The physics of lift and wings

[Medtner]

Of the many brilliant sources of information on internet, the "Sixty Symbols" channel on YouTube is one of my favourites. A bunch of physics nerds discusses various themes, and are joyfully sharing their insights. The enthusiasm is very very contagious.

Have a look at this short video on lift and wings! It's so fascinating!


https://www.youtube.com/watch?v=PF22LM8AbII

[DHenriques_]

Of the many brilliant sources of information on internet, the "Sixty Symbols" channel on YouTube is one of my favourites. A bunch of physics nerds discusses various themes, and are joyfully sharing their insights. The enthusiasm is very very contagious.

Have a look at this short video on lift and wings! It's so fascinating!


https://www.youtube.com/watch?v=PF22LM8AbII

This fellow makes a VERY common mistake made by many who use physics to explain lift. Before the film has gone one minute he equates Bernoulli as being incorrect due to the equal transit theory. HIS explanation is totally incorrect at this point as Bernouli does NOT postulate equal transit (molecules meeting at the trailing edge of the wing.)
Let me be absolutely clear on this. Equal transit is wrong. Bernoulli is correct.

I haven't watched the entire film yet. If I see anything else I think worth mentioning I'll chime in again.
Dudley Henriques

[Medtner]

Of the many brilliant sources of information on internet, the "Sixty Symbols" channel on YouTube is one of my favourites. A bunch of physics nerds discusses various themes, and are joyfully sharing their insights. The enthusiasm is very very contagious.

Have a look at this short video on lift and wings! It's so fascinating!


https://www.youtube.com/watch?v=PF22LM8AbII

This fellow makes a VERY common mistake made by many who use physics to explain lift. Before the film has gone one minute he equates Bernoulli as being incorrect due to the equal transit theory. HIS explanation is totally incorrect at this point as Bernouli does NOT postulate equal transit (molecules meeting at the trailing edge of the wing.)
Let me be absolutely clear on this. Equal transit is wrong. Bernoulli is correct.

I haven't watched the entire film yet. If I see anything else I think worth mentioning I'll chime in again.
Dudley Henriques

Yeah, I think he is referencing the common explanation of the Bernoulli theory with equal transit. He goes on to explain that Bernouilli is indeed correct, as is Newton, as is Euler - and indeed all three are important.

[DHenriques_]

Of the many brilliant sources of information on internet, the "Sixty Symbols" channel on YouTube is one of my favourites. A bunch of physics nerds discusses various themes, and are joyfully sharing their insights. The enthusiasm is very very contagious.

Have a look at this short video on lift and wings! It's so fascinating!


https://www.youtube.com/watch?v=PF22LM8AbII

This fellow makes a VERY common mistake made by many who use physics to explain lift. Before the film has gone one minute he equates Bernoulli as being incorrect due to the equal transit theory. HIS explanation is totally incorrect at this point as Bernouli does NOT postulate equal transit (molecules meeting at the trailing edge of the wing.)
Let me be absolutely clear on this. Equal transit is wrong. Bernoulli is correct.

I haven't watched the entire film yet. If I see anything else I think worth mentioning I'll chime in again.
Dudley Henriques

Yeah, I think he is referencing the common explanation of the Bernoulli theory with equal transit. He goes on to explain that Bernouilli is indeed correct, as is Newton, as is Euler - and indeed all three are important.

Yes. Bernoulli and Newton are simply two explanations for the same thing using two theories each occurring simultaneously as lift is being created.
Back in the "old days", equal transit was included as part of the Bernoulli explanation which was then and always has been incorrect. Thousands of text books were written stating equal transit. All were wrong.
Newton's theory came on board along the way and has become the preferred way to explain lift but even there one has to be extremely careful. There are those today who postulate that Newton and Bernoulli ADD to create a total lift force. THAT also is incorrect as they do NOT add but occur together. The total lift force can be explained IN TOTAL using either Bernoulli or Newton.
The correct way to teach lift and by far the easiest way is to use Newton but INCLUDE Bernoulli as also being correct. The result of doing it this way is that it is not only correct but easier for the student to comprehend. Once Newton is understood it is easier to understand Bernoulli which is by far the more difficult theory to understand.
It is notable that NEITHER Newton OR Bernoulli had any idea what lift was when each put forward their theories which LATER on became associated with lift.
Dudley Henriques

