Which parameters are sensed by a hydromechanical fuel control?

Which parameters are sensed by a hydromechanical fuel control?

• A. Gas generator speed, compressor discharge pressure, burner pressure, exhaust temperature, inlet air temperature and pressure
• B. Throttle position and oil temperature
• C. Exhaust gas composition only
• D. Ignition timing and fuel temperature

Answer: (A)

A hydromechanical fuel control meters fuel based on real engine operating conditions, using signals from several measured parameters to keep the engine running at the desired speed and within safe limits. Gas generator speed is the primary reference because it shows how fast the core is turning and how much fuel is needed to maintain that speed. Compressor discharge pressure provides a direct indication of the air being delivered through the compressor, so the fuel can be scheduled to match the available air. Burner pressure helps the control account for current combustion chamber conditions and pressure losses, while exhaust temperature is monitored as a limiter to prevent overtemp operation. Inlet air temperature and pressure adjust the metering for air density and pressure at different ambient conditions, ensuring the fuel-air mixture remains correct. Other options focusing only on throttle position and oil temperature, or on exhaust gas composition alone, or on ignition timing and fuel temperature, don’t provide the full set of sensed parameters needed for accurate, safe metering across the engine’s range of operation.

A hydromechanical fuel control meters fuel based on real engine operating conditions, using signals from several measured parameters to keep the engine running at the desired speed and within safe limits. Gas generator speed is the primary reference because it shows how fast the core is turning and how much fuel is needed to maintain that speed. Compressor discharge pressure provides a direct indication of the air being delivered through the compressor, so the fuel can be scheduled to match the available air. Burner pressure helps the control account for current combustion chamber conditions and pressure losses, while exhaust temperature is monitored as a limiter to prevent overtemp operation. Inlet air temperature and pressure adjust the metering for air density and pressure at different ambient conditions, ensuring the fuel-air mixture remains correct.

Other options focusing only on throttle position and oil temperature, or on exhaust gas composition alone, or on ignition timing and fuel temperature, don’t provide the full set of sensed parameters needed for accurate, safe metering across the engine’s range of operation.