In the early days of aviation, flights were short, and a pilot's main concern was not crashing to the ground after a few exhilarating moments in the air. As the technology improved, however, increasingly longer flights were possible -- first across continents, then across oceans, then around the world. Pilot fatigue became a serious concern on these epic journeys. How could a lone pilot or a small crew stay awake and alert for hours on end, especially during monotonous sessions of high-altitude cruising?
Enter the automatic pilot. Invented by Lawrence Burst Sperry, son of Elmer A. Sperry, the autopilot, or automatic flight control system, linked three gyroscopes to an aircraft's surfaces controlling pitch, roll and yaw. The device made corrections based on the angle of deviation between the flight direction and the original gyroscopic settings. Sperry's revolutionary invention was capable of stabilizing normal cruising flight, but it could also perform unassisted takeoffs and landings.
The automatic flight control system of modern aircraft differs little from the first gyroscopic autopilots. Motion sensors -- gyroscopes and accelerometers -- collect information on aircraft attitude and motion and deliver that data to autopilot computers, which output signals to control surfaces on the wings and tail to maintain a desired course.