I’m an aerospace engineer who graduated from Embry Riddle, the top rated aviation school in the country. And even there, in our early aerodynamics lessons, the equal transit time fallacy was taught. I remember because I asked - Why does the air on the top HAVE TO reach the trailing edge at the same time as the air on the top? And my professor didn’t know… but to his credit, he came back the next week and taught everyone the fallacy of the equal transit time.

Being a carpenter I remember being taught about Bernoulli's principle and the reason why roof tiles come off a roof during high winds. I have never forgotten about this phenomenon. Love it.

As an instructor, I've been teaching Bernoulli's for straight and level briefs. I tell them it's not a direct translation from venturi tube to an aero foil, but just explain that there is a similar effect of decreasing static pressure above the wing. Didn't realize people were trying to explain the "reason" for it as an equal transit time...

I have a private pilot license, but have not flown aircrafts or even being in contact with the world of aviation for about 7 years. Now UKposts recommends me this video and it reminded me of when I was taking classes, that one of our textbooks warned against these misconceptions regarding aircraft lift. I also remember the book saying that it is still not completely understood, what makes an aircraft fly. I still have the books with me as well as my (expired) private pilot license.

I have been dying to find a good video that actually explains lift for pilots in a correct fashion. As an aerospace engineer it's really hard for me when my student pilots tell me about the Equal Transit Time theory for lift. Thank you for this video!

I still don't get it.

The fact that you can make a flat square fly if you put the centre of gravity in the right place and give it control surfaces and enough thrust and a positive angle of attack tells me that everything else including the aerofoil cross section and other twiddly bits like wingtip vortex generators etc are all about improving efficiency. All you need is enough surface area to direct some air downwards, get the basics right, and it'll fly.

Thank you. This was a good explanation and properly addressed the "equal transit time" assertion, which is STILL incorrectly taught in many flight manuals...

When I used to fly RC models, we took a wing on a 3 channel trainer and put it on backwards. It flew just fine

its was good to see that smoke demonstration clearly showing the air over and under do not get to back of the wing at same time...I've always wondered how people just seemed to conclude it does

There are 12 comments below mine, and they all mirror each other and what I would say. Danke! I'm not sure there's anything else left to say. Science is a process, and you've done it well. As a person studying to be a CFI I think your material would be helpful to future students who care about HOW AND WHY things work. Again, thank you. Ehud Gavron FAA Commercial Helicopter Pilot, Tucson Arizona US. Future CFI because I love to teach. You have helped me today!

You are 100% correct. When I hear people explain this wrong idea I ask them how is it that aerobatic planes can fly and their wings are symmetrical. And how can they fly upside down?

Two other phenomena need mention: Vortex around the wing caused by viscosity, and simple flat plate lift. The wing's lift is actually a sum of those two, and the latter is still active even when the wing is stalled as long as its AOA remains positive.

I'm telling this since decades. Thank you not only to have told, but also to have shown it in practice ❤

The smoke "bursts" show that the airflow is not speeding up over the top of the wing - it is continuing at the same speed it was before encountering the wing. On the other hand, the airflow under the wing slows down.

As a CFII and someone with an undergraduate degree in Aerospace engineering, the reason it is taught the way it is, is because the students seeking their pilots license would neither understand nor are they interested in fully learning how a wing generates lift. I know, I have tried. What an airfoil really does is to rotate the air in a clockwise manner using the diagram of the airfoil used in the video. This rotation accelerates the air above the airfoil, and retards the air below the airfoil. As mentioned, the total pressure around the airfoil is constant and the same. But with the higher airspeed above the wing, it has a higher dynamic pressure than below the wing, and therefore has a lower static pressure. Lift is generated due to the differences between these static pressures, multiplied by the surface area of the wing. Anything that rotates air, will generate lift.

It’s more important for pilots to understand what causes a wing to stop producing lift, so the passengers don’t get upset.

