[wbeaty]

His statement is right, but it requires that tip-vortices and downwash-plumes exist. The air behind the wing is carrying momentum, and is left with downward motion. (In typical 2D airfoil diagrams, this cannot happen.)

Also, his statement is only true if we completely eliminate Bernoulli (since any wing which flings air downwards, is also performing net work, and injecting energy into air-parcels. If the net energy of parcels is changed, then Bernoulli concepts cannot be employed.)

"Simple" is the problem. It's simple to describe wings verbally, but the math is not simple at all. Helicopters are the same: they generate a column of downwash, but this involves performing net work, and involves vortex-shedding, so simple Bernoulli concepts are utterly forbidden.

Simplified: wings are an example of propulsion, and fluid propulsion always involves vortex-shedding, which falls under the heading of Turbulence. It's easy to verbally describe simplified elementary turbulence. It's just a vortex which moves around, and involves work performed on the air as a whole. But jeeze the math involved!