sail design for trim of camber ,twist and leading edge

Discussion in 'Boat Design' started by lunatic, Jul 27, 2008.

  1. lunatic
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    lunatic Senior Member

    Downhaul, vang, mastbend, leech and tip cables control camber. Tip sheet controls twist off. Mast rotation controls leading edge section. See attached drawings.

    Under higher loading, fabric tension can flatten sail but increasing batten compression will deepend camber and, depending on usual stiffness gradation, move it forward. An all tension system might allow better control of camber's depth and position.

    Large twist off, such an advantage on sail boards, seems wasted on stable multihulls with large headed sails, most seem over twisted, especially in apparent wind of high boat speed where wind gradient has less effect. So forget the oversized headboard, bring back the gaff with a tip control line possilbe on the wide base of a mutihull. This would give control, some sail area fo the roach and little weight penalty against a set of full battens.

    A tackable smooth drooping D section leeding edge seems superior to round, elliptical or rotated mast but woulod results be worth the effort?

    I have built a 1/6 model in aniticipation of using a sail board mast for approximately 75sq ft. rig. Sail flattens smoothly but hard to judge scale of loading stritch and bend. With adjustable tip and leech cables, scissors, sewing machine and barge cement I should be able to scale up for a prototype. but with some good feed back and references to previous work in this vein, I might avoid all the work involved.
     

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  2. tspeer
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    tspeer Senior Member

  3. lunatic
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    lunatic Senior Member

    Very much so!

    So it flys but can it sail? Any info of 1948 boat? The deformation of section decreasing chord and AOA, increasing camber balance out, but I assume some drag increase which trailing edge tension control might reduce. Well faired drooping D section seems worth the effort. A previous reference of yours NTIS "Optimisation and Characteristics of a Sailwing Windmill Rotor" shows five fold increase in power coefficient of drooping D spar over round. Now know why rotor, see attached drawing, with unloaded tip speed ratio of 10 could not be loaded and the importance of forward facing lifting surfaces for thrust.

    Princeton work shows 8% drop in power coefficient with wind increasing from 19.6 ft/sec to 31.3. I assume higher load deformation is beyond balancing out and, unaware of the balancing possibility, thought centrifugally driven tensioning could do the trick but maybe round LE was not my only problem.

    Problem is, does this design warrant further effort? The efforts of amateurs and dillitantes could be much more productive with some good feedback from the more knowledgable.

    Questions: Best geometry of drooping D section. Nuances of camber's depth and position especially for upwind sailing with increasing apparent wind.
    Prototype sail might be best in partial double skin 1/4 chord back from LE and cable sleeve at trailing edge to allow easier recutting of planform, curves are unlikely to be catenary since their function is to control camber and look hard to predict. Twist off control seems simple, but I've learned to be skeptical.

    Possible to separate LE D section experiment. Lasers have sleeved sail over round mast and popular enough for comparative testing. Could use some feedback before I harrass those class boat racers.
     

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  4. rwatson
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    rwatson Senior Member

    Reminds me of the Wharram patented sail design. Double skin around the mast, small gaff.

    There have been quite a few double skin sail systems designed over the years to emulate a true aerofoil, some of then were patented, but I never saw much happen after that.

    Maybe you can make the idea work....
     
  5. lunatic
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    lunatic Senior Member

    Main trim control elements are at the bottom of rigs, twist and camber trim at the top might benefit from more direct control even for single skin sails. Double skin is integralto tackable drooping D section but hard to evaluate if any of these complications are worth the effort. And it seems efforts have been made.
     
  6. eponodyne
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    eponodyne Senior Member

    I think you'd have one hell of a time getting it to round up and stop sailing. to the point where it might actually be dangerous. Give some thought to reefing/depower.
     

  7. lunatic
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    lunatic Senior Member

    Experimental may not lead to pracitical. Frightening performance would be a conformation of the design, can always add restraint. Rig is only 75 sq ft, barely off paper, still looking for feedback.
     
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