Bungee at Long Myndd

Strange therefore how our winch drivers at Lasham, including the amateur
volunteers, managed to cope perfectly well with a synthetic cable when we
tried it out on a purely manual driven Tost winch without ANY automatic
gizmos! You still have the climb rate, glider appearance, and any signals
from the pilot to go on. UHMWPE cable does bow a bit, but less than steel.
It also drifts a long way sideways in a crosswind after release. We got
just over 2500 launches from it, with most of the wear being caused by
ground abrasion where it was pulled across our rough concrete cross
runways.

Derek Copeland



At 23:20 14 August 2009, bildan wrote:

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.