What are the basic principles of a hydromechanical fuel control?

What are the basic principles of a hydromechanical fuel control?

• A. Uses electronic interface to compute fuel
• B. Adopts hydraulic-electrical feedback loops
• C. Has no electronic interface and uses cams and servo valves
• D. Relies on fuel-air mixture sensors

Answer: (C)

The fundamental idea is that a hydromechanical fuel control meters fuel using only mechanical and hydraulic components, with no electronic control. Throttle movement sets a cam-driven profile that positions a metering valve, and hydraulic pressure through a servo valve translates that motion into the precise fuel flow the engine needs. A diaphragm-and-spring arrangement uses hydraulic pressure as feedback to keep fuel delivery in balance with engine demand, all without any electronic sensors or control units. That’s why the best description is that it has no electronic interface and uses cams and servo valves. The other descriptions don’t fit because they imply electronic elements or sensors: an electronic interface to compute fuel, hydraulic-electrical feedback loops, or reliance on fuel-air mixture sensors.

The fundamental idea is that a hydromechanical fuel control meters fuel using only mechanical and hydraulic components, with no electronic control. Throttle movement sets a cam-driven profile that positions a metering valve, and hydraulic pressure through a servo valve translates that motion into the precise fuel flow the engine needs. A diaphragm-and-spring arrangement uses hydraulic pressure as feedback to keep fuel delivery in balance with engine demand, all without any electronic sensors or control units. That’s why the best description is that it has no electronic interface and uses cams and servo valves.

The other descriptions don’t fit because they imply electronic elements or sensors: an electronic interface to compute fuel, hydraulic-electrical feedback loops, or reliance on fuel-air mixture sensors.