Winching - Reverse Auto Tow

dropping and rotating propellors are a bad mix. Cotswold stopped when
they decided winching was better (dunno why - we would have continued
pulley launching if we could.) The two clubs developed the method in
parallel, sometimes copying each other amd sometimes going separate
ways. Both copied the idea from a club in Ireland - but I never heard if
they continued, and the English clubs did their own detailed engineering
and development without much learning from the Irish, I believe.

We, I fly from Cotswold and was there at the time that the decision was
made to switch, changed for a number of reasons. The first was that
spares for suitable trucks were getting hard to come by and we were
beginning to wear everything out. The second was that winch launching
offered a more reliable and easier to use system. Those who have done
auto tow will know that a good launch is totally dependant on the skill
of the truck driver. Whilst a winch launch, especially with today's
winches such as the Skylaunch that we have is much more "by numbers".

There are plenty of horror stories from the older members of when we had
lower powered trucks and ending up with gliders passing the truck when
still on the runways.

When we operated at North Weald with reverse pulley (and before that
with straight autotow) we acheived up to 100 launches a day, and could
have done more. Max rate was about 20+ in an hour with reverse pulley.
There is far too much to it than possible to write here, but some points
are as follows.

The launch rate can be very high. However, to attain this you need two
trucks, possibly three and a person at the pulley handling the hooking
on to the truck. It also requires a lot of launch point co-ordination.
This is attainable on open days or comps but not on normal club days.
On a normal day the rate usually fell to sub 10.

Important to have the
auto trans and heavy duty oil cooler option. You could start with just
a big car, but trucks are better for durability.

Yes
Tyre grip is important. It worked on good concrete/tarmac surfaces
(which we have at N Weald). Dirt or gravel sound challenging, but I
guess you can try. To enhance grip, we mounted the tow hitch on the
truck behind the cab, about 5 feet above ground. When towing, this
exerts more pressure on the (rear) driving wheels. The tow hook was a
glider nose hook (Tost) mounted horizontally, with a release cable thru
the back wall of the cab.

Same as ours but with the pressure sensor mentioned later. We also had
a release lever but no guillotine.

The driving technique is to take up the slack slowly of course, then
accelerate until the glider is seen to leave the ground, note the truck
speed, and go on to 5 mph faster than that. As the glider rotates into
the climb, cable tension increases, and slows the truck. The driver
balances the tension with throttle. The truck has to progressively
reduce speed as the glider gets higher. At the top of the launch, back
off the power, even brake if necessary to relieve the cable tension. As
soon as the cable comes away from the glider, accelerate to about 50 mph
to stop the cable falling in a heap. Slow down and stop before you hit
the next glider at the launch point. Aim to go past it if there is room.

This is the same as we used. On a good day (decent wind) you could be
almost stationary as a light glider, Ka8 or 6, was nearing the top of
the wire. Also easy to "kite" . As we have a long runway (just over a
mile) the glider was off by the time you got about two thirds of the way
along the runway unless it was a horrible heavy one. Really big birds
(ASH25 for instance) launched with their motor deployed.

We mostly operated without any cable tension gauge. Cotswold had a
gauge at least part of the time they used the system. You can rig up a
pivoting arm and a brake cylinder to a pressure gauge. Actual units
don't matter, it gets calibrated by finding the optimum pull required
for 1-seat, 2-seat gliders etc. and marking the scale with an indicator
point. We just found it too much trouble to keep the hydraulics free of
air, and it was not too difficult for drivers to learn how much
speed/throttle to use.
Ours was marked in link colour



You need to join it after breaks, unless you throw the cable away after
the first. We eventually joined broken ends copying Cotswold club's
method - a machine was made to twist the two ends together, overlapping
about 18 inches. A
Well, I never saw that, in the two years I used the system we always
tied reef knots in the system. We had a couple of bars with pegs that
you could use to wrap the wire round the main wire.

We cut the knots out and replaced them at the beginning of each day and
regularly got cable breaks during the day. Although the winch system is
incapable of doing the high launch rates that the reverse auto two is
the cable hardly breaks so you gain in the time it takes to tie knots.

Cotswold developed a much larger "pulley" - about 4+ feet dia - but it
was really a collection of small dia rollers mounted round the edge of a
circular frame. I don't know if they had a guillotine.

No
Both systems had large V-shaped guides to keep the cable in the right
part of the pulley. The pulley system has to mounted onto something,
usually a fairly heavy truck - it must not move, or be pulled off the
ground, when the launch takes place.

Yes, ours was an old 3 ton bread van, or something like that.

We had a safety person in the tow truck cab with the driver - to look
out forward when the driver was looking over his shoulder at the glider
high up the launch and by then behind him. We also had a safety person
in the pulley truck, to operate the guillotine if necessary.

Due to the length of the runway we usually got rid of the gliders when
they were overhead so a safety person wasn't used.

We saved the trucks and use them to pull out the cables for the
Skylaunch, the rest of the kit is mouldering in quiet parts of the field
:-)

Cheers

Robin


--
Robin Birch