Editing Dutch roll (section)

==Mechanism==
The most common mechanism of Dutch roll occurrence is a yawing motion which can be caused by a number of factors. As a swept-wing aircraft yaws (to the right, for instance), the left wing becomes less-swept than the right wing in reference to the relative wind. Because of this, the left wing develops more lift than the right wing causing the aircraft to roll to the right. This motion continues until the yaw angle of the aircraft reaches the point where the vertical stabilizer effectively becomes a wind vane and reverses the yawing motion. As the aircraft yaws back to the left, the right wing then becomes less swept than the left resulting in the right wing developing more lift than the left. The aircraft then rolls to the left as the yaw angle again reaches the point where the aircraft wind-vanes back the other direction and the whole process repeats itself. The average duration of a Dutch roll half-cycle is 2 to 3 seconds.

The Dutch roll mode can be excited by any use of [[aileron]] or [[rudder]], but for flight test purposes it is usually excited with a rudder singlet (a short sharp motion of the rudder to a specified angle, and then back to the centered position) or doublet (a pair of such motions in opposite directions). Some larger aircraft are better excited with aileron inputs. Periods can range from a few seconds for [[light-sport aircraft|light aircraft]] to a minute or more for [[airliner]]s.{{Citation needed|date=September 2010}}

[[Tex Johnston]] describes the Dutch roll as "...an inherent characteristic of swept-wing aircraft. It starts with a yaw. In a 35-degree swept-wing airplane, a yaw is accompanied by a simultaneous roll in the direction of yaw. The roll is caused by changing lift factors as the airflow path over the wing changes.  For example, in a left yaw the left wing slews toward the rear so that airflow is displaced spanwise from its normal front-to-rear path over the airfoil section. That reduces lift. Simultaneously, the advancing right wing gets more chordwise flow, and so its lift is increased. In combination the two conditions create a left roll. Similarly, a yaw to the right results in a roll to the right. An oscillation is set up."<ref>{{cite book |last1=Johnston |first1=A.M. "Tex" |url=https://archive.org/details/texjohnston00john/page/140 |title=Tex Johnston: Jet-Age Test Pilot |date=1992 |publisher=Bantam |isbn=9780553295870 |location=New York |page=140 |url-access=registration}}</ref>