This is the latest edition - fully revised and updated - of the standard work on aerodynamic theory, as applied to model flight. Everything is explained in a concise and practical form for those enthusiasts who appreciate that a better understanding of model behaviour is the sure path to greater success and enjoyment, whether just for fun or in competition. The revisions for this edition reflect the significant developments in model aircraft during the last few years, e.g. powerful miniature turbojet engines; vast improvements in motors, propellers and batteries for electric powered models; more very large and very fast models; etc. This fourth edition - twenty years after the first! - created an opportunity not just for text revisions but a complete redesign with larger page size and improved redrawn plans and diagrams.