Why is the top flow faster over an Airfoil?

[@morpheas768]

These 2 videos raised even more questions than they answered for me.

[@mateuszp2038]

go read Batchelor's "fluid dynamics" cuz that video is kinda misleading in my opinion

[@Observ45er]

@@mateuszp2038 NOPE! The only real error is that it is not Coanda above a wing; similar, but not Coanda.

[@bouzinzefabana8217]

@@mateuszp2038 many text book i read on fluid dynamics, are juste time wasting bullshiting. just good for memorising furmulers coming from nowhere just for exame and degres, andforsure 9 to 5 corny engineering jobs.

[@riazhassan6570]

For me also

[@SabinCivil]

Dear friends, Here is the 2nd part of airfoil video series. We are working hard to release the 'Transistor video' by the end of this month. Please support us at Patron.com and make our efforts sustainable. www.patreon.com/LearnEngineering

[@serpentine1983]

Please activate ads on your videos. I do not have money to "patreon" you, and I would hate to see this channel die. (And no, I do not use ad blockers). If you have ads activated please contact youtube cause I have never seen an ad in your videos.

[@SabinCivil]

Ads are already activated. I don't why it is not getting displayed to you.

[@serpentine1983]

+Learn Engineering odd. Hope I am one the few. Thank you for your videos by the way :)

[@aakashmaurya8114]

Learn Engineering

[@theultimateprogrammer6932]

So is this why the airflow seperates from the end of the wing first.

[@professionalprocrastinator8103]

I will explain what happens from a mesoscopical point of view. What happens is that fluid particles tend to travel in a roughly straight line if undisturbed. This is the principle of inertia. However, the presence of the lifting surface disturbs them and they will first deviate off course due to the presence of the leading edge (or whatever they first encounter). Now particles are moving in a roughly straight line away from the lifting surface (upwards or downwards depending on where they were coming from upstream). Because of that, the flow becomes rarefied in the direct vicinity of the lifting surface which induces a pressure decrease close to it. Due to the fact that there exists a pressure gradient force pointing towards the lifting surface, fluid particles that are moving away from it are accelerated towards it. This is why flow remains attached for small values of the angle of incidence and this also explains lift: The action of the lifting surface on the fluid particles is to accelerate them in a certain direction (if the surface is generally cambered or inclined downwards, it will force fluid particles to generally accelerate downwards), hence they give away their momentum to the lifting surface in the opposite direction (principle of reciprocity). Bernoulli's "principle" kinda forgets this dynamical point of view and rather explains things from an energetical point of view: There is a transfer between kinetic energy (velocity) and potential energy (pressure and head) along streamlines: In the absence of source or sink terms in the Bernoulli equation (production and dissipation of energy), kinetic energy is won where potential energy is lost, and vice versa. This does not explain why kinetic energy is lost (or gained) and why potential energy is gained (or lost) since you lose directional information by projecting the Navier-Stokes equations onto a streamline, but along with the "third law explanation" that I gave in the first paragraph, the Bernoulli principle will help provide you with the full picture: That's because whenever fluid particles travel very quickly towards an obstacle, they contain lots of bulk kinetic energy which is transformed into pressure when they hit the leading edge and the pressure side of the lifting surface. Because fluid particles have become compressed when moving past the leading edge along the suction side, the pressure difference between patches of flow away from the surface compared to that close to the surface will become more important, which yet again reinforces the pressure gradient force caused by this rarefaction. Curvature does not magically act as is suggested in this vid: We should rather consider that the geometry curves away from the flow as flow particles move along a straight-ish line and bump into each other, getting a net momentum that forces them to go towards the rarefaction.

[@5ty717]

Yep. So you explain how the acceleration occurs but not seeing how the rarifaction occurs. Allow me. Please bear with me… Boffins extol the air is incompressable in the regime but i suspect it is neither incompressible nor non-rarifiable. … I realize it is a many body complexity microscopically but i wonder if (all) lift rarefaction is a DIRECT result of sink/weight. Poo hoo many times but there are graphic observations in the real world. Consider (the reason i give is) the ability of a paraglider to infinitly loop (tumble) over itself while maintaining same decent rate through the airmass (always decending mesoscopically at ~ 1m/s. Ill find a video for u that shows the inflation of the wing remaining “stiffly inflated” but the lift of the wing remaining vertically UP despite the wing spending more than half the time transiting under the (tumbling) pilot’s cog … where aerodynamically one might expect it to pull the pilot DOWN. It doesnt. Is quite remarkable and would go some way to explaining aerobatic inverted flightpaths.

[@justcarcrazy]

Brilliant video! It's good to see the proper conclusions being drawn from observations for a change, rather than finding a convenient but wrong explanation.

[@kudamurapa8578]

I think the problem is to try and use Bernoulli's theory/equations collectively for both the upper and the lower surface. If for a minute you stop and treat the upper and the bottom part separately and apply Bernoulli's equation you will find out that it's not wrong after all. Let's start with the upper surface: the flow approaches the aerofoil and the area in which it flows converges and then diverges. Bernoulli's theorem states that when the area converges the flow speeds up and the pressure drops and when it diverges the flow slows and pressure starts to increase. This is exactly what happens on the top of an aerofoil. Now considering the bottom surface: when flow approaches the aerofoil the area slightly converges prompting a slight pressure decrease and then the area diverges increasing the pressure and slowing down the flow. Now if you consider the collective contribution of the conditions below and above the aerofoil you will get lift. But I don't think Bernoulli alone is suffic

[@error.418]

Then explain why a flat wing still works. Sorry, but Bernoulli's is not the correct way to understand lift. www.grc.nasa.gov/www/k-12/airplane/wrong1.html

[@Eltaurus]

3:33 "such a sudden drop in pressure will not considerably increase the particle speed" The drop in pressure will change the speed independent of how sudden it is, as Bernoulli Equation demonstrates. The correct explanation here is that change of speed at the end of the trajectory doesn't significantly change the total time the path takes.

[@MrTiti]

yeah this is a bonkers video, quite annyoing, thx for your comment

[@andrewtaco]

I've never been more exhausted from thinking about something that should be obvious.

