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Spill Plates and general aerodynamics.

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  • Ram4x4
    replied
    Vortex generators serve the purpose of delaying airflow detachment from a surface (stall). You'll often see them on STOL aircraft as it helps with high angle of attack flight regimes, or to increase flap effectiveness, etc. Unfortunately, they also create drag, so speed performance can be affected.

    Spill plates (also called wind fences) I believe also serve some structural function as well by adding rigidity to the frame from vertical flex (I may be wrong on that, someone who is a builder could probably answer that better).

    From an aerodynamic perspective, their function should be to minimize lateral flow of the air as it crosses the airfoil of the body. On aircraft, as the air flows over the wing, there is a tendency for the air to want to flow horizontally off the wing tips (span flow), and this lateral movement is one of the forces that create wingtip vortices. Vortices cause drag, so there has been a lot of study put into creating different aircraft wing tip shapes or adding winglets to try to counter span-wise flow or to at least delay vortex generation, pushing it further behind the aircraft to minimize drag.

    In terms of a hydro, I also see them acting as a wind vanes (kind of like throwing an arrow backwards) since our boats don't always travel perfectly straight and even relative to the wind. I don't think there's enough adverse effect there, though to cause the boat to windmill awkwardly.

    Size, placement and, of course, speed of the boat matters.

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  • deeougee
    replied
    Some boats use them some don’t. Depends on how much top wing area. On boats with them built into the design it keeps the front end (boat going straight). I know others who have removed them from their boat and the boat handled terribly after and they had to put them back on. Now keep in mind what air molecules do at subsonic speeds against pointed and rounded objects. Air flow around rounded surfaces is smooth where as on pointed surfaces it is turbulent. Hence the ram wing leading edge can have a big effect on how much and how the air flows over the top of the boat and into the tunnel. Rounded sponson tips versus pointed ones.

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  • Dave Cofone
    started a topic Spill Plates and general aerodynamics.

    Spill Plates and general aerodynamics.

    I was wondering about the need for spill plates running down the topsides of a hydro's deck. I know the basic reason is to straighten out the airflow over the airfoil but frankly I can't believe they do all that much on such a small 'wing area'. Perhaps there is another reason and that is what I am trying to find out. I want to learn as much as I can about the hulls and the aerodynamics of the late model boats. Tunnel width, wing camber, straight bottom or S bottom etc. I have even seen vortex generators on the leading edge......this is very interesting to me, please give me your thoughts.....
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