An airplane in straight and level flight has a lift distribution pattern that looks something like this, the lift generated by one wing is the same as the lift generated by the other wing. Deflecting the right aileron down causes an effective increase in the wing's camber and an increase in the effective angle of attack (AoA), the lift from that section of the wing increases, deflecting the left aileron up, causes an effective decrease in the wing's camber, and a decrease in the effective angle of attack (AoA), the lift from that section of the wing reduces.

The primary effect of aileron deflections is a roll, this is an approximate drag distribution pattern, when the ailerons are deflected extra drag is generated by both wings, however more drag is generated by the down going aileron than the up going aileron, this is induced drag, and it is caused by more lift required on the right wing to help initiate the roll. Combining the lift and drag effects together creates the undesirable tendency for the airplane to roll in one direction but yaw in the opposite direction, this effect is called adverse yaw, this effect is most noticeable at low speeds and on airplanes with high aspect ratio wings, there is another reason for the adverse yaw that is not often mentioned. In straight and level flight both wings encounter the relative airflow head on, but as the airplane rolls and the left wing moves down, a small amount of additional airflow strikes the wing from below, as the right wing moves up a small amount of airflow strikes the wing from above and vice versa, so as the airplane rolls the relative airflow is deflected slightly up on the right wing, and the relative airflow is deflected slightly down on the left wing, as lift always acts at right angles to the relative airflow, the upward deflection of the relative airflow on the right wing causes lift to deflect backward, conversely as the left wing goes down its relative airflow is deflected downward and its lift is deflected forward, the slight deflection of both lift vectors results in an adverse yaw moment to the right. The adverse your moment is felt when the airplane is rolling and it stops when the airplane stops rolling.

Adverse yaw can be prevented by using the rudder to create a yawing moment that helps to turn the airplane in the correct direction to remain coordinated, some aeroplanes incorporate design features to minimise the adverse yaw, one such feature is called differential ailerons, by excessively deflecting the upward aileron drag is increased on the down-going wing, this produces a desired yaw force in the direction of the turn.