On Jun 19, 7:17*pm, Tony V wrote:
We (Greater Boston Soaring Club) had our first Spectra "glider flinging"
session today and were surprised that we saw no altitude improvement
after switching from steel cable. The winds were not favorable and our
heights may improve in time. .... But that's not the question.

We have the option of launching from either asphalt or turf. From a
Spectra wear point of view, which would be preferred?

Tony V. LS6-b "6N"

Launching from turf will extend the rope's life but people launching
from asphalt are also reporting good rope life. The rope tends to
come off the ground far more quickly than steel cable so it suffers
less abrasion regardless of the surface. FWIW, Spectra, (HMWPE) has
10 - 15 times the abrasion resistance of steel.

The major advantage of turf over asphalt is temperature - black
asphalt can get hot in the sun. However, Spectra's rated strength is
valid to 150F (To advertize a strength value, the manufacturer has to
set a maximum temperature - i.e. "Critical temperature".) Strength
trends downward above that until it melts around 283F. It's not
likely your asphalt will exceed 150F.

There are two major failure modes (Other than winch damage.) one is
"snagging" where individual fibers catch on sharp objects and get
broken. This results in "fuzzing" which, counter-intuitively,
actually protects the remaining fibers from further abrasion damage.
The other is melting.

Most rope damage is caused by poorly designed winches. Big crossed
rollers collect rings of melted Spectra indicating the rope has been
terminally damaged. If the rope is stiff and shiny, it's been melted
by the winch. It should remain soft and pliable for it's whole life.
It's worth investing in a Spectra-friendly fairlead for your winch.
(e-mail me and I'll send you drawings and photos of one.)

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.

As to release height, the advantage of light ultra high strength
synthetic rope depends on runway length. The longer rope you start
with, the greater the relative benefit. Below 4000 feet or so, there
isn't much height gain but at 10,000 feet it's really significant.
But, even with short runways, you still get the safety and handling
benefits which, in themselves, are worth it