Which component acts as the propeller governor and is fully electric?

• A. CSU (Constant Speed Unit)
• B. Feathering spring
• C. Counterweights
• D. Piston

Answer: (A)

The key idea is that the propeller speed is controlled by a governor that keeps the RPM at the selected setting by changing blade pitch. In the PC-12 NGX, that job is done by the Constant Speed Unit. The CSU is an electro-hydraulic device: an electric control inside the unit senses the actual propeller RPM and drives a valve that meters oil pressure to the propeller pitch-change mechanism. By increasing or decreasing oil to the pitch-change piston, it raises or lowers blade pitch to maintain the commanded speed. Because the control input is electric, the CSU is described as fully electric.

The other parts play supporting roles but do not govern RPM by themselves. The feathering spring biases the blades toward high pitch when oil pressure is lost, aiding feathering. Counterweights are part of the mechanical balance of the hub and help the system respond across speeds. The piston is the actuator that actually moves the blades under CSU control.