Which statement is correct?
I. Propeller gyroscopic effect occurs during aeroplane pitch changes.
II. Propeller gyroscopic effect is most noticeable during low speed flight at low propeller RPM.
Refer to figure.
On take-off, rotation of a single-engine propeller causes an aircraft to swing to one side, particularly those fitted with a tail-dragger undercarriage. The main causes of this are:
- Slipstream effect
- Torque reaction
- Gyroscopic effect
- Asymmetric blade effect
A rotating propeller has the properties of a gyroscope - rigidity in space and precession. The characteristic which produces “gyroscopic effect” is precession. Gyroscopic precession is the reaction that occurs when a force is applied to the rim of a rotating disc. When a force is applied to the rim of a propeller, the reaction occurs 90° ahead in the direction of rotation and in the same direction as the applied force. As the aircraft is pitched up or down or yawed left or right, a force is applied to the rim of the spinning propeller disc.
Gyroscopic effect only occurs when the aircraft pitches and/or yaws. Therefore, statement 1 is correct.
The Gyroscopic Effect is more significant in situations of high power (RPM) and low forward speed, such as take-off or low speed climbs. Therefore, statement 2 is incorrect.
For a clockwise rotating propeller:
Pitch up - forward force on the bottom, force emerges 90° clockwise, right yaw.
Right yaw - forward force on the left, force emerges 90° clockwise, pitch down.
Pitch down - forward force on the top, force emerges 90° clockwise, left yaw.
Left yaw - forward force on the right, force emerges 90° clockwise, pitch up.
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