Although I don't want to get involved in this somewhat personal argument I'm afraid he is right insofar as for the balance inside a certain frame of reference it is absolutely irrelevant which of the two is moving.
Example?
The fact that the surface of mother earth is moving at 1500km/h plus at the equator has no influence on the behaviour on the airfoil either. Aerodynamic behaviour at the North pole will be the same.
You get the point?
And btw. you don't create energy, you don't lose it, you can only change the form in which it is present. And that also depends on the frame of reference.

henra

"And btw. you don't create energy, you don't lose it, you can only change the form in which it is present. And that also depends on the frame of reference."

Show me please that I posited energy was "created"?

You make the mistake my esteemed opponent is making. Assumption after assumption. To gather an air mass and shape it such that it displaces and affiliates to the structure of the wing is impossible, in this universe. There is a flow, a sequence, that is not well served by constantly defining terms that allow a reversal of logic.

To the student, it is difficult enough to "fix" a wing, and parlay that into movement, outside the enclosed volume.

If you want to discuss a blown wing, fair enough, but to parse a gaseous volume into boundaries ahead of the entry of the wing is bizarre...

I think we are having two distinct discussions. I refer again to the paper linked by Peter Kent. The authors refer to a 'Real Life' wing......

I can summarize in this way. A cambered airfoil produces lift at 0 degrees Angle of attack, AoA as centerline through chord LE/TE.

Remove this definition from the argument. Can a symmetric airfoil produce Lift?
Of course yes. So camber is not a critical precursor of Lift? Of course not.

So if camber is not a requirement, how is it included in the basic description?

These two fellas propose a simple way to understand lift. One that does not require suspension of 'aspects' of gases, and motion.

Hi Hazelnuts,

Sure it is, but you also wrote:
so the area of the affected stream tube is a finite part of an infinite field - doesn't change my view that one cannot quantify mdot ;)

OG;

Yes, if one arbitrarily assumes ... EDIT::
OTOH, if one equally arbitrarily assumes that the uniform downwash velocity is that predicted by Prandtl for the 'lifting line', the area corresponding to the lift momentum mdot*vv is twice as large.

Quite :ok:

Lyman, the laws governing the behavior of energy are completely independent of frame of reference, as long as that frame remains consistent throuought the analysis.

That is fundemental, first day, elememtry physics, yet you want to mock it as "squishy". This ain't "squishy", it's a fact. You can look it up. There's really no point in arguing fundamental, verifiable fact with somone who doesn't have a grasp of them. You really don't have a clue how badly misinformed you really are, do you?

Your insitence that there is something very significant and meaninful in the fact that the airfoil is moving through the air as opposed to the air moving over the airfoil would necessarily demand that a completely different set of aerodynamic principles would keep a J3 aloft when maintaining a stationary position over the earth, flying into a 70 knot headwind than those keeping it aloft when it is flying 70 knots over the earthe surface through still air.

The energy that creates lift comes from the aircraft, not the airmass. You are confusing result with cause. That is the upshot of the paper in question.

Shut the little Franklin engine down? Oh oh. You are so welded to a construct that you cannot imagine a "real-life" wing? For your purpose, donor/recipient is not important. Fine, but that leaves the Aero 101 student to catch up with you.

Like all the other assumptions you make, or remember, you miss the point.

You cannot posit an a/c under power, and then dismiss that power. That is just sloppy work on your part.sloppy. It is power creates the lift; the airmass is a bystander, regardless its relative motion v/v the Earth's surface. Your example is useless.

Why do you ignore airfoil shape? Do you disagree with me, that shape does not play a part in Lift, at its most basic?

I think the motionless wing and "moving air" may have caused the misconceptions that the authors elucidate. Since the air is "moving" it must have energy, right? Since it has energy, it can create its own low pressure area, right?

Having created its own LP, against the Laws of Newton, Lift is created? That is wrong....it does not help to model a wing that produces lift at "Zero Angle of Attack". Magic air, defying Newton, and magic wing, creating Lift from "zero".

Both incorrect, and the source of much confusion, stemming from a sloppy model.

One "assume" after another, and then come two guys ready to provide a workable Newtonian paradigm.......

To build a working model to demonstrate there is no relevance to the energy source that produces identical airflows locally and remotely is impossible. Unless you can confine cubic miles of air and accelerate it as a unit to flow directionally past a fixed airfoil, you need to "imagine" or to "postulate" such a flow. You have my permission to attempt such an experiment.

Likewise, feel free to imagine that air is not viscous, nor possessed of mass.

henra, have you located a quote where I say that energy is "created"?

I've been dieing to get into this thread but after reading the whole thing from the begining I am convinced it's just a wind up.

What were all those tubes fastened to an aerofoil in a wind tunnel showing me all those years ago. There was definately a pressure difference.

Definitions of angle of attack???

