How do Wings generate LIFT?

Have you ever thought how wings of an aircraft work? How do they produce incredible amount of lift? Airfoil technology helped human beings to fly. Airplane wing works due to the interesting fluid mechanics behind the airfoils. Wind Turbines, gas turbines and hydraulic machines, all work on the principles of airfoil. This video will unveil the physics behind the simple shape that revolutionized the engineering world.

Working of airfoil is explained here with help of Coanda effect and flow curvature principle. The drawback of argument based on Bernoulli's prinicple demonstrated here both experimentally and theoretically.

[Lesics]

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[EASYTIGER]

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!

[sabinav]

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

[jessewagner]

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

[gksalf]

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

[Ma-tvqs]

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.

[HatimMech]

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.

[KevinChen]

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!

[millionpercocetplease]

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!

[TheGoldenLizard]

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

[icrazyfish]

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.

[markwaddell]

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.

[eheking]

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

[adhithasimhanraghavan]

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 ;)

[boston]

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

[zsolezk]

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

[Dilidjent]

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

[justcarcrazy]

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

[vonmilash]

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

[tacitdionysus]

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'.