Definition
A mechanical component inside a constant-speed propeller governor that moves in response to changes in engine RPM, acting on the pilot valve to direct oil pressure to or from the propeller hub. Its position determines whether the propeller blades move toward a higher or lower pitch to maintain the RPM selected by the pilot.
Plain English
A small sliding part inside the propeller governor that moves up or down when engine speed changes, telling the propeller to add or remove pitch so the RPM stays where the pilot set it.
Context Anchor
Seen in discussions of constant-speed propellers, blade angle control, and how the propeller control sets RPM.
Derivation
The word 'rack' comes from older mechanical engineering, where it refers to a straight, toothed bar that engages with a gear to translate motion. In the governor, the rack is the moving piece that translates the action of the spinning flyweights into a linear movement that controls oil flow.
Why Pilots Care
Correct function of the governor rack ensures the propeller maintains optimum RPM for engine efficiency, prevents overspeed damage, and allows smooth power management during climbs, cruises, and descents.
Intuition Check
Do not think of rack as a storage shelf here. In this context, a rack is a moving mechanical control part. Do not think of governor as a person in government. Here, it means a device that controls speed.
Example Sentence 1
When engine RPM rises above the selected setting, the flyweights tilt outward and lift the governor rack, which directs oil pressure to increase blade pitch and bring RPM back down.
Example Sentence 2
During preflight, the instructor pointed out wear on the governor rack teeth as a possible cause of sluggish propeller response.