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Wow! I remember when we were taught about the wing and Benoulli at school, I could never understand how or why 2 air particles must meet at the rear of the wing, but I was told I didn't understand. Yes I did!

1:58 "The two particles can leave for a completely different journey and may not meet in their lifetime." I can feel it!

With all the aerodynamic engineers on here arguing with one another its amazing we can even design airplanes that work in the first place.

Thanks you, I had my middle school in China, we were taught with the wrong theory. I never understood why airflow can reach the end at the same time, because it's totally wrong!

Bernoulli himself never said anything about equal time transit, so don’t blame on him!

Bernoulli's equation applied along the streamline. For the streamlines above and below the airfoil, the total pressure is the same. But the static pressure is different (low static pressure on the top and high static pressure at the bottom). This causes a difference in the relative velocities of the particles on the streamlines.

This video was excellent in clearing up potential misconceptions of the theories of lift. I really appreciated how he took the time to talk about each of the misconceptions and offer a more accurate representation of the physics at play. Moreover, the physical demonstrations and CFD simulations helped provide a more intuitive understanding of the true nature of lift. Great work!

Something always felt wrong about the "same time" theory. Why the hell would the air be trying to catch up to its friends on the other side? Lol. Thank you!

As a person that works in aviation and that I currently pursuing the airframe/powerplant license to be a aircraft maintenance technician I could tell you there is a lot of physics and electricity involved in this career

Terrific video and explanation. Im so glad someone took the time to give the correct lift explanation with sound engineering principle. The velocity difference is due to the two different aspects of fluid pressure that the video does not mention. There is static pressure (SP) and dynamic (or velocity) pressure (VP). The total pressure of the fluid remains the same, because TP=SP+VP. As the velocity of the air goes up, the velocity pressure goes up and the static pressure goes down, and vice versus.

Finally! A video that properly explains aerofoil behaviour! Three thumbs up!

The best channel for engineering students, hats off ❤️

Warning: ahead are people who have all sorts of degrees in aeronautical engineering, who are intent on correcting everyone who is wrong. Please proceed with caution.

If you closely examine the Picture at 6:42 you can see a pressure increase at the bottom of the wing which causes a slowed air flow because "the oncoming Air particles have to push against a higher particle density" of the high pressure at the bottom. At the top because pressure decreases, oncoming particles are sucked into some sort of partial vacuum causing an inrease in flowrate at the top of the wing. An increase in flowrate means higher particle velocity at the top

The presented experiment with water sticking to the surface of the bottle is not the Coanda effect, it's just a result of surface tension, adhesion and cohesion of water molecules.

The best scientific channel ever created. Thanks for the interesting videos!

Man u dont know how much u helped me with this 7 minutes god bless u thanks a lot

Very interesting presentation. Your elucidation of the Bernoulli effect is spot on. The Coanda effect, upwash, down wash, drag as well as lift are effects. They are caused by the pressure difference between the top and the bottom of the wing. Lift occurs because of what is happening as the air flow interacts with these surfaces. Precisely at these surfaces the rate of flow is zero or near zero. This is the no-slip condition. The flow rate increases as the normal distance from those surfaces increases. What this means is that fluid shear is taking place. The fluid particles are interacting with one another and with the surface. This is not inviscid potential flow. The concept of a stream line breaks down in this boundary layer. When the wing surface is curving away from the flow, this shearing causes particles to be blown away from the surface. It is this depletion which causes a pressure decrease at that surface. It is this pressure decrease that causes the stream lines to be deflected down along and above the top surface of the wing. It is this effect that is used by the « blown flaps » on supersonic aircraft to maintain lift as they land on an aircraft carrier.

Thank you for my presentation!

this is so amazing LE has really help me in my misunderstanding thanks LE

The Bernoulli theorem can apply if the air can be regarded as a laminar flow like a plastic sheet. The air particles in a layer adhere to each other like an elastic sheet.

Thanks for the Coanda effect.

Excellent learn engineering!!! keep the work...you make very good educational videos!! greeting from venezuela....this videos help you learn a lot better than many classes out there

Great video! I hope to see more.

