Helicopter control relies on motion, or degrees of freedom, of the rotor blades. This video explains why the flapping degree of freedom is essential for controlling a helicopter.
Other topics covered are flapping hinge offset, advancing and retreating blades, the region of reversed flow, forward flight dissymmetry of lift, retreating blade stall and rotor blowback.
Other videos mentioned...
Helicopter Swashplate Control... https://youtu.be/xairCL9m9ec
helicopter rotor control - phase delay... https://youtu.be/-8QzYicgTL8
00:00 Intro
00:48 Rotor Degrees of Freedom
01:36 Flapping in a Hover
02:15 Rotor Coning
03:13 Preconing
03:42 Balance of Forces
04:39 Rotor Tip Path Plane
05:00 Flapping Hinge Offset
05:46 Summary of Control Concept
06:05 Forward Flight Considerations
06:27 Advancing and Retreating Blades
07:43 Region of Reversed Flow
08:28 Forward Flight Dissymmetry of Lift
11:27 Retreating Blade Stall
13:16 Rotor Blowback