> He said the club made over 1000 tows with it and there were no "spurious releases."
>
> Karl Striedieck
This is the 1980 article from Sailplane and Gliding:
https://drive.google.com/file/d/0B1OVcDrcv8ULTDVYSkJ6dkIxM0U/edit
On Tuesday, May 19, 2020 at 5:41:00 AM UTC-7, wrote:
> On Monday, May 18, 2020 at 7:06:34 PM UTC-7, Karl Striedieck wrote:
> > Richard Green of the Wycombe Test Group, High Wycombe, Bucks. UK designed and tested an auto release and offered to sell me one back in 1980. His long hand letter to me said that he was "an old age pensioner" so maybe he and his BGA certified release are something of history.
> >
> > The engineering blue print of it is 3X2 feet in size, but a side view is on a normal size sheet of paper which I'd be happy to send to anyone. A Schweizer release is attached to the device which essentially operates when the angle up exceeds a certain limit.
> >
> > He said the club made over 1000 tows with it and there were no "spurious releases."
> >
> > Karl Striedieck
>
>
>
> This is the 1980 article from Sailplane and Gliding:
>
> https://drive.google.com/file/d/0B1OVcDrcv8ULTDVYSkJ6dkIxM0U/edit
But Chris Rollings later said it didn't work:
https://groups.google.com/forum/#!topic/rec.aviation.soaring/1eZiSHzqC7g%5B151-175%5D
On Tuesday, May 19, 2020 at 1:42:38 PM UTC+1, wrote:
> On Tuesday, May 19, 2020 at 5:41:00 AM UTC-7, wrote:
> > On Monday, May 18, 2020 at 7:06:34 PM UTC-7, Karl Striedieck wrote:
> > > Richard Green of the Wycombe Test Group, High Wycombe, Bucks. UK designed and tested an auto release and offered to sell me one back in 1980. His long hand letter to me said that he was "an old age pensioner" so maybe he and his BGA certified release are something of history.
> > >
> > > The engineering blue print of it is 3X2 feet in size, but a side view is on a normal size sheet of paper which I'd be happy to send to anyone. A Schweizer release is attached to the device which essentially operates when the angle up exceeds a certain limit.
> > >
> > > He said the club made over 1000 tows with it and there were no "spurious releases."
> > >
> > > Karl Striedieck
> >
> >
> >
> > This is the 1980 article from Sailplane and Gliding:
> >
> > https://drive.google.com/file/d/0B1OVcDrcv8ULTDVYSkJ6dkIxM0U/edit
>
> But Chris Rollings later said it didn't work:
>
> https://groups.google.com/forum/#!topic/rec.aviation.soaring/1eZiSHzqC7g%5B151-175%5D
Wouldn't it be better to design a automatic release based on the tug flight parameters such as say primarily sudden change of pitch downwards? I thought that what Chris Rollings wrote in his 2014 RAS post about the difficulty of designing an effective system based on relative angle of the tow rope was long generally accepted.
Once again, aviation reminds us that simplistic solutions (including my own weak-ass ideas) are rarely as "simple" as they first appear. Which brings us full circle to the original question, "How hard could it be?"
Apparently, quite a bit harder. Maybe better training IS the best option.
Look at water skiing. A good slalom skier can slow, and turn a heavy boat. Pro ski boats have a hitch mount on a center pole in the boat instead of the stern, also they have huge rudders and skegs down the center of the boat to resist when the skier pulls over to the side. This is a 200 lb person moving a really heavy boat with a tiny ski in water. Compare this with a 3000 lb towplane pulling a 800 lb glider (with a huge wing) letting an aero tow turn into a winch launch. The glider loads the rope, (2000 lbs) slows, and pitches the towplane down so quickly the tug doesn't have a chance. A glider boxing the wake can pull a towplane all over the place, if he doesn't resist. Towplanes can resist lateral movement by banking the wings. In a kiting situation only the elevator is any good. So, the glider can pitch the towplane down without having an extreme up rope angle. The towplane would need cg hook and a big elevator. The glider pilot must pay attention during tow! If you absolutely have to deal with a problem that takes your attention from the towplane, then release first! Now deal with the canopy or whatever.. Don't fiddle with a cellphone, camera, flight computer, radio, canopy, bug in cockpit, look around, or anything that takes your focus off the tow. Do this before takeoff or before you even move onto the runway. The towplane must be your entire world until 1500 ft at least.
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.
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
Per JPG above... towrope angle has been studied and was determined to not be a viable input, even though it happens first.
Chris Rollings wrote in his 2014 RAS post about the difficulty of designing an effective system based on relative angle of the tow rope was long generally accepted.
