The gyroscope measures the angular velocity of the body around an axis.When the gyroscope is used to measure the axial rotation angular rate of the aircraft body, the measured value is non-zero if the aircraft is rotating, and zero if the aircraft is not rotating.Therefore, the gyroscope on an aircraft with a 60-degree roll Angle has a value of zero for the roll Angle, and zero for the horizontal straight flight.The current roll Angle can be estimated by the time integral of the angular rate value, provided there is no accumulation of errors.The values measured by the gyroscope will drift over time, accumulating additional errors over minutes or even seconds, and eventually leading to a completely false perception of the plane’s current horizontal roll Angle.As a result, gyroscopes alone cannot maintain a specific heading of an aircraft.
In a word, the accelerometer is correct in the long term measurement (determining the aircraft heading) and incorrect in the short term due to the presence of signal noise.Gyroscopes are more accurate in a short time and have errors with drift in a long time.Therefore, both are needed to ensure the correct course.
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