Bernoulli, yes or no?

[Cruiser]

Wings generate lift.
The air in front of the wing is deflected around it.
The angle of the wing bunches up the amount of air under the wing and makes it thicker.
The air going over the top drags the air off the top of the wing along with it causing a void of low pressure.
The wing rises to fill the lower pressure area above the wing.

How is that for a "scientific description" ?
You can fill in the numbers to calculate how this works.

 

[James331]

NY Style.

Thats when they make the pizza so it attacks the constitution and smells like car exhaust and bum pee?




Traditional Italian for me, and per the OPs question, yes.

 

[PaulS]

Bernoulli or Newton?

...and why can I make this happen by going slower?

Chem trail dispenser.

 

[dell30rb]

My take on it is that Bernoulli's principle is the reason we have shaped airfoils.

We all know a paper airplane can fly just fine. You can simply deflect air with a flat, unshaped blade and get lift out of it (and a ton of drag for the lift produced) But the shape of an airfoil utilizes bernoulli's principle - the shape accelerates the air over the top of the wing, lowering the pressure and adding lift while significantly reducing induced drag. It makes airfoils way more efficient.

 

[dell30rb]

Wouldn't that have something to do with the wing angle of incidence?

Yeah I am sure that has something to do with it. My guess is they are designed to keep the fuselage more or less level at very high altitudes (think low IAS) while the plane is loaded down with bombs and fuel. So they might have a higher angle of incidence than an airliner.. who can cruise in the mid 30's without worrying about interceptors and SAM's.

 

[Capt. Geoffrey Thorpe]

My take on it is that Bernoulli's principle is the reason we have shaped airfoils.

We all know a paper airplane can fly just fine. You can simply deflect air with a flat, unshaped blade and get lift out of it (and a ton of drag for the lift produced) But the shape of an airfoil utilizes bernoulli's principle - the shape accelerates the air over the top of the wing, lowering the pressure and adding lift while significantly reducing induced drag. It makes airfoils way more efficient.

You have been taught a very common total misunderstanding of what Bernoulli's principle is and how it works in practice.

 

[Fluffy Bunny Airlines]

In Stick and Rudder, Langewiesche says something about the wang pushing the air down. Reckon that's Newtonian? So, Langewiesche-tonian with a bit of oregano for nostalgia.


edit: So, after doing a little poking in Google, it says Bern. Prin. "helps" explain lift. So, perhaps it isn't a binary thing? Yes, both and....

 

[Cooter]

You have been taught a very common total misunderstanding of what Bernoulli's principle is and how it works in practice.

I’m not following the distinctions are being made among the math enlightened here and who is arguing what. But there are different airfoil types for a reason, and lift isn’t just calculated from surface area alone. So there must be some effect beyond air hitting the bottom of the wing, right?

 

[Clark1961]

Bernoulli or Newton?

...and why can I make this happen by going slower?

Newton. See: cavitation.

 

[Capt. Geoffrey Thorpe]

I’m not following the distinctions are being made among the math enlightened here and who is arguing what. But there are different airfoil types for a reason, and lift isn’t just calculated from surface area alone. So there must be some effect beyond air hitting the bottom of the wing, right?

Lift is not caused by air hitting the bottom of the wing, and Bernoulli's equation has very little to do with wing shapes and also applies to the bottom of the wing as well as the top. Read this for my best shot at what does happen: http://www.pilotsofamerica.com/forum/attachment.php?attachmentid=35238&d=1407775590

Shapes:
Traditionally, the first element of the shape was the camber - the curve that runs halfway between the top and bottom surfaces. More camber typically results in a higher maximum coefficient of lift at higher angles of attack - good if you want short field performance, but it comes at the expense of drag - so not so good for cruise speed.

The second element of shape is the thickness distribution. How thick is it, where is the maximum thickness, what is the radius of the leading edge. These all have some effect on things like drag and stall behavior, but tend to be secondary factors when looking at the lift characteristics. On the other hand, more thickness gives you more room for structure, so there is some trade off between drag and weight.

