Nope the model is correct note the acceleration of the flow in the 'torus' model

The relative wind [flow] is accelerated at the top---which 'pulls' the bottom flow into greater density hence higher pressure--- one wants a pressure increase on the bottom and decrease at the top the FAA publications are all very good

airplane flying handbook,glider flying handbook, aircraft W&B handbook instrument flying handbook, helicopter flying handbook, pilot's handbook/encyclopedia of aeronautical knowledge, seaplanes, ski planes and float and ski equipped helipcopter flying hand book...and although this is biased to FAA rules the instrument procedures handbook and they are very cheap too... those are what I use for ground school with my flock...very accurate!!!
there is some some blatant plagiarizing from Hurt and Davies' but that's ok the government can steal...look at Taxes...:}

:)

two things I meant Rotorcraft flying handbook they cover gyroplanes too

and I realize I'm not being 100% perfect in my explanation like 98%...trust me the real story is quite involed no need for that here... I'm trying to relax too...:)

Edit Chris Weston that's coolway to see it...:):):)

I just needed one more post...cuz I'm a little bit superstitious...:ouch:

this hotty has the theory all worked out...:cool:
boy would I love to do rolling circles and humptybumps with her...:}

Another lovely lady who I love

Out Of My League Here
 

But this is all so very interesting--will keep reading and watching.

Jcb do not be disheartened in some ways aerodynamics is out of everyones's league even Mr. Boeing and Mrs. AirBus

I'd just like too add a few more cheaps books to the ones I listed above

FAA aviation weather..for folks flying in the US ---Aviation weather services

Buck's Weather Flying... Taylor's Instrument Flying..Langwiesche's Stick and Rudder...Webb's Fly the Wing...Mike Goulian's and Geza Sourvizoy's basic and advanced aerobatics... Mallinson and Wollard's Handbook of Glider Aerobatics...good stuff for airplane pilots too

For those who aren't engineers but are interested in aerodynamics H.H Hurt's Aerodynamics for Naval Aviators

For those going to jets of course DP Davies Handling the Big Jets listed earlier
in addition to the book I

if you bought them all they's probably set you back about 300$ or so

I wouldn't recomnend pilots read any of my engineering aerodynamics books though...:\:\:\:eek::eek::eek:...seriously!!!


:):):)

Sites and books
 

Hi John Tullamarine, Pugillistic Animus, Bubbers44, other books lovers,

Perhaps could PPRuNe's "Theory on lift "thread have a list of useful web links (like AF447 list, John ! :ok:) and useful good books ? :)

the J58 was not a turboramjet (TR)
 

Hi Italia,
Don't know if you are still receptive to getting to grips with the J58 as it's been a while since your June post. I don't believe anyone followed up on your points.
Incidentally, Ryman had already correctly killed the TR.
Some of the information in the sources you are referencing is wrong, including classifying the J58 as a TR, unfortunately. One source will reference another source and misunderstandings/errors get perpetuated despite their dedicated authors.

TR was probably coined by someone because it sounded more exotic than bypass bleed engine (which is what P&W called it). They had to fit Mach3's worth of impressive ram into the name somehow.

What follows only needs to look at the engine airflow, not the very significant airflow which goes around the engine and causes so much interest in the intake and exhaust thrust contributions.

First we'll see how similar the airflow is to that in a familiar Mach2-type military turbofan or bypass engine. Then we'll see the reason why it could never have been a TR.

Going one step at a time thro each engine, an F100 at Mach2 say, and the J58 at M3.

F100: all the air destined for the engine goes thro its first compressor, also called the fan.
J58: all the air destined for the engine goes thro the 1st 4 stages of its only compressor

F100: some of the fan exit air goes down the engine bypass duct, the rest goes thro its 2nd compressor ( and combustor and turbines)
J58: some of the 4th stage exit air goes down the 6 external engine bypass or bleed tubes, the rest goes thro the remaining 5 compressor stages (and combustor and turbine)

F100: the engine bypass air mixes with the turbine exit air upstream of the afterburner fuel manifolds
J58: the engine bypass air mixes with the turbine exit air U/S of the A/B fuel manifolds

These air paths are for all intents and purposes identical. If you wanted to classify the two engines you could even put them in the same drawer but it wouldn't have TR on the label. After the above you may wonder what was so special about the J58. Apart from the huge challenges overcome with materials, etc. it was different to an F100 type at lower speeds though because the bleeds were closed. So it had a bypass ratio varying from zero at low speeds to some higher value at cruise. This variable bleed made it unique. An F100 BPR just varies a bit about some nominal value.

