Hi Pugilistic animus !

Karman of course ! and Libchaber, Lorenz, Feigenbaum, and so many great great great physicians, mathematicians....

RIP taboos, and Boltzmann, Navier or Stokes unsolvable equations.

Welcome to all the real BIRDS who know all that from the nest... :) I am jaleous !

The AF447 discussions shows that it is essential to open the door to future.... Really !

roulishollandais it's not really that there's 'no solution' per se, it's just that there's no closed solution to the NS formulations...a complete examination of the equations of motion and thermodynamics, with repect to fluids yields two very important non-dimensional quantities...Mach Number and Reynold's number--- that is exactly where ALL of our problems arise...:\:\:\

Aerodynamics, is for the most part an experimental art, and it is an art, as so many technical field's really are...

Mad(flt)Scientist has a habit of revealing some of the secrets of design on pprune...for serious students of the field I believe his posts are definitely worth a read...;)

of course we must all remember two very important thing to progress with a design... for better or worse, new ideas are always dangerous and that nature laugh at complex mathematics...laughs!!!


:):):)

Isn't that the truth.

It always makes me smile when people get adamant about Newton in discussing where lift comes from. They seem to totally ignore the fact that wind tunnels have been around for quite a while and in those it is easy to measure the actual pressure at the wing surface on both the top and the underside.

I was brought up to believe that to be correct a theory had to fit in with the facts. Hey ho.

Wind tunnels are very useful for making measurements but it is important to acknowledge that they are physically bounded so that airflow is always horizontal at the upper and lower boundaries. In free air the flow differs. Traditional aerodynamic theory is based on dimensional analysis and simple algebra, but with the power of modern computer modelling it would be possible to run large-scale elemental simulations based entirely on Newtonian mechanics and thermodynamic behaviour of each element.

Ah the Professor and Mr. Farley, great company indeed!

:):):)

Humbling, eh, PA? Only a few blokes could make me doubt Newton...

... "Math pures" complexity start as soon at ... zero ! 1 is not simpler, etc. . Heappily we have "mathematiques appliquées" and "calculs astronomiques" to do it simplier ! And Libchaber two little turbulence are no more complex at all !


I did it a little short whith NS ! as I am a little lazy with words (in my "fractured English" as Organfreak said it to me... ) : "no analytical solutions" of course (I knew you knew!). And computer solutions don't get much to see before us (distance and time). And what with cavitation..

Marcel Dassault had that art to be very prudent with "new ideas".

Henri GIRAUD was a geant data base of airflow in free air when he died in nov.1999. I asked to the INRIA of Grenoble if they could work with him, it would have been yes, but as I asked to "Monsieur GIRAUD" he said me "No, it is too late". The civil aviation denied Henri GIRAUD importance during his whole life.


Shall visit Mado with your recommandation !

Windtunnels just like flow dynamic computer codes are alwys just a model of reality, and none gives exact results when compared to free flight measurement. Many phenomena have been discovered in free flight and could not be confirmed in the wind tunnel or by calculation. It is hard to produce a real free air stream in a wind tunnel, there always is some turbulence created by the fan or by the walls of the air intake, there is always some slight speed gradient close to the walls, there is always some restriction in the air flow if you add walls. Vice versa any computer code can just predict what has been part of the model from where formulas have been derived.

A recent example is that a turbulent boundary layer has been found to become laminar again under certain conditions, while mathematics tells you that this is impossible, and wind tunnels can not reproduce this.

Any theory is only good until a better one comes along. Any wind tunnel is only as good as the criteria it was designed for. Any measurement method (pressure by piezo sensors, speed by LDA, drag by wake analysis...) only works if you exactly know what phenomena to measure. There is not a lot of static flow in a steady flight, there is a lot of small amplitude high frequency variations in the parameters required to fully describe certain phenomena.

It looks like we understand aerodynamics for some hundred years, but in fact we are still learning something new every year.

agreed ;)
Let us try to get better teachers to young pilots :)

A good point, however what they teach needs careful consideration.

Being up in the air some way above the ground with an aircraft strapped to your back is essentially a practical problem not a theoretical one.

In my view pilots need to be taught the factors that affect lift not the theory of lift. They may well be interested in the theory – and why not for goodness sake – but not at the expense of thoroughly understanding the factors that determine the lift available when they are flying.

