The Turn Coordinator

The video introduces the turn coordinator, a basic flight instrument found in aircraft, operating on gyroscopic principles. It notes that while attitude and heading indicators often use vacuum power, the turn coordinator typically uses direct current from the aircraft's electrical system. The two main variants, the turn coordinator and the turn and slip indicator, are highlighted for their similar operating principles but slightly different information presentation.

The turn and slip indicator shows if the aircraft is turning, the rate of heading change (rate of turn), and the quality of the turn through an inclinometer. It does not indicate the bank angle. Key components include the rate of turn scale with a needle and the liquid-filled inclinometer with a ball. The rate of turn scale shows straight flight at the center (0 degrees per second) and a standard rate of turn (3 degrees per second) at the side markings, which allows a 360-degree turn in two minutes.

Examples are given for interpreting the turn and slip indicator: a centered needle indicates straight flight; a needle pointing to the right or left mark indicates a standard rate turn in that direction; movement beyond or before the marks indicates a faster or slower turn rate, respectively.

The inclinometer, a simple instrument with a ball in a liquid-filled capsule, measures the quality of a turn. A centered ball indicates a coordinated flight, a ball moving to the side of the turn indicates a slipping turn, and a ball moving to the opposite side indicates a skidding turn. The rule of thumb to correct these is to 'step on the ball,' pressing the rudder pedal on the side the ball is biased towards to center it.

The turn and slip indicator utilizes gyroscopic precession. It incorporates a horizontal rate gyro restricted on one axis, allowing it only two degrees of freedom. When the aircraft turns, a force is applied to the gyro, causing precession at 90 degrees to the applied force. This precession tilts the gyro, and the degree of tilt, directly proportional to the rate of turn, is transmitted to the needle. Calibrated springs limit the gyro's movement and return it to neutral when the turn stops.

Examples demonstrate the indicator's operation: straight flight keeps the needle centered; a right turn causes the gyro to tilt and the needle to indicate a right turn; a left turn causes a tilt and indication of a left turn. The springs always return the needle to center once the turn ceases.

The inclinometer's ball movement is governed by the balance between centripetal and centrifugal forces during a turn. In a coordinated turn, these forces are balanced, and the ball remains centered. A skidding turn occurs when centrifugal force is greater, moving the ball to the opposite side of the turn. A slipping turn occurs when centripetal force is greater, moving the ball to the side of the turn.

The turn coordinator is presented as a variant of the turn and slip indicator. While also using gyroscopic principles, it uniquely indicates how fast the aircraft is banking (in addition to the rate of turn) when starting or ending a turn. Key differences include a miniature aircraft symbol instead of a needle, with rate of turn markings on the sides. It does not provide pitch information, as stated on its dial.

Examples show how to read the turn coordinator: level wings indicate straight flight; banking the miniature aircraft to the marks indicates a standard rate turn (3 degrees per second), and banking beyond or before the marks indicates faster or slower turn rates, respectively.

Similar to the turn and slip indicator, the turn coordinator uses gyroscopic precession, but its horizontal rate gyro is tilted 30 degrees. This inclination makes the gyro sensitive to both heading changes and banking motion. This allows the miniature aircraft to reflect both aspects of the turn. When power is lost, a red flag becomes visible on instruments driven by direct current, indicating it should not be used.