Banktoturn,

In your first post to this thread, you point out that the cause of induced drag is the distribution of downwash along the span of the wing. I think that there is a definite connection between downwash and spanwise flow. One of the simplest induced drag models, Prandtl's Lifting Line Theory, relates the downwash distribution along the wing to the shedding of spanwise circulation to the wake. In addition to downwash, circulation in the wake also induces a discontinuity in the spanwise velocity component (in the inviscid case). This is analogous to the discontinuity in the magnetic field across a current sheet. There are many ways to approach this phenomenon with increasing complexity/fidelity (Helmholtz Vortex Laws, Kelvin's Circulation Theorem), but I think they will all lead to the conclusion that there is an inescapable connection between circulation/vorticity in the wake and spanwise flow.

I think that a "super-duper fence system which eliminates spanwise flow at the surface", would be equivalent to carrying all of the bound circulation out to the wingtips. Certainly possible (such as with a constant-section wing terminating at the walls of a wind tunnel), but it is a very special case that doesn't shed much light on the problem of induced drag.

I am a true newcomer to this forum, and I found this discussion interesting. Along the way, this thread has touched on just about every misconception about induced drag. I think your contributions have been very sound and have done far more that any others to help clear the waters. Even with respect to the spanwise flow issue, I think you were pushing the discussion in the right direction (while spanwise flow is inevitable on a 3D wing, it doesn't really help us understand induced drag)

To Fainjon, who got the discussion started, I think the answer to your question lies in the many responses... It is hard to say definitively which wingtip has lower drag. The answer depends on Aspect Ratio, Planform, Reynolds Number, Wing Section near the tips, Surface Roughness, and the list goes on and on. One of the things that keeps aerodynamics interesting is its complexity and the lack of simple answers. Good Luck! Fly Navy!