Wing mast section, truncated NACA 63015?

Discussion in 'Hydrodynamics and Aerodynamics' started by MichaelRoberts, Sep 6, 2015.

  1. CT249
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    CT249 Senior Member

    Apropos of nothing much, we had the national title of the NS14, the world's most popualr sloop-rigged development wing-masted mono at my club the other week. They are still using elliptical sections. The CST section has apparently taken over from the C Tech (NZ) section because it offers superior bend characteristics.

    There is a distinct discontinuity between the lee side of the main and the lee side of the mast. I'm told by one of the best that it doesn't matter.

    The runner-up was a former national champion in NS14s who is also one of the best in the world in Tasars, the world's most popular wing-masted sloop monohull. The NS14 was a major influence and inspiration for many skiff designers for many years. It all indicates that this is not a tiny class of turkeys sailing primitive boats. If after 50 years they have found that there is no need for a perfect junction between mast and sail it may be significant.
     
  2. Mikko Brummer
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    Mikko Brummer Senior Member

    Is the NS14 mast a small rotating wing mast?
     
  3. CT249
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    CT249 Senior Member

    The standard CST section is 80mm x 40mm. It's over-rotating. The section is, I think, symmetrical fore-and-aft.
     
  4. MichaelRoberts
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    MichaelRoberts Junior Member

    XFoil experiments

    Tom, thanks for the XFOIL encouragement.

    So far this thread contains valuable commentary and anecdotes suggesting possible advantages of a square backed wing mast. We've discussed CFD, trapped vortices and now the C-Tech section. Some hard data is now needed.

    So I've downloaded XFoil and Aerofoil and will put some effort to mapping flow over a mast with a parabolic leading edge, across the cut off back step and onto the offset mainsail. (Offset because the sail flops to the lee side on transverse slides that form part of the cars).

    Why is all this necessary? Two reasons - first to improve the aerodynamics (lift, stall tolerance, attachment) and second a more boxey section is stronger and so the mast can be can be thinner (less weight, less fixed area in a big wind).

    A new question: what about the plan form? At the moment the leading edge is an arc and the trailing edge is a straight line. The proposed mast has a chord of 440 mm at the base, 500 mm one third up tapering to 300 mm at the top. Is a curved leading edge good?

    Great forum, thanks everybody for your expertise
     
  5. tspeer
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    tspeer Senior Member

    Ideally, the planform can be designed by specifying a linear wake wash distribution in the Trefftz plane.
     
  6. MichaelRoberts
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    MichaelRoberts Junior Member

    mast leading edge curve

    Thanks for the paper you cited Tom designed by specifying a linear wake wash distribution in the Trefftz plane.

    These old typewritten documents are so precious - they convey a real sense of dedication and scholarship.

    Meanwhile the section shape is morphing a bit, it was too wide at the cut off aft end. The new shape is a compromise between NACA 0040 and 63018. This new section maintains the high second moment of area, while reducing the vortex where mast meets sail with its narrower tail.
     

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  7. brian eiland
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    brian eiland Senior Member

    Very important, particularly for older sailors.

    ( a proponent of NO mainsails ;) )
     
  8. brian eiland
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    brian eiland Senior Member

    I was reading thru this discussion yesterday and noticed a fair amount of drift in the subject over to computer analysis of wingmast airfoil shapes.

    It got me to wondering why more interest has not been shown in analyzing Chris White' MastFoil developments. I recently posted some questions/observations over here:
    Flaps on Airfoils, the MastFoil concept
    http://www.boatdesign.net/forums/hydrodynamics-aerodynamics/sail-aerodynamics-457-53.html#post765907

    http://www.boatdesign.net/forums/multihulls/chris-white-atlantic-47-mastfoil-40670-5.html

    Interesting, adding that v-shaped foil on the trailing edge of a wing mast. Wonder how the software programs would treat it?
     
  9. brian eiland
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    brian eiland Senior Member

    What do you think of this alternative to your more traditional rig,...a new mast-aft entry??

    Wingmasted aft mast
     
  10. MichaelRoberts
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    MichaelRoberts Junior Member

    Mast half empty?

    Thanks for your suggestions Brian

    An aft mounted mast is an attractive idea, I often do lazy cruising around with just a furling genoa. Furling is so much easier than hauling up a main.

    But now that most of the bridge deck with the strong mast beam has been built, I'm stuck with a mast in the conventional position. The mainsail will have an electrically operated halyard.

    I designed this boat to sail well in light airs. My experience with cruising is that too much motoring happens. With strong winds who cares about some inefficiencies. For light winds I calculated that at least 150 sq m of sail area is needed. So that's why I did not pursue the Chris White idea mainsail-less idea.

    The D shaped wing mast happened primarily because A J Marchaj proved its favourable lift/drag ratio.

    I should add that there are 3" / 75 mm semi-flexible flaps behind the cut off. Their purpose is to shroud the track, reduce leakage from the windward to the lee side and minimise the trapped vortices on both sides.
     

  11. brian eiland
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    brian eiland Senior Member

    I thought this might be the case, ....but thought I just might throw out the idea,...maybe for the next version ;)

    I have a few other thoughts on this aft wingmast plan that I will be adding to the 'aerodynamic subject thread.


    I don't see that you have much 'leakage' problem with or w/o those 'flaps', but smoothing out the flow can't hurt as long as those flaps don't present too many problems with the mainsail's attachment to the mast.

    I thought this was an interesting posting, touching on flow on the windward and leeward sides of the sail, by Tom Speer, over on another subject thread entitled sail camber.
     
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