It's both lower pressure above the wing (~20% of lift) and the reaction force from pushing air down (give or take the remaining 80% of lift). The main wrong thing is that the air travels faster because it has to travel farther causing the air to accelerate causing the lower pressure that's double plus wrong. It's a weird old misunderstanding that gets repeated over and over because it's a neat connection to attach to the Bernoulli Principal when it's being explained to children.
a classic example of how LLM's mislead people. They don't know right from wrong, they know what they have been trained on. Even with reasoning capabilities
That's one of my biggest hang ups on the LLMs to AGI hype pipeline, no matter how much training and tweaking we throw at them they still don't seem to be able to not fall back to repeating common misconceptions found in their training data. If they're supposed to be PhD level collaborators I would expect better from them.
Not to say they can't be useful tools but they fall into the same basic traps and issues despite our continues attempts to improve them.
How can you create a pocket of 'lower pressure' without deflecting some of the air away? At the end of the day, if the aircraft is moving up, it needs to be throwing something down to counteract gravity.
Exactly. The speed phenomenon (airflow speeding up due to getting sucked into the lower pressure space above the wing) is certainly there, but it's happening because the wing is shaped to deflect air downwards.
The point isn't about how the low pressure is created just that the low pressure is a separate source of lift from the air being pushed down by the bottom of the wing.
No, what still matters (when explaining why the wing is shaped the way it is) is how the low pressure is created. In this case it's being pulled down by the top of the wing.
Angle of attack is a big part but I think the other thing going on is air “sticks” to the surface of the top of the wing and gets directed downward as it comes off the wing. It also creates a gap as the wing curves down leaving behind lower pressure from that.
The "wrong" answers all have a bit of truth to them, but aren't the whole picture. As with many complex mathematical models, it is difficult to convert the math into English and maintain precisely the correct meaning.
> The "wrong" answers all have a bit of truth to them, but aren't the whole picture. As with many complex mathematical models, it is difficult to convert the math into English and maintain precisely the correct meaning.
Exactly. The comments in this subthread are turning imprecision in language into all-or-nothing judgments of correctness. (Meanwhile, 80% of the comments advance their own incorrect/imprecise explanations of the same thing...)
It's really not. The wing is angled so it pushes the air down. Pushing air down means you are pushing the plane up. A wing can literally be a flat sheet at an angle and it would still fly.
It gets complex if you want to fully model things and make it fly as efficiently as possible, but that isn't really in the scope of the question.
Planes go up because they push air down. Simple as that.
It's both that simple and not. Because it's also true that the wing's shape creates a pressure differential and that's what produce lift. And the pressure differential causes the momentum transfer to the wing, the opposing force to the wing's lift creates the momentum transfer, and pressure difference also causes the change in speed and vice-versa. You can create many correct (and many more incorrect) straightforward stories about the path to lift but in reality cause and effect are not so straightforward and I think it's misleading to go "well this story is the one true simple story".
Sure but it creates a pressure differential by pushing the air down (in most wings). Pressure differentials are an unnecessarily detailed description of what is going on that just confuses people.
You wouldn't explain how swimming works with pressure differentials. You'd just say "you push water backwards and that makes you go fowards". If you start talking about pressure differentials... maybe you're technically correct, but it's a confusing and unnecessarily complex explanation that doesn't give the correct intuitive idea of what is happening.
Sure. If you're going for a basic 'how does it work', then 'pushing air down' is a good starting point, but you'll really struggle with follow-up questions like 'then why are they that shape?' unless you're willing to go into a bit more detail.
How can you create a 'pressure differential' without deflecting some of the air away? At the end of the day, if the aircraft is moving up, it needs to be throwing something down to counteract gravity. If there is some pressure differential that you can observe, that's nice, but you can't get away from momentum conservation.
The pressure differential is created by the leading edge creating a narrow flow region, which opens to a wider flow region at the trailing edge. This pulls the air at the leading edge across the top of the wing, making it much faster than the air below the wing. This, in turn, creates a low pressure zone.
Air molecules travel in all directions, not just down, so with a pressure differential that means the air molecules below the wing are applying a significant force upward, no longer balanced by the equal pressure usually on the top of the wing. Thus, lift through boyancy. Your question is now about the same as "why does wood float in water"?
The "throwing something down" here comes from the air molecules below the wing hitting the wing upward, then bouncing down.
All the energy to do this comes from the plane's forward momentum, consumed by drag and transformed by the complex fluid dynamics of the air.
Any non-zero angle of attack also pushes air down, of course. And the shape of the wing with the "stickiness" of the air means some more air can be thrown down by the shape of the wing's top edge.
You can't, but you also can't get away from a pressure differential. Those things are linked! That's my main point, arguing over which of these explanations is more correct is arguing over what exactly the shape of an object's silhouette is: it depends on what direction you're looking at it from.
That page is arguing against a straw man. Nobody is claiming that the full dynamics of a wing are exactly that of a flat sheet at an angle (with full flow separation etc).
The point is that a flat plane with full flow separations is the minimum necessary physics to explain lift. It would obviously make a terrible wing, and it doesn't explain everything about how real wings are optimised. That's not the point.
In any case, I only said the wing pushes the air down. I didn't say it only uses its bottom surface to push the air down.
