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Which statement is correct regarding to the Centrifugal Turning Moment?

  • A

    The Centrifugal Turning Moment increases the yaw rate.

  • B

    The Centrifugal Turning Moment tends to decrease the blade pitch angle.

  • C

    The Centrifugal Turning Moment tends to increase the blade pitch angle.

  • D

    The Centrifugal Turning Moment prevents the rotor blades from flapping.

Refer to figures.
The coning angle is a function of the radial component of centrifugal force. This force radiates from the centre of the hub like the spokes of a bicycle wheel throughout the plane of rotation.

If one blade is viewed in profile form the tip, it can be seen that the component T acts at a distance X from the feathering hinge. This is the Centrifugal Turning Moment (CTM) or feathering moment, which will cause a decreased pitch angle.

For the pilot to increase pitch angle by use of collective, the CTM will produce a force opposing the pilot increasing control forces.

Modern helicopters will incorporate powered flying controls, which overcome this problem. However, the use of another principle of centrifugal force can be used to counter CTM.

A rotating mass will always try to align itself 90º to its rotational axis (or plane of rotation). A counterweight is fitted at the rotor blades root so that, as it tries to align with the rotational plane, it increases the pitch angle. This will be in opposition to CTM and will reduce the pilot’s control load.

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