Rotating adjustable hydrofoils

Discussion in 'Hydrodynamics and Aerodynamics' started by mij, Nov 29, 2013.

  1. mij
    Joined: Nov 2013
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    mij Junior Member

    I'd appreciate some feedback on an idea that I have been considering for adjustable foils for rc multihulls. I've been trying to find a very simple system that could switch between foiling and non-foiling modes.

    The idea is to have the foils able to rotate on an axis that is inclined relative to the hull (see attached image). When the foils are vertical they are aligned with the direction of the boat (angle of attack = 0), essentially acting as dagger boards; when they are rotated the angle of attack increases and can be adjusted as required, thus able to act as foils.

    Does this idea look feasible? Has it been tried before?

    Here are a few videos which show how the rotating aspect works, although for these the axis isn't inclined:

    https://www.youtube.com/watch?v=wwQ8OQqCGLw
    https://www.youtube.com/watch?v=BqkIA_WHzTs
     

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  2. Doug Lord
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    Doug Lord Flight Ready

    ==================
    I think it's a very neat idea! Do you have a way to adjust the angle of incidence of the main foils for set up-I'm not sure I saw that?
    You might consider powering the foiler with a "normal" rig just to get the foils right then add the mast aft experiments?
    I designed ,but didn't build a newer version of the F3 with retracting foils. The F3 uses a wand altitude control system so the wands had to retract as well. Maybe I'll try it someday...
    I wish you good luck with your experiments!
    ===========
    This may be worth adding to your data base: for my F3 the foil loading on the main foils was .188lb/sq.inch of foil area.
    For an 8lb 56"X 72"(wide) foiler the main foils were each 17 sq. inches and the rudder foil 17 sq.in.. The main foils supported 80% of the boats weight at takeoff, the rudder foil 20%. The boat would take off in a 5mph(not knot) wind with 1668 sq.in SA.

    Pictures of the F3:
     

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  3. mij
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    mij Junior Member

    The angle of incidence is controlled by the inclined axis of rotation. This wasn't in place in the videos.

    I probably should have switched to a conventional rig or switched to one of my conventional wings, but instead I put hydrofoils on hold and focused on the mast aft sail. The main reason for this is that after a few attempts at foiling I came to the conclusion that my boats are a bit too small (650-800 mm). I'm planning to build a Mini40 (1200 mm) cat in the new year to test my foiling ideas.

    Nice looking boat, thanks for the info.
     
  4. mij
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    mij Junior Member

  5. Doug Lord
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    Doug Lord Flight Ready

    =================
    I get it now-very good. Seems like a design challenge to match dihedral and angle of incidence but I can see how it could be easily adjustable. Good thinking!
     
  6. Baltic Bandit

    Baltic Bandit Previous Member

    Given that its an RC model and you don't really have to worry about crew overload, why run a compromise? why not have a set of foils that are optimized for non-foiling upwind work (the dihedral foil isn't particulary good at upwind work) and a second set of dihedral J foils for foiling? with a programmable TX you can set it up so that your upwind foils can be fully retracted in foiling mode but have the leeward one down upwind I tacks.

    and for offwind foiling mode you can go with the more efficient leeward J foil, or the dihedral you've already built
     
  7. mij
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    mij Junior Member

    What you suggest it probably a higher performance solution, but doesn't really have the simplicity I am after. I'm planning to find a hydrofoil that is a compromise between adequate foiling and upwind performance.

    I'm also planning to try to extend this idea to the rudders: rotating foils that can be rotated above the water-line when not foiling (the opposite of the main foils), with conventional vertical rudders for steering at the ends (these would move closer together and further apart when not foiling and foiling, respectively). Ok, that might be a bit hard to visualise, I'll work on a schematic.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    This is a rough sketch of a retracting T-foil rudder. The "cassette" that the rudder fits into rotates on a horizontal, fore and aft axis. The rudder can be used as a hydrofoil with the blade locked into position, or the whole thing can be rotated and the former "top" of the rudder becomes the non-foiling blade.
    The disadvantage of this system is no rudder "balance"*(area forward of the pivot axis)
    * usually around 15-18% of total rudder area.

    rough sketches: Left=rotating retractable T-foil rudder, Right=illustration of rudder balance.
     

    Attached Files:

  9. Baltic Bandit

    Baltic Bandit Previous Member

    Well except that if you aren't foiling - say upwind mode, ideally you will have enough power to fly a hull won't you?

    you could do a kickup foil of the kind Doug is suggesting, but you are adding a lot of complexity and weight for conditions in which you basically really aren't having much fun sailing anyway
     
  10. mij
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    mij Junior Member

    My aspirations aren't quite so high. If I can build something that can foil down wind with some control and point somewhat upwind I will be happy. Of the few foiling rc sail boats I've come across, only a small fraction appear to be able to do this much.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    ===============
    For what it's worth, the rudder I suggested is not a "kickup" rudder-it slides vertically in a cassette. It would have to be raised manually to avoid grounding.
     
  12. mij
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    mij Junior Member

    It is my turn to be a bit confused by the diagrams. Could you please explain how it works?
     
  13. Baltic Bandit

    Baltic Bandit Previous Member

    Mij - I don't think its really worth digging in hard. Essentially they are just standard kickup rudder heads of the kind you would see on a beech dinghy or a Hobie cat. But since you have a servo holding them down, you don't need a locking mechanism
     
  14. Doug Lord
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    Doug Lord Flight Ready

    =======================
    See the picture below of the port hull of hydroptere.ch: it uses a rudder in a cassette as well. On hydroptere.ch the cassette is like a daggerboard trunk with gudgeons and pintles(or similar) attaching it to the boat.
    My sketch shows the same sort of cassette(trunk), but it is attached to the boat via some sort of pivot-like a carbon tube within a carbon tube that allows the whole cassette + rudder to pivot. The cassette would be attached
    to the carbon tube via a method that allows the rudder to rotate normally.
    The tiller would have to be removable-changed when the whole assembly is rotated within an athwartship plane.
    ---------------
    I'll post a more detailed sketch shortly.

    ---
    Pictures: Left=hydroptere.ch with it's windward rudder retracted in a cassette,Right=the RS600FF monofoiler with its rudder retracted in a cassette.
    click and expand for larger picture-
     

    Attached Files:


  15. mij
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    mij Junior Member

    Thanks, I understand now.
     
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