The TR could have been, on paper at least, but it wasn't as the following shows (ref 'The Engines of Pratt&Whitney' by Jack Connors).
Early versions of the J58 were a plain afterburning turbojet (shown on many web photos).P & W converted it for M3 cruise by adding 6 bypass bleed ducts from the middle of the compressor to the turbine exit (shown on many web photos).
Alternatively, it could have been modified with blocker doors to close off the compressor inlet and a big annular passage around the engine for the ram air which would discharge into a common afterburner. So here, finally, is your TR, but it never happened because it would have been more mechanically complex and heavier. The bleed tubes were a much more elegant solution by virtue of their simplicity. They did the job.
The crucial insight here is you can't turn a turbojet into a TR just by adding a few bypass tubes.

Not wishing to belabor a point, an authoritative source on ramjet configurations (avail on the web) is 'A century of Ramjet Propulsion Technology Evolution' by Ronald S. Fry.
And for the jet engine an equal mine of essentially first-hand, and therefore accurate, information (avail on the web) is 'Gas Turbine Technology Evolution' by Bernard L. Koff.

I hope you have found the above of some value.

Thanks, Peter! That was a nice clarification.

In Figure 5 there are 3 large diameter tubes running along the mid-portion of the engine - those are the bypass tubes, correct?

What's others take on the whole theory for a symmetrical aerofoil in level flight? Could never get a good answer for this one out of the books!

A symmetrical airfoil in level flight has a positive (greater than zero) angle of attack. is: The airfoil may be symmetrical, but it coes not encounter the airflow symmetrically. The airflow patterns around a symmetrical airfoil with a positive angle of attack are very similar to a cambered airfoil, with a greater amount of air flowing over the "top" of the air foil, at a higher velocity than the air flowing underneath.

A symmetrical airfoil at a zero angle of attack will produce no lift, but that ain't the same as level flight.

Haven't been reading the right books then. Off the top of my head, I think that "Aerodynamics for Naval Aviators" gives a clear explanation of this, although I don't have a copy in front of me at the moment. Many other books on aerodynamics also explain this, including diagrams and photos from wind tunnels using smoke streamers to show airflow.


There's nothing mysterious about this at all.

Even an asymmetrical profile does nothing without AOA. At zero AoA its lifting force is downward.... The upper surface has negative AoA due its fatter presentation vice lower, flatter plate.

It is a trick, parlayed into fame by the Swiss plumber.....

See, by the time the flow separates evenly, the aft portion of the flat plate on the bottom has gone Newton.....

Absolutely, 100 percent, purely wrong. Sorry to be blunt, but this is completely untrue. A typical cambered airfoil does produce considerable lift at zero angle of attack.

Here is a wikipedia article about angle of attack It includes a graph of coefficient of lift for a typical airfoil. You will see that the coefficient of lift at zero AoA is non-zero and positive.

If you're not inclined to believe Wikipedia, here's a page from NASA on the wright flyer, which includes another graph of lift coefficient vs AoA. It also shows non-zero, positive coefficient of lift at zero AoA. Additionally it contains a table of lift force, and a graph of same. Both show lift force at zero AoA to be non-zero and positive.

Here's another page showing a a graph of, among other things, the lift coefficient data for the airfoil on a Cessna 172. Coefficient of lift at zero AoA??? non-zero and positive.

Here's a page from the website of the US centennial of flight.

Care to make any bets as to what's on that page?

If you guessed that it contains a graph of coefficient of lift vs AoA, showing Coefficient of lift to be non-zero and positive at zero AoA, you'd be correct.


Obviously, if your understanding of the facts is this flawed, any conclusions you have drawn from the is inevitably equally flawed.

Howdy.

The wing is not connected at leading edges, nor at the trailing edges.