When i was told the faster air stream at the top meet the slower air at the bottom on trailing edge, i was confused, thinking the faster air must be waiting for the slower one at the end....until you come along saying it is just a hypothesis , not a proven theory. I 'm feeling relief. 🤗

Hi Magnar, I am a PPL but more important for this I am an Aeronautical Engineer and also was an Aerodynamics teacher at college. While it is true that Bernoulli's principle applies only to one flow line, it can be also applied to two (or more) flow lines if there is a point where the energy state (speed and pressure) was the same in both flow lines. Sufficiently ahead of the wing, the parcels of air that are going to flow just above the wing and the ones that are going to go just below have the same pressure and speed. So you CAN apply Bernoulli's principle between a point above of the airfoil and another below. Still, transit time is wrong so you can't deduct the speed just by the differences in length. How lift is generated is at the same time more simple, more complicated, and more disappointing (or unsatisfactory explanation) than most people think. Let me know if you want me to expand.

Thank you sir! As an Aerospace Enginnering student, in 1976, and a student pilot in 1980 I was tought this principle, exactly the way you explain it and show it. What has been happening to teaching this principle since those old times?

Having never heard that hypothesis that the top air would catch up to the bottom air, it was really easy for me to be skeptical about it. In my mind, the speeding up has always been about squeezing the flow to make a fluid go faster, and that applies to a single flow as well. I have no reason to believe there is much of any interaction between the streams once they split between above and below the wing. Anyway, great exploration of the topic.

Excellent video, Mrl Magnar! I learned a lot including how many misconceptions I had! Thanks!

The angle of attack has an impact on the lift as well. It correlates to the under the wing lift.

I'm not sure what's being said here. It seems to be a criticism of pilot education, but what is the specific criticism? Bernoulli only holds true when there's non-turbulent flow and when laminar flow starts to break down the forces on a wing (or anything else for that matter) become a far more complicated proposition. It's fine to tell pilots about lift generated by laminar flow around an aerofoil but I'd be surprised if they don't cotton on very quickly, maybe around the time of their first stall, that there's a lot more to the fluid dynamics of lift than just what Bernoulli said.

I’ve had this argument with CFIs and FAA examiners more than once. Myths are hard to overcome.

The wings are pulled up mainly because the wing is tilted up in front. The air hitting under the tilted wing is lifting up the wing. Play with your palm pulled out of a running car. Tilt the palm. The lift of the palm is because the air hiting under. The Bernoully applies too, but the main force is from under the wing. Increasing the tilt will increase the loft force until at near 90 degrees there will be no lifting force.

When I was doing my physics teachers degree I heard my teacher say that the air particles reached the end at the same time. I immediately knew this was wrong and exclamated: "Why, they don't have a date, do they?" I still have much respect for that teacher but that day learned me never trust anybodies word for it.

Thank you. Like so many others I had to "learn" the wrong explanation for lift when I learned to fly. It's good to hear someone debunking it.

Thank you. Beautifully demonstrated!

Thank you for finally stating this. The pressure under the wing is FAR greater than the negative pressure about the wing. If the wing was nothing but a flat surface, it would still work just fine.

Thank you for this video, I like the way you explained this concept, can you please expand upon this and how this applies to exceeding the critical angle of attack which causes a stall, more specifically why does the lift drop so rapidly. Thank you! Waiting for your next video :)

I remember going to a Physics teachers workshop and Bernoulli's Principle came up. So, I asked a few Physics Teachers how it worked. I got the standard answer you heard here; pressure is reduced. When I probed further and asked about the actual physical phenomenon causing this drop in pressure, I got one of two answers, "I don't know," or "because Bernoulli's Principle says so." Teaching Physics is about imparting an understanding about how the physical world operates, not teaching students to memorize laws and equations with no understanding about the underlying phenomena. So, how does Bernoulli's Principle work, in other words, why is the pressure reduced on a surface when air flows over it? Air pressure is the result of molecules of air molecules impacting the surface. Air pressure decreases for two reasons, fewer molecules strike the surface, and the speed with which they strike the surface is reduced. If air is flowing over the surface, fewer molecules will strike the surface because they are being dragged along the surface by the air stream flowing over the surface. Greater speed of the air stream, results in fewer molecules striking the surface resulting in lower pressure. That's it, it is no more complicated than that.

