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What causes the aircraft fuselage to pitch up when rearward cyclic is applied during the flare?
  • A

    An increase in the forward Horizontal Component of Thrust.

  • B
    An increase in Parasite Drag.
  • C
    An increase in the upward Vertical Component of Thrust.
  • D
    An increase in the rearward Horizontal Component of Thrust.

Refer to figures.
When rearward cyclic is applied during the flare, this tilts the disc and, thus, the Total Rotor Thrust (TRT) vector rearwards. As a result, the horizontal component of TRT is rapidly reoriented and now points backwards instead of forwards, opposing to the forward movement.

The horizontal component of TRT reversed, but the airflow from underneath, increases the angle of attack and creates more TRT and as result a greater rearward Horizontal Component of Thrust, as well. In more detail, when the rotor disc is inclined rearwards and whilst the helicopter is still travelling forward, the inflow of the air towards the underside of the disc increases the angle of attack on all the blades.

This rearward horizontal component of TRT acts at the rotor head, which is at some distance from the centre of gravity, so a significant arm is formed, which pitches the fuselage nose up.

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