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?

The K21 does seem to winch launch particularly well, especially when flown
solo. This type holds the current height record for a conventional winch
launch by the way. From memory this is about 5600 feet, set in Holland.

Derek Copeland


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