adverse yaw
In a flat-bottomed wing, air is moving faster over the wing’s top than it is under the bottom. Since faster air has less pressure, the air under the wing is denser. When an aileron is deflected downwards, it develops more drag in the dense air than the other aileron moving upwards. This extra drag causes the wing and fuselage to swing, or yaw, in the opposite direction of the desired bank. A right bank first makes the plane’s nose yaw to the left before the bank develops. This is called adverse yaw.
