"Doug Haluza" wrote in message
oups.com...
I've seen MITSA do a similar operation with an L-23 at Sterling VT with
very similar numbers.


The trick for auto tow is to determine the exact best length for the rope.
If you stretch out 5000 feet of rope on a 5000 foot runway, the tow car has
nowhere to go. If you use a very short rope, the car has lots of room but
you won't get very high. The optimum is somewhere in between and depends on
the acceleration of the tow car and the wind. The more powerful the car
and/or the greater the headwind, the longer rope that can be used.

On dry lakes with essentially unlimited room, I recall that a glider just
can't lift more than about 5500 feet of steel cable but can still reach 3000
feet AGL. Spectra would really pay off here.

George Moore has done some excellent mathematical models for winch launch.
He proves that under ideal conditions a launch can reach a height equal to
half the length of the runway which is quite a bit better than auto tow on a
typical runway. See the Yahoo Group 'winchdesign'.

Auto tow has lower 'up-front' costs but higher long term costs as tow cars
wear out. Winches have high start-up costs but the long term economics are
excellent.

Bill Daniels