FWIW...
If you look at the old NACA 4 digit airfoils (Cessna 1xx typically use 2412) were developed using the above methods - NACA engineers noticed that a lot of the popular air foils in use at the time (1930's) looked kind of similar (Clark Y was one) - so they came up with some pretty wild equations to generate camber and thickness curves that resulted in airfoils with similar shapes. Then they systematically changed the camber and maximum thickness and tested one after another after another in a wind tunnel. So, then, when you wanted to pick an airfoil, you could dig through the NACA data to find one with the thickness you need for the structure and the lift / drag behavior you wanted to get takeoff / climb performance.

Nowadays, it's pretty much all done in CFD and there is less destination between the camber and thickness distributions. And by careful work, you can improve the performance by several percent compared to the old NACA stuff.

 

[SoCal RV Flyer]

In Stick and Rudder, Langewiesche says something about the wang pushing the air down.

Well...that's an interesting use for it.

 

[azpilot]

I realize I'm late to this thread, but I'll give it a shot.

It's both. There is a 'Bernoulli' component to lift, and there is a newtonian component as well. As evidence, I would ask a couple of questions. If lift is purely newtonian, how does icing spoil lift? And if lift is purely Bernoulli based, how do planes fly upside down?

I realize this is probably overly simplistic, but in the end, I really do like pizza.

 

[Clark1961]

I realize I'm late to this thread, but I'll give it a shot.

It's both. There is a 'Bernoulli' component to lift, and there is a newtonian component as well. As evidence, I would ask a couple of questions. If lift is purely newtonian, how does icing spoil lift? And if lift is purely Bernoulli based, how do planes fly upside down?

I realize this is probably overly simplistic, but in the end, I really do like pizza.

Newtonian just requires lift to be produced as a reaction to the mass of air forced down. It does not require air to be forced down by deflection from the bottom of the wing.

Pizza is good and may be the source of all that is right in the world...

 

[Cooter]

Lift is not caused by air hitting the bottom of the wing, and Bernoulli's equation has very little to do with wing shapes and also applies to the bottom of the wing as well as the top. Read this for my best shot at what does happen: http://www.pilotsofamerica.com/forum/attachment.php?attachmentid=35238&d=1407775590

Shapes:
Traditionally, the first element of the shape was the camber - the curve that runs halfway between the top and bottom surfaces. More camber typically results in a higher maximum coefficient of lift at higher angles of attack - good if you want short field performance, but it comes at the expense of drag - so not so good for cruise speed.

The second element of shape is the thickness distribution. How thick is it, where is the maximum thickness, what is the radius of the leading edge. These all have some effect on things like drag and stall behavior, but tend to be secondary factors when looking at the lift characteristics. On the other hand, more thickness gives you more room for structure, so there is some trade off between drag and weight.

FWIW...
If you look at the old NACA 4 digit airfoils (Cessna 1xx typically use 2412) were developed using the above methods - NACA engineers noticed that a lot of the popular air foils in use at the time (1930's) looked kind of similar (Clark Y was one) - so they came up with some pretty wild equations to generate camber and thickness curves that resulted in airfoils with similar shapes. Then they systematically changed the camber and maximum thickness and tested one after another after another in a wind tunnel. So, then, when you wanted to pick an airfoil, you could dig through the NACA data to find one with the thickness you need for the structure and the lift / drag behavior you wanted to get takeoff / climb performance.

Nowadays, it's pretty much all done in CFD and there is less destination between the camber and thickness distributions. And by careful work, you can improve the performance by several percent compared to the old NACA stuff.

So you’re saying a symmetrical airfoil (other dimensions being equal) has the same lift coefficient as a cambered airfoil? What were the wind tunnel tests demonstrating, reduced drag?
I read your link, but I don’t see how it conflicts with what I’ve previously learned. There is low pressure on top of the wing due to accelerated air. The problem for someone reading is that different arguments are being made, or so it seems. I’m all for learning something new, so what specifically is wrong with what has been traditionally taught?

 

[Checkout_my_Six]

yup....it's all good.

 

[PaulS]

http://www.cam.ac.uk/research/news/how-wings-really-work

 

[dell30rb]

Bernoulli or Newton?

...and why can I make this happen by going slower?

My guess is the condensation forms because of Bernoulli's principle. With lower pressure on the top of the wing, air cools to the dew point.

Have at it!