[@wbeaty]

More classic version, still logical: if the flow-pattern is actually the sum of a 'circulation' plus a uniform horizontal flow, then, in the region above the airfoil, the circulation always adds to the average velocity. Below the airfoil, the circulation must subtract from the average velocity. (Works fine for rotating cylinders, works for more complicated 2D airfoils.) Result: any parcels which split at the leading edge, will never meet again, as long as circulation is present. Another result: if the shape and angle of the airfoil gives zero lift, also the circulation becomes exactly zero. In that case, any split parcels at the leading edge will recombine again at the trailing edge. Rule of thumb: if split parcels recombine at the trailing edge, it means that the lifting force is *exactly zero.* The infamous "transit time fallacy" turns out to be a description of a zero-lift airfoil.

[@mixtermuxter8602]

that one went clean over my head...

[@IdiotWithoutBorders]

There's probably a lower pressure above it then

[@mixtermuxter8602]

that sucks...

[@Lexoka]

Did you see the previous videos on the same topic? If not, this one might indeed be difficult.

[@tonayee]

hahahaha good one(s)

[@rameswarboro5195]

Mixter Muxter yes over your head! XD

[@alwayschooseford]

Summary: "An air foil works this way because of the way it is."

[@safenders]

absolutely

[@SammSheperd]

Well no, this will work with a flat plate too. It is primarily due to the angle of attack.

[@safenders]

+Samm Sheperd (SNRS) lmao really??

[@Lexoka]

Yes :) It won't be quite as efficient, but it will work.

[@Observ45er]

+Samm Sheperd (alwayschooseford is being silly) You are correct Samm. Correct. One explanation works for *_ALL WING CONFIGURATIONS_* This is because it is the flow of air around the wing (that is caused by a wing) that is what is important, not simply the airfoil shape. . ..At an Angle of attack above just a few degrees on a flat plate wing, wind tunnel tests show that there is a turbulent layer that effectively duplicates a cambered wing for the air a little further from the surface. The air does not flow smoothly along the surface as many people think or show in their videos. It flows just like the flow of a cambered wing. It creates a lower pressure above and higher pressure below due to the relative movement of air and wing. There is more drag, however. -- Cheers, ScienceAdvisorSteve

[@kansaandre]

Pressure of air is the amount of air molecules at a given place multiplied with the vibration speed of the molecules (higher temperature the more they vibrate and hitting a surface with a speed which gives out a force which on a given area is equal to pressure) The temperature in this scenario can be seen as constant, and the only thing we need to focus on is the amount of air molecules at a given space which will in turn give us the pressure at that area. When the air curves for example in the beginning it is pushed up and some air molecules will detach from the wing surface as the speed gives them enough momentum to leave the wing surface as it hits the sloped surface of the wing. This means it will have a smaller amount of air molecules compared to the atmosphere. Since pressure in our scenario is directly given by the amount of air molecules at a given place it must mean that we will have a lower pressure at the top of the suface of the wing. Less air molecules at the wing surface equals less drag on the air molecules due to the skin effect. This makes this air able to travel much faster than the air beneath the wing. Same thing at the bottom end of the wing. Air molecules follow the path of the wing and is smashed towards the wing at the back because of the momentun they have. This will decrease the speed of the air molecules (skin effect). Air arriving at the surface of the wing will be arriving faster than the air leaving the surface (goes further along the surface of the wing). This makes a traffic jam of air molecules where more molecules is arriving than leaving. Which in turn gives larger amount of air molecules than the atmosphere. As said, the amount of air molecules directly gives the pressure in our scenario and we will have a higher pressure here compared to the atmospheric pressure. Hope this gave any sense! :)

[@kansaandre]

Another thing to note is that this is not the only way a wing creates lift. The Wrights brothers which made the first functional plane had flat wings. It is the direction the air leaves the wing which gives the wing the most lift. So by having a flap at the back which is moveable we can guide the airstream either up and away from the wing as it leaves the wing or force them down. This is why stalling occurs because we loose the air stream on top of the wings and it leaves the wing in a uncontrolled matter. By loosing the air stream we are not able to control it the way we want and cant use it to create lift. See the video «How wings ACTUALLY Creates Lift!», it explains it really well!

[@LeoDias-gu1by]

Best explanation I've seen so far

[@alberthenrique3175]

Hey man, I'd like to say thank you. I'll use this with my students in class 😊

[@JayLikesLasers]

This is by far the best concise video on 2D airfoil flow. There are so many misconceptions out there, it's refreshing to see a video which communicates the main ideas so clearly. Whilst it doesn't directly explain lift and drag, those two forces can be inferred from integrating the pressure field around the airfoil surface. The only part of the picture it doesn't help to show is that of momentum conservation. A net lift necessarily results from a downwards component of momentum imparted to the freestream.

[@ArdalanHamann]

It should be mention that all these explanations are valid in sub-sonic medium

[@carmelpule8493]

One would have thought that this is an obvious conclusion. We must consider that there is an intention behind any shaped structure. Let us assume the conventional shape of an airfoil section has a slight angle of attack. As the foil moves forward, the lower surface is pushing the air down but also forward and the air below the wind has a downward component in addition to a horizontal component. (In a wind tunnel the lower surface slows down the horizontal airflow because of the angle of attack while reflecting the flow downwards). As the air moves above the wing, it enters a divergent shape, the divergent shape causes a downward velocity to be created in addition to the horizontal velocity. There is a pressure zone above the leading edge to accentuate the down acceleration at a later stage. Because of the tapered nature of the upper surface of the wing, towards the trailing edge, the longer vertical distance permits the air particles to gain a higher downward vertical velocity and so this results in the flow above the wing is faster than the flow under the wing. Note that when dealing with lift and drag and control surceases and propeller thrust, one should always deal with the acceleration of the mass particles at any point around the unit in question. It is acceleration that create force and not velocity or location.

[@williamg3215]

One of the best videos I've seen about lift.

[@carlosmaldonado8600]

The answer is because of the shape of the airfoil, the velocities and pressures will be according to match the conservation of energy, conservation of mass and conservation of momentum.. Velocity field is according to pressure field and viceversa. What is shown is quite intuitive but the explanation and the real world is quite more complicated. All is coupled

[@yugsth2236]

0:29 In the curved flow, why is pressure higher outside ?

[@is-ig4zh]

Because to keep the streamline ''attached'' to the airfoil. If P at outside = P inside, the streamline will go in a straight line (not follow the shape of the airfoil). Then, it must be a difference in pressure to bent the streamline to follow the shape of an airfoil.

