Posted for Gary Casey <glcasey@adelphia.net>:

 As I understand it, the winglet thing started when airliner designers  felt
the need to increase wingspan to accommodate higher gross  weights, but there
was a hard limit on span imposed by ramp parking  considerations.  They look
really cool and the rest is history.  If  the wing tip is angled upward and
the angle of incidence very  carefully set with a slight toe-out the normal
inflow at the tip  could be partly stopped, just like an extended tip would
do, and the  resulting "lift" would have a slight forward component inducing a
 thrust that would at least partially compensate for the additional parasitic
drag.  Of course, you could do the same with a strait  wingtip or even a
downward winglet.  As I understand it the benefit  is only close to stall,
where airliners typically cruise.  Also,  swept wings can usually be built
without washout and the winglets  give a little effective washout at the tip.
 I suspect if Charlie had  kept going up or had reduced power so that the
indicated speed would  have been close to best glide or even below, the
winglets might have  been able to show a gain.
 
 Gary Casey