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No One Can Explain Why Planes Stay in the Air, February 1, 2020


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No One Can Explain Why Planes Stay in the Air

Do recent explanations solve the mysteries of aerodynamic lift?

February 1, 2020

 

 

https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

 

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In Brief

On a strictly mathematical level, engineers know how to design planes that will stay aloft.

But equations don't explain why aerodynamic lift occurs.

There are two competing theories that illuminate the forces and factors of lift. Both are incomplete explanations.

Aerodynamicists have recently tried to close the gaps in understanding. Still, no consensus exists.

 

 

In December 2003, to commemorate the 100th anniversary of the first flight of the Wright brothers, the New York Times ran a story entitled “Staying Aloft; What Does Keep Them Up There?” The point of the piece was a simple question: What keeps planes in the air? To answer it, the Times turned to John D. Anderson, Jr., curator of aerodynamics at the National Air and Space Museum and author of several textbooks in the field.

 

What Anderson said, however, is that there is actually no agreement on what generates the aerodynamic force known as lift. “There is no simple one-liner answer to this,” he told the Times. People give different answers to the question, some with “religious fervor.” More than 15 years after that pronouncement, there are still different accounts of what generates lift, each with its own substantial rank of zealous defenders. At this point in the history of flight, this situation is slightly puzzling. After all, the natural processes of evolution, working mindlessly, at random and without any understanding of physics, solved the mechanical problem of aerodynamic lift for soaring birds eons ago. Why should it be so hard for scientists to explain what keeps birds, and airliners, up in the air?

 

Adding to the confusion is the fact that accounts of lift exist on two separate levels of abstraction: the technical and the nontechnical. They are complementary rather than contradictory, but they differ in their aims.

 

 

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Posted (edited)

This is a sensationalist article written for shock factor. Aerospace engineers do understand what keeps airplanes in the air. But it ain’t simple and involves lots of math. 
 

It’s not the famed Bernoulli principle alone and this is often misconstrued so badly by the public. In fact, it’s given a name in engineering, the “equal transit time theory” because it’s so common and so wrong. 
 

Differential pressure is only part of of the equation, and in some circumstances a very small contribution. And it relies on laminar flow and viscosity largely. 
 

Direct lift from the angle of attack and deflection of air below the wing for some shapes can be huge (i.e. symmetric airfoils on the P-51). 
 

And then there’s thrust axis, lifting body dynamics from non-flying surfaces...
 

Anyway, I could go on. But in short, this article should have talked to an aerospace engineer. Not a museum curator. 

Edited by ESzczesniak
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The real mystery is why crap articles like this are written. The real shame is that people might actually believe the crap they are reading.  
 

I don’t read Scientific American but based on thus article they should change their name. 

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Ed Regis has written 10 science books, including Monsters: The Hindenburg Disaster and the Birth of Pathological Technology (Basic Books, 2015). He has also logged 1,000 hours flying time as a private pilot.


So the author claims to have logged over 1,000 hours as a pilot and he thinks how airplanes fly is a mystery?   Sheesh...

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I was in the Air Force and hated to fly.  I would when it was necessary, and I have been in several near air to air accidents, almost went down to a mountain in Alaska,  had some one try to knock us out of the air by trying to blinding the pilot, had some idiot with a airliner try to take off like a fighter pilot once too often when he had a engine on fire, and been to a few crashes.  Let me think, why don't I like to fly and why have I turned down flights in fighters where they would let me get in some stick time?  Beats me.

But the reason that a plane can  fly is simple:  even bricks can fly when enough power is used.  Given some of the things that have flown in the past, you have to wonder just how much power did they use, was it enough, or too much?

 

love the ground

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4 hours ago, ESzczesniak said:

...It’s not the famed Bernoulli principle alone ....

 

Not disagreeing with you but it reminds me of a true story.  (TINS)

 

Many (many) years ago I was dating this girl and, when I finally met her parents, I learned her dad was a pilot.  He was retired USAF, no nonsense about many things including flying and who his daughter dated.  Once he decided I might just might be an OK guy, he invited us to go flying in his twin engine Beech.  His daughter informed me this was a Very Big step in gaining his trust and to not screw it up.

 

So we drive out the the airport that weekend and meet him at the hangar.  He has the pre-flight done and is waiting on us. Before we board he turns to me and says "One question. Do you know what keeps an airplane in the air?"  I met his judging gaze and confidently said "Bernoulli."  After the longest five seconds of my life he smiled and said "Welcome aboard."

 

After the flight we were talking and he told me "Actually you're wrong about what keeps a plane in the air. It's not Bernoulli."

 

(short pause)

 

"It's money."

 

He was an alright guy.  

 

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3 hours ago, Mizar said:

it's because pigs can't fly

 

Luigi

Oh YEAH !!!! tell that to Pink Floyd

images.jpg

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Here's another one to see what the response to it is; https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

 

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HOW IS LIFT GENERATED?

There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments. To help you understand lift and its origins, a series of pages will describe the various theories and how some of the popular theories fail.

