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Assuming that the nominal rotor RPM of a 2-bladed helicopter is 350, what is the principal main rotor vibration frequency?

  • A
    6 Hz
  • B

    1050 Hz

  • C
    24 Hz
  • D

    12 Hz

Helicopters are susceptible to vibration because of their multiple, complex, and various sizes of rotating parts. The need to define vibrations’ intensity is crucial and may be expressed in speed as well as in acceleration.

To calculate the main rotor vibration frequency, apply the following formula:

  • V = RPM/60 x N, where:
    • V, the nominal vibration in Hz
    • N, the number of rotor blades
    • The division by 60 brings revolutions per minute to a value per second

Therefore:

  • V = 350 / 60 x 2 = 11.6 Hz, closest answer 12 Hz.

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