What is blade flapping?

• A. A motion of the rotor blades about their hinge to equalize lift
• B. A Change in Blade Root Thickness
• C. A Device to Increase Rotor Speed
• D. A Method to Reduce Airspeed

Answer: (A)

Blade flapping is the motion of each rotor blade about its flapping hinge that lets the blade move up or down. This movement lets lift be redistributed across the rotor disk to balance the unequal airflow the blades experience in forward flight. The advancing blade, moving into the wind faster, would tend to produce more lift, so it flaps upward to reduce its angle of attack; the retreating blade flaps downward to increase its angle of attack. This up-and-down motion smooths out lift differences, helping keep the rotor more balanced and reducing vibration. It isn’t about changes in blade root thickness, increasing rotor speed, or reducing airspeed.