Moth wings as actual wings

Discussion in 'Sailboats' started by Eric Lundy, Sep 28, 2017.

  1. Eric Lundy
    Joined: May 2017
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    Eric Lundy Junior Member

    I was debating the merits of making moth wings... an actual wing. At the speeds the moth can achieve, is an actual wing under your keister a benefit? Given the max beam of a moth and lets say the moth is traveling at an avg speed of 20kts how much lift could you generate from the air? Or is this making extra drag? Is your big dumb body getting in the way of the airflow too much? Would this require a change in body position or sailing technique? Could you create enough lift from the air (without actual added drag) to counteract some of the weight? If some of the weight could be taken up by the moth wings could it reduce the drag from the foils?
    Cheers,
    Eric
     
  2. Doug Lord
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    Doug Lord Flight Ready

    Here is Bill Beavers analysis of a Moth. Seems like he mentioned something about that but I'm not sure:
     

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  3. OzFred
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    OzFred Senior Member

    You can try Flutter's Moth blog, and this page.

    As far as I know, he was happy with the result in regard to build quality and matching the design (though the tramps were very fiddly). Dunno if it helped performance much, there are other aspects of the design that were a bit radical and it's a one–off home build (everything but the rig, I think even the mast was a hand–me–down prototype from CST), so no direct comparisons.

    He was one of the first to have double–sided tramps and I think still the only Moth where they are genuine aerofoils blended into the hull as opposed to just double–sided and wrapped around tubes.

    I don't think he's sailed it for quite some time.
     
  4. Eric Lundy
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    Eric Lundy Junior Member

    Thanks for the posts. Very interesting reading on both. As far as Nick flutters design: I found it interesting he had the wings lift down so the leward tramp, due to its angle when heeled agressivly to windward, acted like extra sail area sorta and act as aerofairing for the wing bars. I had the opposite thought that the lift would point in the same direction as the foil in the water, up. This would probably force a rigid build and would need to be designed into the hull differently as to not break the "hollow" part of the rules.
     
  5. Eric Lundy
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    Eric Lundy Junior Member

    I took some time to read his analysis of the moth. Very good stuff. My favorite part was the statistic "that the helmsman makes up 42 percent of the total aerodynamic drag and only 4% of the aerodynamic side force" . So wings lifting up may not be as beneficial as being more aerodynamic. But margins matter in the end.

    I was a downhill ski racer in a past life and reducing drag was everything. All the way from skin tight clothing to body position. If your tuck was a better bullet, you were faster. If you held your hands in front of your face in the tuck position you deflected wind and didn't scoop it up. Sailors will either get more aerodynamic fairings or get into an even more aerodynamic position on the boat. The future of all racing is less drag and the lumps of human meat stopping the wind is a big limiting factor. But possibly a "hull" wing the size of 7'4" x 11' could lift a certain amount of weight going 20+ kts. Enough to reduce drag on the hydrofoil at minimum I would think. possibly a wing fairing that lifts the boat a bit and you hide "in" or behind to limit meat drag.
     
  6. Eric Lundy
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    Eric Lundy Junior Member

    Ok, my brain went in a complete different direction on how to win kitefoiling races. you are mounted to your "monoski" on the best hydrofoil facing forward in a leaning aerodynamic tuck position with a speed suit and helmet on. the kite is mounted to a rail that pulls from either hip.

    ...I have too many projects, let alone random ideas. The issue is reducing drag by a factor in body positioning. less windage, less losing.
     
  7. Doug Halsey
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    Doug Halsey Senior Member

    At 20 knots of boatspeed, Moth foils are operating at very low lift coefficients. The foil drag is primarily skin-friction & would not be significantly reduced by adding lift to the wings.
     
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  8. Eric Lundy
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    Eric Lundy Junior Member

    I see, that is reasonable.
     
  9. Lurch723
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    Lurch723 Junior Member

    The biggest drawback you have in trying to generate lift from moth wings is: a wing generates its lift from the upper wing surface, this is a critical surface and guess what - your sat on it (one of them at least) or hiking off it, so robbing any negligible gain totally of lift. If you were to hike off an aerofoil section my guess is you would slide backwards and off the trailing edge into the water.
     
    Last edited: Oct 1, 2017
  10. Eric Lundy
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    Eric Lundy Junior Member


  11. OzFred
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    OzFred Senior Member

    I think if you look at the angle of the wind to the leeward wing, it's very difficult to get any "up" lift from it, so the focus is mostly on drag reduction. Dylan Fletcher's boat doesn't seem to have any root fairing of the wing into the hull, it's more–or–less a butt join. Since it has solid wings, it makes sense to shape the leading edge.

    Dunno if the span–wise curve makes any real difference, it certainly looks different.
     
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