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Dutch Roll

Dutch roll is a combination of yawing and rolling motion that is characteristic of all swept wing aircraft. Disturbances about the yaw axis of an airplane will result in disturbances about the roll axis. This is caused by the dihedral effect of the wings (roll due to yaw). On a swept wing airplane, this effect is due to two causes. First, when a wing with positive dihedral (tips higher than roots) is yawed the forward wing is at a higher angle of attack than the trailing wing. This results in a differential lift situation which causes a rolling moment. If the wing is also swept, the forward wing will also cause more rolling moment than the other wing due to the greater moment arm of its center of lift as well as the increased lift. This rolling produces sideslip due to roll only. This sideslip on a wing with dihedral causes a rolling moment tending to lift the down wing. The net result is a pendulum-like motion similar to the rolling motion of a Dutch ice speed-skater on the frozen canals of Holland, hence the name "Dutch Roll". Loss of directional control can occur if divergent Dutch roll is not properly damped. This is one of the reasons for the development of yaw dampers on modern day jets.

Source: Air Force Flight Test Center, Edwards Air Force Base, CA

The Dutch Roll

The Flying Dutch Girl,  Caroline