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Wanting to start a new glider club



 
 
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  #51  
Old December 31st 18, 06:02 AM posted to rec.aviation.soaring
John Foster
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Default Wanting to start a new glider club

I'm seriously looking at a reverse auto tow set-up to cut the costs down when starting up the club and am playing around with design concepts in my head. As far as rope goes, I am really impressed with Dyneema as a rope material, and from what I can gather, Samson Amsteel Blue Dyneema has a breaking strength of 1400 lbs for a rope only 7/64" diameter. That's about the thickness of a string! I can get a spool of it 3280 feet in length. Our runway is about 4,800, so we'd probably need to splice some additional length to be able to utilize the full length of the runway and maximize the height of the launch. Would need to use a weak link on each end though. For this application, would a single axle wheel like a motorcycle wheel rim work better for the pulley, or would something like the Cotswold design work better? The rope wouldn't have the extra mass that the piano wire did that they used in Cotswold.
  #52  
Old December 31st 18, 06:23 AM posted to rec.aviation.soaring
Frank Whiteley
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Default Wanting to start a new glider club

On Sunday, December 30, 2018 at 10:02:46 PM UTC-7, John Foster wrote:
I'm seriously looking at a reverse auto tow set-up to cut the costs down when starting up the club and am playing around with design concepts in my head. As far as rope goes, I am really impressed with Dyneema as a rope material, and from what I can gather, Samson Amsteel Blue Dyneema has a breaking strength of 1400 lbs for a rope only 7/64" diameter. That's about the thickness of a string! I can get a spool of it 3280 feet in length. Our runway is about 4,800, so we'd probably need to splice some additional length to be able to utilize the full length of the runway and maximize the height of the launch. Would need to use a weak link on each end though. For this application, would a single axle wheel like a motorcycle wheel rim work better for the pulley, or would something like the Cotswold design work better? The rope wouldn't have the extra mass that the piano wire did that they used in Cotswold.


1/8" for 2400lbs. Not sure is the small diameters are easily spliced buy I have a spool of 1/8", so well let you know.

You might get away with a 14" wheel. I wouldn't bother with a motorcycle wheel.

Have to grok on this a bit.

Frank Whiteley
Been there, done that
  #53  
Old December 31st 18, 04:38 PM posted to rec.aviation.soaring
Dave Springford
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Default Wanting to start a new glider club

I bought 4000 ft of 5 mm diameter "dyneema" from the Shanghai Tough Rope and Webbing Company back in 2016 and we have been using it on our winch for 2 years.

http://www.toughrope.com/productshow_261.html

I tested it on the tensile machine at my college and it reached 3800 lbs before breaking. Lower than expected, but I had not mounted it very well in the machine and it was cut, more than it was broken, and 3800 is well above the 2200 lb weak link required for the K-21 so I didn't bother to mount it better and test it again.

Price in 2016 was $0.50 per meter and $200 in shipping. Much cheaper than Amsteel for pretty much the same thing.


  #54  
Old December 31st 18, 09:43 PM posted to rec.aviation.soaring
JS[_5_]
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Default Wanting to start a new glider club

On Monday, December 31, 2018 at 7:38:21 AM UTC-8, Dave Springford wrote:
I bought 4000 ft of 5 mm diameter "dyneema" from the Shanghai Tough Rope and Webbing Company back in 2016 and we have been using it on our winch for 2 years.

http://www.toughrope.com/productshow_261.html

I tested it on the tensile machine at my college and it reached 3800 lbs before breaking. Lower than expected, but I had not mounted it very well in the machine and it was cut, more than it was broken, and 3800 is well above the 2200 lb weak link required for the K-21 so I didn't bother to mount it better and test it again.

Price in 2016 was $0.50 per meter and $200 in shipping. Much cheaper than Amsteel for pretty much the same thing.


HOWEVER...
Cheap Chinese Crap is exactly that.
A friend lost something heavy and valuable by using Chinese "Dyneema" in a winch. While lifting, the bit of string that was "rated" much higher than required broke and the thing fell.
Testing one section of this CCC doesn't mean the rest of it is better than a shoestring.
Jim
  #55  
Old December 31st 18, 09:59 PM posted to rec.aviation.soaring
Dave Springford
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Default Wanting to start a new glider club

As mentioned above, we've been using it for 2 years and it is function as expected. No breaks, no problems, including one day with 90 launches without a stoppage.
  #56  
Old December 31st 18, 10:34 PM posted to rec.aviation.soaring
WB
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Posts: 236
Default Wanting to start a new glider club

On Sunday, December 30, 2018 at 11:02:46 PM UTC-6, John Foster wrote:
I'm seriously looking at a reverse auto tow set-up to cut the costs down when starting up the club and am playing around with design concepts in my head. As far as rope goes, I am really impressed with Dyneema as a rope material, and from what I can gather, Samson Amsteel Blue Dyneema has a breaking strength of 1400 lbs for a rope only 7/64" diameter. That's about the thickness of a string! I can get a spool of it 3280 feet in length. Our runway is about 4,800, so we'd probably need to splice some additional length to be able to utilize the full length of the runway and maximize the height of the launch. Would need to use a weak link on each end though. For this application, would a single axle wheel like a motorcycle wheel rim work better for the pulley, or would something like the Cotswold design work better? The rope wouldn't have the extra mass that the piano wire did that they used in Cotswold.


