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Adverse yaw is a secondary effect of the application of the Ailerons in Aircraft . Its cause and effect can be explained as follows:

When the control column of an aircraft is moved to the left, the left aileron is deflected upwards, and the right aileron is deflected downwards. As the right aileron is lowered, the lift it produces will increase (due to an increase in Angle Of Attack ), however the drag it produces will also increase. For the same reason, as the left aileron is raised both the lift and the drag it produces will decrease. The combined effect of this is to Yaw the aircraft to the right (away from the lowered wing)

It is this effect which is known as Adverse yaw, and the force which causes it is known as '''Aileron drag'''.


MINIMISING THE EFFECT OF ADVERSE YAW

Adverse yaw is countered by using the aircraft's Rudder to perform a co-ordinated turn, however an aircraft designer can reduce the amount of correction required by careful design of the aileron. Two methods are common:


Frise ailerons


Frise ailerons are designed so that when up aileron is applied, some of the forward edge of the aileron will protrude downward into the airflow, causing increased drag on this (down-going) wing. This will counter the drag produced by the other aileron, thus reducing adverse yaw.

Unfortunately, as well as reducing adverse yaw, Frise ailerons will increase the overall drag of the aircraft, and therefore they are less popular in aircraft where minimising drag is important (e.g. in a Glider )





Differential ailerons


As it is the downwards deflection of an aileron that causes aileron drag, a simple way of eliminating adverse yaw would be to rely solely on the upward deflection of the opposite wing to cause the aircraft to roll. However, this would lead to a slow roll rate - and therefore a better solution is to make a compromise between adverse yaw and roll rate. This is what occurs in Differential ailerons.

As can be seen from the diagram, the down-going aileron moves through a smaller angle than the up-going aileron, reducing the amount of aileron drag, and thus reducing the effect of adverse yaw.