Technology

Learn How Airplane Wings Really Work in This 1 Minute Video

You may have been told, that airplanes are lifted because the air flowing over wings has a longer distance to travel and moves faster to keep up with the air underneath the wing. If this is what you believe, you are wrong — at least to an extent.

A University of Cambridge professor is setting the record straight for this misconception, which he says has been around for decades but he doesn’t know quite how it originated.

Watch as aerodynamics expertÂ Holger Babinsky from the university’s department of engineering explains how the wings really lift the airplane:

As the video shows, it is true that the air on the top of the wing does move faster, but it doesn’t reach the end of the wing at the same time as the air traveling under the wing. Below are screenshots from the video showing this:

Gizmodo reports Babinsky’s explanation:

What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes â€” lower pressure on the upper surface and higher pressure on the lower surface. This is why a flat surface like a sail is able to cause lift â€” here the distance on each side is the same but it is slightly curved when it is rigged and so it acts as an aerofoil.

So, it’s all about curvature, not distance.

• Phantom II
Posted on January 26, 2012 at 6:20pm

Well, this has been long taught at flight schools that the differential pressures on the upper and lower surfaces of a wing causes lift. This is not true. Bernoulli Principle claims that the velocity of the airflow over the curved upper surface accelerates to meet the airflow of the flatter bottom surface at the trailing edge at the same time and this causes the pressure difference. So how would one explain inverted flight then? Mmmm. A Cessna 172 would have to taxi at about 300 mph to create enough lift for the little pane to take off. Since compressibility begins at about 250mph on a standard day the airspeed would be measured by Mach ratios, 0.3Mach in this case. The video shows subsonic flow so that’s where I will confine my observation. Now if you introduce 4′ angle of attack at 60 mph, the little plane will jump into the air. What happened? Well Newton’s 3 laws of motion, that’s what. Changes in the airâ€™s momentum will result in forces on the wing. To generate lift a wing must divert air down; lots of air. That means, if one sees a bend in the flow of air, or if air originally at rest is accelerated into motion, there is a force acting on it. Newtonâ€™s third law states that for every action there is an equal and opposite reaction. The lift of a wing is equal to the change in momentum of the air it is diverting down. Momentum is the product of mass and velocity.

• Phantom II
Posted on January 26, 2012 at 6:22pm

This downward velocity behind the wing is called “downwash”. Both the increase in the speed and the increase of the angle of attack increase the length of the vertical arrow. It is this vertical velocity that gives the wing lift. The greater the angle of attack, the greater the vertical velocity. Likewise, for the same angle of attack, the greater the speed of the wing the greater the vertical velocity. What the wing does to the air is the action while lift is the reaction. The bending of the air is the action. The reaction is the lift on the wing. If we estimate that the average vertical component of the downwash of a Cessna 172 traveling at 110 knots to be about 9 knots, then to generate the needed 2,300 lbs of lift the wing pumps a whopping 2.5 ton/sec of air! If a plane were to fly over a very large scale, the scale would register the weight of the plane. The amount of air pumped down for a Boeing 747 to create lift for its roughly 800,000 pounds takeoff weight is incredible indeed. When the tower advises you to allow for wake turbulence from the plane in front of you either in take off mode or on final to land, by all means, distance yourself acordingly.

• Tracy Y. Andersen
Posted on January 26, 2012 at 6:14pm

Look at the flow lines past the trailing edge, and notice that they are farther apart above the wing area, and compressed below the wing. This shows that air has to be displaced downward from the airfoil shape. Air has weight, and the amount (weight) of the downward displacement has to equal the weight of the aircraft, in order to support that aircraft.

The shape of the airfoil, and the angle of attack, determine the percentage of total lift that is contributed by the upper surface and the lower surface, and this percentage ratio may be varied continuously by the speed, angle of attack, and so on.

So, when you see a large hunk of airplane-shaped metal, moving through the air, realize the same weight of air is being deflected downward, supporting it.

• Earl Graystoke
Posted on January 26, 2012 at 4:04pm

Why is his final point relevant?
During the same unit of time, air/smoke travels farther above the wing than under it.
That means it goes faster above than under.
That means fewer molecules per square inch of wing surface above the wing than under.
Fewer molecules per unit of volume yields lower air pressure above than below.
Result is a comparative “suction” upward.
Plane flies.
Yay.

