I think it is all related: wingtip (finite wing and subsequent "leakage"), vortex, induced drag.
We can consider induced drag as an inefficiency, just as friction drag is, only it occurs when there is lift. In fact, it is similar to form drag (indeed due to viscosity). Form drag is related to "eddies". The wingtip vortex is a big eddie.
If we could paint a vortex for just a couple of seconds (not just the core but the whole vortex) would we see it moving forward?
Kutta and Koukowski play in the Manchester United or in teh CIty?