[@dogemabulletjunior2775]

coanda effect

[@kansaandre]

Pressure of air is the amount of air molecules at a given place multiplied with the vibration speed of the molecules (higher temp the more they vibrate and hitting a surface with a speed which gives out a force which on a given area is equal to pressure) The temperature in this scenario can be seen as constant, and the only thing we need to focus on is the amount of air molecules at a given space which will in turn give us the pressure at that area. When the air curves for example in the beginning it is pushed up and some air molecules will detach from the wing surface as the speed gives them enough momentum to leave the wing surface as it hits the sloped surface of the wing. This means it will have a smaller amount of air molecules compared to the atmosphere. Since pressure in our scenario is directly given by the amount of air molecules at a given place it must mean that we will have a lower pressure at the top of the suface of the wing. Less air molecules at the wing surface equals less drag on the air molecules due to the skin effect. This makes this air able to travel much faster than the air beneath the wing. Same thing at the bottom end of the wing. Air molecules follow the path of the wing and is smashed towards the wing at the back because of the momentun they have. This will decrease the speed of the air molecules (skin effect). Air arriving at the surface of the wing will be arriving faster than the air leaving the surface (goes further along the surface of the wing). This makes a traffic jam of air molecules where more molecules is arriving than leaving. Which in turn gives larger amount of air molecules than the atmosphere. As said, the amount of air molecules directly gives the pressure in our scenario and we will have a higher pressure here compared to the atmospheric pressure. Hope this gave any sense! :)

[@gianlucacastro5281]

@@kansaandre Awesome answer, thanks

[@pitachaja124pl]

​@@kansaandre Are you sure that it depends mainly on skin effect? Isn't the pressure distribution along the wing, like shown in this film, depended on shape and curvatures rather than friction and skin effect?

[@comet1062]

As with so much of Aero. It’s slightly more subtle. The pressure gradients are sadly much harder to explain away like you would in a river or other fluid flow. There the total pressure (the integral across the river) is the same before during and after a bend assuming no energy loss to friction. With the airfoil the integral from the ground to the airfoil is higher than before whilst the integral from the top of the airfoil to space is lower than before. This I would argue is due to the velocity increasing as a result of the Chanda effect but that is a active area of debate (what causes what)

[@311hwr]

'wings don't suck, how wings work and planes really fly', is the best and most accurate explanation of how lift is produced.

[@error.418]

You can use links on here.

[@jptrainor]

There is a good bit of tautological reasoning happening in this video. What is important is that the pressure difference exists in this situation, and that a theoretical model of the flow based on first principles agrees with the observation. Attempting, after that, to come up with a simple explanation of "why" risks getting tangled up in circular reasoning. If you want to understand the theoretical models you start with the basic principles of force, mass, and acceleration of the fluid, and the principles of conversation of mass, momentum, and energy. None of which are mentioned in this video.

[@error.418]

Because it was discussed in the previous video.

[@FB0102]

So you’re saying there is no simple way of explaining why the flow is faster on top, other than saying thats the way it is given fluid dynamic principles.

[@FB0102]

Jim Trainor My simple explanation would be that the airfoil acts kind of like a nozzle, accelerating air by forcing it to move through a smaller area. Imagine putting another airfoil on top of this one, but flipped upside down. The two airfoils would act as a nozzle to the air flowing between them, causing the flow to accelerate, then decelerate back to normal speed as it exits the nozzle. Having just the lower airfoil does the same effect, only less pronounced; it still accelerates the flow above it, lowering its pressure, by forcing it to move through a smaller area. The bottom surface is less curved so the acceleration and pressure reduction is less. Thus upper pressure is lower and there is a net up force.

[@nickslens]

This actually really made it click in my head! Thanks!!

[@shashvatbarakin6258]

It could be due to the lower pressure above the wing than below it (higher pressure means more atoms packed together so the harder it is for the atom/ air particles to move through the high pressure(like shoving your way through a crowd). This result’s in slower air speeds) which allows the air to move faster over the wing than below it.

[@MaverickSu-35]

Yes..., that's an explanation trough reduced density. But the density reduces as a reduction in pressure otherwise..., which reduction in pressure is due to the Coanda's effect as the airflow tries to follow the curved pattern along a solid surface. This pressure reduction ultimately generates the increased airflow speed. AND NO..., this airflow speed increase now won't mean that more pressure reduction will take place as a result. No...! The result..., which is the increase in airspeed due to the decrease in pressure has already taken place and now they have settled. Yes..., if you want to increase the airspeed over one side of the curved shape, you will end up with a reduced pressure. They don't self-accelerate each-other, meaning the pressure and speed. Most of the times, only one triggers the other..., either the lower pressure will increase the airflow, or vice-versa. You could make them both happen, but the friction and other back pressures drag will still settle your airflow speed to X value. Cheers!

[@MaverickSu-35]

At 0:50 it says just that. Due to the high curvature..., the pressure decreases. That's the first trigger and the rest come along.

[@hamdanalharbi2206]

first part of the pressure is not consistent! i was lost when he started talking about the pressure in the lower part of the airfoil!

[@sassyblondel]

The angle of attack is too shallow. The bottom of a wing is pressing a lot more air down than shown.

[@AltMarc]

I really like this one. Did get into my favorites playlist to share. You could also understand why trailing edge turbulence were created.

[@johnlaudenslager706]

When air molecules hit an oncoming wing, wherever they are jammed, pressure builds. Whether the wing is domed on top or a flat shape angled up, air jammed at the front, then upward, is pressured, and any jammed down and underneath is also pressured, but then things change. As air flows further back the jam over the top of the wing lessens and there comes a relative vacuum, but air underneath continues to be jammed if it ever was. In any case air passing the main jam on top of the wing encounters a relative vacuum and is pushed to speed up and fill it and, with the air molecules bouncing along and hitting all or most of the top of the wing at more of an angle than any hitting the bottom, accounts for less pressure on top. Lift.

[@adhithasimhanraghavan7516]

The initial upper part of the air foil is synonymous with an orifice inlet where your area decreases and velocity increases for the same potential of fluid flow; in which air in higher vicinity acting as wall of the orifice. That is why higher speed is achieved at the top and there is no significant curvature at the bottom to cause the very same effect.

[@error.418]

This is incorrect.

[@feelingzhakkaas]

Thanks for this Eye-opener informative video. During our study days We have been taught wrongly. God Bless you for sharing true knowledge.

[@SabinCivil]

Prakash, I am glad that you enjoyed the new information in our video and thank you for your support.

