Incorrect Flight Theory in Flight and Motion Book

In the 641 page grand scale educational text Flight and Motion The History and Science of Flying, we read on How an Airplane's Wing Creates Lift:

• The shape of a wing, curved on top and flatter underneath, is called an airfoil. 
• When it slices through air, some of the air rises up over the curved top of the wing and down the other side. 
• The air that travels over the top of the wing speeds up and, according to a scientific law known as Bernoulli’s Principle, the pressure above the wing falls. In addition, air flowing over the wing is directed downward by the wing’s shape. According to another scientific law, Newton’s third law of motion, this downward motion of the air results in an upward motion of the wing. 
• The force that pushes a wing upward is lift. If a wing is tilted up at the front, air is deflected downward even more powerfully by the curved top and also by the angled bottom of the wing. This produces more lift.

In this description lift is somehow generated by the shape of the wing. As explanation it is empty of content. Circulation is not mentioned. The reason can be that it is considered to be too complicated for younger minds, although it is the correct explanation but has to be x-rated. Another reason is that an explanation by circulation is not convincing at all, not even to already educated minds. 

Incorrect Flight Theory at Federal Aviation Adm

The Federal Aviation Administration presents in the basic text  Aerodynamics for Naval Aviators among Aviation Handbooks and Manuals, the following explanation of the generation of lift of a wing:

• An important phenomenon associated with the production  of lift by an airfoil is the “circulation” imparted to the airstream.
• The generation of lift by an airfoil is dependent upon the airfoil being able to create circulation in the airstream and develop the lifting, pressure distribution on the surface. In all cases, the generated lift will be the net force caused by the distribution of pressure over the upper and lower surfaces of the airfoil.
• If the airfoil is given a positive angle of attack, changes occur in the streamline pattern 
and pressure distribution similar to changes caused by the addition of circulation to a cylinder. The positive angle of attack causes increased velocity on the upper surface with an increase in upper surface suction while the decreased velocity on the lower surface causes a decrease in lower surface suction.

We see that FAA teaches pilots that an airfoil somehow creates circulation which generates velocity difference and thus pressure difference above and below the wing and thus lift,  as the top level of the science of flight. But this is nonsense! Nothing is explained! The natural mystery of flight presenting itself to the innocent uneducated mind, is here only made deeper by introducing a physically incorrect casual connection between circulation and lift.  

Another piece of evidence that aerodynamics education is today in free fall with zero lift and only drag.

Incorrect Flight Theory at the Smithsonian

Let us take a look at how the Smithsonian National Air and Space Museum presents How Things Fly to 4-8th graders:

• Using this poster, students can explore the fundamental physics of flight. 
• Students will be able to describe how Bernoulli’s principle enables airplanes to fly.
• Wings are designed so the air moving over the top of the wing is forced to speed up more than the air moving below the wing.
• A common explanation of lift states that air moves faster over a wing’s curved upper surface because it has farther to travel than air moving under the flatter lower surface. This explanation is wrong!
• How can an airplane fly upside down? Wing tilt is the trick. Tilting the upside-down wing upward forces the air traveling over the wing to speed up more than the air passing beneath the wing. The difference in air pressure results in lift.
• Activities on the following pages (4-6) enable students to discover for themselves how moving air creates changes in air pressure and how Bernoulli’s principle is put to use in wing design. The results are often surprising! 

OK, so young students are taught that lift comes from lower pressure above, which does not come from longer distance above (wrong explanation!), but somehow from tilting at least for an upside-down wing. 

But this is confusing nonsense which does not explain anything. To say that lift comes from lower pressure above is a trivial tautology. To say that tilting forces the air to travel faster above without telling why and how, gives no information, only further mystery.

The fact that the National Air and Space Museum feeds to minds of interested students with nonsensical disinformation is one of many indications that present aerodynamics education has collapsed. Who is responsible? AIAA?

Compare with US Centennial of Flight Celebrated by Dead Theory.

PS Today I sent the following question to the Smithsonian:

• On the web site The Secret of Flight I present a New Theory of Flight (submitted to AIAA) giving a new explanation of the generation of lift and drag of a wing, which is fundamentally different from classical text-book theory, see also Incorrect Flight Theory at the Smithsonian.
• My question: How does the Smithsonian explain the generation of lift of a wing? 

