Acceleration due to gravity 32 ft/sec/sec = approx 20 knots/sec. If the
system were completely frictionless and the glider had zero drag that's
still 2 seconds to accelerate from 0 to 40 knots. At an average of speed
32 ft/sec, that's 64 feet or about 20 metres, not 5. Then you need to
figure the extra margin needed to overcome the frictional losses and the
glider's drag, quite likely doubling the run and you might want a bit of
margin above 40 knots which is around Vs on most modern gliders.

I believe something similar was used somewhere a long while ago, dropping
the weight down a disused mineshaft - don't recall the details.


At 07:52 21 October 2011, Jim White wrote:
At 18:16 20 October 2011, Bill D wrote:

Arguably, a better description is "trebuchet effect".

I have often wondered whether a sort of trebuchet could be useful for
launching a glider off a ridge. One can imagine a short bit or tarmac 5m
x
1m heading off the ridge and a large counter weight on a cable running
down
it. One would then only need to wind up the weight, secure it, get in,
have
some brave soul hook you up and release....

Jim