[@WarjoyHeir]

I wish you provided more information about why the pressure gets lower above the airfoil. I just can't get what makes the pressure lower there.

[@monichka7]

It has to do with Bernoulli's equation; basically pressure and velocity are inversely proportional. That is, as pressure increases, velocity decreases and vice versa. You can google it, and here's a reddit discussion about it: www.reddit.com/r/AskEngineers/comments/7h1i7y/why_pressure_decrease_when_velocity_increases_in/

[@fadoobaba]

curvature of the flow makes the pressure gradient.

[@hemendraravi4787]

basically its just a suction force

[@orchidahussuhadihcro9862]

"suction force" doesn't say anything at all about why this suction exists. Simply put, the lower pressure exists on top of the airfoil, because part of the air that was supposed to be there, was deflected by the bottom of the wing

[@Talon19]

You should clarify the assumptions used. For example, positive cambered airfoil with no concave areas at relatively low angles of attack and subsonic flow throughout.

[@hafizuddinmohdlowhim8426]

Admin at min 3:08 you made a mistake. For top surface V decrease and then V increase. But you made it opposite. You asked why different speed? Because the shape of airfoil is curvy downwards. Like when you are sliding from on top a hillside. Your speed is increasing right?

[@b.w.1386]

The high pressure point on the leading edge reminded me of a similar problem for shooting bullets underwater. they fixed the problem with a concave tip that super cavitates and gets 60 METERs! Could a big leading edge divot work on a wing?

[@riazhassan6570]

Please permit this small observation from far away. What you have just said makes a lot of sense. Years ago I made a model with a sharp leading edge wing with some equal thickening near the middle and an equal flaring skirt at the back, the section looking somewhat like a small-headed eel with a fin. Strangely, the model flew quite well, even in its glide pattern. I had often wondered why a blunt nose had to be offered to the airstream. I cannot tell how many of these explanations, charts, smokey streamlines, theories, formulas, arguments and proofs I have visited over the years. A phenomenon I observed through the window as we flew through rain still baffles me. The droplets on the wing should have been torn away backwards in the airstream at about 400 miles an hour. Instead they remained attached to the wing and crept forward! What is going on around a wing in flight? I still have no idea, but I shall some day try a wing with a concave leading edge on a model some day. Thanks for bringing it up

[@godoftestoe7956]

Aren’t jet wings concave tipped?

[@hediabdellah8791]

now answer why the pressure is higher at the outside of a curve

[@atauygur8104]

Don't think like this is a curve so pressure must be higher outside, if you think this way you can't find any reason but if you think like there is a pressure difference so there must be a curve, you can see why it is. The continuous pressure difference between both sides of a particle makes particle curve, curve of particle doesn't create pressure difference.

[@onebylandtwoifbysearunifby5475]

If you have an object (air) travelling in a curve, it must have a force (centripetal) to the inside. Otherwise, it would go in a straight line. Additionally, the velocity reduces pressure (pressure+velocity is a constant. Bernoulli). So the pressure above the wing must be lower than atmospheric pressure. Moving up, the velocity of air stream is slower, so pressure is higher. It keeps going like that, always with the longer arc having higher pressure than the shorter (closer) arc. This is why a tornado has its highest pressure on the outside, and such low pressure in the center it can pick up objects into the central vortex. Check out some explanations of Bernoulli Principle if that explanation didn't answer your questions completely. [You could also look for "coanda effect". Both could help give a picture.]

[@waynebert7357]

see comment above

[@rbmaserang]

it is because the integral is an area of the wing under the top half, above the bisection and air being disturbed must accelerate so that angular momentum may be conserved and it is inversly proportional to bernoullis equation describing increased velocity and lower pressure within a tube's bottle neck.

[@typebin]

Thank you for easy logical explanation!

[@pjb2960]

Anyone else find this video better at explaining how airfoils work than the official video of how airfoils work..... just me?

[@error.418]

The official video? Wat?

[@aviationbird1962]

Hello, can you please explained why Pout has greater pressure than Pin ? This is the part I am currently stuck at, I dont get why a curved line the pressure outside of the curve is higher than pressure inside the curve? if that is the case why the curve not bending downward instead is bending upward? isnt pressure suppose to flow from high to low ? thank you

[@captainshipman7377]

This part took a long time for me to understand. Think of swinging a tennis ball on a string around your finger. In order for the ball to constantly curve in a circle, there must be a centripetal force accelerating the ball. Likewise, he’s explaining why air follows the curve of the wing. If there’s no force, air would continue to travel in a straight line. Yet it doesn’t, air follows a curved path around the top of the wing. It changes direction. There must be a force causing that to happen, and in this case it’s a pressure gradient force (PGF) lower pressure closer to the wing and higher pressure away from it causes air to curve in the direction of lower pressure.

[@rochakbadyal1856]

Thanks for explaining this in a very easy manner

[@islandfd3s]

Thanks for clearing this up! I definitely had the wrong idea about this.

[@matthewbriggs2805]

wait, Bernoulli says higher velocity fluids have a lower pressure, which counteracts what you said at the end about pressure distribution effecting speed and not the other way round

[@GZA036]

Misapplication of Bernoulli's principle. Bernoulli's principle is about conservation of energy and mass flow rate inside of a tube... a wing is not inside of a tube. Lift is the result of the flow being curved due to viscosity, a pressure gradient generated, driving acceleration. Air is given a downward momentum and Newton's 3rd law says the airplane experiences an equal and opposite force

[@yasirmahsud4129]

@@GZA036 could you please explain, "due to curvature pressure gradient generated"?

[@aeroboi2862]

The order is The Airfoil Shape and Coanda Effect Pressure Differences (And Corresponding Forces) Velocity Gradients *special note. If the pressure gradient on the second half of upper airfoil surface becomes big enough, velocity might decrease to the extent that the flow will start reversing. This causes loss of pressure at/near that separation point, loss of lift, increase in drag and called stalling

[@pratsdrawing7884]

so the reversed flow cause turbulence??

[@aeroboi2862]

@@pratsdrawing7884 reversed flow would be turbulent flow. But turbulence is originated from there. Turbulence originates due to high Reynolds no.

[@pratsdrawing7884]

@@aeroboi2862 yeah, but the reverse flow would cause more turbulence right?

