# Calculating Drag Force due to air on a Pedestal Fan blade

## Main Question or Discussion Point

I am doing a project where in a pedestal fan is alternatively powered using a flywheel. The flywheel is brought to some initial angular velocity by the electric motor. Now, if the power goes off, the fan blades would be coupled to the flywheel and it continues to rotate for the next 10 minutes.

After the power goes off, we have considered that

Energy-flywheel + Energy-fan = ∫ (Torque-drag force * ω -fan) dt

I'm having trouble calculating the torque due to the drag force and how to geometrically simplify the fan blades.

Any solution would be very much helpful.

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russ_watters
Mentor
Welcome to PF!

Why don't you just measure the electrical input to the fan?

Yes, but that would give me the power consumed at some constant fan speed( during operation).

When my flywheel is engaged, the rpm keeps on reducing and is a function of time.

If I know how the drag force is related to angular velocity and how much torque is generated, I would then be able to solve.

Any idea about drag force, Russ?

russ_watters
Mentor
Yes, but that would give me the power consumed at some constant fan speed( during operation).

When my flywheel is engaged, the rpm keeps on reducing and is a function of time.
Well, once you have the peak, you can use the fan affinity laws to calculate the power at any rpm. Basically, power is a cube function of rpm.