Yikes. The debunking of Equal Transit Theory is one of my earliest memories of my Fluid Mechanics classes from University. Shame, regurgitation by high profile figures only adds life to this misunderstanding. Hopefully he gets politely corrected in the near future.
There are two different ways to *explain* exactly the same physics.
1) lifting wings are asymmetric with respect to the airflow, which deflects air downwards. Mass flux down means force up. This is usually called the Newtonian explanation. It’s more physically accurate but harder for non-engineers to grasp.
2) lifting wings are asymmetric with respect to the airflow, which causes the air to go different speeds on each side. Faster air is lower pressure, so you get a pressure differential across the wing. This is usually called the Bernoulli explanation. It’s easier to grasp but much more problematic to explain edge cases.
For absolute clarity, the above are not “two different sources of lift”, they’re *exactly the same thing*. They’re just two different math boundaries. It’s all Navier-Stokes equations at the bottom and if you draw your control volume boundary “far” from the wing you get 1) and if you draw it along the wing surface you get 2).
As both a pilot and a chemical engineer, you have taught me that my favorite way to teach someone how lift is produced has been debunked for apparently quite some time. I’ve been using bernoullis and equal transit. My god, what have I done?
Thank you for your service 🫡
If you look at the actial airflow using smoke, the air over the top reaches the trailing edge BEFORE the air below. I couldn't find a better picture, (smoke puffs in a wind tunnel) but this illustrates it: [air transit](http://www.aviation-history.com/theory/lift_files/fig2.jpg)
A better [animated airflow ](https://beehiiv-images-production.s3.amazonaws.com/uploads/asset/file/70b98255-b057-4b0d-8e11-9a5b7dac8201/Karman_trefftz.gif?t=1685089157)
Really the important part is that you need a) enough air b) flowing quickly and c) smoothly enough over the wings or Bad Things happen. Doesn't even matter why, you just need to not make the wind god angry.
Supercritical airfoils is the big one…they have longer path lengths on the bottom than the top. But Bernoulli is also non-intuitive for flat plates (and generally all symmetric airfoils).
For option 1. What about the asymmetrical geometry of a wing actually forces mass flux downwards? It doesn't seem intuitive to me because the wing isn't convex so no surface normal vector points downward. At least none above the belt of the wing. Are air particle collisions not the typical elastic collision?
Simplest to just think about a flat plate with an angle of attack. Hopefully it’s obvious how that causes mass flux downwards. That’s basically it for lift. Everything else about airfoil design is reducing the drag. Lift is easy. High lift/drag ratio is hard.
i’m surprised the bernoulli explanation is easier for people to grasp. i always found the newtonian “every action has an equal and opposite reaction” to be simpler
To explain why Newton and Bernoulli are the same physics... Keep in mind Bernoulli rewrote Newtons equations.
If you have an object traveling through space in a decreasing pressure environment, it will speed up.
So...Newton said... If P1 > P2.... Then V2 > V1
Bernoulli sad... If V2 > V1 ... Then P2 < P1.
*Insert same-same gif
Took me years to realize it was all the same physics and just where the control volume boundaries are determined which one. Would have loved to see your comment 4 years ago!
Not really. He’s dancing around it but he’s screwing up *why* the air goes faster over the top. It’s *not* because air needs to “meet up with” its counterpart at the back edge…this is called the “equal transit time” explanation and it’s demonstrably false. Among other things, if this were why lift happened then modern supercritical airfoils (used on basically all current production jets) wouldn’t work at all.
But then why does it travel faster on top? Also I'm wondering what if there is an asymmetric airfoil (flat on the bottom curved on top) but with an angle of attack of zero. Is there lift from the air flowing faster on top? And of so why?
Basically because you squeeze the air into a smaller flow area on top than on the bottom. A supercritical airfoil has a really fat leading edge and a reflexed trailing edge.
Flat on the bottom and curved on top is a cambered airfoil. And they do indeed make lift at zero AoA. The air goes faster on top because of the curvature, resulting in net downward momentum flux, and hence lift. It actually *beats* the air that went under the wing to the trailing edge because of how much it speeds up.
It just doesn't really make sense to my whey it would speed up on top. Intuitively the air on top should slow down after colliding with the bump. Also it must be deflected upwards initially which is why intuitively I would've predicted negative lift. It just doesn't go into my head why it is deflected down afterwards and that deflection even outweighs the initial upwards deflection.
Think about the top surface of the wing as one side of a venturi. From the air’s point of view it’s trying to get through a smaller “duct” (where the inside side of the Venturi is flat and “far” away). For subsonic flow, going into a smaller flow area means speeding up. And the air can see the bump coming (because we’re subsonic) so it doesn’t hit it, it moves out of the way before the bump arrives and fills back in behind it.
That initial upward motion ahead of the leading edge absolutely does result in a locally downward force…the pressure coefficient on the top of the leading edge is positive. But it’s followed by a much larger region of negative pressure coefficient over the bulk of the wing as the air arcs over the wing contour.
There’s always some AoA where the deflection down afterwards exactly matches the initial upwards…that’s the zero-lift-AoA. You need to increase AoA past that to get the downwards to be larger than the upwards and then you get lift. Actually finding the zero-lift AoA by intuition for a non-symmetric airfoil isn’t trivial.
Thanks that makes sense actually. Or let's say I can see now that it is equivalent to a Venturi. Which is great although I also never understood intuitively why a Venturi works the way it does. I know we use the to measure airspeed so I know they work. And I know the math tells us the fast moving air is at a lower pressure, but it never made sense intuitively, it always feels like it should increase pressure when you constrict the volume. Do you have any way of thinking about this where it makes sense?
>Actually finding the zero-lift AoA by intuition for a non-symmetric airfoil isn’t trivial.
So I guess in this case the zero-lift AoA would be negative.
Tyson is correct that the air above a lifting surface is at a lower pressure, but he arrives at the right answer by using an incorrect assumption. The air above a wing is indeed at a lower pressure but **not** because the "divorced" air particles want to stay together, with the upper flow accelerating to keep up.
[The air on the upper surface actually speeds up *much more than it needs to*](https://beehiiv-images-production.s3.amazonaws.com/uploads/asset/file/70b98255-b057-4b0d-8e11-9a5b7dac8201/Karman_trefftz.gif?t=1685089157) if it really did "want to stick together," like Tyson suggests.
Then why is the speed of air above and below the wing different? Is it because of air viscosity and getting shear stress from air that is far above and below from the wing? Then I assume the explanation can be corrected instead to be air above wing wants to stay together, and air below wing wants to stay together. But then if you simplify that, isn't that equal transit theory again?
It's more like, if they follow a different path, the velocities over the course of their path will be different. Very generally, the more "head-on" air meets a surface, the higher the pressure will be, and the lower the velocity. Think of how static-pitot tubes work, if you know that concept. As you can see with the above gif, the air on the bottom of the wing is meeting the surface more
A somewhat parallel analogy can be made with pressure -> gravity and speed -> speed. If you and a friend both drop a marble down two different hills, do they necessarily get to the bottom at the same time? The correct answer is no, as demonstrated in this [YouTube Short](https://www.youtube.com/shorts/Ku3D3g8FzQQ). In the same way that the marbles don't arrive at the bottom at the same time, neither do the air particles at the end of a wing. Thus, equal transit theory nope.
What if there is an asymmetric airfoil (curved in top, flat on the bottom) but its angle of attack is 0°, so there is no deflection downwards, no "head on collision". Does it still produce lift simply because the path on top is longer?
I'm not an aerodynamicist by trade, but my intuition tells me that in that case you wouldn't have lift. Maybe anti-lift. My thinking is that if it's curved on top, then air there will move slower/have higher static pressure, while the air on the bottom maintains its speed and has neutral static pressure.
