Talk:Wing/Archive 1

This is an archive of past discussions about Wing. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.

Archive 1

Debunking the Coanda explanation

I have just reduced the status of the Coanda explanation in the section on how a wing works and here is why.

Professional aerodynamicists use the conventional explanation every day and in doing so produce successful aircraft, not by trial and error but with mathematics. Unlike conventional aerodynamics, the 'Coanda theory' cannot be used to make further calculations, such as predicting the depth of the boundary layer. This is the ultimate test of any scientific theory, which it fails.

There is a real Coanda effect, which has been used to generate lift using a jet blowing over a curved surface. However it needs the flow from high speed jet to produce enhanced lift, and it does it through turbulent mixing that does not occur above a normal wing.

The 'Coanda-ists' claim that the air “sticks” to the surface because of viscosity. This implies that if the viscosity of the fluid changes, the amount of lift an airfoil produces should change in proportion. Experiments show that the amount of lift produced by a real wing is independent of viscosity over a wide range. In fact the real Coanda effect requires turbulence, so it only occurs if the viscosity is sufficiently low.

The air speeds up the air above its upper surface. Coanda-ists assume that the relative air-flow meets the wing at the same velocity as in free air and then follows the curve. This understates the pressure gradients by an order of magnitude. JMcC 11:43, 29 November 2005 (UTC)

Science of Wings

I strongly suggest that the section "Science of Wings" basically refer the reader to the article Lift (force). At present, the section duplicates much of what is over at the other article, which has been active for much longer and has been discussed at very great length by contributors. The duplication here is also slightly at odds with the general explanation that we have, over countless discussions, arrived at. For Wikipedia to be consistent as well as efficient, I think that a long-winded explnation here should be discouraged. Better to give a very brief explanation, and link to the other article. If the other article needs further work - for example to work in more (or less, depending on your POV) about the Coanda effect, then please come over and contribute! Graham 22:12, 29 November 2005 (UTC)

Quite right. I edited the Wing article when I was unaware of the Lift (force) article. I should have looked around more before diving in. It is a good indication of how mature Wikipedia is getting that there are few big holes on major subjects. I will pare down the science of wings article forthwith. JMcC 08:35, 30 November 2005 (UTC)

Personally I have a big problem with all articles which give the Bernoulli law as the only affecting factor in lift, and it seems that this "Wing" article falls into this too. The classic counter-argument to the "bernoulli-only" explanation is that it would not explain how a plane is able to fly upside down. Another classic is the issue of how a plane with completely flat wings can fly (which it demonstrably can do). However, I have other problems with that explanation as well.

I once saw a TV document where a F1 engineer (nonetheless) gave Bernoulli's law (with the classic "air flows different distances" explanation) as the only explanation for the downforce of the car. He did not mention anything else as a causing factor. I would have liked to ask that engineer: "If only the air flow difference between the upper and lower sides of the wing is the explanation for downforce, then why is the wing heavily curved up?" And also: "Are you telling me that air colliding with the highly curved upper surface of the wing, thus being deflected upwards, causes no downforce whatsoever?"

That's my main problem with the Bernoulli-only explanation: It doesn't address the issue of the wing changing the direction of the airflow. This direction change happens in F1 wings as well as helicopter blades, and in fact also in airplace wings. Since only Bernoulli is given as an explanation for lift, it would mean that the wing is somehow able to change the direction of airflow for free (eg. in the case of a F1 car wing, the airflow which comes directly from the front is deflected upwards). But of course we know from basic Newtonian laws that this just isn't true: If the wing changes the direction of the airflow, it experiences a force opposite to the direction change of the airflow.

This is how I personally explain wing lift to people who ask me: "The wing changes the direction of airflow and (due to Newton's law) experiences a force to the opposite direction. There may be other minor affecting factors too, such as air pressure differences, but those are not really relevant."

