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#11
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Cable vs rope pulling glider from field
On Oct 13, 7:31*pm, Martin Gregorie
wrote: On Thu, 13 Oct 2011 06:39:38 -0700, Auxvache wrote: Thanks very much for your answers--sounds like Dyneema with a weak link and Tost ring would be a good set-up. Yes, I'd agree, but with one warning I should have mentioned: a naked Dyneema cord is not a good idea because the slightest handling abrasion tends to fluff it up into an unusable woolly caterpillar-like thing. I discovered this when trying to use a thin woven Dyneema (80 lb) line to control the VIT stop on a free flight power model - even expecting it to handle a 90 degree bend by sliding round a 3mm brass tube was too rough and caused it to fluff up and become unusable. What I've found to be excellent is a core of unwoven Dyneema inside a woven Dacron casing. I've used 100 lb kite bridle (about 0.7mm diameter) as model glider towline. This was very easy to handle and almost totally abrasion resistant. I believe you can get this type of line in up to at least 3mm diameter. -- martin@ * | Martin Gregorie gregorie. | Essex, UK org * * * | Martin, you must have had some really crappy rope mislabeled as Dyneema . The 12 strand hollow braid we use has 15x the abrasion resistance of steel. The off road 4x4 guys use it on their bumper winches with it going over sharp rocks and trees. I've never seen the problems you describe. |
#12
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Cable vs rope pulling glider from field
On Oct 13, 7:18*pm, Bill D wrote:
Martin, you must have had some really crappy rope mislabeled as Dyneema . *The 12 strand hollow braid we use has 15x the abrasion resistance of steel. *The off road 4x4 guys use it on their bumper winches with it going over sharp rocks and trees. *I've never seen the problems you describe. Yes, that sounds more like aramid (such as Kevlar (tm)) behavior. Thanks, Bob K. |
#13
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Cable vs rope pulling glider from field
On Thu, 13 Oct 2011 19:18:12 -0700, Bill D wrote:
Martin, you must have had some really crappy rope mislabeled as Dyneema . The 12 strand hollow braid we use has 15x the abrasion resistance of steel. Well, it looked and felt like Dyneema/Spectra/whatever brand you prefer, i.e. dead slippery to handle. As I said it was naked - just a fairly loosely woven braid with a circular cross section that was sold as 80 lb fishing line - I've seen the same sort of line and thickness in Dacron but then, of course, it would have been around 18-20 lb line, say somewhere between 0.3 to 0.5mm in diameter. Since it felt so slick I was sure it would slide round the outside of something as relatively large and smooth as 3mm brass tube, but nooo - the stuff had fluffed up before I even got the model out of my workshop, so I replaced it immediately with Dacron, which worked as I'd expected the Dyneema to do. but The off road 4x4 guys use it on their bumper winches with it going over sharp rocks and trees. I've never seen the problems you describe. But is that stuff naked or has it got a woven Dacron tube as its outer layer? Obviously some of the stuff that was used as winch cable had such an outer shell or the splicing method I saw described (threading one end in and out of the casing with a big needle for 50cm or so) would never have worked. -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#14
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Cable vs rope pulling glider from field
On Oct 14, 2:22Â*pm, Martin Gregorie
wrote: On Thu, 13 Oct 2011 19:18:12 -0700, Bill D wrote: Martin, you must have had some really crappy rope mislabeled as Dyneema . Â*The 12 strand hollow braid we use has 15x the abrasion resistance of steel. Well, it looked and felt like Dyneema/Spectra/whatever brand you prefer, i.e. dead slippery to handle. As I said it was naked - just a fairly loosely woven braid with a circular cross section that was sold as 80 lb fishing line - I've seen the same sort of line and thickness in Dacron but then, of course, it would have been around 18-20 lb line, say somewhere between 0.3 to 0.5mm in diameter. Since it felt so slick I was sure it would slide round the outside of something as relatively large and smooth as 3mm brass tube, but nooo Â*- the stuff had fluffed up before I even got the model out of my workshop, so I replaced it immediately with Dacron, which worked as I'd expected the Dyneema to do. but Â* The off road 4x4 guys use it on their bumper winches with it going over sharp rocks and trees. Â*I've never seen the problems you describe. But is that stuff naked or has it got a woven Dacron tube as its outer layer? Obviously some of the stuff that was used as winch cable had such an outer shell or the splicing method I saw described (threading one end in and out of the casing with a big needle for 50cm or so) would never have worked. -- martin@ Â* | Martin Gregorie gregorie. | Essex, UK org Â* Â* Â* | This is the stuff the 4x4 guys use - it has no sheath. http://www.okoffroad.com/stuff-winchrope-atv.htm Dyneema/Spectra/UHMWPE rope or whatever you call it has 15x steels abrasion resistance, 10x steel's strength per weight and a friction coefficient lower than Teflon plus a lot of other engineering superlatives. It simply can't be beat as winch rope for 4x4's or gliders. It does "fuzz up" as it wears but the fuzz actually protects the rest of the rope. Even this miracle material is being significantly improved. "Abstract: This paper reports the use of multiwalled carbon