Delighted that Magnar clearly lays out that "theory" and "hypothesis" are not the same thing.

I believe the Bernoulli principal work for super lightweight aircraft that can take off and land at almost zero speed, but when a plane is in the air flying, it acts just like a fish in water. It slices through the medium, in this case air, and that is what keep sit afloat.

Great explanation, I like the intermittent smoke air flow

I used to be a flying instructor in the late 80's. We would explain this to our students and the easy way to confirm it was the propellor wash you could feel behind an aircraft. If Bernoullie was the reason for lift a propellor would produce no wash and a helicopter would not create any downwash. (That would be nice - I flew rescue helicopters for years and the downwash was always an issue during a winch rescue)

Why can't people get this right? 1. Bernoulli is only valid along a stream tube in an inviscid flow. The inviscid flow part is usually pretty valid for high Reynolds number flows outside of the boundary layer and shear layer trailing the wing. The stream tube is much more restrictive except when you assume that the far field has a uniform velocity and static pressure. Under this assumption (which is usually pretty good), all fluid starts with the same total pressure and thus has the same total pressure around the wing. Your statement about how Bernoulli isn't valid because the wing divides the airflow into two parts is wrong. 2. Curvature in the wing is important for keeping the adverse pressure gradient under control and keeping flow attached at high angles of attack, but it still misses the point. Just as the symmetric airfoil befuddles the equal transit time nonsense, the flat plate airfoil (commonly found on small RC foam models) and the supersonic diamond airfoil (with a sharp leading edge) befuddle curvature as the source of lift. IMHO, the best conceptual explanations don't even mention Bernoulli, but instead focus on what the forces are doing to individual masses of fluid. Air is under pressure and will expand when given the chance. As it passes over the top of the wing and the upper surface deflects down, air accelerates into what would otherwise be a void behind the wing. This is accomplished through a vertical pressure gradient resulting in reduced pressure on the upper surface. However, pressure is a scalar and the reduced pressure also corresponds to a horizontal pressure gradient which first acts to speed up and then slow down the flow. At the same time, the bottom of the airfoil has to deflect flow away from it which has the opposite effect and produces a high pressure region which slows flow down and then speeds it up. This is why the transit time over the suction side is faster than the transit time over the pressure side. The exact geometry determines where the peak pressures occur. On most subsonic airfoils, fluid begins to be deflected from the pressure side to the suction side a short distance ahead of the airfoil. Because it already has an "up" component (or down component for negative lift), it has to expand around part of the leading edge resulting in much higher normal accelerations (from the high curvature) and lower pressures which move the location of the minimum pressure forward. In a completely inviscid flow, this perfectly balances out the normal force experienced over most of the wing (which is tilted back towards the trailing edge) and results in no drag. In a real flow, there is some pressure drag, but most drag comes from viscous forces in the boundary layer. I suspect someone will mention circulation. There are enough people who view circulation as fundamental that I won't completely dismiss it, but I personally view it as a convenient mathematical relationship derived from complex analysis (one derivation literally just uses a conformal map of a complex valued function) that is largely divorced from what is actually happening.

I did watched all your videos all your videos about secret of lift. Great explanation ! My favourite videos which I watched is from professor Alexander Lippisch. Can I post a link for UKposts video here ?

Nothing can be accelerated instantly. Because it has inertia. That is why air molecules are literally forced apart at the top faster than it can accelerate toward the wing, becoming less dense (lower pressure), by a wing at speed. The air at the bottom of a wing is forced by the wing so fast it becomes compressed faster than it can accelerate away from the wing. (Higher pressure)

Glad to hear you explain the real science behind lift. In the early70's I was taught in junior high science that lift was not created by increase pressure under the wing but decreased pressure above it. I was always interested in flying but this explanation always left a question in my mind because it didn't make sense that enough negative pressure alone could create enough lift. With my education with internal combustion engines, hydraulics and other machines operating on the laws of physics I began to realize that it is the pressure differential that causes lift. Lower pressure above and higher pressure below do to Bernoulli's law creating differential pressure is the cause of lift.