 

[Checkout_my_Six]

yes....Bertolli with Newdools...yum.

 

[Clark1961]

My guess is the condensation forms because of Bernoulli's principle. With lower pressure on the top of the wing, air cools to the dew point.

Have at it!

Charles law

 

[Capt. Geoffrey Thorpe]

So you’re saying a symmetrical airfoil (other dimensions being equal) has the same lift coefficient as a cambered airfoil? What were the wind tunnel tests demonstrating, reduced drag?
I read your link, but I don’t see how it conflicts with what I’ve previously learned. There is low pressure on top of the wing due to accelerated air. The problem for someone reading is that different arguments are being made, or so it seems. I’m all for learning something new, so what specifically is wrong with what has been traditionally taught?

No - adding camber generally increases lift (and drag) at the same angle of attack. Wind tunnel tests determined lift and drag (and sometime pressure distributions) as a function of angle of attack - that's how you get the curves in that I had linked.

A common mis-explanation is that Bernoulli's principle has something to do with curves and/or distances and applies to what happens on top of the airfoil while air hitting the bottom is deflected and that's the "Newton" part of lift. Both of those concepts are wrong. I got the impression from your previous post that this was in line with your thinking.

There is low pressure on the top and high pressure on the bottom of an airfoil when it is generating lift. This correlates with changes in velocity on the top (faster) and on the bottom (slower). Bernoulli's equation gives the mathematical relation between the velocity and pressure (and is not specifically related to airfoils at all) and can be applied both above and below the airfoil. And, you do the same calculations for curved top/flat bottom, symmetrical and flat plate airfoils. Similarly, the net deflection of air flow downwards (downwash) correlates to lift through Newton's equations. The deflection of the air happens due to the flow both on the top and the bottom of the airfoil. And, his happens with curved top/flat bottom, symmetrical and flat plate airfoils.

Adding or subtracting curves / thickness does not change the basic physics which have applications far beyond airfoils.

Given that an airfoil is generating lift (cambered, flat, symmetrical, whatever):

Is there a lower than static pressure on top where the air is faster than the free stream velocity? Yes.
Is there higher than static pressure on the bottom where hte air is slower than the free stream velocity? Yes.
Can Bernoulli's equation be used to calculate the relation between the pressures and speeds? Yes, on both the top and bottom. (There are some assumptions built into the original equation such as inviscid, incompresible flow but that's a side discussion.)
Does this have anything to do with curves? No.
Does this have anything to do with distances? No.
Do different principals apply to different kinds of airfoils? No
Do the top and bottom of an airfoil do different things? No.
Do different equations apply to the top vs. the bottom of an airfoil? No.
Can lift be divided into a Bernoulli component and a Newton component? No
Can you explain 100% of lift using Newtons equations? Yes.
Can you explain 100% of the lift using Bernoulli's equation given that the velocities are different over the top and bottom? Yes.
Does Bernoulli's equation explain why air is faster on the top and slower on the bottom? No.
Do Newtons laws explain why air is faster on the top and slower on the bottom? Not directly.
Why is the air faster / slower over the top/bottom? This is where the whole thing gets sticky. The easy answer is "circulation" but then you need to do vector addition of different components of the air flow.
Why is there circulation? The "Kutta Condition" which states that velocity at the trailing edge must be finite. And it goes downhill from here...

​

 

[Half Fast]

Bernoulli principle?

Bah.

Peter principle. The airplane rises to the altitude at which it is no longer competent to fly.

 

[Pilawt]

And it goes downhill from here...

Not enough lift ... ?

 

[azure]

Bernoulli's equation is equally applicable on the lower surface as on the upper. The problem seems to be the misapplication of the equation and the principle to apply it only to the upper surface and "suction." The airflow deflection results in lift. The pressure distribution (high on the bottom, low on top) causes airflow deflection. Newton and/or Bernoulli are different means to the same end. You might not find a 'scholarly paper' on the difference (or you might, I don't know) because the 'difference' is largely one of misunderstanding.

Nauga
and misapplied science

There is almost certainly a paper out there on the subject. Since it's all well-understood classical physics, I would suggest looking in one of the "teachers'" journals like Physics Teacher or American Journal of Physics. If no one has published on the subject I would be truly astonished.

