Moment of inertia formula for a propeller

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SUMMARY

The moment of inertia for a two-bladed propeller can be estimated using the formula for a rod rotating about its center, specifically 1/12 ml², where m is the mass and l is the length of the propeller. This approximation is suitable for high school physics problems, assuming the propeller behaves like a simple rod. However, for more accurate calculations, especially in engineering applications, detailed models from manufacturers that account for the actual geometry and mass distribution of the propeller are necessary. An alternative formula mentioned in the discussion is 2/3 mr², though its derivation remains unclear.

PREREQUISITES
  • Understanding of basic physics concepts, particularly rotational dynamics.
  • Familiarity with moment of inertia calculations.
  • Knowledge of mass distribution in physical objects.
  • Basic algebra for manipulating formulas.
NEXT STEPS
  • Research the derivation and application of the moment of inertia formula 2/3 mr² for various geometries.
  • Explore detailed models of propeller design from manufacturers to understand mass distribution.
  • Study the principles of rotational kinetic energy and its calculations.
  • Learn about advanced modeling techniques in physics, such as finite element analysis (FEA) for complex shapes.
USEFUL FOR

Students studying physics, engineers involved in propeller design, and anyone interested in the dynamics of rotating bodies will benefit from this discussion.

localrob
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Is there a moment of inertia formula for a 2 bladed propeller?
If you only have the mass and the length of the propeller, I would think a good estimate would be using a rod rotating about the middle. 1/12ml2
 
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localrob said:
Is there a moment of inertia formula for a 2 bladed propeller?
If you only have the mass and the length of the propeller, I would think a good estimate would be using a rod rotating about the middle. 1/12ml2

"Good" depends upon what you want to use the estimate for. Does a simple rod adequately describe the geometry and mass distribution of the propeller you have in mind?
 
I think that for a high school physics problem, it can be assumed to act like a rod. So when finding the rotational kinetic energy of a spinning propeller, I could use the rod formula.
But I was curious if there were another generally accepted formula for a propeller that I could use. I'm not sure what the distribution of mass is for an actual propeller, and nothing other than the mass and length are provided.
 
No doubt manufacturers of propellers will have detailed models of their propellers, including all the geometry and mass distribution. But for a problem where the only information you have is mass and length you're rather constrained to choose the rod as a model.
 
That's how I feel too. I did see a post on these forums where someone found the formula to be 2/3mr^2, but I don't know where that came from.
 

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