Anti-Bernoulli theorists always use the 'equal time' argument. It makes it look like the wing is static and the air is moving (so the idea of two separated particles meeting again seems odd). In fact it's more the other way around; the air is static and the wing moves through it. As it slices through the air it separates particles momentarily, some going above and some below the airfoil . Inertia means that these particles tend to stay in a similar orientation to each other and substantially meet again at the trailing edge of the wing. However, the shape of the upper wing surface and the overlaying layers of air act rather like a Venturi. The air particles relative speed to the airfoil surface between those layers increases in order for the airfoil surface to flow past the same number of particles as before. This increase in dynamic pressure is countered by a loss in static pressure, due to the principle of conservation of energy, as no energy is being added to the system, the total energy (static + dynamic) must remain the same. (Coanda advocates usually express the same proposition by depicting the particles stretch further apart.) It is this lowered static pressure that generates lift; which by the way can be directly measured in wind tunnel tests and is definitely there. You can simulate it by blowing over the top of a model airfoil or even across the top of a straw stood in a liquid. The Coanda effect and reaction to the downward redirection of the relative airflow also play a part, but to dismiss the Bernoulli effect entirely is inaccurate. Differences in airfoil design can also influence the relative significance of each (e.g. a specific type of trailing edge is needed to maximise Coanda). For it all to work the airflow needs to be relatively smooth and laminar; if it becomes turbulent the effect can be substantially lost. Thats why odd (non-airfoil) shapes with longer upper surfaces are not effective for generating lift. A typical subsonic airfoil will also break down into turbulent flow at about 15 degrees angle of attack, commonly referred to as an aerodynamic stall. It results in a loss of about two thirds of the lift being generated. BTW. The compressibility of air becomes an issue as you approach the speed of sound and the fluid dynamics changes. Supersonic airfoils are a different proposition in many ways. Even today supersonic aircraft try to spend as little time as possible in the transonic phase, when the fluid dynamics transitions from one to another, and different relative airspeeds around different parts of the aircraft make things 'interesting'. NASA have a good simple explanation of much of the above on at www.nasa.gov/sites/default/files/atoms/files/foam_wing_k-12.pdf

great job +Learn Engineering. We appreciate all your hard work. Keep spreading the knowledge. We hope you get all the supports you need and carry on your work with great momentum in future. :)

Total energy of a fluid that is flowing is separated into its pressure(potential energy) and kinetic energy. So, if there is a decrease in pressure, eventually the velocity component takes the edge and therefore the particle at the top travels faster than the particle at the bottom. So the tortoise never meets the cheetah ;)

Thank you very much as such teaching stuff not available else anywhere that I learnt from this channel....

Where were you 20 years ago when I was arguing with my fellow instructors about this? :-))))

*I could binge watch science videos forever, this was well done!*

The newton 3 law argument was so beautiful and simple that it made my day.....its beauty of proof cant be contradicted

Oh my god what a great explanation is it :D

Even since grade school I called bs on the equal time theory. It just never made sense to me.

This is exactly what I thought when I was learning fluid dynamics at university "why they should travel with equal time?". Thank you for clearing my mind I love your channel.

thank you, awesome video indeed!

Excellent video, thank you!!

as the pressure decreases it gets converted into kinetic energy and moves faster than the air below the airfoil

Wow! The most complete and accurate information on the net!

I spent many years windsurfing and studying sail design. In windsurfing, you can feel all the forces on the sail, when it's in the sweat spot, powered up and pulling the way you want. When the draft is moving around and how a little downhaul or a carbon mast can make a lot of difference. 10 times more than on most sailboats with a fixed rig. Speaking of sails and not wings the equal and opposite forces make a lot of sense to me. Over the years, as sail technology advances and the mast become more streamlined with the sail the corresponding performance increase comes up short possibly because they are always counting on two-thirds of the lift coming from the lee side of the sail? I think like you said, it's simply how much force/ air you can bend... or stall in at times. It doesn't matter what side of the sail the power comes from. Often a larger sail will do more good than one with a more streamlined entry. Also not mentioned, and sailors know, as you get closer to the water surface the wind speed drops on average but also becomes erratic and full of flaws, eddies and swirls. Hard to generate lift in those conditions and easier to get a push.

hey ...does the reaction turbine works on coanda effect also ?? i always thought it is due to the nozzle type shape between blades which causes fluid to accelerate and turbine moves due to reaction from fluid to this acceleration ?

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Wow great video I am impresssed at your hard work on this

I'm impressed by your knowledge about every electronic thing

I’ve neard his voice in my CBT for a320. No wonder it sounds familiar

I love your channel and videos, very open minding! but for this video when the plane flies upside down shouldnt it fell towards the ground?

I enjoyed your video! I liked how you incorporated computational fluid dynamics plots as well as creating your own experiments to back up your points. Great job pointing out the Equal Transit Time fallacy. The Coanda effect is only applicable to jet flows, as you have even stated in the video, but air acts as a continuum and does not behave like a jet in the atmosphere so it is not applicable. The shape of the airfoil causes air to stay attached, otherwise a vacuum. Great job with Newton's 3rd Law and the pressure theory!