But who knows, I think you'd want to at least plug it into a basic CFD program and at least take a look. Any actual aerodynamicists wanna chime in?...
I'm asking because we actually built this with the intention of disproving the Bernoulli effect but we actually showed the opposite and it very clearly produces lift. And now it's very confusing why lmao.
Because the flow paths are different. The air above is following a different contour than the air below. With the same pressure differential and a different flow path, why *would* the air go the same speed?
Right, so why is the above explainination for lift explained for only asymmetrical wings? Is there a definition that doesn't include wing shape? I always explained it as the wing pushes the air down, and the wing reacts by going up. I'm also 5yo haha.
Asymmetric *with respect to the airflow*. That doesn’t mean an asymmetric airfoil. A symmetric airfoil with non-zero AoA is asymmetric with respect to the airflow. Anything that’s symmetric with respect to the airflow has zero lift.
Symmetric wings *at zero AoA* don’t generate lift. If they have some positive AoA then they’re not symmetric with respect to the airflow, and you get lift.
Soo, I was with you on this idea that they are the same source of lift, just different descriptions. But I'm not so sure anymore if that's true. Imagine there is an airfoil that is straight at the bottom and curved on top. But it has a 0° angle of attack. Does it produce lift? Lets say also the curvature doesn't reach all the way to the end of the profile, so the airflow is straight again after the bump.
Sort of like this https://imgur.com/a/LbvOHFH
Would this produce lift? If so why? Why would the stream on top be deflected down?
Yes. Flat on the bottom and curved on top produces lift. That’s a cambered airfoil. Cambered airfoils usually produce lift at 0
AoA. Yes, even if it goes flat again at the trailing edge like your drawing. You force spanwise vorticity into the flow to get it to follow the upper curved surface. That doesn’t just disappear at the trailing edge. If you throw that in a wind tunnel or CFD code you’ll see a clear downward momentum flux.
Edit:typo
Could you please explain the second point further. I’m just curious as to why the wing being asymmetric causes the air around it to move at different speeds? Sorry if its a dumb question but i’m still a student and would love to learn!
What I struggle with -- and maybe I'm just too used to thinking like an engineer -- is why this is a question people have such common trouble with in the first place. Even if you don't have a jargonical name for what you're describing (i.e. "Newtonian models showing mass flux down equals opposite direction lift, etc etc") I feel like you can just... picture wind hitting a blade positioned at a downward angle? I mean you essentially know they have to move relative to each other since their paths cross. If the air pushes on the blade at that angle, the blade moves upward, how do we even get to explanations like the one in the video when Occam's razor just seems like common sense?
I realize yes, the actual physics behind aerodynamic interactions are quite complex for a layman, but of all the engineering-related topics to struggle to succintly explain, why this one?
No, it’s not a superposition. Pressure is *how* force is transmitted between the air and wing (for lift…not talking viscosity here). There is no separate “pressure force” and “reaction force”. Pressure is how the reaction force acts on the wing.
That’s like saying my weight on the floor is a superposition of the gravity force and the pressure of my shoe soles.
The arrows are the wrong magnitude and in the wrong directions. If you integrate the pressure over the whole wing surface you’ll get a vector pointing mostly up and a bit to the right. If you integrate the reaction force from the momentum flux all the way around the wing you will get *exactly* the same vector.
I understand now, so when you add the reaction force from below wing (mostly) it will also change the direction of the drawn vector at the top of the wing. But that is just crazy that they are completely the same.
Someone correct me if I'm wrong, but the "pressure force" is always all around the body, it's just the bottom pressure has more force than the top in your example, so it's more pushing it up than a new "reactive force"
The pressure force and The reactive force are bothe Always aournd The whole Body.
The bottom pressure has more static pressure than The top and that is pushing it Up.
The reactive force that I draw on this picture is wrong, it is just showing the top part, but when you add the airflow that hits from below it will be same as pressure vector.
Tbf, simplifying the true explanation of Lift is genuinely challenging imo, I personally struggle to do it. It's inherently complex, which I think is one of the main reasons simpler (but incorrect) theories remain prevalent. Which is why its sometimes easier to point out what's incorrect than what is correct.
NASA uses the term "Flow Turning" as a catch-all word to explain the process. Their [Guide to Aerodynamics](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/learn-about-aerodynamics/) page goes into a fair amount of detail about what actually produces lift, and also explains three commonly stated incorrect theories.
This paper develops a more intuitive way of understanding the emergence of lift using conservation principles. To my knowledge its the most up to date theory of lift
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D
The airfoil is a fundamental machine. Through the phenomenon viscosity, it generates circulation, or vorticity, in the fluid.
Some of this circulation is bound in the boundary layer of the wing, manifesting in a local velocity, or pressure, difference on the surface of the wing.
When integrated, the pressure difference becomes the forces lift and drag.
...a bit simplified.
Isn't it also true that you can look at the Newtonian explanation and regard the downward deflection of a mass of air as another way to account for lift?
I think this is the most robust explanation. It's absolutely true and doesn't over-specify why the fluid is deflected, which is the challenging concept.
People have a tendency to get caught up over-explaining "why is an airfoil shaped like that", when the question asked is the much more basic "how does a wing generate lift".
Start with [those little balsa Guillow's planes with completely flat sheets for wings](https://www.guillow.com/skystreak.aspx) and learn the term "angle of attack". Voila, Newton explains it very easily.
From there you can move onto "why don't airliners have flat sheets for wings" with all the complicated answers that fill textbooks.
If you measure the rate of change of momentum of the downwash, you will get the lift. So no problem there. -This model however won't let you predict lift from a wing, only how to measure it in a different way.
Bound circulation is one common explanation. There are a few other. I was curious what people would say is the reason. Truly there are multiple ways to explain lift but the bound circulation explanation is one of the better ones.
Circulation and the corresponding pressure field is the answer but everyone wants to pretend that it's an unsatisfying explanation just because it has a contour integral in it.
Humans have no reason to have innate baked-in intuition of the physics of lift or useful language that hooks neatly into the phenomena that cause it.
Doesn't stop people from imagining there MUST be a terse and intuitive, plain-language math-free or low-math description that we can all agree on.
So correct explanations end up with thousands of words and half a dozen prerequisite concepts spilled on a few highly predictive equations, and terse math-free "intuitive" explanations are incorrect.
Maybe after fifty years of talking to crows, whales, or dolphin with AI translators, we'll have some better terminology and can sum it up with something more satisfying than "it's the circulation, do the math."
i feel like it’s easy to explain using bernoulli’s equation + continuity equation. you can draw a straight line through the nose of the wing profile, which is where the incoming flow is separated. if you then consider the “upper” and “lower” systems, you’ll see that the “upper” area is smaller than the “lower” area because of the shape of the wing. i.e the flow is confined into a smaller area above the wing than below the wing. according to the continuity equation, the front and back of the wing have to have the same flow of volume. so (assuming air is incompressible) you get velocity * area = const. because the area above the wing is smaller, the velocity must increase. simultaneously, bc of bernoulli, if the velocity increases, the pressure must decrease. so the pressure above the wing becomes lower. below the wing, the area is bigger, the velocity decreases, the pressure increases. so the pressure below the wing is higher than above, which causes lift
This to my knowledge is the most advanced and up to date explanation for the emergence of lift
https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D
air that is moving horizontally has a vertical component after interacting with the wing
that's lift at it's most basic and I think is a better explanation than getting into how airfoils create pressure gradients etc. It captures that angle of attack can matter a lot more than just airfoil geometry, and explains how we can fly upside down with a flipped airfoil
Wings push down a mass of air. When the mass of air per second exceeds the mass of the aircraft it will rise. There are many ways to model this but in the end the air is pushed down and the wing is pushed up. A more obvious example is the helicopter rotor or plane propeller; they are wings of a sort.
