What is NOT a parameter for a hydromechanical fuel control unit?

In the context of hydromechanical fuel control units, the parameters primarily monitored are those that directly influence the fuel delivery and combustion process in an engine. Fuel temperature, fuel flow rate, and engine temperature are critical factors in determining how much fuel is injected and when, ensuring optimal engine performance and efficiency.

Fuel temperature is important as it affects fuel density and viscosity, impacting the atomization and combustion process. Engine temperature helps in determining the operational status of the engine and can influence fuel management decisions based on operating conditions. Fuel flow rate is a direct measurement that indicates how much fuel is being supplied to the engine, which is vital for proper functioning.

Ambient humidity, however, does not directly affect the operation of a hydromechanical fuel control unit. While humidity can have an influence on engine performance, it is not a measured parameter within the control unit itself. The primary focus of a hydromechanical fuel control unit is on fuel characteristics and engine conditions rather than environmental factors such as humidity. This makes ambient humidity an irrelevant parameter for the functioning of the fuel control system.