On 6 Channel RC Helicopters, you get a radio controlled model which have the main blades which can change their pitch angle. Basically, to see this you put
your rc helicopter on a table and look at the tip end of the main blades, the chordline of the blade can be tilted through a range of angles by the servos.
In this sense, the rotor disk of a heli is a bit like a variable-pitch prop on an airplane. If your helicopter is hovering in the air, and you want to make it climb straight
up in the air, you just increase the pitch of the main blades and turn up the throttle which means the helicopter can overcome the drag which increases and the blades
keep turning at the same rotation speed before the throttle was increased and the helicopter will rise
Overall the more you increase the pitch of the blades, the more the lift given to the rc helicopter. At high throttle the engine puts out more power, but there is a corresponding increase in the load on the engine due to increased main rotor blade pitch, and so the engine stays at the same RPM’s.) The general increase in pitch means that the helicopter will climb and is called collective control.
On a 4 channel rc helicopter, the pitch angle of the blades is fixed in places but as we said above, the 6 channel helicopters blades can be changed in pitch.