-- Juha Nieminen

Science of wings - edit required

I'm an Aerospace Engineering student at OSU, so I'll make a full edit of this section today (yes you are correct in thinking that it is, sadly, mostly incorrect). I'll do my best on it, and I do have several sources, so PLEASE say something before changing it back AGAIN.

Given the discussions on this page, shouldn't somebody change the section "Science of Wings" once an for all in this article? It still credits the Bernoulli effect as a major factor in creating lift which is simply not true as many of you on this page have pointed out. While the Bernoulli effect occurs over conventional assymetrical wing designs it is not responsible for lift. I notice an attempt was made recently to change the article pointing out this common misconception but someone changed it back! Given how widespread this misconception is we should probably do everything we can to stop its further spread, particularly on a resource as well read and trusted as Wikipedia.

Fthiang 12:22, 7 September 2006 (UTC)

Ah, from the message on my talk page I see where the trouble is now. Yes the “equal transit time” theory is baloney. However:

If a wing is lifting then the pressure above it is lower than that below it. The lift force is exactly accounted for by the pressure distribution on the surfaces. As the pressure is different, so it the velocity, the two linked by Bernoulli’s principal which remains in effect as always. If a wing is lifting then it is deflecting air downwards. The lift force is exactly accounted for by Newton’s laws, which also remain in effect as always. These are not two conflicting explanations, just two of several different views of a single process.

In the lift force article some of the “equal transit time” idea has misleadingly been attached to the bottom of the Bernoulli section. That is where a clarification is needed. Meggar 05:31, 8 September 2006 (UTC)

I find this section disappointing. Surely what is required is a simple statement outlining the mechanism of lift. Newton, Bernoulli and all the others are not differing theories about how a wing works, that has been pretty well understood for centuries. Rather, they are general principles that can be applied, inter-alia to the mechanism of a wing in order to allow the production of mathematical models. We should provide an explanation that the layman can appreciate, which is accurate and does not mislead. I will give it some thought and see what I can come up with. Rolo Tamasi 20:34, 10 September 2007 (UTC)

WikiProject class rating

This article was automatically assessed because at least one WikiProject had rated the article as start, and the rating on other projects was brought up to start class. BetacommandBot 10:06, 10 November 2007 (UTC)

Introduction

"A wing is a device for generating lift. Its aerodynamic quality, expressed as a Lift-to-drag ratio, can be up to 60 on some gliders."

This is misleading. While the overall lift to drag ratio is say 60:1 on gliders, this applies to the whole aircraft - NOT just the wing. The wing's LD ratio is much higher. —The preceding unsigned comment was added by 203.206.12.93 (talk) 03:15, 15 April 2007 (UTC).

I don’t find it misleading at all, how can a wing generate any L/D ratio without the associated structure to maintain the angle of attack? The concept of L/D requires the existence of the rest of the aircraft.

No it doesn't. You can compare the qualities of different wing profiles in a wind tunnel and examine their L/D ratios. If we were talking about L/D ratios in an aircraft article then I would agree with you. This is the WING article. Using 60:1 as an example is misleading because it implies the wings by themselves of a glider could have an LDR of 60:1 when they are in fact much higher. I'll reword the statement to try and reach a compromise. 123.243.237.83 (talk) 12:27, 21 January 2008 (UTC)

I disagree, a wind tunnel replaces the aircraft and effects the L/D (walls, floor, ceiling) just as much as glider fus + tail. What is more it is extremely unusual to measure the L/D of "wing" in a wind tunnel - they are used to compare the performance of different sections, not of "wings". Further, in addition to the structural purpose of the fus it is also an important part of the aerodynamic mechanism, if you could remove the fus the L/D of the wing would get worse!

