Turn Indicator and Turn Coordinator: Rate-1 Turns, Slip, and Skid
These instruments indicate the rate of turn (yaw) and the quality of the turn (coordination).
Turn Indicator vs. Turn Coordinator
- Turn Indicator (Turn and Slip):
- Gyro: Horizontal axis, 1 degree of freedom (Gimbal frame).
- Sensitive to: YAW only.
- Display: A "needle" or "bat" indicates the rate of turn.
- Turn Coordinator:
- Gyro: The gimbal is canted (angled) at 30° to the longitudinal axis.
- Sensitive to: ROLL and YAW. It reacts faster to the start of a turn (roll) but stabilizes to show rate of yaw.
- Display: An aircraft symbol banks to show the rate of turn.
Rate 1 Turn (Standard Rate)
- Definition: A turn rate of 3° per second.
- 360° Turn: Takes 2 minutes.
- Rule of Thumb for Bank Angle: $\text{Bank Angle} \approx \frac{TAS}{10} + 7$.
- Example: At 120 kts TAS, Bank $\approx 12 + 7 = 19^\circ$.
Balance (Slip) Indicator
Consists of a ball in a fluid-filled curved tube (inclinometer). It indicates the coordination of the turn (Balance of Centrifugal Force vs. Gravity/Weight).
- Ball Centered: Coordinated turn.
- Ball Inside turn (Same side): Slip (Not enough bank for the rate of turn, or too much rudder into the turn).
- Ball Outside turn (Opposite side): Skid (Too much bank, or too much opposite rudder).
- Mnemonic: "Step on the ball" to center it.