How does the hydromechanical fuel control sense engine speed?

The hydromechanical fuel control system senses engine speed through being driven by the gas generator gear train. This mechanism is integral to the system's operation, as the gas generator gear train directly correlates with the rotational speed of the engine. As the engine speed changes, the gear train transmits this information to the fuel control unit. This allows for adjustments in fuel flow to match the engine's power requirements, ensuring optimal performance and efficiency.

Using throttle position, monitoring fuel pressure, or utilizing temperature sensors are not primary methods employed by hydromechanical fuel controls for sensing engine speed. While these factors may influence fuel delivery in other ways, they do not provide a direct correlation to the engine's speed as effectively as the gas generator gear train does.