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
Sci Fi
May 20th 20, 12:21 PM
>
>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.
James Metcalfe
May 20th 20, 01:03 PM
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.
Tango Whisky
May 20th 20, 01:39 PM
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
Sci Fi
May 20th 20, 04:45 PM
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.
Steve Thompson[_2_]
May 20th 20, 05:02 PM
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.
>
>
>
Morgan[_2_]
May 20th 20, 05:45 PM
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.
On Wednesday, May 20, 2020 at 7:30:05 AM UTC-4, 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.
SiFi - if you check your POH under 'Weak Link', you will find a mfg recommended weak link breaking strength for winch launch AND one for aero-tow. They may be different, depending on the glider.
We must get away from this 80%-200% 'rule'! There is an FAR out there that states that if the glider has an approved POH at the time of certification, whatever is in this book takes precedence over the FARs.
So if we were to start using stronger (i.e. thicker) ropes like our European brethren do, instead of one from the aviation department of your local hardware store AND outfit it with the proper weak link, we may actually kill tow birds with one stone: reduce or eliminate rope breaks due to wear and tear and increase safety by having the proper weak link installed, which may actually break in a kiting event.
Uli
'AS'
I'm neither a software nor mechanical engineer, but I think the relationship between force and deflection might be linear, not exponential
On Wednesday, 20 May 2020 19:49:22 UTC+1, wrote:
> 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.
On Wednesday, May 20, 2020 at 2:57:36 PM UTC-7, wrote:
> I'm neither a software nor mechanical engineer, but I think the relationship between force and deflection might be linear, not exponential
>
>
> On Wednesday, 20 May 2020 19:49:22 UTC+1, wrote:
> > 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.
I know you can upset a towplane w/o breaking the rope or weak link because it has happened. The towplane's elevator may be able to generate 10-15% of its all-up weight, or 250-300 lb, and it is probably already using half of that in normal flight. And even if the rope or weak link breaks that does not guarantee that the towplane can recover. The rope did break in the 1999 towplane upset accident at Ephrata, WA.
Tom
On Wednesday, May 20, 2020 at 5:57:36 PM UTC-4, wrote:
> I'm neither a software nor mechanical engineer, but I think the relationship between force and deflection might be linear, not exponential
Yeah, was thinking energy, ie. stored energy that's going to come back also.
With a linear-ish shock absorber, the energy dissipated is linear.
With a bungee/spring alone relying on a weak(er) link, not much happens until you get very close to the breaking condition. With linear energy dissipation you can tune the release condition much better, and you won't have the springback effect.
On Wednesday, May 20, 2020 at 5:42:13 PM UTC-7, wrote:
> On Wednesday, May 20, 2020 at 5:57:36 PM UTC-4, wrote:
> > I'm neither a software nor mechanical engineer, but I think the relationship between force and deflection might be linear, not exponential
>
> Yeah, was thinking energy, ie. stored energy that's going to come back also.
> With a linear-ish shock absorber, the energy dissipated is linear.
>
> With a bungee/spring alone relying on a weak(er) link, not much happens until you get very close to the breaking condition. With linear energy dissipation you can tune the release condition much better, and you won't have the springback effect.
Show me the data that any such tuning is even possible. I have just described how it isn't.
Tom
On Wednesday, May 20, 2020 at 11:09:55 PM UTC-4, 2G wrote:
> On Wednesday, May 20, 2020 at 5:42:13 PM UTC-7, wrote:
> > On Wednesday, May 20, 2020 at 5:57:36 PM UTC-4, wrote:
> > > I'm neither a software nor mechanical engineer, but I think the relationship between force and deflection might be linear, not exponential
> >
> > Yeah, was thinking energy, ie. stored energy that's going to come back also.
> > With a linear-ish shock absorber, the energy dissipated is linear.
> >
> > With a bungee/spring alone relying on a weak(er) link, not much happens until you get very close to the breaking condition. With linear energy dissipation you can tune the release condition much better, and you won't have the springback effect.
>
> Show me the data that any such tuning is even possible. I have just described how it isn't.
>
> Tom
The only comment I've seen from you wrt shock absorbing was about bungees. I should make it clear that that's not what I'm talking about when referring to shock absorbers. I'm talking about the shock absorbers you use in car/motorcycle suspensions. The racing stuff is fully tunable via preload setting, compression resistance and rebound.
