# Help..Propeller Moment Of Inertia Calculation

Discussion in 'Props' started by sam_antony, Jan 26, 2011.

1. Joined: Jan 2011
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### sam_antonyNew Member

Now i am calculating for design propeller kaplan type, but i can't determine/calculate moment inertia of propeller,on air condition and in the water condition.
anybody can help me?
thank you...

2. Joined: Mar 2005
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Location: Durham, NH USA

### DMacPhersonSenior Member

Let me refer you to a paper by our staff: MacPherson, D.M., Puleo, V.R, and Packard, M.B., "Estimation of Entrained Water Added Mass Properties for Vibration Analysis", SNAME New England Section, Jun 2007

You can find it on our Knowledge Library page: www.hydrocompinc.com/knowledge/library.htm

In this paper, you will find some calculation techniques and parametric prediction methods for the moments of inertia. Unfortunately, most of the parametric methods were for open propellers (that, of course, have a different blade profile than a Kaplan propeller), so these will probably not be useful. However, an approach is described for a "blade element" calculation that would be suitable. It requires radial definition of some of the geometry, so you'll have some work to do, but it is an appropriate technique. (This is the approach that we use in our commercial PropCad propeller modeling tool.)

Don MacPherson
HydroComp

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### sam_antonyNew Member

Thanks so much for the reference, we have try to calculated with Burril Estimates formula (base on your article), the result has 3517.76 kg.m^2. I think this value are too high.
We have two comparison data for the Moment of inertia in the water and on the air as follows :

> Prop Diameter 2.4m
Wk^2 in air = 295
Wk^2 in water = 351

> Prop Diameter 2.2m
Wk^2 in air = 212
Wk^2 in water = 307

Maybe you have another formula for Moment of Inertia on Air.

Sam Antony
MCCI

4. Joined: Mar 2005
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### DMacPhersonSenior Member

I have reviewed the original paper, and find a publication error. The Diameter in the Burrill simple estimate of IE should be in feet, not inches. The output is LBM-FT^2. (This would be corroborated in the Appendix examples.) Also remember that this is for the supplemental inertia of the water (not the mass+water), and is for open propellers, not ducted porpellers of the Kaplan style (as described previously).

Don MacPherson
HydroComp, Inc.

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### sam_antonyNew Member

OK, thank you very much...
nice to discuss with you

Sam Antony
MCCI

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