OK, I am calculating the velocity in a trailing vortex 4 ft laterally from the wingtip at a distance of 1 span behind the wing. I figured out that V = G/4*pi*r so in my situation, r = 4 ft, G = 2647.33 ft^2/s (this was found earlier in the problem). I get a V of ~52 ft/s. What is this? the induced downwash velocity? it seems to be high, my V_0 is 337 ft/s. I am just trying to get a check on my reasoning here, because this seems to be too high to me. I should mention that lift is assumed to be constant along the span. But in the case of elliptical circulation distribution, how is there any trailing vortex at the wingtip? since G is 0 there, there is no velocity, and thus no vortex.