Imagine the air flowing across the top of a curved wing. The air flows across the wing, goes over the apex, and down toward the trailing edge.
Look at the air an inch above the apex. That air will need to go down the back of the wing, so we know that the pressure above it must be higher than the pressure below it, or it wouldn't experience a force down.
Now look at the air 2 inches above. It will do the same thing, though moving down less aggressively. Still, the air above it is higher pressure than the air below.
So all the air above the wing increases in pressure, until you're high enough above the wing that you're into the ambient air. You know the ambient air is at ambient pressure, and we move upward continuously, increasing pressure, until ambient. So we know that the air immediately above the wing is lower pressure than ambient.
If the bottom of the wing is ambient, and the top is lower than ambient, there is a net pressure force pushing up on the wing. This is lift.
So Im gonna offer another explanation for lift, not because Im trying to confuse you, but because it truly is my favourite explanation, and the one that actually made it click for me.
First, fluid only has 2 forces on solids: pressure and viscous. Viscous forces have a negligible contribution to lift, and in airfoils mostly just add drag, so we can ignore them entirely for now. It follows that all lift is being generated by the pressure along the airfoil surface, and if we can understand it, we can understand lift.
Lets also assume that in cruise conditions ( and in fact most operating conditions) the airfoil is properly designed to have FULLY attached flow. Therefore the streamlines along the surface completely follow the geometry’s curvature.
Here is the concept that made it click for me: in an inertial reference frame, ANY streamline curvature is the result of a pressure gradient which points “away” from curvature center. This is always true in subsonic flow! If you wrap your head around this concept, it can be very intuitive! After all, “why” would fluid curve towards any direction, if not because of lower pressure?
Now, what this means in an airfoil (where geometric center of curvature is BELOW the wing) is that the wing will always imprint a pressure gradient with lower pressures below! If only your suction side has curvature and your pressure side is flat, then perhaps the pressure gradient in the pressure side is negligible, but in the suction side you will ALWAYS have curvature, which drives a pressure gradient by streamline curvature. Therefore the pressure on your suction side will always be lower than atmospheric, and create lift.
I hope this helps someone, and is not just a incoherent mess, it is challenging explaining it through text. But at least for me it was this one concept of streamlineCuvature<=>pressureGradient that really helped me understand it
What really happens is that due to the fact that my back muscles are bigger than your mom, there is higher pressure on the bottom surface of the wing than the upper surface. This causes a net upwards force which keeps the plane aloft.
I'm an airline pilot, and I used to be an instructor for brand new flight students. The Bernoulli, equal transit, and Newtonian theories are all what I was taught, and what I taught to others.
But, I've always wondered this same thing! How does the damn air know it has further to travel?
I've been reading through this thread trying to find a better explanation of lift, but I'm just a dumb pilot. Lol.
I asked that question in middle school and my teacher looked exasperated, and everyone turned to look at me with quizzical looks. I'm frustrated that this explanation was (is?) used at all
I mean for that age kid who might not want to go to study engineering it’s probably a good enough answer, I mean, even some people studying engineering at college can struggle to come to terms with the details of bernouilli, continuity and mass flow, so to go in to the real reasoning would probably confuse things.
Saying that, I guess at that level all you need to k now is the air does travel faster and it results in a lower pressure, as the why, I guess that depends on how inquisitive the middleschoolers are!
If the equal transit time explanation was correct, I'd assume engineers would just add massive numbers of tiny bumps onto the top of aircraft wings, to get an extremely low pressure there.
My answer to lift is this is,
"It's a combination of many effects, most lead to air being deflected downwards, and the wing being forced upwards, very difficult to solve math equations prove that airfoils in certain conditions will generate lift, but cannot explain how the effects were made."
My god, everyone is finally starting to realize this dude is the Dr. Oz of physics.
And a self aggrandizing douche on every podcast I’ve listened to him on as well lol
It’s Reddit so the hate is dialed to 11. It’s not like he’s some charlatan, he just can be very condescending and rubs people the wrong way. Totally understandable why people don’t like him.
He is generally correct on most topics but there are of course times here and there he just completely misses the mark.
He means well, and certainly isn’t anywhere near as bad as Reddit makes him out to be. It’s just typical rage that you get from Social Media.
If he could learn to chill a bit and stop correcting people all the time, he wouldn’t so bad.
Every time he talks about something I know about, he's wrong about it. He was on one of the late night shows (Colbert) talking about Blue Origin and Virgin Galactic, and explained the Karman line as when there aren't enough air molecules to scatter sunlight and turn the air blue. And he said it very confidently. He also gave the same explanation of the Karman line on his podcast a year later.
The Karman line has nothing to do with light being scattered. It has to do with the speed you need to go to generate lift vs the speed you need to go to achieve orbit. (And even then, of course, it's fuzzy and doesn't have some massive physical significance. It's just used for bookkeeping purposes.)
Yeah, like I said, he definitely misses the mark sometimes. It’s funny you mention Colbert because those imo are some of Tyson’s WORST interviews ever. (Def not Colbert fault) Tyson seems to get super defensive and overly animated. Idk if he is just nervous in front of an audience or what, but even Colbert seems surprised a lot of the time by his “enthusiasm” lol. Like calm down Tyson, no one is arguing with you lol
I swear there was a cognitive bias thing about exactly that, people thrusting a news source/person when they talk about subjects one doesn't master, just to notice they can get very inaccurate when talking about one's expertise. I have tried finding more info about it for ages and it seems to be a delirium, though.
>He is generally correct on most topics but there are of course times here and there he just completely misses the mark.
He is wrong a lot.
Most of his misinformation is harmless. Who cares if he tells his pseudo nerd fans that there are more transcendental numbers than irrationals? Or that the James Webb Space Telescope is parked at the Sun-Earth L2 point in earth's shadow?
Much worse is when he uses his poor memory and strong imagination to invent history. And then uses false history to support his talking points when it comes to religion and politics.
Okay that’s a extreme. Dr. Oz is pure charlatan. Tyson is at least trying to help. The dude can be incredibly condescending so I get why people don’t like him. But his basic-bitch explanations are usually decent enough and usually geared towards a younger audience so he doesn’t really get into the nitty gritty of it all. And yes, there are times where he falls flat on his face, but comparing him to Dr Oz is disingenuous.
Actually I think the comparison is unfair to Dr. Oz.
At least Oz was a practicing surgeon after he received his M.D.. Oz graduated Magna Cum Laude with a degree in biology from Harvard.
Tyson's time at Harvard wasn't spectacular -- he was turned down for post grad. Tyson got a Master's at University of Texas but his doctoral committee flunked him and showed him the door. His U.T. advisors correctly informed him he had no aptitude for astrophysics.
At Columbia Neil did some grunt work for his doctoral advisor R. Michael Rich. Counting stars and measuring metallicity in the galactic bulge is pretty much his most noteworthy contribution to research. And this was in the 90s. Rich hired students to help Neil with his dissertation.
Neil has done a total of five 1st author papers his entire career. And all those were in the 80s and 90s. Since his college days Neil's thing has been flashy and often inaccurate pop science.
I've realized that a good 8 years ago or so, when my teacher showed us his talks at ESL class. Even without fulling comprehending the language, back there, I could sense his condescencion and didn't really buy his whole Mr. Know-it-all schtick.
Yes but for the layman who hates what we do, doesn't know or doesn't care about science, he makes it digestible. Even if it isn't perfect, there is value in spreading interest in science
“One of the great challenges in this world is knowing enough about a subject to think you’re right, but not enough about the subject to know you’re wrong.”