I will report the answer.

AIAA Defends Old Incorrect Theory of Flight 4

                                   Incorrect pressure distribution at trailing edge.

Let us see how the Old Theory of Flight, defended by AIAA in its rejection of our New Theory, is expressed in Fundamentals of Aerodynamics prepared for Naval Aviation Schools Command by the Naval Training, US Navy (1998). The goal of Chapter 4 on Lift and Stalls is stated as

• The purpose of this lesson is to aid the student in understanding lift and stalls as they relate to aerodynamics. 
• Upon completion of this unit of instruction, the student aviator will demonstrate knowledge of basic aerodynamic factors that affect airplane performance.

We read:

• Lift and drag are produced by different physical processes. Lift is produced by a lower pressure distribution on the top of an airfoil than on the bottom.
• A cambered airfoil is able to produce an uneven pressure distribution even at zero AOA. Because of the positive camber, the area in the streamtube above the wing is smaller than area in the streamtube below the wing and the airflow velocity above the wing is greater than the velocity below the wing.
• As the angle of attack of an (symmetric non-cambered) airfoil is increased, the leading edge stagnation point will move to a lower point on the leading edge. This shift has the effect of causing the area of the stream- tube above the airfoil to decrease. As with an increase in camber, the velocity of the airflow above the airfoil will increase, lowering the static pressure above the airfoil, increasing the differential pressure and, therefore increasing lift. 

We see that US Navy seeks to make pilots believe that lift is generated by "larger distance lower pressure above", which is the most common popular explanation. But this is known by everybody with the slightest knowledge of aerodynamics to be an incorrect pseudo-scientific explanation of the generation of lift of a wing.

In addition US Navy imprints into the pilots minds a picture of the pressure distribution at the trailing edge (displayed above) which is incorrect: The high pressure at the trailing edge seen in the picture is not present for a real wing and in the correct New Theory, only in the incorrect Old Theory.

If the above is representative of the level of the science delivered by AIAA to the US Navy, no wonder that our New Theory is not understood by AIAA and therefore is rejected.

PS The Naval Avaiation Schools Command sends the following  SAFETY / HAZARD AWARENESS NOTICE:

• Safe training is the number one goal. Each year at training commands, lives are lost and thousands of man hours and millions of dollars are wasted as the result of accidents. Most of these accidents could have been prevented. They are the result of actions performed incor- rectly, either knowingly or unknowingly, by people who fail to exercise sufficient foresight, lack the requisite training, knowledge, or motivation, or who fail to recognize and report hazards. 
• It is the responsibility of all Department of Defense personnel to report all mishaps and near misses. If a mishap, hazardous condition or near miss occurs let your instructor know immediately. 
• Students will report all hazardous conditions and near misses to the command high-risk safety officer via their divisional/departmental high-risk safety officer.

Although not DoD personnel I hereby report to the high-risk safety officer that there is a serious mishap in the explanation of lift presented. 

AIAA Defends Old Incorrect Theory of Flight 3

Let us continue the analysis of the message from associate editor Greg Blaisdell when rejecting our article New Theory of Flight submitted to AIAA Journal.

Blaisdell formulates his goal to be to re-educate (or brain-wash) us and teach us the Old Theory, which is exactly the theory which we have studied very carefully and found to be incorrect:

• I can see several misconceptions you have concerning basic concepts in fluid mechanics.
• My goal below is ... to help you see some of the areas where you need to improve your understanding.
• ...there are basic concepts in fluid mechanics that you do not understand.
• What you seem to be missing ... is that this (our) view of the classical theory is “truncated”; it is not a correct view.... it is the truncated form of the classical theory that you object 
• Unfortunately, the complete theory is not always taught, with the result that many students have misunderstandings concerning flow over airfoils and wings.
• Another set of basic concepts that you misunderstand deal with circulation and vorticity. They are related, but they are not the same, and both are important to understanding the fluid mechanics of airfoils and wings.

