how does an airplane stay in the air?

Question

it weights a lot, how come that huge thing can stay in the air and i cant fly like superman :(

Answer 1

Not to be rude, but most people in this forum are wrong. Lift generated by a wing is a combination of Bernoulli's princible and fron Newton's second law. Most of these explanations were probably taken from a high school physics text book. These are wrong and many of us aerospace engineers consider it a big problem.

People think that since the top of the wing surface is longer, the air particles have to travel faster to "meet up" with the ones below the wing, called the "equal transit theory". This is completely wrong. There is no reason why the air has to meet up with itself at the same time. As my aerodynamics professor once said "It's not like the air particles are quantum entangled".

In fact, if you look at wind tunnel tests, the flow does not behave like how people have been describing. It does not meet up with itself.

Basically, most wings have curved shapes which help create the pressure distribution that many people have stated. However, if you do the calculations on a real wing, it is much much much less than what is required to lift an aircraft.

In fact, most commercial aircraft such as Boeing's, Airbus's actually have a LONGER bottom surface to the wing! This is due to some complex aerodynamic issues that I won't discuss here.

Another piece of evidence: many aircraft have nearly symmetric wing cross sections! (many stunt aircraft) If they have such cross sections, how in the world do these fly?

The real reason for the shape of the wings is the fact that these shapes TURN the air downwards which generates a force. This is where Newton's 2nd law comes in. We are pushing the air downwards, thus we are creating a force pointing up.

Of course, in order to turn the air this way, there is a pressure distribution along the surface of the wing that helps "pull" the airflow down. This pressure distribution also helps out the lift a bit.

If you still don't believe me, here are some NASA articles on it:

Correct:
http://www.grc.nasa.gov/WWW/K-12/airplane/right2.html
http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html

NASA explains the Incorrect "theories":
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong2.html
http://www.grc.nasa.gov/WWW/K-12/airplane/wrong3.html

Answer 2

It's all based on thrust and the shape and length of the wings. Aircraft wings are shaped so that the upper surface has more surface area than the bottom surface. When air runs over the surface of the wing, the air pressure on the bottom is greater than on the top. This creates lift. The shorter the wing, the more thrust is required to create the lift. The weight of the aircraft also is a factor. The more weight you are trying to get in the air, the more wing and/or thrust that needs to be generated. Fighter jets have less wing for streamlining purposes. This means that a great deal of thrust and forward speed is necessary to get the necessary airflow over the available wing. Super large jets just add more wing until the numbers are right. What is truly amazing is the strength of the wing structure. Humans do not possess the wing to weight ratio necessary to produce lift nor the thrust necessary. The shape of the arms is also not right to promote lift. The human body is aerodynamic however. Ask any experienced skydiver about how they fly their body. In freefall, the body can be accelerated from around 120 mph to over 200 mph. Horizontal speeds of around 60 mph can also be achieved. The thrust in this case is cause by the freefall. If artificial thrust could be used and the shape of the arms could be modified, who knows....

Answer 3

A concept called the Bernoulli Principle is at the heart of all flight. This principle accounts for the three aspects of flight: lift, thrust, and drag. Obviously, the engine for a large jet is powerful enough to create the necessary thrust needed to force the plance off of the ground and continue forward. And, an airplane is made aerodynamically-sound so that it can reduce drag and make its flight easier. Yet, an airplace retains airborne through the lift created by the wings. An airplace wing is curved on the top, and flat on the bottom. The curved top forces air flying over the wing in flight to move faster, making air pressure on the wing top spread out and put less force on the top of the wing. The flat wing bottom does the exact opposite, causing air to move slower, remaining more concentrated, and thus, creating the stronger air pressure force to lift the plane up, outweighing the weak force on the wing top. You cannot fly for the three reasons mentioned above. A human being is not aerodynamically-sound, doesn't have quality wings, and cannot create nearly enough thrust to even push you off of the ground for long amounts of time. Keep in mind that these are the very basics of flight, and a number of smaller principles come into factor. But, I'm positive these concepts should answer your question.

Answer 4

Several responders have noted the Bernoulli principle, claiming that that principle (based on the longer path length across the top of the wing as compared with the bottom) is what makes airplanes fly. Not so; if it were true:
- Helicopters could not fly: they have (for technical reasons) symmetrical airfoils on which the distance across the top is the same as the distance across the bottom.
- The Wright Flyer could not fly: it had a single-surface wing, so the distance across the top is the same as the distance across the bottom.
- Airplanes could not fly upside down. (The record endurance for inverted flight is over 4 hours; the flight ended because the pilot ran out of endurance.)
So, if not Bernoulli, what? The non-zero angle of attack of the airfoil deflects the impinging airstream and deflects it downward, imparting a downward momentum to it. By Newton's third law, there must be a corresponding upward momentum imparted to the airfoil. It's called lift. There is, of course, a pressure difference between the top and bottom surfaces of the wing, and it turns out that the reduction of pressure on the upper surface is somewhat more than the increase of pressure on the lower one; this arises, of course, because the air that would be pressing on the top of the wing were it standing still has been shoved out of the way by the wing's leading edge.
My Cessna 172 has wings of typical shape, on which the distance along the top surface is about 1.5% longer than the distance along the bottom. This does provide some Bernoulli lift, but calculation shows that it is only about ten percent of the total lift. A Cessna Aerobat, with a similar wing, will happily fly upside down; since in that configuration the Bernoulli lift is working against you instead of for you, the angle of attack has to be slightly increased to maintain level flight at the same airspeed.
If you still have doubts, stick your hand out the window of a moving car and have it make like an airfoil. You can get lift, and obviously Bernoulli has nothing to do with it.

Answer 5

The wings of the plane are shaped so that the air going over it has farther to travel and is going faster then the air below it. Since more energy is going into moving the air on the top of the wing than the bottom there is less energy to push on the wing. The pressure on the top of the wing is less than on the bottom causing a net force or a push upwards.

The best example is try blow between two pieces of paper. Contrary to what most people would expect the pieces are pushed together instead of apart. This is because the air is moving faster between the two pieces causing a lowering of pressure making the air on the outside press in.

Answer 6

The shape of the plane and especially the shape of its wings is how it stays in the air. As it moves forward, the wing "cuts into" the air in front of it. Since it is a longer distance for air molecules to go over top off the wing than it is for the ones that go under, the air pressure above the wing is much lower than that below it. That creates lift (by "sucking" the wing upwards.)

If the airplane stopped suddenly, it would have no lift, and would fall down.

Answer 7

B/c the airplane creates enough lift and/or thrust to exceed it's weight/gravity. You can't fly b/c you have nothing that can create enough lift to lift you, and superman sucks.

Answer 8

pressure, shape of wings, see bernoulli's principle