Anti Vortex Plates instead of boards?

Discussion in 'Hydrodynamics and Aerodynamics' started by DennisRB, Oct 7, 2011.

  1. PAR
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    PAR Yacht Designer/Builder

    I played with this idea some years ago, as an answer to some builders that were trying to retro fit some of Bolger's ideas on their boats. There has also been previous discussion here a few years back. The net result was the runners worked fairly well on deep bellied, yet still shoal craft, but not as well as conventional appendages. In shallower hull forms, they were much less effective. They worked on Bolger's heavily rockered flat bottoms, but truly sucked on shallower, long, flatter run, sharpie models.
     
  2. DCockey
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    DCockey Senior Member

    There is a very fundamental difference between winglets on an airplane wing and endplates/wings/winglets on a boat keel.

    Transport aircraft wings only need to produce lift in one direction, and the winglets are not symmetric.

    Boat keels need to produce lift in both direction unless the boat will only sail on one tack. So the endplates/wings/winglets on a keel have to be symmetric which makes them fundamentally less effective than if they were optimized for lift in one direction.

    Basic fact, but rarely recongnized or mentioned.
     
  3. DCockey
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    DCockey Senior Member

    I've seen technical papers in the distant past about the benefits of properly designed winglets on transport aircraft, and about how they need to properly designed.

    Why would Boeing and Airbus increase their costs with winglets if they didn't improve performance? Airlines buy aircraft based on performance and cost.
     
  4. DennisRB
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    DennisRB Senior Member

    The PDF file is in reference to catamarans. Each hull is treated like a wing which produces lift in one direction, thanks to heel which lifts one hull (even it it is not fully clear of the water) and submerges the other. There is also reference to a-symmetric hulls which are very similar to aircraft wings. My original post was in reference to catamarans, sorry for the confusion. I do not think winglets would work on a mono hull due to the high angles of heel and wide hulls.

    Anyway, so there seems to be no actual scientific testing done on these devices as leeway preventers? What works in theory may not work in practice, and Bernds cats may be naturally good at preventing leeway due to the long narrow hardchines. Just how much his tiplets help is unkown. Possibly an RC test catamaran might be of some help to find out exactly how much the tips do or do not work compared to more traditional methods of leeway prevention.
     
  5. DennisRB
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    DennisRB Senior Member

  6. Richard Woods
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    Richard Woods Woods Designs

    I've been thinking some more about this claim and it just seems so unlikely.

    For example, see this thread here:

    http://www.boatdesign.net/forums/multihulls/cruising-catamaran-average-speeds-20402.html

    And then a racing 60ft monohull in the Vendee Globe here:

    http://www.vendeeglobe.org/en/news/9664/rich-wilson-finishes-9th-in-vendee-globe.html

    The relevant quote is: "Wilson averaged 9.84 knots on the water covering 28,590 miles. "

    I think it is extremely unlikely that an 11.6m plywood cruising catamaran would average the same speed WHEN CRUISING as a 60ft racing monohull

    Especially considering that much of the Vendee is a downwind/high wind/surfing sail, whereas a cruiser will sometimes sail to windward, often sail in light winds and usually sails slow to stay comfortable.

    I also doubt the 2.2T cruising displacement claim. Especially if you consider that the F40 12m long multihulls weighed 1800Kg in day racing trim.

    So if those claims are questionable, then why not his others?

    Having said that I'll be the first to congratulate the designer if he publishes the detailed logs for the last 11 years of cruising to back up his claim

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  7. DennisRB
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    DennisRB Senior Member

    I agree Richard. The claim seems fantastic. I would also like to know how he came to the figure of 9.8K. I guess with ocean racing, you keep sailing when there is no wind. And possibly if you have no time frame in life when cruising you can just stay at anchor forever until the best wind conditions??? That's drawing a long bow though...
     
  8. bscally
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    bscally Junior Member

    If you look at the Boeing wingtips vs Airbus

    See http://en.wikipedia.org/wiki/Wingtip_device

    Boeing are tending to use an upper surface blended vertical airofoil. The 787 is different as the wingtip appears to form in flight due to designed wing flex.

