The common explanation about how an aerofoil works is something like: the air travels faster over the lee of the sail, which creates low presure and lift is then provided by suction. But surfing the web today it seems this is backwards and that the air travels faster bacause of the low pressure at the lee and lift if provided by a reaction to a downwash; also that any old shape at an angle to the wind will create lift; it's just that an aerofoil is more efficient (which makes sense). Similarly, it seems the 'slot effect' is a "myth". Does anybody have any comments about this. I would like to understand the dynamics of my sails better but I'm getting well confused...

Example sites:-

http://world.std.com/~fhapgood/texts/sails.htm
http://www.aa.washington.edu/faculty/eberhardt/lift.htm
http://www.avweb.com/news/airman/183261-1.html
http://www.av8n.com/how/htm/airfoils.html
http://www.idra.unige.it/~irro/profilo1a_e.html

Frank Bethwaite still talks about suction...

Colin