what is the physical principal of lift?

Answer 1

Brendan B is a little confused. He is dead on about the bottom of the wing, the angle of the wing into the wind does cause stagnation on the bottom of the wing. The top of the wing, however, is the more important part. The top of the wing actually accelerates the flow up and over itself, causing a drastic drop of pressure starting at the rounded leading edge (as the air encounters the leading edge its forced to turn upwards over the wing, but the rest of the air forces the wind to move at the same speed horizontally, so the air goes much faster then it would have normally). The airflow is then turned parallel to the wing, directing the flow downwards, as the other explanation above said. If you were to measure the flow of air downwards from the wing, you would have a very good way of quantifying the lift of the wing.

So we have air on the bottom being slowed causing high pressure, and being turned downwards, along with much faster moving air along the top of the wing causing low pressure, also being turned downward.

The Bernoulli myth is dead wrong, however Bernoullis principal is dead on. The air along the top of the wing goes much faster then the air on the bottom of the wing, so much faster that the particles are no where near each other if you were to trace it.
Bernoulli's principal states that the faster air moves along a streamline, when no work is applied to it, the lower its static pressure is.

Answer 2

Wow, did you get some wild answers. Old B said that the faster air travels the lower its static pressure. Wings are made to stretch the air over the top of the wing making it go faster than the air on the bottom of the wing. This means the static pressure is lower on the top. The difference gives you lift per unit of area of the wing. To demonstrate this you can do some experiments. 1 take a beach ball and a leaf blower and put the ball in the air stream blowing out. Make sure to point it upwards. The ball will stay in the middle of the air stream. If it tries to go off to one side the air will go faster in the middle and draw the ball back to the middle. 2 Make a 15 " collar out of cardboard to go on the end of the leaf blower that blows out. Star cut out the middle and make the points turn down so that you can duct tape the stars to the leaf blower and have the collar level with the outlet of the blower. Now cut a similar circle out of cardboard and put a 12 inch dowel in the middle of it. Secure the dowel with some wrapped rubber bands so the dowel will stay in one position. Then turn on the leaf blower and put the dowel in the end of the tube where the air comes out. First the cardboard will try to blow away. But as you bring the two circles together they will suck together. The fast moving air is creating a below atmospheric pressure and bringing them close together.

Answer 3

It's all Newton's law. For something to stay in the air, you have to push an equivalent amount of air downward. Here's a lengthy definition which shoots down the Bernoulli myth. If Bernoulli's principle applied, the plane could never fly upside down or wing over wing. Watch an aerobatic show and you see planes can fly both ways.

http://www.allstar.fiu.edu/aero/airflylvl3.htm

Answer 4

Bernoulli's Principle: Air flowing past a wing, bottom of the wing interferes with the flow, top does not. You create an air 'build up' beneath the wing (high pressure) while air flows smoothly over the top of the wing (low pressure). High pressure underneath and low pressure on top --> pressure difference creates an upwards force, lift.