Winch Launch Safety Study

As I have tried to explain to Bill on numerous occasions, and on various
forums, the uncontrollable over-rotation you get from an over-powered
winch launch is caused by the pull line to the belly hook being below the
glider's centre of gravity and centre of pressure. This causes a rotation
for mechanical rather than aerodynamic control reasons. This is why high
winged gliders, such as the K6 and K8 are most at risk.

If you get such a launch, even holding the stick hard forward all the time
from 'take up slack' will not prevent the over-rotation, although it
might slightly reduce your chances of instant death from a flick spin.

Such events can be easily avoided by by controlling the winch so that the
ground run acceleration is not more than about 1.0g (or less for the types
mentioned above). This will still get you airborne and climbing within
about 3-4 seconds, which most pilots find quite fast enough! It will also
make very little difference to the achieved height.

Derek Copeland

At 22:41 19 March 2009, bildan wrote:
As the glider leaves the ground, the inertial rotation will begin but
if the acceleration continues, the elevator effectiveness will also
continue to increase with the square of the airspeed. Rotation can't
happen instantly because the glider has mass and rotational inertia.
In fact, the pilot has to start backing off the down elevator to allow
the glider to rotate into the climb.

Now, contrast this with a slow acceleration. The glider staggers into
the air and the nose-up inertial couple starts the rotation but the
low speed and acceleration doesn't provide adequate control. The nose
rises as the pilot struggles to control it with inadequate
airspeed.....

I've collected stories on this type of accident for decades and they
ALWAYS happen with slow acceleration.