Milt,
"My definition would leave out 'in the horizontal plane' and would include 'normal to the vertical axis' and there are probably a few ways of saying the same thing."
While one can resolve the vector to the aircraft plane, why bother for this qualitative discussion ? Depending on whether the bird is going up or down at the time, the vector elevation will follow the performance .. with a definite effect on forces developed by the fuselage. ... and, in any case, how does this alter the situation ?
"there is dynamic pressure on the right side of the fuselage to balance the tendency to yaw left."
Are we considering only the skidding zero rudder deflection situation here ? Why would not the pilot input rudder to reduce the skid (slip) ?
"Immediately you change the rudder angle by a nat's whisker you have changed that finite side force and you are no longer in straight balanced flight"
If we ignore minor effects (such as rolling moments) due to rudder deflection, surely the rudder input simply alters the lateral force system along with the yawing moment balance ? Why is this fundamentally different to the free/fixed rudder case ? Why can we not input an additional force in the opposite sense by playing with bank angle ?
"I see confusion in appreciating a requirement for a balance of forces. An overly concentration on balances of moments and couples/torques."
The two considerations (forces and moments) need to be balanced for steady flight (which would then be straight). It is implicit that varying the rudder input requires an opposing lateral force adjustment via a bank variation. Perhaps you can offer an explanation of how the observed airflow direction as rudder and bank is varied fits into your thesis ?
"Any aircraft in straight and level balanced flight having total drag offset from the fore and aft axis will be unable to have a direction of flight along its fore and aft axis. This applys equally to wings level and banked flight."
Why is this offset necessarily so ? Why can not one vary the drag components to alter the drag vector ?
"Where are you getting that "horizontal force at the stabiliser" if it is not being generated by the very sideslip you think you have made go away."
This would be quite OK if we were looking at a rudder free/fixed environment, but why is it that one cannot input rudder to achieve the force desired ? Indeed, the arguments suggests that ailerons and elevators, similarly, can't work ?