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

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

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

Answer: (A)

The key idea is how the blade is attached and how it moves. In a rigid rotor, the blades are connected to the hub without hinge joints. There are no hinges to allow independent movement at the hub, so any flap (up-and-down motion) or feather (pitch change to align with airflow) happens because the blade itself flexes and twists under load. That means blades are fixed to the hub, yet still able to flap and feather through their own elasticity. Other rotor types rely on hinges or joints at the hub to permit motion: fully articulated rotors have individual hinges for each blade for flap, lead-lag, and pitch; semi-ridged rotors combine some hinging with a flexible hub, giving limited, coordinated motion; interconnected rotors link blades in a way that changes how they move as a group.

The key idea is how the blade is attached and how it moves. In a rigid rotor, the blades are connected to the hub without hinge joints. There are no hinges to allow independent movement at the hub, so any flap (up-and-down motion) or feather (pitch change to align with airflow) happens because the blade itself flexes and twists under load. That means blades are fixed to the hub, yet still able to flap and feather through their own elasticity.

Other rotor types rely on hinges or joints at the hub to permit motion: fully articulated rotors have individual hinges for each blade for flap, lead-lag, and pitch; semi-ridged rotors combine some hinging with a flexible hub, giving limited, coordinated motion; interconnected rotors link blades in a way that changes how they move as a group.