On Sep 5, 10:42 am, Gezellig wrote:

So is the vertical winglet

1) To increase wing length while
2) Looking cute

?

3) Is sometimes used as a marketing tool, I think, like fins on
cars in the late '50s and '60s.

Winglets improve efficiency by controlling wingtip vortices. A
vortex represents lost energy or drag, whichever way you want to see
it, and if the airflow that forms the vortex can be directed in some
way that minimizes the loss, then winglets are worth it. Some winglets
are claimed to convert some of the reclaimed energy into thrust. Burt
Rutan could speak to that one.
Laying it down would have the effect of making the wingtip very
small, of short chord, and such tips make smaller vortices. Famously
fast and efficient airplanes have often used sharply tapered wings;
think Spitfire or DeHavilland DH88 Comet. Or Google those images.