Aerodynamics - thundercat racing inflatable

Discussion in 'Hydrodynamics and Aerodynamics' started by Roflhat, Oct 13, 2015.

  1. Alumination
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    Alumination Junior Member

    Would there be an advantage to locating the engine more rearward behind the transom? This would push the drive down into the water the more the bow pitches up, cause drag and bring the bow down, sorta like trim tabs do. Might start to help before the bow can get too high to begin with.
     
  2. Roflhat
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    Roflhat Thundercat - 70.10mph

    Thanks very much for the reply Jim, I'll send you a reply via PM as well

    This has been tried by a few people, using setback plates to position the engine further aft. However, when the boat is in waves the increase in stress on the transom caused by the setback caused the transom to come away from the tubes.
     
  3. Alumination
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    Alumination Junior Member

    More power and/or less drag is how you go faster.

    Accomplishing this without creating compromises is the tricky part.
     
  4. Roflhat
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    Roflhat Thundercat - 70.10mph

    I think I've got the power covered, got a list of things to do over the winter to the engine, should take it to close to 90hp. Got a good selection of propellers as well, but I wanted to turn my attention to the aerodynamics, as you say reducing the drag. I don't think many folk have looked into this for thundercats. The manufacturers change the shape of the nose cones at the bow of the boat, although I think this is based on aesthetics rather than wind tunnel testing.

    Some of the bigger RIBs used in racing have covered bows, which apparently gives around 3-4 knots at a top speed of ~50 knots. I was thinking of trying the same principle on the thundercat
     
  5. Jimboat
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    Jimboat Senior Member

    There are indeed, design related mod's that can be made to reduce overall aerodynamic drag. The total aerodynamic drag, including cockpit drag is significant on a hull such as a thundercat hull, so there's opportunity there for sure. Covering in a significant part of the open cockpit area will definitely reduce 'cavity drag' if you can accommodate the change in your design/setup. Also, Roflhat, your suggestion of improving the shape of the leading edge (nose cone) of the RIB design will also improve aerodynamic drag. There are other things that you can do also, to reduce the overall aero drag of your hull.

    Here is an article on Aerodynamic drag in performance boats and also articles on "How Tunnel Boats Fly"
     
  6. claydog
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    claydog Junior Member

    This would be my thought, get the pilot, co-pilot and motor in still air behind a fairing and clean up all of the airflow. I'm not an areo expert by any means, but have spent many hundreds of hours in a wind tunnel on automotive projects. The true experts always start cleaning up air flow at the front of the vehicle first. If you look at your truck diagram you can see cab to trailer and under trailer are both cleaned up then a boat tail is added. You may also want to look into the Kamm effect on areo.

    Maybe something like this...
     

    Attached Files:

  7. Roflhat
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    Roflhat Thundercat - 70.10mph

    Interesting idea, I can see that working.
    The Kamm tail is a good read too, it makes the shape of a lot of modern cars make sense.
     
  8. Roflhat
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    Roflhat Thundercat - 70.10mph

    Another thing I was lookin at is the roof flaps used in NASCAR, which deploy when the car spins due to an area of low pressure. Not sure how I could employ this design on the thundercat though.
     
  9. Alumination
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    Alumination Junior Member

  10. claydog
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    claydog Junior Member

    Good stuff Jim. :)
     
  11. claydog
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    claydog Junior Member

    I don't see how you could apply that type of device on a boat, they function only when the car in in a spin.

    https://en.wikipedia.org/wiki/Roof_flap
     
  12. Roflhat
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    Roflhat Thundercat - 70.10mph

    Latest idea - teflon coating the bottom of the hijackers. Would this work?/is it possible?
    Or would something with a a rougher surface be beneficial? So as to trap air beneath it
     
  13. whitepointer23

    whitepointer23 Previous Member

  14. markdrela
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    markdrela Senior Member

    Teflon will reduce solid/solid friction. It won't do anything for liquid/solid friction, for which the chemical composition of the solid doesn't matter. The only thing that matters is the smoothness of the solid surface, or a specialized surface texture like riblets.

    One exception where chemistry matters is a for surface which continuously sheds long-chain molecules, or so-called "fish slime", which can reduce viscous drag by suppressing turbulent mixing in the boundary layer. That's surely not practical here.
     

  15. Alumination
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    Alumination Junior Member

    I just assumed this was a joke although it may actually be a real system. Not sure I'd feel real comfy relying on it though.
     
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