It was Essex GC (UK - and the club I belong to), not Essex & Suffolk,
that also did pulley launching. We stopped several years ago because
the Council, who own North Weald Airfield where we operated the system,
banned it when they allowed more and more powered aircraft there. Cables
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.

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.

We used Ford F250 trucks with 7.5 litre engines for our most successful
power units. (In earlier days we used F100's.) 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.

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.

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.

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.

We used 11 gauge piano wire (had used 13 gauge but it broke too often).
It had to be unrolled from its reel by a special unrolling device, to
avoid laying it in spiral twists. We towed a new length round the
pulley system a few times with a tractor tyre on the other end, to help
straighten it. Spirals rub the ground in one place and result in breaks
too soon.

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. Alternatively you can do a spiral knot, or use
ferrules. Whatever, it has to go thru the guide mechanism, fairly
smoothly onto the pulley, and be flexible enough to go round the pulley
rim without breaking thru fatigue. We got about 200+ launches per
cable. Cotswold got more - up to 600-700, IIRC. The knot machine makes a
lot of difference - ours was not very good.

We eventually developed a two-pulley system, pivoting every which way to
ensure the cable ran true from truck to pulleys to glider. Between the
two pulleys (about 30 inches dia each) there was a short straight run,
past the horizontal pivot. the pivot was hollow, had a chisel with a
motor cyle spring thru its centre, and could guillotine the cable
against a short anvil mounted between the pulleys.

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.

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.

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.

When really busy, we used two tow trucks. The second one followed the
glider being launched. Two thirds along the runway, the launch finishes,
the glider pulls off, the first tow truck proceeds to the launch point
to deliver its end of the cable for the next glider, and the second tow
truck proceeds to the pulley to do the next launch. The cable is double
ended, with the usual rings, strop, weak link, drogue, swivels etc. at
each end. The pulley safety person hooks the cable onto the second tow
truck and the system is ready to do the next launch. It is as fast as
any way of doing successive launches, because the cable is retrieved at
the same time as the launch is happening. (The only rival is the Long
Mynd winch system, with a retrieve winch - only suitable for non-tarmac,
I believe, and where you don't care about damage to the ground when the
metal triangle/sled joining the two cables and the glider strop all meet
as it falls to earth.) In less busy times, a single tow truck can be
used - it has to go back to the pulley ready to do the next launch,
which takes another 1-2 minutes per launch.

I don't know of any photographs or engineering drawings - tho some
people surely took some pics in its day. I could do some sketches, but
the detailed engineering would have to be done again to replicate it.

We sold our equipment to the Connell Gliding Club (Scotland, UK) but
they have no website and I don't know if it is still used there.

Chris N.