# Moment of Inertia for a blower

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1. Aug 3, 2017

### Zarathuztra

I have a blower within a system, and I'm trying to calculate the system inertia. I'd like to get the moment of inertia for this component as would be seen by the shaft. It's shape has me a little stumped (considered perpendicular axis theorem) on what method to use for finding the inertia. Any direction to help get me started would be much appreciated. See the image attached.

2. Aug 3, 2017

### Nidum

Moments of inertia about a common axis can just be added together . So break the component into individual parts , calculate their individual moments of inertia about the central axis and sum them . The symmetry of the component can be used to reduce the amount of calculation necessary .

3. Aug 11, 2017

### tygerdawg

OR you can take the easy route. Get, or create a reasonably-accurate copy, of the CAD model. Assign a material density to the model components. Use the mass properties function of the CAD package to determine the MMO about any arbitrary axis.

4. Aug 11, 2017

### Dr.D

Looks to me like you need to break this into 8 parts: 6 blades, 1 back plate, 1 central hub, and then calculate the MMOI for each one about its own CM. Then use the parallel axis theorem to transfer to the common axis of rotation.

5. Aug 11, 2017

### CWatters

+1.

1) divide a blade it into standard shapes like this...