In his re-education mission Blaisdell seeks to force us to accept precisely what we have shown to be incorrect physics:  

• At small angles of attack the skin friction contribution can be much larger than the contribution from the pressure; while pressure or form drag is more important at higher angles of attack where the airfoil acts more like a bluff body.
• The trailing edge vortices in your simulations form in counter-rotating pairs. Their net circulation is zero, and their presence does not alter the circulation or the lift on the airfoil. 
• What reviewer 1 stated about vorticity not being generated in the interior of the flow under the assumptions of (i) incompressible flow and (ii) a conservative body force, is correct.
• Kelvin’s theorem, that circulation does not change for a closed loop moving as a material curve (moving with the fluid), only depends on the assumptions of (i) inviscid flow, (ii) incompressible (low-speed) flow, and (iii) a conservative body force (e.g., gravity).

However, Blaisdell is struck by disbelief from the mounting difficulties in his presentation and seeks to encourage himself by twisting lack of evidence into its opposite:   

• Many of the concepts associated with viscous boundary layers, viscous-inviscid interactions, circulation, vorticity and the generation of lift, are not intuitively obvious. 
• The generation of vorticity on solid surfaces is one of the more difficult subjects included in my graduate introductory fluid mechanics course. 
• The fact that some of the concepts are difficult to understand does not make them wrong.

Blaisdell's long lecture is essentially a repetition of the long lecture by Reviewer 2 analyzed in a previous post. 

Like Blaisdell, Reviewer 2 not only lectures but also admits that aerodynamics education of today is a mess:

• Aerodynamics today is therefore almost always taught in a truncated version that retains all of the utility, but has lost much of the profundity. 
• Even the truncated version is no longer as highly respected as it used to be, because Computational Fluid Dynamics delivers, with no requirement for deep thought, most of the practical answers that are needed. In consequence, there are many employed today in the aerospace industry, and even in academia, whose grasp of the basic theory of flight contains many gaps. 
• These gaps are apparent to thoughtful students, who frequently attempt to fill them in for themselves, although the remedy is usually worse than the disease. 
• ... simplified or discarded in modern presentations to create a pragmatic treatment focusing on utility. 
• Undergraduate textbooks these days all too often simply omit anything that students find difficult.
• I believe that the authors ... are right to quarrel with the truncated version that they, like others, have apparently received. 

Reviewer 2 cannot but acknowledge important merits of our article, which Blaisdell ignores:

• The authors have put their fingers accurately on many of the defects in the truncated versions of aerodynamic theory that are now current.
• However, the authors are correct that separation might be fundamentally different in 3D than in 2D. 
• The authors have then sought their own explanations, stimulated by interesting results from their Navier-Stokes code.

Reviewer 1 acknowledges one of our key points:

• At most, perhaps they present a numerical model of the governing equations which avoids the need to discretize the boundary layer.

But Reviewer 1 does not understand that this suddenly makes the Navier-Stokes equations computable from being uncomputable by Prandtl's dictate of boundary layer resolution, and thus fundamentally changes both theory and practice of aerodynamics.

Summary: What is specially remarkable is the fervor of the re-education the editor and reviewers want us to undergo (like e.g. the Emperor in Red China): They want to be sure that we come out of the process fully re-educated to the correct belief of basic concepts.  No effort should be spared to reach this goal, as if our ideas somehow are dangerous to AIAA and thus have to be suppressed.  But why spend so much energy on cranks?

The Effect of the Green-House Conspiracy with 20 Year Delay

It is illuminating to watch the CH 4 UK documentary Green House Conspiracy from 1990. We see that the hoax of CO2 global warming was effectively deconstructed twenty years ago, by media which then turned into one-sided propaganda machines for CO2 alarm leading up to its peak at the beginning of the Copenhagen Climate Conference in 2009. Media which were unable to counter the collapse of CO2 alarmism that followed the collapse towards the end of the conference.

Evidently, the effect of the media documentary came out full force with a 20 year delay.

AIAA Defends Old Incorrect Theory of Flight 2

Let us now analyze the response of AIAA associate editor Blaisdell to our rebuttal of the referee reports recorded in the previous post.

AIAA does not respond to any point in our rebuttal connected to our article. In fact, AIAA does not give any evaluation of the New Theory of Flight at all, and in particular does not claim that it is incorrect. What AIAA does is only to defend the Old Theory according to the following plan:

• After reading your paper and your responses to the reviewers’ comments, I can see several misconceptions you have concerning basic concepts in fluid mechanics. My goal below is not simply to reiterate the comments of the reviewers, but to help you see some of the areas where you need to improve your understanding. I will try to be clear and direct in my comments to avoid any misunderstanding.

