Hello Nifalen

Easy stuff, really, and I can do it out of my head.

The air current divides at the leading edge of the wing.

One part goes across the bottom of the wing, which is a shorter path than the top surface.

The other part goes across the top part of the wing, which is shaped to be a longer path than the bottom surface.

Now as that wing moves forward, the both air currents (top and bottom) have to arrive at the trailing (rear) edge of the wing, because "Nature abhors a vacuum", and if one current was faster than the other there would be major problems (a vacuum in the middle of the air).

Now from very basic Physics, as the speed of a fluid (air) increases, it's pressure decreases.

And from the same basic principle of Physics, as the speed of a fluid decreases, it's pressure increases.

It has to be that way, as a basic Law of Entropy (Look that up in Wikipedia, I have placed a hyperlink for you just above to click on, if you don't know what it means).

So in consequence of following well-established Laws, the pressure below the wing surface, becomes greater than the pressure on the upper surface of the wing.

The difference in air pressures is easily calculated out, and when applied to the under-wing surface area, is what is called "The Lifting Moment" or simply "Lift" of the wing.

Obviously the difference in relative pressures does increase with the speed at which the wing travels through the air, and if the speed drops below "stall level" the wing ceases to be able to support whatever is attached to it = the aircraft.

The principle is easily demonstrated with a simple diamond shaped kite.

Higher wind speed gives more lift.

As the angle increases, there is more lift, above a certain angle, less lift.

The kite angle for optimum (most lift), is normally found by trial and error, but may be calculated by an experienced person.

As with the plane wing, the faster the wind speed, the higher (within limits of string etc) will fly, until at over 100MPH wind level, most kittes will disintegrate, or the string break, or you are lifted off the ground.

Kites are a good and cheap way to experiment, and you don't feel like an idiot, because you are like a fisherman with a rod "doing something".

Years ago, I made box kites for my children, with over a mile of strong braided nylon for each, and one day I flew 3 kites, one above the other, until a plane flew around them, at which time I pulled them down, as we departed before the local authorities met up with us. (500 feet maximum height was the limit) and my box kites were 6 feet long and 2 feet square, on a good day over 1800lbs of lift, which we checked with a spring meter - tied onto a well-concreted in concrete post (never fly one in a thunderstorm).

So there, now you know a bit more, get out and experiment, take notes, learn something new, share with others, train your children, have fun.

I never used a "bridle" on my box kites, as shown in the big picture, because they self-adjusted better to New Zealand's gusty wind much better without a "bridle".

Kind Regards....

Thank you, Sparkstation :)

It hard to explain without having to explain circulation. This is my version:

Wing turns airflow and this causes a counterforce on wing. This force lifta the plane.

This is a bit over simplistic, but this explains the idea not exactly how it happens. To do so Lord Kelvin's circulation should be understood.

Has anyone had any experience on Coanda Effect i.e. liquids tendency to stick on a surface (Dip a spoon into water. When you take it out water tend to follow the back of the spoon and not fall straight off)? I mean experience so that it has been used to explain the lift force?

Hello again, Nifalen

<"....liquids tendency to stick on a surface (Dip a spoon into water. When you take it out water tend to follow the back of the spoon and not fall straight off)....">

That is simple surface tension of the liquids, combined with intermolecular attraction.

The intermolecular attraction exists between the molecules of the liquid, also between the molecules of the liquid and the molecules of the spoon, and air has difficulty breaking in between the molecules of the liquid and the spoon, because of the combined forces, which may be calculated.

You should find that simple basic reasoning will provide most explanations.

After all, that is how we ended up with Laws of Physics, rules for Engineering and the like.

Early thinkers thought much, they had no Internet, no TV, no Playstation, no books, just thought a great deal, discarding the useless and the distractive, and thus we have so many things, abstract things like geometry, algebra, Radio, glass, gunpowder, Internet, Atomic Power, and so much more....

Kind Regards....

Thanks, Sparkstation.

Fine explanation there, but what I actually ment was not an explanation of how this works but if you have heard it used as an explanation to how an aeroplane flies. Long ago a professor of thermodynamics told me that was also one commun misconception. I haven't ever had a chance to hear that one.

