§27.547 Main rotor structure.

(a) Each main rotor assembly (including rotor hubs and blades) must be designed as prescribed in this section. [(b)] The main rotor structure must be designed to withstand the following loads prescribed in Secs. 27.337 through 27.341: (1) Critical flight loads. (2) Limit loads occurring under normal conditions of autorotation. For this condition, the rotor r.p.m. must be selected to include the effects of altitude. [(c)] The main rotor structure must be designed to withstand the loads simulating-- (1) For the rotor blades, hubs, and flapping hinges, the impact force of each blade against its stop during ground operation; and (2) Any other critical condition expected in normal operation. [(d)] The main rotor structure must be designed to withstand the limit torque at any rotational speed, including zero. In addition: (1) 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-- (i) The maximum torque likely to be transmitted to the rotor structure in either direction; and (ii) The limit engine torque specified in Sec. 27.361. (2) The limit torque must be distributed to the rotor blades in a rational manner.