Rope Tension Meter for Auto Tow

On Dec 21, 10:27*pm, "Larry Goddard" wrote:
" wrote in message

:



On Dec 20, 1:40 pm, Craig wrote:
On Dec 20, 9:07 am, bildan wrote:

On Dec 19, 3:52 pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

You can buy strain gauge based electronic tension systems with hand
held readout units either wired or wireless. They are sometimes
called "crane scales" or "dynomometers". Just Google "tension load
cell". You'll want a 0-2000 Lbf unit.

There are also clevis attached USB tension load cells which plug into
your laptop which come with appropriate software. The USB units are
nice since they are powered by the USB bus - just plug and play.

There are others too. I've been looking for a similar inline load cell
and will probably purchase fromhttp://www.futek.com/. I don't have
any relation to the company, but have been looking for a while and
their offerings appear to be pretty solid.
Craig- Hide quoted text -

- Show quoted text -

Great information

Thanks to all

Bill Snead

Just out of curiosity, where is one of the items placed in the system???

They look like a big "S". *Where do you attach what?

Larry

There will be threaded holes in the top and bottom of the "S" for I-
Bolts. The "S-Beam" shape is to maximize the deformation (strain)
under load so the thin film strain gauges have a larger signal to work
with. It's a good idea to enclose the load cell in a housing to
protect it.

On Dec 22, 9:05*am, bildan wrote:
On Dec 21, 10:27*pm, "Larry Goddard" wrote:



" wrote in message

:

On Dec 20, 1:40 pm, Craig wrote:
On Dec 20, 9:07 am, bildan wrote:

On Dec 19, 3:52 pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

You can buy strain gauge based electronic tension systems with hand
held readout units either wired or wireless. They are sometimes
called "crane scales" or "dynomometers". Just Google "tension load
cell". You'll want a 0-2000 Lbf unit.

There are also clevis attached USB tension load cells which plug into
your laptop which come with appropriate software. The USB units are
nice since they are powered by the USB bus - just plug and play.

There are others too. I've been looking for a similar inline load cell
and will probably purchase fromhttp://www.futek.com/. I don't have
any relation to the company, but have been looking for a while and
their offerings appear to be pretty solid.
Craig- Hide quoted text -

- Show quoted text -

Great information

Thanks to all

Bill Snead

Just out of curiosity, where is one of the items placed in the system???

They look like a big "S". *Where do you attach what?

Larry

There will be threaded holes in the top and bottom of the "S" for I-
Bolts. *The "S-Beam" shape is to maximize the deformation (strain)
under load so the thin film strain gauges have a larger signal to work
with. * It's a good idea to enclose the load cell in a housing to
protect it.

eye bolts?

On Dec 19, 5:52*pm, " wrote:
We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

LCM Systems can offer various solutions, depending on what the force
range is that you want to measure.

Try this link for the sensor http://www.lcmsystems.com/sta-4

and for a handheld display, we would recommend:-

http://www.lcmsystems.com/TR150

You could but the complete kit, calibrated an ready to go for less
than $550

On Dec 23, 6:37*am, STEVE SARGEANT wrote:
On Dec 19, 5:52*pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

LCM Systems can offer various solutions, depending on what the force
range is that you want to measure.

Try this link for the sensorhttp://www.lcmsystems.com/sta-4

and for a handheld display, we would recommend:-

http://www.lcmsystems.com/TR150

You could but the complete kit, calibrated an ready to go for less
than $550

Could someone describe how you use the tension meter when auto
towing? Once you are towing at a constant tension, does it change how
you fly the glider on tow? What is the typical tension maintained
when towing a 2-33? Also some pictures how the electronic load cell
is rigged with the release hitch would be helpful. Thank for all the
good information

Bill Snead

On Dec 24, 8:12*pm, " wrote:
On Dec 23, 6:37*am, STEVE SARGEANT wrote:



On Dec 19, 5:52*pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

LCM Systems can offer various solutions, depending on what the force
range is that you want to measure.

