not trying to shoot you down NWSRG...
Yaw = rotation about the VERTICAL axis
Isn't vertical a constant 90 degrees upright from the horizontal?
Pilot training 101: effects of control, primary and secondary
... ailerons: primary = roll
secondary = yaw
Again, I'm not trying to contradict anyone, just explaining my understanding of it (until someone explains it better to me).
The pig