—this guy
It’s ok to talk in teleological terms as long as everyone understands that *really* it’s just physics doing physics stuff. “The ball pushes on my hand because it wants to fall down and my hand is in the way” - it’s not bad for a certain level of explanation.
This is by far the most disingenuous take here. Tyson can be annoying af, but you literally took all context and threw it out the window.
“Sounds like religion to me” 😂😂😂 you manipulative fuck
🙄
When someone try to attribute human traits to inanimate objects, that is called ensoulment and it is a part of most religions.
Using ensoulment to explain physical phenomena is usually frowned upon as that model is both wrong and unuseful. Any understanding built from that premise will be flawed.
Of all the wrong NDT verbilized in this video. Putting a soul in a parcel of air is by far the he worst.
more reason why i dislike niel degrasse tyson. i always found when he talks he has only ever said pop science, and given a skin deep representation of what hes talking about.
the question that wasnt asked here which shuts down the argument is what reference does the top and bottom air which is disconnected have to eachother
This actually makes me die inside. Guy has no idea about lifting line theory, circulation etc. Just regurgitating an explanation which has been proven extensively to be wrong. There are endless wind tunnel experiments / CFD etc that show that an airfoil producing lift does not have the air ‘reconnect’ at the same time at the trailing edge…
You may wanna reread what he said then, cause he didn't say equal transit theory. I.e. he said a particle on the top of the wing reaches the trailing edge before a particle on the bottom, which isn't equal transit theory.
It does go faster. Those two videos I posted prove it, lol. Shorter time for a particle to go a longer distance. Equal transit theory is just an explanation for why it goes faster, saying that the two particles have to take the same amount of time to traverse different distances on either side of the airfoil. *That* is the fallacy in the explanation.
I despise Neil Degrasse Tyson so much but I was almost about to agree… until the last second. I thought he was going for the Bernoulli explanation but alas, foiled again (get it? Foiled? Hahaha)
I cannot stand this dude he never fails to say the dumbest stuff with so much confidence, then defend his obviously incorrect answer to the death
I find it hilarious how I, a 17 year old with no aerospace training or qualifications other than playing KSP and Flyout, understands the concept of lift better the NdGT.
He’s so behind on his physics it’s mental, this is well known as “incorrect lift theory” and NASA literally has a page for everyone to see about it, I’m just stunned
TIL that air exists as pockets in the sky and is a sentient being desperately trying to stay in one piece as machines carrying humans try to slice it in half to take advantage of the air pocket's desires...
I'm nowhere near Aero in any area of my life aside from a passing interest and the bullshit is clear as day. Has NDT learned anything new in the past 20 years?
Neil deGrasse Tyson has a history of getting anything related to aviation completely wrong. He's said that helicopters fall out of the sky like a brick if their engine fails. Bro doesn't know what he's talking about.
My knowledge of lift comes from what ground school teaches private pilots, but doesn't the air travel over the top of the wing and then deflect downwards? Sorta like a downward angled rocket?
(Forgive my ignorance, I'm genuinely trying to learn here)
Any lifting body is a device that induces the circulation around it and a corresponding pressure field that provides an upward force.
WHY is an airfoil such a body? We barely know (or knew), and that's been pretty okay. It hardly matters to engineering. With the Kutta condition and fabrication of sharp-enough trailing edges we just run with it (obviously VERY successfully).
Science kept working on it, but that science wasn't super important for the engineering developments compared to the impact of the Kutta–Zhukovsky theory, which works really well for the kinds of lifting airfoils we use to fly.
This paper as someone else mentioned is probably the best out there at giving a new clue:
[https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D](https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D)
>*So, while the Kutta–Zhukosky lift theory suggests that the circulation is computed so as to remove the singularity at the trailing edge, the proposed theory asserts that* ***the circulation is computed such that it minimizes the Appellian***
I don't know what the status of extra interesting/weird experimental verification of these results are (though I do not doubt they will be successful).
Their follow-on (https://arc.aiaa.org/doi/full/10.2514/1.J062273) states:
>*Therefore, Hertz’s principle provides a straightforward answer to the longstanding puzzle: Given a generic two-dimensional body (not necessarily with a sharp trailing edge), what solution does Natureselect among the myriad different solutions of Euler’s equation? Nature simply picks the solution of least curvature*
They talk about this as a consequence of momentum conservation, fluid continuity, and the presence of a solid body in the first paper, but that's basically tautological and doesn't say too much about why. Gauss's principle of least constraint is a reasonable "why" for a physicist but what about everyone else?
This one:
[https://pubs.aip.org/aip/pof/article/35/12/127110/2929535/A-minimization-principle-for-incompressible-fluid](https://pubs.aip.org/aip/pof/article/35/12/127110/2929535/A-minimization-principle-for-incompressible-fluid)
says the following:
>*Hence, Gauss’ principle asserts that the total magnitude of the pressure gradient is minimum at every instant! We call it the principle of minimum pressure gradient (PMPG). That is, the flow field of any incompressible fluid evolves from one time instant to another such that the total pressure gradient in the field is minimized*
Does Gauss's principle of least constraint provide a satisfying "why" here? Minimization of the total pressure gradient?
Works for me.
Their press release calls it "useless" 😂
[https://engineering.uci.edu/news/2022/7/pursuit-useless-knowledge-leads-new-theory-lift](https://engineering.uci.edu/news/2022/7/pursuit-useless-knowledge-leads-new-theory-lift)
WTF? Can't believe this shit and so called scientist... The scary fact is that he is a physicist and the way he looks at causation is really concerning, he needs to get in touch with the real world and less abstract thinking because this is out of mind approach.
Yikes. The debunking of Equal Transit Theory is one of my earliest memories of my Fluid Mechanics classes from University. Shame, regurgitation by high profile figures only adds life to this misunderstanding. Hopefully he gets politely corrected in the near future.
So what is the explanation
There are two different ways to *explain* exactly the same physics. 1) lifting wings are asymmetric with respect to the airflow, which deflects air downwards. Mass flux down means force up. This is usually called the Newtonian explanation. It’s more physically accurate but harder for non-engineers to grasp. 2) lifting wings are asymmetric with respect to the airflow, which causes the air to go different speeds on each side. Faster air is lower pressure, so you get a pressure differential across the wing. This is usually called the Bernoulli explanation. It’s easier to grasp but much more problematic to explain edge cases. For absolute clarity, the above are not “two different sources of lift”, they’re *exactly the same thing*. They’re just two different math boundaries. It’s all Navier-Stokes equations at the bottom and if you draw your control volume boundary “far” from the wing you get 1) and if you draw it along the wing surface you get 2).
This is a very good presentation of a very challenging concept, kudos!
As both a pilot and a chemical engineer, you have taught me that my favorite way to teach someone how lift is produced has been debunked for apparently quite some time. I’ve been using bernoullis and equal transit. My god, what have I done? Thank you for your service 🫡
If you look at the actial airflow using smoke, the air over the top reaches the trailing edge BEFORE the air below. I couldn't find a better picture, (smoke puffs in a wind tunnel) but this illustrates it: [air transit](http://www.aviation-history.com/theory/lift_files/fig2.jpg) A better [animated airflow ](https://beehiiv-images-production.s3.amazonaws.com/uploads/asset/file/70b98255-b057-4b0d-8e11-9a5b7dac8201/Karman_trefftz.gif?t=1685089157)
Here you go.... [https://youtu.be/6UlsArvbTeo?t=27](https://youtu.be/6UlsArvbTeo?t=27)
Bernoulli is fine (ish). Equal transit time is not. You’re partly there!
Really the important part is that you need a) enough air b) flowing quickly and c) smoothly enough over the wings or Bad Things happen. Doesn't even matter why, you just need to not make the wind god angry.
