Sorry Rigga, that should be John Fay, not Peter. "The Helicopter, History, Piloting and How it Flies" published by David & Charles, Newton Abbot, ISBN 0 7153 7249 1. A super little book, it was a great help to get me through the helicopter theory of flight part of my A&C (Rotorcraft) licence many years ago. Another good read on this topic is "Basic Theory of the Helicopter" by Roger Raletz and published (free?) by the Product Support Department of Aerospatiale - Helicopter Division (now Airbus Helicopters of course). Ask your local friendly Airbus Helicopters representative to get you a copy, it's available in hardcopy or electronic format.