For towing gliders, the preload should be set to somewhere near expected 'normal' tow load on the rope. Compression set so that by the time the absorber has travelled the full length (and releasing) the energy dissipated is less than would cause the tow-plan to stall. Rebound setting should be relative to the energy gain for the ow-plane in 'normal' tow. With such settings, it should be impossible to pull on the rope enough to cause the tow-plane to stall.
This doesn't solve the pitch issue, but I'd rather be nose down not stalled than stalled.
Unfortunately, I think we can discount any load sensing concepts (weak links, load cells, etc) for the following reason. Kiting events are rare and so for any system to be widely adopted, the frequency of any nuisance releases of any system need to be similarly rare or hopefully less rare. Otherwise the system will be a PIA and will be removed because of the nuisances.
Two situations that come to mind that would/could occur that would lead nuisance releases are the following
1. This spring the ground was soft and it took 100% power from the Pawnee to get a 2 seat glider to start to move.
2. Slack line situations, either real or simulated for training. The impact load when the slack comes out will likely overpower any weak link and then we've created a PTT.
As such, I suspect for a KGARS system to be workable, it needs to go back to a parallel operation of the mechanical tow release in the cockpit, but only when very specific upset conditions are detected. (airspeed, pitch angle, elevator position, etc.)
KISS is nice, but if weak links worked reliably for upsets, we'd probably be doing it already.
With all due respect.
Mark
I've had two kiting incidents as an aerotow pilot, both above 2000agl, when the glider didn't release as desired. In both cases it felt like a mild aerobatic maneuver: a smooth, uncontrollable pitch down, not alarming to me due to the safe altitude. My attention was so focussed on the pitch-down that I didn't notice any airspeed decrease, although it probably occurred. At that altitude, I was more curious than worried, and decided to delay releasing, and waited to see what happened. The glider released quickly, and I then recovered easily, although I didn't think to note the altitude loss.
From those experiences, I wonder if it might be a good thing for all aerotow pilots to experience this intentionally, at altitude, as part of training, akin to the 200ft 'ptt' practice we do. The practice could be pre-agreed, and take place after the tow pilot did a clearing turn and said (by radio) he was ready. The glider would start an abrupt climb, and the proper procedure would be for the towpilot to release or cut the rope as soon as full back elevator was reached and the pitch down had not stopped. The rope would however be lost, or dropped somewhere by the glider.
It would be best if the towpilot was comfortable with mild aerobatics before trying this. Chris Rollings did not mention any sense of danger in his kiting tests. Such intentional kiting exercises might build up a practical body of knowledge about best recovery methods, and height loss, and would increase the awareness of tow and glider pilots to the danger of low-altitude kiting.
On Thursday, May 21, 2020 at 4:53:54 AM UTC-7, wrote:
> Unfortunately, I think we can discount any load sensing concepts (weak links, load cells, etc) for the following reason. Kiting events are rare and so for any system to be widely adopted, the frequency of any nuisance releases of any system need to be similarly rare or hopefully less rare. Otherwise the system will be a PIA and will be removed because of the nuisances.
>
> Two situations that come to mind that would/could occur that would lead nuisance releases are the following
>
> 1. This spring the ground was soft and it took 100% power from the Pawnee to get a 2 seat glider to start to move.
>
> 2. Slack line situations, either real or simulated for training. The impact load when the slack comes out will likely overpower any weak link and then we've created a PTT.
>
> As such, I suspect for a KGARS system to be workable, it needs to go back to a parallel operation of the mechanical tow release in the cockpit, but only when very specific upset conditions are detected. (airspeed, pitch angle, elevator position, etc.)
>
> KISS is nice, but if weak links worked reliably for upsets, we'd probably be doing it already.
>
> With all due respect.
>
> Mark
Doing proper state estimation would prevent any unexpected KGARS activation.. For example, your ground roll situation the towplane is obviously not flying (inadequate airspeed, still at ground elevation and no increase in pitch angle). I assume that you mean a slack line will break the weak link, which isn't an inadvertent activation of KGARS. This IS a solvable problem.
Tom
George Haeh
May 22nd 20, 04:21 AM
FAA and other CAAs seem to have no interest in the rope. So a KGARS could be installed between the towplane weak link and the main rope.
You would need angle sensors (as available for digital levels) on the towplane elevator and stabiliser to send a flash to the KGARS unit when release parameters are satisfied.
That would be when the stabiliser is pointing downhill while the elevator is at a steeper angle.
There are remote photoflash units that trigger on a flash from a master unit.
So you need a KGARS that on receiving the flash would let go as long as it's not from a Whelen strobe.
Alternatively Bluetooth can transmit over that distance. A stick switch could also signal via Bluetooth, but might need the transmitter at the tail.
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