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A directional gyroscope may drift over time due to:

1. Rotation of the Earth.
2. Altitude.
3. Aircraft manoeuvring.
4. Aircraft movement over the Earth’s surface.
5. Magnetic dip.
6. Piloting errors.
7. Wind correction.

  • A

    1, 2 and 3.

  • B

    1, 3 and 4.

  • C

    1, 3 and 5.

  • D

    2, 4 and 5.

The Directional Gyro Indicator (DGI) is initially synchronized manually with the direct reading magnetic compass. This initial synchronization must be checked at regular intervals and re-aligned with the aircraft compass for the most reliable indications because it will drift over time due to earth rotation, aircraft manoeuvring and transport wander.

The following may affect the readings of a DGI:

  • Gimballing error – produced due to the shape of the gimbal system.

  • Random wander – change of direction in space of the rotor’s spin axis due to manufacturing imperfections.

  • Apparent wander due to Earth’s rotation – the gyro is initially aligned with a given meridian, but over time this meridian has moved due to Earth’s rotation, and the gyro is not correctly aligned anymore.

  • Rotor speed variations – which will be sensed and corrected by streaming more air to the bucket vanes of the rotor.

  • Transport wander – apparent wander due to the change of aircraft position.

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