On Airplane lift

Cecil's Columns/Staff Reports
143

“Happenstance” is a word only really used in a small part of the world (less than 5%), North America.

I believed that a reader would have to be far less intelligent that those found in here to misunderstand the wording, maybe you posted your message before reading the rest of the sentence you quoted?

I felt that, while the context would have made the usage clear to most people, I should not risk it and thus took extra steps for some potential minorities. Thus I made it clear that I was contrasting “coincidental” with “causational” and that specifically the meaning was that “both caused by the same thing and not by each other”.

Cleary, when writing any piece the argumentation and vocabulary need to be appropriate for the target audience. If anyone feels they have any difficulty in understanding the sentence then it is almost certain that several other parts of my piece will be unintelligible to them also. Would anyone in this position please feel free to email me directly and I will be extremely please to explain using simpler words.

May I thank Mr Kennedy for drawing our attention to this particular issue within my posting, without his assistance I would not have appreciated the importance of the matter and the value in devoting time to it.

Guy

144

While I’m thrilled to have written an article that just…won’t…die, I can’t say much in response to our new guest that I haven’t already said at several points in this thread (sometimes too repetitively).

Guy Glover, I have no fundamental argument with almost anything you said. The issues you have taken with my explanation pretty much all boil down to nit-picking the way I simplified things. And that’s fine with me. I have admitted freely and repeatedly that I wrote this article for the masses, and a lot of shortcuts were necessarily taken through the physics. It’s not dumbing it down, and it’s not incorrect…it’s making it apporpriate for the audience. If I were writing a college text, it would be different. If I were writing a journal paper, it would be different still. Face it, engineering textbooks make shitty entertainment.

If you haven’t reviewed this thread in all its length, I encourage you to see the preceding discussion, and you’ll find most of your valid points debated and illustrated ad nauseum.

The one point of yours I do take issue with concerns your assertion that we can easily design real air vehicles from basic principles. I stand firmly by my statement at the end of the article that we can’t analytically design real aircraft very well. No doubt airfoil analysis has progressed to the point where the performance of 2-D sections is pretty good nowadays. But take it to the third dimension, and things break down. Only the most basic, canonical 3-D aircraft features are tractable by straight analysis. Real things, like your typical 3-D wings, are just too difficult to design on paper alone.

Perhaps your point was that we can make a lot of real things based mostly or solely on CFD. I maintain that that doesn’t count as analytical design…it’s simulation-based. Any CFD code used to study and design complicated bodies must take shortcuts and make assumptions to work. Direct, full-blown Navier-Stokes solvers that can do it all are a long way off. So the fact remains that you cannot sit down with basic physics formulas and predict the exact performance details of an existing aircraft, much less design a new one from scratch. It’s not because we don’t know what we’re doing, it’s just because the real world is more complicated than that. Just the same, no one can sit down with a big pile of differential equations and initial conditions, and use those to predict the weather a month from now.

Again, I’m not arguing with your well-written and thoughtful post. Your points are valid, but it’s still important to remember that I wrote in a manner that I felt to be more beneficial to the cause of fighting ignorance. It thought it was more imprtant to give as many people as possible an intuitive sense of what’s going on, while dispelling some of the misconceptions that have become so prevalent.

Now let me go find my zombie-killing handbook…this thread wants braiiiiins.

145

Thanks for your reply, I appreciate its style.

It appears that the only thing we have a fundamental disagreement about is the meaning of nit-picking!

It was the combination of the fighting ignorance epithet, the inteligent way it was written and the fact that it continues to be used to promulgate substantial missconceptions that caused me to feel I should give a more thorough response than those entangle with many other comments in this thread.

I have no doubt that the intention was excellently founded but, IMHO, the result has been the reverse of that intention.

I guess that sets me up for a challenge to do better myself.

Guy

PS 2d lift has a load of complexities that 3d does not have. We have to understand them well because we need to in order to apply 2d experimental data in a 3d world. However all of that complexity is only necessary to allow 2d physical experimentation. There is no need to introduce 2d matter into a 3d debate, it only adds to the confusion.

146

It is always interesting how most designers and engineers will not go on the first test flight.

YMMV

147

[QUOTE=Guy Glover]
We can be absolutely certain that, as the interaction of the wing and air imparts a force to the wing, there will be an equal and opposite force applied to the air. The only real question is what is the mechanism that delivers this?
[/quote]
Newton on fluids.

