I created This in 2.49, the contrails from the wings and the vapor trails off the engines are simple particle systems assigned to planes. I am getting that smooth curve with a curveguide assigned to well a Curve.
However if i load in 2.53 I cant make the particles from the planes follow the same curves. I have the curves told to be a CurvePath but it seems the particles all bunch up at sea level or just dont follow any path. Just wondering if i am missing something or if this is something that is still being worked on since it is of course beta so id expect bugs do apply.