Civil Engineer here. Lift has always conceptually made sense from observation. But, being familiar with hydraulic behaviors, the explanations by PPL instructors and videos have always left me incredibly dissatisfied. Thank you for correctly explaining this concept. It's unnerving to see the perpetuation of such a large fallacy!

[Another perspective] Here is how I see it, the upper part of the aerofoil has a longer distance as it is curved, the lower part has a shorter distance. Now let's stream an imaginary 100 molecules of air to the tip of the aerofoil, 50 molecules go up and 50 go down. The shorter part (lower) has more molecules per distance than the upper part where the molecules are less dense. Now we know denser particle have more pressure compared to lower, this is why the molecules below try to push upward, Hence, lift. I completely agree with everything else.

This has created great discussion! The wind tunnel test could do with more examples. For example an asymmetric wing and different AOA. More importantly 'zooming out' and visualisation of air much higher and lower from the wing. The example shown seems to result in the upper surface air (close to the wing) having the same speed as the air above. The lower surface in contrast, has markedly slower air (close to the wing) than the air below. In this specific example you could argue that lift is caused by high pressure below the wing and not low pressure above. It does easily disprove the equal transit time hypothesis however.

In that particular demonstration, not only was equal transit time wrong, the air over the wing went even faster than equal transit time would suggest. Meaning that lift due to Bernouli's Principal is even greater than equal transit time would predict.

Bernoulli's principle is often (and mistakenly) used by sailing instructors to try to explain how a sail propels a a boat despite the fact that a sail is a sheet of zero thickness and therefore has exactly equal distance on each of its sides. A sail works because it deflects the airstream. Newton's law: an action results in a reaction. Deflecting the airstream results in an equal and opposite reaction.

As an Instructor Pilot for 20 yrs I couldn't agree more. Very misunderstood concept. Bravo! Lift is Bernoulli living on top of the wing while Newton lives on the bottom. Two separate operations but both must work together or.... Bernulli, on it's own, would never make enough lift for flight.

Many illustrations of air flowing around a wing have an error. Some of them show the air continuing to flow horizontally after it has left the wing. That does not happen! Any time a wing is producing lift, it is also causing a downdraft behind the wing! There is a loss of lift when the airflow separates from the top surface of the wing. Then the air DOES continue horizontally after it has left the wing. Drag also increases sharply. The aluminum overcast turns into aluminum precipitation!

Wow! So the top air stream actually arrives at the trailing edge *sooner!* This phenomenon is *more* than equal transit time: the lower air stream x velocity is slowed more than the upper air stream (which is perhaps sped up). The problem with equal transit time for pilots is they might assume an inverted (fixed wing) aircraft will inherently produce a lift that pushes them toward the ground. No lift would produce a "zero gravity" experience, so negative Gs indicate that negative angle of attack can overcome airfoil effects to produce negative lift.

Tell that Bernoulli bloke I'm fed up seeing his crappy fan heater ads.

As any glider pilot will tell you : 'A barn door will stay up on a good day!'

Wow, this is one of the most beautiful videos I’ve seen! Thank you.

Anyone who has ever put their hand palm-down out of a window in a moving car knows that a wing doesn't "generate" lift. The pressure of the air against the palm pushes up your hand. There is no "low pressure area" pulling your hand up.

As you mentioned, the wing's curvature causes the acceleration of the air over it. I'd like to add that this acceleration is further enhanced by the suction effect, drawing air towards the area of lower pressure. This pressure difference is influenced by the angle of attack, not just the air's acceleration due to the wing's curvature.

