Control is a fundamental part of the aeronautical sciences playing a necessary role in the design of all air-vehicles whether they are aircraft or balloons, missiles or kites. The early years of aircraft research were characterised by the amount of effort devoted to the control of the aircraft, and the shortcomings of early aircraft designs were frequently due to instability and to poor handling characteristics. Indeed the triumph of the Wright Brothers in 1903 when their first sustained powered flight was made at Kitty Hawk was due as much to their mastery of the problems of control as to their work on aerodynamics, structure or powerplant, vital though these latter were.

There are inherently two ways of obtaining an aircraft design having the desired control characteristics, either by so designing the structure and the aerodynamics of the aircraft itself or by providing some ‘artificial’ or ‘automatic’ control to change its characteristics. The latter method uses the signal from some sensor in essentially the same way that the human being uses signals from his vestibular organs to stabilise himself, and the crane fly similarly stabilises his flight using signals from his vestibular organs to stabilise himself, and the crane fly similarly stabilises his flight using signals from his halteres. The technique was tried even before 1903, and Sir Hiram Maxim in 1891 had produced a patent for an aircraft using a pendulous gyroscope for pitch stabilisation (Fig. 1). For various reasons most of these early efforts were rather unsuccessful, and in the period up to the Second World War the principal advances in the science of aircraft stability and control came largely from the refinement of the basic aerodynamics of the vehicle.