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.

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.

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 |

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."

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 |

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

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 |