What causes the retreating blade to flap down?

What causes the retreating blade to flap down?

• A. Increased Lift
• B. Centrifugal Force
• C. Turbulence
• D. Reduced Lift

Answer: (D)

In forward flight, the rotor experiences dissymmetry of lift: the advancing blade meets the air faster and generates more lift, while the retreating blade sees slower air and generates less lift. The rotor is mounted on a flapping hinge, so these lift differences cause the blades to move up and down to balance the disk. Since the retreating blade has less lift, it moves downward about the hinge, while the advancing blade tends to move upward. This downward flap of the retreating blade is the natural response to the reduced lift on that side. Turbulence or centrifugal force aren’t the primary causes for this specific downward flap—the key factor is the lower lift on the retreating blade.

In forward flight, the rotor experiences dissymmetry of lift: the advancing blade meets the air faster and generates more lift, while the retreating blade sees slower air and generates less lift. The rotor is mounted on a flapping hinge, so these lift differences cause the blades to move up and down to balance the disk. Since the retreating blade has less lift, it moves downward about the hinge, while the advancing blade tends to move upward. This downward flap of the retreating blade is the natural response to the reduced lift on that side. Turbulence or centrifugal force aren’t the primary causes for this specific downward flap—the key factor is the lower lift on the retreating blade.