To differentiate between autopilot and stability augmentation system components, Cool City uses the nomenclature of servo for the parallel-installed, electromechanical devices used in the autopilot systems. The series-installed, electromechanical devices of the SAS/SCAS are referred to as actuators; however, in general, the terms actuator and servo are interchangeable.

The parallel servo is considered the most critical element in the autopilot system because it is the only component attached to the flight controls. Therefore, the servo capstan incorporates an internal spring mechanism and has an internal gradient that may be overridden in the case of a servo failure or the pilot’s need to “fly through” the autopilot.

The servo capstan gradient requires increasing force as you move the cyclic from the original override point. Upon releasing the cyclic, the spring mechanism will return the cyclic to the original position.

The autopilot servo is manufactured on CNC machinery from 6061 billet aluminum for strength and corrosion protected per MIL-DTL-5541. For long life and smoothness of operation, the capstan rides on straddle-mounted roller bearings. Additionally, all servo gearing and shafts are manufactured from stainless steel and the shafts run on ball or roller bearings as well.
Cool City uses a commercial, size 17 stepper motor to drive the servo. Stepper motors are not subject to “starting voltage” problems so prevalent in older systems. Also, from a safety standpoint, there is no single-point failure that can cause the stepper motor to have a “runaway”.

The parallel servo is used in roll, pitch, and may be optionally installed in the yaw axis of rotorcraft installations. The servo is connected to the aircraft’s primary control system through the use of either push-pull rods or bridle cables, dependent upon the specific requirements of the installation.

In addition to the attributes listed above, consider these additional features:

  • “Smart” servo design with precision servo position feedback
  • Servo engage-disengage mechanism tested to 500 in. lbs
  • Machined mating surfaces prevent internal contamination from external sources
  • 90° electrical connector for installation in confined areas

As with all autopilot systems, the servo is most critical to optimum autopilot performance and system longevity. Cool City has successfully subjected our servo to the most strenuous of environmental testing. We have also life-tested our servo over a half-million cycles without failure. We believe our servo is the most robust servo available on the market.