if you spend some time with fan laws and electrical motor power, you can overlay ohms laws with he fan laws.
if there is blockage, means no power being used to move air, the current and voltage will be at one place on a plot.
if the blade is off the motor, it will be on another location on the plot
if the unit is stalled, another.
the propeller blade fans you are using have horrible fan curves for this purpose. a blower would be much easier, but the values exist nonetheless.
a sensorless sensor.