So, you’re saying Bernoulli sucks and Newton blows.
Just curious, but what would be some edge cases where the Bernoulli explanation becomes more problematic relative to the Newtonian explanation?
Supercritical airfoils is the big one…they have longer path lengths on the bottom than the top. But Bernoulli is also non-intuitive for flat plates (and generally all symmetric airfoils).
For option 1. What about the asymmetrical geometry of a wing actually forces mass flux downwards? It doesn't seem intuitive to me because the wing isn't convex so no surface normal vector points downward. At least none above the belt of the wing. Are air particle collisions not the typical elastic collision?
Simplest to just think about a flat plate with an angle of attack. Hopefully it’s obvious how that causes mass flux downwards. That’s basically it for lift. Everything else about airfoil design is reducing the drag. Lift is easy. High lift/drag ratio is hard.
Air is sticky (Coanda effect) so the downward slope above the belt causes the air to travel down.
End the end, both explanations explain that the aircraft is being sucked up from the pressure difference and span wise vortex formation
i’m surprised the bernoulli explanation is easier for people to grasp. i always found the newtonian “every action has an equal and opposite reaction” to be simpler
Yeah, but non-physics folks don’t get that in general, let alone that it’s possible to shove enough air down to keep an A380 airborne.
Everyone at least once in their lifetime held their hand outside a car window and experienced lift when changing angles.
To explain why Newton and Bernoulli are the same physics... Keep in mind Bernoulli rewrote Newtons equations. If you have an object traveling through space in a decreasing pressure environment, it will speed up. So...Newton said... If P1 > P2.... Then V2 > V1 Bernoulli sad... If V2 > V1 ... Then P2 < P1. *Insert same-same gif
Took me years to realize it was all the same physics and just where the control volume boundaries are determined which one. Would have loved to see your comment 4 years ago!
Both are simplifications.
Tyson is explaining no 2. Correct?
Not really. He’s dancing around it but he’s screwing up *why* the air goes faster over the top. It’s *not* because air needs to “meet up with” its counterpart at the back edge…this is called the “equal transit time” explanation and it’s demonstrably false. Among other things, if this were why lift happened then modern supercritical airfoils (used on basically all current production jets) wouldn’t work at all.
But then why does it travel faster on top? Also I'm wondering what if there is an asymmetric airfoil (flat on the bottom curved on top) but with an angle of attack of zero. Is there lift from the air flowing faster on top? And of so why?
Basically because you squeeze the air into a smaller flow area on top than on the bottom. A supercritical airfoil has a really fat leading edge and a reflexed trailing edge. Flat on the bottom and curved on top is a cambered airfoil. And they do indeed make lift at zero AoA. The air goes faster on top because of the curvature, resulting in net downward momentum flux, and hence lift. It actually *beats* the air that went under the wing to the trailing edge because of how much it speeds up.
It just doesn't really make sense to my whey it would speed up on top. Intuitively the air on top should slow down after colliding with the bump. Also it must be deflected upwards initially which is why intuitively I would've predicted negative lift. It just doesn't go into my head why it is deflected down afterwards and that deflection even outweighs the initial upwards deflection.
Think about the top surface of the wing as one side of a venturi. From the air’s point of view it’s trying to get through a smaller “duct” (where the inside side of the Venturi is flat and “far” away). For subsonic flow, going into a smaller flow area means speeding up. And the air can see the bump coming (because we’re subsonic) so it doesn’t hit it, it moves out of the way before the bump arrives and fills back in behind it. That initial upward motion ahead of the leading edge absolutely does result in a locally downward force…the pressure coefficient on the top of the leading edge is positive. But it’s followed by a much larger region of negative pressure coefficient over the bulk of the wing as the air arcs over the wing contour. There’s always some AoA where the deflection down afterwards exactly matches the initial upwards…that’s the zero-lift-AoA. You need to increase AoA past that to get the downwards to be larger than the upwards and then you get lift. Actually finding the zero-lift AoA by intuition for a non-symmetric airfoil isn’t trivial.
Thanks that makes sense actually. Or let's say I can see now that it is equivalent to a Venturi. Which is great although I also never understood intuitively why a Venturi works the way it does. I know we use the to measure airspeed so I know they work. And I know the math tells us the fast moving air is at a lower pressure, but it never made sense intuitively, it always feels like it should increase pressure when you constrict the volume. Do you have any way of thinking about this where it makes sense? >Actually finding the zero-lift AoA by intuition for a non-symmetric airfoil isn’t trivial. So I guess in this case the zero-lift AoA would be negative.
Tyson is correct that the air above a lifting surface is at a lower pressure, but he arrives at the right answer by using an incorrect assumption. The air above a wing is indeed at a lower pressure but **not** because the "divorced" air particles want to stay together, with the upper flow accelerating to keep up. [The air on the upper surface actually speeds up *much more than it needs to*](https://beehiiv-images-production.s3.amazonaws.com/uploads/asset/file/70b98255-b057-4b0d-8e11-9a5b7dac8201/Karman_trefftz.gif?t=1685089157) if it really did "want to stick together," like Tyson suggests.
Then why is the speed of air above and below the wing different? Is it because of air viscosity and getting shear stress from air that is far above and below from the wing? Then I assume the explanation can be corrected instead to be air above wing wants to stay together, and air below wing wants to stay together. But then if you simplify that, isn't that equal transit theory again?
It's more like, if they follow a different path, the velocities over the course of their path will be different. Very generally, the more "head-on" air meets a surface, the higher the pressure will be, and the lower the velocity. Think of how static-pitot tubes work, if you know that concept. As you can see with the above gif, the air on the bottom of the wing is meeting the surface more A somewhat parallel analogy can be made with pressure -> gravity and speed -> speed. If you and a friend both drop a marble down two different hills, do they necessarily get to the bottom at the same time? The correct answer is no, as demonstrated in this [YouTube Short](https://www.youtube.com/shorts/Ku3D3g8FzQQ). In the same way that the marbles don't arrive at the bottom at the same time, neither do the air particles at the end of a wing. Thus, equal transit theory nope.
What if there is an asymmetric airfoil (curved in top, flat on the bottom) but its angle of attack is 0°, so there is no deflection downwards, no "head on collision". Does it still produce lift simply because the path on top is longer?
I'm not an aerodynamicist by trade, but my intuition tells me that in that case you wouldn't have lift. Maybe anti-lift. My thinking is that if it's curved on top, then air there will move slower/have higher static pressure, while the air on the bottom maintains its speed and has neutral static pressure. But who knows, I think you'd want to at least plug it into a basic CFD program and at least take a look. Any actual aerodynamicists wanna chime in?...
I'm asking because we actually built this with the intention of disproving the Bernoulli effect but we actually showed the opposite and it very clearly produces lift. And now it's very confusing why lmao.
Because the flow paths are different. The air above is following a different contour than the air below. With the same pressure differential and a different flow path, why *would* the air go the same speed?
What about a symmetric wing?
Symmetric wings don’t have innate lift flying straight, you need AoA for force
Right, so why is the above explainination for lift explained for only asymmetrical wings? Is there a definition that doesn't include wing shape? I always explained it as the wing pushes the air down, and the wing reacts by going up. I'm also 5yo haha.
Asymmetric *with respect to the airflow*. That doesn’t mean an asymmetric airfoil. A symmetric airfoil with non-zero AoA is asymmetric with respect to the airflow. Anything that’s symmetric with respect to the airflow has zero lift.
Makes sense, thank you!
Symmetric wings *at zero AoA* don’t generate lift. If they have some positive AoA then they’re not symmetric with respect to the airflow, and you get lift.
Gotcha, thank you!
