Gyroscope Basic Principles: Rigidity, Precession, and Wander
A gyroscope is a rotating mass that maintains its orientation in space unless acted upon by an external force. This property makes it essential for flight instrumentation (Attitude Indicator, Heading Indicator, Turn Indicator).
Key Properties
- Rigidity in Space: The tendency of a spinning mass to maintain its plane of rotation fixed in space.
- Depends on: Mass (heavier = more rigid), Radius (mass at periphery = more rigid), and Speed (faster = more rigid).
- Precession: If a force is applied to the spinning rotor, the reaction occurs 90° later in the direction of rotation.
Degrees of Freedom
- 1 Degree of Freedom: The gyro can move around only one axis (besides its spin axis). Used in Turn Indicators.
- 2 Degrees of Freedom: The gyro can move around two axes. Used in Artificial Horizons (Pitch/Roll) and Directional Gyros (Heading).
Wander
Wander is any movement of the gyro axis from its intended orientation.
- Real Wander: Physical movement of the axis due to mechanical imperfections (friction, unbalance).
- Apparent Wander: The gyro stays fixed in space, but the Earth rotates beneath it, making it appear to move.
- Drift: Horizontal movement. Max at Poles ($15^\circ/hr \times \sin \text{Lat}$).
- Topple: Vertical movement.
- Transport Wander: Apparent wander caused by moving the aircraft across the Earth's curved surface (changing longitude).
Gyro Types by Axis
- Vertical Axis Gyro: Used for Attitude Indicators (detects Pitch and Roll).
- Horizontal Axis Gyro: Used for Directional Gyros (detects Yaw) and Turn Indicators (detects Rate of Yaw).