The plane truth: Scientist reveals how wings really work

[dipsydoodle]

The classic explanation of how a wing generates enough lift to keep a plane or a bird in the air is wrong, according to a Cambridge University physicist.

Many textbooks and aircraft manuals say that a wing produces lift because air travelling over the curved topside of a wing has to travel further than wind flowing around the flat underside and so has to travel faster to keep up, generating lift. But this standard explanation has been shown to be wrong by a simple experiment where a wing is placed in an air tunnel with jets of smoke flowing over the upper and lower surfaces, said Professor Holger Babinsky.

"A wing lifts when the air pressure above it is lowered. It's often said this happens because the airflow moving over the top, curved surface has a longer distance to travel and needs to go faster to have the same transit time as the air travelling along the lower, flat surface," he said.

"But this is wrong," said Professor Babinsky. "In the worst case, [this explanation] can lead to a fundamental misunderstanding of aerodynamics.".

http://www.independent.co.uk/news/science/the-plane-truth-scientist-reveals-how-wings-really-work-6294130.html

[Loudmxr]

1. I was just thinking of this last night.

First off who trusts a man named Babinsky?

It sounds what I call my Jewish cousins.

My father was born before man could fly and he lived to see men walk on the moon.

Leonardo De Vinci imagined air flight but it took a couple of hundred years for science to evolve so that it could happen.

Pride in ignorance does not advance us.

I wish conservatives understood this.

Thank you for this post I had the wrong impression too.

[RC]

2. Yeah, this has nothing to do with the wind hitting the air at an angle and

compressing the air under the wing. Sure it don't
As long as the wind is moving fast enough to compress enough air under the wing to support the aircraft, in will stay airborne.

This commenter gets it.
Ste_H
The overwhelming proportion of the lift generated in aircraft comes from the angle of attack, not the aerofoil shape. That is why a) planes can fly upside down, and b) planes with parallel wings can still fly. The lift is generated by the change in direction of the airflow. Air underneath the wing is forced downwards. To do this the wing must provide a force normal to its lower surface, which must be offset by a force acting in the opposite direction. This force then resolves into a vertical component (lift) and a horizontal component (drag).

This has been known for years. Why is there still any controversy?

[wandy]

7. Thank you. Reading the artical I thought; he's saying the same thing differently.

You're pointing out 'angle of attack', parted the curten.

[JohnnyRingo]

3. As an old R/C modeler and av buff, I thought this was the accepted explaination.

It should be evident to anyone who looks at the airfoil cross section of an aerobatic wing, like that on a Pitts Special. On a plane designed to fly inverted as well as right side up, the airfoil doesn't have a flat bottom and curved upper surface. Both surfaces are equally curved symmetrically, so it's clear that the air doesn't move further over one surface.

The reason these wings provide lift is predominately through deflection, or the angle of attack to the relative wind as the plane moves forward. The trick of the designer is to reduce the inherent drag by keeping this angle as small as they can, and provide as much lift through aerodynamics as possible by way of a lowered air pressure on the top surface. As airspeed increases, this deflection becomes less pronounced and inherent drag becomes less critical.

Thanks to Daniel Bernoulli we know that faster moving air creates a lower pressure as evidenced in a venturi. In the throat of a carburettor the diameter is reduced, causing the air to move faster through that section where the fuel jets are located. Just like in an atomizer, the lowered pressure generated by the faster moving air sucks in the fuel to the airstream. The air doesn't move further through the venturi, it travels faster. On a symmetric airfoil, a slightly increased angle causes air to move faster over the top surface to meet the air that travelled a more direct route along the bottom.

As I understand it, ideally 80% of lift is caused by deflection, and 20% is via a difference in air pressure. Indeed, one of my early models as a younger man was a flying balsa wood license plate that had no airfoil at all. This flat wing created much more drag than an aerodynamic airfoil, but with enough power even a barn door can create lift. An airfoil merely reduces this drag by creating a more efficient form of lift.

[pokerfan]

4. What am I missing?

From physorg:

It’s often said that this happens because the airflow moving over the top, curved surface has a longer distance to travel and needs to go faster to have the same transit time as the air traveling along the lower, flat surface. But this is wrong,” he explained. “I don’t know when the explanation first surfaced but it’s been around for decades. You find it taught in textbooks, explained on television and even described in aircraft manuals for pilots. In the worst case, it can lead to a fundamental misunderstanding of some of the most important principles of aerodynamics.”

To show that this common explanation is wrong, Babinsky filmed pulses of smoke flowing around an aerofoil (the shape of a wing in cross-section). When the video is paused, it’s clear that the transit times above and below the wing are not equal: the air moves faster over the top surface and has already gone past the end of the wing by the time the flow below the aerofoil reaches the end of the lower surface.

http://www.physorg.com/news/2012-01-wings.html

I'm not seeing the distinction. Air moves faster over upper surface creating a reduced pressure according to Bernoulli's principle.

[muriel_volestrangler]

10. The point is it doesn't move faster 'because it has a longer distance to travel'

There is no requirement for the a molecule of air that passes over the top to meet up with one that it was adjacent to, but that passed underneath, when they get to the trailing edge. The transit time is different. So the claim that a longer distance travelled implies a greater speed is wrong. Here, for example, is Yale getting it wrong in 1988:

The lift action of an airfoil can also be explained by Bernoulli’s theorem which states that the pressure on any fluid is least where the velocity is greatest and the pressure is greatest where the velocity is least.

The air moving over the upper surface of an airfoil is forced too travel farther, therefore velocity is increased. The increase in velocity caused a decrease in pressure. This causes lift in the upper surfaces. The air that passes beneath the airfoil has less distance to travel, this results in increase in air pressure on the lower surfaces and in decrease in air pressure on the upper surfaces. The total lift produced by the airfoil is equal to the difference downwards. The wing is said to have a relative angle of attack.

http://www.yale.edu/ynhti/curriculum/units/1988/6/88.06.07.x.html#d

[ashling]

5. I'm nor aeronautical engineer, but I used to work at a Holiday Inn Express

here is one of the comments:

As (another) Cambridge University physicist I'm not clear on the difference between what the Prof is saying and the classical explanation - perhaps he's misunderstood the classical explanation?

He agrees with the classical explanation that the upper airflow is faster, causing a pressure differential by Bernouilli's Theorem. Then he says that this is because of the wing shape rather than to 'catch up', but this is a distinction without a difference. ...

My (extremely) basic understanding was the same as the comment.

here is another comment:

Does anyone at the Independent ever read what they right (sic). What a load of piffle!
Just another scientist btw.

[bongbong]

6. Interesting

I've heard of the "debunking" of the standard airfoil theory before, but I'm frankly astounded that the True Facts about wings & lift are still in question.

As for the "new" theory being correct, it doesn't explain how sailboats can sail upwind. So, back to the drawing board, I'm afraid.

[JohnnyRingo]

8. I'm not a sailor, but I thought the same effect applies

When tacking upwind at an angle to the breeze, the properly inflated sail adopts the shape of an airfoil. The air moving faster over the outboard side produces a low pressure on that side, pulling the sailboat along forward.

The angle has to be just right and coordinated with the rudder to prevent luffing or an inefficient attack to the wind that heaves the boat over.

[HopeHoops]

9. None of it works without laminar flow. The easiest way to observe it is de-icing droplets.

I've gone through entire flights with the same droplets of that sickly pink de-icing fluid just spinning around like little ball bearings. A picture says more than a thousand equations.