Thank you LE for video😃

It's not Coanda!!!!!!! Coanda doesn't work in non-accelerated flows if at all. It is viscosity and static atmospheric pressure that causes attachment. Fluids attach to curved surfaces because of viscosity. The more viscous the fluid the better is sticks and resists and the more it curves, Newton's 1st law. If you get ice contamination, even as fine as grains of sand on the aerofoil, the viscous attachment is affected as the surface is rough and attachment is not uniform. The boundary layer can break away stalling the upper surface even though it is well below the stall angle for that aerofoil. DC-9s/MD-80s are particularly sensitive to this. Attachment is a function of air's viscosity and is taken into consideration in lift calculations. As NASA says and you you can prove with a paper plane, lift is caused by turning a fluid. Bend the fluid one way and your wing goes the other. Airspeed or AOA provide the change F=MA A flat plate will generate excellent lift and low drag at a positive AOA. The pressure differences are a result of lift production from AOA, not the cause. Shaping only refines lift production. No effective AOA no lift. Remember too that all airliners have super-critical wings that are flatter on top and curved underneath. My video here explains lift production in detail that is easy to understand. kzfaq.info/get/bejne/jdOIpJyY0pfZfaM.html

Good explanation! Thank you for the research. And for those who ask about the Coanda effect, search Henri Coanda, he made the "first" plane with a jet engine in 1910, named the Coanda-1910

thank you for teaching me what is bernoullis principle

This helps a lot. Thanks.

Very Interesting, but I think that the truth is between theses two theories. As you shown airflow above the wing is faster, so along this streamline Bernoulli principle applies and lower the pressure of the air flowing above the wing. In the mean time the airflow below the wing is not as fast so the pressure doesn't drop as much, this creates lift too! So Bernoulli principle can explain lift even if equal time argument is wrong. Speaking about the equal time argument. I agree that in a wind tunnel where there is an airflow over a stationnary wing nothing tells us that the air should travel the same distance. But there is two things to take in consideration. First (I'm not sure about that ) the air flow above the wing go through a narrower path, and since the pressure doesn't go up(no flux) , it must flow faster to conserve the flux. Second, in real airplane it's the wing that is moving through relatively static air, in that case the equal time argument makes sense because the air is displaced verticaly but not horizontaly, so the horizontal position relative to the wing stays the same for all the air (due to inertia). In that case the geometry of the wing lead to a longer path for the same horizontal distance. And at last I'm not convinced by your argument about the reversed shape, yes the third law of motion is stronger in your example but none of your wings are aerodynamic and the dragging that this generate could counter any lift produced by Bernoulli principle. I'm no physicist so any feedback are welcome.

I CANT UNDERSTAND THE STATEMENT "THE SAME REASON PRESSURE SHOULD INCREASE AS WE MOVE TOWARD THE AIRFOIL AT THE BOTTOM"

Excellent and fantastic and excellent effort and explaining. Thank you very much for a golden information

excelent video guys, keep the good work

3:19 is bit confusing. Why would the pressure difference have in the first place? because the wing has served as a barrier and the wind will be deflected? the direction of wind flow thus creates the air pressure difference?

I guess in 2:29, the figure actually has a deep CONCAVE surface in its middle so the airflow cannot be bent that way like it does in airfoil (COANDA EFFECT) and thus it doesn't create any lift.....hope my explanation is correct 😊😊

the explanation was way more crisp and easy to understand!!!!!!!

well explained, appreciated !!!

The reason the air moves faster over the top is the same reason that explains why water moves faster coming out of a funnel than it goes in. The air above the wing is 'sucked' towards the wing by the Coanda effect, which squishes the streamlines together. This forces them to move through a smaller space, which increases their relative speed.

Well explained........But have a question! Due to coanda effect,the pressure is decreasing from top to bottom as we go towards the airfoil on the upper side. I agree to that! However,why can't we apply the same concept for the air flowing on the lower side of the airfoil.What I mean to say is that even if the pressure is considered to be decreasing from atmospheric value to some lower value towards the airfoil on the lower side,still the coanda effect will be met! Please clarify!

OMG thank you!!! My intuition always told me the equal time concept did not make sense. I feel so much better after watching your explanation! Thank you again!

Thank you so much sir I am not from engineering yet but I search it for my concept thank a lot....

Bernoulli's theorem CAN be applied to two particles in different streamlines provided the flow is irrotational.

If the particles don't reach the trailing edge at the same time, doesn't that mean there is a discontinuity in the flow or flow separation?

