The problem with all the simplified examples is that they disregard the concept of l/d; The wing (rotor, propeller...) airfoil generates a large amount of lift at a relatively small expense in induced drag. I think this is the "free energy" MustangFlyer refers to.
If an 800,000# 747 has an l/d of 16 (just guessing - corrections welcome) then its drag is 50,000#. Therefore 50,000# of thrust (total) is needed to maintain stable level flight.