[AKar]

A couple of derivations of Bernoulli's principle by John Denker.

https://www.av8n.com/physics/bernoulli.htm

Note that these are not in context of lift, because Bernoulli's principle in itself does not (nor does it attempt to) explain how lift is generated. Bernoulli's principle is directly related to Newton's laws of motion, however, Newton's laws are not completely inclusive on their own without adding some ideas to describe gas (or fluid) in macroscopic scale - essentially what Bernoulli did after his experiments.

It is not that any of the associated laws would be "wrong" but they are very commonly misapplied, or interpreted to explain things that they don't actually consider at all, taking those for granted. All these sort of principles essentially describe balances that must hold as a two-way street, but don't readily explain or care how such balance builds bottom-up. This may lead in confusion when attempting to do so.

-Esa

[DHenriques_]

A couple of derivations of Bernoulli's principle by John Denker.

https://www.av8n.com/physics/bernoulli.htm

Note that these are not in context of lift, because Bernoulli's principle in itself does not (nor does it attempt to) explain how lift is generated. Bernoulli's principle is directly related to Newton's laws of motion, however, Newton's laws are not completely inclusive on their own without adding some ideas to describe gas (or fluid) in macroscopic scale - essentially what Bernoulli did after his experiments.

It is not that any of the associated laws would be "wrong" but they are very commonly misapplied, or interpreted to explain things that they don't actually consider at all, taking those for granted. All these sort of principles essentially describe balances that must hold as a two-way street, but don't readily explain or care how such balance builds bottom-up. This may lead in confusion when attempting to do so.

-Esa

Where it gets complicated is when flight instructors begin to insert Navier-Stokes, Euler, Magnus effect, Coanda, etc into our lift explanations. All are relevant in some way and connected and of course relevant if the student wishes to delve into the variations involved with fluid dynamics, inviscid and viscous flow, etc. But for practical purposes, we can explain lift quite well using Newton and Bernoulli basic explanations. The KISS principle in action..........or the Occam's Razor approach if you will.
The rest we can encourage as home work. LOL
DH

[Killratio]

My favourite thing was to point out to young instructors that they were wrong to tell students that the aircraft flys if lift = weight. In any aircraft with a tail plane, this is incorrect. I've only ever had a couple of old instructors who knew what I was getting at (apart from the one who told me). A perfect example of how all of the complicated physics arguments can overlook a simple, practical fact...a tail plane creates downforce, which must be counteracted in addition to the weight of the aircraft. If you look at one part of any process you can apply all of the science you want and still not get the right answer

All people who eat carrots die eventually, therefore eating carrots will kill you...

[AKar]

A couple of derivations of Bernoulli's principle by John Denker.

https://www.av8n.com/physics/bernoulli.htm

Note that these are not in context of lift, because Bernoulli's principle in itself does not (nor does it attempt to) explain how lift is generated. Bernoulli's principle is directly related to Newton's laws of motion, however, Newton's laws are not completely inclusive on their own without adding some ideas to describe gas (or fluid) in macroscopic scale - essentially what Bernoulli did after his experiments.

It is not that any of the associated laws would be "wrong" but they are very commonly misapplied, or interpreted to explain things that they don't actually consider at all, taking those for granted. All these sort of principles essentially describe balances that must hold as a two-way street, but don't readily explain or care how such balance builds bottom-up. This may lead in confusion when attempting to do so.

