Bernoulli's Principle, Busted?

[SpiceWeasel]

Stumbled across this article on "cracked".... yes it's a "comedy" website but still... very interesting. The other busted "myths" are strange too, but I couldn't pass up putting this in front of a panel of experts. The second link, below the article, goes into a lot more in-depth of an explanation as to why Bernoulli's Principle is "BS".

http://www.cracked.com/article_20669_6-ridiculous-science-myths-you-learned-in-kindergarten_p2.html

#2. Why Airplanes Fly

The Myth:

The explanation goes like this: The wings of a plane are designed in such a way that they make air travel faster over the top of the wing than under the bottom. This means the pressure over the wing is less than the pressure underneath, causing lift. It's called the Bernoulli principle, and even the pimp daddy of all nerds, Einstein himself, is said to have given it his thumbs up. Cased closed. Right?

The Reality:

Sorry to decompress your flight cabin there, Einstein, but the "differing pressures" explanation of flight isn't correct. Instead, what's really happening has a much simpler explanation -- one that you also learned in school. You see, according to a guy named Isaac Newton and his third law of motion, for every action there is an equal and opposite reaction. Therefore, if you want something to go up -- like, let's say, a plane -- then what you want to do is force air to go down and back so that the "opposite reaction" propels the object up and forward.

And that's where the shape of the wing comes in. It's true that a plane's wing must have a very specific shape -- just not the one that's postulated by the Bernoulli principle. Instead, the wing is angled so that it forces the air on top to go down toward its back end (downwash), creating upward force toward the front (upwash).

David Anderson/Florida International University

The wing generates lift not by magically manipulating air pressure, but by using basic Newtonian physics. While the Bernoulli principle is a real thing, it has very little to do with the reason mankind can spit in God's eye from his hurtling metal tubes. And nobody is quite sure why your school's science textbooks, television, and, most alarmingly of all, goddamn pilot manuals have the wrong explanation for flight. But they don't need to know why the plane flies to fly it ... r-right?

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

 

[mshunter]

Everyone knows that it's money, copious amounts of money that make airplanes fly. This was proven years and years ago.

 

[chrisreedrules]

I'll teach it however the FAA wants it taught. They say Bernoulli, I say Bernoulli.

 

[Cory Trevor]

I'll teach it however the FAA wants it taught. They say Bernoulli, I say Bernoulli.

The new PHAK really seems like it is pushing the circulation theory

 

[Jimflyfast]

The new PHAK really seems like it is pushing the circulation theory

you mean the one that real aerodynamicists have been teaching for 80 years?

 

[TWP]

My inflated ego and undeserved sense of self satisfaction keep the plane aloft. Also my insane amount of "humbleness".

 

[Cory Trevor]

you mean the one that real aerodynamicists have been teaching for 80 years?

Yeah, that one. I hadn't seen it mentioned at all in the previous PHAK that I had, but when I bought a new one for my CFI I noticed they added it

 

[FlyingPoke]

I always taught both principles, since both are applied in wing aerodynamics.

 

[chrisreedrules]

I teach 1) Newton, 2) Bernoulli, and 3) Magnus Effect... My PHAK is a couple years old but those are what is in it for lift. Maybe I should check out an updated one.

 

[Screaming_Emu]

PFM

 

[Itchy]

That's it then. I'm going out in the morning and taking off all those silly vortex generators up on the top of the wing. Useless and look ugly. Boss will see it my way once I show him that web page.

 

[KHanson]

I teach 1) Newton, 2) Bernoulli, and 3) Magnus Effect... My PHAK is a couple years old but those are what is in it for lift. Maybe I should check out an updated one.

See, that's what I teach, too. Wouldn't #3 pretty much null and void #2..... I've heard 30283598238423948 answers from DPE's, and FAA inspectors...

 

[DE727UPS]

It's the Coriolis effect combined with Prestone anti-freeze. No, make that Quaker State...

 

[thevideographer]

The Telegraph article isn't busting Bernoulli's principle, it's busting the idea that the air on top of the wing has to move faster to 'catch up' to the air on the bottom. That IS false, and most pilots should know it, but it surprisingly is still taught in schools up until high school. It's what I learned until one day I read the wikipedia article on lift and found out it was wrong. Cracked just didn't read the article that they used as a source.

 

[knot4u]

Bernoulli came up with that when or before airplanes were lucky to exceed 30 mph. An Old Guy told me once "A barn door will fly at the correct angle of attack". Attack seems like a mean word, I call bullying and will send a strongly worded letter.

 

[chrisreedrules]

The Telegraph article isn't busting Bernoulli's principle, it's busting the idea that the air on top of the wing has to move faster to 'catch up' to the air on the bottom. That IS false, and most pilots should know it, but it surprisingly is still taught in schools up until high school. It's what I learned until one day I read the wikipedia article on lift and found out it was wrong. Cracked just didn't read the article that they used as a source.

So just to clarify to any CFI that stumbles across this in the future... When you say things like, "The air on top of the airfoil has to move faster to catch up to the air on the bottom of the airfoil because of the camber of the upper surface... This creates higher pressure below the airfoil and pushes the wing up" you are teaching it wrong. ...I know because that's what I used to teach until an older and much wiser CFI explained to me why I was wrong. So don't do that.

 

[DBrown]

So just to clarify to any CFI that stumbles across this in the future... When you say things like, "The air on top of the airfoil has to move faster to catch up to the air on the bottom of the airfoil because of the camber of the upper surface... This creates higher pressure below the airfoil and pushes the wing up" you are teaching it wrong. ...I know because that's what I used to teach until an older and much wiser CFI explained to me why I was wrong. So don't do that.

Yep,
All it takes is one student to say "what about a symmetrical airfoil" to make most CFI's eyes glaze over and force them into a fetal position

 

[Fly_Unity]

1. Anyone who says Bernoullis principle is a myth, have never seen a wing in action providing lift with a negative angle of attack in relation to the relative wind.

2. Chrisreed is correct in that the air moving over the wing dont have to move faster than the air on the bottom to meet up. That part is a myth.The air wont meet up with the same air that it left.

3. A symmetrical airfoil still uses Bernoullis principle. The difference is that there needs to be a AOA to produce it.


http://www.grc.nasa.gov/WWW/k-12/airplane/wrong1.html (Best site IMO for lift that I show my students)

 

[PhilosopherPilot]

You're all circling around the same thing. The reason an airplane flies it that it puts downward pressure on air. The reason it puts downward pressure on air is Bernoulli. I'm not sure why people want to separate the laws of motion from fluid dynamics. They are all related and intertwined.

The notion that an aircraft isn't pushing down on the air is just ludicrous. It clearly is, and you can even see that it is from the airflow behind the aircraft.

If the plane doesn't push air down, the air won't hold it up. Simple. Why is this hard?

 

[z987k]

Bernoulli came up with that when or before airplanes were lucky to exceed 30 mph.

I have not laughed that hard in awhile.

I'm going to go with before they could exceed 30mph, since he died in the late 1700s.