OP wrote:
On 12 Mar 2006 16:18:44 -0800, "Tony" wrote:


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?



According to something I read somewhere :-) either up or down
winglets (or tiplets if you prefer) accomplilsh the same thing with
the same efficiency... increase the effective wingspan of the
aircraft. Most commercial aircraft (Boeing, Airbus, etc.) turn them
up for ground clearance.

Don't know about tip plates.

Ron

Airbus has plates that go both up and down at the end......
Michelle