[QUOTE=Guy Glover]
No force is created by the “deflection” of the air;
[/quote]
Deflection of air creates the force of air pressure differential. The force of air pressure differential deflects both airmass and wing.

[QUOTE=Guy Glover]
The movement of the wing through the air causes the pressure forces, but how?
[/quote]
Air mass inertia.

[QUOTE=Guy Glover]
However this extra lift is absolutely offset by the negative lift created earlier during the air’s acceleration to give it the upward component in the first place.
[/quote]
Part of the extra lift generated by the upward acceleration of air is offset by drag.

[QUOTE=Guy Glover]
Many people appear to believe that Bernoulli states (for example) that if air accelerates this will cause its pressure to reduce.
[/quote]
Bernoulli clearly states that higher fluid velocity over a surface will result in decreasing pressure; that decreasing pressure over a surface will result in greater velocity.

[QUOTE=Guy Glover]
The explanation that the air goes faster (for reasons we are can not be told about!) and Bernoulli decrees that means it has lower pressure (which it doesn’t, many other things could change instead) is nothing more than obfuscation.
[/quote]
The air goes faster over a wing because of the lower pressure induced by the inertia of air mass over the wing – as per Bernoulli.

Peace
rwj

148

Lift is created by accelerating airmass downward.

A wing parts airmass. As airmass flows over the height of contour, the upper surface of the wing falls away. Fluid inertia causes lower pressure behind the highest line of a wing. In turn, air velocity increases as pressure differential lifts the wing.

Peace
rwj

A wing provides lift by harnessing a segment of vortex.
A vortex is the dance between Newton and Bernoulli.

149

[QUOTE=rwjefferson]

Deflection of air creates the force of air pressure differential. The force of air pressure differential deflects both airmass and wing.

[/QUOTE]

This is a tautology, where is the value in this type of construction?

Is part of the mechanism.

Most conventions consider lift and drag to be perpendicular and thus unable to offset each other.

A pragmatic simplification of Bernoulli does this, not Bernoulli. After all, we know that energy is transfered into the air (there is no lift without it) and that other energy changes take place. But within appropriate narrow range of physical limitations and accuracy it can be applied prudently by those who understand the limitations.

Of course Bernoulli observes that energy is maintained, it does not describe causational links.

This is another tautology and not one that was ever expressed by Bernoulli.

I fear we are close to mearly exchanging contradictions, I will bow out.

Guy

150

This is false. The force of air pressure differential is created by the deflection of the airmass.

[QUOTE=Guy Glover]
This is a tautology, where is the value in this type of construction?
[/quote]
Action creates equal and opposite reaction. Let me say it again if it still has not imparted additional clearness. The force of air pressure differential is created by the deflection of airmass (by the action of the wing). The reaction of the force of air pressure differential is air mass accelerated downward and lifted wing.

The mechanism is F=MA. In this case the mass is fluid (chaotic).

A lifting wing parts (deflects) airmass. In reaction, the fluid mass inertia causes a lower pressure (eqivalent mass inertia over greater volume) over the wing. This pressure differential accelerates airmass downward and the wing upward.

Increasing velocity increases pressure differential by one-half square the velocity. As air is compressed by the leading edge, its increased escape velocity/vector over the height of contour (and the resulting enhanced lowered pressure over the wing) more than compensates for the downward force of its being accelerated upward. The air compressed as drag balances the force of the greater lift.

It is derived from Bernoulli and it holds true.

That is why Bernoulli and your posts fail to describe lift.

It is not a tautology if it is true and clarifies confusion and obfuscation. Lower pressure over a surface means higher fluid velocity. It matters not whether Bernoulli recognized this any more than it matters whether Einstein recognized his equations predicted black holes and atomic bombs.

A lifting wing deflects airmass with its height of contour. The action of airmass deflection results in an equivalent and inverse reaction of air pressure differential. The force of air pressure differential accelerates airmass downward and the wing upward. Thus a wing harnesses a segment of vortex.

There is nothing to contradict, but I will be happy to discuss the mechanism of lift even further.

Please forgive.

Peace
rwj

151

It is a little embarrassing that we cannot agree on one of the basic principles of forces.

I see the pairs of forces as caused by the same thing and not causing each other.

You see one as the cause and one the effect.