BTW: I think I have to put some more attention to what I write. It seems that people get me wrong all the time. English is not my native language nor my mind is an Anglo-Saxon one so maybe there is the reason.

Hello Nifalen:

I think you may mean the Coriolis effect?

Coriolis effect

From Wikipedia, the free encyclopedia Jump to: navigation, search Figure 1: In the inertial frame of reference (upper part of the picture), the black object moves in a straight line. However, the observer (red dot) who is standing in the rotating frame of reference (lower part of the picture) sees the object as following a curved path. For the psychophysical perception effect, see Coriolis effect (perception).

In physics, the Coriolis effect is an apparent deflection of moving objects when they are viewed from a rotating frame of reference.

The effect is named after Gaspard-Gustave Coriolis, a French scientist who described it in 1835, though the mathematics appeared in the tidal equations of Pierre-Simon Laplace in 1778. The Coriolis effect is caused by the Coriolis force, which appears in the equation of motion of an object in a rotating frame of reference. The Coriolis force is an example of a fictitious force (or pseudo force), because it does not appear when the motion is expressed in an inertial frame of reference, in which the motion of an object is explained by the real impressed forces, together with inertia. In a rotating frame, the Coriolis force, which depends on the velocity of the moving object, and centrifugal force, which does not depend on the velocity of the moving object, are needed in the equation to correctly describe the motion.

babybear

One reason the Bournelli "myth" of wing lift persisted so long is that the FAA test question required citing this theory to get a "correct" answer. It has been years since I have had to know what is on the FAA test, so maybe the question has been removed or corrected for current knowledge.

Hello Nifalen:

this may help also...................

In every-day life there are many observations that can be successfully explained by application of Bernoulli's principle.

• The air flowing past the top of the wing of an airplane, or the rotor blades of a helicopter, is moving much faster than the air flowing past the under-side of the wing or rotor blade. The air pressure on the top of the wing or rotor blade is much lower than the air pressure on the under-side, and this explains the origin of the lift force generated by a wing or rotor blade to keep the airplane or helicopter in the air. The fact that the air is moving very fast over the top of the wing or rotor blade and the air pressure is very low on the top of the wing or rotor blade is an example of Bernoulli's principle in action, ^[8][9] even though Bernoulli established his famous principle over a century before the first man-made wings were used for the purpose of flight. (Bernoulli's principle does not explain why the air flows faster past the top of the wing and slower past the under-side. To understand why, it is helpful to understand circulation, the Kutta condition and the Kutta–Joukowski theorem.)
• babybear

Check the previous Forum Thread at http://cr4.globalspec.com/thread/2673/Lies-More-Lies-and-Arithmetic.

The conclusion was the Bernoulli equation only contributes about 2% of the lift to fly an aircraft. The rest is from other factors.

Hello Ried,

I will accept that. And am not arguing.

I feel the original posted question/statement is very confused. And several 'theories' seem to have been mixed beyond comprehension. I followed the original poster to this, his/her own thread and it is still not explained very well. I know English is his native tongue and this could be part of the problem.

It would perhaps help if we knew where he gets his ideas from? And, why does he/she continue to say the 'facts' that aircraft builders use for design and which make the planes fly, are totally wrong? He/she called these facts bogus, which I think is just not true.

babybear

Hopefully he will clarify what he is looking for.

Hello Ried,

just to point out a mistake I made.

I know English is his native tongue and this could be part of the problem.

This should read: "I know English is >>not<< his native tongue"..........etc

Sorry and no insult intended to the original poster.

stay safe

babybear

This is the fact I was pointing out. Good thread there, thanks Ried! On that tread there was a link to Jef Raskin's great article:

http://jef.raskincenter.org/published/coanda_effect.html

Babybear, you wouldn't happen to remember where were you introduced to this Bernoulli -idea? And what did you mean by explaining Coriolis? Were you refering to this claim that Coriolis would cause water to rotate in sink ceartain direction always. That is false claim of popular science. I understand why this is made in the beginning. That is a nice way to explain how this force works in a way that young kid in school would remember it. I don't know how about you, but I was also told in school that you could see the Great Wall of China on the moon (at the age of 11 I got my first detention for "disrespecting teacher" because of his claim). These are anyhow only small details making no harm to anybody, but this myth about flight is a big deal. Do you know any other false theorems of this magnitude commun in popular science?