Like one of the reviewers, Blaisdell then sets out on a mission to teach us about the Old Theory, which is exactly the theory we have studied very carefully and found to be incorrect. Blaisdell starts out with:

• High Reynolds number flow around an airfoil (or a wing in 3-D) is, as reviewer 1 said, a singular perturbation problem, where a small parameter (1/Re) multiplies the term in the momentum equation with the highest order derivative. The potential flow solution you object to is only the leading order inviscid (outer) solution. The complete theory treats the coupled viscous-inviscid interaction by determining the viscous boundary layer (inner) solution, finding the displacement thickness of the boundary layer, adding that to the starting geometry to find the effective shape of the airfoil (thus accounting for the viscous displacement of the streamlines in the outer inviscid part of the flow field), recomputing the potential flow solution, and then iterating this process until a converged solution is found. This results in a pressure distribution that does not have a high value of pressure at the trailing edge, in agreement with experimental measurements. This iteration process is what is done by the airfoil analysis program XFOIL, which reviewer 2 mentioned. XFOIL is widely used in teaching aerodynamics, and I use it in my classes.

But XFOIL is a 2d panel code which is unphysical, because the physics is true 3d.  The fact that Blaisdell teaches incorrect physics signifies the present sad state of aerodynamics education, acknowledged by Blaisdell himself:

• Unfortunately, the complete theory is not always taught, with the result that many students have misunderstandings concerning flow over airfoils and wings. In my department we do not require our students to take a course in perturbation methods; as reviewer 1 said, aerospace engineers today use computational fluid dynamics; and, as a result, they lose sight of some of the theoretical underpinnings of what we study.

Blaisdell continues with more confession:

• Many of the concepts associated with viscous boundary layers, viscous-inviscid interactions, circulation, vorticity and the generation of lift, are not intuitively obvious. 
• One of my main jobs as an educator in the area of fluid mechanics is to build up my students’ intuition by increasing their understanding of basic concepts. 
• The generation of vorticity on solid surfaces is one of the more difficult subjects included in my graduate introductory fluid mechanics course. The fact that some of the concepts are difficult to understand does not make them wrong.

No, it does not necessarily make them wrong, but neither correct. After more defense of exactly what we criticize (Kelvin's theorem, boundary layer generation of vorticity, circulation et cet), without reading our criticism, Blaisdell concludes by renewing the advice to take some fluid mechanics course at KTH: 

• Lastly, both reviewer 1 and I had suggested that you contact colleagues at KTH who could help explain some of these concepts to you. In response to one of your previous comments, I want to say that doing so is not a requirement for submitting papers to AIAA. That suggestion was made because there are basic concepts in fluid mechanics that you do not understand, and it is easier to explain those concepts face to face over a period of time, rather than through the limited medium of email. I know some of your colleagues in the Mechanics Department at KTH, and I have a lot of respect for their knowledge of fundamental fluid mechanics and applied mathematics. I strongly suggest you talk with them, or take some of the courses they offer.

These are my so respected colleagues at KTH,  who are so good friends with Blaisdell, but refuse to speak to me. What a world of science.

Summary:  AIAA does not claim that the New Theory is incorrect, that our 3d Navier-Stokes/slip computations do not describe the real physics of the flow around a wing, or that our analysis of the computations is incorrect. AIAA only defends the Old Theory, while admitting that it is so difficult that it cannot be taught to new generations of engineers responsible for constructing the new airplanes to carry new generations of people safely and efficiently.

AIAA actively suppresses discussion of a very important scientific issue, by intimidating power play.  It is not admirable and will not work in the long run.

AIAA Defends Old Incorrect Theory of Flight 1

Below is the the response from AIAA associate editor Greg Blaisdell on our rebuttal of the 

referee reports. An analysis of the position of AIAA is given in the next post.

Dear Professors Hoffman, Jansson and Johnson,

I have read your response to the reviewers’ comments and gone back over 
the reviews and your paper. I agree with the reviewers’ assessment of 
your paper. (Note: below I refer to Reviewers 1 and 2 as they are listed 
in the AIAA manuscript review system; on Professor Johnson’s website the 
two are reversed.) Reviewer 1, especially, has given a thorough, 
articulate and gentle explanation of the deficiencies of your paper. 
After reading your paper and your responses to the reviewers’ comments, 
I can see several misconceptions you have concerning basic concepts in 
fluid mechanics. My goal below is not simply to reiterate the comments 
of the reviewers, but to help you see some of the areas where you need 
to improve your understanding. I will try to be clear and direct in my 
comments to avoid any misunderstanding.

