2 MIN TURN  DC ELEC  L R  Gyro rotation Inclinometer Gimbal rotation Standard rate turn index Horizontal gyro Gyro rotation Gimbal Standard rate turn index Canted gyro Gimbal rotation Figure 5-34. The rate gyro in both turn-and-slip indicator and turn  coordinator. made with too shallow a bank angle, the inertia is greater than  gravity and the ball rolls upward to the outside of the turn. The inclinometer does not indicate the amount of bank, nor  does it indicate slip; it only indicates the relationship between  the angle of bank and the rate of yaw. The turn indicator is a small gyro spun either by air or by an  electric motor. The gyro is mounted in a single gimbal with its  spin axis parallel to the lateral axis of the aircraft and the axis  of the gimbal parallel with the longitudinal axis.  [Figure 5-34] When the aircraft yaws, or rotates about its vertical axis, it  produces a force in the horizontal plane that, due to precession,  causes the gyro and its gimbal to rotate about the gimbal’s  axis. It is restrained in this rotation plane by a calibration  spring; it rolls over just enough to cause the pointer to deflect  until it aligns with one of the doghouse-shaped marks on the  dial, when the aircraft is making a standard rate turn. The dial of these instruments is marked “2 MIN TURN.”  Some turn-and-slip indicators used in faster aircraft are  marked “4 MIN TURN.” In either instrument, a standard  rate turn is being made whenever the needle aligns with a  doghouse. A standard rate turn is 3° per second. In a 2 minute  instrument, if the needle is one needle width either side of  the center alignment mark, the turn is 3° per second and the  turn takes 2 minutes to execute a 360° turn. In a 4 minute  instrument, the same turn takes two widths deflection of the  needle to achieve 3° per second. The major limitation of the older turn-and-slip indicator is that  it senses rotation only about the vertical axis of the aircraft.  It tells nothing of the rotation around the longitudinal axis,  which in normal flight occurs before the aircraft begins to turn. The inclinometer, similar to the one in a turn-and-slip  indicator, is called a coordination ball, which shows the  relationship between the bank angle and the rate of yaw. The  turn is coordinated when the ball is in the center, between the  marks. The aircraft is skidding when the ball rolls toward the  outside of the turn and is slipping when it moves toward the  Rather than using a needle as an indicator, the gimbal moves  a dial that is the rear view of a symbolic aircraft. The bezel  of the instrument is marked to show wings-level flight and  bank angles for a standard rate turn.  [Figure 5-35] A turn coordinator operates on precession, the same as the  turn indicator, but its gimbals frame is angled upward about  30° from the longitudinal axis of the aircraft.  [Figure 5-34] This allows it to sense both roll and yaw. Therefore during  a turn, the indicator first shows the rate of banking and once  stabilized, the turn rate. Some turn coordinator gyros are  dual-powered and can be driven by either air or electricity. Turn Coordinator 5-21 Figure 5-33. Turn-and-slip indicator.