Can someone explain Bernouilli's Principle to me in regards to airfoils and air(fluid) movement over them?

Answer 1

A certain amount or volume I guess of air will move from point A to point B. Simple enough. Now when the air flows around an airfoil, it still wants to flow together. So, now it has to go a little further over the rounded part of the airfoil than it does across the straight part. It therefore has to go faster in order to flow together with the part that went the shorter distance. When this happens, the air exerts less pressure on the rounded part of the air foil. Since this side has less pressure, the other side where there is greater pressure gives the air foil more push. This causes lift.

Answer 2

Previous responders give a reasonably correct view of Bernoulli's principle. However, Bernoulli's principle has very little to do with how an airplane flies. The usual explanation is that the curvature of the airfoil gives a longer path length on top of the wing than below it, so the pressure is lower on top and lift is created. There are just a few tiny flaws in this argument; if it were true:
- Helicopters could not fly -- for technical reasons, they have symmetrical airfoils.
- The Wright Flyer could not fly -- it has a single surface wing, so path lengths on top and bottom are equal.
- No airplane could fly upside down. Which, of course, is silly.
So, how does it work? The wing impacts the airstream asymmetrically: it is tilted, and the angle is called the angle of attack. This pushes on the air underneath the wing, compressing it, and steers air away from the top of the wing, reducing the pressure. Voila -- lift! The forcing of the air downward results (Newton's Third) in an upward force on the wing. You can do a little geometry and see that the lift is proportional to the sine of the angle of attack -- at angles that are not too large. However, an overly large angle causes the air to not move smoothly over the wing, and lift decreases; this is called stall.

Answer 3

Bernoulli's Priniciple essentially states that as the velocity of a fluid moving over a surface increases, the pressure that fluid exerts decreases. The general idea behind the airfoil is that the surface area on top is greater than on the bottom. Air is moving faster on top than on the bottom of the airfoil. So, the pressure that air exerts on the surface is greater on the bottom than on the top, resulting in lift. In reality, how airplanes fly is much more complex (that's why "aerospace" engineers are usually regarded as waaaaaay too smart), but this is the basic idea.

A fairly standard classroom experiment is to blow between two pieces of paper. Your breath (moving fluid) is moving at a higher velocity, thus exerts low pressure on the paper. Therefore, the paper will move together, rather than apart. The same can be done with a ping pong ball attached to a string set near flowing water from the tap. The ping pong ball will move towards the flowing water rather than away.

Answer 4

Bernoulis Theorem is a statement of the law of conservation of energy:

It states that at any point along a streamline the sum of the pressure head, the dynamic head, the potential head and pressure losses will be a constant.

This means that if the static/burst pressure reduces, the dynamic/velocity pressure increases.
On an arofoil air moves faster on top of the arofoil than under it. Therefore there is a low pressure area on top and this gives the wing lift.