Gyroscopic Instruments - Turn Coordinator
Turn Coordinator
Aircraft Instruments

The turn coordinator is a development of the turn-and-bank indicator, and is adopted in lieu of this in a number of small types of aircraft. The primary difference, other than the display presentation, is in the setting of the precession or output axis of the rate gyroscope. This is set at about 30° with respect to an aircraft's longitudinal axis, thus making the gyroscope sensitive to rolling or banking as well as turning. Since a turn is initiated by banking, then the gyroscope will precess, and thereby move the aircraft symbol to indicate the direction of the bank, enabling a pilot to anticipate the resulting turn.

Airspeed Indicator (ASI)
Figure 1 - Turn Coordinator

The turn is then controlled to the required rate as indicated by the alignment of the symbol with the graduations on the outer scale. Coordination of the turn is indicated by the ball-type indicator remaining centred in the normal way. In some indicators, a pendulous type of indicator may be adopted for this purpose.

The gyroscope is a dc motor operating at approximately 6000 rev/min; in some cases, a constant frequency ac motor may be used. The annotation 'no pitch information' on the indicator scale is given to avoid confusion in pitch control which might result from the similarity of the presentation to that of a gyro horizon.

Damping of the gyroscope may be effected by using a silicone fluid or, as in the indicator illustrated, by a graphite plunger sliding in a glass tube (figure 2).

Operation of the Airspeed Indicator (ASI)
Figure 2 - Turn Coordinator