[@agnarrenolen1336]

The problem I have with this explanation is that the air is not moving, the airfoil is. So the air above the wing is sucked backwards as the airfoil passes, and the air below is pushed forward. This results in a net clockwise circulation of air around the airfoil. What people fail to explain is what happens in the wake of the airfoil with two layers of air, the upper moving to the right and the lower moving to the left, meet up again behind the airfoil.

[@brinzanalexandru2150]

Actually Jukovskii theorem explains it very well using air circulation around the wing

[@fiatmultiplaa]

Can you make a video explaining in detail how calculators work...?

[@fiatmultiplaa]

+pantagruel I know basics but I want nice detailed animated video about it. But thanks anyways!

[@buzzmas8068]

Oi i just gotta know, why are plane wings and noses blunt at the tip rather than pointed? Wouldnt it help to separate the flow seamlessly, without causing that high pressure area at the front? Why do we not use that

[@anutsasipongpreecha7761]

Here is a great explanation aviation.stackexchange.com/questions/26532/why-should-the-leading-edge-be-blunt-on-low-speed-subsonic-airfoils And we DO use a pointed leading edge airfoil but for supersonic aircraft because aerodynamics is different in supersonic flow.

[@saravananvenkatesh5717]

Well explained. Thank you

[@Yournextlevel369]

I think lift is produced due to the centrifugal effect arises at both the upper and lower curved surfaces.This result in the throwing away of air to both upper and lower part of the airfoil, at the bottom surface there is the ground to provide the reaction force but throwing away of air at the upper surface will not get any reaction force thus air pressure decreases over it . Thus air plane takes off, am I correct ? Please comment on this theory...

[@shoutitallloud]

First you state that in curved flow pressure is greater outside. And right very next statement is that outside a flow, curved by upper surface of airfoil pressure is lower.

[@sujatharekha3036]

Mind-blowing explanation...

[@AndrewPa]

It is faster above because of gradient in pressure (slope) between front side(stagnation point) where pressure is maximal ( and velocity is zero) and top side where pressure is lower due to fluid motion ( Bernoulli principle)

[@charleswesley9907]

Air has weight .The shape of the wing forces the air molecules to follow a path across the wing which is changing direction . That flow following the wing is attached by a boundary layer . This transfers to the wing surface the effects of the centrifugal force providing lift when the speed of that air across the wing is fast enough . The lift is from the weight of the air being forced to change directions across the wing . There is no lift on the last 1/3rd of the wing .The Tailwind wing has very little upper camber and has a higher stall speed as a result .

[@FB0102]

My explanation would be that the airfoil acts kind of like a nozzle, accelerating air by forcing it to move through a smaller area. Imagine putting another airfoil on top of this one, but flipped upside down. The two airfoils would act as a nozzle to the air flowing between them, causing the flow to accelerate, then decelerate back to normal speed as it exits the nozzle. Having just the lower airfoil does the same effect, only less pronounced; it still accelerates the flow above it, lowering its pressure, by forcing it to move through a smaller area. The bottom surface is less curved so the acceleration and pressure reduction is less. Thus upper pressure is lower and there is a net up force.

[@AmbientMorality]

This would imply a flat plate at an angle of attack would not generate lift, yet it does. Venturi is not a great explanation.

[@Observ45er]

Not so FB. That is the half-Venturi fallacy. A force is required to accelerate a mass and air HAS MASS!. The force comes from the Pressure Gradient (Pressure Difference between two locations). F-MA for fluids. It is simply the relative motion of air ans wing which changes the pressures around a wing. See: www.quora.com/q/rxesywwbdscllwpn/Understanding-Lift-Correctly

[@cesardanielcruzochoa9129]

hey! can you tell me what program do you use to generate those simulations at 0:16... or you just paint it by hand... Thanks a lot

[@Guciacia]

I don't know what they are using, but in my work I'm using Comsol or Ansys Fluent. Comsol is a little better when considering also chemical reactions, but Fluent is overall better in my experience (more accurate). Both are sadly on paying license, although many universities can provide it for students/stuff (which is my case). Hope it helped a little :)

[@FlyingRagilein]

Is the lower pressure on the top of the wing the result of the faster flowing airflow (Bernoulli) or is the faster flowing airflow the result of the lower pressure on the inside of the curved flow that accelerates the air ?

[@jacobjasch4397]

I think this is a helpful way of thinking about it: Imagine water going through a pipe, as the water passes a narrow point in the pipe (a venturi) the water accelerates. Imagine that the airflow around the wing is the pipe, and the free flowing air that has atmospheric pressure is the wall of that pipe.. Increasing the camber of the wing will tighten that space, the Venturi, causing the air to accelerate faster over the top of the wing as opposed to the bottom. Then, as the air accelerates over the top MORE pressure drops. So pressure causes the acceleration, then acceleration further causes more pressure drop.

[@shortscreator9977]

since bernoulli's theorem cannot be applied on two streamlines then how bernoulli's principle is resonsible for the BLOWING OFF of the ROOF DURING STORMS ????????????? PLS ANSWER

[@Observ45er]

Shorts, It is caused by the curved flow above the roof, atmospheric pressure holding the flow close to the roof and the air's inertia (Newton's First Law). This video uses a wing, but the same thing happens above a roof. *kzbin.info/www/bejne/aX62opWkl7B3o68* .. Not really. First, Coanda does not occur around a wing. Coanda is for a JET of air into an otherwise still environment. . Second, while there is *some* occurrences of examples of Bernoulli "happening" around a wing, the vast majority of explanations you will find using it, are wrong. Speed does NOT cause a lower pressure PERIOD! . To word it like you do: It is MUCH BETTER to say that the pressure distributions around a wing are due to the wing pushing the air around. These pressures then cause all accelerations of air around a wing AND the lift. .. Look at these: First, VERY Important thing to remember: Air HAS MASS! Pressure on the outer part of a curve will always be higher because the fluid wants to go straight! This ALSO makes the pressure less in the inside of a curve. Then, try these: *Understanding Lift Correctly: **rxesywwbdscllwpn.quora.com/* *Understanding Bernoulli Correctly: **kyuoyckftflurrpq.quora.com/* *Flow along a Convex Surface: **kzbin.info/www/bejne/aX62opWkl7B3o68*

[@tolissailor]

Bernulli's principle assumes non-viscous, non-frixtion flow and is therefore correct for such cases (i.e 2 particles should meet together at the trailing edge etc. ) . Experiments do not agree with the theory because, well. real fluids are viscous and have friction in a non linear way. Navier-Stokes equations account for all of it though.