-Esa

Where it gets complicated is when flight instructors begin to insert Navier-Stokes, Euler, Magnus effect, Coanda, etc into our lift explanations. All are relevant in some way and connected and of course if the student wishes to delve into the variations involved with fluid dynamics, inviscid and viscous flow, etc. But for practical purposes, we can explain lift quite well using Newton and Bernoulli basic explanations. The KISS principle in action..........or the Occam's Razor approach if you will.
The rest we can encourage as home work. LOL
DH

Yea, I always think that intuition should be placed at higher priority than thoroughness, unless absolutely necessary. With good intuition, deeper concepts are much easier to learn. If speaking of aerodynamic force such as lift, itself impossible to describe even half-thoroughly in a chapter or two, my favorite 'pure idiot's introduction' has always been a simplified Newtonian approach. Something like follows:

For air to push the aircraft up, the aircraft must also push air down. A mass of free-flowing substance such as air will then accelerate downwards, and the mass of the aircraft accelerates upwards - in level flight exactly enough to cancel the gravitational acceleration of the mass of our aircraft downwards. The amount of air accelerated downwards depends on its density and the speed we go through it. How sharply it is accelerated downwards depends on our speed again, and our angle of attack. Thereby, our lift produced depends on the density of the air, it depended twice on our speed, that is, velocity squared, and on our angle of attack [insert a pair of pictures here for intuition], in a quite linear way up to the point.

This is almost entirely the Newton's laws simply restated, only assuming the air behaves the way it does, with no real explanation on why all this functions, and it does not attempt to explain why the flow adheres to the wing in a way it does (neither does the Bernoulli's principle, directly, without added discussion of viscosity). Yet, the relationships are rather clear and hold valid even when going deeper into discussion.

To add Mr. Bernoulli here would usually serve to link in how this mentioned acceleration works out, introducing fluid's ability to inflict pressure on itself (Bernoulli's important addition to Newton's):

For a tiny 'parcel' of air to accelerate, it must move from higher pressure towards lower, because the only force acting on it is the net pressure resulting from the gradient that is of higher pressure on one side, and lower on the other.

This intuitively links the Newton's first and second in particular to the Bernoulli's principle - actually, it is possible to derive a portion of Bernoulli's this way.

Again, not much at all is deeply understood by this, but intuition maybe gained again holds thorough some deeper discussion. I don't think it servers much purpose to go into Navier-Stokes or such in early pilot training any more it would make sense to dig deep into theories of friction in driving lessons. Yet, the intuition behind above actually do hold way deep into Navier-Stokes.

As you say, Occam's razor. My personal addition has always been that never unnecessarily introduce anything that needs to be unlearned later. Unfortunately, this is something in which some "explanations" of lift attempting simply too much fail in this. Human mind is surprisingly comfortable in not understanding something if simply having an intuition for it, but not really the other way around. That's why comfortable learning should go intuition first.

-Esa

[AKar]

My favourite thing was to point out to young instructors that they were wrong to tell students that the aircraft flys if lift = weight. In any aircraft with a tail plane, this is incorrect. I've only ever had a couple of old instructors who knew what I was getting at (apart from the one who told me). A perfect example of how all of the complicated physics arguments can overlook a simple, practical fact...a tail plane creates downforce, which must be counteracted in addition to the weight of the aircraft. If you look at one part of any process you can apply all of the science you want and still not get the right answer

All people who eat carrots die eventually, therefore eating carrots will kill you...

Well, net lift = weight in level flight anyways, you simply end up canceling the moments rotating the thing in pitch as well while at it. Of course, tail plane can create "up-force" as well, or almost nothing at all, depending on the CoG envelope of the aircraft in question.

-Esa

[DHenriques_]

My favourite thing was to point out to young instructors that they were wrong to tell students that the aircraft flys if lift = weight. In any aircraft with a tail plane, this is incorrect. I've only ever had a couple of old instructors who knew what I was getting at (apart from the one who told me). A perfect example of how all of the complicated physics arguments can overlook a simple, practical fact...a tail plane creates downforce, which must be counteracted in addition to the weight of the aircraft. If you look at one part of any process you can apply all of the science you want and still not get the right answer

All people who eat carrots die eventually, therefore eating carrots will kill you...

