Bob Cook wrote:
You can change the reference or axis system all you want, But then you
also change the direction of "down".


Gravity acts downward and no other diredtion.


Lift plus grivity act together and form a resultant force parallel to the
direction of flight. Drag acts in the opposite direction at equal
magnitude.

Gravity (alone) is not the force that provides forward motion to a
glider.

Maybe we are wordsmithing/semanticizing a bit. Take away gravity and
air movement and place a glider somewhere up in the still air (I know,
suspend disbelief for a moment) and let go of the glider. No initial
motion is given to the glider, it is just "suspended in air". How much
lift and/or forward motion do we then get? None. Add gravity to the
same scenario and the glider will then move forward (after an initial
drop). So perhaps gravity *is* the sole force required for forward
motion. Of course we need air as well. But still air is a gaseous
mass, not a force or even a source of force. The reaction force caused
by the combination of gravity (sole source of force) and the presence of
air (air is not a force) leads to the forward motion of the glider.

Regards,

-Doug