Throttle Control Governor/Correlator  Collective Pitch Control The collective pitch control (or simply “collective” or “thrust  lever”) is located on the left side of the pilot’s seat and is  operated with the left hand. The collective is used to make  changes to the pitch angle of the main rotor blades and does  this 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 3-1] An adjustable friction control helps prevent inadvertent  collective pitch movement. The function of the throttle is to regulate engine rpm. If  the correlator or governor system does not maintain the  desired rpm when the collective is raised or lowered, or if  those systems are not installed, the throttle must be moved  manually with the twist grip in order to maintain rpm. In  most helicopters, rotating the twist-grip throttle away from  the pilot (counter-clockwise), increases engine rpm; rotating  the twist-grip throttle towards the pilot (clockwise) decreases  engine rpm. [Figure 3-2] A governor is a sensing device that senses rotor and engine  rpm and makes the necessary adjustments in order to keep  rotor rpm constant. In normal operations, once the rotor  rpm is set, the governor keeps the rpm constant, and there  is no need to make any throttle adjustments. Governors are  common on all turbine helicopters (as it is a function of the  fuel control system of the turbine engine) and used on some  piston powered helicopters. A correlator is a mechanical connection between the  collective lever and the engine throttle. When the collective  lever is raised, power is automatically increased; when  lowered, power is decreased. This system maintains rpm  close to the desired value, but still requires adjustment of  the throttle for fine tuning. Changing the pitch angle on the blades changes the angle  of incidence on each blade. With a change in angle of  incidence comes a change in drag, which affects the speed  or revolutions per minute (rpm) of the main rotor. As the  pitch angle increases, angle of incidence increases, drag  increases, and rotor rpm decreases. Decreasing pitch angle  decreases both angle of incidence and drag, while rotor rpm  increases. In order to maintain a constant rotor rpm, 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 governor,  which automatically adjusts engine power. Figure 3-1.  Raising the collective pitch control increases the pitch angle, or angle of incidence, by the same amount on all blades. 3-2