It's just a simple question about the pressure under and over the plane's wing problem that I'm trying to answer. Well, actually I've already answered it, but one just keeps bugging me. Why don't we consider the difference in altitude of the lower and upper points of the fluid (air) when we use Bernoulli's equation on the fluid on the plane's wings? A possible answer I've thought of is that the fluid is in horizontal motion so there is no work done by the gravity, but I'm not sure if that's a sufficient explanation, it might not even be correct. Maybe a more general question is, given a fluid traversing some object horizontally, and we are considering the upper and lower portion of the fluid in contact with the object, why do we omit the terms (rho)*g*y in Bernoulli's equation?