nanotubes (MWCNT) to reinforce and toughen gel-spun ultra high molecular weight polyethylene (UHMWPE) fibers. By adding 5 wt% MWCNT, ultra strong fibers with tensile strengths of 4.2 GPa and strain at break of ∼5% can be produced. In comparison with the pure UHMWPE fiber at the same draw ratios, these values represent increases of 18.8% in tensile strength and 15.4% in ductility. In addition, a 44.2% increase in energy to fracture has also been observed. The mechanism of reinforcement has been studied using a combination of high resolution scanning electron microscopy (SEM) and micro-Raman spectroscopy. Carbon nanotube alignment along the tensile draw direction has been observed at high elongation ratios. Such alignment induces strong interfacial load transfer both at small and large strains to enhance the stiffness and tensile strength of the composite fiber. Consequently, the mechanical properties of the composite fiber follow closely with the rule of mixtures. Our work also reveals potential for positive deviation from rule of mixtures if the CNT alignment can be further optimized." |
#15
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Cable vs rope pulling glider from field
On Fri, 14 Oct 2011 14:05:13 -0700, Bill D wrote:
This is the stuff the 4x4 guys use - it has no sheath. http://www.okoffroad.com/stuff-winchrope-atv.htm Actually it does have a short section of sheath. There is explicit mention of a 5 foot length of anti-abrasion tube on the winch cable so it can be slid to where its needed, and you'll have noted the warning about using the winch's payout brake, so the stuff may not be as bullet-proof as you think. There's also a comment, alongside the storage bag they sell for it, of the need for careful storage. That said, those products look like a good, if relatively expensive, thing to have in your glider landout retrieval kit, but a section cut from a discarded aero-tow rope would be a lot cheaper! -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
#16
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Cable vs rope pulling glider from field
On Oct 14, 3:36*pm, Martin Gregorie
wrote: On Fri, 14 Oct 2011 14:05:13 -0700, Bill D wrote: This is the stuff the 4x4 guys use - it has no sheath. http://www.okoffroad.com/stuff-winchrope-atv.htm Actually it does have a short section of sheath. There is explicit mention of a 5 foot length of anti-abrasion tube on the winch cable so it can be slid to where its needed, and you'll have noted the warning about using the winch's payout brake, so the stuff may not be as bullet-proof as you think. There's also a comment, alongside the storage bag they sell for it, of the need for careful storage. That said, those products look like a good, if relatively expensive, thing to have in your glider landout retrieval kit, but a section cut from a discarded aero-tow rope would be a lot cheaper! -- martin@ * | Martin Gregorie gregorie. | Essex, UK org * * * | For what it's worth, energy storage is not necessarily bad due to the fact such storage results in reduced shock loading. As a practical example, the yachting community will usually moor/anchor their vessels with a nylon rode or dock line in order to minimize shock damage due to wind/wave loading. Larger boats using a chain rode depend on the catenary and weight of the chain to provide cushioning. Three strand nylon is inexpensive, abrasion resistant and readily available. Experienced boat folk will also recommend using smaller rather than larger line in order to maximize "springiness". Obviously, the chosen line has to be strong enough to do the job though. I think you'll find most primary climbing ropes contain a parallel strand nylon core for the same reason. Fred Weir Deming, WA |
#17
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Cable vs rope pulling glider from field
On Sat, 15 Oct 2011 16:35:08 -0700, Fred Weir wrote:
For what it's worth, energy storage is not necessarily bad due to the fact such storage results in reduced shock loading. As a practical example, the yachting community will usually moor/anchor their vessels with a nylon rode or dock line in order to minimize shock damage due to wind/wave loading. Larger boats using a chain rode depend on the catenary and weight of the chain to provide cushioning. Three strand nylon is inexpensive, abrasion resistant and readily available. Experienced boat folk will also recommend using smaller rather than larger line in order to maximize "springiness". Obviously, the chosen line has to be strong enough to do the job though. I think you'll find most primary climbing ropes contain a parallel strand nylon core for the same reason. Understood, and a good point when you're dealing with that sort of situation. I use something very similar to the climbing rope you describe on my tie- downs: I bought a set of those super-cute Claw tiedowns, which came with exactly that type of rope. Its nice and soft, so can't damage the gel coat if its kept clean. However, for ground handling I'd rather use a non-springy rope: personally I prefer the glider to not catapult itself forward as the wheel comes out of a mud hole, something I've experienced when moving club gliders with a golf buggy and a thin, stretchy bit of rope. Thanks to that infinitely variable transmission a buggy can put out a surprising amount of torque in those circumstances, really stretching that rope, with the result that the glider pops out of the hole much faster than you'd expect. YMMV of course! -- martin@ | Martin Gregorie gregorie. | Essex, UK org | |
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