First, one of your major objections to the classical theory of the 
generation of lift is that the potential flow solution has a stagnation 
point at the (sharp) trailing edge and, therefore, produces a pressure 
distribution with a high value of pressure at the trailing edge. This 
high value of pressure is not observed in experimental measurements. 
Also, the pressure distribution from the potential flow solution does 
not give rise to any drag, which is incorrect from common experience 
(d’Alembert’s paradox). What you seem to be missing, which reviewer 1 
alluded to, is that this view of the classical theory is “truncated”; it 
is not a correct view.

High Reynolds number flow around an airfoil (or a wing in 3-D) is, as 
reviewer 1 said, a singular perturbation problem, where a small 
parameter (1/Re) multiplies the term in the momentum equation with the 
highest order derivative. The potential flow solution you object to is 
only the leading order inviscid (outer) solution. The complete theory 
treats the coupled viscous-inviscid interaction by determining the 
viscous boundary layer (inner) solution, finding the displacement 
thickness of the boundary layer, adding that to the starting geometry to 
find the effective shape of the airfoil (thus accounting for the viscous 
displacement of the streamlines in the outer inviscid part of the flow 
field), recomputing the potential flow solution, and then iterating this 
process until a converged solution is found. This results in a pressure 
distribution that does not have a high value of pressure at the trailing 
edge, in agreement with experimental measurements. This iteration 
process is what is done by the airfoil analysis program XFOIL, which 
reviewer 2 mentioned. XFOIL is widely used in teaching aerodynamics, and 
I use it in my classes.

The pressure near the trailing edge differs from that of the leading 
order inviscid potential flow solution because of the displacement 
effect of the viscous boundary layer. As a result the pressure does 
contribute to the drag; this is termed “form drag”. Both pressure and 
skin friction contribute to drag. Which one is dominant depends on the 
airfoil design, angle of attack and Reynolds number. At small angles of 
attack the skin friction contribution can be much larger than the 
contribution from the pressure; while pressure or form drag is more 
important at higher angles of attack where the airfoil acts more like a 
bluff body. D’Alembert’s paradox is no longer a paradox. His potential 
flow solution lacked two effects due to viscosity that create drag – 
skin friction and form drag due to the displacement effect of the 
boundary layer. Please note that, contrary to what is sometimes stated, 
form drag does not only occur due to boundary layer separation. Even if 
the boundary layer does not separate, the displacement effect of the 
boundary layer will alter the potential flow solution and result in drag 
due to pressure.

As reviewer 1 said, it is the truncated form of the classical theory 
that you object to. Unfortunately, the complete theory is not always 
taught, with the result that many students have misunderstandings 
concerning flow over airfoils and wings. In my department we do not 
require our students to take a course in perturbation methods; as 
reviewer 1 said, aerospace engineers today use computational fluid 
dynamics; and, as a result, they lose sight of some of the theoretical 
underpinnings of what we study.

Many of the concepts associated with viscous boundary layers, 
viscous-inviscid interactions, circulation, vorticity and the generation 
of lift, are not intuitively obvious. One of my main jobs as an educator 
in the area of fluid mechanics is to build up my students’ intuition by 
increasing their understanding of basic concepts.

Another set of basic concepts that you misunderstand deal with 
circulation and vorticity. They are related, but they are not the same, 
and both are important to understanding the fluid mechanics of airfoils 
and wings. I do not have the time or space to elaborate in detail; these 
are concepts that are taught over the course of a full semester. 
However, there are two points I want to clarify. First Kelvin’s theorem, 
that circulation does not change for a closed loop moving as a material 
curve (moving with the fluid), only depends on the assumptions of (i) 
inviscid flow, (ii) incompressible (low-speed) flow, and (iii) a 
conservative body force (e.g., gravity). The flow can be unsteady, 3-D 
and rotational (nonzero vorticity) and the theorem still holds. It is 
not invalidated by there being fluctuations in the freestream or 
instabilities in the flow (more on that below).

