The science of aeronautics has developed rapidly in a very short space of time, when one reflects on the remarkable achievements which have been made since the advent of powered flight just over fifty years ago. This rapid advance has made the aircraft designer more keenly aware of any new design techniques which would assist him in his further understanding of the problems involved. In the pioneering days of aircraft development the aerodynamic characteristics were obtained largely at the flight test stage of a design. Through time, however, the designer learned that quite a lot of useful information could be obtained from ground tests in wind tunnels, and he therefore made use of an aerodynamic simulation in its broadest terms, in the form of a wind tunnel model. This was an important advance in design technique in that the concept was established of evaluating performance by means of a “model,” in the initial stages of a project design. A much later generation of aircraft resulted in the need for automatic and power control aids to flight. Further advances have resulted in completely pilotless and automatic flight.