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Precession

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What is a Precession?

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3 Answers



  1. Kris Kortokrax on Jun 14, 2015

    There is a detailed explanation of gyroscopic precession on page 4-27 of the Pilot’s Handbook of Aeronautical Knowledge.

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  2. Robert Andreas on Jun 19, 2015

    Precession is when the spin axis of the gyroscope moves. Recall a gyro should display “rigidity” in space. The axis is not supposed to move. When it does, it is called precession. Hope that helps.

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  3. Kris Kortokrax on Jun 29, 2015

    The definition of precession you quote looks like a definition of astronomical precession one might find in Wikipedia. It has nothing to do with aviation.

    Precession with respect to aviation dictates that when a force is applied to a spinning disc such as a propeller or helicopter rotor, the resultant force shows up 90 degrees after the force was applied in the direction of rotation.

    It explains why pitch change links on a rotor system apply changes to the rotor 90 degrees prior to the point that the designer wants the force to take effect.

    It also explains why you need to apply more right rudder when you raise the tail on a tailwheel airplane or why you need more left rudder when you let the tail down during a wheel landing.

    We also speak of precession when describing the drifting of a Heading Indicator due to bearing friction.

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