What is Brenulies Principle?

Someone posted about it in another thread but no details were given.

I'm not 100% sure but I think its this “Bernoulli's Principle” ?

http://www.mste.uiuc.edu/davea/aviation/bernoulliPrinciple.html

Good job, and an excellent link.

Hey, thanks for bringing this up - this ties in perfectly with an explaintion of the physics of rotary aircraft I was writing something on. Here it goes, just dont mind the stuff bout choppers in the begining:

The principles found in rotary aircraft are in fact the same principles that would be found on any fixed wing aircraft - namly Bernoulli's theory. This theory suggested and now explains how if you have an airfoil in which it take longer to travel aross the top than it does the bottom, it will generate lift. Now, to briefly explain this theory of lift (Bernoulli's Principle), let me tell you this: First off, theres this thing called air pressure, were air molecules are bouncing around everywere. All the time you are under a great amount of air pressure that, in fact, holds you together. But, when air starts moving, the air molecules become more 'busy' with moving in the direction there being blown than they would just sitting there. So, to take advantage of this, you can generate an 'Airfoil' which is a object that, when blown through air, causes the air beneath it to move slower than the air above it, which means the airfoil is receiving more upward pressure than it is downward, since the air on top of the airfoil is busy trying to make its way over the 'Camber' or curvature in the wing. These differences in air pressure cause the airfoil (or Wing) to be lifted upward (in a direction 90 degrees realitive towards were-ever the wings are going).

Ptotal=Pstatic+½RO*V²

V-sub-2 or V-squared? And are any of 'em vectors?

Heh..... I found another way to waste MY time!!! And yours as well!

V squared and scalar.


and works only for low speeds, that is below 250kts which is considred incompressible flow.

Alrighty then. Thanks.

Mine own explanation of Bernoulli's principle:

Try to imagine an airplane's wing. The top is curved, the bottom flat. As the wing gets forced through the air, air gets forced over the wing. But under the wing, nothing happens.

The air going over the wing is squeezed between the air above it (which doesn't move) and the curved surface below it (the wing). Squeezed, it moves. Fast. The faster air moves, the thinner it gets, and, by the way, the colder it gets. That's how a refrigerator works. It has Freon, which it moves speedily and which therefore cools down. Fans work the same way.

The cold, thin air moving over the wing 'spends' its energy on moving faster. Remember, energy is never lost or gained. Except for exceptions, like matter-antimatter reactions and stuff. But no matter-antimatter reactions are happening here.

So the energy has to come from somewhere. That energy comes from the air pressure! Also from heat. So the air above the wing cools down, looses pressure, and speeds up all at the same time.

At the same time, the air below the wing is speeding up alot less than the air above the wing, since it has less length to travel (the top being curved).

So you have low pressure above the wing, high pressure below, and so the wing is pushed upward by the high pressure below!

Bernoulli's principle has very little to do with actual wing lift. Sure, it's there, but most planes would shed wings if they were to rely on the pressure differential. The difference in flow length for regular GA airfoils are around 10%, more exotic foils may have equal lengths or even longer flow on the bottom.

Unfortunately, if the air directly above the wing was "squeezed" as you suggest, that would logically create a high-pressure zone, causing any airfoil-shaped object to fall like a rock.



Speed is energy, speed creates friction, which itself generates heat. Stuff moving fast gets hotter, not colder. Stuff expanding gets colder. Fans work by causing the sweat that naturally accumulates on our skin to gain energy (due to the friction of the air molecules on the sweat molecules) and evaporate, taking energy from our bodies with them, thus cooling us off. This is why if you stand out in a high wind for an extended period of time, your skin dries out and you get "windburned"



Actually, even then the total energy level of the universe doesn't change, the energy merely changes states: E=mc^2. Energy and mass are interchangeable. You're not only made out of stardust, but starlight as well.



That part basically describes Bernoulli's principle.

However, I greatly prefer the physical description posted earlier in this thread.

1) It depends how you define squeezing. I didn't mean compressed. I mean the air above the air moving over the wing isn't bumped upward.
2) Never criticize me. I have a fragile ego.
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1) Okay. Your rephrasing works. Barely. (just kidding -- that definition works.)

2) I'm not criticizing you, friend. Just correcting. Criticism is useless, but corrections are a part of skepticism and the scientific method.