Reciprocal auto tow works better the cable is pulled through a pulley at
the other end. as each launch is finished the car returns to the pulley
end and picks up the other end of the cable ready for next launch.
Some British clubs use a "Skylaunch" commercially built retrieve launch
system see their web site.

At 02:24 22 September 2008, Bill Daniels wrote:

wrote in message
...
It seems that a payout winch similar to those used for hang gliders
might be useful as a more efficient alternative to auto tows. You can
make better use of the runway length and have perhaps a safer launch
with proper calibration. Is anyone using such systems? Are they
practical? Are they in fact better than a straight auto tow?

It comes down to how much room you have and how fast you are willing to
drive. The typical glider will need about 60kts from a tow car on a
straight auto tow. That sixty knots will cover 6000 feet of runway in a

minute.

To that 60 kts, you have to add whatever speed you intend to use for rope

payout. If you intend to pay out 2000 feet of rope in that minute, the
car
will have to go a third faster or 80 kts or 92mph. 92mph cuts your climb

time to 39 seconds on a 6000' runway not allowing for acceleration and
stopping distances. Of course you have to iterate these number again
since
you'll need to pay out that 2000 feet in only 39 seconds. You'll also
need
to add distance for accelerating and stopping the tow car.

Ninty is already getting kinda fast for me but there's more. To that
92mph,
you will need to add about 2% for each thousand feet of density altitude.

Say your DA is 5000 feet then you need to drive the car at 101mph on a
calm
day (Don't even think about 10,000' DA's). Of course, if you have a
15
knot
headwind, that drops it to 'only' 85 or so.

So, if you are willing to drive that fast and have that much room, will
it

result in a usable release height? Probably. 39 seconds is enough to
reach
about 1800 feet AGL on a 2000' rope.

Most people who have worked this out have a winch. A winch with 6000
feet

of rope can deliver 3000 feet AGL and use only about a quart of fuel
doing

it.

Bill D