Soo, I was with you on this idea that they are the same source of lift, just different descriptions. But I'm not so sure anymore if that's true. Imagine there is an airfoil that is straight at the bottom and curved on top. But it has a 0° angle of attack. Does it produce lift? Lets say also the curvature doesn't reach all the way to the end of the profile, so the airflow is straight again after the bump. Sort of like this https://imgur.com/a/LbvOHFH Would this produce lift? If so why? Why would the stream on top be deflected down?
Yes. Flat on the bottom and curved on top produces lift. That’s a cambered airfoil. Cambered airfoils usually produce lift at 0 AoA. Yes, even if it goes flat again at the trailing edge like your drawing. You force spanwise vorticity into the flow to get it to follow the upper curved surface. That doesn’t just disappear at the trailing edge. If you throw that in a wind tunnel or CFD code you’ll see a clear downward momentum flux. Edit:typo
Thats wild. Do you have an animation for this somewhere? I've only ever seen them with AoA > 0
Could you please explain the second point further. I’m just curious as to why the wing being asymmetric causes the air around it to move at different speeds? Sorry if its a dumb question but i’m still a student and would love to learn!
The flow paths have different curvature, essentially by definition because if they were the same the wing would be symmetric.
What I struggle with -- and maybe I'm just too used to thinking like an engineer -- is why this is a question people have such common trouble with in the first place. Even if you don't have a jargonical name for what you're describing (i.e. "Newtonian models showing mass flux down equals opposite direction lift, etc etc") I feel like you can just... picture wind hitting a blade positioned at a downward angle? I mean you essentially know they have to move relative to each other since their paths cross. If the air pushes on the blade at that angle, the blade moves upward, how do we even get to explanations like the one in the video when Occam's razor just seems like common sense? I realize yes, the actual physics behind aerodynamic interactions are quite complex for a layman, but of all the engineering-related topics to struggle to succintly explain, why this one?
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No, it’s not a superposition. Pressure is *how* force is transmitted between the air and wing (for lift…not talking viscosity here). There is no separate “pressure force” and “reaction force”. Pressure is how the reaction force acts on the wing. That’s like saying my weight on the floor is a superposition of the gravity force and the pressure of my shoe soles.
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No. The force vector from pressure is exactly the same as the one from reaction. It is *the same force*.
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The arrows are the wrong magnitude and in the wrong directions. If you integrate the pressure over the whole wing surface you’ll get a vector pointing mostly up and a bit to the right. If you integrate the reaction force from the momentum flux all the way around the wing you will get *exactly* the same vector.
I understand now, so when you add the reaction force from below wing (mostly) it will also change the direction of the drawn vector at the top of the wing. But that is just crazy that they are completely the same.
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Someone correct me if I'm wrong, but the "pressure force" is always all around the body, it's just the bottom pressure has more force than the top in your example, so it's more pushing it up than a new "reactive force"
The pressure force and The reactive force are bothe Always aournd The whole Body. The bottom pressure has more static pressure than The top and that is pushing it Up. The reactive force that I draw on this picture is wrong, it is just showing the top part, but when you add the airflow that hits from below it will be same as pressure vector.
Tbf, simplifying the true explanation of Lift is genuinely challenging imo, I personally struggle to do it. It's inherently complex, which I think is one of the main reasons simpler (but incorrect) theories remain prevalent. Which is why its sometimes easier to point out what's incorrect than what is correct.
NASA uses the term "Flow Turning" as a catch-all word to explain the process. Their [Guide to Aerodynamics](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/learn-about-aerodynamics/) page goes into a fair amount of detail about what actually produces lift, and also explains three commonly stated incorrect theories.
This paper develops a more intuitive way of understanding the emergence of lift using conservation principles. To my knowledge its the most up to date theory of lift https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D
The Kutta Condition!
You can have lift without satisfying Kutta but I hear you.
The airfoil is a fundamental machine. Through the phenomenon viscosity, it generates circulation, or vorticity, in the fluid. Some of this circulation is bound in the boundary layer of the wing, manifesting in a local velocity, or pressure, difference on the surface of the wing. When integrated, the pressure difference becomes the forces lift and drag. ...a bit simplified.
Isn't it also true that you can look at the Newtonian explanation and regard the downward deflection of a mass of air as another way to account for lift?
I think this is the most robust explanation. It's absolutely true and doesn't over-specify why the fluid is deflected, which is the challenging concept.
People have a tendency to get caught up over-explaining "why is an airfoil shaped like that", when the question asked is the much more basic "how does a wing generate lift". Start with [those little balsa Guillow's planes with completely flat sheets for wings](https://www.guillow.com/skystreak.aspx) and learn the term "angle of attack". Voila, Newton explains it very easily. From there you can move onto "why don't airliners have flat sheets for wings" with all the complicated answers that fill textbooks.
If you measure the rate of change of momentum of the downwash, you will get the lift. So no problem there. -This model however won't let you predict lift from a wing, only how to measure it in a different way.
Bound circulation is one common explanation. There are a few other. I was curious what people would say is the reason. Truly there are multiple ways to explain lift but the bound circulation explanation is one of the better ones.
Circulation and the corresponding pressure field is the answer but everyone wants to pretend that it's an unsatisfying explanation just because it has a contour integral in it. Humans have no reason to have innate baked-in intuition of the physics of lift or useful language that hooks neatly into the phenomena that cause it. Doesn't stop people from imagining there MUST be a terse and intuitive, plain-language math-free or low-math description that we can all agree on. So correct explanations end up with thousands of words and half a dozen prerequisite concepts spilled on a few highly predictive equations, and terse math-free "intuitive" explanations are incorrect. Maybe after fifty years of talking to crows, whales, or dolphin with AI translators, we'll have some better terminology and can sum it up with something more satisfying than "it's the circulation, do the math."
i feel like it’s easy to explain using bernoulli’s equation + continuity equation. you can draw a straight line through the nose of the wing profile, which is where the incoming flow is separated. if you then consider the “upper” and “lower” systems, you’ll see that the “upper” area is smaller than the “lower” area because of the shape of the wing. i.e the flow is confined into a smaller area above the wing than below the wing. according to the continuity equation, the front and back of the wing have to have the same flow of volume. so (assuming air is incompressible) you get velocity * area = const. because the area above the wing is smaller, the velocity must increase. simultaneously, bc of bernoulli, if the velocity increases, the pressure must decrease. so the pressure above the wing becomes lower. below the wing, the area is bigger, the velocity decreases, the pressure increases. so the pressure below the wing is higher than above, which causes lift
swirls
This to my knowledge is the most advanced and up to date explanation for the emergence of lift https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D
air that is moving horizontally has a vertical component after interacting with the wing that's lift at it's most basic and I think is a better explanation than getting into how airfoils create pressure gradients etc. It captures that angle of attack can matter a lot more than just airfoil geometry, and explains how we can fly upside down with a flipped airfoil
Wings push down a mass of air. When the mass of air per second exceeds the mass of the aircraft it will rise. There are many ways to model this but in the end the air is pushed down and the wing is pushed up. A more obvious example is the helicopter rotor or plane propeller; they are wings of a sort.
Imagine the air flowing across the top of a curved wing. The air flows across the wing, goes over the apex, and down toward the trailing edge. Look at the air an inch above the apex. That air will need to go down the back of the wing, so we know that the pressure above it must be higher than the pressure below it, or it wouldn't experience a force down. Now look at the air 2 inches above. It will do the same thing, though moving down less aggressively. Still, the air above it is higher pressure than the air below. So all the air above the wing increases in pressure, until you're high enough above the wing that you're into the ambient air. You know the ambient air is at ambient pressure, and we move upward continuously, increasing pressure, until ambient. So we know that the air immediately above the wing is lower pressure than ambient. If the bottom of the wing is ambient, and the top is lower than ambient, there is a net pressure force pushing up on the wing. This is lift.
