When the Constant Speed Unit (CSU) is running "on speed", what is balanced?

When the Constant Speed Unit (CSU) is running "on speed," the correct understanding involves the balance of forces that govern the operation of the CSU. In this scenario, the governor weight's centrifugal force must balance the spring force of the CSU itself.

This balance indicates that the CSU is operating at the designed rotational speed, where the centrifugal force generated by the governor weights, as they rotate, perfectly matches the opposing force exerted by the springs. When these two forces are equal, it maintains a consistent engine speed by allowing for adjustments in fuel flow, ensuring that the engine does not slow down or speed up beyond its set point.

The other options do not accurately describe the functioning of the CSU when it is operating "on speed." For instance, while oil pressure is important in the operation of the CSU, it is not directly balanced against centrifugal force or spring force in this context, and the notion of shutting off the oil supply contradicts the operational principles required for the CSU to function correctly. Thus, the correct answer highlights the dynamic equilibrium that occurs within the CSU when it is operating as intended.