The "kicker" with this explanation is that although true, it's only true if the lift force being created is being created on an airfoil wing surface attached to an airplane. It's the aircraft scenario alone that requires a counteracting tail plane. Even then we have tailless delta's etc. Lift force can exist on surfaces not attached to an aircraft thus making the creation of lift a separate issue althogether that can be discussed outside the lift force created on an airplane's wing.
We can create a lift force involving all the standard theory simply by carting a barn door at a slight angle of attack in the back of a pickup truck where it addresses a relative wind. ))))))
DH

[DHenriques_]

A couple of derivations of Bernoulli's principle by John Denker.

https://www.av8n.com/physics/bernoulli.htm

Note that these are not in context of lift, because Bernoulli's principle in itself does not (nor does it attempt to) explain how lift is generated. Bernoulli's principle is directly related to Newton's laws of motion, however, Newton's laws are not completely inclusive on their own without adding some ideas to describe gas (or fluid) in macroscopic scale - essentially what Bernoulli did after his experiments.

It is not that any of the associated laws would be "wrong" but they are very commonly misapplied, or interpreted to explain things that they don't actually consider at all, taking those for granted. All these sort of principles essentially describe balances that must hold as a two-way street, but don't readily explain or care how such balance builds bottom-up. This may lead in confusion when attempting to do so.

-Esa

Where it gets complicated is when flight instructors begin to insert Navier-Stokes, Euler, Magnus effect, Coanda, etc into our lift explanations. All are relevant in some way and connected and of course if the student wishes to delve into the variations involved with fluid dynamics, inviscid and viscous flow, etc. But for practical purposes, we can explain lift quite well using Newton and Bernoulli basic explanations. The KISS principle in action..........or the Occam's Razor approach if you will.
The rest we can encourage as home work. LOL
DH

Yea, I always think that intuition should be placed at higher priority than thoroughness, unless absolutely necessary. With good intuition, deeper concepts are much easier to learn. If speaking of aerodynamic force such as lift, itself impossible to describe even half-thoroughly in a chapter or two, my favorite 'pure idiot's introduction' has always been a simplified Newtonian approach. Something like follows:

For air to push the aircraft up, the aircraft must also push air down. A mass of free-flowing substance such as air will then accelerate downwards, and the mass of the aircraft accelerates upwards - in level flight exactly enough to cancel the gravitational acceleration of the mass of our aircraft downwards. The amount of air accelerated downwards depends on its density and the speed we go through it. How sharply it is accelerated downwards depends on our speed again, and our angle of attack. Thereby, our lift produced depends on the density of the air, it depended twice on our speed, that is, velocity squared, and on our angle of attack [insert a pair of pictures here for intuition], in a quite linear way up to the point.

This is almost entirely the Newton's laws simply restated, only assuming the air behaves the way it does, with no real explanation on why all this functions, and it does not attempt to explain why the flow adheres to the wing in a way it does (neither does the Bernoulli's principle, directly, without added discussion of viscosity). Yet, the relationships are rather clear and hold valid even when going deeper into discussion.

To add Mr. Bernoulli here would usually serve to link in how this mentioned acceleration works out, introducing fluid's ability to inflict pressure on itself (Bernoulli's important addition to Newton's):

For a tiny 'parcel' of air to accelerate, it must move from higher pressure towards lower, because the only force acting on it is the net pressure resulting from the gradient that is of higher pressure on one side, and lower on the other.

This intuitively links the Newton's first and second in particular to the Bernoulli's principle - actually, it is possible to derive a portion of Bernoulli's this way.

Again, not much at all is deeply understood by this, but intuition maybe gained again holds thorough some deeper discussion. I don't think it servers much purpose to go into Navier-Stokes or such in early pilot training any more it would make sense to dig deep into theories of friction in driving lessons. Yet, the intuition behind above actually do hold way deep into Navier-Stokes.

As you say, Occam's razor. My personal addition has always been that never unnecessarily introduce anything that needs to be unlearned later. Unfortunately, this is something in which some "explanations" of lift attempting simply too much fail in this. Human mind is surprisingly comfortable in not understanding something if simply having an intuition for it, but not really the other way around. That's why comfortable learning should go intuition first.

