Talk:Wing

From Academic Kids

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.

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)

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)

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)