It is hollow, and typically cambered, fat section forward. In the wind tunnel, air starts to flow over the wing, at zero angle of attack. The upper surface wants to move, which portion of the upper surface leaves first, trailing edge, or leading edge?

IOW, where is the center of lift on the upper surface, chordwise? Behind the equidistant point LE/TE? And how does this orient the chordwise axis to the longitudinal centerline? Negative?

You have no tail surface, only wing. How will you fly? Worse still, how will you increase the decreasing AoA?

I have to agree with A Squared. Lyman, you're talking about a phenomenon that is separate and more involved than what was being discussed. The simple, and correct, answer to what was being discussed is that an asymmetric wing will produce positive lift at zero AoA. How the wing is held at zero AoA is not relevant.

Just to be clear - the discussion so far seems to be discussing the geometric AoA, which is in reference to the chord line. The zero lift AoA is the geometric AoA required for a lift coefficient of zero. Absolute AoA is the geometric AoA minus the zero lift AoA - any airfoil, symmetrical or not, will produce zero lift at zero absolute AoA.

The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero.

Angle of Attack Awareness and Angle of Attack Management [Ch. 2 of See How It Flies]

http://faculty.washington.edu/lum/aa.../lecture27.pdf

The lift does nothing useful, it requires long methodical experimentation, and months and years of frustration, snd many dead airmen.

Ahhh....."wiki". So many sharp as a tack partisans, so much smarter than the average bear...

Those arrows, are they on your airplane? There are arrows, right? I must look sometime...

:ok:

Italia: "The zero lift AoA of an asymmetric airfoil will be negative. The zero lift AoA of an asymmetric airfoil will be zero."

Que paso?

That's right Italia.

Hi peter kent

I rebel against illogic, and squishy nomenclature. The potential for mistaking a value of lift should not be dependent on a formula that is merely an arbitrary definition.

At the point where an airfoil begins to develop lift becomes my datum. Zero means zero, or should. Just a quirk of mine, but not just me. It is an accepted datum in the industry,

There should not be confusion, and associating "Zero" angle of attack with actual work does just that. I prefer to let the design drive the nomenclature, not the reverse.

No problemo, peter :ok:

Hi Lyman,
I apologise for being sloppy in my post. I was answering Italia on the J58 question he had addressed to me. I know nothing worth contributing on lift unfortunately.

A different slant on Bernoulli, I think
 

Perhaps someone can help with this one.

My brain generally reels reading the lift posts but I do have a question on what the authors are saying below.
The relevant bit is
"The BE is a statement of the conservation of energy. For it to be applied the system must be in equilibrium and no energy added to the system.... A great deal of energy is added to the air.... A 250 ton plane is doing a lot of work to stay in the air."
and the crucial statement:
"We have shown that the pressure and velocity of the air over a real wing in flight are not related by BE."

http://home.comcast.net/~clipper-108/Lift_AAPT.pdf

This seems at odds with people who use Bernoulli to trade off static pressure with velocity when designing real aircraft. These professional plane makers mention no qualifiers as regards work transfer.
Just one example
'Ch 10. The relation between supervelocity and pressure coefficient'
in a book bursting at the seams with Cp plots and much, much more for all airliners from DC-8 on and written by a Fokker man.

Aerodynamic Design of Transport Aircraft


So shouldn't the college aerodynamics professor author at the top of the post be preparing students to go into industry?

Lyman..

Zero lift AoA is a geometric AoA measurement, meaning it's the angle between the chord line and the relative wind. Zero lift means that the airfoil is producing no net lift force in either the positive or negative direction - ie: there is not net deflection of the air either up or down.

The zero lift AoA for an asymmetric airfoil will be negative (ie: -3 degrees), the zero lift AoA for a symmetrical airfoil will be zero degrees.

Peter...

I briefly read through that paper and here are my thoughts on it. That paper seems to be written to just talk about false theories of lift. I can't speak for what the author's thoughts were but it seems he is passionate about correcting errors in popular theories of lift and he might have given the impression that Bernoulli isn't really responsible for lift... which isn't exactly correct.

This is one that he mentioned: Incorrect Lift Theory

I'd recommend just going through the other wrong theories on that NASA site.