Using Bernoulli to explain wing lift is only partially correct but is easy for students to understand. A flat plate will develop lift as its incidence is increased, it's just that it's not very efficient and stalls at low incidence. A sailboat sail develops lift even though it has no thickness (between upper and lower surfaces), only camber. It's very easy to do a calculation of the pressure difference created by a notional aerofoil in accordance with Bernoulli but you will soon find out that the lift generated is nowhere near that actually generated by a real wing. The full description of the generation of lift is best explained by newton's Third Law. Lift is the reaction to the motion of the wing deflecting the air downwards as it passes through it. Lift is equal and opposite to the vertical component of the algebraic sum of the rate of change of momentum of all the air as the aircraft passes through it. In the horizontal direction it is induced drag.

Good explanation. I knew Bernoulli's didn't explain it all. RC pilots have made flat boards fly (not efficient, but they fly)

As someone else commented- the wind tunnel demonstration is misleading because the wing is inclined at a steep angle. Like every other video that I have viewed about 'lift' this video debunks the common Bernoulli explanation yet doesn't give an alternative explanation for lift. A diagram and a few hurried equations with P and PA is all we get.

Haha, back in the 90ies I already told my flight students to just forget about Bernoulli and stick with Newton and almost got kicked out of flight school. Of course there are additional fluid mechanical affects on different shaped bodies, but lift is simply caused by Newtons laws by 98 %. The rest if playing around with details.

The flow of a liquid or gas following along the outside of a curved surface is the COANDA EFFECT!

That makes so much sense in contrary what we see always explained the wrong way. This is a great video, thank you.

A great demo. It has always bugged me how people parrot this lift principle, as if it's very simple, without really thinking about it, and without understanding Bernouilli's principle.

Boyles law I think also applies i.e. Pressure x volume = a constant. Comparing the still air just before the impact of the leading edge of the wing. The volume of air flowing over the top surface of the wing is larger so the pressure reduces as the leading edge strikes the still air. Conversely the volume of air passing under the wing is lower so the pressure increases. As folk rightly observe this effect (high and lower volumes - a volume differential) is caused by the angle of attack of the wing, and holds true for the aerobatic plane flying upside down, as long as that low pressure is on the heavens side you get to see the stars and live to tell the tale…..else take a dive to the ground.

Nice experiment! Thanks!

Most lift is produced by angle of attack: The airfoil shape allows for the same lift at a lower angle of attack, presenting less frontal area or lower coefficient of drag and less turbulence, thus increasing efficiency.

I thought that lift is achieved by the momentum created by the downward air mass acceleration by the wing. This effect can be visualized by the huge air vortex following a plane. The shape of the wing helps to minimize the disturbances and losses and increase the flow stability. I must be wrong somewhere.

Good explanation. Especially at 3:04 where the velocity of air over the wing is shown. Someone should make that venturi apparatus with only one side pinched to model air flow over an airfoil. * Of course now you have the problem of showing the tube of liquid which shows the pressure differential. But this isn't difficult to over come. *The demonstrator as it now is shows two wings mirrored with the liquid filled tubes modeling the pressure above the air foil against the pressure in front of the 'wing'. You actually want three measuring tubes. One on the 'airfoil' (at the venturi), one before the venturi and the third under the 'wing'. These could work if you just have a reservoir of liquid feeding all three tubes, then each tube would show the air pressure before the wing, on top of the wing and under the wing (which might be made to show how angle of attack increases air pressure.)

Very simple and concise explanation, however I would add why the velocity increases over the top surface of the airfoil. This is actually due to curvature of the airfoil, which causes a curvature in the streamline due to the coanda effect. An increase in curvature of a streamline causes an increase in velocity. Hence why the top surface of the airfoil has a larger velocity than the bottom due to it being curved more.

You can also take the opposite of a flat wing and use a round rod shaped wing but add a little wingtip votrix by spinning the rod. All you need is to direct more of the air down than up and it will fly. Note that the wing shown in the UKposts thumbnail for this clip will not generate lift because it does not direct or pust the air down so the air will not push the wing up.

