Talk:Wing

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[edit] 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)

[edit] Bird/insect wings missing

I missed some brief introduction to the parts of bird and insect wings. --213.6.97.225 09:48, 11 Nov 2004 (UTC)

The disturbing thing about many of the so-called explanations of how aircraft wings generate lift rely on the SHAPE of the wing - specifically a curved upper surface and a more or less flat lower surface. However, many aerobatic and combat aircraft have fully symmetrical wing cross-sections (so they fly equally well when inverted) - and I have personally built and flown a powered radio controlled model aircraft with rectangular cross-section foam polystyrene wings specifically in order to show this theory of flight to be false.

Whatever explanation wins this debate, it cannot rely entirely on the shape of the wing. If a rectangular cross-section wing can generate lift - then downward deflection of the air due to the angle of attack of the wing into the airflow is surely the key factor. This business of air moving faster over the upper surface 'because it's a longer distance' - and hence taking advantage of the Bournoulli principle - can at best only be a small part of the explanation because the distances over and under a rectangular wing are exactly the same.

rectangular wings work due to their angle of attack - they deflect air downwards, the equal and opposite reaction is lift. However they also create a great deal of drag so are not very efficient. The shape of the wing only confers efficiency - it has no "magic properties" that creates lift by virtue of its shape. The rectangular wing argument is actually very useful in explaining lift. A simple chuck glider with a flat wing works, because it has an angle of attack. If you build it so that there is no angle of attack, it doesn't fly very well (though actually achieving a totally neutral angle of attack is quite hard in practice). If you build a model with a curved aerofoil section, it can still generate lift at zero or even small negative angles of attack, because a curved aerofoil is still able to have a positive lift coefficient at these angles. It is still deflecting air downward, because of the tendency of the air to stick to it and follow its curvature - only in this sense does the shape matter, and it only has an effect on the efficiency. The "longer path over the top" argument is totally bogus, and as you say, the rectangular wing proves it. The pressure distribution above and below the wing is an EFFECT of Newton's laws operating on the air, not a CAUSE of the lift produced. You will see a similar pressure difference even with a rectangular wing, though less pronounced and disturbed by turbulence. Graham 03:26, 23 Nov 2004 (UTC)


[edit] 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)

[edit] 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

[edit] 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)

[edit] 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)

[edit] WikiProject class rating

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