[@williamfra]

So Bernoulli's principle has no effect on generating lift? Couldn't we say that the pressure distribution due to the Coanda effect creates different speed but then these different speeds amplify the difference of pressure because of Bernoulli's principle?

[@RahulSharma-oc2qd]

I did not get, why the pressure field would change on upper side of foil from being low to high at the tail end?

[@raveeshmalhotra7347]

That was really good. I loved it.

[@tinolino58]

Think about it! The air is actually stationary and does not flow over the wing. The air just gives way to the wing upwards and dawn wards. The generated pressure degreases with distance. The air turns counterclockwise around the pictured profile.. Start thinking and let go the hypnosis of the windtunnel.

[@kitchencone]

The visual is misleading after 1:46. The airfoil is shown with a negative angle of attack, but the pressures shown can only come from a positive angle of attack.

[@vascoribeiro69]

What happened in an airfoil is that it accelerates a mass of air downwards, the vertical component of the AOA. That is why lift increases with higher AoA. How efficient it is what is called Cl, function of the design and AoA. A mass that is accelerated creates an opposite force, in this case, lift. A force distributed in a surface is the pressure. That is why if you put a hand out of the car like a wing, it will go up and down. You are deflecting (accelerating verticaly) a mass of air, producing an opposite force.

[@karhukivi]

A flat wing works but is not efficient as all the lift would be coming from the downward deflection as you say. A curved upper surface also produces lift and a lot more, up to about 80% and makes the typical aerofoil much more efficient that a flat sheet. The spoilers ("lift dumpers") are on the upper surface of a wing for that reason. Every pilot knows about the effect of ice or even dirt on the upper surface, the lower surface has flap hinges, actuators, etc as it is not so important. Your hand is not a flat plate, the upper part (back, opposite the palm) is also curved!

[@vascoribeiro69]

@@karhukivi that is the Cl. You can't violate Newton's laws. That is why wings and helicopters rotors have a downwash, i.e a mass needs to be accelerated to create a force. At slow speeds the efficiency of the airfoil is critical, at high speeds a razor blade will do. With enough power even a brick can fly.

[@karhukivi]

@@vascoribeiro69The curved wing is far more efficient than a thin plate, which is why aircraft manufacturers use them. The downwash is when a helicopter is hovering and is also called "maximum performance t/o" because it is inefficient and a lot of engine power is needed. In forward flight a helicopter also gets "translational lift" form its forward motion, which is then a rotary wing mode. Aircraft in forward motion don't have "downwash" they have vortex turbulence following them as the low and high pressure air flows re-unite. You are obviously not a pilot!

[@vascoribeiro69]

@@karhukivi I am an engineer, studied for pilot, designed several aircraft for simulators, but that is not the point. The point is that there is no black magic. You always need to displace a certain air mass to fly and to have thrust, either an helicopter, a propeller aircraft, jet or whatever...

[@karhukivi]

@@vascoribeiro69 Then as an engineer you can measure the drop in air pressure above the wing and you will find that the force across the area of the wing surface is equal to or greater than the mass of the aircraft. Look at a jet fighter and see the amount of equipment below the wing, guns, rockets, ordnance, etc. The upper surface is almost devoid of equipment of any kind, because that is where the majority (up to 80%) is being generated. If air is accelerates it is reduced in density (same mass of air into a larger volume) hence a low pressure area above the wing. The air is displaced horizontally by the forward movement of the wing. Think of buoyancy in a boat, and where is the thrust? No continuous downward displacement of water.

[@ThrashLawPatentsAndTMs]

I've spend two hours looking at videos and searching bing/google and NO ONE wants to discuss the speed of the airflow across the top of a cross-section of an airfoil vs. the speed below the airfoil vs. the relative air speed. I know this varies based on the distance from each surface, but WHY (??!!) are there no videos on the topic? If you know of one/some, please comment and direct me to them!

[@alexgallegos4526]

Why location of the pressure changes with AOA?

[@rahulsannigrahi8550]

the answer may be given by Bernoulli principle where the pressure at the top is low and hence velocity is high

[@shamiljamaldeen]

great video explanation sir, really appreciate it.

[@jatinshilen]

Great Explanation!

[@SuperZardo]

You should have started with a symmetrical airfoil at 0° AoA and develop your arguments from there, comparing the pressure and particule speeds over and below the wing with the pressure and particle speed of the air outside of the influence of the wing, and only once it is understood what happens in a zero lift condition, develop the explanation of lift.

[@si_vis_amari_ama]

Can someone please clarify for me: Why does the pressure increase on the underside? At 2:51 it shows that the net force is reversed (why?) I know this fits in somehow but its not computing for me. My basic understanding of an airfoil, is that lift is generated by a differential of *relative* higher P underside, as to the lower P of the topside. If you look at a smoke test with an increased AoA of the wing, you can see this effect is evident where the molecules slam into the underside, hence drag would slow them (???), but in the video it also states that it is not fact that pressure=speed works both ways. Also, the underside of the airfoil is slightly curved, so in level flight how is the P increased? Thank you.

[@carmelpule6954]

sandi x, May I try and explain. When the wing is forced forward, it forms a compression zone at its leading edge acting slightly above and below this edge. The position of the leading edge with respect to the lowest point on the airfoil section decide on size and overall location of this compression zone. The air particles that enter this compression zone are shot "half" towards the upper and "half" towards the lower direction, where they try to separate from the associated surfaces and so create low pressure areas further back than the leading edge, above and under the wing. You must appreciate this before we go any further. So under the wing there could be a lower pressure zone just like there could be above the wing. Now the idea is to redistribute these areas of low pressure above or under the wing, by making the aerofoil unsymmetrical and it could also be given an angle of attack where the low pressure on the underside can be turned into a high pressure zone, by the fact that the down directed particles at the leading edge and elsewhere on the lower side are not allowed to leave the lower surface, but push on it. The high pressure on the underside also helps to counteract the high pressure zone above the leading edge that accelerated the particles up, otherwise the wing will dive down!!

[@feizal7554]

Carmel Pule Best explanaion, but you can add that when the airfoil's aoa is upward, the surface just behind the leading edge has almost no molecules pushing against it , hence the relative low pressure, compared to below.

[@plumtiger1]

Excellent video!

[@Milkinporsche]

this is very helpful, thanks!

