On airplanes equipped with a controllable propeller the pilot's manual control of the propeller is maintained by a control lever adjacent to the throttle. It is used for the selection of the desired propeller or engine speed. Any rotational speed (revolutions per minute) within the prop governor's operating range can be selected by adjusting the lever fore and aft between the full DECREASE RPM position to the full INCREASE RPM position.
The propeller control lever is connected to a propeller governor unit which, in turn, adjusts the propeller blades to establish the selected RPM settings. As the propeller control lever is moved forward, propeller and engine speed (RPM ) will increase; if the control is moved aft, RPM will decrease.
In a constant speed propeller system the governor automatically maintains the selected engine speed by varying the pitch of the propeller blades to compensate for varying engine loads, regardless of the airplane's attitude. A setting introduced into the governor by the pilot determines the RPM to be maintained and the governor then controls the pitch required to maintain the RPM.