flapping to equality

During the movement of a helicopter rotating blade, the speed of airflow over the advancing blade is higher than the retreating blade, resulting in production of an unequal amount of lift. This is called a dissymmetry of lift. To correct this aerodynamic imbalance, the blades are allowed to perform a series of controlled movements to produce equal amounts of lift. This process of equalization is called flapping to equality. See also dissymmetry of lift.