    Airbus use tend to use upper and lower tip fences.

    An airbus wing designer I know claims that though the Boeing approach was better at specific operation points it was not as good over the full operating range.

    I am sure Boeing wing designers claim their approach is better for exactly the same reason.

    --

    The Windrider Rave community found that adding tips to the foils was a huge performance increase. 10% would not be a bad guess.

    Brian
     
  9. DCockey
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    DCockey Senior Member

    Don't think that's how it works. The NASA website has some papers about optimum wings for minimum induced drag when root bending moment is the constaint as opposed to wingspan and/or use of an exisiting wing design concept being the constraint . The papers show planforms very similar to the 787 wings.
     
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  10. Petros
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    Petros Senior Member


    You did not read my earlier post very carefully, these very large aircraft are already restricted to only land on airports than can accommodate their large wing spans. If they want to increase the capacity of the aircraft they have to increase the size of the wing, which would bring even further restrictions on the number of airports they are allowed to operate out of. So adding the winglets allows them to increase performance without having to increase the wing span. This would not be necessary on small aircraft.

    Furthermore, no current aircraft manufacture will design winglets per old NASA studies, nor would they use the old airfoil and wing design if they were redesigning the wing anyway. This is obsolete information. They always develop their own new shapes around the design objectives for the aircraft. Be they limiting the max span to accommodate more airports, or to reduce drag, extend range, increase gross weight capacity or whatever. Each of these design objectives will take different approaches to how to shape the wingtip and foil shape. All are designed using modern 3D CFD programs around three dimensional flow considerations, none are designed around 2-D concepts. Many years ago I had done this kind of work for a defense contractor.
     
  11. DCockey
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    DCockey Senior Member

    Actually I did read it very carefully, but did not agree with your statement "That is the only place they have an advantage, all the rest used on small buiz-jets are just marketing."
    Some recent, not so "very large aircraft" have winglets. For example the Boeing 737-700, 737-800 and 737-900 which increase wingspan but provide significant performance advantages.
    http://www.boeing.com/commercial/737family/winglets/index.html
    http://www.boeing.com/commercial/737family/winglets/wing2.html
    http://www.boeing.com/commercial/737family/winglets/wing3.html
    http://www.boeing.com/commercial/737family/pf/pf_winglets.html

    Boeing has developed blended winglets for the 757 and 767 which also provide performance advantages:
    http://www.boeing.com/commercial/aeromagazine/articles/qtr_03_09/pdfs/AERO_Q309_article03.pdf
    These are retrofits to exisiting designs. Since these winglets increase span they are not being added due to wingspan limitations.

    Airbus has put winglets on most of their aircraft, not just the largest. http://www.airbus.com/innovation/proven-concepts/in-design/winglets/

    I never claimed anything about what data aircraft manufactuers would use when designing wings or winglets. I remember some sessions at AIAA Applied Aerodynamics Conferences in the 1980's where the design of wings and winglets using 3D CFD codes was presented. One of the things I took away was that a generic design was far from optimum. So I don't disagree with your statement about design objectives drive design solutions.

    I would not disagree that some early applications to business jets were primarially for marketing. But that does not mean that all applications to smaller aircraft are without merit.
     
  12. Richard Woods
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    Richard Woods Woods Designs

    But remember these are winglets fitted to WINGS, not directly to the fuselage, which is effectively where the anti-vortex generators are fitted (ie straight onto the hull, not onto a LAR keel)

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  13. DCockey
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    DCockey Senior Member

    Yes. The discussion diverged for a while.

    I would not be surprised at all to find out that NACA/NASA or someone else has tested, analyzed or otherwise evaluated the effectiveness (or lack of effectiveness) of endplates, etc on the sides of very low aspect ratio bodies.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    Lear jet ventral fins

    Low aspect fins on a Lear jet rear fuselage:
     

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  15. DennisRB
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    DennisRB Senior Member

    I wonder what those ventral fins do since planes do not usually fly with yaw besides landing in a cross wind?
     
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