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Moment of inertia formula for a propeller

  1. May 13, 2012 #1
    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
     
  2. jcsd
  3. May 13, 2012 #2

    gneill

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    Staff: Mentor

    "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?
     
  4. May 13, 2012 #3
    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.
     
  5. May 13, 2012 #4

    gneill

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    Staff: Mentor

    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.
     
  6. May 13, 2012 #5
    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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