Automatic flight control system (AFCS), sometimes called an automatic pilot or autopilot, is a device that automatically steers aircraft. The device controls a craft using information provided by sensors along with a detailed set of computerized instructions. An AFCS reduces the amount of work a pilot must do, makes navigation easier, and improves fuel economy and flight safety. In addition, an AFCS can take over control of particularly difficult flight operations from a pilot. It can thus aid a pilot faced with such situations as landing in poor visibility or flying low to avoid radar detection.
How an AFCS works.
An AFCS is part of the avionics (flight electronics) of an aircraft. The heart of a modern AFCS system is a computer with many high-speed digital processors. The processors communicate with other airplane systems and equipment, including gyroscopes, accelerometers, a compass, and an air-data system. The gyroscopes, accelerometers, and other equipment provide information about the vehicle’s attitude (orientation in relation to the horizon), altitude, and velocity. A special compass provides information on the craft’s heading (direction) relative to magnetic north. The air-data system provides data associated with the movement of the aircraft through the atmosphere.
The AFCS processors perform complex calculations using a set of control modes. Typical modes include those that maintain an aircraft’s altitude, airspeed, heading, and designated flight path. The processors then issue control signals to various servo (or servomechanism) units. These units have motors and hydraulic devices that move the throttle and the craft’s control surfaces—the ailerons, elevator, and rudder.
In a fly-by-wire system, a computer combines instructions from the pilot with those of an AFCS to improve flight safety. Such a system can, for example, prevent a pilot from endangering the aircraft by exceeding a certain airspeed or angle of descent or ascent.
Many airplanes include a device called a Global Positioning System (GPS) receiver that can contribute data to the AFCS. A GPS receiver can determine a plane’s position in space by calculating its distance from 3 or more satellites in the GPS network. Each of the 24 satellites in this network continually broadcast their positions.
History.
In 1912, Lawrence Sperry invented and flight-tested an automatic gyroscopic stabilizing device for airplanes using four gyroscopes. In 1932, the Sperry Gyroscope Company, founded by Lawrence’s father, Elmer A. Sperry, developed an automatic pilot. This device enabled American aviator Wiley Post to make the first solo flight around the world in 1933 (see Post, Wiley ).
In 1998, the Insitu Group, a developer of long-range unpiloted aircraft, together with the University of Washington, flew a pilotless plane across the Atlantic Ocean for the first time. The aircraft was directed by an AFCS using a GPS receiver for navigation. It took off from Newfoundland and landed in Scotland, crossing 2,030 miles (3,270 kilometers).
See also Global Positioning System ; Gyroscope ; Servomechanism ; Sperry, Elmer Ambrose .
