In normal operation, where is the oil pressure from the CSU applied to affect blade position?

• A. Rear of the sliding piston
• B. Front of the sliding piston
• C. To the feathering spring
• D. To the counterweights

Answer: (A)

The blade angle is changed by a hydraulic actuator inside the CSU, and the oil pressure from the CSU is applied to the rear face of the sliding piston. This pressure pushes the piston forward, and through the linkage it adjusts the propeller blades to the commanded pitch. The front face is related to the spring and other mechanical biases, but in normal operation the active hydraulic force comes from the rear of the piston. The feathering spring provides a bias toward higher pitch when hydraulic pressure is low, and the governor’s weights respond to RPM changes to set the pressure, while the counterweights themselves are not the direct recipients of the oil pressure for blade movement.