Windknife trifoiler build

Discussion in 'Multihulls' started by revintage, Dec 7, 2018.

  1. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Have fine tuned the foil section, with Doug Halsey helping me doublecheck it in XFOIL.

    I have also made the router file for the paulownia core.

    Think this is as good as it gets for a DIYer, using the Foil Nose for the first 27% and a flat bottom. The new N12FLATZ still uses the added +/- coordinates from NACA0012, where I have slightly manipulated the thickness from 27-46% chord length in Excel. Used the Pressure Coefficient Cp function in JavaFoil, to visually check the result and tame the irregularities.

    The first two XFOIL graphs was kindly supplied by Doug H.

    cpdoug.png cavZ2.PNG N12FLATZCROSSCUT2x10.png Skärmklipp.PNG cp.PNG
     
    Last edited: Nov 21, 2019
  2. nwguy
    Joined: Feb 2010
    Posts: 15
    Likes: 3, Points: 3, Legacy Rep: 10
    Location: Poulsbo, WA

    nwguy Junior Member

    It actually foiled very well. I just had structural failures when sailing at high speed with 2 people. Repaired one thing, then another thing broke, then another.
     
    revintage likes this.
  3. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Sorry Jim, had to read your reports again. I understand it foiled well with only you on it, found the image below. It would probably only have needed more SA for two persons to foil earlier? Get the impression that you couldn´t adjust incidence on the rudder foil and because of that had to stand to balance it lengthwise?

    [​IMG]
     
  4. nwguy
    Joined: Feb 2010
    Posts: 15
    Likes: 3, Points: 3, Legacy Rep: 10
    Location: Poulsbo, WA

    nwguy Junior Member

    It foiled well with 2 people, only took about 12-13 knots of wind too. It just was weak in some critical locations. The final straw was a big crack in the junction of the forward aka and one of the side plates that were welded on the ends to attach the amas. The main foils' angle of attack were adjustable via 3 bolts per foil. You had to go to shore and use wrenches to do it. The rear t-foil's angle of attack was adjustable via a pin that went through the rudder cheeks and through various holes in the top of the rudder. You could do it while sailing, but you had to stop to do it. So no, the foils were not actively adjusted like a moth, with the feeler out front. That's a very hard problem to solve. I actually enjoyed "riding" it by moving around to change the angle of attack. You could instigate getting up on a foil that way and then leveling it out once you got going. Very exhilarating. I windfoil (windsurfer with hydrofoil) too, and you need to weight shift on that too to maintain level flight.

    What are your plans to control angle of attack?
     
  5. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    The rudder incidence will be set by turning the tiller extension, as I have bought a Waszp rudderbox and the gears inside it. It is actually the same system as Doug Halsey has built himself. About the mainfoils both will at first be manually controlled from where you sit. We have discussed adding an electronic system but that will be when and if we can make the boat work.
     
  6. nwguy
    Joined: Feb 2010
    Posts: 15
    Likes: 3, Points: 3, Legacy Rep: 10
    Location: Poulsbo, WA

    nwguy Junior Member

    I'll be interested to hear what happens with this.
     
  7. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Hi Jim,
    We have discussed this a while ago on my Frankenfoil Sverige group . If you are on FB, please join.
     
  8. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    These are the N12FLATZ section coordinates.
     

    Attached Files:

  9. tspeer
    Joined: Feb 2002
    Posts: 2,228
    Likes: 185, Points: 63, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    You might want to run those Xfoil analyses again using 1<Ncrit<3. I don't think you'll ever get the kind of laminar flow in water that is predicted using Xfoil's default Ncrit=9.
     

  10. revintage
    Joined: Nov 2016
    Posts: 211
    Likes: 41, Points: 28, Legacy Rep: 10
    Location: Sweden

    revintage Senior Member

    Thanks for pointing that out. Anyway this might be of less importance as the analyses are just for comparision between sections?

    Adding a *.dat/txt file if you wish to check it, I would really appreciate if you did, makes me curious and eager to find out.
     

    Attached Files:

    Last edited: Nov 27, 2019
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.