 

 

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Someone told me once that helicopters fly because they're so ugly the ground repels them. :whistle:

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Farts can fly too, they are lighter than air and float around, sometimes lingering for quite sometime.  As an experiment, let one fly in your car with the windows up before you get out.  Hours maybe the next morning it will still be flying in a racetrack pattern waiting for clearance until you open the window to let it fly out. 😚

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19 hours ago, habu2 said:

Not disagreeing with you but it reminds me of a true story.  (TINS)

 

Many (many) years ago I was dating this girl and, when I finally met her parents, I learned her dad was a pilot.  He was retired USAF, no nonsense about many things including flying and who his daughter dated.  Once he decided I might just might be an OK guy, he invited us to go flying in his twin engine Beech.  His daughter informed me this was a Very Big step in gaining his trust and to not screw it up.

 

So we drive out the the airport that weekend and meet him at the hangar.  He has the pre-flight done and is waiting on us. Before we board he turns to me and says "One question. Do you know what keeps an airplane in the air?"  I met his judging gaze and confidently said "Bernoulli."  After the longest five seconds of my life he smiled and said "Welcome aboard."

 

After the flight we were talking and he told me "Actually you're wrong about what keeps a plane in the air. It's not Bernoulli."

 

(short pause)

 

"It's money."

 

He was an alright guy.  

I can absolutely hear your ex honey's admonition to not mess up.

 

 

Do you know the difference between TINS and "Once upon a time"?

A fairy tale starts with "Once upon a time." A sea story starts with TINS.

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Remember, an aircraft is just a series of nuts and bolts flying in loose formation around a fuel leak.

 

 

And it will always get you to the scene of the crash.

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Birds have wings and planes have wings.  Pull the wings of a bird and it wont fly.  Shoot the wings off a plane and it crashes.  Wings make things fly!  😁

 

Geoff M

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Perhaps a more serious post in relation to the original article. John Anderson is a highly respected aerodynamacist - I have several of his textbooks on my shelf. His book "Modern Compressible Flow with a Historical Perspective" is regarded by myself and many of my peers as a classic. The problem here lies more in how Scientific American presented what he said. I studied aerospace engineering and my Ph.D. was in applied aerodynamics, yet I cannot recall once walking into a lecture where the prof said: "Right, today we will discuss how a wing produces lift". It is a workup through basic gas dynamics, more advanced general gas dynamics, potential flow, viscous flow, wing theory, boundary layer theory, compressible flow, transonic aerodynamics, etc. At undergraduate level these topics are covered as modules over two or three courses but at graduate level, each one is explored separately in its own full-blown semester course - sometimes more than one semester course, in fact. In my case my understanding was further filled in by many hours, days, nights, weekends, summer vacations, etc. spent in the wind tunnel. When you discuss a specific application of aerodynamics in class - let's say 2D flow over an airfoil, most students already have such a solid background that the relations between pressure and velocity, shear forces, streamlines, vorticity, etc., are second nature - or at the very least should just require a bit of a review. They just have to apply their knowledge to the specific application in front of them and there is no reason to invent a simplified explanation for the physics. At least, this is how we did it in the United States where I studied, but I suspect the approach is very similar at all universities around the world that teach aeronautical engineering.

 

That approach is in stark contrast to how popular science magazines, books and pilot manuals explain aerodynamics. When I did my PPL, there was literally about two pages about "how a wing produces lift". So, this material naturally needs to be simplified to a point that someone would supposedly understand it after looking at a picture and reading a paragraph. Most resulting explanations then end up being not just simplified, but often wrong and counter to the actual physics at play. Some of those theories are used so often that we eventually gave them names: "Bernoulli theory" (very little relation to the actual work done by the real Bernoulli who is one of the fathers of modern aerodynamics), "skipping stone-" or "bullet theory", "equal transit-time theory", etc. The excellent NASA website posted by SouthWestForrests above explore some of these so-called theories a little and they are also mentioned a bit further down in the Scientific American article. It is these oversimplified and incorrect explanations that John Anderson tried to highlight - but the journalist misinterpreted it to the point where he seems to suggest that even scientists and engineers don't understand how it works. That is not the problem - the problem is that they have a hard time explaining it in a few sentences, something that I also have difficulty doing without immediately going off in tangents about some of the underlying physics.

 

The main title of the article itself, therefore, is perhaps not completely wrong. It should probably have read something like "No one can explain in a few sentences why planes stay in the air". If that is what he meant to convey (and I think that is what John Anderson had in mind) - then he does have a point. The subtitle: "Do recent explanations solve the mysteries of aerodynamic lift?" is completely out of place, however. There is no "mystery of aerodynamic lift" that needed "recent explanations". The journalist should have stopped after the main title.

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Posted (edited)
On 7/4/2020 at 11:05 AM, Raptor01 said:

Farts can fly too, they are lighter than air and float around, sometimes lingering for quite sometime.  As an experiment, let one fly in your car with the windows up before you get out.

 

When driving through the refinery area of Pasadena, Tx, when one farts, one rolls the windows up.  Of course, this is a very old joke that requires knowing that automotive air conditioners were not universal as they are today.  Back when nearly everyone used "4-60" A/C... four windows down at sixty miles-per-hour.

Edited by Slartibartfast
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@Mfezi, you identified the real issue with the article. Scientific American is looking for simple explanations. To be sure, this isn't new; it  has long been their goal.

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