Thanks dude for the description

Thanks for making this video....otherwise I would have believed myself to be stupid my entire life...you are the best.

my whole life is a lie...

A video that does a great job at explaining why one system doesn't work, but totally fails at explaining why another does work. Fantastic.

great explanation!

awesome, really cool video.

As you get closer to the upper surface of the wing, the acceleration of the air is increasing due to conservation of angular momentum.

India waalein like thoko yaha saala 11th mein hi jee ke liye ye sab padha Diya tha.Damn we are ahead of the curve.but anyway this video was so much better than teacher explanation though

thank you so much sir , i understand very well

The air doesn't move past the wing, the wing moves past the air. The air particles only move up and down, not left to right. The air particles above the wing move farther than below the wing from their original position, and are pulled downward as the wing passes the particle by the Coanda effect. The air is not moving fast or slow, it is stationary.

The speed of air is higher at the top of the wing and slower at the bottom, as the speed of a fluid increases it’s pressure decreases, so that the pressure at the top is lower so the lift is created

Hey, I think flow separation also might cause lift. when flow past the upper layer of foil and curvature is quite large in that flow separation might take place at lower portion of foil. Thus causing vacuum in that region. thus ultimately leading to pressure gradient and upward lift.

This video was great! Most videos fail to address any misconceptions surrounding lift and you hit one of the larger ones on the spot, that being the equal time transit fallacy. The CFD diagrams and streamline demonstrations really help with understanding the material as these things can be difficult to visualize. However, your reference to the Coanda effect was incorrect as this phenomena only applies to jet flows, which are usually not present in standard airfoil flow. Great video and keep it up!

Great video guys!

"We know in a curved flow outside pressure should be larger" Why? "Outside" with respect to what?

98 people applied Bernoulli's equal time equation incorrectly

Really thank you.

the video was extremely useful...please,make more interesting videos

4:24 why does pressure increase towards the bottom of the wing?

The answer is simple: REASONS!

Great video. Congratulations.

wowww....Thank you for sharing.

Sorry, there is no explanation to be found here. "curvature leads to pressure difference" - that is not explained.

How planes can still fly upside down then?

wow its amazing sir

Thanks for the video

whole aeroplane body is an airfoil structure pressure below the aeroplane is more compared to pressure above the aeroplane hence lift

The water running over the bottle isn't surface tension? Also I don't get this diagram at 4:23, if equilibrium goes from High to low, why does your diagram point the opposite direction? If there's high pressure above the wing, and low below the wing, wouldn't that push the wing down and thus the entire plane with it, since the plane is attached to the wings? 4:51 This airfoil-profile example would be better if it was upside down, that blunt-face at the bottom would be better at the top. I believe(haha) that a higher camber would be better/make sense to be applied at the top of a wing than the bottom. Otherwise it's almost like an upside-down flat-bottom airfoil. I think overall the lift-factor comes from deflecting air-downwards not because of "coanda effect" but just by pushing the air downwards like a ramp pushes something upwards, the airfoil/tear drop shape is to reduce drag. edit: yeap and apparently what I said is wrong (of course) www.grc.nasa.gov/www/k-12/airplane/wrong2.html I am not aerospace engineer. I'm probably wrong I suppose. Although I've built a lot of model planes, have obsessed about aviation, read/watched a lot of material but I will admit I still can't mathematically or even verbally explain lift to prove that I can lift something. I only work with a "known good airfoil shape" wing loading, and watts/lb rating to make sure something flies. But then again these are just toys and I am not an aerospace engineer.

I love the way this channel dont show any annoying adds or stupid intro

BROOO!!! THIS VIDEO LITERALLY CLEARED ALL MY DOUBTs, I used to keep wonder how how how, and now this finally all made sense tysm,mgby

You lost me at 4:10 to 4:25. The video seems to be contradicting yourself. Pout > Pin for the top, but it is the opposite for the bottom of the foil. Also, in the example given, the curvature at the top is greater than the curvature at the bottom, so according to their own explanation, there should be a net downforce on the wing. Can someone help me understand? Other than the angle of attack, why is the pressure greater at the bottom? Is it just because the pressure drop at the top is greater than the pressure drop at the bottom (so the bottom of the wing is closer to atmospheric)? Thanks.

But then why does my flat winged planes fly? Shouldn't the air travel on both sides of the wings at the same rate thus creating no lift. Now I know that you are likely going to say that the wing being tilted up will generate lower pressure at the top. But still... this has bothered me.

thanks, needed this for my essay

Well done ❤