Physics in a Minute: How wings really create lift

How does air flow across a wing to generate lift? Since a wing's top surface is curved, it covers a greater distance compared to the flatter bottom edge. A common explanation is that air moves faster over the top so that it reaches the end of the wing at the same time as the bottom flow, lowering the pressure on the top surface.

But this pressure explanation is just a myth, explains Holger Babinsky, professor of aerodynamics at the University of Cambridge. In an attempt to debunk the misconception, he filmed pulses of smoke flowing around an aerofoil. He pauses the motion in the video to show that the transit times over the top and bottom are not equal. The lines of smoke from the top have already surpassed the bottom ones once they reach the wing's tip.

Babinsky explains that, although lift is caused by a pressure change between the top and bottom surfaces, it's due to the change in the shape of the air flow, rather than its speed. "This is why a flat surface like a sail is able to cause lift," he says. "In this case, the distance on each side is the same but it is slightly curved when it's rigged, acting like an aerofoil."
New Scientist TV (c)

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[haic83]

In summary, this "wing" in question is hardly an airfoil being nearly symmetrical on both sides. It's at an absurd angle of attack and not terribly by from stalling, thus there is a pressure buildup on the bottom as a direct result. Furthermore the increased speed differential between upper and lower flow increases the pressure difference and creates even more lift even though it's also substantially increasing drag.

[haic83]

Who is the self confident yahoo that analyzed and voiced this video? Clearly does not have an understanding of aerodynamics and flow properties. I'd state all the errors in OP's deductions, but there are plenty of comments correctly correcting him already in the original post by user CambridgeUniversity!?!?

[everinterested]

Why is aerfoil more efficient? it is better streamlined, an elongated, and distorted, teardrop shape.

[everinterested]

Further comment. Could somebody please explain in simple way why airflow heading towards the undersurface streams upward to join the airstream above the wing? The air heading to the rounded blunt leading edge of the wing ought to be divided into two streams at the pint of the wing: the watershed, but this is not what happens. Why???????

[everinterested]

This shows flow above wing to be faster; below, slower. Is this not wat is to be expected from first principles? Air under increased pressure decreases in volume, so will move slower. Convers, air under reduced pressure. Air stream reducing in pressure will increase speed. Air stream increasing in speed will exert less lateral pressure. All these are pretty much the same thing; all lead to increse speed with decreased pressure and vice-vers.

[Climaticsman]

@davidmpearce1 Hi David, thinking about the Formula One car, when we see them racing in wet conditions the spray plume demonstrates what happens to the air over the rear spoiler - whether the effect is cauesd by the upper or lower surface is unclear to me, but there is a definite net uprush of air, gaining a downwards reaction on the car. But it is the forwards motion (thrust) of the car producing this downwards force (also thrust, in my opinion), since the secondary resultant is drag hence DRS

[Climaticsman]

@davidmpearce1 Hi David, thinking about the Formula One car, when we see them racing in wet conditions the spray plume demonstrates what happens to the air over the rear spoiler - whether the effect is cauesd by the upper or lower surface is unclear to me, but there is a definite net uprush of air, gaining a downwards reaction on the car. But it is the forwards motion (thrust) of the car producing this downwards force (also thrust, in my opinion), since the secondary resultant is drag, hence DRS

[locky0803]

@wbeaty Sorry, my bad. Thinking that lift results from two separate principals is indeed incorrect. I understand a flat wing, and a cambered wing lift in the same way - although with different efficiencies. I suppose what I really meant is that this video is really stating the obvious (and something that's been known for a long time). A video showing an asymmetrical airfoil in kutta condition, describing why it is more efficient than a flat wing would in my opinion be much more informative.

[Climaticsman]

@davidmpearce1 Hi David. I am rapidly coming to the conclusion, literally in the last day or two, that we specifically should not separate thrust and lift. They are both thrust, but often in different directions. A rocket flies, yet employs only thrust. A glider has no thrust and always goes downwards. Climb is the word we need, I think, and that is only ever achieved by thrust. A glider may go up briefly due to kinetic energy, converting speed to height, but thats a different matter.

[davidmpearce1]

@Climaticsman We need to separate thrust from lift. Take a racing car. The curved top produces lift, which reduces the grip of the rear tyres. The spoiler fin breaks the air flow at the back of the car, and restores the grip. There is very little air passing under the car - they fit an air dam at the front to prevent this. So the lift has to come from the top.