One important difference to see between circulation and vorticity is 
that when a vortex is stretched, as by a strain field discussed in your 
linear stability analysis, the vorticity is increased as the vortex 
radius decreases and vortex lines become concentrated, but the 
circulation remains fixed, in agreement with Kelvin’s theorem. The 
vorticity is twice the local rotation rate of fluid elements, and the 
increase in vorticity is similar to the increase in rotation rate of an 
ice skater when he spins and then brings his arms in tight. His rotation 
rate increases, but his angular momentum remains constant (not 
accounting for friction). Kelvin’s theorem deals with circulation, and 
it is in fact the circulation around the airfoil that is important to 
the lift.

The second point I want to make concerns the generation of vorticity. 
What reviewer 1 stated about vorticity not being generated in the 
interior of the flow under the assumptions of (i) incompressible flow 
and (ii) a conservative body force is correct. This can be proved 
mathematically from the basic governing equations. In the discussion 
above about a strained vortex, the vorticity increases locally because 
the vortex lines become more concentrated; however, no new vorticity is 
generated. New vorticity is generated on solid surfaces through the 
action of pressure gradients or unsteady motion of the solid surface. 
This point is discussed well in the text Incompressible Flow by Panton. 
The generation of vorticity on solid surfaces is one of the more 
difficult subjects included in my graduate introductory fluid mechanics 
course. The fact that some of the concepts are difficult to understand 
does not make them wrong.

The last technical point I want to make concerns the trailing edge 
instability and your linear analysis. It is well known that vorticity in
a strain field, such as near a stagnation point, results in vortex
stretching and an exponential increase in vorticity. The solution for
this is worked out in the book The Structure of Turbulent Shear Flow by
Townsend and is part of the rapid distortion theory of turbulence. As
discussed above, the increase in vorticity magnitude does not mean an
increase in circulation. The trailing edge vortices in your simulations
form in counter-rotating pairs. Their net circulation is zero, and their
presence does not alter the circulation or the lift on the airfoil. I
also want to point out a flaw in your analysis. Fluctuations in the flow
are not introduced by a non-conservative body force, as you state. For
flow over an airfoil or wing, there is no such non-conservative body
force. The only body force acting is gravity, and it is conservative
and, therefore, does not generate vorticity. Instead fluctuations come
from the freestream, as turbulence from upstream is convected toward the
airfoil; fluctuations near the trailing edge also come from turbulent
flow in the boundary layers or, in the case of a separated boundary
layer, turbulence produced in the free shear layer.

Lastly, both reviewer 1 and I had suggested that you contact colleagues
at KTH who could help explain some of these concepts to you. In response
to one of your previous comments, I want to say that doing so is not a
requirement for submitting papers to AIAA. That suggestion was made
because there are basic concepts in fluid mechanics that you do not
understand, and it is easier to explain those concepts face to face over
a period of time, rather than through the limited medium of email. I
know some of your colleagues in the Mechanics Department at KTH, and I
have a lot of respect for their knowledge of fundamental fluid mechanics
and applied mathematics. I strongly suggest you talk with them, or take
some of the courses they offer.

Sincerely,

Greg Blaisdell
AIAA Journal Associate Editor

Burt Rutan and Scaled Composites: SpaceShipOne

Burt Rutan is famous for innovative flight designs including SpaceShipOne, the Voyager and an early rigid sail for Ameriacs Cup developed at his company Scaled Composites. I have sent an email to the company to see if there is interest in our new theory of flight.

New theory may open to new innovative designs, or at least remove obstacles to new designs set by Old Theory.

As concerns the aerodynamics of the Voyager, we read:

• The respectable lift-to-drag ratio of approximately 32 was achieved by careful shaping of the wings for laminar flow, avoiding drag-producing protuberances, and careful design of the engine cooling air paths.

We see here an influence of the Old Theory supporting a common belief that laminar flow can generate large lift-to-drag ratio by maintaing lift and reducing drag. But is the flow around the Voyager really laminar? Can laminar flow generate large lift?  The speed of the Voyager was about 200 km/hour.

Well, the Reynolds number is larger than 100 millions and so the flow is most likely not laminar.

New Blog on Blackbody Radiation

I have started a new blog on blackbody radiation:

• Computational Blackbody Radiation

where I will collect old and add new material on this subject, which made classical physics collapse into modern physics through the work of Max Planck.