As far as I understand, winglets and raked wingtips help to reduce drag, stopping the airflow from the top and bottom of the wings colliding at the wingtip and causing drag.
I shot the following picture from a Singapore B777-300ER wing whilst in the climb out of Singapore. The condensation on the upper wing seems to stop short of the wingtip about where the raked wing starts.
Does anyone know is this just coincidence, or does this show how the raked wing stops the airflow on the top of the wing from reaching the wingtip itself?
Any info would be greatly appreciated.