Thanks for the replies - I don't know who is right, but I must admit my understanding was similar to WF's - although I had not heard the forward thrust vector theory.
An aircraft model with 'plain' wingtips flying through a smoke cloud clearly shows a rotation of the air at the wing tips. I haven't seen the equivalent thing with a winglet equipped model, so I don't know how the vortices are affected.
I'm not necessarily doubting you, FPOBN, but if winglets just improve laminar flow, then would not the manufacturers fit the little vortex generators one sees on some wings and around the fuselage tail cones of some Boeings, instead of huge great heavy fins attached to the end of the wings, with all the structural issues that implies?
Winglets improve overall fuel consumption by around 4%, allowing aircraft a greater range - the majority of that extra range being in the cruise, when a lower lift coefficient is required. But from what you say, there is no advantage to winglets when a low lift coefficient is used?
Also, you say that the vortices are caused by the wing and flap settings, yet in the cruise obviously the flaps are in - surely this does not imply that the vortices disappear with a clean wing? (and I know they don't - having had to offset our track on more than one occasion to get out of the trailing vortices of another 'heavy' ahead of us when crossing the Atlantic).
I'm confused !
Last edited by Uplinker; 7th Jun 2013 at 00:07.