"ir. K.P. Termaat" wrote:
...
During standard circling no accelleration forces in the longitudinal
direction of the glider are required to keep the IAS constant when the
glider makes perfect circles relative to the moving layer of air. From
the ground this looks quite different of course. But that is indeed
irrelevant.


You may consider it as irrelevant but it nevertheless complies with the
same laws of dynamics as seen from the air. An observer moving with
the airmass sees a glider with a bank angle generating an horizontal
component of the lift which remains perpendicular to the speed and has
no effect on the magnitude of the speed but only on its direction:
the glider circles. An observer on the ground sees the same horizontal
force but it does not remains perpendicular to the speed and so has an effect
on its magnitude as well as on its direction. The final resulting effect
is that the glider has increased its speed relative to the ground.
The force needed for this longitudinal acceleration that you were calling
for in your previous post is just the horizontal component of the lift.