The essence of free-flight is that the aircraft have no need for any form of external control, for instance by radio. Aircraft of this type have been flown for over two centuries. They are designed to be inherently stable in flight; if disturbed by a gust of wind or a thermal up-current they will return automatically to stable flight. For this reason most free flight aircraft are not replicas of man-carrying ones, for they are designed for a quite different purpose. Their stability is achieved by a combination of design and trim, - the relationship between centre of gravity, wing and tailplane incidence and rudder setting.
Because they are much lighter with respect to their wing area, free-flight aircraft fly much slower than the engine-powered radio-controlled models that many people first think of when ‘model aircraft’ is mentioned. Most of them glide at little more than walking pace and few weigh more than 500 grams.
Usually the sole object in free-flight is flight duration, and one of the sport’s fascinations and challenges is to design the most efficient aircraft within the various competition limits on such parameters as minimum weight, maximum wing area and motive power. It is solely a stopwatch, rather than any judge’s opinion, that decides the result.
