14 CFR § 29.547

A rotor is an assembly of rotating components, which includes the rotor hub, blades, blade dampers, the pitch control mechanisms, and all other parts that rotate with the assembly.

Each rotor assembly must be designed as prescribed in this section and must function safely for the critical flight load and operating conditions. A design assessment must be performed, including a detailed failure analysis to identify all failures that will prevent continued safe flight or safe landing, and must identify the means to minimize the likelihood of their occurrence.

The rotor structure must be designed to withstand the following loads prescribed in §§ 29.337 through 29.341 and 29.351:

Critical flight loads.

Limit loads occurring under normal conditions of autorotation.

The rotor structure must be designed to withstand loads simulating—

For the rotor blades, hubs, and flapping hinges, the impact force of each blade against its stop during ground operation; and

Any other critical condition expected in normal operation.

The rotor structure must be designed to withstand the limit torque at any rotational speed, including zero.

The limit torque need not be greater than the torque defined by a torque limiting device (where provided), and may not be less than the greater of—

The maximum torque likely to be transmitted to the rotor structure, in either direction, by the rotor drive or by sudden application of the rotor brake; and

For the main rotor, the limit engine torque specified in § 29.361.

The limit torque must be equally and rationally distributed to the rotor blades.