I find people, naturally, want to find THE responsible thing for an event. If someone was killed, they want THE murderer. But in both cases, it isn't just one thing or person that is responsible for an event. Lift happens. We can see its effects, and the science of aerodynamics and physics studies it to try to understand how to manipulate lift forces favourably (for people to get to England in less than 2 weeks!). The thing is, no body really knows why lift happens. It can be explained why up to a certain point but then it breaks down pretty quickly, however, we do know quite a bit about how lift is created and to explain different aspects of it we have different laws and theories. There is no ONE theory that explains it all. Newton can describe how the forces that are created by the wing will actually lift it, Bernoulli helps explains the pressure differences around the wing, coanda/reynolds numbers/friction help explain how air is bent and how it reacts to different inertial and viscous forces, Kelvin's circulation theorem explains the circulatory flow around the airfoil in flight, etc. They all explain a little piece of the puzzle.

What this paper's goal seems to be is to let people know that Bernoulli doesn't explain EVERYTHING about lift, etc. I was taught the equal transit time theory (which is incorrect) when I was first learning and I notice it in books and have seen other instructors teach it. I think all these incorrect theories come about because people who aren't qualified to do so are 'simplifying' these theories so that it's intuitive and easy to understand for themselves and their students. The problem is that a lot of things aren't intuitive unless you have an understanding of physics and have studied these aerodynamics problems. Other instructors believe that EVERYTHING can be simplified and explained easily, which is not true. There is only so much simplifying that can be done before you end up with an explanation that is partially or completely wrong.

Does that provide any clarity to the paper?

If the wing section at AoA of zero degrees produces no lift, then the lift associated with a wing section must be associated with Newtonian physics rather than Bernoulli gas laws...

Actually, IF the wing section did produce lift, with the current thrust provided, the wing section would be near a negative AoA, attempting to contain lift... (ie even at a negative AoA, the top surface is still longer than the bottom, hence a negative AOA would push the ac forward...)

Italia. You realize the shaded box in your post is me quoting you? You claim two LIFT values for one AoA. The cross section for any chord is not relevant.

Hence the confusion. Zero Lift cannot be other than 0 AoA. Regardless of shape.

Asymmetric, Symmetric, flat plate, etc. It is not related to cross section.

Also reread your posit, AoA cannot be both negative and zero at zero lift. Any AoA other than zero produces lift, though in one case it would be inverted.

Do you not see this? Angle of Attack describes an "attack" angle, eg "other than "ZERO" Whether the lift is up or down, there is lift, hence other than zero AoA. To say otherwise draws attention to a deliberately arbitrary Incidence.

Zero AoA can be replaced with "LIFT NEUTRAL" if you wish.....

Please assume velocity sufficient to create lift....initiating....

FlightPathOBN.....

'If the wing section at AoA of zero degrees produces no lift, then the lift associated with a wing section must be associated with Newtonian physics rather than Bernoulli gas laws...'

muchas gracias.....

To validate Bernoulli requires something for nothing.... 0 degree angle of attack producing LIFT, in other words. Bernoulli's "accelerated upper flow" violates Newton's first LAW. Failing "accelerated", the argument defaults to "it travels further". No, it does not..... separated airflow needn't (and does not) arrive to meet at the trailing edge......

OKay, so attempting to decipher your gibberish, apparently you are trying to claim that the only true AoA is that measured relative to the zero lift axis of the airfoil. Certainly there are occasions when that is convenient. But there in other contexts in which is is more convenient to express AoA as relative to the physical chordline of the airfoil, which can be seen and measured using ordinary measuring instruments. Doesn't really mater as long as the terms are defined clearly, but you'll find that the latter is a lot more common than the former, regardless of how firmly you you are convinced of it's superiority. Oddly, you seem unable to wrap your own mind around the two, as evidenced by your own words: If we accept your definition of AoA as being the angle relative to the neutral lift axis, an airfoil can hardly have a nonzero lift force at zero AoA, now can it?

If that is indeed true, it would appear that your own posts would be an excellent starting point for your rebellion.

