Thank you for the additional information Frank. 1500 - 1800 ft winch
launches from a 3900ft cable run is in the range 38-46%, which is about
what you would expect with a manually driven winch fitted with synthetic
cable in such conditions.
I am rather curious to know why this particular winch is so highly geared?
This probably justified your decision to launch in second gear. With a more
sensible axle ratio, automatic gear changes during the full climb in
'drive' would have been avoided. Our experience in the UK suggests that
automatic gearbox up changes during the ground run do not cause any
problems.
You cannot succesfully repair winch cables by tieing knots. The same is
also true for aerotow ropes. Synthetic cables and ropes have to be
spliced, and steel cables have to be spliced or crimped with brass
ferrules. We tried out synthetic cable at our club, but went back to steel
cables, partly for reasons of cost, but also because it seemed to take an
age to splice broken cables back together. As Frank rightly points out
below, having the right tools for the job and a bit of training in how to
do it for the winch drivers would have speeded things up a lot.
For general information, there are some computer controlled winches being
developed that should give higher and better controlled winch launches
still. The existing semi-automated Skylaunch winch will already give 45%
of cable run or better launches in zero head wind, using lightweight
synthetic cable and about 42% using heavier (but much cheaper) 4.5mm steel
cable. Achieved height also depends on pilot skill. Terms and conditions
apply!
Derek Copeland
At 18:27 24 May 2008, Frank Whiteley wrote:
Monday was never more than 5kts, normally less. Tuesday 12-18kts. Weds
10kts and a bit cross.
On May 24, 10:44 am, Derek Copeland wrote:
1800ft launches from a 3900ft cable run is 46% of that run, including
the ground run, which is pretty good. How much headwind component were you
launching into?
At 15:13 24 May 2008, Frank Whiteley wrote:
1. 1800agl (private K21), ~3900ft run.
2. Aborted launch. There were variations due to pilot training,
winch driver training, wind, so there a few may have been 1300ft.
Average with the Grob seemed to be about 1500agl. Bill will have to
comment further.
3. Actually, the K21 just seemed to perform better than the G103,
but
a very small sample. Again Bill will have to comment.
4. The rope used was 1/4" Amsteel II type (not clear which type,
see
www.samsonrope.com), rated at nominally 3800-5300lbs minimum
strength. This is a 12-strand Dyneema 75 core with a double braided
polyester cover. 2.2 times the weight of uncovered rope. No specific
knowledge of how well used the rope was. The is a temporary splice
that can be made using a double fisherman knot and duct tape, but we
found those failed after about 20 launches. The knots didn't fail,
but the knot appeared to cause damage near the end of the knotted
area. A better repair was to slide back the covering, tuck splice
the
12-strand, then work the covering back over the splice. I suspect
the
rope had been pretty well used before we used it. I make a good
field
fid from the tip of a 10 1/2 (6.5mm) knitting needle and aluminum
tube that greatly accelerate the splicing process. Don had a large
fid that was a chore to use and a plastic fid that just wouldn't
work.
We figured the final drive ratio at 2.92, which is too tall. The
winch came with instructions to only launch in 3rd, but after the
first launch, I used and trained on 2nd (1-2 upshift) for the rest of
the clinic. 3.55-4.11 final would probably allow use of 3rd,
depending
on engine torque/hp/redline. This appears to be an LT-4 350/330hp 4-
bolt, with Holley 4bbl. 340lbs@4500 and 330hp@5800. Redline 6300.
There were tags riveted on the winch indicated the transmission was a
TH400 installed in 1999 and engine an LT-4 installed in 2003. There
are some tweaks that could make this a better winch, but it wasn't
bad
and fairly easy to drive and train on.
Frank Whiteley