Lift onset, planing, and lift coefficient

Discussion in 'Hydrodynamics and Aerodynamics' started by sandhammaren05, Aug 13, 2018 at 1:45 AM.

  1. sandhammaren05
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    sandhammaren05 Senior Member

    New paper posted on lift onset with planing defined. Delta wing-type lift coefficient provided in agreement with Clements' data on v-bottoms.
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    What the hell is a "finite transom", used several times in the discussion ?
     
  3. sandhammaren05
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    sandhammaren05 Senior Member

    The hell finite transom is finite beam.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Are there boats that don't have finite beam ?
     
  5. latestarter
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    latestarter Senior Member

    I think they are referring to the analysis, with a theoretical infinitely wide surface there is no lateral flow so easy to calculate, with a finite beam it is much more difficult to calculate the real world position.

    "A 1950s era discussion of planing as lift (Du Cane[9])is based on a back of the envelope calculation that predicts a lift coefficient proportional to cos α , with finite lift at no attack angle. This is wrong.
    Lift must vanish as α goes to zero. The calculation is based purely on leading edge spray for a boat of infinite beam (two dimensional flow), neglecting the side spray and waves that are the main cause of lift-reduction and drag."
     
  6. sandhammaren05
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    sandhammaren05 Senior Member

    Are you asking 'are there boats that do not have a finite beam at the transom, where the transon meets the bottom? Yes, plenty of them.
     
  7. sandhammaren05
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    sandhammaren05 Senior Member

    DuCane assumed 2D flow with no Kutta condition and got a lift coefficient that makes no sense
    (see the end of the paper) because it remains finite as trim angle vanishes. I treat only 3D flow.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    Maybe there is a language or translation confusion here.
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    A theoretical convenience ? Maybe so.
     
  10. sandhammaren05
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    sandhammaren05 Senior Member

    You should not be confused. Look at fig. 1 and 2.
     
  11. sandhammaren05
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    sandhammaren05 Senior Member


    No, clearly defined. Again, see figures 1 and 2.
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    No, I'm not confused, just wondered about the usefulness of talking about finite beam transoms.
     
  13. DCockey
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    DCockey Senior Member

  14. sandhammaren05
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    sandhammaren05 Senior Member


  15. sandhammaren05
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    sandhammaren05 Senior Member

    Good thing to think about because that's the key to lift and planing.
     
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