AUTOROTATION (FORWARD FLIGHT)
Autorotative force in forward flight is produced in exactly the same manner as when the helicopter is descending vertically in still air. However, because forward speed changes the inflow of air up through the rotor disc, all three regions move outboard along the blade span on the retreating side of the disc where angle of attack is larger, as shown in figure 3-23. With lower angles of attack on the advancing side blade, more of that blade falls in the driven region. On the retreating side, more of the blade is in the stall region. A small section near the root experiences a reversed flow, therefore the size of the driven region on the retreating side is reduced.
 
 

3-12

Note: In this chapter, it is assumed that the helicopter has a counterclockwise main rotor blade rotation as viewed from above. If flying a helicopter with a clockwise rotation, you will need to reverse left and right references, particularly in the areas of rotor blade pitch change, anti-torque pedal movement, and tail rotor thrust.
There are four basic controls used during flight. They are the collective pitch control, the throttle, the cyclic pitch control, and the antitorque pedals. 
 

COLLECTIVE PITCH CONTROL
The collective pitch control, located on the left side of the pilot’s seat, changes the pitch angle of all main rotor blades simultaneously, or collectively, as the name implies. As the collective pitch control is raised, there is a simultaneous and equal increase in pitch angle of all main rotor blades; as it is lowered, there is a simultaneous and equal decrease in pitch angle. This is done through a series of mechanical linkages and the amount of movement in the collective lever determines the amount of blade pitch change. [Figure 4-1] An adjustable friction control helps prevent inadvertent collective pitch movement.
Changing the pitch angle on the blades changes the angle of attack on each blade. With a change in angle of attack comes a change in drag, which affects the speed or r.p.m. of the main rotor. As the pitch angle increases, angle of attack increases, drag increases, and rotor r.p.m. decreases. Decreasing pitch angle decreases both angle of attack and drag, while rotor
r.p.m. increases. In order to maintain a constant rotor r.p.m., which is essential in helicopter operations, a proportionate change in power is required to compensate for the change in drag. This is accomplished with the throttle control or a correlator and/or governor, which automatically adjusts engine power.