(a) Introduction
This AMC supplements FAA AC 29-2C, § AC 29.927 and should be used in conjunction with that AC when demonstrating compliance with CS 29.927.
(b) Variable rotor speed (NR)
(1) Explanation
The variable rotor speed (NR) function allows running at different NR levels to achieve, for instance, lower noise levels and better rotorcraft performance.
In addition to the endurance test prescribed in CS 29.923, additional tests may be necessary to demonstrate that rotor drive systems of rotorcraft with a variable NR are safe.
(2) Procedure
In order to substantiate an acceptable vibration and dynamic behaviour of rotor drive systems when using the available range of rotor speeds within the variable NR function, the applicant should consider performing specific test investigations, as prescribed in CS 29.927(a). The need for representative test runs at the different torque and rotor speed combinations, covering steady states and transient conditions to be encountered in operation, should be evaluated by and agreed with the Agency.
[Amdt No: 29/11]
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