Of the articles available, the following links to the Collin Mill's Practical theories article at W3MH are some of the best and well worth reading.Colin Mill's Practical Theories Articles.
From the very early days of W3MH, Colin's articles are well worth reviewing as the theory of helicopter flight hasn't changed! All eleven of Colin's W3MH articles are here, they give a superb insight into the later development of the CSM gyro, whilst dealing with the theory of model helicopter flight and control in a very readable manner. Supported by an array of excellent line drawings.
Parts 1 & 2 Introduction, general aerodynamics and servo linkages.
Parts 3 & 4 Collective pitch and throttle.
Parts 5 & 6 Main rotor, tail rotor and gyro basics.
Parts 7 & 8 How a gyro works and rotor head dynamics.
Parts 9, 10 & 11 Cyclic control, flybar systems and detailed rotor blade aerodynamics.