In a hydromechanical/engine control system, what is the function of the fuel control servo?

• A. It reads commanded speed input and adjusts fuel metering to meet commanded speed and stability requirements.
• B. It controls the lubrication oil flow to the bearings.
• C. It senses exhaust gas temperature to adjust air intake.
• D. It measures vibration to adjust blade clearances.

Answer: (A)

The fuel control servo meters fuel to the combustor based on the commanded engine speed, turning the speed command into precise fuel flow to achieve and hold that speed while staying stable. It uses hydraulic pressure to position the fuel metering valve so that increasing the speed command opens the valve more (adding fuel) and a decreasing command or signs of instability closes it (reducing fuel). This creates a responsive loop that balances fuel delivery with the engine’s air supply to prevent overspeed or surges, keeping the engine operating smoothly at the desired speed. It isn’t responsible for lubrication oil flow, exhaust temperature sensing for air intake, or vibration-based blade clearance adjustments.