Page:CAB Accident Report, Boeing Test Flight Crash on 19 October 1959.pdf/11



The term Dutch Roll applies to a wallowing motion characteristic of swept-wing aircraft. During this motion the aircraft rolls right and left around the longitudinal axis while yawing right and left around the vertical axis. Angle of bank and degree of yaw are dependent upon the amount of force applied in initiating the Dutch Roll.

Normally the motion is caused by turbulent air or lateral overcontrol. The low lateral direction damping of swept-wing design allows the motion to continue at slow i. a. s.

Compensating for the Dutch Roll may be made by simply keeping the wings level. When the airplane is rolling one direction or another, the aileron should be used to stop the roll and keep the wings level.

Another method is to apply cross-control. For example, if the aircraft is Dutch Rolling, left rudder and right aileron should be applied when the nose has started to swing from left to right with control forces slowly relieved as the aircraft's yaw angle diminishes.

Rudder application must be applied in the right direction or the Dutch Roll will be further aggravated. If there is uncertainty as to the rudder required, application of aileron only is recommended for recovery.

The damping in the lateral-direction mode is lowest when the angle of attack is high, so that at low indicated airspeeds with flaps up or down, the Dutch Roll will seem to be more pronounced. At high indicated airspeeds the natural yaw-damping forces minimize or tend to zero out any Dutch Roll tendencies.

The purpose of Dutch Roll familiarization is to introduce to the pilots who are generally not acquainted with swept-wing airplanes this inherent characteristic peculiar to this design.