However, let us take care this does not turn into a series of irrelevant contradictions and loose sight of the reason someone included those words. The purpose was to give the reader some feel for the order of magnitude of L/D, not for a couple of pedants to argue how many angels can stand on a pin head.Rolo Tamasi (talk) 19:31, 21 January 2008 (UTC)

I have modified your edit that included "The lift generated by a wing at a given speed and angle of attack is at least 1-2 orders of magnitude greater then the drag" for a number of reasons - first many will interpret it as meaning that the L/D is always an order of magnitude ratio, clearly it is not, it can be unity or lower. - Secondly it is illogical to specify a range as "at least", the lower end of the range is redundant. - Thirdly many people these days interpret "orders of magnitude" as "whole factors of 10" and this phraseology could be taken to imply L/Ds of 1,000. In any event, I would be interested in any authority describing ratios of over 100, we should include them in the article.

I am also concerned by the sentence that follows it, although I have not modified it. I fear it may entice some into that well know trap of thinking a wing is giving something for nothing. Of course this is not the case; L/D is a statement of inefficiency, a 100% efficient wing has an L/D of infinity. I don’t understand what value this statement has here. I also regret the removal of the words indicating that very efficient gliders can achieve an L/D of 60 - it was a useful statement of fact that improves the understanding of the reader. Rolo Tamasi (talk) 20:40, 21 January 2008 (UTC)

Proposed split

Many Wikipedias in other languages have separate articles about wings of aircraft:

I believe that this should be done here, too. This is just my common sense - unfortunately i don't know anything about aeronautics.

Note also, that there already is Insect wing. --Amir E. Aharoni (talk) 23:05, 8 September 2008 (UTC)

Wing materials and construction types

What isn't mentioned in the article is what "types" of wings there are; ie the wings used in the wright flyer and other old aircraft are called "ladder wings" (see http://www.pouchel.com/english/index_eng.php?p=pouchel_eng.htm ) More recent wing types (WW2) were made of metal (not sure whether these wings were hollow or full) and wood (see De Haviland Mosquito), even more recent wings are made of plastics or composite metals

Check this, add references, and add the section to the article 91.182.194.98 (talk) 07:17, 15 July 2010 (UTC)

--> In essence, two types of wings exist, namely flexible wings and rigid wings. Flexible wings are flexible to some degree and are the oldest types of wings, being used in the Wright Flyer and comparable aircraft. Rigid wings appeared later. Both can have a suitable wing profile; in the beginning of aviation, "flexible" wings were made quite similar to the method used for rigid wings, consisting of

wooden spars
wooden ribs (having a profile; ie thicker to the front, thinner to the back)
a sail or "canvas" (linnen, more durable textile around the first world war)
metal Wing_configuration#Wing_support wire braces for support

Later-on, flexible wings were also made consisting of only the sail, as seen with the Rogallo (delta) wing and various other ultralight (straight) wings (see http://en.wikipedia.org/wiki/Eipper_Quicksilver )

Another main advantage of the early flexible wings is the fact that they can utilise wing warping, and does not require heavy ailerons, despite the fact that still have wooden ribs under the canvas (hence still profiting from a perfect wing design, rather than simply having a flat sail). KVDP (talk) 13:45, 26 July 2010 (UTC)

Typical KVDP edit, ignore the real content and drop straight into an invented taxonomy of "rigid" and "flexible" wings, which you then compound by classifying the Wright Flyer as flexible!

If there is a distinction between groups of wings like this (which would be a bad idea in a top-level article for a general readership encyclopedia) Wright's Flyer is a rigid wing. Yes, it used wing warping rather than movable control surfaces. However the distinction of flexibility per Rogallo et al is that the wing surface is defined by a framework (simply rigid or purely by tension, in Rogallo's case, inflated by aerodynamic forces) which is then spanned by a flexible membrane in tension. The shape of such a flexible membrane depends on the tension within it, and the effect of the framework. Flyer's wing, although warping under control inputs, was intended to stay rigid under its flight loads.

