16. Variable Pitch Axial Fans: Dynamic Control for Changing Airflow Demands The development of the Variable Pitch (VP) ac axial fans Fan represents a significant leap in air movement technology, allowing dc fans to dynamically and precisely control airflow in response to changing system demands[4]. Unlike fixed-pitch fans, where the blade angle is set during manufacturing, VP fans incorporate a sophisticated hub mechanism that allows the angle of the fan blades to be mechanically adjusted while the fan is running[4]. This capability is critical in large, complex systems, such as cooling towers or large industrial ventilation where the required airflow might fluctuate dramatically based on factors like ambient temperature, production load, or humidity[13]. By precisely adjusting the pitch angle, the fan can modify the volume and static pressure it produces[5].