• fcbs46
Posted on January 26, 2012 at 11:29am

The push up or pull up debate has been around for a 100 years (or close) and as people can see it is both. Where as the air moves faster on the top or reaches the end at the same time is mute. The main thing today is with the engines we have the airplane hardly needs wings at all during take off and really only makes it more efficient to fly the thing (airplane for those in Rio-o-Linda) and land it for control. Ask any jet pilot and he will tell you that today’s planes have so much push that are almost rockets ships in the sky.

• CaptainEmeritus
Posted on January 26, 2012 at 8:56am

The wing is pushed through still air.
There is no air rushing over or under the wing.
The air is stationary.

• theninthplanet
Posted on January 26, 2012 at 9:43am

Change your frame of reference and the air is moving.

• CaptainEmeritus
Posted on January 26, 2012 at 1:15pm

Does the atmosphere when compressed, accelerated and blasted at supersonic/subsonic speeds past a fixed airfoil have the same properties as still air?

• dbk4939
Posted on January 26, 2012 at 7:15am

This is a great illustration of what we were taught years ago about how lift is created. Any surface that is flat enough will produce lift when pushed through the air with good angle of attack. The video clearly shows the angle of attack and the air moving faster over the top surface. Bernoulli’s Principle confirmed, faster air has reduced pressure so we get lift. The only difference between the hand, flat plywood, or a carefully designed airfoil is the efficiency of the process. The Wright brothers were the first to figure this out, wind tunnel testing their airfoils. They also worked out 3 axis control and the airplane was born!

• SgtB
Posted on January 26, 2012 at 9:05am

Wrong. Bernoulli’s principle is crap. Bernoulli’s principle states that faster moving air over the wing has a lower air pressure than the air under a wing. While it is true that a fast moving fluid exerts lower pressure than a static fluid, the real reason why a wing or any surface causes lift is DRAG.

When any surface is forced through a fluid at angle, it causes pressure to build on the side that is leading. Most often the leading side is the underside as people want such craft to rise and not fall. This increase in pressure is caused by the compression of the gas as it hits the surface. At the same time, the top or back side of the wing is physically causing a vacuum. It is this vacuum that causes air from over the wing to speed up. Nature hates a vacuum. So what you end up with is compressed air on one side and a vacuum on the other. Depending on the angle of the surface to the direction of travel, you can achieve anything from down force / lift to simple drag. A good example of simple drag being produced would be a semi truck. It has a zone of compressed air in front and a vacuum behind.

• Bobb
Posted on January 25, 2012 at 8:24pm

He should have attended my classes on Aerodynamics and Theory of Flight years ago. Try blowing over a sheet of paper draped over your fingers…………..LIFT!

• Gary747
Posted on January 25, 2012 at 8:11pm

This is simplistic and still validates that air on top of the wing moves faster than the air on the bottom. Everyone recognizes that Angle of Attack (AOA) and airspeed also provide a large amount of lift. That’s how symetrical wings work on aerobatic airplanes… they have the same curve (shape) on the top and bottom of the wing. Heck, a sheet of plywood could be used as a wing, but would have very low AOA capability and horrible handling qualities. A child can discover this when they place their flat hand out of the window of a car moving at a good clip, and change the angle into the slipstream. Their hand “flies” up as they increase AOA, then suddenly the airflow trips and their hand moves back with the rapid increase in drag. They just stalled their hand! But a vector of this drag force also contributes to lift. The game is to change the angle of their hand just to the point where the lift to drag ratio peaks, A wings lift is a combination of the lower pressure on top of the wing (as the video shows) and the force of impact air striking the bottom (can also be seen in this video)

• wildbill_b
Posted on January 25, 2012 at 7:43pm

Good grief. It is http://en.wikipedia.org/wiki/Bernoulli%27s_principle . Used to be like 8th grade science. Now the man claims it is a mystery to most people. LOL

• Stu D. Baker-Hawk
Posted on January 26, 2012 at 9:23am

Unfortunately, for the generation up and coming it IS a mystery. I’ve never seen a dumber group of young people than today’s product of the American education system. Very sad.