Which rotor system has blades fixed to the hub but free to flap and feather?

Which rotor system has blades fixed to the hub but free to flap and feather?

• A. Semi-Ridged Rotor
• B. Rigid Rotor
• C. Fully Articulated Rotor
• D. Interconnected Rotor

Answer: (A)

Understanding rotor head design helps explain how blades move relative to the hub. In a semi-rigid rotor, the blades are mounted to the hub with a single teetering hinge, so the blades are effectively fixed to the hub but can flap as a unit about that hinge. Pitch changes can feather the blades, giving you the feather capability as part of normal collective control. There aren’t independent hinges at each blade root like in a fully articulated rotor, and there isn’t the complete rigidity of a rigid rotor, where flapping occurs mainly through blade bending rather than a true hinge. This combination—blades fixed to the hub but free to flap together and feather via pitch control—fits the semi-rigid design.

Understanding rotor head design helps explain how blades move relative to the hub. In a semi-rigid rotor, the blades are mounted to the hub with a single teetering hinge, so the blades are effectively fixed to the hub but can flap as a unit about that hinge. Pitch changes can feather the blades, giving you the feather capability as part of normal collective control. There aren’t independent hinges at each blade root like in a fully articulated rotor, and there isn’t the complete rigidity of a rigid rotor, where flapping occurs mainly through blade bending rather than a true hinge. This combination—blades fixed to the hub but free to flap together and feather via pitch control—fits the semi-rigid design.