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How can the state of "Dutch Roll" be described when experienced by a helicopter?
  • A
    Cross coupling between pitch and roll.
  • B
    Cross coupling between roll and yaw.
  • C
    Cross coupling between pitch and yaw.
  • D
    A disturbance in yaw.

Refer to figures.
Dutch roll is a continuous rolling and yawing motion. It is the result of a strong static lateral stability, induced by a high dihedral effect, linking roll and yaw or by relatively weak directional stability.

The presence of dutch roll doesn’t mean that there is no directional stability. It simply means that the balance between lateral and directional stability is biased towards lateral stability.

Dutch roll will be most pronounced at high speed when the increased thrust and torque result in a large static roll stability together with a small directional stability may lead to a Dutch roll.

Therefore, Dutch roll is a cross coupling between roll and yaw.


NOTES:

Stability is the property of a body to resist displacement or if displaced its response and has:

  • Static (immediate) and
  • Dynamic (subsequent) values.

Static stability is the initial response to displacement and it can be:

  • Positive (the helicopter returns back to its original position).
  • Neutral (the helicopter remains at its displaced attitude).
  • Negative (the helicopter continues moving away).

Dynamic stability is what the helicopter does over time when displaced and it can be:

  • Positive;
  • Neutral and
  • Negative.

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