I don’t understand this and can see little value in your construction that deflection of the air causes lift (why don’t you say the lift causes the deflection?). I see the deflection of the air is caused by a force and cannot understand how it can cause a force.

Perhaps you can help me understand your point of view by taking the example in my original post concerning the two forces of gravity. Which force do you see as the causing force and which the caused force, and why – the force of the earth’s gravity on me or the force of gravity I impose on the earth?
Guy

152

[QUOTE=Guy Glover]
As I sit on my stool typing this, the reaction to the gravity on my body is nothing to do with any forces experienced by the stool. It is the equal yet opposite gravitational force that my body applies to the Earth. Neither of these two forces causes the other. I will leave others to explain what causes gravity.
[/quote]
Gravity is the force of mass acceleration. The wing and the air, and the stool and you, all experience the force of earth’s mass acceleration of spacetime as 1G from center of mass.

Yet between you and stool, the force of electromagnetic still holds sway over the force of spacetime mass inertia. Thus, even as the flow of spacetime accelerates by earth’s mass, your inertia in spacetime is countered by the force of earth and stool.

When mass acts on mass; mass reacts inversely and equally. The interaction of wing and air causes the inverse reaction on each other. As a wing deflects airmass inertia downward; the wing lifts inversely.

You can get the same effect by strapping a rocket to your stool.

Peace
rwj
From our relative frame of reference, spacetime flows into the future.
Observation of the force does not require understanding of the force.

153

I guess we need to read between the lines in order to see the straight answer to my question.

Best wishes.

Guy

154

[QUOTE=Guy Glover]
I guess we need to read between the lines in order to see the straight answer to my question.
Best wishes.
Guy
[/QUOTE]

Please tell me which lines you do understand.

Let us start with f=ma; g=ma. Do you understand, or at least accept, Newton’s observations of mass and gravity?
Is it possible that it is your understanding of relative spacetime that fails?

There is no need to read between the lines if the lines are understood.
What if first, you try to understand the lines?

Wings lift because they deflect airmass downward as per Newton.
You experience 1g against your stool because earth’s mass accelerates spacetime as per Einstein.

Please help me understand where your understanding fails.
Peace
rwj

155

What don’t I understand? - Why you continue to ignore the point I am making and do not respond simply to the questions I ask. The rest is all crystal clear to me.

Newton states that momentum is always conserved it does not attempt to define how it will be conserved in any particular process.

My hypothesis - The same thing causes the pairs of forces; they are not caused by each other.

Your hypothesis – One force causes the other.

Neither of us disagree that momentum is conserved and thus the forces will always be equal.

Where you now say: -

You appear to accept my hypothesis, the cause is the interaction of the wing and the air and that causes the two forces.

But the remainder of your text appears to invite the interpretation that you disagree with me.

The formulae you quote apply universally (e.g. the mass of the air x acceleration of the air = the force on the air). They do not explain how, as you claim, the force on the air or the acceleration of the air CAUSES an entirely different force on the wing.

This is not a pedantic argument; it is at the root of a substantial part of the confusion surrounding the misunderstandings of the simple mechanism that causes lift.

Let us look at it another way. You appear to explain the causation of lift as follows –

“Lift is caused by the downward acceleration of the air and the downward acceleration of the air is caused by the lift.”

This short but circular description does not appear to offer any of the attributes of true description of cause. For example we cannot hold this up against scenarios as a test to determine whether or not lift and deflection would occur.

If a young child were to ask you what makes car go would your really respond – “By making the Earth turns slowly in the opposite direction”? For that is the exact equivalent of what you are saying.

The fact is that many experts who understand very well what makes cars go (from drivers through to designers) have never even contemplated that what makes cars go also causes the Earth to rotate in the reverse direction. This is because it is not the cause; it is merely a secondary effect of the cause.

I fear we may be boring the spectators to this discussion.

Guy

156

[Quote=Guy Glover]
Newton states that momentum is always conserved it does not attempt to define how it will be conserved in any particular process.
[/quote]

Newton defines the conservation of force of momentum (inertia) as f=ma. Bernoulli and Einstein et al have even further defined particular processes. Yet, still we always seek better definitions of particular processes.

[Quote=Guy Glover]
Your hypothesis – One force causes the other.
[/quote]

Change in force is not a separate force. A wing lifts because the force of inertia acts on the force of inertia. Change in vector or velocity or fluidity is not an other force.