Ummm, no. Beginning by defining angle of attack as the angle relative to the zero lift axis, then attempting to draw conclusions from the fact that the lift at a zero angle of attack is relative to the zero lift axis is ........wait for it............... zero (surprise!!!!!) is nothing more than a very obvious exercise in circular reasoning. Illogic, if you will.

To clear it up partially, The second quote is true only if 0 angle of attack produces Lift, as per Italia's posit. No need to get hostile...

Look, the quote above 149 is from FlightPath OBN, please keep your quotes accurate. Your response to it is unintelligible.

You are completely disorganized, quoting one person as though someone else, etc.

I would ask you to correct your post, please, and utilize correct attribution.

Thank you.

Ahhh, and so it is. But then, in your post, you quote him, and thank him for bringing up that point and agree with it, amd build from it in your own words.

Don't try to distance yourself from that thought now.

It is your response that requires distance, with respect. I do agree with FPOBN, would you like reference?

Which was exactly my point, you agree with the obviously circular reasoning.

Reference for what? The fact that lift, at zero angle of attack, when defined as the angle which produces zero lift, is zero?

No thanks, I think I can work though that on my own.



Incidentally, I've edited the quote attribution, as you requested

It is not circular, how so? Bernoulli requires Lift at 0 AoA to sustain, if there is none, Lift is explained via Newton. There is a reference in the paper posted by peter kent. Did you catch it? The paper also proves that upper surface airflow velocity is less than the lower airstream. substantially less. Additionally, if Bernoulli applies on a real wing, the upper surface would be shaped like half a circle.



Thanks for the re-do.....

Wrong Again!

Yeah, I caught it. the trouble is, it says exactly the *opposite* of what you claim it says.

Here's what the paper says (verbatim quote) Notice that part in red? The air over the top of the wing travels faster than the air below.

the author is merely addressing the "equal transit time" myth, which pretty much everyone understands is a myth.

My recall is the upper air arrives later, I'll look.

And herein lies the problem: most of what you "know" is wrong.

On a cambered wing that is producing upward lift the airflow over the top is faster than the airflow over the bottom. This is one of the basic facts that is not in question and is demonstrated unambiguousky by more than a century of wind tunnel data.

You don't have even this most basic piece of information correct. yet you presume to lecture others on the *truth* of aerodynamics.

Probably a complete waste of my time but here goes:

There are several valid ways to define angle of attack.

You chose to define angle of attack as the angle relative to angle where it produces zero lift.

There's nothing wrong with that definition as far as it goes.

But.......


Inevitably, if you define angle of attack in this manner, the lift at zero angle of attack is by definition, zero. This is a result of your definition of angle of attack, not a demonstration of some overriding physical principle, yet you attempt to use it as "proof" of some principle.

If you can't follow how this is nothing more than circular reasoning, I can't help you.

It seems I got well ahead of myself, I read it wrong, and didn!t stop to think about it, my apologies. Also for my tone, it was insufferable.

The paper makes reference to "effective angle of attack", which I mean to take as the zero lift position for any lifting surface, regardless of shape, is this how you read it? I'll leave some room here for others and will read for now.

Thanks.

This looks like a whole bunch of non-sense going on here!

Lyman...

:ugh: Of course I realize that's you quoting me...

Re-read my post where I defined the AoA terms that I was using and where I provided references to further expand on my definition. It might take time to sink in but what I said makes sense.

FlightPath...

That's a false premise.

In earlier posts I stated a few definitions of AoA... I'm not sure you have the same understanding of those definitions as I do.

Prandtl
 

I learned a lot seeing the old "polaires de Prandtl"...:ok:
they are the Cz(Cx) closed graphs at a definite airspeed.
Would anybody know where we could find them on the Web ? Thanks

Lyman...

I have no idea what you're trying to say... I don't think you understand the definitions that I've already mentioned: geometric angle of attack and absolute angle of attack. It's generally accepted that, unless otherwise specified, when ever you mention AoA you are talking about the geometric angle of attack. If you did understand them you'd either understand what I've already said or you'd be able to specifically point out an error I might have made.

Please explain why you believe this definition dismisses Bernoulli. Effective angle of attack is yet another definition that is completely different from geometric and absolute. Do you know what effective angle of attack means?