Turn and slip, and the turn coordinator

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How a spring-held rate gyro shows rate of turn, the rate 1 numbers, what the ball says about slip and skid, and the tilted gyro of the turn coordinator.

Remember

Rate gyro: one gimbal, horizontal axis across, held by a spring; slow rotor on purpose.
Rate 1 = 3°/s; bank ≈ TAS/10 + 7; time = degrees ÷ 3; circle TAS/30 NM round.
Ball same side as the turn = slip (too much bank); opposite = skid (too little). Step on the ball.
Taxi turn: needle in the turn, ball outside. Low suction: under-reads.
Turn coordinator: gimbal tilted 30°, senses roll too; no pitch information.

How does a gyro measure how fast you turn?

A rate gyro on a spring

On the panel • Bottom left of the six: the turn coordinator. • It answers two questions: how fast am I turning? and is the turn balanced?
What it looks like in a turn • Watch the little aeroplane tip, and the world tilt outside. • Wing on the mark: a standard rate 1 turn.
Open the case • A rotor spins with its axis across the aircraft, in one ring. A spring holds the ring level. • That is a rate gyro.
Turning twists it • Turn the aircraft and the rotor is dragged round. It precesses, tilting the ring against the spring. • Faster turn, more tilt. The tilt moves the little aeroplane.
Rate 1 • On the mark: rate 1: 3° a second, a full circle in 2 minutes.
Bank alone does nothing • Bank without turning: no precession, so no reading.

Bank angle, time and circle size for a rate 1 turn

Rate 1 numbers

How much bank • Rule of thumb: bank = TAS ÷ 10 + 7. At 160 kt, 23°.
How long • 3° a second: a 120° turn takes 40 s.
How big • In 2 minutes at 300 kt you fly 10 NM round. • Across the circle: about 3.2 NM.
Faster needs more bank • Same rate at a higher speed needs more bank. Weight makes no difference.