-Esa

I have always said that discovery in science is for the most part the discovery of what "isn't" as opposed to what "is". LOL
DH

[AKar]

Actually, my favorite ridicule of all the discussions of the physics of lift and wings was by certain young impromptu lecturer known for his dry humor. He had a slide with a photograph of an aircraft wing, and asked the question of what keeps the airplane in the air. The course was about electrodynamics if I recall, and the audience was mostly of students in IT and telecommunications, so all the usual fallacies were introduced, he dismissing them immediately.

"The force that enables an aircraft to fly", he finally stated, "is primarily an electrical force." This made the discussion to quiet down, adding a joke about an all-electric airplane being around since Orville and Wilbur.

Of course, his moderately lengthy explanation was that the "touch", the solidness that makes up the wing surface by locking the atoms together to form a structure and the repulsive force responsible for the elastic collisions of molecules making up the air in perpetual motion as described in the kinetic theory of gases (making Bernoulli's work and Newton's to apply), are actually of electrical origin in microscopic scale. He also stated that just about every phenomena we see or feel in our macroscopic scale are of this electrical origin - ironically, to our current knowledge, excluding the very gravity we attempt to escape from by using this wing.

He concluded: "Often phenomena are 'explained' so simplified that no real knowledge is transferred. Yet, it appears that when we look very, very, very close of what is actually happening, the nature is simplified again into a point of abstractness, only made real by the sheer scale of everything when compared to our view when looking so close. As nobody apparently understands what happens beyond that point in the abstract world of quantum mechanics, all the understanding as we know it as humans seem to lie in between. I recommend we take a good look of this gap forming a pool of human knowledge in a bottom-up way."

Something to think about.

-Esa

[Blitzer]

Of course the simpler and easier to understand explaination is... its magic!

[DHenriques_]

Actually, my favorite ridicule of all the discussions of the physics of lift and wings was by certain young impromptu lecturer known for his dry humor. He had a slide with a photograph of an aircraft wing, and asked the question of what keeps the airplane in the air. The course was about electrodynamics if I recall, and the audience was mostly of students in IT and telecommunications, so all the usual fallacies were introduced, he dismissing them immediately.

"The force that enables an aircraft to fly", he finally stated, "is primarily an electrical force." This made the discussion to quiet down, adding a joke about an all-electric airplane being around since Orville and Wilbur.

Of course, his moderately lengthy explanation was that the "touch", the solidness that makes up the wing surface by locking the atoms together to form a structure and the repulsive force responsible for the elastic collisions of molecules making up the air in perpetual motion as described in the kinetic theory of gases (making Bernoulli's work and Newton's to apply), are actually of electrical origin in microscopic scale. He also stated that just about every phenomena we see or feel in our macroscopic scale are of this electrical origin - ironically, to our current knowledge, excluding the very gravity we attempt to escape from by using this wing.

He concluded: "Often phenomena are 'explained' so simplified that no real knowledge is transferred. Yet, it appears that when we look very, very, very close of what is actually happening, the nature is simplified again into a point of abstractness, only made real by the sheer scale of everything when compared to our view when looking so close. As nobody apparently understands what happens beyond that point in the abstract world of quantum mechanics, all the understanding as we know it as humans seem to lie in between. I recommend we take a good look of this gap forming a pool of human knowledge in a bottom-up way."

Something to think about.

-Esa

What's interesting from a scientific standpoint is that people who fly airplanes don't need this level of knowledge in order to fly safely. It's fine to seek this level of understanding and we do encourage pilots to delve ever deeper into the science and physics............BUT...........it has been proven over time that the learning curve is better spent with strong emphasis on the simple mechanics and physics that make safe flight possible. Once these are understood, safe flight is made possible and each individual will then proceed forward at a learning pace dictated by their natural ability to seek knowledge. Some will absorb this knowledge to match an astronaut level while others may never progress beyond what they have learned that allowed them safe travel through their aviation tenure.
Naturally as a good flight instructor I encouraged my students to engage in further study that expanded their knowledge as the more understood the safer the pilot. But it's critical to understand that safe flight is possible without that higher level of understanding.
It is notable along the lines of this discussion that when it comes to flying a plane, one can actually reach a level of understanding concerning the science that a mistake can be made causing an accident due to over thinking the problem where a basic application of flying skill would have avoided that mistake. I have actually had to deal with this scenario more than once dealing with human factors involving accidents.
Dudley Henriques