[@austinsloan9769]

the pitch of the wing and pitch of the slope on the wing creates a pressure differential

[@feizal7554]

!00% correct and simply put. The velocities do not create the pressure difference in this case, rather the pressure differences create a difference in velocity.

[@enbinzheng-line]

Speed difference is not the cause of lift. The increase in speed is due to the increase in pressure at the stagnation point.

[@Manikandan-hm3fc]

What about for symmetrical airfoil geometry

[@saurabhvyas682]

@Learn Engineering The starting vortex theory explains how the velocity over the airfoil and below differ which in turn produces a difference in pressure. Check the starting vortex theory it makes sense mathematically as well as logically.

[@Observ45er]

Math is a model of the physics. This explains the physics that is modeled by the math. ...Don't get me wrong. The math (and various techniques developed in the math) is critical in calculating lift, but the physics phenomena are easily explained without math.

[@david_porthouse]

I have been plugging the starting vortex in all these videos. Vorticity of opposite rotation is bound up with the wing, and generates lift by the Magnus effect. Simple! The Kutta-Joukowski circulation theorem is just the Magnus effect by another name.

[@GahSoonChan]

What is the direction of the air flow in the cfd?

[@anonymousanon6163]

Coanda effect is only for fluid jets. Wings don't naturally experience coanda effect except from jet engine exhaust. Airflow follows the wing due to air viscosity. While the concept of Coanda vs. flow attachment due to viscosity is similar, Coanda effect is only considered applicable for fluid jets.

[@patw52pb1]

You may want to rethink your statement, maybe do some additional research.

[@GiorgiBranquinho]

Very Nice! it's so simple. thank you!!

[@Esparzamx]

great video, thank you!

[@shivkumar-qh7dx]

pls make fluid flow analysis on aircraft fuselage

[@hamzamashood3544]

You just clear me thank you keep it up

[@fredrickmutua5338]

its a good and inspiring explanation for aeronautical engineers

[@DucTra]

Could anyone explain for me why pressure at the outside curve is higher?

[@manishmaurya3092]

plz someone explain

[@henrycoldrain8151]

Bro let me put it this way. İmagine you are on the street running away from a cold blooded killer. Since you are running forward your body collapses with air molecules which would grant those molecules a motion around your body. So imagine the velocities between the air molecules 1st top of your hair 2nd 5m higher than your head. Which one you think would move faster. Well since you granted a motion to the the air you collapse it should have higher velocity than the one 5m away from ur head. So higher velocity would have lower pressure therefore the pressure above your head is lower than pressure that is 5m above your head. Same goes for plane wings.

[@dnomyarnostaw]

Its easier thsn you think. Imagine if the air particles were little plastic balls. When they hit a curved surface at velocity, they would be rapidly shoveled aside like a plough. but Because they are air, that shovelling aside would create a vacuum, which atmospheric pressure would need to fill quickly. So, the low pressure is just air particles trying to form a vacuum as they are forced aside by the wings velocity.

[@TonyGrant.]

As Ray Watson said "that shovelling aside would create a vacuum" this is because the air molecules are trying to leave the wing in an upward direction. However, there is no way for air to fill it so lift results because it is the wing that moves into the vacuum instead.

[@mm-sw6qp]

may I just ask :) if we admit that the particles move faster along the upper surface (even though not because of the travelled distance), is it possible that Bernoulis principle still plays some role in the lift? I understand that it only applies along the flow, but if we consider similar characteristics of the upper and lower flows, could it still generate some pressure difference? thank you :)

[@error.418]

Bernoulli's does not predict nearly enough of the actual value of observed lift.

[@AmbientMorality]

@@error.418 It predicts the entire actual value of lift. If you wrongly assume equal transit, calculate velocities from that bad assumption, and then calculate lift then that's your fault for making a bad assumption that Bernoulli never said.

[@error.418]

@@AmbientMorality I already linked the resource from NASA refuting this in a separate comment. You can also look it up yourself.

[@AmbientMorality]

@@error.418 What do you mean by "Bernoulli's"? If you mean equal transit theory, then sure, but that's a bad assumption. If you mean the pressure distribution over the airfoil does not predict the entire value of lift, then you are wrong as per every aerodynamics textbook ever written

[@pradgadagkar8557]

You did not explain why the pressures are different. Just due to curvature? Holy cow

[@Observ45er]

The curved flow is the DIRECT cause of the pressure change. *kzbin.info/www/bejne/aX62opWkl7B3o68*

[@shubhakashyap5578]

LearnEngineering Can you please do a video on A/C compressors?

[@bigboat8329]

basically air compresses and bam cold air woo hoo

[@frankkky7375]

So then based off this theory using coanda effect, bernoullis principle has nothing to do with lift?

[@dremr2038]

provide further information for that argument he made near the end : DIFFERENT SPEEDS ---> PRESSURE DISTRIBUTION

[@josemanuelmunoznaranjo5669]

Coanda effect doesnt take place in order to explain this fact, just for jet fluids. Main reason is the geometry and distribution of pressures around the wing.

[@alexgallegos4526]

Coanda effect is not just for jet fluids, it is used in Formula 1

[@Observ45er]

@@alexgallegos4526 The issue is that Coanda does not happen around ANY wing-like shape. It is defined for a jet or sheet of *forced air* into an otherwise *motionless air environment.* A wing does not have that and it is improper to call that COANDA- - However, there certainly similarities.

[@blainetubungbanua8236]

The lower pressure gradient on top foil is lower than the bottom foil BECAUSE the fluid particle is moving faster. This is the result of the Bernoulli principle, which states that fluids at higher velocities induce lower pressures. This explanation uses the consequence of the acceleration to justify its existence.

[@error.418]

No, you have it backwards. The faster rate is due to the lower pressure. It's common to get this backwards. www.grc.nasa.gov/www/k-12/airplane/wrong1.html

[@richardhill286]

Who's here for there CFI check ride?

[@sakn415]

isn't the different speeds caused by boundary layer formation?

[@frankyboy1131]

If it was, the speed should be lower, the closer it is to the wing. This is not the case. I think boundary layers are just neglected here, which is okay in my view. Also, I think the AIR SPEED measured along a gradient vertically to the flow would first (1) increase slowly from far away ( atmospheric) to minimal pressure line near the upper surface, then (2) decrease rapidly on the last section from minimal pressure line to the (upper) surface. (Please read carefully, I hope I was clear.) If I get it right, the boundary layer is a result of adhesion and friction. Does anybody want to comment on that, and does anyone know if the boundary layer varies in thickness along the airflow?! Have a nice day everyone.

