During a dive, if power is not reduced, constant speed propellers may move onto which stops?

During a dive, if power is not reduced, constant speed propellers can indeed move onto coarse pitch stops. This scenario is primarily due to the aerodynamic forces acting on the propeller blades as the aircraft gains speed during the descent.

In a constant speed propeller system, the propeller governor adjusts the blade angle to maintain a specific engine RPM. However, during a dive, if the power remains unchanged and the aircraft accelerates, the increased airflow can cause the engine RPM to rise. If the governor does not react quickly enough, the propeller may inadvertently be driven towards a coarse pitch angle, which is designed to decrease RPM and maintain control of the engine speed. Selecting a coarse pitch increases the angle of attack for the propeller, creating more drag and thus reducing the RPM to a more manageable level in high-speed situations.

This mechanism is crucial for preventing overspeed conditions, which can lead to potential engine and propeller damage. Consequently, moving to the coarse pitch stops is a safety feature that ensures the propeller can handle high-speed conditions without exceeding specified RPM limits.