Experimental sail 2 needs analysis

Discussion in 'Boat Design' started by lunatic, Nov 21, 2008.

  1. lunatic
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    lunatic Senior Member

    Searching soft wing sails brings up many designs, from simple, www.wingsails.com, to the complex, www.omerwingsail.com, and close to mine, www.rcsailing.net/forum1/showthread.php?t=3184. Considering the dates of these projects, successful development and practicality seems elusive, but at least I have company.
    Unable to lower sail in first prototype at http://www.boatdesign.net/forums/boat-design/experimental-sail-needs-analysis-24894.html, this rig inconvenient and impractical to scale up. Second prototype, drawings attached, solves this and might improve performance. Once outboard end of gaff is raised by topping lift, halyard and outhaul raise sail, which envelopes gaff allowing leeward surface to have good camber variation. Distortion of windward surface and chafe might trade off with less aerodynamic disturbance and drag of external half wishbone. Sail must be bent on over top of mast, not too practical.
    Leading edge D section is rotated on fixed mast by local sail pressure on flexible trailing edges to match angle of attack to twisted flow, looks tough to get on first shot. If it does produce intended shape, what should it be? What is the best geometry of a drooping D section in this application? Torsional loads on D section are limited by leech cable but excessive twist could wreak havoc, though discontinuity due to inertia and friction more likely.
    First prototype was promising, when second is rigged on, and repeatedly sailed against a Laser, I will know more or less. I would appreciate any critique or suggestions for improvements.
     

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  2. Stumble
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    Stumble Senior Member

    I am a little confused here how is this design different, other than being more complicated than a modern high aspect main?

    Not to say it isn't at all different, but the two look very similar, and to some degree I have to think they have investigated your idea. The same goes for a modern AC90 main that is also a large roached high aspect main.
     

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  3. lunatic
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    lunatic Senior Member

    Design closer to sailboards and original AC schooner, never been on the grand boats in photo but they are pushing limit of battens, even vertical ones, heading toward a rigid wing. Same planform can be done with single gaff and no battens, but will sail better? Daylight, in photo, between mast and luff is the biggest difference in theory, but in practice?
     
  4. lunatic
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    lunatic Senior Member

    Drooping D section

    May not be apllicable to sailing but good graphics. "Variable droop/camber compliant leading edge... The significant challange remains in the structural design and actuation of a relizable adaptive compliant rotor blade", last paragraph of conclusions at www.rollinghillresearch.com/Aero_Research/Files?AIAA-2005-1365_AdaptiveBlade.pdf. Can variable loading and fabric tension controlled by sheet,downhaul and vang, on fixed length and flexibility of D section's trailing edges produce right droop/camber compliance? as sail flattens should droop diminish? Another drooping site www.flxsys.com/Projects/MACW/Leading Edge/ with much lower flow speed. Any drooping D sailors out there?
    Delusion is so easy on paper. Prototypes often dictate their own forms. Built full size mock-up of 2' section, 4' chord 11/2' sleeve and D section as in drawing. 5-20mph flow from grated fan produced 5-10* droop and, using cassette tape on wand as indicater, more upwash and closer windward surface flow than on round section. No numbers here what is a simple way to quantify effect of changing shapes?
    Tear drop D section is an obvious rotating mast, why resist? Drooping D will not conform to twisted flow, canterlevered mast needs bearings and devises,even if assisted by boom and gaff some cam devise must rotate mast another 5-10*, if system is to be self regulating. Stiffer section restricts mast bend and 360* rotation would prevent halyard and other lines being from mast. Continuous D section suffers distortions on a long and fragile shell from twisting and mast bending, once deformed, high friction from hoops binding is evident even in 2' mock-up. If articulated,each section is free to conform to local sail pressure, follow twisted flow and mast bend. Nylon ribbon helps in gradiation and prevents fouling in sail raising. This is much easier on non-tapered mast, but more weight and less mast bend aloft where trim is most needed, though gaff's clew outhaul might earn its weight here.
    Much of this project is determined by external forces: materials at hand,weather,humor and,hopefully, some feed back.
     

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    Last edited: Nov 28, 2008
  5. ancient kayaker
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    ancient kayaker aka Terry Haines

    I have been looking for similar ideas and solutions myself, for use on sailing canoes and kayaks. There the problem is how to dismantle the whole thing and store it on deck to allow one to proceed under paddle power, and is closely related to reefing and taking down sail. These are my thoughts to date.

    I have been looking at hard wings: they can't reef or furl but they have the advantage of efficiency so, for a given amount of driving power less area is needed, and drag when feathered is much lower. This may eliminate the need for reefing.

    Most winds used for sailing have a symmetrical profile. An assymmetrical profile has better lift/drag although the difference is not always great. Land sailers and ice boats use a 2-piece sail which is a flapped sail arranged so the flap can be offset to either side.