Ye gods. Chord line and airflow, (direction of flight).

Camber has ne effect on lift? What!!!


This is my favourite...

Been there, done it and watched the sunset from 1000ft agl, parked into wind, hands off, going nowhere, dynamic (ridge) lift over the Derbyshire Peak Ditrict (UK).

I do not apologise for not understanding the deep maths quoted but try this, wrap the first inch or so of an A4 piece of paper around a pencil. Blow over the top of the paper, it will rise. Why? Diff pressure? Diverted airflow down somhow pulls the paper up?

Discuss.

I'll be back in a week.

Hi TURIN

"Camber has no effect on lift? What!!!"

Who said such a thing? Not I.

From A Squared....

"Lyman, the laws governing the behavior of energy are completely independent of frame of reference, as long as that frame remains consistent throuought the analysis."

I think we are talking past each other. A wing flying through Still air produces specific characteristic flow. If you propose to isolate this system and Examine the airflow, then you are correct, a dynamic system can be analysed that way.

The point is, to get identical airflow by anchoring the wing, and accelerating the air mass, You can not possibly replicate the specific airflows produced by the first system. The air is not still. It is not still because no way has been found to accelerate an airmass in perfect uniform fashion, you will get turbulence.

Again, the paper under discussion proposes a linear and sequential process. The supposition is still air, a moving wing, and camberless chord section.

Since the proposal is to replace the standard model with Newton, the model is more basic, and seeks to eliminate camber and false premise from the model.

By false premise they refer to the mistaken, and seemingly taken for granted meme that air creates a low pressure by accelerating. Since they clearly show that the old model relies on conservation of energy, there is no additive energy, and the premise cannot be correct. It is low pressure that creates the acceleration.

TURIN, in your quote above, the evidence is that you had a conclusion before you understood my statement. You expected that what I was saying is that camber does not affect lift, so even though I said no such thing, you chose to conclude that, in astonishment....

What I said is that Camber is not necessary to explain lift, further, it truly does not do so. It can be used to explain the development of a high pressure area. The wing mightily disrupts airflow, yes?

To judge by recent postings one might assume that any debate on lift generation is done and dusted and that the simple (simplistic?) Newtonian explanation is the only game in town. But the only fault, and it was a major killer fault, in the so called “standard” description of lift generation was that the explanation offered for different velocities on upper and lower surfaces was a load of crap. Nobody AFAIK, disputes that the air flows faster over the upper side of a lifting wing than over the lower, and no one with any real understanding of basics has any problem with using Bernouill’s theorem to associate those velocity changes with pressure changes that give lift.
Any half decent scientific explanation should cover all known facts, which in the case of a lifting wing are not only the upper/lower velocity differential but also the generation of upwash ahead of the LE and downwash at and behind the TE. In addition it is well established that if one moves vertically either up or down from the TE the downwash reduces. The Newtonian explanation ignores most of these.
But what if there should be a valid alternative explanation for the velocity differences? The rest of the standard model then comes back into play giving a complete alternative to the Newtonian explanation.
With apologies to both those who think the following is dumbed down and those who think it too complicated, this is an attempt to put the math into plain words. If you are happy with the Newtonian explanation far be it from me to seek to change your mind, better switch threads or have a drink and watch a ballgame on TV, but if your curiosity extends further it might be worth a read.


http://i1081.photobucket.com/albums/...tiontheory.jpg


The basic premise is that the flow around a lifting wing has two components (bottom left) – an "irrotational" flow plus a rotational velocity generated by a vortex whose axis lies along the wing quarter chord line. It should, I think, be fairly straightforward to see how such a rotational flow would increase velocity over the upper surface and reduce it over the lower. Note that this is NOT suggesting that any particular air molecule does circles around the wing section. Because the freestream velocity is greater than the rotational velocity the air is always swept past the airfoil on one side or the other – it just takes longer on the bottom.


Where most get stuck is seeing how such a vortex might come about; isn’t it a figment of a mathematician’s imagination? I think not, we have all seen part of this vortex. A picture is worth a lot of words they say, so this is a composite from several sources which I hope might serve as a plain man’s guide to lift generation.
What you need to know is that a vortex cannot suddenly start or stop in midair. It must either go on to infinity or be a closed system. In the case of a finite wing it is the latter. When the wing vortex (technically called the bound vortex) arrives at the wingtip the changed flow conditions cause it to change direction and continue rearwards as a trailing (aka wingtip) vortex. Since for any vortex the velocity increases and the static pressure drops as you move towards the core if the conditions are right any water vapour condenses out and we “see” the vortex as a contrail. These vortices are real!

All well and good perhaps, but how does the vortex system get started?

