Has anyone tried putting a row of tell tales all the way from luff to leach, say every foot or so, and then one on the leach too, both sides of the main, just to see where the flow does separate? They do this with airplane wings in the wind tunnels and in flight too, to see at what angle of attack the wing will stall and how much of the wing is stalling at any given angle of attack. Some slight separation will happen at the takeoff and landing phase of flight, where you want the maximum lift from the wing. You will also be at maximum drag but the engines are at takeoff power and they can overcome the drag.

But at cruise, you want minimum drag and the engines are only at cruise power, which is much less than takeoff power, even though you are flying 300% faster. You could equate that to sailing in very light wind vs. very high wind speeds and trying to shape your main sail for maximum lift vs. minimum drag. In the maximum lift phase you will have separation. In the minimum drag profile, you should have very little separation, so you must vary it according to the conditions, which is what makes sailing (or sail shape) so much harder than flying! <img src="http://www.catsailor.com/forums/images/graemlins/blush.gif" alt="" />