On Jun 19, 9:07*pm, bildan wrote:
On Jun 19, 7:17*pm, Tony V wrote:


Whatever the ultimate failure mode, if you get 1500 launches or so,
the extra per-launch cost of about $0.50 is trivial for most people.

The cost difference of UHMWPE ropes over steel amortized over 1500
launches is about $1.05/launch if purchased in bulk. If you need to
splice, that will be cheaper than splicing steel. You should do a lot
less splicing that with steel. For 3/16" 12 strand, I recommend
making a fid from a 10 1/2 knitting needle bonded with a 9/32" round
brass tube. Field splices using a 12" 3x tuck splice in either
direction are fine. Leave the proper splice for non-flying days.

I would suggest actually amortizing your first run over 1000 launches
until you get some experience with your actual results. That puts the
cost differential nearer $1.58/launch. At that rate, you should be
well on your way to funding replacement rope before you exhaust your
current length.

Costs are based on 5000ft bulk purchases at best available prices.

Impact damage from loops striking parts of the winch causes breaks.
Loops may result for both design and operational issues. Snagging
objects on the ground can have similar results. I'm aware of a club
that damaged $200 (~500ft) worth of Dyneema 75 that way recently. The
more power your winch has, the more technically sophisticated your
line feeds should be as the tendency to 'melt' the line increases with
load. Your launches will be higher also but the real gains from the
reduced weight of these ropes shows up when the run length approaches
5000ft. 5000ft of UHMWPE (3/16") is 50 lbs. The same length of steel
is over 300 lbs. The winch should be at the fence. Your airport is
only about 3100ft max. I don't think you'll see 100ft different in
launch heights.

If you can use a soft surface for retrieves, I'd recommend it. Runway
verges work fine and keep the line clear of the hard surface so it may
be used by other aircraft while the glider winch launch is staging.
Up slack may pull some of the line onto the hard surface for a very
short while, but it'll be in the air right away.

Frank Whiteley