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 behavior is the sure path to greater success and enjoyment. The revisions for this new edition reflect the significant developments in model aircraft, including radio frequency (RC) model aircraft and drones, over the last few years. New content including the chapter on aerofoils has been extended to take account of the vast amount of testing carried out recently in the USA at the University of Illinois. A new chapter explains the latest research into the flight of birds and insects which is being applied now to small drones and miniature surveillance aircraft. Older wind tunnel test reports have been replaced with the latest trials and measurements. Full-color photos and line drawings featured throughout. Topics include factors affecting lift and drag, scale effect and the boundary layer, basic model performance problems, reducing induced draft, aspect, ratio, and more.