"Dan G" wrote in message
...
On Nov 29, 5:38 pm, "Bill Daniels" bildan@comcast-dot-net wrote:
Yes, they certainly pull against the heavy payout brake - they have to,
they're using steel cable. You have to keep steel under tension to
prevent
tangles. Spectra/Dyneema doesn't need that tension.

The pay-out brake is not to keep the line under tension, it's to stop
the drum when the retrieve stops, or the drum keeps turning and paying
out cable which forms great big loops hanging down from the drum. A
drum of UHMWPE will of course be much lighter than a steel one, but
the drum itself is heavy enough. If the brake is weak you have to tow
very slowly, which is frustrating.

I bet it's frustrating. Why don't you re-engineer it so it works right.

You need to re-think tension. Steel needs to be kept under tension any time
you are moving it. If it is just laying in the grass, it's still under a
little tension due to friction with the grass.

If it takes 70hp to pull out the cable, you're using way too much brake.
Tension control winches use the hydraulic motor to provide light reverse
torque, not a brake. It takes very little reverse torque to prevent over
runs with UHMWPE.



Derek says Dyneema doesn't work because it's too expensive, wears out
faster
than steel and doesn't provide any aditional height. Evedence from many
other sites successfuly using Dyneema is to the contrary on all points.
The
difference is that successful sites did their homework and made all the
neccessary changes.

Lasham isn't the only club that tried UHMWPE and abadonded it.
Pocklington tried it too - with a brand new Skylaunch winch - and also
abandoned it. Another club I know well is only using up their current
stock of it before reverting to steel. A number of sites had initially
very favourable results with UHMWPE but I've never seen any follow-up
results, which were promised by the BGA but have never materialised
(afaik).


The start of this thread was about some very talented folkes in Belgium who
set a release height record using UHMWPE on a winch designed for it. UHMWPE
is a spectacular success as a winch rope. It beats steel on all counts
including wear and life. In fact it lasts long enough to actually be
cheaper than steel on a per launch basis. BUT, you have to understand it
AND you winch has to be designed for it.

Skylaunch is a great steel cable winch. However, it would need a lot of
modifications to make it a successful UHMWPE winch. I sincerely hope they
do this since it would be easier than trying to convince the world that
UHMWPE doesn't work.

UHMWPE has never failed anyone but some people trying to use it have failed
to use it properly. If you want to know how to use it right, talk to the
people who succeeded not the ones who failed. Make a call to Belgium.

Bill Daniels