What makes wings work

As air flows over the surface of a wing, it sticks slightly to the surface it is flowing past and follows the shape. If the wing is angled correctly, the air is deflected downwards. The action of the wing on the air is to force the air downwards while the reaction is the air pushing the wing upwards.

Both the upper and lower surfaces of the wing act to deflect the air. The amount of lift depends on the speed of the air around the wing and the density of the air. Speeding up means the wings force more air downwards so lift is increased. Increasing the angle of attack means the air flowing over the top is turned downwards even more and the air meeting the lower surface is also deflected downwards more, increasing lift. There is a limit to how large the angle of attack may be.

If it is too great, the flow of air over the top of the wing will no longer be smooth and the lift suddenly decreases. Birds and planes change their angle of attack as they slow to land. Their angle of attack is increased to ensure their lift continues to support their weight as they slow down. Wings and tails need to be movable so that their shapes can be changed to control their flight. To understand this principle, we need to understand air pressure. Air is composed of several invisible gases that have mass.

This mass is made up of molecules, moving in rapid random motion, and exerts a force called air pressure. We are unaware of this pressure because it is evenly pressing all around us. If the air pressure is not even, the greater pressure pushes an object in the direction of the weaker or lower pressure. In , Bernoulli found that, when a gas like air moves, it exerts less pressure. Normally, air moves along smoothly in streams, but airflow is disturbed when a wing moves through it, and the air divides and flows around the wing.

The top surface of the wing is curved aerofoil shape. The air moving across the top of the wing goes faster than the air travelling under the bottom. In other words, air below the wing pushes on the wing more than air above the wing. When the rudder is turned to one side, the airplane moves left or right. The airplane's nose is pointed in the same direction as the direction of the rudder.

The rudder and the ailerons are used together to make a turn. The pilot controls the engine power using the throttle. Pushing the throttle increases power, and pulling it decreases power. The ailerons raise and lower the wings. The pilot controls the roll of the plane by raising one aileron or the other with a control wheel. Turning the control wheel clockwise raises the right aileron and lowers the left aileron, which rolls the aircraft to the right.

The rudder works to control the yaw of the plane. The pilot moves rudder left and right, with left and right pedals. Pressing the right rudder pedal moves the rudder to the right. This yaws the aircraft to the right. Used together, the rudder and the ailerons are used to turn the plane. The elevators which are on the tail section are used to control the pitch of the plane.

A pilot uses a control wheel to raise and lower the elevators, by moving it forward to back ward. Lowering the elevators makes the plane nose go down and allows the plane to go down. By raising the elevators the pilot can make the plane go up. The pilot of the plane pushes the top of the rudder pedals to use the brakes. The brakes are used when the plane is on the ground to slow down the plane and get ready for stopping it.

The top of the left rudder controls the left brake and the top of the right pedal controls the right brake. If you look at these motions together you can see that each type of motion helps control the direction and level of the plane when it is flying.

Sound is made up of molecules of air that move. They push together and gather together to form sound waves. Sound waves travel at the speed of about mph at sea level. When a plane travels the speed of sound the air waves gather together and compress the air in front of the plane to keep it from moving forward.

This compression causes a shockwave to form in front of the plane. In order to travel faster than the speed of sound the plane needs to be able to break through the shock wave.

When the airplane moves through the waves, it is makes the sound waves spread out and this creates a loud noise or sonic boom. The sonic boom is caused by a sudden change in the air pressure.

When the plane travels faster than sound it is traveling at supersonic speed. A plane traveling at the speed of sound is traveling at Mach 1 or about MPH. Mach 2 is twice the speed of sound. Sometimes called speeds of flight , each regime is a different level of flight speed.

The fallacy here is that there is no physical reason that the two parcels must reach the trailing edge simultaneously.

And indeed, they do not: the empirical fact is that the air atop moves much faster than the equal transit time theory could account for. It involves holding a sheet of paper horizontally at your mouth and blowing across the curved top of it.

