"Del C" wrote in message
...
Bill,

At Lasham we still use vehicle retrieves and a 2 drum
main winch set up on days or evenings when demand for
winch launches is low, say when we are operating 5
gliders or less. Also the last launch of the day is
always done without the retrieve winch connected so
that we can wind the cable fully into the main winch.
Although I don't have a large data set, comparisions
between the last two launches of the day suggest that
we lose about 80 feet off a typical 1600 ft launch
due to the retrieve winch, which is 5%. This is using
steel cables on both winches. We have used an all synthetic
cable set up in the past when the losses were almost
negligible. Only problem was that the small diameter
synthetic cable on the retrieve winch wore out within
6 weeks due to ground abrasion!

I can't see that there should be any realistic limits
on the length of retrieve cable, as long as you can
keep it light - see UHMWPE cable below. However sideways
drift in a crosswind needs to be a consideration. You
may need a very wide as well as a very long airfield.
The retrieve cables we use are about half the diameter
of the main cables, so only weigh a quarter of the
amount for a given length. The back pull may initiate
a slightly earlier back release,

Our retrieve winch is fitted with a 1.9 litre industrial
VW engine developing about 90 hp, and even that labours
a bit during the retrieve (even with synthetic cables)
so the starter motor idea, if you will excuse the pun,
is a non-starter!

UHMWPE cable, such as Spectra, Plasma or Dyneema (trade
names) is pretty amazing stuff. It looks like washing
line, but is stronger than steel whilst being 10 times
lighter. Unfortunately it is also about five times
more expensive than the equivalent steel cable and
requires modifications to the winch. For the lengths
of winch run we use, normally about 4200ft, it wasn't
found to give that much improvement in height, less
than 100ft, and was deemed by our Committee not to
be cost effective. It would certainly come into its
own on 5000 feet or longer runs, when steel cable starts
to become significantly heavy.

Del Copeland

We actually tested the power required to retrieve Spectra and the starter
motor is way more powerful than needed. Not sure what your problem is at
Lasham.

The cost of Spectra is more like three times the cost of steel not 5 times -
I checked the prices this morning. It takes a LOT of power to pull steel
cable across an airfield - I can pull a mile of Spectra with one finger.

We need verifiable data from retrieve winches. Your tests at Lasham are not
verifiable since you did no controlled experiments.

Bill Daniels