Try this link for the sensorhttp://www.lcmsystems.com/sta-4

and for a handheld display, we would recommend:-

http://www.lcmsystems.com/TR150

You could but the complete kit, calibrated an ready to go for less
than $550

Could someone describe how you use the tension meter when auto
towing? *Once you are towing at a constant tension, does it change how
you fly the glider on tow? *What is the typical tension maintained
when towing a 2-33? *Also some pictures how the electronic load cell
is rigged with the release hitch would be helpful. *Thank for all the
good information

Bill Snead

With constant tension, the pilot controls airspeed with pitch attitude
(Nose up, slow down - nose down, speed up) just as in free flight. In
a thermal, the car will back off to maintain constant tension as the
thermal provides a fraction of the energy. In a downdraft, the tow
car will add power to maintain tension. It's a very pleasant way to
launch.

A 2-33 is a special case since the elevator is so small and the hook,
even the "compromise hook", is so far forward. The limited elevator
authority makes it difficult to control airspeed at any tension
value. Also, Schweizer didn't provide information on weak link or
best climb speed for ground launch. At any tension greater than about
75% of the gross weight, a 2-33 will accelerate even with full up
elevator. Most people find 55 MPH works as well as anything.

Note that winch or auto towing puts stress on the wing roughly equal
to a loop. (~3.5G) I seem to remember a letter from Schweizer around
1980 strongly discouraging loops due to the age of the 2-33. 30 years
on, I'm not comfortable ground launching one.

The tension load cell fits into the tow line at the tow car right at
the attach point. Usually in the rope just aft of the tow ring.
However, while a bit more complicated, it's safer for the load cell to
be part of the cars tow release mechanism. The full towing force
must pass through the load cell to get a correct reading.

On Dec 24, 9:03*pm, bildan wrote:
On Dec 24, 8:12*pm, " wrote:





On Dec 23, 6:37*am, STEVE SARGEANT wrote:

On Dec 19, 5:52*pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

LCM Systems can offer various solutions, depending on what the force
range is that you want to measure.

Try this link for the sensorhttp://www.lcmsystems.com/sta-4

and for a handheld display, we would recommend:-

http://www.lcmsystems.com/TR150

You could but the complete kit, calibrated an ready to go for less
than $550

Could someone describe how you use the tension meter when auto
towing? *Once you are towing at a constant tension, does it change how
you fly the glider on tow? *What is the typical tension maintained
when towing a 2-33? *Also some pictures how the electronic load cell
is rigged with the release hitch would be helpful. *Thank for all the
good information

Bill Snead

With constant tension, the pilot controls airspeed with pitch attitude
(Nose up, slow down - nose down, speed up) just as in free flight. *In
a thermal, the car will back off to maintain constant tension as the
thermal provides a fraction of the energy. *In a downdraft, the tow
car will add power to maintain tension. *It's a very pleasant way to
launch.

A 2-33 is a special case since the elevator is so small and the hook,
even the "compromise hook", is so far forward. *The limited elevator
authority makes it difficult to control airspeed at any tension
value. *Also, Schweizer didn't provide information on weak link or
best climb speed for ground launch. *At any tension greater than about
75% of the gross weight, a 2-33 will accelerate even with full up
elevator. * Most people find 55 MPH works as well as anything.

Note that winch or auto towing puts stress on the wing roughly equal
to a loop. (~3.5G) *I seem to remember a letter from Schweizer around
1980 strongly discouraging loops due to the age of the 2-33. *30 years
on, I'm not comfortable ground launching one.

The tension load cell fits into the tow line at the tow car right at
the attach point. *Usually in the rope just aft of the tow ring.
However, while a bit more complicated, it's safer for the load cell to
be part of the cars tow release mechanism. * The full towing force
must pass through the load cell to get a correct reading.- Hide quoted text -

- Show quoted text -

I'm a little confused. If the weak link is less than 200% of the max
AUW of the glider, how is is possible to generate ~3.5G?

I'm a little confused. If the weak link is less than 200% of the max
AUW of the glider, how is is possible to generate ~3.5G?

During a winch launch, the load from the winch line is concentrated at
the wing root. It is not distributed along the wing span as normal
flight loads are. While the pilot may be experiencing something around 1
g during a winch launch, the wing roots may be "feeling" the equivalent
of high g loads.

