Here a cross posting from some info I posted yesterday on the Yahoo
winchdesign group for those of you who are interested in winch
launching. It might be that we managed to successfully establish the
highest winch launch operation in the world here in Bogota, Colombia,
at an altitude of 8478 feet (2584 meters) with density altitudes
commonly around 11,000 feet sometimes approaching 12,000 feet
(3350/3660 meters). This might be of interest especially to glider
operations in the Western US since high density altitudes are very
common out there.

Markus Graeber
Aeroclub de Colombia/Albuquerque Soaring Club

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I am pleased to announce that over the last 8 days we have
successfully completed our winch trials and initial winch driver
training here in Bogota. The first 6 launches were done on Sunday, Jan
27th, with the club's IS-28B2 Twin Lark on a great soaring day with
density altitudes approaching 11,000 feet. Over the week we
accumulated some more launches culminating in the official winch
inauguration on this past Sunday, Feb. 3rd. During the festivities
which were attended by some 200 members & guests we managed to put in
24 launches mostly on Sunday afternoon launching our Blanik L-13 and
IS-28B2 as well as a member's Janus CM with guests in the second seat.

We used about 1800m (5900 feet) on the initial launches leading to
launch heights in excess of 2000 feet even with relatively
inexperienced winch drivers (trainees) and pilots. Later we shortened
the run to about 1400 meters (4600 feet) to allow the gliders to roll
up directly to the launch point for higher launch frequencies and
commonly achieved launch heights in excess of 1600 feet. Density
altitude was probably in excess of 11,000 feet during Sunday's hot
afternoon. All launches were done in almost nil wind conditions which
sometimes increased to about 5 knots max headwind component.

Our setup is a single drum Skylaunch 3 winch with 2500 meters of 5mm
Dyneema cable and a Chevy 502HO big block engine with a Holley 870 cfm
four barrel carburetor rated at 450 HP at sea level delivering some
315 HP (estimated) at 11,000 feet density altitude. Transmission is a
Hughes Performance Heavy Duty TH400 without reverse gear using all 3
forward gears with their Tow Master 2000 RPM stall converter.

Even launching the Janus CM 2 up with a launch weight near 650 kg was
no problem at all, gear changes to 3rd gear during the initial ground
acceleration are not noticeable at all. Revs at rotation for the
relatively fast Janus CM are in the mid 4000s, since the engine has a
rev limit of 5500 rpm it gives us a nice reserve should it be needed
in case of an unexpected emergency.

I will collect some more hard data with the help of our telemetry
system and GPS traces over the next few weeks and report back with
more details. Initial experience suggests that at our density altitude
with inexperienced pilots and winch drivers you can expect about .35
launch heights (in relation to the cable run) which are probably
around .40 once everybody is tuned in. In comparison, at sea level the
Skylaunch winches routinely reach .45 with experienced pilots and
winch drivers sometimes reaching .5 with the right glider/pilot/winch
driver combination in near nil wind conditions.

Thanks for all the input and feedback I have received during the
course of the last 1.5 years while bringing this project to a
successful conclusion,

Markus Graeber
Aeroclub de Colombia