 

[Dan Thomas]

https://www.av8n.com/how/htm/airfoils.html

 

[Cruiser]

an Bernoulli's equation be used to calculate the relation between the pressures and speeds? Yes, on both the top and bottom. (There are some assumptions built into the original equation such as inviscid, incompresible flow but that's a side discussion.)

So, if you fudge the formula, Bernoulli is responsible for global warming !

 

[Brad Smith]

All I can tell you is that RC slope gliders fly great with fully symmetrical airfoils. Right side up or upside down, it really doesn't mater. I've flown both asymmetrical and symmetrical and now fly only symmetrical for the slope. I believe that AoA and airspeed has more to do with performance than any pressure differences and I will continue to fly in spite of what 18th century physics says about what does or doesn't work.

 

[MauleSkinner]

All I can tell you is that RC slope gliders fly great with fully symmetrical airfoils. Right side up or upside down, it really doesn't mater. I've flown both asymmetrical and symmetrical and now fly only symmetrical for the slope. I believe that AoA and airspeed has more to do with performance than any pressure differences and I will continue to fly in spite of what 18th century physics says about what does or doesn't work.

Good news..19th century physics says it works. Bernoulli and Newton agreed on it.

 

[Checkout_my_Six]

So, if you fudge the formula, Bernoulli is responsible for global warming !

Oh no....that can't be good.

 

[dmspilot]

Symmetrical airfoils don't produce any lift at zero angle of attack. I don't know why people keep bringing it up, it's a red herring.

 

[Half Fast]

Interesting videos of transition between negative and positive lift. This was a Mercedes at LeMans, 1999.

(forward up to 7:45)​

I read several technical articles about this crash at the time. I seem to recall that it related to when they transitioned out of a leading car's draft and were under hard acceleration. Pretty impressive.

 

[paflyer]

The hand out the car window thing made it really clear to me when I started flying that the books were leaving something big out. But you take the tests and answer the way the tester wants you to or you don’t pass.

Cooperate to graduate.

BTW, Newton makes airplanes fly, Bernoulli's "low pressure" is a side effect and is just lower than the bottom face of the wing- which is higher than still air due to the 3rd Law..

 

[Clark1961]

Interesting videos of transition between negative and positive lift. This was a Mercedes at LeMans, 1999.

(forward up to 7:45)​

I read several technical articles about this crash at the time. I seem to recall that it related to when they transitioned out of a leading car's draft and were under hard acceleration. Pretty impressive.

Over rotated, stalled, spun in.

 

[bflynn]

My guess is the condensation forms because of Bernoulli's principle. With lower pressure on the top of the wing, air cools to the dew point.

Have at it!

Sure, we have all agreed to go with that, remember. It's good plausible deniability to hide the high speed chemtrail dispensers.

Are we are supposed to be talking about this in the open?

 

[paflyer]

Sure, we have all agreed to go with that, remember. It's good plausible deniability to hide the high speed chemtrail dispensers.

Are we are supposed to be talking about this in the open?

ix nay!

 

[Salty]

show me a wing that will generate lift (Bernoulli) without an angle of attack (Newton)

Only airflow on the top of this "wing", yet lift is clearly generated. Forgive the poor quality example, I spent all of 6 seconds doing this. You can replicate it yourself easily enough.

 

[Clark1961]

Only airflow on the top of this "wing", yet lift is clearly generated. Forgive the poor quality example, I spent all of 6 seconds doing this. You can replicate it yourself easily enough.

Now all that you need is someone to stand in front of your wing and blow.

 

[Sundancer]

Does it matter? Suck or push, or some of both?

I go up, which is the main thing. . .

 

[Tarheelpilot]

Does it matter? Suck or push, or some of both?

I go up, which is the main thing. . .

That is the main thing for roughly half the population.

 

[Cruiser]

Only airflow on the top of this "wing", yet lift is clearly generated. Forgive the poor quality example, I spent all of 6 seconds doing this. You can replicate it yourself easily enough.

I don't think that "wing" will get off the ground.

 

[Salty]

I don't think that "wing" will get off the ground.

You've never seen paper flying in the wind before? I have many times.