Think About It A fan motor turns at a given angular speed Ho

Think About It A fan motor turns at a given angular speed. How does the speed of the tips of the blades change when a fan of greater diameter is on the motor? Explain.

Solution

Blades with a greater diameter mean more surface area (assuming everything else is constant). More surface area means more drag. More drag means more power is required to sustain a given speed. If the motor is not capable of increasing its power output, the rotational speed must decrease.

However, if the motor has plenty of power to spare, and always operates at the same rotational speed, then a larger blade will have a higher tip velocity due to traversing a larger circle in the same time.