[AKar]

Actually, my favorite ridicule of all the discussions of the physics of lift and wings was by certain young impromptu lecturer known for his dry humor. He had a slide with a photograph of an aircraft wing, and asked the question of what keeps the airplane in the air. The course was about electrodynamics if I recall, and the audience was mostly of students in IT and telecommunications, so all the usual fallacies were introduced, he dismissing them immediately.

"The force that enables an aircraft to fly", he finally stated, "is primarily an electrical force." This made the discussion to quiet down, adding a joke about an all-electric airplane being around since Orville and Wilbur.

Of course, his moderately lengthy explanation was that the "touch", the solidness that makes up the wing surface by locking the atoms together to form a structure and the repulsive force responsible for the elastic collisions of molecules making up the air in perpetual motion as described in the kinetic theory of gases (making Bernoulli's work and Newton's to apply), are actually of electrical origin in microscopic scale. He also stated that just about every phenomena we see or feel in our macroscopic scale are of this electrical origin - ironically, to our current knowledge, excluding the very gravity we attempt to escape from by using this wing.

He concluded: "Often phenomena are 'explained' so simplified that no real knowledge is transferred. Yet, it appears that when we look very, very, very close of what is actually happening, the nature is simplified again into a point of abstractness, only made real by the sheer scale of everything when compared to our view when looking so close. As nobody apparently understands what happens beyond that point in the abstract world of quantum mechanics, all the understanding as we know it as humans seem to lie in between. I recommend we take a good look of this gap forming a pool of human knowledge in a bottom-up way."

Something to think about.

-Esa

What's interesting from a scientific standpoint is that people who fly airplanes don't need this level of knowledge in order to fly safely. It's fine to seek this level of understanding and we do encourage pilots to delve ever deeper into the science and physics............BUT...........it has been proven over time that the learning curve is better spent with strong emphasis on the simple mechanics and physics that make safe flight possible. Once these are understood, safe flight is made possible and each individual will then proceed forward at a learning pace dictated by their natural ability to seek knowledge. Some will absorb this knowledge to match an astronaut level while others may never progress beyond what they have learned that allowed them safe travel through their aviation tenure.
Naturally as a good flight instructor I encouraged my students to engage in further study that expanded their knowledge as the more understood the safer the pilot. But it's critical to understand that safe flight is possible without that higher level of understanding.
It is notable along the lines of this discussion that when it comes to flying a plane, one can actually reach a level of understanding concerning the science that a mistake can be made causing an accident due to over thinking the problem where a basic application of flying skill would have avoided that mistake. I have actually had to deal with this scenario more than once dealing with human factors involving accidents.
Dudley Henriques

Yeah, I'd agree to the fullest. And I think it was kind of his point. Going deeper and deeper in some 'thing' will eventually abstract it beyond all usefulness in the original context. Of course, new ideas maybe introduced but they often are beyond the scope of usefulness of our original situation. Such as the theory of relativity: it has almost no meaning at all even in fastest supersonic flight of an atmospheric aircraft, but does have a shitload of importance in workings of a GPS. If we only care of aerodynamics, it still is beyond our scope of usefulness anyways. And as a casual flyer, so would be a bulk of what is understood in classical aerodynamics, such as those Navier-Stokes equations that to our best knowledge describe the motion of the air to an arbitrary accuracy.

As said, intuition first! Then it is up to us to decide how far to carry on, if we find a hobby in that. When flying, I find little time to think about all the engineering and physics anyways, so it is mostly about stick & rudder and basic flying - given by lessons of a good instructor...hopefully!

-Esa