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What is the apparent drift of a directional gyro with a north-south spin-axis located at a latitude of 30°S due to the Earth's rotation?

  • A

    2° per hour to the left.

  • B

    7.5° per hour to the left.

  • C

    11° per hour to the right.

  • D

    15° per hour to the right.

Apparent drift caused by earth rotation is a function of the sin of the latitude.

It is zero at the equator and a maximum of 15°/hour at the poles. In between, it is calculated by the formula:

  • Apparent Drift = 15 x sin lat = answer in °/hour

In the Southern hemisphere, the drift of the gyro axis is counter clockwise/left-hand and the indicated heading increases.

So, after the formula implementation:

  • 15 x sin 30 = 7.5°/hour to the left.

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