There are so many ways at explaining lift or movement. When a vehicle traveling at a high rate of speed collides at an oblique angle with a stationary vehicle, it moves the stationary vehicle because of impact and not Bernouli"s Principle. Call it what you want, but the wing is colliding with a mass of air.

Dear Magnar, I'm an aerospace engineer who has been unconvinced by the 'conventional' explanation of lift since I was an apprentice, but for different reasons to those explained in this video. I have never been shown proof, or even an explanation why it makes sense to talk about air flowing over the wing when in fact, the wing is passing through static air. In a flying aircraft the air molecules do NOT flow over the wing from leading to trailing edge. They go up and down, ending up lower than where they started. In other words they are accelerated downwards. Surely lift is a reaction force? I'm retired now, you clever physicists are running out of time if you are ever going to explain why I'm wrong without simply saying "it doesn't matter which is moving, air or wing - just accept that." I can't accept unsupported statements.

Spot on and well done. Thanks greatly.

The same thing that causes the drag causes the lift, the wing vortex. It produces upwash at the tip, lowering lift, because it blocks the suction surface, but when it reverses direction it produces downwash which then blocks and slows flow on the pressure surface side, and draws air across the suction surface accelerating it. Winglets just move the tip vortex exposing more surface area to air flow, allowing slightly lower AOA, thus improving fuel efficiency. The vortex strength remains the same, ie proportional to lift. Extending flaps just increases and strengthens the vortex sheet. There's a reason Prandtl equated downwash with lift.

The Bernoulli effect arguments the lift created by an airfoil. A flat wing, or fully symmetrical airfoil, or semi symmetrical airfoil will all generate lift due to dynamic forces striking the bottom of the wing. The higher the angle of incidence and/or angle of attack (to the point of stall), the higher that dynamic force and subsequent lift. At an equivalent angle of attack, a semi symmetrical airfoil will be more efficient as it will generate lift both from dynamic forces and Bernoulli effect. Hold a piece of paper by the edges and blow over the top of it. The paper will lift up because of Bernoulli forces….no dynamic forces present. The wind tunnel test in this video is interesting. Thanks for posting it.

I believe this misconception comes from the effects of a venturi. In the Pilots Handbook of Aeronautical Knowledge, concerning explaining Bernoulli's principle, it says that for a venturi tube "The mass of the air entering the tube must exactly equal the mass exiting the tube. At the constriction, the speed must also increase to allow the same amount of air to pass in the same amount of time as in all other parts of the tube." In a constricted environment like the tube, this would apply, however in the open space an airfoil operates in, this is not the case and thus two particles flowing over and under an airfoil do not meet at the same time.

In 5th grade, I wouldn't let my science teacher off without explaining the Equal Transit Time "theory" -- fallacy in fact -- to my satisfaction. I did not understand where the air molecules on the upper surface of the airfoil got the memo that "You must meet your lower counterparts at the same time at the end of the airfoil. You have a longer distance (being on a curve), so you must run faster."

the air did move faster over the top of the wing and had lower pressure, so the same principle as a sail boat.

Nice explanation.

As a physicist, I have the impression Bernoulli's principle does not even apply to the problem, it is merely a side effect: That is because it relates a pressure gradient along the flow line with the acceleration along said flow line. However, the problem of lift is about a pressure gradient, and hence acceleration, perpendicular to the flow line. This has to do with he curvature of the flow, not it's speed.

What would happen, if the air below the wing gets stopped at the end of the wing? Like with full flaps down, does it negate the lift and at how much percentage?

I always thought it was reaction lift when taking off and the Coanda effect during normal flight. Schools still teach nonsense about flight as far as I am aware.

When an aerofoil at a small angle of attack starts from rest, it dumps a starting vortex in the flow which would be anti-clockwise in the example shown. If it is then stopped, it dumps a stopping vortex of clockwise rotation. While the stopping vortex is associated with the aerofoil, it generates lift by the Magnus effect. These vortices can be visualised. I can explain about non-superfluidity, the Kutta condition and the Kutta-Joukowski circulation theorem if you like, but here I have given the basics which are not difficult to see and to understand. Bernoulli’s Theorem is a secondary explanation. It doesn’t work in liquid helium.