The page rises, supposedly illustrating the Bernoulli effect. The opposite result ought to occur when you blow across the bottom of the sheet: the velocity of the moving air below it should pull the page downward. Instead, paradoxically, the page rises.

On a highway, when two or more lanes of traffic merge into one, the cars involved do not go faster; there is instead a mass slowdown and possibly even a traffic jam. That lower pressure, added to the force of gravity, should have the overall effect of pulling the plane downward rather than holding it up. Moreover, aircraft with symmetrical airfoils, with equal curvature on the top and bottom—or even with flat top and bottom surfaces—are also capable of flying inverted, so long as the airfoil meets the oncoming wind at an appropriate angle of attack.

The theory states that a wing keeps an airplane up by pushing the air down. The Newtonian account applies to wings of any shape, curved or flat, symmetrical or not. It holds for aircraft flying inverted or right-side up.

The forces at work are also familiar from ordinary experience—for example, when you stick your hand out of a moving car and tilt it upward, the air is deflected downward, and your hand rises.

But taken by itself, the principle of action and reaction also fails to explain the lower pressure atop the wing, which exists in that region irrespective of whether the airfoil is cambered.

It is only when an airplane lands and comes to a halt that the region of lower pressure atop the wing disappears, returns to ambient pressure, and becomes the same at both top and bottom. But as long as a plane is flying, that region of lower pressure is an inescapable element of aerodynamic lift, and it must be explained. Neither Bernoulli nor Newton was consciously trying to explain what holds aircraft up, of course, because they lived long before the actual development of mechanical flight.

Their respective laws and theories were merely repurposed once the Wright brothers flew, making it a serious and pressing business for scientists to understand aerodynamic lift. Most of these theoretical accounts came from Europe. In the early years of the 20th century, several British scientists advanced technical, mathematical accounts of lift that treated air as a perfect fluid, meaning that it was incompressible and had zero viscosity. These were unrealistic assumptions but perhaps understandable ones for scientists faced with the new phenomenon of controlled, powered mechanical flight.

These assumptions also made the underlying mathematics simpler and more straightforward than they otherwise would have been, but that simplicity came at a price: however successful the accounts of airfoils moving in ideal gases might be mathematically, they remained defective empirically.

In Germany, one of the scientists who applied themselves to the problem of lift was none other than Albert Einstein. Einstein then proceeded to give an explanation that assumed an incompressible, frictionless fluid—that is, an ideal fluid.

To take advantage of these pressure differences, Einstein proposed an airfoil with a bulge on top such that the shape would increase airflow velocity above the bulge and thus decrease pressure there as well. Einstein probably thought that his ideal-fluid analysis would apply equally well to real-world fluid flows. He brought the design to aircraft manufacturer LVG Luftverkehrsgesellschaft in Berlin, which built a new flying machine around it.

Contemporary scientific approaches to aircraft design are the province of computational fluid dynamics CFD simulations and the so-called Navier-Stokes equations, which take full account of the actual viscosity of real air. Still, they do not by themselves give a physical, qualitative explanation of lift. In recent years, however, leading aerodynamicist Doug McLean has attempted to go beyond sheer mathematical formalism and come to grips with the physical cause-and-effect relations that account for lift in all of its real-life manifestations.

McLean, who spent most of his professional career as an engineer at Boeing Commercial Airplanes, where he specialized in CFD code development, published his new ideas in the text Understanding Aerodynamics: Arguing from the Real Physics.

Considering that the book runs to more than pages of fairly dense technical analysis, it is surprising to see that it includes a section 7. I was never entirely happy with it. Where these clouds touch the airfoil they constitute the pressure difference that exerts lift on the airfoil. The wing pushes the air down, resulting in a downward turn of the airflow. In addition, there is an area of high pressure below the wing and a region of low pressure above. It is as if those four components collectively bring themselves into existence, and sustain themselves, by simultaneous acts of mutual creation and causation.

There seems to be a hint of magic in this synergy.