PTK

Bernoulli vs. Newton

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On a recent flight across the Atlantic on an Airbus and in a window seat right behind the wing I was in heaven! Who needs movies?! Gave me a lot of quality time to watch that beautiful wing in action and contemplate about lift and how wings fly. So is it Bernoulli or Newton? 

I'm starting to think that they are both correct as they both deal with the same physics. Bernoulli talks about pressures and velocities of air molecules and Newton about forces and acceleration. There can be no pressure differential as Bernoulli says without acceleration just as there can be no acceleration of the air without pressure gradients. Isn't this why we first need to accelerate the wing down the runway before it starts flying? 

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..... The colors on the radar are pretty

Sent from my XT1254 using Tapatalk

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Then,of course, there is Marconi. How could we fly without a radio?

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1 hour ago, PTK said:

On a recent flight across the Atlantic on an Airbus and in a window seat right behind the wing I was in heaven! Who needs movies?! Gave me a lot of quality time to watch that beautiful wing in action and contemplate about lift and how wings fly. So is it Bernoulli or Newton? 

I'm starting to think that they are both correct as they both deal with the same physics. Bernoulli talks about pressures and velocities of air molecules and Newton about forces and acceleration. There can be no pressure differential as Bernoulli says without acceleration just as there can be no acceleration of the air without pressure gradients. Isn't this why we first need to accelerate the wing down the runway before it starts flying? 

Bernoulli theories are based on motion in a fluid, while Newton theories are base on motion in space. Is all a matter of the medium in which you travel. A fish can travel through water but not through air or land. A car can travel through land but not through water or air. Is all a matter of interfacing power to the travelling medium like a propeller or wheels. Or an antenna to the ether medium. We indeed exist in a nested multi medium environment.

José

Edited by Piloto
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The more I think about it the more I start to realize that it is Newton's third law that explains lift. Bernoulli talks about speed of airflow and pressure changes but it doesn't tell us the why and how these changes occur.

We need to alter the way we teach lift. Bernoulli is overtought to the point of being abused and incorrect. For example we teach the classic Bernouli model that air molecules travelling on top of the wing have to speed up in order to meet up again at the trailing edge with air molecules travelling on the underside of the wing. I don't see how or why they should meet! Especially when compressibility issues are introduced at higher speeds. Another classic example is that the wing is half a constricted pipe. I remember my ppl ground instructor drawing this on the board to explain it. I don't think airfoils are designed with these goals in mind. I think the real goal is how to most efficiently deflect air downwards, i.e. Newton, at design airspeeds, with the least drag. A cambered top air foil just happens to achieve this. 

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You actually don't need a Bernouli airfoil shape for flight. Simple paper planes and rubber band powered balsa planes achieve flight with simple flat wings.

José 

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Bernouli/Newton/Einstein...who cares!  It's all theory.  Experience is what counts.

Anyone with one scintilla of experience knows money is what makes aircraft fly.

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4 hours ago, PTK said:

On a recent flight across the Atlantic on an Airbus and in a window seat right behind the wing I was in heaven! Who needs movies?! Gave me a lot of quality time to watch that beautiful wing in action and contemplate about lift and how wings fly. So is it Bernoulli or Newton? 

I'm starting to think that they are both correct as they both deal with the same physics. Bernoulli talks about pressures and velocities of air molecules and Newton about forces and acceleration. There can be no pressure differential as Bernoulli says without acceleration just as there can be no acceleration of the air without pressure gradients. Isn't this why we first need to accelerate the wing down the runway before it starts flying? 

Go back to looking at teeth before you think too hard and hurt your brain.

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46 minutes ago, 201er said:

Go back to looking at teeth before you think too hard and hurt your brain.

:ph34r:

Check the cabin....hypoxia for sure!

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You guys are cruel to the good dentist!

In fact, there has been quite a bit written lately about the overuse of Bernouilli when teaching about how planes fly. The general consensus I have seen is that people are coming back to angle of attack (aka Newton) as much more critical to breaking the surly bonds. I'm no engineer, but I remember putting my hand outside the window as a kid (heck, as an adult!) and flying it just by angling it into and out of the wind.