The lift equation contains all the factors but only one term in that equation (the lift coefficient) is available for the pilot to vary in order to adjust the lift during the normal course of flying. It is the lift coefficient that is controlled by pulling and pushing on the stick (or wheel) as that varies the Angle of Attack on which the value of the lift coefficient depends.

Only Angle of Attack not speed makes a wing stall. Believing in that and living your life by it is vital to junior (and senior) pilots . The theory of how lift happens will not help you when turning finals. Only a proper appreciation of how to control lift will keep you alive.

The pilots of AF447 seemed to be ignorant of AoA.
Airbus considered that showing the AoA on the display was not useful.
Certification administrations accepted such equipped aircraft to be used for passengers public transport, not matter of AoA.
Air France buyed that aircraft without AoA display.
Pilot unions (SNPL SNPNAC SPAF UNAC, etc.) did never any strike to get AoA.
In other Countries it was the same.
ICAO did no global recommandation.
AESA accepted that mix of AoA ignorance.
WHY?
Many pilots knew enough physik before to get pilot (math sup or mor fo someone.
BUT : At the first page of any aerodynamics book for airline pilot you see the figure of a wing with airstreams thiner when passing over the wing : Well! And then it is written that these airstreams are independant (Bolzmann theory of gas). Question:How does the third airstream knows the wing is there to get thinner?
The pilot trainee decides then to forget definitively the logic and the physic laws!!! And in flying lessons it is said that good pilots are "stupid"...
NO NEED OF AOA!
Some aerobatics flights would SHOW him he is wrong. But it is the time for "NEW METHOD" (Thank you Monsieur DEBIESSE, who initiated that method in the French DGAC)
NO NEED OF AOA SENSORS!
Only a good theoric teaching can bring back confidence to physic reality.

mount a bubble in the cockpit...its as easy as that.

Old school AoA angle and inertial speed..
on a side note, if the pilot has an iPad, use the level bubble app.

there are many concepts in the works that use these types of concepts...

Just to make a quick point...regarding Rn Mn

we simply use Rn as a rough guide depending on what types of forces are dominant-to predict flow separation point and when laminar becomes turbulent---in reality it's not so simple as there are usually mixed flows...plus the interaction with shockwaves etc

At slow speeds and low altitudes and 'conservative' airfoils rather simplistic treaments can be used...as one goes higher and faster it gets progressively harder; but they try to get it as good as possible on paper---and these complex treatments are for designers-not pilots; the wind tunnel provides a better picture and is still cheaper than lots of full scale models provided you do your tests at representative Rn and Mn [or EAS] ---but the aforementioned limitations---described by mike-wsm and Volume---also prevent a full appreciation of the flight characteristics---only through flight testing can we be sure---but even at the most esoteric level---Newton still rules---i.e wing pushes air down---air pushes wing up---that never changes---the mathematical mess is for designers---John Farley's word once again ring true...Brian Abraham's synopsis of the various formulations is very interesting just hope this post puts it into some more perspective...also there are many different treatments with different limiting conditions different acuracies/precision depending on exactly what you're doing...Von Karman corrected most of Prandtl's formulations...he was probably the most exacting one...;)

roulishollandais
your assesment is correct 'pilots are not supposed to be too smart'..:}:ouch:
and don't worry about your typing I'm a native English/Spanish speaker and I can guarantee that at times mine is much worse...:uhoh:

Il y'a etait depuis tres longue temps lorsque j'ai parlait Francais aussi ---J'ai oublie comment tout de mon Francais...I think I said that right...sorry for the missing accent marks too lazy... :)

I forgot most of my Italian too...:uhoh::uhoh::uhoh:


:):):)

Old school AoA angle and inertial speed..

Could be just my dotage and old timer's disease taking hold again .. but, how does that work ?

I can follow the argument for body angle (rather than AoA) under non-accelerated steady state flight conditions but no more than that.

John...I was wondering the same thing!

Now that I think of it I get AoA part but the inertial speed???

why can't one just use AoA in isolation? ... unless are you discussing the lift slope curve dCl/alpha you could get the TAS in order to compute Cl and perhaps through that get a lift slope curve, but I dont think that's a usual method, just guessing though... :)

.. an inclinometer knows naught about AoA, the latter involving the windy bits as well as where the wing might be pointed ? and not much about anything if there be other than gravitational forces involved.

In the same category as the old furphy about using a pencil suspended on a bit of string to let the pilot fly in IMC without an AH etc.

Or am I just getting too old for all this heavy stuff ?

