Are solid wingsails practical with high lift slats?

Discussion in 'Sailboats' started by fenfen, Jul 18, 2017.

  1. fenfen
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    fenfen Junior Member

    Has anyone seen a solid wing sail with slats! Or with flaps? Or with vortex preventive measures?(winglets, under side strakes, leading edge notches ect)

    Why haven't solid wing sails taken advantage of 100 years of aviation improvements upon the air foil? =/

    I want to build bi-wing tops joined by a plate, stol style An-2 high lift wing cord/shap with fixed slats and flaps like the jünker. And i'll use a large coaxial load barring.
    I wanna know if anyone has encountered such advanced foils in boating?
     
  2. gggGuest
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    gggGuest ...

    You'd have more trouble finding a solid wing sail without at least some of those features. In the C Class catamarans especially the typical wing has 3 elements with slots that open and close according to camber. With the likes of Airbus associated with C class campaigns they are not short of very high end aerodynamic expertise.
     
  3. Doug Lord
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    Doug Lord Flight Ready

  4. DCockey
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    DCockey Senior Member

    Leading edge notches are usually an attempt to prevent separation and stall at higher angles of attack, not to prevent vortices.

    What would be the advantage compared to a simpler foil? Slats and flaps can allow operation without stalling at higher angle of attack than a single element airfoil, but the drag is usually higher at lower angles of attack and lift than a single element airfoil.

    Are you assuming more "features" means "better"?
     
  5. tspeer
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    tspeer Senior Member

    Arthur Rothrock built a landyacht with a rigid wing equipped with slats. The slats were mounted on a four-bar linkage that allowed them to move from side to side when the wing tacked. They didn't prove to provide any improvement in performance.

    Nearly all wingsails use slotted flaps. Single element wingsails have been built for landyachts, but they lack the ability to accelerate and are not competitive in racing. On the water, you need the high-lift capability of a flapped wingsail because of the higher drag of the hull.

    Leading edge notches are not necessary, either, for the same reason slats are not needed. You'd only be adding drag to cure a problem that doesn't exist.

    It's difficult to make a winglet that will work on both tacks and still provide a net drag reduction. It's always more effective to use the same area as a winglet to extend the span. The only reason to consider a winglet is if class rules constrained the height of the rig and did not constrain the size of winglets, and I know of no class like that. The AC72 and AC Catamaran class rules didn't allow winglets and constrained the size of control arm fairings to prevent them from becoming winglets.


    Leading edge slats aren't generally found on wingsails because they aren't necessary. The purpose of a slat is to prevent separation at the leading edge, leading to leading edge stall. It's not difficult to design a wingsail section such that separation occurs at the trailing edge first, and leading edge separation is not a problem. So there's no need of a slat, and it would just be added drag.

    Generally, the parts of a wingsail are called the main element and the flap, even though the flap may be more than 50% of the chord (as on the ETNZ AC72 Aotearoa). From an aerodynamic point of view, you could just as legitimately call the main element a slat for the after element.

    I think you'll find that wingsails are designed using state-of-the-art aeronautical technology.

    The slotted flaps used on wingsails are similar to the Jünker external flaps. They are hinged on centerline because of the symmetry requirement to work on both tacks. The hinge line is ahead of the trailing edge of the main element so the flap moves to windward when deflected. The deflected flap is in much the same location as the Jünker flap, although much larger in chord.

    The Walker Planesail used a large bearing like you describe:
    [​IMG]
     
  6. fenfen
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    fenfen Junior Member

    Ah i see i've not seem this particular schematic before thanks! Yeah slew ring bearing, that's what kind.
    The perpose of the leading edge part that hinges in this case is to change the camber to switch wich side makes more lift (even though a fully semtercal foil will lift at certain angles of attack)
    The Slats i speak of on the other hand bleed under side air to the top side of the foil to improve laminar flow over much greater angles of attack.
    As to cord, less width wings of infante lenght are better, like a sail plane/glider.
    I forgot, that example has no features to stop air from flowing to the end of the wing creating drag/vortex.
    I was thinking asymmetrical foil and a shunting boat, have you seen one before?
    Why hasnt anyone done a bi-wing?
    Also how do the take the sails down in bad weather or anchoring?
     
  7. fenfen
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    fenfen Junior Member

  8. gggGuest
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    gggGuest ...

    Most things have been tried. Asymmetric wings have typically been disastrous on racing craft, although of course the outright 500m speed record holder has one.
    There are two huge disadvantages to shunting on a course racing boat. The first is that a hull which is symmetrical fore and aft is hugely compromised in terms of shape, and the second is that shunting itself, requiring the boat to come to a halt and reverse direction, loses so much time against tacking. This is less important in an ocean sailing craft that might tack once or twice a day, but in course racing its a massive disadvantage.

