Actually, I'm not sure the economic effect would be positive. The rope that
winds onto the drum first doesn't see much wear so the effect of using cheap
rope might not be significant. Looking at the big picture, the cost
difference per launch for cable replacement might not be worth the hassle of
using two kinds of rope. The price of high-strength synthetics is coming
down anyway.
All the engineering data I have says Spectra will outlast lesser synthetics
by a factor of 10 or more. Nothing wrong with experimenting with cheaper
materials though. If you want a "bungee effect", then nylon would be a
better material than poly.
The bungee effect is a way to store engine power and then release it at the
point of peak power demand with the result that a smaller engine can do the
work for a larger one. My gut reaction is that it would be better to use a
larger engine and no bungee effect - an engine is controllable and the
bungee effect is not. A stretchy rope is a step away from precise control
of the launch.
In my experience, most problems that arise in winch operations come from
poorly thought out efforts to save money up front. The best way to save
money is to do the thing right the first time.
Bill Daniels
"F.L. Whiteley" wrote in message
...
1. with a hybrid solution on a LONG (=5000ft) run, you still get 2500ft
of
bungee effect at the beginning of the launch (not sure that 5000ft of
bungee
effect is wanted)
2. then ELIMINATE the sag as the launch gets higher using the lighter and
thinner and more expensive rope
I'm not suggesting this for launch runs of 1000m, but those about 1400m
length or greater where someone has already demonstrated that 10mm poly
has
issues of weight and drag.
Frank
"goneill" wrote in message
...
Big point ,the bungee effect is VERY DESIRABLE at the initial
acceleration
and rotation into the full climb,this is where the extra height is
coming
from ,
no wasted field length ,the penalty for the bungee effect is at the top
of
the
launch where the the winch needs to have the release with no tension
so the rope does not catapult at the winch and snag in the feed guide.
A number of single seaters are requesting 70 knots on the winch and
dipping the nose for release then pulling up with the residual speed
often
getting 1600-1700ft.
Overall the good effects outweigh the few minor problems created ,these
problems are negated by operational changes
gary
"F.L. Whiteley" wrote in message
...
"goneill" wrote in message
...
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
Gary,
Thanks for the information. Now, if the poly could be spliced ~50/50
or
so
with something like 1/8" Validator 12
http://www.samsonrope.com/admin/data...dator12_LR.pdf ,
(Vectran) http://www.pelicanrope.com/peli05c.htm both the bungee and
sag
effects could be reduced with some cost benefits. This could be a
solution
for long runs. When we launched with 1000ft of Spectra on the end of
the
wire rope, we didn't pull the Spectra through the rollers. Two
synthetics
with a reasonable join might work well as a hybrid solution.
Vectran is stronger than Spectra with a higher critical temperature,
but
with somewhat less abrasion resistence.
There are some interesting 1/4" vectran sheathed products
http://www.pelicanrope.com/new04.htm
for improved abrasion resistence.
And Plasma 12
http://www.cortlandcable.com/psrope/...PlasmaRev9.pdf
Spectra in a variety of sizes.
Frank Whiteley
Colorado