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The asymmetry of lift in a tail rotor...

  • A

    Cannot occur since the relative airflow velocity is the same at any position.

  • B

    Cannot be reduced in any configuration and therefore has to be accepted.

  • C

    Is essential for the correct functioning of the helicopter.

  • D

    May be reduced by allowing blade flapping.

Conventional tail rotors are affected by the asymmetry (or dissymmetry) of lift. That means that there is an advancing side flapping up (towards the direction of thrust) and a retreating side flapping down. To compensate for this, the tail rotor blades are allowed to flap.

Also, conventional tail rotors are exposed to confused airflow from the main rotor downwash and disturbances from the fuselage.

Thus, forward speed creates asymmetric thrust and a neat solution to this is to place the tail rotor in a duct and having a “shrouded tail rotor” or “fenestron”.

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