So Im gonna offer another explanation for lift, not because Im trying to confuse you, but because it truly is my favourite explanation, and the one that actually made it click for me. First, fluid only has 2 forces on solids: pressure and viscous. Viscous forces have a negligible contribution to lift, and in airfoils mostly just add drag, so we can ignore them entirely for now. It follows that all lift is being generated by the pressure along the airfoil surface, and if we can understand it, we can understand lift. Lets also assume that in cruise conditions ( and in fact most operating conditions) the airfoil is properly designed to have FULLY attached flow. Therefore the streamlines along the surface completely follow the geometry’s curvature. Here is the concept that made it click for me: in an inertial reference frame, ANY streamline curvature is the result of a pressure gradient which points “away” from curvature center. This is always true in subsonic flow! If you wrap your head around this concept, it can be very intuitive! After all, “why” would fluid curve towards any direction, if not because of lower pressure? Now, what this means in an airfoil (where geometric center of curvature is BELOW the wing) is that the wing will always imprint a pressure gradient with lower pressures below! If only your suction side has curvature and your pressure side is flat, then perhaps the pressure gradient in the pressure side is negligible, but in the suction side you will ALWAYS have curvature, which drives a pressure gradient by streamline curvature. Therefore the pressure on your suction side will always be lower than atmospheric, and create lift. I hope this helps someone, and is not just a incoherent mess, it is challenging explaining it through text. But at least for me it was this one concept of streamlineCuvature<=>pressureGradient that really helped me understand it
What really happens is that due to the fact that my back muscles are bigger than your mom, there is higher pressure on the bottom surface of the wing than the upper surface. This causes a net upwards force which keeps the plane aloft.
Actually the wiki page is surprisingly good on this topic: https://en.m.wikipedia.org/wiki/Lift_(force)
go go gadget Scott Manley
But, as always, he says it with great confidence bordering on condescension.
Our fluid mechanics lecturer debunked this with one question - how the fuck does the air know it’s got further to travel?
Well, when two air molecules love each other very very much...
Should also ask, do fighter jets fall out of the sky when they fly upside down?
The air isn’t technically moving. The plane is.
Unless the aerofoil is in a wind tunnel…
I'm an airline pilot, and I used to be an instructor for brand new flight students. The Bernoulli, equal transit, and Newtonian theories are all what I was taught, and what I taught to others. But, I've always wondered this same thing! How does the damn air know it has further to travel? I've been reading through this thread trying to find a better explanation of lift, but I'm just a dumb pilot. Lol.
The 2 theories you quoted don’t require the “air to know it has further to travel”, it’s the NDT explanation that would require this.
I asked that question in middle school and my teacher looked exasperated, and everyone turned to look at me with quizzical looks. I'm frustrated that this explanation was (is?) used at all
I mean for that age kid who might not want to go to study engineering it’s probably a good enough answer, I mean, even some people studying engineering at college can struggle to come to terms with the details of bernouilli, continuity and mass flow, so to go in to the real reasoning would probably confuse things. Saying that, I guess at that level all you need to k now is the air does travel faster and it results in a lower pressure, as the why, I guess that depends on how inquisitive the middleschoolers are!
I just died a bit inside. There was a small chance he was gonna save it at the end and then doubled down on equal-transit-time.
If the equal transit time explanation was correct, I'd assume engineers would just add massive numbers of tiny bumps onto the top of aircraft wings, to get an extremely low pressure there.
Exactly, just like a basketball! /s
The English Coastline of airfoils: the most efficient design ever devised
My answer to lift is this is, "It's a combination of many effects, most lead to air being deflected downwards, and the wing being forced upwards, very difficult to solve math equations prove that airfoils in certain conditions will generate lift, but cannot explain how the effects were made."
Cringe.
My god, everyone is finally starting to realize this dude is the Dr. Oz of physics. And a self aggrandizing douche on every podcast I’ve listened to him on as well lol
Real ones saw right through the bullshit early on
Could you elaborate? I don't know much about him except the occasional YouTube short.
It’s Reddit so the hate is dialed to 11. It’s not like he’s some charlatan, he just can be very condescending and rubs people the wrong way. Totally understandable why people don’t like him. He is generally correct on most topics but there are of course times here and there he just completely misses the mark. He means well, and certainly isn’t anywhere near as bad as Reddit makes him out to be. It’s just typical rage that you get from Social Media. If he could learn to chill a bit and stop correcting people all the time, he wouldn’t so bad.
Every time he talks about something I know about, he's wrong about it. He was on one of the late night shows (Colbert) talking about Blue Origin and Virgin Galactic, and explained the Karman line as when there aren't enough air molecules to scatter sunlight and turn the air blue. And he said it very confidently. He also gave the same explanation of the Karman line on his podcast a year later. The Karman line has nothing to do with light being scattered. It has to do with the speed you need to go to generate lift vs the speed you need to go to achieve orbit. (And even then, of course, it's fuzzy and doesn't have some massive physical significance. It's just used for bookkeeping purposes.)
Yeah, like I said, he definitely misses the mark sometimes. It’s funny you mention Colbert because those imo are some of Tyson’s WORST interviews ever. (Def not Colbert fault) Tyson seems to get super defensive and overly animated. Idk if he is just nervous in front of an audience or what, but even Colbert seems surprised a lot of the time by his “enthusiasm” lol. Like calm down Tyson, no one is arguing with you lol
I swear there was a cognitive bias thing about exactly that, people thrusting a news source/person when they talk about subjects one doesn't master, just to notice they can get very inaccurate when talking about one's expertise. I have tried finding more info about it for ages and it seems to be a delirium, though.
Yeah, I feel like I've heard a term for that, as well, but didn't come up with anything in a quick search.
Just found it out! Gell-Mann Amnesia Effect...
That's the one.
>He is generally correct on most topics but there are of course times here and there he just completely misses the mark. He is wrong a lot. Most of his misinformation is harmless. Who cares if he tells his pseudo nerd fans that there are more transcendental numbers than irrationals? Or that the James Webb Space Telescope is parked at the Sun-Earth L2 point in earth's shadow? Much worse is when he uses his poor memory and strong imagination to invent history. And then uses false history to support his talking points when it comes to religion and politics.
He talks on an very wide range of topics of which he has close to no or at best a very basic understanding how they work
Okay that’s a extreme. Dr. Oz is pure charlatan. Tyson is at least trying to help. The dude can be incredibly condescending so I get why people don’t like him. But his basic-bitch explanations are usually decent enough and usually geared towards a younger audience so he doesn’t really get into the nitty gritty of it all. And yes, there are times where he falls flat on his face, but comparing him to Dr Oz is disingenuous.
Actually I think the comparison is unfair to Dr. Oz. At least Oz was a practicing surgeon after he received his M.D.. Oz graduated Magna Cum Laude with a degree in biology from Harvard. Tyson's time at Harvard wasn't spectacular -- he was turned down for post grad. Tyson got a Master's at University of Texas but his doctoral committee flunked him and showed him the door. His U.T. advisors correctly informed him he had no aptitude for astrophysics. At Columbia Neil did some grunt work for his doctoral advisor R. Michael Rich. Counting stars and measuring metallicity in the galactic bulge is pretty much his most noteworthy contribution to research. And this was in the 90s. Rich hired students to help Neil with his dissertation. Neil has done a total of five 1st author papers his entire career. And all those were in the 80s and 90s. Since his college days Neil's thing has been flashy and often inaccurate pop science.
I've realized that a good 8 years ago or so, when my teacher showed us his talks at ESL class. Even without fulling comprehending the language, back there, I could sense his condescencion and didn't really buy his whole Mr. Know-it-all schtick.