Oh J_T I was on my phone not my laptop, couldn't see clearly...I thought that was an AoA indicator...now I see; you can't get any information from the above set -up...but you, as you know, can get the curve from AoA and TAS data...:)

Pass, brother.

You can. Naval aviators use it as the prime source on a carrier approach.
You not telling me you can't JT? :E A certain test pilot from over the water not far away writes in a book that that was his back up on a round the world venture.

But I'm only an average jock with low level test work under my belt. Not up the the standard of a real TP.

I have no problem with the pencil trick .. it's just that I get confused when upside down during an I/F loop and it's still telling me I'm straight and level ... just one of my many shortcomings, I guess .. all happily married men are well aware of their many shortcomings ..

that was his back up on a round the world venture.

OK if it's a TSO'd pencil on a string ..


We still have to catch up for that beer at Jack's ...

I had no ground school, just bought books until my instrument rating. Worked great for me. I even got my instructors rating reading a book. I went to take the test because I wasn't sure how to study for the test because of all the philosophy of teaching BS. Well, I passed so never learned it. Taught my self aerobatics out of a book, then taught it for Art Scholl, one of the best, with his school. Books are great if you can do it without someone to help you.

My first job when I got my commercial license was crop dusting with zero training. Loved it. After soloing with 5 hrs total I was doing solo spins and finally a loop solo before 10 hrs. It was fun learning that way. With 5 hrs back then you could fly cross country anywhere you wanted to go so would go out and land in the desert on the sand just for fun. I had a AAA map for nav, no aviation charts and did just fine. That 15 degrees variation didn't bother me a bit because at that time I didn't know what it was. Well guess it was in one of the books.

Ended up flying with the largest airline in the world at the time flying a B727. Ended up in the B757 and B767. Funny how things can end up mainly reading books, isn't it.

Naught wrong with reading good books, my friend.

I am in two minds about the internet, though. On the one hand, it opens up a mass of links to all sorts of good stuff .. but, at the same time, it isn't a patch on lounging back in the rocker and flicking through a good book.

I guess what I am saying is don't blame who trained you if you don't train yourself and use your own initiative. We should all take it upon ourselves to be as competent as possible and not throw that responsibility on your company. Take charge yourself.

We are in heated agreement.

JT, my first instrument class was at a junior college and was a total waste of time, had to go back to the books. I know things are different now but this was in the 60's. Usually the ground school teacher reads the book and repeats it soon after the best he can.

My roomate when I was flying a Jetstar was teaching ground school in a high school and I told him he was teaching it wrong. He passed the private pilot written exam but didn't understand what he was teaching. His students would have been much better off reading the manual than listening to him.

I went to Flight Safety in Teterbero in the 70's and he was explaining how to use reversers on a Falcon 20. He said pull the TR levers back then advance the throttles. My Mexican students were going into the sim that night and I said just pull the thrust levers back, don't advance the throttles. They both said no, he said push the thrust levers forward. I just said see you in the morning. Of course the next morning I asked did you push the thrust lever up and they sheepishly said no.

Sometimes reading the manual is the best thing if your instructor is weak.

JT, I agree. Us old timers grew up in a different time and it doesn't work this way now. Now we have a lot of rules that I am happy 9 yrs ago I could leave at 60. I loved the profession but it wouldn't be as much fun now with all the new stuff. I spent my last years flying into Tegucigalpa, Honduras just because the only way we could land was to break all the present rules like 1200 fpm to flair or you couldn't land. We had to fly beside a hill and were not wings level in a B757 until 100 ft, loved it plus the 70 ft cliff at the end of the 5400 ft usable runway made you do it right every time. That is the only part I miss.

Then, at some stage, we should have a convivial ale and reminisce on such things.

Certainly, having done a lot of class room teaching over the years ranging from tertiary aviation/engineering through secondary math/science and on to pilot training, unless the instructor is many levels above the student in technical competence, it is a waste of time. No point in the blind leading the blind.

Mr. Abraham it was a semi rhetorical question re: AoA...;)

I taught myself how to fly...of course legally you need an instructor but for the most part it was a game of Simon says...i.e
CFI says do this...ok
CFI says, do this...ok
do this....no, no,no, need to use the checklist first

Mostly me and my instructors talked about girls, life, plane crashes, etc... never the task at hand...I almost miss those days...:)

Thank you md80fanatic for these two beautiful examples of no rudder nor fin :)


@ Lyman
Just look the shape of the wings in math language.
They have fractal flight law and not continuous function like NS :p

Lot's of credit to man. No mention to the one who understands lift better then all of them put together.Two of his designs pictured above.



