A turn and bank instrument is the first blind flying instrument and was enough to keep the airplane upright in the clouds. The advantages of the horizon were recognized immediately but they were more costly and less reliable so the turn and bank remained as backup for the horizon and dg. In a turn and bank the axis of the gyro is parallel to the longitudinal axis of the airplane so it responds only to yaw inputs from the rudder.
During the 60s wing levelers and auto pilots became more popular in airplanes but the problem was sensing that the airplane was turning so you could apply a counter force to return the desired course. The turn and bank worked but it was too slow which meant that the airplane wandered around too much. The turn coordinator was created by inclining the gyro 15 degrees above the longitudinal axis which made the instrument respond to roll and yaw. This improved the sensitivity of the instrument for use with wing levelers and made the instrument better for use as a backup for the attitude gyro but added the well known placard "No pitch information" which none of us would have otherwise known. The only significant difference between the two is the 15 degree inclination of the gyro axis. Bob Condon
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