    Multi rig boats are nothing new, of course, but in general, whether in line or on separate hulls, they have been disappointing. Sometimes its a compromise worth making for operational reasons, but generally a single rig is better if practical.

    And to your third question : how indeed!
     
  9. tspeer
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    tspeer Senior Member

    If you want to have a fore-aft symmetrical section for a shunting boat, then you have a bigger problem than slats. The issue becomes what kind of trailing edge to use? If you go with a sharp trailing edge you end up with a sharp leading edge, like an ogival section as described in NACA Report 365. If you elect to use a rounded trailing edge, then your section might look like this:
    [​IMG]
    A fixed slot, like the illustration you posted, will require a leading edge that is shaped to maintain attached flow at high angles of attack. There's no point in having the slot if the flow is going to separate from the leading edge ahead of the slot. This will be too blunt of a shape to serve as the trailing edge. You also have the problem of needing to have a slot at both ends of the section, and the rearward slot will be facing in the wrong direction and having the flow reversed in the slot. The end result will be a lot of drag and poor lift at high angles of attack.

    You could go with something like a Kruger flap that stowed on the windward side. It would be deployed to act as a slat at the leading edge and stowed at the trailing edge. That would allow you to use sharp leading and trailing edges and still maintain attached flow at the leading edge. You would, of course have to reconfigure the wingsail on every shunt.
     
  10. tspeer
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    tspeer Senior Member

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  11. JosephT
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    JosephT Senior Member

    The AC-72 boats use a rigid wing without a slat, though it does provide similar performance according to the design study referenced below. They mention "For high lift cases the headsail acts like a leading edge slat reducing the suction peak on the leeward side of the main element and allowing for an impressive increase in maximum lift."

    There are several barriers that prevent rigid wings from taking off in the sailing industry.

    • Cost: Aircraft-like structures are expensive to design, build and maintain.
    • Maintenance: Working on tall rigid wings is more difficult as compared to sails.
    • Safety: Handling during poor weather/storms is also a huge factor in my opinion. Fabric & mylar sails can be dropped within seconds/minutes to de-power the sails. A rigid wing, on the other hand, is always aloft and catching all that storm wind. It would be a almost certain to CAPSIZE in a squall or unexpected wind.
    There are probably additional reasons, but these are the main ones in my opinion. This is partially why the AC-72 boats have a constrained wind speed envelope for their events. If the winds are too great they postpone the race. Even then they see rather frequent capsizes.

    Anyone planning to design & build a boat with a rigid wing will need more money and will have to factor in the items above. Most opt for regular sails as they get the job done.

    Ref: http://vm2330.sgvps.net/~syrftest/images/library/20150803102956.pdf
     
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  12. fenfen
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    fenfen Junior Member

    Hey thanks this helps me alot to learn with is Orthodox in the boating world. Yup i ment slots! Tspeer is Right thanks.
    Oh i am not racing just wanna get to point nemo one day =P
    I've given these ridge wings alot of thought and even moked up in a 3D simulation.
    While construction is straight forward. The issue is reefing!
    In my mind I can't get around trying to have a heavy base hinge and ram to fold them down and up...and then where to out a wheel house??.
    I've calculated below for my wing shape design. Basicly 100 mph winds would break it all, even 50 mph. I project that 40 mph winds are doable.
    8lbs per foot of wing in 100mph wing being 25 by 4, 100 sqr feet, 12,000 inches
    204 lbs total.
    100mph wind= 0.17psi , 12,000*0.17=204 lbs.
    204/25=8.16lbs
    For every foot if vertical wing there is 8.16lbs
    Torque, foot pounds.
    25*8+24*8...
    2641.0
    Round to 2650lbs of torque!
     
  13. fenfen
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    fenfen Junior Member

    Oh what is a typlical Bermuda rig sail mast total torque in a less than in the reach mode, at 100mph wind in foot pounds, for a 25 foot rig, or 50 foot rig?
     

  14. Lurch723
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    Lurch723 Junior Member

    I think the question should be: are solid wing sails (with or without second element) a practical proposition for mainstream sailing applications?

    Financially and practically I think they are compromised and in the bottom end of their efficiency envelope where the gains are marginal. A soft wing design would negate most of the practical problems and reduce the cost financially. Furthermore in the event of the wing hitting the water surface or another object the energy dissipation would be far greater without compromising the rest of the structure.
     
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