MTSU Aerospace Practice Test

A propeller that uses a governor to hold RPM is designed to keep the engine at a chosen speed by automatically adjusting blade angle. In a constant speed propeller, a governor senses the propeller RPM and changes the pitch of the blades to maintain that set RPM. If the load on the engine increases and RPM would drop, the governor moves the blades to a finer pitch to reduce drag and let RPM rise back toward the target. If RPM tends to climb, the blades move to a coarser pitch to increase drag and slow the engine back down. This automatic pitch adjustment keeps engine speed steady, which is why this type is described as constant speed.

Fixed pitch propellers have a single blade angle and cannot automatically adjust to changes in load, so their RPM varies. A variable pitch propeller can change blade angle, but without the governor's automatic control, it wouldn’t reliably hold RPM at a chosen setting. A feathered propeller is a high-pitch state used to reduce drag, typically in an engine-out condition, and isn’t the mechanism chosen to maintain constant RPM.