Advancing blade-relative wind. Retreating blade- no relative wind. Result=dyssemetrical lift. Solution-flapping or teetering head opposite equal reaction. Other heads-retreating flap in order to increase pitch thus produce same as advancing blade having a holiday due relative wind. Purpose of ddrag hinge is to absorb increase in drag on retreating blade due increase in pitch thus blade allowed to "fall behind" and catch up again when it enters the advancing halve of the disc. Retreatingblade stall due higher pitch on retreating blade so higher the pitch on the disc, the smaller the stall margin on the retreating side.
Could have it completely wrong, but thats how I understand it in simplicity?