As a CFI friend of mine likes to say, you can fly a brick if you put enough power behind it.

In truth both principles are probably in play...but it's not in my nature to contemplate it much more than that. To quote Ricky Bobby: "I [just] wanna' go fast!"

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Bernoulli's theorys make a wing efficient, they don't make it fly. If they did, sustained inverted flight would be inpossible without a shape shifting wing.

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I'd say airliner flight has more to do with, GE, Rolls or P&W.

Clarence

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Wonder which Italian invented the selfie. Another essential to modern flight.

image.jpeg

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On September 3, 2016 at 5:52 AM, PTK said:

On a recent flight across the Atlantic on an Airbus and in a window seat right behind the wing I was in heaven! Who needs movies?! Gave me a lot of quality time to watch that beautiful wing in action and contemplate about lift and how wings fly. So is it Bernoulli or Newton? 

I'm starting to think that they are both correct as they both deal with the same physics. Bernoulli talks about pressures and velocities of air molecules and Newton about forces and acceleration. There can be no pressure differential as Bernoulli says without acceleration just as there can be no acceleration of the air without pressure gradients. Isn't this why we first need to accelerate the wing down the runway before it starts flying? 

So good questions, it's been recently a big question in aerospace. I follow a Pod Cast called Omega Tau. He really has some interesting discussions on everything that I would say it's very cool stuff. In episode #025 he gets into a few debates backed up with some serious math. 

This Guy is awesome!!

It was an earlier episode. It comes up when you search omega tau 025. 

Be careful, all of the episodes are addicting. It's the only way to make LA traffic better. 

http://omegataupodcast.net/25-aerodynamic-lift-explained/

enjoy,

-Matt

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Bernoulli's effects and its relationship to aeronautical engineering is not a separate theory on equal footing contrasting to Newtonian dynamics.  Newton is a superset theory - that covers all things aerodynamics, and many many other areas of engineering and physics too.  That doesn't mean that knowing the broad stroke statements made knowing Newton will get you all the way to building an airplane.  Sir Isaac certainly didn't know how.

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Cl = 2 * pi * a

the coefficient of lift is equal to 2 x pi x AoA

I don't see anything in the equation about Bernoulli.........

see Shadrack's comment above ^

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Wow that sure generates a lot of lift at 89 degrees of AOA !

 

thst formula you posted is only valid for the thin airfoil theory, which basically excludes anything but dynamic pressure. It's a piece, but not the whole puzzle. 

Edited by jetdriven

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Exactly..........and an improper use of the equation.

Put the lift question another way.......... If Bernoulli produces lift then an airplane should continue to rise when the AoA is zero.

Can anyone point to an example where that is true?

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BD Petersen

Looks like you are ready for a pilot relief tube. I used to have the same expression until I got mine:D

José

Edited by Piloto

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On September 3, 2016 at 0:54 PM, Piloto said:

You actually don't need a Bernouli airfoil shape for flight. Simple paper planes and rubber band powered balsa planes achieve flight with simple flat wings.

José 

I have pondered this. i think its a little of both...if you don't have power you need camber and a bernoulli brother. if you have gobs of power, newton will do.

mike

 

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23 minutes ago, Mike261 said:

I have pondered this. i think its a little of both...if you don't have power you need camber and a bernoulli brother. if you have gobs of power, newton will do.

mike

 

The efficient, Mooney way is to use both!

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Exactly..........and an improper use of the equation.

Put the lift question another way.......... If Bernoulli produces lift then an airplane should continue to rise when the AoA is zero.

Can anyone point to an example where that is true?

It will if it goes fast enough, isn't that the design of the laminar flow wing, 0 AOA results in minimum drag?

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You don't even need an air foil to demonstrate Bernoulli. Shoot an air steam across a flat sheet of paper and it will rise. A wing provides lift in three ways. 1. Newton; down flow of air causes equal and opposite reaction (lift) 2. Differential pressure; high pressure under wing causes lift like a kite on a string!or your hand out the window.) 3, Bernoulli: laminar flow across top wing shape causes a low pressure area on top creating lift. 

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