    An interesting variant has a freely pivoting wind sail with a stabiliser (like the tailplane of an aircraft) to control its angle of attack, it uses a symmetrical profile and the stabiliser can be set to a neutral position for feathering: see http://www.ivorbittle.co.uk/The wing-sailed yacht for the web.htm

    Currently I am investigating using wingsails in a triplane configuration to obtain more drive without increasing the height of the rig. For me it may simplify the problem of dismantling the rig; it may lead to a reefing concept for you.
     
  6. lunatic
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    lunatic Senior Member

    Mobility and attachment points for sail trim quite a challange on such a small craft, makes me more appreciative of my Sunfish. I would think simplicity, weight and ability to scandalize rig best path. Good luck and stay dry.
     
  7. lunatic
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    lunatic Senior Member

    drooping D section drawing

    Drawing for above text
     

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  8. ancient kayaker
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    ancient kayaker aka Terry Haines

    I am starting to see the advantages. You can lower or reef the fabric part leaving articulated sections with a wing-like profile which can feather.

    Some thoughts: the fabric pocket will have to slide smoothly over the sections during a change of tack to avoid creasing. Controlling trailing edge may require a lot of tension between gaff and boom to set the sail smoothly; a tapered sail may be easier, but then the wing sections would each have to be different, complicating build. Maintenance/repair of all those bearings on the mast while at sea may be a problem.
     
    Last edited: Nov 29, 2008
  9. lunatic
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    lunatic Senior Member

    The rotating D section is only a leading edge form to initiate optimum flow for changing conditions over length of mast, a nuance probably not worth the complication. 2' mock-up shows no problem tacking. I am using high trailing edge cable tension through vang to bend mast and flatten sail. Each section, if supported by ring fixed to mast, is lightly loaded, and well within the life of the prototype.This may never a practical rig ,it is performance before maintenance for now. I hope some of this has been useful but sailing kayake design seems unique.
     
  10. ancient kayaker
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    ancient kayaker aka Terry Haines

    Thanks for explanation. The main challenge with a kayak sailing rig is the low stability of the hull. I deal with that by using Bruce foils instead of a leeboard, usually supplemented by a lifting type sail.

    The other problem is the need to remove most if not all of the rig for paddling. The paddle blades typically reach to somewhere between the knee and ankle of the paddler and are pulled well past the body before exiting the water so anything off the side of the craft in this area has to be hauled out. If left up, the mast can be a damn nuisance when getting in or out. And of course you can't stand up (well, not for long!) or walk around on deck to get to the rig, so everything has to come to hand while you are seated down in the cockpit. I make the Bruce foils retract in and lift up onto the foredeck; the mast and sail used to fold umbrella style but I am currently experimenting with a telescopic mast.

    I am also considering a hard wing sail as previously mentioned. I have been looking very hard at a telescopic wing but I haven't yet solved the engineering problems. Thanks for the interest.
     
  11. lunatic
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    lunatic Senior Member

  12. ancient kayaker
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    ancient kayaker aka Terry Haines

    I have dabbled in the proa world. Overall it wasn't too exciting except for the time when the ama was lifted clear of the water and the canoe really started to move! I had not realized that the ama has to be about as long as the canoe or it will slow things down to its own hull speed.

    The best part thing was, it made the canoe was stable enough to walk around. So much so, that my boat-phobic wife was persuaded to sit in it and get paddled around an island or two. She was very brave but I don't think it was that great an experience for her; the only boat I have been able to get her onto since was a pontoon boat about the size of our living room.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

  14. ancient kayaker
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    ancient kayaker aka Terry Haines

    Lunatic: I revisited your drooping D section concept at http://www.boatdesign.net/forums/at...mental-sail-2-needs-analysis-d.section-1-.pdf

    I just had an idea that I realized is very similar. I will explain it as a variant of your concept if I may.

    First remove the double thickness fabric sail, then join the D section shells together to form a single, full-height shell, essentially leaving a hard wing-sail with a high aspect-ratio. Now cut a slit along the entire length of the trailing edge and install a single thickness fabric sail with its leading edge (luff) in the slit. Reefing can be done using a horizontal roller. Alternatively reefing can be done with a vertical roller inside the D shell, which would suit a loose-footed sail eliminating the hard boom for safety in smaller boats.

    A number of things result from this. Some twist is introduced into the sail rather nicely because the camber of the sail is greater at the foot, and when furled or fully reefed the sail is a smooth-surfaced hard-wing, providing maximum lift/drag ratio.

    This may deliver many of the advantages of your inital concept with an overall simpler system. Most of the requirements for this concept have already been demonstrated on existing sail rigs.
     

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  15. lunatic
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    lunatic Senior Member

    Thanks for the interest. My prototypes are sailed on a Sunfish hull which capsizes at rest with present rig so weighty rigs are out. If next rig http://www.boatdesign.net/forums/boat-design/slow-leaning-curve-sail-design-30447.html shows promise I will attach a full length larger diameter tapered foam cylinder behind the mast with a continuous sleeve so it can swing to leeward creating a drooping D section; but waiting for warmer weather, and especially water,and a comparison boat to sail against.
     
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