Because they are much lighter with respect to their wing area, free-flight aircraft fly very much slower than the engine-powered radio-controlled models that many people first think of when model aircraft are considered. 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.