“Now how about winglets and drag reduction?”
Sure!
“Wingtip vortices create turbulence, originating at the leading edge of the wingtip and propagating backwards and inboard. This turbulence ‘delaminates’ the airflow over a small triangular section of the outboard wing, which destroys lift in that area. The fence/winglet drives the area where the vortex forms upward away from the wing surface, since the center of the resulting vortex is now at the tip of the winglet.”
This effect is demonstrated in this national geographic video:
http://www.youtube.com/watch?v=CnvIf3vFEYA
Man, you knocked it out of the park with that one!
So let’s review:
Winglets reduce drag.
Winglets reduce noise.
Winglets help with obstacle clearance.
Winglets help with turbulence.
So an aircraft manufacturer would be an idiot not to include winglets in the design or their aircraft, right?