[Quote=Guy Glover]
But the remainder of your text appears to invite the interpretation that you disagree with me.
[/quote]
Apologies. I thought I made any disagreements clear by demonstrating why I found some statements false or misleading. Yet if text of universal law invites appearance of disagreement with your hypothesis, you might wish to reconsider.

[Quote=Guy Glover]
They do not explain how, as you claim, the force on the air or the acceleration of the air CAUSES an entirely different force on the wing.
[/quote]

Changes in vector or velocity or fluidity do not cause entirely different forces. A wing lifts by the force of mass acceleration. The force of electromagnetic mediates the interaction.

[Quote=Guy Glover]
This is not a pedantic argument; it is at the root of a substantial part of the confusion surrounding the misunderstandings of the simple mechanism that causes lift.
[/quote]

Amen.

[Quote=Guy Glover]
You appear to explain the causation of lift as follows –
“Lift is caused by the downward acceleration of the air and the downward acceleration of the air is caused by the lift.”
[/quote]
For every action, there is an equal and inverse reaction. Lift and downwash are caused by the force of acceleration of mass; only the velocity and vector and fluidity differs. This is indeed an interaction, a circle, a vortex.

[Quote=Guy Glover]
The fact is that many experts who understand very well what makes cars go (from drivers through to designers) have never even contemplated that what makes cars go also causes the Earth to rotate in the reverse direction. This is because it is not the cause; it is merely a secondary effect of the cause.
[/quote]

Indeed this is the heart of the confusion. It is force of mass acceleration that is primary to the efficiency of car or wing. How this is achieved by designers and engineers, whether by trial and error or by understanding of the force is always secondary to the force.

A wing lifts by deflecting airmass downward.

Peace
rwj

157

Do you understand my point and why I see value in it?

Guy

158

[QUOTE=Guy Glover]
Do you understand my point and why I see value in it?
[/QUOTE]

In truth, it has been difficult to follow your point in the noise of misinterpretations of Newton and lift and my own understandings.

[QUOTE=Guy Glover]
My hypothesis - The same thing causes the pairs of forces; they are not caused by each other.
[/quote]

The same thing (the force of mass acceleration) causes changes in the force recognized by vector, velocity and fluidity differential. Vector and velocity and fluidity do not cause each other, they are simply measurements of the force.

How would you more clearly define your point?

Peace
rwj

159

Good night Mr Jefferson.

Guy

160

[QUOTE=Duke of Rat]
While I’m no aeronautical engineer, this portion of aerodave’s report apparently isn’t totally correct:

In fact, flat plate wings do work, at least at the Reynolds Numbers encountered in small model airplanes.

Here is a site that specializes in flat plate winged planes, with links to a few videos that appear to show them actually flying.

Not sure how this all figures into the original report, just thought it might be worth consideration.
[/QUOTE]

Sure, those symmetrical wing planes will fly. It’s just that the wings are no good for generating lift. The lift is generated by the engine, and the plane will lose altitude whenever the engine is pushing horizontally.

161

Flat wings will produce lift just fine - they have a narrower operating band in terms of wing loading and speed and, of course, they don’t have room for some important stuff like structural members to carry the load and fuel etc. but they produce good lift.

Paper darts don’t have engines. There are a very few powered aircraft with virtually symmetrical wings, particularly aerobatic aircraft.
Guy

162

[QUOTE=Mosier]
Sure, those symmetrical wing planes will fly. It’s just that the wings are no good for generating lift. The lift is generated by the engine, and the plane will lose altitude whenever the engine is pushing horizontally.
[/QUOTE]

Although I will certainly agree that a symmetrical wing is not as good as a wing that gently guides airmass downward, as long as a symmetrical wing has a positive angle of attack, even a horizontal engine will produce lift.

In lift, the lower surface of a symmetrical wing sweeps airmass forward. In spite of the downward airmass acceleration and increased air pressure differential (same airmass by smaller volume) under the wing, the increase in friction (drag and heat) is costly to efficiency and even integrity.

Yet the inertia of airmass over the wing not only creates greater pressure differential (greater volume by same mass), the lower pressure results in less friction and even greater airmass velocity downward (in curve of vortex).

A symmetrical wing is inefficient for lift because airmass deflection is more efficient in curve of vortex. Yet even a symmetrically winged glider can perform loops by the engine of velocity.

Peace
rwj