Posted for "Rienk Ayers" <rienk.ayers@sreyaaviation.com>:

According to NASA studies, it almost doesn't matter what kind of
winglets you add - they help reduce drag and increase lift (I know this
is a generalized statement). Basically, adding a winglet with a similar
airfoil to the wing, is the same as adding that same area to the
wingtip. What they've discovered is that it doesn't really matter if you
add the wing area straight out or mostly straight up - it has virtually
the same net effect.
My understanding is that companies, especially airlines, are adding the
wingtips so that they don't impinge on ramp area (or in hangar space),
by keeping the real span lower than the effective span.
There is nothing magic about winglets - if you want lower wing loading,
better span efficiencies, and lower drag - add more wing (span).
In this case, aspect ratio rules!
RA