Aileron thrust automatic control Mk1A. Part of the first successful 3 axis British autopilot. Used on aircraft such as the Virginia, Heyford, Ouestrand, Stranraer, etc.

The gyro access is athwart the aircraft the outer ring being pivoted horizontally to detect roll. The servomotor is operated through a relay valve and follow-up is as for the rudder unit. The gyro is erected as follows...

A weight is attached to the outer ring so that if the ring is displayed from the vertical the weight will exert a force precessing the inner ring.

When the inner ring moves a spring attached to it applies torque which returns the outer ring to the vertical. At the same time the movement between the two rings is detected by a valve which admits air to the precessing cylinder allowing the torque to the outer ring and returning the inner ring to its former position.