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#61
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Wanting to start a new glider club
On Monday, December 31, 2018 at 8:21:47 PM UTC-7, WB wrote:
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. Wally Wally is right, using a direct pulley offers some advantages. Turn around time is a bit longer, but if you're only launching a few gliders, this might be fine. I would suggest it would be a challenge to do 30 launches a day if you required that many launches. Reverse pulley is capable of doing a launch every 90 seconds to 3 minutes, so a large club can make good use of this method. Even a two drum winch, which can outperform any tow plane operation in terms of vertical feet/day, is of little concern if you run out of gliders at the launch point. So when creating a business model, what are your current requirements and what are your future requirements. Can you current require help you reach your future requirements? 3/16 UHMWPE rope provides good margins for wear and longevity. Yes, higher up front cost, but this can and should be amortized in the launch costs. Launch vehicles cost money also. I've done reverse pulley launches years ago at the Essex GC in the UK. Solid wire, K-13, with, IIRC, an 1100cc Vauxhall manual transmission. Each shift, the drogue chute inflated over the canopy of the K-13. Dodgy, yes. Launch height, minimum safe height. Nevertheless, there's wear and tear on the launch vehicle. You might contact Stephen Layton at Hobbs Soaring Society about this. They have a simple auto launch system, lots of experience, but they also have lots of room to do what they do. https://sites.google.com/site/hobbss...ociety/contact Frank Whiteley |
#62
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Wanting to start a new glider club
On Monday, April 23, 2018 at 4:56:24 PM UTC-4, John Foster wrote:
Hi everyone I just started glider flying lessons and I'M HOOKED!!! Unfortunately, the closest glider club is 3:45 hr drive away. I also live in an area that looks to me to be perfect for ridge soaring, with a range of mountains facing the west that runs for at least 85 miles, and possibly longer. We have an airport close by with a 4800' runway, about 2-3 miles west of the mountains. A friend is a CFI and A&P, and is interested in getting his "glider ticket" as well. There are a few other folks in the area that have expressed varying interest in flying gliders as well. But as it currently stands, no one (except one possible individual that I haven't yet talked to) in the area actually flies gliders. My friend and I have talked about the possibility of starting a local club. What would be the best way to go about doing this? Start with one tow pilot, one tow plane, and one glider. Start towing at your field and like, "field of dreams", they will come unless your GP is a sinkhole! |
#63
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Wanting to start a new glider club
On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote:
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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org |
#64
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Wanting to start a new glider club
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote:
On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: 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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org That books looks promising. Thanks for the link. With regard to the pulley: what diameter would it need to be? I've seen somewhere that a higher grade of UHMWPE--New England STS-12 (formerly Endura 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Somehow that just doesn't seem like a good idea in this application though, but I don't know. So I'm asking. If this were the case then, one could simply order these items off Amazon and be done with it: https://www.amazon.com/Smittybilt-27...s=snatch+block https://www.amazon.com/dp/B01I25Z5F4...v_ov_lig_dp_it |
#65
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Wanting to start a new glider club
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote:
On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: 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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org Derek's insights on ground launching are very good. There are a number of variables that need some additional consideration. Here in Colorado summers, we can have density altitudes approaching 10,000ft at 5500MSL field elevation, which affect performance of both winches and gliders and auto tows, if used. The OP's location is at 3000MSL with slightly lower expected seasonal temperatures. I'm not aware of any operations that have used direct or reverse-pulleys with UHMWPE ropes. 30 plus years ago, the old Enstone GC attempted to use a pulley with Parafil and the results were not successful. Could have been a design issue. Parafil worked a treat for auto tow and could be retrieved quickly for the next launch. I'm not certain UHMWPE ropes would work in those cases, however, Amsteel II is a sheathed rope, so might work in a similar role. Direct pulley and auto tow is often done without a drogue chute so the rope will drop without much drift. A chute could result in considerable drift without any control. A drogue chute on a reverse pulley allows the end of the rope to be landed next to the pulley and it will be set up for the next launch. A rope break is the only real problem. The OP's airport has runway lights, which in my opinion makes direct pulley and auto tow not viable. There is a second airport option, very close to the mountains, which might allow easy access to ridge soaring. If the wind is enough for ridge flight, it would also maybe help with the launch heights to reach for the lift and/or return to the airport. A reverse pulley would allow for operations from both sites, though there is the problem of different run lengths. John, what was that second airport? Frank Whiteley |