Forget the "reverse auto tow" and you don't need Dyneema to start (although it has definite advantages). My club, Southern Eagles (aka Sufferin' Eagles) started with 4000 feet of dacron rope and a truck wheel mounted on a steel bar the went into a hitch receiver on the back of a very old Ford LTD with an automatic trans. One end of the rope goes to an anchor (another vehicle or big metal stake in the ground). The rope goes over the pulley and to the glider. The car pulls from the middle of the rope, thus giving a 2:1 mechanical advantage. We would just put the old LTD in low gear and leave it there. Launching a 2 seater, the car would get up to maybe 28 miles per hour at most, then slow down from there. We were usually going about 18 mph when the glider was at the top of the launch. We got hundreds of launches off that dacron and that was on asphalt pavement. I think this is the best autolaunch system. The car is going slow so it's easily controllable and you can do this on less than smooth surfaces. Acceleration at the glider end of the rope is very fast, pretty much just like a winch. Simple, simple, simple. We sometimes got our single seat gliders to 2000 agl with a bit of headwind. Email me at if you want details.
  #57  
Old December 31st 18, 10:40 PM posted to rec.aviation.soaring
RR
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Default Wanting to start a new glider club

John, you should oversize the launch line, so as it wears from abrasion and uv it won't become the weak link in the system.

RR
  #58  
Old December 31st 18, 11:57 PM posted to rec.aviation.soaring
John Foster
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Posts: 354
Default Wanting to start a new glider club

On Monday, December 31, 2018 at 2:34:54 PM UTC-7, WB wrote:
On Sunday, December 30, 2018 at 11:02:46 PM UTC-6, John Foster wrote:
I'm seriously looking at a reverse auto tow set-up to cut the costs down when starting up the club and am playing around with design concepts in my head. As far as rope goes, I am really impressed with Dyneema as a rope material, and from what I can gather, Samson Amsteel Blue Dyneema has a breaking strength of 1400 lbs for a rope only 7/64" diameter. That's about the thickness of a string! I can get a spool of it 3280 feet in length. Our runway is about 4,800, so we'd probably need to splice some additional length to be able to utilize the full length of the runway and maximize the height of the launch. Would need to use a weak link on each end though. For this application, would a single axle wheel like a motorcycle wheel rim work better for the pulley, or would something like the Cotswold design work better? The rope wouldn't have the extra mass that the piano wire did that they used in Cotswold.


Forget the "reverse auto tow" and you don't need Dyneema to start (although it has definite advantages). My club, Southern Eagles (aka Sufferin' Eagles) started with 4000 feet of dacron rope and a truck wheel mounted on a steel bar the went into a hitch receiver on the back of a very old Ford LTD with an automatic trans. One end of the rope goes to an anchor (another vehicle or big metal stake in the ground). The rope goes over the pulley and to the glider. The car pulls from the middle of the rope, thus giving a 2:1 mechanical advantage. We would just put the old LTD in low gear and leave it there. Launching a 2 seater, the car would get up to maybe 28 miles per hour at most, then slow down from there. We were usually going about 18 mph when the glider was at the top of the launch. We got hundreds of launches off that dacron and that was on asphalt pavement. I think this is the best autolaunch system. The car is going slow so it's easily controllable and you can do this on less than smooth surfaces. Acceleration at the glider end of the rope is very fast, pretty much just like a winch. Simple, simple, simple. We sometimes got our single seat gliders to 2000 agl with a bit of headwind. Email me at if you want details.


A few questions come to mind: how long was your runway? We are limited to 4800ft, at an altitude of 3100 (higher density altitude in the summer). Our runway is about 3 miles upwind from the ridge/mountain range, with elevation gradually climbing about 500ft to the base of the mountains over that 3 miles. I'm anxious to maximize the altitude we would get from a launch, thus the idea of a reverse auto tow where you could use the full length of the runway for rope. Plus, with the reverse tow and pulley, you don't waste runway length with static unused rope to the starting location. Longer rope = higher launch, everything else being equal.
  #59  
Old January 1st 19, 04:21 AM posted to rec.aviation.soaring
WB
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Posts: 236
Default Wanting to start a new glider club

On Monday, December 31, 2018 at 4:57:48 PM UTC-6, John Foster wrote:
On Monday, December 31, 2018 at 2:34:54 PM UTC-7, WB wrote:
On Sunday, December 30, 2018 at 11:02:46 PM UTC-6, John Foster wrote:
I'm seriously looking at a reverse auto tow set-up to cut the costs down when starting up the club and am playing around with design concepts in my head. As far as rope goes, I am really impressed with Dyneema as a rope material, and from what I can gather, Samson Amsteel Blue Dyneema has a breaking strength of 1400 lbs for a rope only 7/64" diameter. That's about the thickness of a string! I can get a spool of it 3280 feet in length. Our runway is about 4,800, so we'd probably need to splice some additional length to be able to utilize the full length of the runway and maximize the height of the launch. Would need to use a weak link on each end though. For this application, would a single axle wheel like a motorcycle wheel rim work better for the pulley, or would something like the Cotswold design work better? The rope wouldn't have the extra mass that the piano wire did that they used in Cotswold.


