"Gary Boggs" wrote in message
...
I really appreciate all this good input, thank you all for responding.
Now
for a new twist, one of our members has built a "pay out winch". A pay
out
winch is a drum with a break on it. The glider hooks up about 200' behind
the tow vehicle, and as the glider climbs, the line spools out. Does
anybody have any experience with this type of launch? How much runway do
you need for this type of launch, how high can you get, ect?

Boggs


I've done lots of auto tows and winch launches but no payout winch launches.
But, I have done some back of the envelope calculating for payout winches.
Payout winches seem to work fine for hang gliders where the towing speeds
are far lower than sailplanes. The speeds needed for sailplanes really jack
up the numbers.

Assuming no wind, (Given enough wind, anything works - even a large stake.)
the tow car has to accelerate to the normal towing speed plus the payout
rate. The normal glider airspeed at the beginning of the climb will be
about 55 - 60 Knots. Correcting this for True Airspeed, depending on
density altitude, may be 70 - 75 MPH on the tow car speedometer. To pay out
enough wire to make the effort worthwhile, (Say, 2500 feet in 60 seconds)
the payout rate will be about 45FPS or 30MPH which brings the tow car speed
to 105MPH - a bit fast for my taste. Now the tow car speed will decrease as
the glider climbs so the distance required will be less than that covered at
100MPH for one minute. But you have to add in the distance to accelerate
and stop the tow car.

Juggle the numbers for yourself but it looks like you will need a 12,000
foot runway and really fast car - or lots of headwind. Consider also that a
heavy two-seater will demand nearly 250 HP at the tow hook and a wire
tension of about 1300 pounds. Your tow car had better be heavy as well as
fast.

This starts to make a standard winch launch look good.

Bill Daniels