Hi Delta,
I found two great books that helped me, they may have been mentioned prior! Phil Crouchers 'Private Helicopter Pilot Studies' with a full chapter on the principles and Pooleys 'JAR PPL-CPL Helicopter Manual-Principles of Flight, Technical H' in addition Helen Krasners 'Flying Helicopters-A Companion to the PPL (H) is a cracking read! All the very best