Moving from six o’clock anticlockwise back to three we start with the theoretical streamlines around a flat plate at incidence. In a perfect fluid the underwing flow can move around the TE and join up with its mates on the upper surface (btw it needs to develop infinite velocity as it does so!). In real life of course the flow separates, but in an attempt to flow round the corner it develops some swirl. This rolls up into what is described in the jargon as a ‘starting vortex’. Once again, this is real and the flow visualisation photograph (taken by Prandtl) shows such a starting vortex (which is in fact generated when the wing first starts to move through the fluid).
So now we have a closed vortex system. Three sides of the rectangle we can see in the right circumstances, the fourth, along the wing is more difficult, but it is there. Its presence explains not only the velocity differential between upper and lower wing surfaces but also the existence of upwash ahead of the LE, downwash behind the TE and the variation of downwash with height above or below the TE. Once you have that of course an application of Bernouilli's theorem gets you to suctions on top and pressure below and Bingo, you have lift.

I hope this is not too confusing, and I certainly hope it does not read as patronising, but having consulted an eminent PPRuner we thought the terms of the discussion might be widened – as someone said recently (I think the post has been deleted) – it is a technical forum after all.

Thanks Owen for bringing a touch of reality and truth to what I feel has been generally one of the most incorrect threads ever on the subject.

Owain, that was me. I became so frustrated with the nonsense being posted I deleted all my posts. An individual claims he wants to learn, but is dismissive of scientific facts presented, seemed little point in continuing. I doubt he will accept your profferings, excellent though they be. Keep up the good work if you have the stamina and fortitude.

Brian, I am prepared for that; there is a mental autoignore list. My intended "audience" was others who might be tempted to believe the rubbish being posted.

If I may be permitted the luxury of indulging in a little heresy ...

One of the benefits in having a variety of views expressed -expert (and for those who don't know who OG is .. he is, most assuredly, an expert in these matters) ranging through to technically naive or even incompetent - is that the various levels of technical competence represented within our group are provided with the opportunity to test and challenge their particular knowledge sets.

This process, if approached in a mature way, results in learning and general improvement of knowledge.

If Tech Log achieves nothing else during the life of PPRuNe, such education as might be facilitated ... will be its legacy.

Howdy. Much of the "rubbish" I brought up was from the paper written by the two boffins. I will own my own, but in dismissing mine, without addressing the points from the Newton screed, well....baby/bathwater?

Specifically, Newton's second Law defeating any added energy from the airmass, per "bernoulli"? Shape of airfoil as irrelevant to lift, save at Stall?*

Owain, if your fear is that some innocents may be harmed by rubbish, could you address the scientists' 'rubbish' specifically?

Re the condensation above the DC10 wings, and the low pressure that created it.

My question is a general one. From whence comes the force supporting that monstrous mass in the air? Beneath the wing, as pressure, or above the wing, as "pull"?

Thanks for your patience.....



* "We should point out that the shape of the wing does affect the stall characteristics and efficiency of the wing, but it is not the primary factor in determining its lift."

I didn't say that the Anderson/Eberhardt paper was rubbish. I think it simplifies things a little too much and it can be misleading. For example this business that Bernouilli's equation cannot be applied to the flow around a wing (or indeed any surface where there is an energy transfer from body to air). As they say, Bernouilli's equation applies in a constant energy situation, and strictly applies along a streamline. But the energy variations are confined to areas inside the boundary layer where the flow is chaotic and there are no streamlines. However, there is no transverse static pressure gradient across the boundary layer, so the pressure at any point on the actual wing surface is the same as that immediately above that point on the streamline at the edge of the boundary layer where Bernouilli can be applied.

But if I criticise some points I should also say where I agree. For example, they are correct when they say:

Put another way [Holger Babinski "How do wings work?" ww.iop.org/journals/physed


This may be at right angles to the direction of acceleration most think of in connection with wing flow, but it is correct.

Again, my diagram was an attempt to explain circulation theory. Their paper says:


and:

I was trying to give an intuitive description of this way of looking at the problem - a theory they accept as accurate btw.

You know the answer to that! Bit of each but mostly from above and most of that from suctions in the first 30% (ish) of the chord.

Owain...

Thank you for all that, your patience is notable, and I appreciate it.

I would like to pose some questions, of a very basic nature, in the interest of establishing a foundation.

1 How accurate is it to use the term, "flow" when teaching lift? Would a better term be "displacement"? The salient vectors are Normal to the streamlines, not horizontal, yes?

2. So are we saying that the air in proximity to the wing is accelerated instantly to say, 250 knots? Or is it forced to inhabit somewhat less volume than prior to entry of the wing? If it accelerated, would there be enough energy to accomplish lift?

3. Last, I don't believe in suction, because I was taught not to. Differential, yes.
If you do, could I describe suction as:

The inability of the airmass to form a "void"?

Sorry Lyman, but when you ask "questions" like that my notable patience runs out.

Those are earnest and sincere questions, do you not understand them? Do you fear them? Are they rubbish?

Is the discussion ended?