#66
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Wanting to start a new glider club
On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John Foster wrote:
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote: On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: 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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org That books looks promising. Thanks for the link. With regard to the pulley: what diameter would it need to be? I've seen somewhere that a higher grade of UHMWPE--New England STS-12 (formerly Endura 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Somehow that just doesn't seem like a good idea in this application though, but I don't know. So I'm asking. If this were the case then, one could simply order these items off Amazon and be done with it: https://www.amazon.com/Smittybilt-27...s=snatch+block https://www.amazon.com/dp/B01I25Z5F4...v_ov_lig_dp_it 8 inches is okay, but there are other reverse pulley considerations. If you want the wheel to track the glider climb and drift, as in the old Cotswold system, a larger diameter is probably better. It was an effective 50" radius using using small rollers to reduce any stored energy in the system, which was an issue with the Essex GC system. With UHMWPE rope, you want to eliminate both stored energy and the ability for slack rope to tuck into any gaps or result in loops that might impact on the ground or equipment. Larger rope types might help with some of this, but there are always compromises of performance and price. UV resistence, abrasive resistence, fatigue (as a result of loading cycles), and ease of handling (including splicing) are all considerations. This might be a suitable substitute for UHMWPE ropes for reverse pulley, http://www.novabraid.com/rope/oletec-12/ though they make no claims on abrasion resistance. 3/8" might be so heavy as to cause abrasive issues. This was true on the Cotswold system using solid wire. 10 gauge was heavy enough to cause excessive wear on the "memory loops" on the wire, so 13 gauge was found to give the best performance. Use of solid wire is not recommended at public use airports wherever you are because a large clear zone is needed in case of wire breaks. Many of these new ropes have negligible stretch, thus no recoil issues. Solid wire and steel wire ropes have significant recoil hazards. Frank Whiteley |
#67
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Wanting to start a new glider club
On Wednesday, January 2, 2019 at 2:11:23 AM UTC-7, Frank Whiteley wrote:
On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote: On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: 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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org Derek's insights on ground launching are very good. There are a number of variables that need some additional consideration. Here in Colorado summers, we can have density altitudes approaching 10,000ft at 5500MSL field elevation, which affect performance of both winches and gliders and auto tows, if used. The OP's location is at 3000MSL with slightly lower expected seasonal temperatures. I'm not aware of any operations that have used direct or reverse-pulleys with UHMWPE ropes. 30 plus years ago, the old Enstone GC attempted to use a pulley with Parafil and the results were not successful. Could have been a design issue. Parafil worked a treat for auto tow and could be retrieved quickly for the next launch. I'm not certain UHMWPE ropes would work in those cases, however, Amsteel II is a sheathed rope, so might work in a similar role. Direct pulley and auto tow is often done without a drogue chute so the rope will drop without much drift. A chute could result in considerable drift without any control. A drogue chute on a reverse pulley allows the end of the rope to be landed next to the pulley and it will be set up for the next launch. A rope break is the only real problem. The OP's airport has runway lights, which in my opinion makes direct pulley and auto tow not viable. There is a second airport option, very close to the mountains, which might allow easy access to ridge soaring. If the wind is enough for ridge flight, it would also maybe help with the launch heights to reach for the lift and/or return to the airport. A reverse pulley would allow for operations from both sites, though there is the problem of different run lengths. John, what was that second airport? Frank Whiteley The second airport is St Ignatius (52S). Elevation is about the same at about 3K ft. Runway is only 2600 ft though. It also has runway lights. Again, the purpose of this thread is to look at (cheap) options to get a club STARTED in a rural area in a low population density state. There is not a lot of money around here. Obviously there are better ways to launch gliders, but it costs more, and I'm looking for ways to make this affordable, at least until we can achieve critical mass to make this club self-sustaining. At that point we could start looking at options to improve launch equipment. At this point we don't even have sufficient interest to generate enough capital to buy a two-seater glider, even one that is only $6000. There is interest, but not enough people to put money on the table yet. That's my challenge. |
#68
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Wanting to start a new glider club
I learnt to glide and instruct in the late 1960s and 70s at a club that
