I'm not talking about yaw, I'm talking about roll in a crosswind, where the upwind wing tends to get picked up and sometimes the downwind wing touches the ground. The winglets have a large moment arm on which to counteract the roll (negative* feedback) if they're tipped down, and emphasize the roll (positive* feedback) if they're tipped up.
Just seems that way to me.
/
___________________/ <--------------- crosswind
WING
Wind from the right tends to tip the wing up, a positive feedback situation
___________________
WING \ <------------- crosswind
\
Wind from the right tends to tip the wing down, a negative feedback situation.
All depending on angles and airfoil and so forth, but it looks like the down-tipped winglet (giving negative feedback) would be inherently desirable.
But they don't do it that way, so this must be wrong.
Terry, 230RN
* "Negative" and "positive" are in the mathematical sense, not the emotional sense.