Isn't there a much simpler explanation: there's less space under the wing than above (because of the angle of the wing), but the same amount of air is pushed under as above and so the pressure under the wing is higher than above.

I was taught Bernoulli's Principle in the 50's and 60's, when I was flying model planes. No one could explain to me how little balsa chuck gliders with flat plate surface could create lift or why the control line and R/C models with symmetrical airfoils still flew just fine. I now know that there are many factors, Flat Plate theory and the Coanda Effect among them. Someone calculated that Bernoulli's Principle created only about 3 to 9% of the total lift. I gather that Coanda provides the biggest % of the total.

Hi Magnar. Many have an issue with Bernoulli, and they are mistaken. As long as you are outside the boundary layer Bernoulli's principle applies. In fact, when most engineers use the pressure coefficient it is directly related to Bernoulli, as the ratio of the change in static pressure to the dynamic pressure. The ETT was initially a hypothesis of D'Alembert, and is a result of potential flow, the first real attempt to apply Newton's laws of motion to a fluid. In this situation the curvature of the streamlines at the training edge and leading edge are symmetric, and you get no resultant lift force. As such, saying that the curvature is responsible for the acceleration (while true), neglects the resolution to D'Alembert's paradox which resulted because viscosity was not understood until Navier and Stokes 100 years later. So, the asymmetric acceleration around an aerofoil is due to viscosity. There are two specific effects, the Kutta condition, which moves the rear stagnation point to the TE. and the induction of more flow upwards ahead of the wing. The end result is an asymmetric velocity of the flow (circulation) which at the surface of the wing is given as a pressure force, which will also be asymmetric, with lower pressure above and relatively speaking higher pressure below.

The air at the leading edge is not accelerated directly by the curve, the bottom is also curved and there the air decelerates. It is accelerated by a difference in pressure(force), the pressure gradient is created by the overall wing profile. Even adding a tiny 90 degree flap to the trailing edge will change the gradient and flow near the leading edge.

@ Kevin Barry symmetrical wings do have lift coefficient and it is incidentally more than a flat plate (flat plate has only reactionary lift) Planes with cambered aerofoil also can fly inverted. Symmetrical aerofoil for that. Symmetrical aerofoils are used for high speed flight (transonic and supersonic)

Last century, this was the way FAA taught it. The "FAA correct" answer on the written exam was Bernouli's theory. Even though it was wrong, that was the answer to pass the exam.

I have been an instructor for about 30 years. I have argued your point with aeronautical engineers for years. If each particle at the front had to get back with its respective particle at the end then how would we be able to stir our soup? Each pea that has a neighbor pea would have to get back with its neighbor pea after traveling around the spoon?

At 2.39 notice how the air is being forced downwards. The lift can can also be determined using this. A wing works in the same as a propeller. Stand behind a propeller at full thrust and you will get the idea.

I never got how Bernoulli works and this is a step in the right direction in disproving equal transit time. But it still doesn't explicitly say wy the pressures are different. I believe the answer is shown by the greater distances between the air molecules above the wing; the density and therefore pressure is lower.

Why we get it wrong, that is because we have to answer some of the questions wrongly to pass our theoretic tests. The same goes for some questions about p-effect and stability.

Now I’ve retired, it’s fantastic to know after 35 years and 20,000 hours of flying jets (mostly in command) without accident or incident. Is this an example of what they call a ”firm grasp of the non essentials”?

I believe your wind tunnel example may be slightly misleading with what is causing the change in airspeed around the airfoil. I looks to me that the AoA of the foil is deflecting air down slowing all of the air in the lower portion of the demonstration making it harder to determine if the air over the top of the airfoil is actually speeding up as you mentioned in the video or is actually remaining constant. Would a more cambered airfoil with a flat bottom parallel with the relative be better conditions to demonstrate how the shape effects the airspeed?

