On Aug 3, 7:30*am, Peter Higgs wrote:
Hi All, I have flown from the Long Myndd, which at 1600ft asl is the
highest gliding club in UK, situated on a 4 mile long N/S ridge.
So as long as there is more than a 15 knot Westerly wind it does not
really matter how high you get on the winch... * you WILL GO UP !
They are the only club still able to use Bungee Launching, to catapult a
glider the 50 or so yards from the ridge top, into the rising ridge lift.

As for the recent Winch Launching debate, we did find that the woven
Dynema cable used on a SkyLaunch winch did break quite often. * This was
thought to be because it was used in muddy conditions, or on an abrasive
tarmac runway. *It was replaced by some sort of normal 3 strand plastic
rope (8 and 10 mm.) which was easier to splice, and gave better results.
These nylon ropes do stretch a bit first on 'All Out' and can give a
very quick initial acceleration, only limited by the weak link I guess.

A good winch driver is the best 'constant tension' device, he can judge
the tension from the cab, by looking at the bow in the cable. *If its too
much he winds it in a bit faster, and if it is as tight as a bow string,
he just backs off the power a little.

Pete

Pete,

Dyneema/Spectra is so light that it doesn't' bow enough for the winch
driver to get much tension information from it. There has to be an
automatic method of limiting or controlling rope tension. Anyway,
tension recordings show it changes way too fast for a human to react.

I spent today walking and inspecting the Spectra (Plasma rope) on the
Hydrowinch prototype and found it to be in very good shape. It was
still soft and pliable - almost like new. I'd predict at least 3000
launches on this rope and maybe 5000. That's in line with other good
winch designs.

The airfield is a mix of about 2500 feet of old rough asphalt (tarmac)
plus 6000 feet of rough weeds, wild grass and cactus patches. Most
people wear protective footwear.

Spectra/Dyneema provides considerable warning of airfield surface wear
- it gets very fuzzy long before the strength deteriorates to where it
would need to be replaced. This is caused by individual micro fibers
snagging on the rough surface. I don't know of anyone who has
replaced Dyneema for this reason

Damage due to poor winch design is also easy to see. The rope gets
hard, stiff, squared off and shiny due to local overheating on
cylindrical rollers or poorly designed sheaves. There will be cut
strands visible where the rope gets nicked on sharp metal edges. Rope
breaks will be experienced at about 100 launches. This will limit the
useful live to only a few hundred launches which makes it uneconomic
to use with old steel wire winch designs.

The winch itself is by far the worst source of rope damage.
Airfields, even very bad ones, do little damage.