Credit where credit due...:D

Ah yes, indeed, flight of animals-immensely complex--it's quite a shame we can't go to the birds to obtain the answers really...:}

Not sure about fractals and such; they use Newton too...they just know what the hell they're doing unlike us...:ooh::ouch:

:}:}:}

Less complex that Navier Stokes equations!
We would like to ask the drop of water in the river flowing toward the bridge how they recon their acceleration, speed, position, spin, deformation, ASO!
:*
Newton? Of course! Like for galaxies from HENON and Laurent NOTTALE. The latter uses fractals to join Relativity theory and Theorie quantique (Paris -Meudon Observatory CNR'S Dr of Research) .:O

roulishollandais
I didn't say you were wrong or anything just that I am unfamiliar with fractals as a part of conventional aerodynamics, as I've never seen such a treatment before within the subject...I have some idea about fractal geometry but I admit I'm having some trouble with your line of reasoning...but I guess there's always more than one way to peel a potato...

Bon soir

:)

http://www.newscientist.com/blogs/cu...500_AA300_.jpg
Hi Pugillistic Animus,

I am glad to tell about fractals also known as Theory of chaos.

This excellent and cheap book (1987) tells many things about fractals and mekanik of fluids.

Chaos: Making a new science by James Gleick (1987)
The first popular science book to tackle the emerging field of chaos theory, journalist James Gleick’s Chaos earned the author a Pulitzer prize. Not only did the book bring this complex physics to the public, says our features editor Ben Crystall, “It helped kick-start the subject into a host of other fields”.

This book exists also in French pocket version and new edition is from 2008. (editions Flammarion, 10€ !)

Why is the conventional aerodynamics still ignorant of fractals ? You know, for a long time a divorce existed between mathematicians and physicians. Physicians wrote some equations, writing integrations of not continuous functions for example, doing mathematicians angry. But math had other goals, like topology, math for computers, and was late to help physicians. Something changed really in the middle of the 20.century with "fractals".

With fractal geometry and theory, sundely physicians were behind, they were struggling with automation and theory of systems, and mathematicians had advantage. In reality we need to work together... but it is not enough to say that !

Things changed when fractals brought new solutions for non-linear dynamic system, new thinking.

As always in science it needs still 15 years or more to update technology.

Discussing C* about AF447, I discovered that derivating don't go higher than 2. (position, speed, acceleration). Why not tendance of acceleration, for instance ? Every thing needs TIME !


I have seen you are very active in the climate change debate. The meteorologist Edward Lorentz has been a great pionnier of climate prevision and discovering the meteorologic part of fractals...

Read Gleick ! You will get good surprises !

I certainly will check it out mon ami---I just hope it's written so that my little brain can understand...engineering and science math is very easy--- just tedious that 'math-people's math is almost incomprehensible to me...i'm no mathematician that's for sure

Hi Pugillistic Animus,
You will see birds, rivers, hurricanes, FCS, etc. otherwise after reading James Gleick about fractals ... A good index will help you to sort different matters after a first cross-reading (just a suggestion). Math is often showed as interesting at abstract objects, Nobody knows what an abstract object is ! We have only senses to discover new objects. In our brain we can only play with them !:ok:

Some teacher will tell about "linear combination" :Eanother about "linear shape" :) for the same thing : you see, smell, taste, listen, and touch the latter, the first stays a mystery... Go with the good teacher !

Faites de beaux rêves !

Je vous voudraise la meme chose

merci beaucoup...:)

Airflow around a rotating cylinder
 

The picture shown in the FAA explanation makes no sense to me.

To look at the rotational direction, it shows pressure increasing at the bottom and decreasing at the top, hence a resulting up force.

Should this not be the other way around because, the way I understand it,
the cylinder part rotating into the wind creates an increase of the relative airflow speed (pressure drop) over the surface (in the illustration; at the bottom) and the top shows relative airflow slowed down (pressure increase) accross the surface.

Are there effects causing my understanding not to be true ?

Just curious, because aerodynamics have served me well in my 60 years of flying.:confused:

121 Sir

Flying is a matter of surfing on a mixture of gases, most of the rest is simply managing the drag using tedious mathematics.

If you rotate a rigid cylinder as suggested there will be more collisions with the gas phase per unit time with that structure than if it were static.

Hence more lift.