3:18 This is the main point. The curvature leads to a change in direction of the air molecules creating a centripetal acceleration speeding up the airflow on the top of the wing. (velocity being a vector having both magnitude and direction)

The problem with the video shown at 2:36 is that that is not what happens with the wing at that angle of attack (other than in a headwind situation). Since it is the wing that is moving through the air. So in this situation the air should be hitting the wing at the same angle that the wing is at (other than in a head wind situation), The air is accelerated at the leading edge of the wing, because the air is being pulled down by gravity, The leading edge pushes the air up causing a squeezing effect of the air, which then accelerates the air relative to the air below the wing.

So is there any lift from a wing if it is at 0° AOA? What is the purpose of asymmetrical camber of the wing ?

Oh thats great! I very often asked myself why the the divided airflow had to reunite in the same position. It is not a zip-fastener, is it ?

The main reason of lift generation is down deflection of flow due to the angle of attack. There are airfoils with more curvature on the bottom than the top (for instance ) and they provide ample lift provided there is enough AA. Besides, pilots generally don't understand aerodynamics past very basic level. They understand and follow rules and procedures.

Instead of equal transit time, think of conservation of mass. You can draw a control volume around the wing and show that mass entering and exiting are equal. From there you can derive L/D from Bernoulli

So the only misconception part is that the top and bottom airflow end up in the same place at the same time, which is immaterial anyway. Is that right?

I see MORE misunderstanding! Bernoulli principle is correct and applicable to airfoils. It is not the only aspect and maybe not the most significant aspect but to say everyone is *wrong* is extremely misleading. Take a sheet of paper and blow across it, just above the paper. it will lift into the airstream. It will also oscillate, like a flag flapping in the wind. Why does it do this? Bernoulli principle; the movement of air reduces the air pressure within the airstream and the static air under the paper will lift it. So what about that curved leading edge? If it was just a flat knife edge, then right at the edge you are going to get a disconnection, a turbulence, and the air will change direction suddenly. To be sure, there will be a small area of low pressure directly behind the leading edge, but as the air comes back down, it will press on the wing and that particular lift is canceled. not only that, but you have a narrow region of lift, followed by a wider area of depression, and this is (partly) why flags flap in the wind. It is unstable; lift is not distributed across the wing. Examine the Coanda Effect. As air gradually changes direction, it produces a low pressure on the curved surface simply because of inertia of the air itself. Might there be a high pressure? Indeed there is; the ram effect of the wing hitting the air compresses the air directly in front of the wing; so what is the vector? To aft (rear). As the air then follows the upper curved surface it accelerates and is compelled to change direction; creating a low pressure along the entire upper surface of the wing since you maintain a curvature but extend the radius as the air is accelerating. This creates a low pressure along most of the upper surface and meanwhile the air under the wing is compressed, somewhat uniformly all along the underside, which creates lift. Some underside wing shapes are concave where the upper surface is convex. The faster the aircraft the less curved are the surfaces. Anyway, an actual wing is a compromise since the Bernoulli effect will dominate at only one angle of attack (AOA) and is very dependent on airspeed. So good old Newtonian reaction is also part of it particularly at lower speeds and higher angle of attack. Why might FAA emphasize the Bernoulli aspect over other aspects? Because the low pressure region of air will condense moisture and freeze up, and you lose the Bernoulli effect because the low pressure region is filled with ice. Likewise, the leading edge ceases to be round (invoking the Coanda Effect) and becomes a knife edge. The combination of these effects means the wing can only fly because of Newtonian reaction; inducing way too much drag and your aircraft is going down. I have had this on my drone (quadcopter) rotor blades in two minutes in cold humid air; the upper surfaces of the blades were coated in ice, also the leading edges, but not the underside of the blades. The Bernoulli effect is undoubtedly the leading contributor to lift, but not the only contributor. An iced-up wing loses Bernoulli effect and that's all it takes to bring your aircraft down.