Yaw is controlled by the rudder. The yaw damper operates the rudder to dampen the un commanded yaw. The book says with most aircraft, control the roll with aileron, should the YD be u/s. Why? The yaw can be dampened manually with gentle rudder input. There is quite a lag. Hint, "control column left, apply right rudder gently and momentarily" to reduce, then almost eliminate the unwanted oscillations. Get it wrong and you could have a problem of course. I am talking heavy, 4 engine first generation jets, with under slung engines. Worked for me and I haven't "wiped off any pods" due to side loads using this method.
I never wrote that!
