Other info now obtained
poly is 10 millimetres diameter and with use shrinks to 8ml
Durability is 1000-1500 launches on grass field being dragged out
by 4wd from stationary winch
Our local cost is $245US for 1000metres of rope.DO THE MATH.ITS CHEAP
We charge round $8US per launch this to help fund another winch
The winch motor is a 5.7ltr V8 petrol driving through an auto box to an
old truck axle with diff modified to drive one side at time (your common
winch)
The difference is the drums.The drums have a centre core cut from the old
front wheel
of a road roller 12ml thick hardened steel (we got it for free)and the side
plates
10ml thick with a welded on bevel at the top to act as a guide.
All this to stop the crushing effects.of the stretched rope
I have the email of one of the main members who helped in the
experimentation stage
and is on the instructor,s panel so can explain the changes to the flight
training on
winch launching with our style of winch.
Another club has also switched to this method and is having the same success
as we are on a similar strip length.Most single seaters are getting close to
or +50% of
rope length in height.
Trials at another club with 5400ft of runway found that the sag in the rope
with longer
lengths tended to get premature releases in top third of launch as angle of
the rope
into the release was not as flat.
This was a limited number of launches.
gary


"goneill" wrote in message
...
My club has converted to poly and been running it for nearly 2 yrs now
I am not directly involved in the winch operation and most of the club
is away on the summer camps at present so I can only relate what I
have heard and will get the people who organise the winch system to
reply.
The club had wire but we have 3300ft(3100ft usable) of runway and it was
marginal
as a result usage was way down.When news of spectra type of ropes
became available, interest in the winch was stirred up because our
towplane is getting old (Pawnee manf in 50s)and requires more expensive
maintenance these days and replacement was being considered.
It was cheaper to see if spectra was going to help on getting more height
off the winch before buying a new towplane.
The experiment was a success, heights improved dramatically enough
that the majority of launches were getting away without problems.
The spectra is not made locally and the rope cost was a big part of the
operation budget.The winch still made a bigger per launch profit
than the towplane
Poly was suggested as it was very cheap in comparison and locally
available,
no supply problems as we had with spectra.
Rope diameter started with smaller then switched larger ,I dont know the
actual rope diameter.
Splices require 2 extra tucks as they slowly slip and let go at the
recommended
number.
The biggest difference is the elasticity which has a number of effects on
the
launch practises and the equipment.
The hub of the drums had to be strengthened considerably as the rope was
slowly crushing them as it shrank back to normal length..
The winch driver radios the pilot and says nose down and generally stops
the
drum
totally until released to stop releases under tension sending loops down
to
the
winch and snagging and breaks occurring .
We have not had pay on guides but are considering it to stop over and
under
loops
on the drum releasing suddenly during pulling out the ropes and snagging
and
breaking
The big difference at the glider end is a very strong acceleration as the
winch can
be at full power taking stretch up in the rope then you are often airborne
in 20-30 feet
as the rope almost bungees you
The pilot MUST maintain tension on the rope ,if you ease the tension too
rapidly .a
slow/fast/slow/fast pio starts to occur and you have to bung off.
Once you get used to the very rapid acceleration to flying and maintain
the
tension
then you get very good launches in comparison to wire .
Opinion seems to be that the big gain is in the acceleration and being
able
to rotate
to full climb very quickly as you have a lot of energy available and the
large V8 pulling
does not slow down much, if at all (except maybe with the Duodiscus turbo)
Heights depend on all the usual variables but often single seaters will
get
35-50%+ of
cable length in our case 3100ft length in still to 10kts, and increases
with
wind speed .
Our site lies parallel to a small 700-800ft ridge and seabreeze is often
present ,most
launches are crosswind so the majority of launches have only a small
headwind component
Other clubs have come to see our operation and are changing or in the
process of changing
because of good launches and more profit per launch.
gary
Auckland Gliding Club


"Robert Curry" wrote in message
m...
With all the talk about Spectra for winch wire replacement, one thing
comes to mind. COST! I just replaced our armored cable with 7X19
3/16 inch stranded steel cable. The cost for a five thousand foot
spool was $500. If the Spectra costs 40 cents per foot that equals
$2000. I recently heard of a club that was using standard poly rope
to replace their wire. They were claiming 2000 foot tows on a 4000
foot runway. Does anyone know where this operation is and if they
were using 1/4 inch poly or a beefer size? I wouldn't think that 1/4
inch poly would last very long.