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Automatic Pilot

aircraft control system altitude

The automatic pilot has it roots in the gyroscope, a weighted, balanced wheel mounted in bearings and spinning at high velocity. As early as 1852 the French scientist Jean-Bernard-Léon Foucault had experimented with the gyroscope and found that it tended to stay aligned with its original position and also tended to orient itself parallel to Earth's axis in a north-south direction. Thus, he reasoned, the gyroscope could be used as a compass because it designated true, or geographic, north rather than magnetic north, as traditional compasses did, which varied according to their location.

By the early 1900s the gyrocompass was a crucial part of navigation. A German manufacturer, Hermann Anschutz-Kaempfe, and an American, inventor, Elmer Sperry, had produced two gyrocompasses for use on board ships. Sperry also invented the first automatic pilot for ships, named " Metal Mike," which used the information from the ship's gyrocompass to steer the vessel.

Soon interest arose in applying this method to control aircraft. Sperry again led the way when one of his devices was used aboard a Curtiss flying boat in 1912. It used a single gyroscope which, like all spinning masses, tended to resist any change in the plane's axis of rotation. Whenever the airplane departed from its original altitude, a small force was applied to a spring connected to one end of the gyro axis, and this, magnified mechanically, was used to restore movement of the aircraft controls. In 1914, Sperry's son, Lawrence, competed in Paris with fifty-three other entrants to win a prize of fifty thousand francs for the most stable airplane. He demonstrated his plane's stability by flying low over the judges while he took his hands off the controls and a mechanic walked out on the wing.

All simple autopilots since that time have used similar principles. However, for airplane control in three directions (left/right, up/down, wing up/wing down) three gyros are needed. By 1930 the British Royal Aircraft Establishment and several private companies had developed refined autopilot systems that were gradually introduced to both military and civilian aircraft. During World War II much more complicated autopilots were produced. By a simple movement of a control knob, the aircraft could be held on a steady heading at a constant altitude, made to turn at a steady rate in either direction, or even change altitude in a precise manner.

A German, Irmgard Flugge-Lotz (1903-1974) played a key role in developing these automatic controls. As a child in Germany she spent her time at the movies watching engineering documentaries rather than Charlie Chaplin comedies. During World War II she developed methods of controlling aircraft during acceleration and in flying curves; with faster planes, pilots had no chance to correct for any miscalculations. She worked on what she called "discontinuous automatic control," which laid the foundation for automatic on-off aircraft control systems in jets.

After World War II the United States armed forces became interested in developing an inertial guidance system that used autopilots for rockets, submarines and manned aircraft. Such a system would not rely on any information from the outside, such as radio waves or celestial bodies, for "fixes." Instead, it would plot its course from information via gyroscopes and from calculations accounting for the rotation of Earth. The United States Air Force turned to a Massachusetts Institute of Technology professor, Charles Stark Draper, to develop such a system. He worked on improving gyro units, specific force receivers, amplifiers, servodrives, and other elements. On February 8, 1953, his equipment was aboard a B-29 bomber that left Bedford, Massachusetts, for Los Angeles, California, on a twelve-hour flight. It kept course without deviation, corrected for wind and currents, rose to clear the Rocky Mountains—all with no input from the ground or from the pilot and co-pilot. The inertial guidance system sensed every change in the forward velocity, every move right and left and up and down. By continually digesting these changes, and remembering the plane's take-off point, the system was able to determine in-flight position with great accuracy.

Today, much of the burden of flight has been transferred to autopilots. They can control attitude and altitude, speed, heading, and flight path selection. One great advance has been in landings: signals from an instrument landing system control an aircraft automatically during approach, to land the plane down the glide slope beam, keep it on the runway, and even turn it onto the taxiway, all in totally blind conditions.

Automation - History, Types Of Automation, The Role Of Computers In Automation, Applications, The Human Impact Of Automation - In the home [next]

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