On Dec 29, 3:26*pm, Grider Pirate wrote:
On Dec 24, 9:03*pm, bildan wrote:



On Dec 24, 8:12*pm, " wrote:

On Dec 23, 6:37*am, STEVE SARGEANT wrote:

On Dec 19, 5:52*pm, " wrote:

We at the Fault Line Flyers Glider Club in Briggs Texas want to build
or buy a tension meter for our auto tow operation.

Does anyone have experience that might be helpful.

Bill Snead
6W

LCM Systems can offer various solutions, depending on what the force
range is that you want to measure.

Try this link for the sensorhttp://www.lcmsystems.com/sta-4

and for a handheld display, we would recommend:-

http://www.lcmsystems.com/TR150

You could but the complete kit, calibrated an ready to go for less
than $550

Could someone describe how you use the tension meter when auto
towing? *Once you are towing at a constant tension, does it change how
you fly the glider on tow? *What is the typical tension maintained
when towing a 2-33? *Also some pictures how the electronic load cell
is rigged with the release hitch would be helpful. *Thank for all the
good information

Bill Snead

With constant tension, the pilot controls airspeed with pitch attitude
(Nose up, slow down - nose down, speed up) just as in free flight. *In
a thermal, the car will back off to maintain constant tension as the
thermal provides a fraction of the energy. *In a downdraft, the tow
car will add power to maintain tension. *It's a very pleasant way to
launch.

A 2-33 is a special case since the elevator is so small and the hook,
even the "compromise hook", is so far forward. *The limited elevator
authority makes it difficult to control airspeed at any tension
value. *Also, Schweizer didn't provide information on weak link or
best climb speed for ground launch. *At any tension greater than about
75% of the gross weight, a 2-33 will accelerate even with full up
elevator. * Most people find 55 MPH works as well as anything.

Note that winch or auto towing puts stress on the wing roughly equal
to a loop. (~3.5G) *I seem to remember a letter from Schweizer around
1980 strongly discouraging loops due to the age of the 2-33. *30 years
on, I'm not comfortable ground launching one.

The tension load cell fits into the tow line at the tow car right at
the attach point. *Usually in the rope just aft of the tow ring.
However, while a bit more complicated, it's safer for the load cell to
be part of the cars tow release mechanism. * The full towing force
must pass through the load cell to get a correct reading.- Hide quoted text -

- Show quoted text -

I'm a little confused. *If the weak link is less than 200% of the max
AUW of the glider, how is is possible to generate ~3.5G?

Your question has implied two parts. One is the approved weak link
for winch launch and the other is the "G equivalent" wing spar bending
moment.

First, the approved weak link. The well known 80-200% rule (FAR
91.309 a (3) ii) applies only to aero tow, not winch launch, and then
only to those gliders whose Approved Flight Manual did not otherwise
specify a weak link since an AFM trumps 91.309 a (3) ii. AFAIK, only
Schweizer failed to specify weak links. Expect this to be clarified
in future updates of the FAR's.

All JAR-22 gliders will have a weak link specification in their AFM
for both aero tow and winch launch. Sometimes the aero tow and winch
launch weak links are the same, sometimes different. Almost
universally, a plus or minus 10% tolerance will also be specified.
FAR's require compliance with an AFM and therefore the use of weak
links with these specifications including the tolerance specification.

An example is an ASK-21 whose AFM specifies a 1000 daN +or- 100 daN
weak link (Tost Black Link) for winch launch and 600 daN +or- 60 daN
for aero tow. (1 daN = 1Kg-force)

The second part of your question involves the concept of "equivalent
G". Since the force vector of a winch rope passes through the
longitudinal axis and is not distributed along the span like the
weight of the wing structure, the spar bending moment is higher than
the force alone would indicate. The "3.5G" is only an estimate and
first order calculations suggest it could be slightly less but a winch
launch is indeed roughly equivalent to a loop in terms of wing stress.

Bill,
I’m revisiting this subject now as I have acquired an ultralight glider that can’t be aerotowed by anything I have access to due to very low redline. I gather there are now wireless line load cells available that could be very handy for our ground launching purposes. If you know of any specific ones especially in the lower load ranges that would be useful to me please let me know. I can imagine that having an easy to use smart phone displaying load cell that can clip into a tow line would be a great safety and performance enhancement for glider ground launching.

Matt Michael