Patent US 4,094,479

A yaw axis stability and command augmentation system (SCAS) particularly applicable to STOL type aircraft includes three primary control terms proportional to side slip angle, side slip angle rate and rudder pedal force, wherein side slip angle rate is synthesized from measures of yaw rate, bank angle and lateral acceleration. These primary system feedback terms are supplied to the rudder electro-hydraulic secondary actuator which is positioned in accordance with their sum. The system serves to provide improved automatic damping of the Dutch roll modes, to suppress aircraft motion transients in yaw and roll under engine failure situations, to provide automatic turn-coordination in maneuvering flight, and to provide a side slip angle command capability to improve manual control precision in approach and landing under crosswind and lateral wind shear conditions.