"nafod40" wrote in message
...
Bill Daniels wrote:

The rule I learned was that ground effect became measurable at one
wingspan
above the ground and near the ground could double the L/D. Running in
ground effect is a lot of fun but you'd better be very smooth on the
elevator since the pitch control gets 'twitchy'.

(I strongly suspect that unanticipated elevator sensitivity in ground
effect
is a secondary cause of some of the G103 "PIO" accidents.)

Interesting observation. Flying in ground effect places the center of
pressure of the wing at about mid-chord, while out of ground effect the
center of pressure is about 1/4 chord. So in short, ground effect
usually has a stabilizing effect by essentially shifting the CG forward
with respect to the center of lift.

Al I can say is put a G103 in ground effect and see for yourself.
Obviously, flying qualities in ground effect deals with the whole glider and
not just the wing. No doubt the flow over the tail is involved as well.

Bill Daniels