Flight Controls

adjustments are necessary until the aircraft no longer skids Adjustable stabilizer left or right during normal cruising flight. [Figure 6-22] Nose down Adjustable Stabilizer Rather than using a movable tab on the trailing edge of the Nose up Jackscrew elevator, some aircraft have an adjustable stabilizer. With this arrangement, linkages pivot the horizontal stabilizer about Pivot its rear spar. This is accomplished by the use of a jackscrew mounted on the leading edge of the stabilator. [Figure 6-23] On small aircraft, the jackscrew is cable operated with a trim Trim motor or trim cable wheel or crank. On larger aircraft, it is motor driven. The trimming effect and flight deck indications for an adjustable Figure 6-23. Some aircraft, including most jet transports, use an stabilizer are similar to those of a trim tab. adjustable stabilizer to provide the required pitch trim forces. Autopilot The autopilot system also incorporates a disconnect safety Autopilot is an automatic flight control system that keeps an feature to disengage the system automatically or manually. aircraft in level flight or on a set course. It can be directed by These autopilots work with inertial navigation systems, the pilot, or it may be coupled to a radio navigation signal. global positioning systems (GPS), and flight computers to Autopilot reduces the physical and mental demands on a pilot control the aircraft. In fly-by-wire systems, the autopilot is and increases safety. The common features available on an an integrated component. autopilot are altitude and heading hold. Additionally, autopilots can be manually overridden. Because The simplest systems use gyroscopic attitude indicators and autopilot systems differ widely in their operation, refer to magnetic compasses to control servos connected to the flight the autopilot operating instructions in the Airplane Flight control system. [Figure 6-24] The number and location of Manual (AFM) or the Pilot’s Operating Handbook (POH). these servos depends on the complexity of the system. For example, a single-axis autopilot controls the aircraft about the Chapter Summary longitudinal axis and a servo actuates the ailerons. A three-axis Because flight control systems and aerodynamic autopilot controls the aircraft about the longitudinal, lateral, and characteristics vary greatly between aircraft, it is essential vertical axes. Three different servos actuate ailerons, elevator, that a pilot become familiar with the primary and secondary and rudder. More advanced systems often include a vertical flight control systems of the aircraft being flown. The speed and/or indicated airspeed hold mode. Advanced autopilot primary source of this information is the AFM or the POH. systems are coupled to navigational aids through a flight director. Various manufacturer and owner group websites can also be a valuable source of additional information. Figure 6-24. Basic autopilot system integrated into the flight control system. Figure 6-22. A ground adjustable tab is used on the rudder of many small airplanes to correct for a tendency to fly with the fuselage slightly misaligned with the relative wind. 6-12