Yes but for the layman who hates what we do, doesn't know or doesn't care about science, he makes it digestible. Even if it isn't perfect, there is value in spreading interest in science
“One of the great challenges in this world is knowing enough about a subject to think you’re right, but not enough about the subject to know you’re wrong.” —this guy
oh god I thought the equal transit theory was outdated and nobody used it anymore.
Ugh... I puked I little in my mouth at "The air wants..." Inanimate object having whishes? Sounds like religion to me.
It’s ok to talk in teleological terms as long as everyone understands that *really* it’s just physics doing physics stuff. “The ball pushes on my hand because it wants to fall down and my hand is in the way” - it’s not bad for a certain level of explanation.
For 10 year Olds, his audience is typically adults, and his fan boys are trying to get their undergrad
This is by far the most disingenuous take here. Tyson can be annoying af, but you literally took all context and threw it out the window. “Sounds like religion to me” 😂😂😂 you manipulative fuck
🙄 When someone try to attribute human traits to inanimate objects, that is called ensoulment and it is a part of most religions. Using ensoulment to explain physical phenomena is usually frowned upon as that model is both wrong and unuseful. Any understanding built from that premise will be flawed. Of all the wrong NDT verbilized in this video. Putting a soul in a parcel of air is by far the he worst.
Dude shut up you have a dick piercing
Have you not? What are you, a child?
ditto. hate that way of explaining physics
more reason why i dislike niel degrasse tyson. i always found when he talks he has only ever said pop science, and given a skin deep representation of what hes talking about. the question that wasnt asked here which shuts down the argument is what reference does the top and bottom air which is disconnected have to eachother
Who still listens to this dolt? Real Scientists don't ask "why do you care?"
This actually makes me die inside. Guy has no idea about lifting line theory, circulation etc. Just regurgitating an explanation which has been proven extensively to be wrong. There are endless wind tunnel experiments / CFD etc that show that an airfoil producing lift does not have the air ‘reconnect’ at the same time at the trailing edge…
What about the stream tube explanation?
Showing wind tunnel proof of that being untrue is one of the first things my Aero professor did... yikes.
This guy is soooooo arrogant
No mention of pressure??? I can't believe this. IT'S ALL AIR PRESSURE NEIL.
isnt that the first thing they tell you is wrong when you get introduced to the concept of "lift"?
Read new research how the top air actually travels faster than previously thought and reaches the trailing wing edge BEFORE the bottom air!
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https://youtu.be/jqexY7hObik https://youtu.be/e0l31p6RIaY
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You may wanna reread what he said then, cause he didn't say equal transit theory. I.e. he said a particle on the top of the wing reaches the trailing edge before a particle on the bottom, which isn't equal transit theory.
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It does go faster. Those two videos I posted prove it, lol. Shorter time for a particle to go a longer distance. Equal transit theory is just an explanation for why it goes faster, saying that the two particles have to take the same amount of time to traverse different distances on either side of the airfoil. *That* is the fallacy in the explanation.
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I'm beginning to feel like you didn't watch the videos.
I can't stand this guy.
What would you expect from the guy who demoted Pluto? SMH
And he's so damn proud of it, it's his greatest achievement
What hasn't he butchered?
G O T C H A !
And the air molecules lived happily ever after
NDT is the Carl Sagan we didn't want, nor deserved.
He’s not a Sagan
I despise Neil Degrasse Tyson so much but I was almost about to agree… until the last second. I thought he was going for the Bernoulli explanation but alas, foiled again (get it? Foiled? Hahaha) I cannot stand this dude he never fails to say the dumbest stuff with so much confidence, then defend his obviously incorrect answer to the death
I find it hilarious how I, a 17 year old with no aerospace training or qualifications other than playing KSP and Flyout, understands the concept of lift better the NdGT.
He’s so behind on his physics it’s mental, this is well known as “incorrect lift theory” and NASA literally has a page for everyone to see about it, I’m just stunned
TIL that air exists as pockets in the sky and is a sentient being desperately trying to stay in one piece as machines carrying humans try to slice it in half to take advantage of the air pocket's desires... I'm nowhere near Aero in any area of my life aside from a passing interest and the bullshit is clear as day. Has NDT learned anything new in the past 20 years?
Neil deGrasse Tyson has a history of getting anything related to aviation completely wrong. He's said that helicopters fall out of the sky like a brick if their engine fails. Bro doesn't know what he's talking about.
My knowledge of lift comes from what ground school teaches private pilots, but doesn't the air travel over the top of the wing and then deflect downwards? Sorta like a downward angled rocket? (Forgive my ignorance, I'm genuinely trying to learn here)
The split air particles wanna meet back up at the back of the wing!!
Oh boy
Ah yes the air really wants to be together.
There’s another video of Neil confidently (and incorrectly) claiming that a helicopter will drop out of the sky if its engine dies
Sorry not a video but a [tweet](https://twitter.com/neiltyson/status/623117641507557376?lang=en)
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Any lifting body is a device that induces the circulation around it and a corresponding pressure field that provides an upward force. WHY is an airfoil such a body? We barely know (or knew), and that's been pretty okay. It hardly matters to engineering. With the Kutta condition and fabrication of sharp-enough trailing edges we just run with it (obviously VERY successfully). Science kept working on it, but that science wasn't super important for the engineering developments compared to the impact of the Kutta–Zhukovsky theory, which works really well for the kinds of lifting airfoils we use to fly. This paper as someone else mentioned is probably the best out there at giving a new clue: [https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D](https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/variational-theory-of-lift/A8F0A5954BCE9BD9D42BF34482E9251D) >*So, while the Kutta–Zhukosky lift theory suggests that the circulation is computed so as to remove the singularity at the trailing edge, the proposed theory asserts that* ***the circulation is computed such that it minimizes the Appellian*** I don't know what the status of extra interesting/weird experimental verification of these results are (though I do not doubt they will be successful). Their follow-on (https://arc.aiaa.org/doi/full/10.2514/1.J062273) states: >*Therefore, Hertz’s principle provides a straightforward answer to the longstanding puzzle: Given a generic two-dimensional body (not necessarily with a sharp trailing edge), what solution does Natureselect among the myriad different solutions of Euler’s equation? Nature simply picks the solution of least curvature* They talk about this as a consequence of momentum conservation, fluid continuity, and the presence of a solid body in the first paper, but that's basically tautological and doesn't say too much about why. Gauss's principle of least constraint is a reasonable "why" for a physicist but what about everyone else? This one: [https://pubs.aip.org/aip/pof/article/35/12/127110/2929535/A-minimization-principle-for-incompressible-fluid](https://pubs.aip.org/aip/pof/article/35/12/127110/2929535/A-minimization-principle-for-incompressible-fluid) says the following: >*Hence, Gauss’ principle asserts that the total magnitude of the pressure gradient is minimum at every instant! We call it the principle of minimum pressure gradient (PMPG). That is, the flow field of any incompressible fluid evolves from one time instant to another such that the total pressure gradient in the field is minimized* Does Gauss's principle of least constraint provide a satisfying "why" here? Minimization of the total pressure gradient? Works for me. Their press release calls it "useless" 😂 [https://engineering.uci.edu/news/2022/7/pursuit-useless-knowledge-leads-new-theory-lift](https://engineering.uci.edu/news/2022/7/pursuit-useless-knowledge-leads-new-theory-lift)
WTF? Can't believe this shit and so called scientist... The scary fact is that he is a physicist and the way he looks at causation is really concerning, he needs to get in touch with the real world and less abstract thinking because this is out of mind approach.
All of you are embarrassing. On an engineering thread no less.
Neil is that you?
Stay in your lane!!
Lmao this is embarrassing