Working on sailwing blades for winmill rotor. Drawing #1 shows twist, pitch and camber changes due to centrifugally driven mast extension, deflexion and wind load and how trailing edge cabel restrains twist off of tip. Unloaded tip speed ratio of 8 and unnerving view in plane of rotation indicates no tendencies to luff or twist off in high apparent wind. Load tests gave poor results as have searches for sailwing reference material but found Princeton's 1976 report "Optimization and Characteristics of a Sailwing Windmill Rotor" website (
http://www.techo-point.com/en/library/sustainable-development/wind-energy-wind-power/pdg/optimization-andcharateristics-of-a-sailwingsindmill-rotor.pdf.) which gives a circular leading edge one fifth the power coefficient of a drooping D section. My prototype has round golf club shafts, would like to keep the research ahead of construction; any other sources out there? Any enthusiasts for sailwings in any application, or a good argument against pursuing this further?
"Thus, the amount of tension in the Sailwing's trailing-edge cable controls the important trade-off between CLmax and (L/D)max." from page 22 of Princeton Report, yet the design does not actively control cable tension. I think some confounding (even to the report's authors) results are caused by changing cable tension due to deformation of supporting structure which gains little stiffness from the flexible skin. Tension and distortion seem critical design factors for sailwing "optimization".
"...at lower angles-of-attach (up to approximately five degrees), most Sailwings have a lift-curve slope which exceeds the theoretical maximum for rigid wings. This occurs because the section is continually varying camber over the angle-of-attack range. At higher angles-of-attack, the section is unable to deform as much as when it is less loaded. Therefore, the lift-curve becomes increasingly more like that of a rigid wing when the angle-of-attack is increased to higher values." (page 24) , or sooner by increasing cable tension. Why no further development after 30 years, was there a dead end? I would like to know before I bash more metal and fabric.
Drawing posted somewhere (?)
