"Tony" wrote in message
oups.com...
Most winglets I've seen point upward, but thinking about the physics of
the things, if they had to extend in only one direction wouldn't down
be better, and wouldn't a plate -- extending both up and down, be best
for sub sonic flight?


Ground clearance, for one. As for your latter, that would be like a vortex
generator such as Bonanza wings have.