I would also like to know if anyone has been taught this Coanda effect? I had never seen that one before I dug deeper into this subject.

Hello Nifalen:

I live in Europe and have not been to Australia to check out the so called Coriolis affect. I take what is said with a 'pinch of salt', believing what I can actually see mostly.

The reason I mentioned the Coriolis Affect is because I was trying to find out exactly what 'effect' you were referring to in relation to explaining what you meant on your flight ideas.

I learned none of this at school. I spend maybe half my time at school as I was a sickly child. I learned what I know from books and doing stuff, thats all.

As I said in another reply, the people here at CR4 are a clever lot so do not think they will not understand the theorem you refer to. How about copying and pasting it directly to CR4? You would not have to find the English, which I understand in not your native tongue, to explain your ideas. By the way I think you manage English just fine, I would like to talk your language as well as you talk English

stay safe

babybear

I live in Europe and have not been to Australia to check out the so called Coriolis affect. I take what is said with a 'pinch of salt', believing what I can actually see mostly.

Where here are you talking about to check it out??

Hello Snaketails:

I have seen programs on TV where a man stands just inside the northern hemisphere and the match floats and twists clockwise. Then he moves just a metre and stands in the southern hemisphere and the match twists anti-clockwise. I know the Coriolis effect exists. But I have read that a move of just one stride will make no appreciable difference to how the effect is seen. That is all.

And the reason I mentioned the Coriolis effect was because I was trying hard to understand the originator of this thread. I just mentioned two the Coriolis and the Bernoulli effect. He had mentioned the coriander effect I think, or something similar. I had not heard of this so suggested a couple of theorems which may have a connection with flight.

I am really interested in all of the original thinkers of the 14 C onward and all the various theories they were able to prove. Unfortunately, I have a real bad memory and cannot recall very many and certainly can't recall the principles of how a aeroplane wing is lifted into the air. If I did I would really love to talk about it. But I find it frustrating I can't! Sorry

I actually have a set of three books by different Authors I think which really need to be read in a certain order. I can't read them at this moment because I can't recall what I have read about when I pick the book up again. It is really getting me down. It has to do with mu Epilepsy and the tablets I take to control it, I know that much. And things do change. In maybe six months to a year I may well be able to remember where I got to the previous night. And, so have a proper discussion.

I am not getting at you in any way, please believe that. It is me not having hardly any short term memory that upsets me and means I cannot hold a conversation without constant references to the subject on-line.

Take care, and get back to me if you want OK?

stay safe

babybear

Hi babybear!

Sorry to hear you had to miss school. Maybe you are a lucky one to avoid a load of bs given there. ;)

Coriolis effects on toilet sink allright, but there are many other greater factor so that its effect is insignificant there.

I know people at cr4 are very smart and could understand all I can. I suppose theorem you are talking about is Coanda effect? It is explained here:

http://en.wikipedia.org/wiki/Coanda_effect

But be careful - read it with a critical mind. Check also Jef Raskin's article I posted earlier.

As I mentioned, I haven't ever heard anyone to use this as an explanation to lift force. I suppose it was more like a thing of the 70's.

Hello Nifalen:

Yes you are probably right about the school BS etc

Sorry I could not recall the effect you give the link to.

Can you not put the answers given by the link on your thread? It would make it more interesting and easier to check on facts etc.

I learned nothing about these effects at school. It came from books. But it has been maybe 10 years since I last read a 'flight book' and I do not recall the details now. I will check the link you give again. I have gone back and forth to it but there is always something more urgent like the phone and getting meals etc. I have to go out today so will study it tonight. Thank you for posting it.

stay safe

babybear

Very briefly, very many years ago, in college I took a Fluidics Control course that discussed the Coanda effect. That is about the extent of what I remember, unfortunately. I have not been in a position to need or use the knowledge, and I would need to start at the beginning for review.

