Air does not behave like a bunch of bullets hitting a wing. It's a fluid with velocity and pressure everywhere, not simply in the vicinity of aircraft surfaces. A wing is a pump that sets up circulation in the airflow, upward of the leading edge and downward off the trailing edge. The downward momentum of the air flowing off the trailing edge produces an equal and opposite reaction by Newton's third law which is the lift.

This is clearly demonstrated by this incident. Many tons of air deflected downwards by the A380's wings had enough force to flip the unfortunate plane below several times.

> Air does not behave like a bunch of bullets hitting a wing

Yes it does. And those bullet impacts are the very definition of pressure.

The aerodynamics snobbery that you're trying to invoke is that those bullets also hit each other, so you can't make ideal gas assumptions and must model the whole system as a giant system of differential equations (c.f Bernoulli) if you want numbers out.

That doesn't change the fact that air pressure at the surface of the body is what causes the force on the body. That busybodies feel the need to argue against this bleedingly obvious point says some very bad things about the way the aviation community has tried to teach aerodynamics.

Nonsense. See here:

https://www.av8n.com/how/htm/airfoils.html#sec-fluid

Yeah, that site is indeed one of the worst offenders. Try a fluid dynamics textbook. I genuinely don't think you understand what I'm saying. Air isn't magic fairy dust that pushes on airfoils from a distance. Pressure is impact.

If you hit a slice shot in tennis, the ball will travel considerably further because the backspin produces circulation which generates lift. If air was a bunch of bullets, the effect wouldn't happen at all. If you raise a spoiler on a Grob's wing, its lift-producing capabilities drop considerably because the spoiler interferes with the circulation. If air was a bunch of bullets, a spoiler wouldn't do anything.

> Air isn't magic fairy dust that pushes on airfoils from a distance.

No. Like I said, it's a fluid that has pressure and velocity everywhere. At low enough Reynolds numbers, like for model gliders, you can even get away with treating it as a non-compressible fluid with decent results.

> Pressure is impact.

And contact between two objects is really about Pauli exclusion surfaces at the atomic level. So what?

No, the effect is negligible if it wasn't planes wouldn't be able to fly upside down. It's the pitch of the wing that generates most of the lift. That's why helicopters don't alter the rotor RPM they adjust the pitch of the blades to take a larger bite.

The poster wasn't talking about the 'curved upper surface' myth. You can understand the lift to be a consequence of the pressure differential, and that is not inconsistent with planes flying upside down.

And the pitch of the wing causes one side of the wing to be hit harder by air molecules than the other, just like GP said. Maybe you hit reply on the wrong post?

The 'air molecules impinging on the airfoil' theory of lift is not wrong, but does not account for a large fraction of the lift generated either. In a dense enough medium such as air at normal flight altitudes, you have to take into account how those air molecules interact with other air molecules and not only the airfoil. Sum up all those interactions, and you get fluid dynamics rather than a molecule hitting a surface in vacuum.

Fluid dynamics is a useful, but simplistic model. It's not actually true, but can accurately model truth.

Do you have a better model?

Better for what? Fluid dynamics is actually great for a huge number of stations. For pure realism you can use Quantum Mechanics, but good luck simulating that for a protean let alone a 747.

My point was you can still find a lot real world issues for example wing icing. So, that you need to be aware of what you are and are not simulating.

No, the correction is valid. The main component of lift is an upwards reactive force produced by pushing a mass of fluid downwards, in accordance with Newton's third law.

That is the only component of lift --- unless you think that Newtin's laws can be violated on a macro scale. But owing to the way that pressure is defined, the same phenomenon can also he understood in terms of a pressure differential.

this is just an argument in whether you want to explain the phenomenon mechanically or in terms of thermodynamics.

pushing a mass of fluid downward is equivalent to creating a net downward pressure. its the same thing, just expressed in different terms. the unit of pressure is force per square inch, for you americans. by integrating over all the area, you get the force that you are talking about.

The Coanda [or "coma daily" as my iPad helpfully autocorrects] Effect also contributes to lift.

The air "sticks" to the surface of the wing and leaves the trailing edge in a partially downward direction i.e the air is deflected downward by the top of the wing not just the bottom.

For a quick demo of this, hold the bowl of a spoon under a running faucet and see how it pulls the spoon into the stream.