It is often said that the lift on a wing is generated because the flow moving over the top surface has a longer distance to travel and therefore needs to go faster. This common explanation is actually wrong.

If you really want to know what is happening look up Doug McLean on YouTube and watch his lecture at Michigan on aerodynamics

thanks for the share

"The 'longer path = must go faster to meet at trailing edge' myth is wrong. No law says air parcels must reunite at the same time. In reality, top air moves much faster & arrives earlier. It also fails for symmetric wings, flat plates, or inverted flight. Real lift: wing turns air downward → pressure difference (lower on top) + Newton's 3rd law."

Lift is like life, complicated; which is why there are so many simplistic explanations. It's a classic 'the deeper you go, the harder it gets' thing. Here is a detailed walk through of the principles and forces involved. Well worth 14 mins of you time if you are interested.

Flying a flat bottom airfoil upside down will fix any incorrect notions you have lol

Well, I will try that 😄

This demonstration shows what seems to be an unusually high angle of attack. Am I wrong?

Shape of the wing matters…. if bottom of wing was flat and top curved I’d like to see the repeat slow mo

fair point

Ironically, because Bernoulli’s Principle is an actual physical law the mere fact the air moves faster above means the pressure is reduced there which will cause the wing to rise. Then the question is why does air moves faster above the wing?

the equal transit time theory falls apart the second you realize planes can fly upside down. it's all angle of attack, but the wrong version is so intuitive it's basically impossible to kill.

Faster air equals spread out air molecules, which equals lower air pressure. So there's higher pressure under, and lower pressure over, the wing. That creates lift.

Lift is caused by action and reaction. The deflection of air molecules downwards, causing lift. Bernoulli perpendicular air pressure, is a secondary resultant. RE

The "heavy lifting is simply done by deflecting the air flow downward, resulting in a reactionary upward force. A completely flat angled board would work, too.

That visual demonstrates exactly that. The angle of attack is confounding here. But even so, the air above the wing is moving faster as it’s filling the vacuum created by the wing, the air below is compressed and moving slowly. Pressure differential is created. Lift results.

OK, so are you going to give us the true explanation?

coming up in a followup post

Yes, I used to stump PhD's with this all the time. The lift is indeed from the pressure difference, but almost anything at an angle of attack makes a pressure difference. The trick (which takes hard thinking), is how does a properly shaped wing manage to make lift with little drag. The answer (which you can see in the video above) is that the nose has suction part of which is *forward*, which acts to cancel a good part of the drag.

Given the gravity of the question, I was hoping for an uplifting answer but found some of the comments to be a real drag. Still, I powered through to end.

Lift is from both the bernoulli and newton components. An airliner is more bernoulli than newton because of the larger airfoil. A fighter jet with almost no airfoil relies more on newton and this is why they require higher airspeeds to maintain sufficient lift.

The angle of the wing in this demonstration is not how a wing continuously moves through the air. This would be a demonstration of control surface - like an elevator flap or aileron - creating drag to change the direction of the plane.

Any kid who ever stuck his hand out the side window of the family car at 60 mph and tilted it at different angles knew immediately that the conventional explanation he or she got from a teacher was BS.

Let me slow this down and show you how the common explanation is wrong by demonstrating that it is correct.

So what makes it move fahstah?

😆

I haven’t seen anything here that counters Bernoulli. Ptot = Pstat + 1/2 rho V^2. In simple terms, total pressure is the sum of static and dynamic pressure terms. Total pressure does not change in a control volume without external energy. Therefore, the total pressure at the front of the airfoil must be the same at the back of airfoil (neglecting friction) site over the top of the wing must travel faster over the top, this resulting in a higher dynamic pressure above the wing and a lower static pressure. Structures only care about static pressure, and thus we have lift. If there is another principle I’m missing (backed by data) please let me know.

Years ago in my Flight Dynamics class we had a discussion about how a flat wing, with no airfoil, can also fly by simple deflection. We never found a competent explanation as to what % of lift is due to deflection vs B Principal but we all agreed that both must be involved.

Isn’t that how airplanes were designed from the start? What’s wrong with Bernoulli?

Air does have lines in it! this is AI!

Video literally says "we use smoke"

yer kiddin!

😀 smoke is used to visualize those stream lines

Firkin unbelieveable.

The simple explanation is that the air pressure below the wing is higher, and the pressure above is lower, with a minimal level of drag created.

Lift is also created by the angle of attack. Here there is about a 10 degree AOA creating deflection which causes a lift. I completely flat surface will do the same.

No, it's not you fucking retard and your video proves it!

😄 how?

Discussions of how wings work oscillate between the trivial and the incomprehensible. My current position is "If you have the right airfoil shape the Navier-Stokes equations give a flow that pushes a lot of air downwards".

Try it with a proper wing. This picture is more of a flight control connect to the back of a wing. A wing is shaped different with less of a attack angle. It should be flatter on the bottom, rounder on the top and is much more streamlined.

Just about any shape will generate lift; the airfoil is simply an optimization to reduce the drag while retaining lift. Bonus points for non-abrupt loss of lift at/near stall; a rounded leading edge helps here.

The angle of attack is too great. Near stall

Well, in reality the upper side of the airfoil (wing) generates about 2/3 of the total lift by lower pressure and lower side generates 1/3 of it by higher pressure then ambient air. The pressure differences are in fact based on Bernoulli principle and the total lift is at the same (low) speed mostly function of angle of attack, chord camber and lenght.

Bernoulli rulez Newton drools!

The correct explanation, I always had in mind... 1. Wing lift is due to Newton's third law of motion. The wing is compressing air below as it moves forward. The compressed air reacts in the opposite direction, a lift.. 2. If you see near the top of the wing, there is an instantaneous vacuum. A vacuum at the top of the wing implies -> air below the wing tries to go up, pushing the wings up.. Air molecules try to reach to that vacuum from both top and bottom. In the bottom, there is wing, the airmolecules have no other option but to take wing along with them.

The funniest part of this is all the comments talking about the “Air moving faster”… the air IS NOT moving, the wing is. The curved top of the airfoil causing the molecules to spread out reduces pressure and allows for the higher pressure underneath to LIFT the wing.