used autotow and would suggest that if you are startng up and your site can manage the rope issues with ground based cable launching then start with straight autotow. 1500' to 1800' of cable and a pick up truck. It's the simplest system. The turn round time will be slower but to start with that won't be an issue. We tried reverse pulley and couldn't make it work reliably because it was very easy to launch too far and what happened then was that the cable broke, thus making the whole thing a mess. If you do then you will find that your pulley assembly needs to move about two axes, both horizontally and vertically. The vertical axis handles the situation where the glider is to one side of the runway. But if the airfield is being used by other air traffic I'm not sure if any wire launch system will work because of the risk to things such as lights and the risks of mixing aircraft and cables. Chris At 09:39 02 January 2019, Frank Whiteley wrote: On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John Foster wrote: On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote: On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: =20 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 Pig= got wrote a book that is a great resource for learning about ground launc= h in it's many forms. Unfortunately, it appears to be out of print. ITYM "Gliding - A handbook on Soaring Flight" =20 Edition 7, which I have (blue cover showing a DG-800B with its motor=20 out), has two chapters on ground launching and is currently on offer fr= om=20 Amazon for $3.60. His books may be out of print, but you can easily fin= d=20 copies. Amazon even has a Derek Piggott author page.=20 =20 =20 --=20 Martin | martin at Gregorie | gregorie dot org =20 That books looks promising. Thanks for the link. =20 With regard to the pulley: what diameter would it need to be? I've seen = somewhere that a higher grade of UHMWPE--New England STS-12 (formerly Endur= a 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for= a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Som= ehow that just doesn't seem like a good idea in this application though, bu= t I don't know. So I'm asking. =20 If this were the case then, one could simply order these items off Amazon= and be done with it: https://www.amazon.com/Smittybilt-27...k/dp/B003CG9P= IC/ref=3Dsr_1_3?ie=3DUTF8&qid=3D1546415068&sr=3D8-3&keywords=3Dsnatch+block https://www.amazon.com/dp/B01I25Z5F4...&colid=3D1CG4= T3YDCVWF8&psc=3D0&ref_=3Dlv_ov_lig_dp_it 8 inches is okay, but there are other reverse pulley considerations. If yo= u want the wheel to track the glider climb and drift, as in the old Cotswol= d system, a larger diameter is probably better. It was an effective 50" ra= dius using using small rollers to reduce any stored energy in the system, w= hich was an issue with the Essex GC system. With UHMWPE rope, you want to = eliminate both stored energy and the ability for slack rope to tuck into an= y gaps or result in loops that might impact on the ground or equipment. La= rger rope types might help with some of this, but there are always compromi= ses of performance and price. UV resistence, abrasive resistence, fatigue = (as a result of loading cycles), and ease of handling (including splicing) = are all considerations. This might be a suitable substitute for UHMWPE ropes for reverse pulley, ht= tp://www.novabraid.com/rope/oletec-12/ though they make no claims on abrasi= on resistance. 3/8" might be so heavy as to cause abrasive issues. This w= as true on the Cotswold system using solid wire. 10 gauge was heavy enough= to cause excessive wear on the "memory loops" on the wire, so 13 gauge was= found to give the best performance. Use of solid wire is not recommended = at public use airports wherever you are because a large clear zone is neede= d in case of wire breaks. Many of these new ropes have negligible stretch,= thus no recoil issues. Solid wire and steel wire ropes have significant r= ecoil hazards. Frank Whiteley |
#69
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Wanting to start a new glider club
Peter Whitehead gave some information on an earlier post showing a reverse pulley launch but had no video of the business end - I can add this here and hope it is of some help. https://www.youtube.com/watch?v=Q0rv1zOmyWg&t=51s Peter is the best contact for technical information regarding equipment used - the bearings on the first trials were not up to the speed and were replaced due to overheating. Overall the results were superb for an expatiation from another new site in the Lake district. JY At 19:01 02 January 2019, Chris Rowland wrote: I learnt to glide and instruct in the late 1960s and 70s at a club tha used autotow and would suggest that if you are startng up and your site ca manage the rope issues with ground based cable launching then start wit straight autotow. 1500' to 1800' of cable and a pick up truck. It's th simplest system. The turn round time will be slower but to start with tha won't be an issue. We tried reverse pulley and couldn't make it work reliably because it wa very easy to launch too far and what happened then was that the cabl broke, thus making the whole thing a mess. If you do then you will find that your pulley assembly needs to move abou two axes, both horizontally and vertically. The vertical axis handles th situation where the glider is to one side of the runway. But if the airfield is being used by other air traffic I'm not sure if an wire launch system will work because of the risk to things such as light and the risks of mixing aircraft and cables. Chris At 09:39 02 January 2019, Frank Whiteley wrote: On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John Foster wrote: On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote: On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: =20 There is nothing new under the sun when it comes to groun launching, auto tow, winch, whatever. It's pretty much all been tried. Derek Pig= got wrote a book that is a great resource for learning about ground launc= h in it's many forms. Unfortunately, it appears to be out of print. ITYM "Gliding - A handbook on Soaring Flight" =20 Edition 7, which I have (blue cover showing a DG-800B with it motor=20 out), has two chapters on ground launching and is currently on offer fr= om=20 Amazon for $3.60. His books may be out of print, but you can easily fin= d=20 copies. Amazon even has a Derek Piggott author page.