Interesting article re Dyneema

[John Smith]

Lately there has been a discussion re Dyneema in this group.
Incidentally, on the DG home page there's an interesting article to this
theme (originally published by "Magazin Segelfliegen"). It's German and
I'm not aware of an English translation.
http://www.dg-flugzeugbau.de/windenseil-d.html

[Bob Kuykendall]

On Sep 1, 6:37*am, John Smith > wrote:
> Lately there has been a discussion re Dyneema in this group.
> Incidentally, on the DG home page there's an interesting article to this
> theme (originally published by "Magazin Segelfliegen"). It's German and
> I'm not aware of an English translation.http://www.dg-flugzeugbau.de/windenseil-d.html

Here's the typically-awkward-but-mostly-usable Google translation
(long link):

http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&sl=de&tl=en&u=http%3A%2F%2Fwww.dg-flugzeugbau.de%2Fwindenseil-d.html

Thanks, Bob K.

[Frank Whiteley]

On Sep 1, 8:51*am, Bob Kuykendall > wrote:
> On Sep 1, 6:37*am, John Smith > wrote:
>
> > Lately there has been a discussion re Dyneema in this group.
> > Incidentally, on the DG home page there's an interesting article to this
> > theme (originally published by "Magazin Segelfliegen"). It's German and
> > I'm not aware of an English translation.http://www.dg-flugzeugbau.de/windenseil-d.html
>
> Here's the typically-awkward-but-mostly-usable Google translation
> (long link):
>
> http://translate.google.com/translate?js=n&prev=_t&hl=en&ie=UTF-8&lay...
>
> Thanks, Bob K.

Good article as far as it goes. This is the US angle.

Essentially there are four 12-strand ropes suitable for winch
launching in the nominal 3/16" diameter commonly used on winches.

Dyneema 75, DSM, ~3500lbs BS
Spectra, Honeywell, ~3500lbs BS
Amsteel Blue, modified Dyneema 75 from Samson Ropes, ~5400lbs BS
Plasma 12, modified Spectra from Puget Sound Ropes (Cortland
Industries), ~5400lbs BS

There are sheathed options, but those add weight, expense, and larger
drum capacity for the same length.

The two brands result from two patented processes for creating the
Ultra High Molecular Weight Polyethylene (UHMWPE) fibers. Honeywell
acquired the Spectra patent when it bought Allied Signal. I don't
know about the production locations or capacities of Honeywell. DSM
is Dutch based, but has more production capacity in the US than the
Netherlands at this point.

The price of these ropes quadrupled from about 2002-2006 due to the
rise in ethane and ethylene to some extent, demand, and the rise in
natural gas used is post production. It has been stable for a least
the past two years.

Proper treatment and handling is essential with appropriate winch
modifications needed, particularly a fairlead feed, possibly a
guillotine modification and clearance to avoid any loops hitting hard
parts.

Best results are achieved with longer winch runs where heights above
1500ft are common as the reduced weight becomes a bigger factor in the
system. Rope weights and diameters are less a factor on launch runs
around 3600ft.

Some are considering looking at other ropes and hybrid solutions using
polyofelin (blended) ropes. If the launch run is >5000ft, then
perhaps 3000ft of polyofelin with 2000ft of Amsteel Blue at the glider
end. Polyofelin of sufficient strength will be larger diameter and
heavier, but still lighter than steel.

We can now get mobile 3rd party liability insurance for winching
through Costello, but the underwriter restricts us to synthetic
ropes. I've heard that one other underwriter allows steel, but that
is at a fixed base.

If interested, you are invited to join the fray at Yahoo Groups
winchdesign and winchengineering.

Some winch presentations are being considered for the SSA Conference
in Philadelphia.

Frank Whiteley

[Andreas Maurer]

On Wed, 01 Sep 2010 15:37:24 +0200, John Smith
> wrote:

>Lately there has been a discussion re Dyneema in this group.
>Incidentally, on the DG home page there's an interesting article to this
>theme (originally published by "Magazin Segelfliegen"). It's German and
>I'm not aware of an English translation.
>http://www.dg-flugzeugbau.de/windenseil-d.html


Very good analysis that is completely consistent with out experiences.

A quick translation of the conclusion:

--- snip ---
Most users will not assess the performance gain, but the simple
handling of Dyneema as its main benefit, especially if there are more
than two cables or great lengths to be pulled on loose surfaces.

Dyneema cable only reaches a longer life in an enviroment where steel
cables have to be replaced prematurely because of bad winch design and
adverse ground conditions. Under normal conditions, its life with
about 3,000 departures per cable is the same, but Dyneema is 3 to 5
times more expensive. Not all of the operators who have tested Dyneema
have kept using it.

Not to be underestimated is the cost and effort of the adaptation of
the winch to Dyneema. Because of its high price much time is being
spent with repaires and reduced cable tensile strength towards the end
of its life cycle.

It is recommended to use Dyneema only if all other optimization
possibilities have been utilized.

--- snip ---


Andreas

[John Smith]

For me, the most interesting part was the notion that applying more than
20 to 30 percent of the advertised breaking load will significantly
accelerat the rope aging. I suspect that this may have contributed ot
our early problems with frequent rope breaks, even more so when I
remember how many hardened parts the ropes showed after the first season.

[Frank Whiteley]

On Sep 1, 10:29*am, John Smith > wrote:
> For me, the most interesting part was the notion that applying more than
> 20 to 30 percent of the advertised breaking load will significantly
> accelerat the rope aging. I suspect that this may have contributed ot
> our early problems with frequent rope breaks, even more so when I
> remember how many hardened parts the ropes showed after the first season.

Steel wire or UHMWPE rope on a glider winch are operated well outside
of rated load limits and normal speeds. 1/6 to 1/5 of breaking
strength is the normal rating.

The expense of using of UHMWPE means that the cost of consumption
must be based on anticipated minimum life. My baseline is 1000
launches. Once that price point is built into the unit cost of a
launch, then additional launches are gravy, which can help fund the
next winch, rope replacement, gliders, etc. Yes, it means an increase
in launch rates, but it's also somewhat safer to use than steel.

Frank Whiteley

[Berry[_2_]]

I have winched with steel and Plasma rope and car towed with Dacron. Not
having to tear up my fingers trying to untangle a steel bird's nest
makes the cost of the synthetic rope worth it in my book...