Adverse yaw is the natural and undesirable tendency for an
aircraft to yaw in the opposite direction of a roll. It is caused by the difference in profile drag between the upward and downward deflected
ailerons, the difference in lift and thus
induced drag between left and right wings, as well as an opposite rotation of each wing's lift vector about the pitch axis due to the rolling trajectory of the aircraft. The effect can be greatly minimized with ailerons or other mechanisms deliberately designed to create more drag when deflected upward than downward and/or mechanisms which automatically apply some amount of coordinated
rudder. As the major causes of adverse yaw vary with lift, any fixed-ratio mechanism will fail to fully solve the problem across all flight conditions and thus any manually operated aircraft will require some amount of
rudder input from the pilot in order to maintain
coordinated flight.