=20 =20 =20 --=20 Martin | martin at Gregorie | gregorie dot org =20 That books looks promising. Thanks for the link. =20 With regard to the pulley: what diameter would it need to be? I'v seen = somewhere that a higher grade of UHMWPE--New England STS- 12 (formerly Endur= a 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for= a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Som= ehow that just doesn't seem like a good idea in this application though, bu= t I don't know. So I'm asking. =20 If this were the case then, one could simply order these items off Amazon= and be done with it: https://www.amazon.com/Smittybilt-27...versal-Snatch- Block/dp/B003CG9P= IC/ref=3Dsr_1_3?ie=3DUTF8&qid=3D1546415068&sr=3D8- 3&keywords=3Dsnatch+block https://www.amazon.com/dp/B01I25Z5F4/? coliid=3DIC5446KT2CY9R&colid=3D1CG4= T3YDCVWF8&psc=3D0&ref_=3Dlv_ov_lig_dp_it 8 inches is okay, but there are other reverse pulley considerations. If yo= u want the wheel to track the glider climb and drift, as in the old Cotswol= d system, a larger diameter is probably better. It was an effective 50" ra= dius using using small rollers to reduce any stored energy in the system, w= hich was an issue with the Essex GC system. With UHMWPE rope, you wan to = eliminate both stored energy and the ability for slack rope to tuck into an= y gaps or result in loops that might impact on the ground or equipment. La= rger rope types might help with some of this, but there are always compromi= ses of performance and price. UV resistence, abrasive resistence fatigue = (as a result of loading cycles), and ease of handling (includin splicing) = are all considerations. This might be a suitable substitute for UHMWPE ropes for reverse pulley, ht= tp://www.novabraid.com/rope/oletec-12/ though they make no claims on abrasi= on resistance. 3/8" might be so heavy as to cause abrasive issues. This w= as true on the Cotswold system using solid wire. 10 gauge was heavy enough= to cause excessive wear on the "memory loops" on the wire, so 13 gauge was= found to give the best performance. Use of solid wire is no recommended = at public use airports wherever you are because a large clear zone is neede= d in case of wire breaks. Many of these new ropes have negligible stretch,= thus no recoil issues. Solid wire and steel wire ropes have significant r= ecoil hazards. Frank Whiteley |
#70
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Wanting to start a new glider club
On Wednesday, January 2, 2019 at 2:39:13 AM UTC-7, Frank Whiteley wrote:
On Wednesday, January 2, 2019 at 12:59:47 AM UTC-7, John Foster wrote: On Tuesday, January 1, 2019 at 8:13:46 AM UTC-7, Martin Gregorie wrote: On Mon, 31 Dec 2018 19:21:45 -0800, WB wrote: 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. ITYM "Gliding - A handbook on Soaring Flight" Edition 7, which I have (blue cover showing a DG-800B with its motor out), has two chapters on ground launching and is currently on offer from Amazon for $3.60. His books may be out of print, but you can easily find copies. Amazon even has a Derek Piggott author page. -- Martin | martin at Gregorie | gregorie dot org That books looks promising. Thanks for the link. With regard to the pulley: what diameter would it need to be? I've seen somewhere that a higher grade of UHMWPE--New England STS-12 (formerly Endura 12), recommends a sheave:rope diameter ratio of 8:1. That would mean for a 1/8" rope, one could get away with a sheave of only 1" in a pulley. Somehow that just doesn't seem like a good idea in this application though, but I don't know. So I'm asking. If this were the case then, one could simply order these items off Amazon and be done with it: https://www.amazon.com/Smittybilt-27...s=snatch+block https://www.amazon.com/dp/B01I25Z5F4...v_ov_lig_dp_it 8 inches is okay, but there are other reverse pulley considerations. If you want the wheel to track the glider climb and drift, as in the old Cotswold system, a larger diameter is probably better. It was an effective 50" radius using using small rollers to reduce any stored energy in the system, which was an issue with the Essex GC system. With UHMWPE rope, you want to eliminate both stored energy and the ability for slack rope to tuck into any gaps or result in loops that might impact on the ground or equipment. Larger rope types might help with some of this, but there are always compromises of performance and price. UV resistence, abrasive resistence, fatigue (as a result of loading cycles), and ease of handling (including splicing) are all considerations. This might be a suitable substitute for UHMWPE ropes for reverse pulley, http://www.novabraid.com/rope/oletec-12/ though they make no claims on abrasion resistance. 3/8" might be so heavy as to cause abrasive issues. This was true on the Cotswold system using solid wire. 10 gauge was heavy enough to cause excessive wear on the "memory loops" on the wire, so 13 gauge was found to give the best performance. Use of solid wire is not recommended at public use airports wherever you are because a large clear zone is needed in case of wire breaks. Many of these new ropes have negligible stretch, thus no recoil issues. Solid wire and steel wire ropes have significant recoil hazards. Frank Whiteley WRT Cotswold 50" diameter. |
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