On Aug 19, 9:23*am, Derek C wrote:
On Aug 18, 11:32*pm, bildan wrote:

On Aug 18, 5:54*am, Andreas Maurer wrote:

On Wed, 18 Aug 2010 06:16:56 -0500, brian whatcott

wrote:
I see, abrasion and low density blow down. Perhaps a little drogue and
post partum pull back - or is that the way it is?

That's the way it is, unfortunately.

Generally we found that Dyneema is simply much less fault-tolerant
than a steel cable - small handling errors (like using a little too
much power to pull it out of the wood) often result in a really
expensive damage.

Andreas

And yet there are many user finding Dyneema is far, far more tolerant
than steel. *Go to a manufacturer's spec sheet and look at the
numbers. *It has 15x the abrasion resistance of steel and absolutely
no tendency to twist or kink. *It handles shock loads much better than
steel. *It has only three weaknesses - chlorine bleach, heat and sharp
edges.

Users with excellent rope handling winches see no breaks until it
wears out. *If it's breaking before it's worn out, it's getting
damaged - most likely by the winch. *Undamaged Dyneema just doesn't
suffer random breaks like steel.

Poor fairlead design is the biggest culprit. *Allowing the rope to
contact sharp edges somewhere in the rope path runs a close second.
Airfield surfaces, even really rough ones, do little damage.

Fairleads must use sheaves, not rollers. *The grooves in the sheaves
must have a very specific cross section called out by the rope
manufacturer. *Industrial studies have shown this is critical to long
life. *On every winch I've seen without a Dyneema-specific sheave,
I've been able to pull strips of melted Dyneema off the fairlead.

Drums must be boxed. *It's not unusual for a loop to form on the drum
for a fraction of a second and whip the rope against a sharp edge on
the winch frame before it gets pulled tight on the drum again. *One
winch operator declared this couldn't happen or he would have seen
it. *I pointed to bits of torn rope on a frame bracket 8 feet behind
the drum as evidence it was happening.

Dyneema is wonderful stuff and it will last up to 15x steel but it
needs a different rope path design and handling protocol.

At our somewhat abrasive airfield at Lasham (UK) we normally get about
1900 launches from a steel cable and the one trial Spectra UHMWPE
cable we tried lasted 2500 launches. The winch we used for this trial
was a modified Tost fitted with what Bill calls sheaves, level wind
paying on gear and specially reinforced drums to prevent drum-
crushing. All the parts that came into contact with the cable had been
highly polished as recommended. According to Bill that cable should
have lasted for 28,500 launches, which is over ten times what was
actually achieved! Other users of UHMWPE (Dyneema or equivalent) cable
have reported similar results to what we found. I wonder how many
launches Bill's 'American Superwinch' has carried out so far?

I believe that Bill has put the cause of winch launching in the US
back by at least 5 years by insisting that only fancy and very
expensive computer controlled diesel hydraulic or electric winches
fitted with Dyneema are capable of giving safe launches. This is in a
country where there are many potential donor vehicles fitted with
suitably large powerful engines and good automatic gearboxes that
could be used as a basis for good and low cost conventional winches.

Derek C- Hide quoted text -

- Show quoted text -

The other thing about Bill Daniels and the Yanks in general, is that
they are trying to re-invent the winch launching wheel and ignore any
advice from the other side of the pond from people who have been winch
launching for years and have a lot of experience in that technique. In
Germany, Holland and the UK about two-thirds of all glider launches
are done by winch.

Derek C