Automatic pilot

The automatic pilot, or autopilot, is a way to automatically steer aircraft, spacecraft, ships, and other vehicles based on a pre-determined course and without human intervention (such as with a pilot). It has it roots in the gyroscope, a weighted, balanced wheel mounted in bearings and spinning at high velocity. As early as 1852, French physicist Jean-Bernard Le´on Foucault (1819–1868) 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. German manufacturer and scientist Hermann Anschutz-Kaempfe (1872–1931), and American inventor and entrepreneur Elmer Ambrose Sperry (1860–1930) had produced two gyrocompasses for use onboard 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 that, 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 (1939–1945), 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.

German-American engineer 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 the Earth. The U.S. Air Force turned to Massachusetts Institute of Technology professor Charles Stark Draper to develop such a system. He worked on improving gyro units, specific force receivers, amplifiers, servo-drives, 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 that rely on computer software. 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, lead the plane down the glide slope beam, keep it on the runway, and even turn it onto the taxi-way, all in totally blind conditions. NASA’s (National Aeronautics and Space Administration’s) space shuttle fleet uses a programmable automatic pilot called the Digital Auto Pilot, or DAP. There are different DAPs depending on the flight phase for which the shuttle is operating. For instance, during various times from launch to insertion into orbit about Earth, DAPs decide when to fire the reaction control system (RCS) jets and the orbital maneuvering system (OMS) engines.