Thanks for the link. There are several items we think we know to be fact that is actually the result of bad teaching and hearing the same mis-information repeated enough to fill our thought process. In general, I probably fit the mold of a lazy thinker that does not take time to fully sort out and analyze the facts.

In the case of the FAA exam I took many years ago, I knew Bernoulli had little influence on wing lift. However to get the question right (multiple choice, computer graded) I was told to provide the "wrong" answer to get the question graded "correctly" and get a better score on the exam.

Doesn't it make you angry to be forced to answer wrong...

I think these misconceptions are so commun also because of this flood of information. Nowadays even the smartest and most energetic one can not double check all the information she receives. You just have to believe some of it.

As an example a friend of mine, doctor in physics and an ethusiastic sailor believed the lift was caused byt the form of the wing. When pointed it isn't so, he quickly saw himself the origin of the force. By his education he would have had all the tools and the mind to understand, but he just didn't question the teaching he received in school. He admitted he wondered the obvious fault on that theory, but still never questioned it.

Not for long, I only considered it aa bureaucratic hoop to go through to get a license. At least I was warned about it and avoided a "wrong" answer on the exam!

Hi everyone.

Let's try the simple explanation for Lift. You will see that someone who knows a bit of Fluid Mechanics may skip most of the words. On the other hand, someone else will need all of them, as well as a drawing...

1. Forget viscosity and friction. Forget drag. Forget compression.

2. Imagine a simple horizontal wing section, flat on the lower surface and curved on the upper surface. Imagine a rectangle (control volume) around the wing section with sides 4 to 5 times longer than the wing length. This means the rectangle sides will be far from the wing.

3. Imagine air flowing steadily towards the wing. It's the simplest linear flow, with horizontal direction, pressure P and speed U.

4. The flow rate across the left side and the right side of the rectangle will be the same. Why? Because otherwise the air mass inside the volume would increase... (Continuity or Mass Conservation Theorem, which is common sense). So the flow speed in and out of the rectangle will be the same, equal to U.

5. Imagine the streamlines around the wing, divided at the leading edge and rejoined at the trailing edge:

- Below it, they will be perfectly horizontal, because the lower wing surface is flat; there will still be speed u and pressure P;

- Above it, they will bend along the curved wing surface, but will stretch to the original horizontal shape as we look upwards away from the wing. If we go far enough upwards, the streamlines will not be influenced by the wing presence, so speed and pressure will be equal to U and P.

6. Next thought: the part of the flow above the wing will have less room to pass as it goes up the wing surface. So, in the same manner as inside a narrowing pipe, the speed will increase (again the Continuity Theorem).

7. Now comes Mr. Bernouilli: One form of the Bernouilli Principle states that the Total Pressure in a flow remains constant and is equal to Static plus Dynamic Pressure:

P_total = constant = P_static + P_dyn = P

This is also an Energy statement, relating the potential (static) and the kinetic (dynamic) forms.

As we've seen before, speed will increase above the wing, so static pressure will have to decrease below P. Since below the wing we still have the original P, a Pressure Gradient will appear, causing a Lift Force.

Finally, an important detail is that P_dyn is proportional to U² (kinetic energy), thus explaining the importance of velocity in obtaining a considerable Lift value.

As for initial simplifications, compression is irrelevant for subsonic flight, whereas viscosity will induce drag and turbulence, which consequently causes the downstream wake, Lift decrease, and other issues. But that is the complex part of it!

By the way, all this can be deduced from the Circulation Theorem...

This is not popular science, this is part of Fluid Mechanics Course.

Now please post your comments.

RGO

Thanks for the comment. Your explanation is true, but only part of the whole truth. You do not need an aerofoil to fly - a plane on an angle of attack to air (or water or whatever) flow creates lift. If you have an airfoil in a flow as you see usually on school books - flat bottom parallel to the flow, is your actual angle of attack negative. That makes your plane actually nose dive specially when on low speeds. When you speed up things get interesting and mr Benoulli gets to be more important factor...

Given enoutgh thrust anything can be made to fly, (I said fly... control ability is another issue)