It is difficult to add quality content to an encyclopedia, it's especially difficult to do this to a high-level article and still maintain a readable editorial structure. It is not achievable by reading two or three trivial refs and then spewing unbalanced factoids into it. Andy Dingley (talk) 15:50, 26 July 2010 (UTC)

Bernoulli versus Coanda

A Contribution to the Bernoulli/Coanda Effect

The entire discussion on the Bernoulli or the Coanda effect is in itself remarkable as one is familiar with some relatively simple considerations.

It is correct that if one checks a series of “scientific” types of sources, there is a predominance of the Bernoulli principle, and that this predominance has been current in many years. The problem is, that it is obviously inadequate. And that the Bernoulli principle is merely a rough calculation for the Coanda effect. And that the Bernoulli effect is only one of the ways to create a change of direction and force effect of the air current.

If you are interested in such wing-technical topics, you can log onto www.av8n.com/how#contents . It is a comprehensive specification on Flying Theory, which also contains a thorough discussion on the function of the wings.

Initially I was impressed, but if you examine it more closely, you are to find some grave gaps. E.g. in chapter 3, which contains a number of beautiful air pictures of the air motions above and below the wing and which you at first perceive as a documentation of the Bernoulli principle. But if you are to read more carefully, it turns out that these beautiful models are made by means of computer simulation with programs that the author himself has developed. So when the author incorporate the Bernoulli principle as an important part of the wings’ function in his programs, this principle of course also appears in the turned-up models. But it does not prove anything physically – it is more suitable for deceiving its readers.

Furthermore, I feel fairly confidant that the whole discussion on the Bernoulli effect is turned upside down and that the relation between cause and effect is equally turned upside down. The connection is not that the partial vacuum comes into existence because the air commences to stream faster above the wing. No, the connection is reverse; the air begins to stream faster because of the partial vacuum arisen above the wing. This goes to imply that the Bernoulli effect is only a part of the total carrying capacity and that it is practically a rough calculation of the actual effect. Namely Newton’s third law – the law of action and reaction. The Bernoulli effect merely increases the power effect which arises via Newton’s third law.

You are correct in the observation that the air goes faster over a wing because of the lower pressure above it. I would like to correct you on one point tho'. All of the lift caused by a wing is the result of the deflection of the airflow. The lift is NOT partly from this, and partly from that... The deflection of the air flow causes all of the change in pressure above and below the wing, which in turn cause the air above the wing to accelerate and that below it to decelerate. The "Bernoulli effect" in this instance is simply that the air will accelerate into a lower pressure region. (I know this is not a normal way to describe the B effect, but it is what is happening here). As a result of this, the use of the word Bernoulli, and all references to it are counter productive in any explanation of the reason a wing produces lift and should be totally removed from any such discourse except to explain that it is NOT valid as part of any explanation of wing lift. Dave Fowler 15-Feb 2006

In order to understand how an airplane remains in the air, one must approach the matter in a different way. Namely: How does the air change after the wing has passed through it, for this is exactly what must be measured and calculated. Because if for instance it turns out, that the directional vector for the total air mass has changed direction per second, and that this corresponds to the airplane’s gravitational acceleration per second – well, then it is proven that the Bernoulli principle at the very most, is a rough calculation of the airplane wing’s carrying capacity. And that it is Newton’s third law which bears the main responsibility. I.e. the airplane wing pushes a certain air mass downward and thereby maintains the airplane in the air. And just that is certainly worth calculating.

Let me remind you, that the very same method is applied when you want to acquire knowledge of particles in the atomic area when you can neither “see, hear nor smell” the particles. You send such particles through the medium and measure to what extent it effects the medium.

