To differentiate between autopilot / stability augmentation system components, Cool City uses the nomenclature of actuator for the series electromechanical devices used in the SAS/SCAS systems. The electromechanical devices of the autopilot system are referred to as parallel servos; however, in general, the terms actuator and servo are interchangeable.
Cool City manufactures two models of series actuators, a linear and a rotary series actuator. As implied in the name, the linear actuators move in and out and are installed in push-pull control tubes. The rotary actuators are used in control systems incorporating a torque tube that rotates for control travel.
The series actuator is manufactured on CNC machinery from 6061 billet aluminum for strength and corrosion protected per MIL-DTL-5541. Cool City uses a commercial, size 17 stepper motor to drive the actuator. Also, key to the structural integrity of the Cool City actuator is the dovetail mechanical joint that holds the actuator housing and the electronics box together without depending upon fasteners for strength.
The Cool City actuators are fast-action units with very limited control travel authority. In most instances, the actuators operate full travel in less than a second and have approximately 10% control travel authority. The actuators have a very high duty cycle when operating in turbulence. When quiescent or at system shut-down, the actuators automatically re-center.
The series actuator provides SAS/SCAS actions in a short, but fast motion. Mounted in the main flight control tubes, these actuators have very limited travel authority, usually less than 10 percent of full control travel. While limited in travel distance, these actuators operate at a high rate of speed. Full travel for the actuator occurs in less than one second.
For safety purposes, the actuators have an internal electrical and mechanical stop. The mechanical stop is located just beyond the electrical stop and is not reached in normal operation. Other than the obvious improvements in the aircraft stability, operation of the actuators is transparent to the pilot.