[@solaaar3]

i don't understand why p_out is more important than p_in ?

[@Thankorish]

Consider this. A vile of very concentrated gas is released in the center of a larger container. No gas was present in the large container until the release. To simplify it think about a cross section in 2D. A molecule on the edge of this new circle of gas will have some random velocity, but the only important part is whether it is pointed away from or towards the ball of gas. If it is pointed away from it, it will continue unobstructed, but if it is pointed towards, it will hit other other molecules and be slowed down or turned around. This is basically why high pressure areas push against low pressure areas of gas. Molecules going towards the higher pressure area are much more likely to be slowed down, stopped, and turned around because there are more molecules they might hit. The force on a body of gas comes from the average number of molecules to potentially deflect or otherwise obstruct the path of individual molecules. So the air forced against the wing's underside creates the high pressure zone. The molecules adjacent to the wing either will be moving away from or towards it. The one's that hit the wing is deflected downward, while the one's moving away just keep going. This results in pushing the wing up. You may say that the same thing is happening on the top of the wing, and it is. However, since the top of the wing has a lower pressure, more of the molecules which are going away from the wing continue without being knocked back towards it. There are also few molecules in total to potentially hit the wing and push it downward. So to answer your question, the molecules on the top of the wing are pushed downward by the highly pressurized air created above the wing, while the molecules below the wing are pushed down by the wing itself (and and also some pressure).

[@AliKhan-xe4wb]

Pressure is high in beneath side of the airfoil because of weight and when the plane fly upsidown then also the high pressure exists in beneath side because of totally weight...

[@majidmahjoob8424]

It means that the decreased pressure condition is the cause of acceleration of air above the wing, has been there before movement of air !!!!!

[@eswarakrishnanvenkatasunra9619]

If so , can you explain the lift generated by symmetrical aerofoils based on your theory please?

[@alanmakoso1115]

A symmetrical airfoil creates no lift at no angle of attack. That is because the curvature is equal on both surfaces and have equal pressure gradients. Now when you tilt it at an AoA the leading edge of the upper surface creates a lower pressure gradient and then it works just like how its explained in the video. Just be careful not to stall.

[@ouas26]

Why does the pressure increase if air moves towards the bottom of the airfoil?

[@102wingnut]

This is like the chicken/egg question. Does the speed difference cause the pressure difference or the other way around?

[@isaacjohnson8752]

I think the pressure is what creates the increase in speed on top. There’s several effects at play though, for example the angle of attack of the wing pushes the air underneath the wing downwards slightly, so then Newton’s 3rd law explains a net upward force on the wing. Also if the wing has an angle of attack then on the bottom of the wing particles stack up with each other due to being slowed slightly. Whereas on the top of the wing there is a decreased pressure because the air has been directed away from the wings surface. This also creates more turbulent air above the wing and less turbulent air below. I’m fairly confident the pressure is the instigator for the velocity difference. But there are many different concepts at work. There are many false claims as well as to the reasoning behind lift, it’s entirely possible I misunderstand the concepts as well.

[@Observ45er]

The cause-effect chain is clear if you follow the fundamental principles. In SIMPLE cases, a Precure Gradient Accelerates air toward the lower pressure region. Simple. .. The lower pressure directly causes the speed increase ( acceleration) away from the Leading Edge toward the middle of the upper surface. FOR SURE! .. .. .. .. .. .. BUT it is the COMBINATION of: the flow moving + the curved surface + the air pressure holding the flow against the curve AND the inertia of the air "trying to go straight". All of that TOGETHER are THE CAUSE OF THE LOWERED PRESSURE! ALL of that is REQUIRED to go from speed to pressure reduction,. it is NOT simply speed > lower pressure > speed. NOPE! It is FALSE that fast moving air 'causes' a lower pressure. .. Please see this very short video and upvote it if you understand it. It is correct! BUT... it ONLY explains ONE STEP: The cause of the lowered pressure above the wing. *kzbin.info/www/bejne/aX62opWkl7B3o68* .. This Blog explains the Bernoulli Principle fully: *kyuoyckftflurrpq.quora.com/* Regards

[@Observ45er]

@@isaacjohnson8752 YES, YES, YES!! There is a combination of factors that you Must understand. See my other answer in this thread to michael spencer... [but it is NOT "more more turbulent air above the wing". The turbulence doesn't become meaningful, for the most part, until you get close to stall. .. YES! FOR CERTAIN "pressure is the instigator for the velocity difference." In the mid 1700s, it was Euler, following up on Bernoulli's work, that figured out that a Pressure Gradient Accelerates a fluid. This is NOTHING other than Newton in Fluids !!! . The TWO pressures work together to Accelerate air toward the lower pressure (away from a higher pressure). YOU'VE GOT IT!! .. BTW: Did you know that Euler derived what we call Bernoulli's Equation?? There is no indication in Bernoulli's notes that he understood the cause of the pressure-velocity thing...! . Please try to spread this word around to dispel these myths that have lasted so long among the well meaning amateur scientists. . Please see this very short video and upvote it if you understand it. It is correct! BUT... it ONLY explains ONE STEP: The cause of the lowered pressure above the wing. *kzbin.info/www/bejne/aX62opWkl7B3o68* .. This Blog explains the Bernoulli Principle fully: *kyuoyckftflurrpq.quora.com/* - - Regards

[@gracechang9659]

Yes

[@vibhusingh8815]

how a symmetrical aerofoil wing produce a lift??

[@TheOne-go7yb]

Vibhu Singh In case of symmetrical airfoil the angle of attack is used to create the required lift.

[@dhyeybhavsar3842]

Can someone explain the pressure gradient on the lower side of the wing of an airfoil?

[@feizal7554]

because of the typical shape of an aircrafts airfoil, the top has a larger travel surface area than below. The air molecules hitting the leading edge is dispersed both upwards as well as downwards. However because of the leading edge's higher angle at the top relative to the wind, the air is deflected higher upward, leaving a void of impact area just behind the leading edge. Below the air is relatively hugging and even impacting ( depending on flap settings) the underside of the wing creating a higher pressure and therefore lift. The natural property of air is to balance out and will therefore push towards the lower pressure area anything in its way, the wing in this case.