The issue can also be approached without all the mathematics involved. Because if the Bernoulli principle in fact has an independent carrying capacity that doesn’t result in a downward air stream behind the wing, then it must signify, that a wing could move through a medium, use this medium to stay in the air without the medium itself being significantly influenced by it. And this does sound as a physical impossibility. Nevertheless, this is how the interaction between a wing and an air mass most frequently is depicted in the models. E.g. see Lademanns Lexicon CD ROM.( a Danish Lexicon)

This "Independant carrying capacity" demonstrates that you are not doing a thorough analysis of the problem using physics rather than a general understanding. If you apply physics, and only physics to this problem you will find that Bernoulli has nothing at all to do with the cause of lift. Deflecting air is a total explanation for the generation of lift. Dave Fowler 15-Feb 2006

Conclusively I will attach a model picture of a sailing boat. The sails are arched pieces in streaming fluid where its surface is made visible by means of powder. And just that shows what it is all about. Namely that the sails obtain their moving power by changing the direction of the wind. That is to say the physical law of action and reaction. Newton’s third law.

The model picture is from my article from 2000 on www.maximalt.dk/Faerdigheder/sejlteori.htm

May I conclusively remark

This inversion between cause and effect brought on by the Bernoulli effect, may quite possibly be rooted in the following: Indeed, one has to do with an airplane and want to explain why it maintains in the air. One therefore seeks to establish the forces that keep it in the air. One ascertains that there is a partial vacuum above the wing and that the stream of air accelerates above the wing. I.e. a Bernoulli effect.

As one seeks the forces that keep the airplane in the air, they yield to the psychological need, and let the effect go that way around, which apparently explain the problem that is wanted to be solved. But the coherence is false, namely that the casual connection is that the faster airstream creates the lover pressure. But as told, the connection is indeed the opposite around: the lower pressure ( arisen in a different way), creates the higher velocity above the wing. The Bernoulli principle is an energy preservation principle and it can therefor go both ways. Henning Rolapp

I doubt this is the appropriate forum for this discussion, but I will say this: Nobody seems to be suggesting that the essential principle here is not Newton - air is deflected downward and that gives rise to the lift force. What does appear to be in dispute is how this comes about. Personally I feel that the Coanda vs. Bernoulli "argument" is moot - both effects arise. What seems unclear is why the Coanda effect occurs at all (i.e. what makes air "stick" to a curved wing even though it must expend energy to do so), but maybe that problem has been solved since I last looked at the literature. To me the most important point to get across is this: there is no "catch-up" effect going on. By this I mean the explanation that an aerofoil "forces" the air over the top to go faster in order to catch up with the air below, hence lowering its pressure and sucking the wing upward. I see this explanation in book after book after book - usually those that seek to explain science to the layman. These books are wrong, they are misleading and bad. At least the site you mention above does take pains to squash this myth, and the very nice animations do help to make this clear. Incidentally nobody seems to be saying that there is no net effect on the air either - as you rightly point out, there must be, and there is. I don't think that is in dispute. As an aside, I recently heard some UFO-apologist ranting on about how UFOs might fly, by "somehow" (he was vague on this point!) displacing the air around the craft such that there was no net disturbance (hence allowing instantaneous acceleration and hypersonic flight without a shockwave, etc). If this were "somehow" possible, there would be no net lift force on the craft, so presumably it would just fall out of the sky. Of course aliens sufficiently advanced would have invented antigravity, so you can never win an argument with these people ;-) Graham 00:26, 10 Sep 2004 (UTC)

I’m amazed that this guff is still here after all these years.

Let us all spend some years arguing - does the chicken create the egg or the egg the chicken? Or rather let us not because the question is invalid - the two are in no way mutually exclusive.

Can you have a force without there being its equal and opposite partner? – NO Can a gas impart a force to a solid without there being a pressure difference? – NO Are the two mutually exclusive? – NO they are both inevitable and essential parts of the mechanism.

The more talk there is of this the more we encourage misconceptions and confused thinking – Can we archive this section? Rolo Tamasi (talk) 00:54, 30 September 2010 (UTC)

The aerodynamics of wings

Today I edited this section to bring it in line with the treatment over at Lift(Force) and in accordance with WP:NPV. I also added some citations. Hopefully I can add some more citations so that we can remove the refimprove tag.

