A problem though. At about 18:09 on the last line of his presentation cell is the item "mass conservation not a direct reason for acceleration." He says according to Newton there has to be a force associated with the acceleration. And claims no one can tell him what the force would be. That kind of ruined it for me. The restriction the asymmetrical geometry presents to the mass flow rate is a hurdle to the free flow of mass supply, thus changing the density profile. This is synonymous with the formation of a pressure gradient. And that pressure gradient is the force he is claiming can't be explained. So, the "law" of mass conservation is itself directly responsible for the force that results in the acceleration. The total mass in must equal total mass out, and any move toward an imbalance creates the pressure gradient force necessary to accomplish sufficient acceleration. I mean, for gosh sakes, the (mass) continuity equation is one of the fundamental Navier-Stokes rules formally describing the interconnected process. He needs to go back to his previous view cell at 16:09 and rethink the "equal transit time" fallacy to bring that dead end into the proper significance of what it was no doubt aiming for in the "collective subconscious" (or whatever), in terms of his "missing force" from the continuity equation that Navier-Stokes take dead aim at.

@@davetime5234 Mass conservation would indeed be a direct reason for acceleration if you could rigorously establish the cause-and-effect for stream tube pinching. As McLean points out, he can't find a validly argued mechanism for stream tube pinching. I agree with you about the pressure gradient. But I can't, for example, explain the upflow well ahead of the wing leading edge, so this whole problem space is riddled with the danger of oversimplification. I would say that McLean is talking and thinking at a level above what we normally see. My brother taught Aeronautical Engineering at the USAF Academy, they relied on F=mA and mass conservation, and that's indeed a much more rigorous way to treat the subject than that equal transit time nonsense. If a section of the flow were actually constrained by a tube, and that tube constricted, then mass conservation would give rise to the exact force we're looking for. But where there is no tube, the problem is more subtle, it seems to me.

@@Tordvergar "danger of oversimplification" NS equations are able to handle extraordinary complexity (to the point of useful solutions being a challenge). But the driving laws of NS are simple in concept: conservation of mass, energy and momentum, each to be enforced separately but with interconnecting consequence. We don't actually need to worry about a constraining tube if we know the entire extended relative flow has to exhibit continuity (without mass flow interruption taken across the entire area of influence), resulting in logical consequences for the other basic properties, of energy and momentum conservation, when that continuity is challenged. "the upflow well ahead of the wing leading edge" The pressure gradient due to the restrictive path to the mass flow, has to settle in some kind of 3D configuration to keep the mass transit rate logjam from stagnating, which would continue to build static pressure (due to the mass accumulation). This obviously has to form in "cooperation" with a flow rate deficit tendency to form at the exit end: the pressure will continue to drop from mass depletion until the acceleration is high enough to maintain the thruput rate. I think it's reasonable to relate that up-flow ahead of the wing as analogous to backed up traffic due to an incident downstream at an intersection, and with vehicles exiting by alternative routes, preserving some of the vehicle thruput rate. But in the case of the airfoil, the continuity equation says, that for the whole system, the traffic rate cannot be impeded after reaching a steady state situation (pathways naturally self-facilitate via the formed pressure distribution to keep the traffic flowing). So, the backed-up traffic of air mass is facilitated by its self-imposed pressure gradient profile, to continuously fully clear according to the continuity rule (a scenario also consistent with conservation of momentum: the quantity of motion cannot be destroyed). edit: The high transport speed at lower pressure (the Bernoulli conservation of energy notion of higher dynamic pressure at the expense of static pressure) has to result from the pressure gradient effectively filtering out the molecular velocities at the higher end of the thermal velocity distribution, in producing an average higher directed speed of flow (consistent with conservation of energy).

And these are all lacking in one aspect or another: Newton's (secret, apparently) 4th law hodge podge- the Kutta condition, viscosity, and the Coanda effect, and various takes on centripetal/centrifugal circular logic....not