Blade pitch angle is increased on the retreating blade side to compensate for decreased blade airspeed on that side. These changes in blade pitch are introduced either through the blade feathering mechanism or blade flapping. When made with the blade feathering mechanism, the changes are called cyclic feathering . Pitch changes are made to individual blades independent of the others in the system and are controlled by the pilot's cyclic pitch control. The tail rotor experiences dissymmetry of lift during forward flight, because it also has advancing and retreating blades.
Dissymmetry is corrected for by a flapping hinge action.
Two basic types of flapping hinges, the delta and the offset hinge, are used on most contemporary helicopters. One important advantage of offset hinges is the presence of control regardless of lift condition, since centrifugal force is independent of lift.