Please discuss here before reverting the edits. Thanks. Mr swordfish (talk) 20:48, 28 June 2011 (UTC)

Thanks for adding some extra citations. Reference No. 4 ("The cause of the aerodynamic lifting force is the downward acceleration of air the by airfoil") is apparently a quotation from Weltner and Ingelman-Sundberg. You have appended a tag saying 3 and I guess that is pointing to reference No. 3 but I find it ambiguous and unsatisfactory. If the quotation at reference No. 4 is from Weltner and Ingelman-Sundberg I suggest you state that explicitly in the citation rather than rely on the tag-ref notation. Dolphin (t) 23:24, 29 June 2011 (UTC)

I struggle with Wiki citations, and your suggestion for improvement is appreciated. I've edited the cite per your suggestion. Mr swordfish (talk) 13:58, 30 June 2011 (UTC)

The aerodynamics of wings - near atmospheric pressure below a wing

This higher pressure on the bottom of the wing is generally the normal atmospheric pressure, plus or minus a small percentage.

No citation is given for this, and it's mis-leading. The pressure above a wing isn't much lower than atmospheric pressure either. For most aircraft in level flight, wing loading is around 0.7% atm to 7% atm. Split this evenly above and below a wing and the range is .035% atm to 3.5% atm, already small percentages of atmospheric pressure. I'm aware that typically the pressure above a wing is reduced more than it's increased below, but I'd like to see some actual data for typical aircraft.

Rcgldr (talk) 07:34, 21 October 2010 (UTC)

I added a citation needed note to this assertion. I'll see what I can turn up wrt research and either provide a citation or remove it. Mr swordfish (talk) 20:43, 28 June 2011 (UTC)

Here's what Holger Babinsky has to say in "How Wings Work" (Physics Education Nov 2003):

...consider the difference between the streamlines over a thin and a thick aerofoil... Despite the difference in thickness, both have similar flow patterns above the upper surface. However, there is considerable difference in the flow underneath. On the thin aerofoil the amount of flow curvature below the wing is comparable to that above it and we might conclude that the overpressure on the underside is just as large as the suction on the upper surface—the two sides contribute almost equally to the lift. In the case of the thick aerofoil, however, there are regions of different senses of curvature below the lower surface. This suggests that there will be areas with suction as well as areas with overpressure. In this case the lower surface does not contribute much resultant force and we can conclude that thin aerofoils are better at generating lift. This is generally true, and birds tend to have thin curved wings. Aircraft do not, because of the structural difficulties of making thin wings, and also because the volume contained in the wing is useful, e.g. for fuel storage.

So it appears that the assertion may be partially true for thick airfoils, but not true in general. I'm going to remove it. Mr swordfish (talk) 20:33, 29 June 2011 (UTC)

I'm not familiar with Holger Babinsky or his writings, but I disagree with the content of his quotation above. For example, he concludes that thin aerofoils are better at generating lift. This is not a conclusion that is supported by a century of research into aerofoils. See Abbott & von Doenhoff's Theory of Wing Sections which summarises an extraordinarily thorough assessment of many aerofoil sections by the US National Advisory Committee for Aeronautics (NACA) in the 1930s and 1940s.

Diagrams showing the distribution of pressure coefficient around an aerofoil that is generating lift show that the pressure distribution over the upper surface of the aerofoil is not uniform - it is almost triangular. There is a region of intense low pressure on the upper surface, just behind the leading edge, as the air travels at high speed around the curvature of the leading edge. Once the air has passed around the curvature of the leading edge it progressively decelerates until it leaves the aerofoil at the trailing edge, and as a result the pressure rises in almost linear fashion to the trailing edge just as Bernoulli's principle predicts. (A supercritical airfoil aims to avoid this triangular distribution of pressure coefficient by chopping off the top and extending the region of low pressure further towards the trailing edge - "flattening" the triangle, avoiding such a high peak value of pressure coefficient and delaying the onset of the shock to a higher Mach number.)

