Not so much 'yaw damping' (which indeed exists to prevent Dutch Roll), but aileron/spoiler-rudder cross feed......
Earlier swept wing a/c suffered from excessive 'dihedral effect' due to their sweep angle and positive dihedral; at high level any sideslip would cause a powerful restoring rolling moment in the opposite sense to the sideslip; thus the yawing moment resulting from the fin would become out of phase with the rolling moment caused by dihedral stability and at higher levels with adverse IAS/TAS ratios this could become divergent if left uncorrected. Rate gyros were thus fitted to detect the onset of sideslip and apply corrective signals to the rudder PCUs before the Dutch Roll could start.
The Russian solution was cleverer - pronounced anhedral (Il 62, Tu 154) to prevent the rolling moment ever becoming excessive!
Incidentally, anyone flying at such heights/weights that 15 deg of bank is the maximum to avoid low speed buffet boundary problems would be flying way, way outside the certification limit of a modern airliner! Even in the dark ages when we used to operate with a 20 knot spread between the 1.2 g HSB and LSB, we always had 25 deg of bank available! Really the 15 deg AoB detent is only there to enhance 'passenger comfort' - and to avoid unnecessary performance-sapping large angles of bank in the cruise (less drag, obviously).
Last edited by BEagle; 3rd February 2005 at 06:51.