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The variations of the tip path plane level on an articulated rotor system are due to the…

  • A

    Collective pitch.

  • B

    Blades' flapping angles.

  • C

    Blades' setting angles.

  • D

    Blades' angle of attack

Refer to figures.
On a fully articulated rotor system the blades are allowed to flap, feather and lead/lag.

Each rotor blade is attached to the rotor hub by a horizontal hinge, called the flapping hinge, which permits the blades to flap up and down. Each blade can move up and down independently of the others.

The tip path plane is the plane traced out by the blades tips and is often what the pilot sees from the cockpit as the blades rotate.

The tip path plane is parallel to, but not necessarily the same as the plane of rotation. This is because the blades can flap up, owing to their flexible attachment to the rotor head.

Since the blades are free to flap up, their flapping angles will vary, causing variations to the tip path plane level.

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