These diagrams also show that the pressure distribution over the lower surface of the aerfoil does not experience this dramatic variation. The pressure distribution over the lower surface is almost uniform. There is no region of intense high pressure (or low pressure) as there is for the upper surface.

I will try to locate a diagram that I can post on this Discussion page. Dolphin (t) 02:53, 30 June 2011 (UTC)

I would not take Babinsky's article as the final word on the subject of how the pressure is distributed along the wing surface. If we're going to treat the topic in the article we would need to seek out several more references (and if there's disagreement, present both sides). I look forward to seeing the diagrams.

In this case I was just trying to find support for the assertion that the pressure on the underside remains at or near atmospheric pressure, and finding nothing supporting it and one article contradicting it, it seemed appropriate to remove the assertion from the article. Perhaps we should replace it with something more accurate (i.e. discuss the distribution of pressure and note that for some foils the pressure on the top decreases much more than it increases on the bottom), but I'm not ready to do that at this time. Mr swordfish (talk) 14:14, 30 June 2011 (UTC)

In Theory of Wing Sections by Abbott and Van Doenhoff (1949, 1959) there is a great diagram at Figure 34 (in Section 3.7). It shows the chordwise distribution of pressure coefficient about a NACA 4412 airfoil section at an angle of attack of 8°.

Along most of the lower surface the pressure coefficient is about +0.25. This means that along most of the lower surface the air pressure is greater than atmospheric pressure by 25% of the dynamic pressure (

{\tfrac {1}{2}}\rho V^{2}

). Expressed in terms of airspeed, and assuming slow speed (incompressible flow), a pressure coefficient of +0.25 means the airflow past much of the lower surface of the wing is slower than the speed of the wing through the atmosphere by a factor of square root of three quarters, or 87% of the speed of the wing through the air. (eg if an aircraft is flying at 100 knots true airspeed, the air flowing past much of the lower surface of the wing is traveling at 87 knots relative to the surface of the wing.)

The distribution of pressure coefficient along the top surface is approximately triangular. At the leading edge the pressure coefficient goes almost vertically to about -2, and then the hypotenuse of the triangle slopes linearly to about zero at the trailing edge. (Pressure coefficient of zero means the air pressure is no different from atmospheric pressure.) This gives a vaguely triangular shape. Pressure coefficient of -2 means the air pressure is less than atmospheric pressure by twice the dynamic pressure. Expressed in terms of airspeed, and assuming slow speed (incompressible flow), a peak pressure coefficient of -2 means at the point of the peak the airflow past the wing is faster than the speed of the wing through the atmosphere by a factor of square root of 3, or 73% faster than the wing through the air. (eg if an aircraft is flying at 100 knots true airspeed, just behind the leading edge of the wing the air is traveling at 173 knots relative to the surface of the wing.)

The shape of the chordwise distribution of pressure coefficient varies rapidly with changes in angle of attack (or lift coefficient) so my examples above for the NACA 4412 airfoil are only valid at 8° angle of attack. Abbott and Von Doenhoff don't make any narrative comment about the shape of this diagram or the implications for the pressure on the lower surface of the wing. Empirical data is the best way for gauging what is happening. The data provided by Abbott and Von Doenhoff show that the major contributor to lift is the triangular distribution of pressure coefficient over the upper surface of the wing. The lower surface does not have this strong variation in pressure - the pressure on the lower surface is approximately constant and slightly higher than atmospheric pressure, showing the airflow past the lower surface is slightly slower than the speed of the wing, or the aircraft, relative to the freestream. Dolphin (t) 12:51, 1 July 2011 (UTC)

