What happens when the CSU senses the blades need more RPM?

• A. Increases oil pressure to the rear of the sliding piston, moving blades to low pitch/high RPM
• B. Decreases oil pressure to the rear of the sliding piston
• C. Opens the bleed valve
• D. Engages feathering

Answer: (A)

The propeller RPM is kept by the CSU by changing blade pitch with hydraulic pressure. When the sensed RPM is below the target, the CSU increases oil pressure to the rear of the sliding pitch piston. That pressure pushes the piston forward, moving the blades to a finer (lower) pitch. A finer pitch lowers the aerodynamic resistance of the propeller at a given engine speed, allowing the engine to speed up toward the commanded RPM. The system will keep adjusting until the target RPM is reached. Decreasing pressure would move to a higher pitch and slow RPM, while bleeding off pressure or feathering would either reduce responsiveness or dramatically increase drag, not raise RPM.