Originally Posted by
cwatters
It's not so easy to adjust the AOA of the winglet. So the winglet might have to be optimised for one particular speed (eg cruise).
Boeing has done some tweaking of the toe-out of the winglets on the 737 NG. Background was to reduce wing bending moment in order not to overload the structure.
They ended with a 2 degree toe- out.
Comparison of parasitic drag showed no appreciable difference to the 0 degree starting point.
However the AoA reducing effect off the winglets decreased slightly, thereby reducing the efficiency improvement by a small amount with flaps extended.
However, this is more then compensated by the reduction in wave drag, profile drag and trim drag (see figure 9 in linked document).
As a conclusion it appears the Winglet AoA is rather tolerant.
http://www.boeing.com/commercial/aer...7/winglets.pdf