Forget the "reverse auto tow" and you don't need Dyneema to start (although it has definite advantages).

A few questions come to mind: how long was your runway? We are limited to 4800ft, at an altitude of 3100 (higher density altitude in the summer). Our runway is about 3 miles upwind from the ridge/mountain range, with elevation gradually climbing about 500ft to the base of the mountains over that 3 miles. I'm anxious to maximize the altitude we would get from a launch, thus the idea of a reverse auto tow where you could use the full length of the runway for rope. Plus, with the reverse tow and pulley, you don't waste runway length with static unused rope to the starting location. Longer rope = higher launch, everything else being equal.


We were at about 600 msl and used 4000ft of a 5000ft runway. We set up the launch point about 1000ft down the runway so gliders could land and roll up to be launched again. The reverse pulley will get you more run, but it takes a lot longer to accelerate to launch speed when using a 1:1 system straight line or reverse pulley launch. The 2:1 pulley launch gets you in the air very quickly.

The amount of usable rope, and thus climb, will be limited by the angle of the rope to the pulley. Once the rope gets to about a 70 degree angle relative to the ground, you are pretty much done climbing. After that, you are being pulled down more than forward, so you are just loading up the wings. With the moving pulley, the pulley is moving with the glider, so you can climb longer before you reach that 70 degree angle. Depending on wind, acceleration of the tow vehicle, and skill of the tow driver and glider pilot at ground launch (very important, that) the reverse pulley may very well get you some higher than the 2:1 pulley launch, but the difference won't be as much as you might expect. We stopped doing auto tows when our winch became operational. It was a beast of a winch with a 455 cubic inch GM engine driving the drums. A winch has the same line length advantages as the reverse pulley tow, yet we did not get significantly higher launches with the winch than with the 2:1 pulley launch.

There is nothing new under the sun when it comes to ground launching, auto tow, winch, whatever. It's pretty much all been tried. Derek Piggot wrote a book that is a great resource for learning about ground launch in it's many forms. Unfortunately, it appears to be out of print. I will hunt down my copy and send to you if you'd like. I am jammed up with some serious family issues at the moment, so it may be a few days before I can get to it. Feel free to ping me if you don't hear from me in a week or so.

  #60  
Old January 1st 19, 04:42 AM posted to rec.aviation.soaring
Frank Whiteley
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Posts: 2,099
Default Wanting to start a new glider club

On Monday, December 31, 2018 at 8:38:21 AM UTC-7, Dave Springford wrote:
I bought 4000 ft of 5 mm diameter "dyneema" from the Shanghai Tough Rope and Webbing Company back in 2016 and we have been using it on our winch for 2 years.

http://www.toughrope.com/productshow_261.html

I tested it on the tensile machine at my college and it reached 3800 lbs before breaking. Lower than expected, but I had not mounted it very well in the machine and it was cut, more than it was broken, and 3800 is well above the 2200 lb weak link required for the K-21 so I didn't bother to mount it better and test it again.

Price in 2016 was $0.50 per meter and $200 in shipping. Much cheaper than Amsteel for pretty much the same thing.


The web site seems to indicate the rope is a blend of sk65 and sk75. Amsteel is strictly sk75. There are two grades of Amsteel and Spectra, which are the basic ropes. The performance ropes are Amsteel Blue and Plasma12 respectively, which are rated to about 5400lbs breaking strength. AFAIK, these are not blended ropes. If the surface is benign, as in lush turf, the basic ropes will give plenty of launches. Our surface is what I would describe as harsh, though the harshest was on a runway that had an abrasive slurry coating. Regardless of the rope and surface, I think a cost amortization over 1,000 launches is reasonable and if banked, may well pay for the next rope after the original rope is paid for. So this could be $2-3/launch. A good surface could result in 2000 launches. A benign surface may well result in a rope life above 4000 launches.

Your rope may well reach very economic performance results, which would be good news. Total launches will be of more interest than service years. FWIW, I have a bird feeder on an untreated, flat weave, sample of Spectra that we attached to the end of our steel wire rope many years ago. No only do the squirrels not like climbing on it, they don't chew through it. It's been out there for at least 13-14 years, so very UV resistant.

I think we are very near 1000 launches on our original Amsteel Blue, which is run over high plains prairie, buffalo grass, clay loam soil with small rocks chips slight larger than sand and encounters the occasional rock, weed, or other obstacle. We have the occasional rope break or less common splice failure (old 4/3/2 tuck splices). We use a different method now, more like the recommended method. The cost was amortized over 1000 launches, so any launch above this is gravy.

Frank Whiteley
 




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