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

At 23:12 28 November 2007, Bill Daniels wrote:
It could be you're right but I'd still like to see
an actual comparison with
and without the retrieve winch at longer and longer
distances. Some
validated metrics would help sell the idea. It has
yet to be determined
just how long ropes can be with a retrieve winch.

What I'm worried about isn't the weight of Dyneema/Spectra
ropes it's the
pull angle at the hook. If the retrieve rope drags
back enough to change
that angle it will adversely affect the height achieved.

I know an engineer who was working on a simple 'spinner
reel' type design
for a retrieve winch that would use 1 or 1.5mm Dyneema.
Calculations showed
that the power required is minimal - you could power
it with a small car
starter motor and a battery. 2000 meters of thin Dyneema
would fit on a
drum not much bigger than a coffee can. With the 'spinner
reel' concept
Dyneema would pay off the retrieve winch with no rotation
of the tiny drum.

On the bright side, using a retrieve winch would cut
the fuel use by half.

Bill Daniels


'tommytoyz' wrote in message
.
com...
Back in Germany we used two twin drum Tost winches
on our field and
launched all day long back to back, as long as there
were planes
needing to be launched. Wires were retrieved with
a retrieve vehicle,
two at a time.

I think the British method of using a single drum
winch in combination
with a retrieve winch to be a very sensible idea -
even for long
fields and high launches.

The cable is being retrieved before it even hits the
ground. So the
retrieve process is shorter and faster than using
a retrieve vehicle
by dragging the entire cable length along the ground.
The winch
retrieve should there for also save on wear and tear
on the cable as
most of th retrieve occurs in the air after the glider
releases.

On very high tows, a long portion of the cable is
never wound up into
the tow drum and there for a high altitude launch
should actually
reduce the cable retrieve process using a cable retrieve
winch. The
light weight of the newer cables makes a launch penalty
negligible.
The retrieve cable need not be very strong or even
in good shape
anyway, as it's only function is to retrieve the cable.

I like this approach and seems the cheapest way to
introduce high
frequency winch operations in the USA. I wish Commercial
Glider
Operators would buy a single drum winch and a retrieve
winch and offer
this launch method. Even at 10-15 a launch - it's
still heaps cheaper
and the operator would probably make more money at
the end of the day.

Not to speak about the fact that winch launches a
far and away more
fun and exiting than aero tows.