COPTR Stage 1 Practice Test

Blade flapping is needed to compensate for dissymmetry of lift in forward flight. As the rotor turns, the blade moving into the direction of travel (advancing blade) sees higher airspeed than the blade moving opposite (retreating blade), so it tends to generate more lift. If the blades were rigid, this would create uneven loads and a pitching moment that tilts the rotor and causes vibrations. The flapping hinge lets blades move up or down: the advancing blade flaps upward, reducing its effective lift, while the retreating blade flaps downward, increasing its lift. This up-and-down motion balances the lift across the rotor disc, keeps the rotor plane more stable, and lessens the pilot’s required cyclic input.