Automatic control systems and autopilots

The earliest form of automatic control or autopilot consisted of a device to keep the aircraft flying on a steady heading at constant height. They normally employed a number of mechanical gyroscopes which were used to sense the motion of the aircraft and apply suitable corrective control inputs. These so-called ‘inertial’ systems have been developed to a high level of precision and sophistication, particularly in military aircraft and missiles, and can provide highly accurate guidance and control. Laser-based electronic inertial and GPS sensors have now largely replaced the mechanical gyroscopes.

During the Second World War, guidance and navigation systems using ground-based radio transmissions were developed, primarily for bombing missions, and these were subsequently adapted for civilian applications. Nowadays, an autopilot may be linked to a complex set of navigation systems and instruments, and can be programmed so that the aircraft follows a pre­determined flight pattern, including variations in speed, altitude and direction.

Satellite-based navigation systems can now provide pinpoint positional indica­tion and may eventually replace the older ground-based systems altogether.

As we shall describe in later chapters, automatic control systems can be used to help enhance stability, to improve performance and manoeuvrability, and to help provide safe landing, particularly in poor visibility. A good introduction to avionic systems is given in D. H. Middleton’s book.