We intentionally turned off both yaw dampers in the 727 once. As part of a post maintenance inspection. I can't remember the exact altitude but it was above FL300.
Initial reaction in the smooth air was no effect. Then a small amount of rudder input was made and as expected, the yawing started. not really bad but it was there. No doubt, the greater the input, the greater the motion would be.
The procedure for maintaining control was to avoid any further rudder input and use sharp, properly timed aileron inputs to minimize the oscillation. Choose a particular wing as your reference. When that wing starts rising from its maximum amount of downward displacement, initiate the quick, aileron input and return to neutral. But while the oscillations were controllable, they did continue. Just like in the sim. Make sure to use the chosen wing as your reference in your mind. Upgoing right wing means the right side of your artificial horizon line is going down. It is easy to mix up and make the wrong input.
What would also happen is while initially, you might have say 20° of bank either side of neutral with neutral being wings level, that neutral position would move to one side or the other, so now there might still be 20° banks happening but on either side of a new neutral point of, for example, 10° left bank. Weird.
The true initial effective measure to counteract this phenomenon in the 727-200 was to use speedbrake. Problem solved it seemed to me.
Last edited by JammedStab; 5th September 2013 at 23:22.