Interesting stuff. Unfortunately, I don't have easy access to Theory of Wing Sections, but I did dust off my copy of High Performance Sailing (Frank Bethwaite) and there are similar diagrams to what you describe. Depending on the angle of attack, the low pressure on the leeward ("top") side of the foil is much larger than the corresponding high pressure on the windward ("bottom") side, and is shaped much as you describe. This difference depends on the angle of attack and foil shape:, some examples have the dramatic "triangle", others do not, and when the foil is stalled the pressure is almost entirely on the bottom. Take a look at the graph on page 6 of http://www.arvelgentry.com/techs/The%20Aerodynamics%20of%20Sail%20Interaction.pdf - for 25° AOA, the Cp is more or less evenly distributed along both upper and lower surfaces with the upper surface about a factor of two larger than the lower, but for 35° AOA we see the dramatic "triangle" with the Cp on the leading edge of the upper side larger than the lower side by a factor of 6.

So, since this depends on the foil shape and the AOA, I'm not sure how to phrase this to put it into the article without being so overly broad that the resulting statement is incorrect, or so vague as to add little value. I'm now fairly convinced that the assertion that was in the article until recently ("This higher pressure on the bottom of the wing is generally the normal atmospheric pressure, plus or minus a small percentage.") is incorrect; 25% is not a "small percentage". So, while removing the assertion was the right thing to do, perhaps we should replace it with something more accurate (and verifiable). I'm not ready to do that at this point. Mr swordfish (talk) 19:11, 5 July 2011 (UTC)

Thanks for the link to the article by Arvel Gentry. Figure 9 is closely similar to the diagram I described from Abbott and Von Doenhoff, and illustrates our point perfectly. Notice in Figures 9, 12, 14 and 16 the common practice of inverting the C_p axis so that the line representing the upper surface of the airfoil is shown above the line representing the lower surface.

I agree that trying to describe the situation with the lower surface by saying the pressure is generally the normal atmospheric pressure, plus or minus a small percentage is unsatisfactory. I will keep thinking about a way to get a copy of one of these diagrams into the article. Dolphin (t) 23:21, 5 July 2011 (UTC)

Where they got the idea of that airfoil shape

Nice article.

I was thinking - how about grounding the article in terms of where they got the idea of that airfoil shape. I discovered that sailors have been talking about lift and that airfoil shape since Egypt ruled, it's really a basic principle of sailing. For wings you just point the lift up, in sailing the lift goes to the side. I think I'm going to copy this to the wiki reference on wing as well.

When I started looking into this I thought these guys like George Cayley were pretty esoteric thinkers to just sit there with Bernoulli's Equation in the 1700's and come up with the airfoil. If you look at it, he was just describing a long-known phenomenon in the lab. In fact I'm a little shocked at how long it took to develop the airplane wing, historically speaking. We've known this for a real long time. This may be obvious you folks on the coast, but it wasn't obvious to this land lubber.

Just a sentence in the intro like...

Pb8bije6a7b6a3w (talk) 21:05, 12 February 2013 (UTC)

The earliest man-made wings had airfoil sections copied from birds' wings. Birds' wings have a very thin cross-section so those first man-made wings also had thin cross-sections. Wings with thin cross sections can't carry much weight per unit of wing area so in order to carry the weight of an aircraft, the earliest designers usually employed two or three or even more wings in the biplane, triplane or multiplane configuration. Dolphin (t) 01:30, 14 February 2013 (UTC)

How are they connected?

I have realized from looking at different flying animals, that dragonflies or hawks, eagles or mosquitoes, bats or moths, all of these animals have NO evolutionary link yet they all have the complicated system needed for flying. I challenge you to ACTUALLY find a good reason for why these completely different animals all have working wings. — Preceding unsigned comment added by 50.190.101.143 (talk) 15:11, 10 November 2016 (UTC)

Please limit discussion on this talk page to the article, not your personal observations. The article, of course, must be based on citations from reliable sources. User:HopsonRoad 03:01, 11 November 2016 (UTC)

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