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  • #76
    Originally posted by Gabriel View Post
    I don't remember what this part said, how how he got to that conclusion (because the guy doens't just say something like that without a previous explanation).
    This was in the context of steady, level flight.

    For the airfoil in figure 3.6, under cruise conditions, there is almost no high pressure on the bottom of the wing; indeed there is mostly suction there.5 The only reason the wing can support the weight of the airplane is that there is more suction on the top of the wing. (There is a tiny amount of positive pressure on the rear portion of the bottom surface, but the fact remains that suction above the wing does more than 100% of the job of lifting the airplane.)
    Of course it doesn't violate my Newtonian explanation.
    I'm not saying it does. I'm saying it seems to. I'm not questioning your grasp of aerodynamics, I'm questioning your (and apparently every other aeroengineer's) grasp of explaining things in a consise, succinct manner (a summary that can be widely understood, especially by pilots and the people who train them) without introducing confusion. This is, itself, an art (if not a science).

    Here's where I want to start:

    The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli’s principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton’s laws. This causes the wing to lift upward.

    Not a bad start.

    Now, there are things here that I call "conveniences". Think of them like plot conveniences. You are asked to accept them without understanding them. Annoyingly curious five-year-olds don't do that, and they shouldn't have to (up to a point where things become too technical for them, which is beyond, I think, where we need to go with this).

    To begin with, 'The wing produces circulation' is, at this stage, a 'convenience'. It needs further explanation...

    So, when I find time, I'm back to reading your link...

    Comment


    • #77
      Holy left winglet!

      Comment


      • #78
        Originally posted by 3WE View Post
        It's inappropriate to put personal stuff like this up- but his face is obscured, BUT his aircraft is not.- hopefully the mods won't mind.

        Is this suitable for uploading to the photo database?

        PS- Do not over think this, the intent is light humour.

        Click to see full size.
        [ATTACH=CONFIG]21966[/ATTACH]
        Oh, don't you try to be funny, on his 51st birthday... please.

        That's what airlines are good for, amongst others,
        The Gold Member in the 747 club, 50 years since the first LH 747.
        And constantly advanced, 744 and 748 /w upper and lower EICAS.
        Aviation enthusiast, since more than 35 years with home airport EDDL.

        Comment


        • #79
          Originally posted by ATLcrew View Post
          Holy left winglet!
          The best part is that LHBs post just above reminds me that, on post #1 of this thread, I said, “Don’t over think this”.
          Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

          Comment


          • #80
            Originally posted by 3WE View Post
            The best part is that LHBs post just above reminds me that, on post #1 of this thread, I said, “Don’t over think this”.
            Now I know why Gabe is my friend. He's able to write longer forum entries than me. Let's combine his #23 here and his #33 and his #62, together that must be more than I've ever written here on this platform since more than 10 years.

            The problem really is time. Let's say that Gabe's entries at least are always 10 or 41 (!) times longer than the average jp forum entry which you or me write. Further let's assume that if I really try to control myself, as in the recent A380 topic, you need 15 seconds to read one of my entries.

            That would mean, for an average Gabe entry, we need 41x15 = 615 seconds, or a little bit more than 10 minutes, only to read it, without the answer.

            That's the truth, isn't it. I'm too old today to lie!

            PS: Another problem is, that Gabe's entries (most of the time) contain good stuff. Not for nothing I call him a flight instructor. So, most of the time, it's even worth the 10 minutes.
            That's what airlines are good for, amongst others,
            The Gold Member in the 747 club, 50 years since the first LH 747.
            And constantly advanced, 744 and 748 /w upper and lower EICAS.
            Aviation enthusiast, since more than 35 years with home airport EDDL.

            Comment


            • #81
              Well, I tried Lift = k * r *V^2 * AoA.
              I also tried "Wing pushes air down, air reacts pushing wing up".

              But that didn't work.
              Then I tried with #23, #33, #62 and others.









              That didn't work either.
              So I stopped trying,

              --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
              --- Defend what you say with arguments, not by imposing your credentials ---

              Comment


              • #82
                You can call me a Pseudo-Italian, or not-a-half-Genovese, but there is one thing which we all understand.

                The connection with O'Hare airport. The newest thing is, Alitalia only goes ORD seasonal?! And Fiumicino refused money and knowlegde from a source which
                definitely better treats the LIMC (Milano Malpensa), LIMJ (Genova) and LIRQ (Firenze) airports,
                better than AZ ever tried?!

                Lord forgive me, it's Carnival Sunday. Experienced aviation enthusiasts are Boeing enthusiasts, or what would you say, Rick Santelli.

                The news, Alitalia only goes ORD seasonal. Ok.. I know that his a/c type does not need any further recommendation but..

                Take 'the replacement flight', LH #430 (a/c type B748_), code share with UA, AC, AI, and Thai Airways (TG).

                PS: Sorry, but there should be 1 Italian moment each week. And be it 1956 in Chicago. Btw, a little bit too much NBC friendly is better than a little bit too less criticism for the Regime. Holt again is such a brilliant example, first of all the Regime thought that he's a flawless Democrat, because Holt almost destroyed what appeared after Obama, in a first interview.
                Criticism for the Regime does not only take place amongst Democrats. I really love Holt (who is an officially listed Republican member) for that interview!
                That's what airlines are good for, amongst others,
                The Gold Member in the 747 club, 50 years since the first LH 747.
                And constantly advanced, 744 and 748 /w upper and lower EICAS.
                Aviation enthusiast, since more than 35 years with home airport EDDL.

                Comment


                • #83
                  Originally posted by Gabriel View Post
                  Well, I tried Lift = k * r *V^2 * AoA.
                  I also tried "Wing pushes air down, air reacts pushing wing up".

                  But that didn't work.
                  Then I tried with #23, #33, #62 and others.

                  That didn't work either.
                  So I stopped trying,
                  We should open a contest with 'the shortest forum entry'. The Academy Award for the longest, or for the most forum entries is for you (not quite true..).
                  For the most forum entries, that seems to be a discipline where still another 'senior' based on DUS has a slight advantage (tennis). Probably I should warn him
                  ('Gabe reaches 7000 within the next 30 minutes. Be aware.') .

                  D/arn, I tried to avoid Politics as much as I can, but could you imagine a Regime that only communicates via the jetphotos forum? And after all, only failures? 'I took a 747 to Hanoi, and the result will be nothing.'
                  That's idiocy. If Hanoi were part of the LH winter schedule, there is always a result. We need time, we need fuel, you don't get something like that for nothin.

                  Probably I should stop here, with the result, ask Holt (or me) if you honestly like to hear something about international diplomacy!

                  PS: That one was not really for meant you Gabe. Only part of my internal thoughts for the early sunday.. 41.. Does it get better with 42, less sorrows?
                  That's what airlines are good for, amongst others,
                  The Gold Member in the 747 club, 50 years since the first LH 747.
                  And constantly advanced, 744 and 748 /w upper and lower EICAS.
                  Aviation enthusiast, since more than 35 years with home airport EDDL.

                  Comment


                  • #84
                    So, my 2c,

                    Wings on yachts. In the 'old days' a cloth sail was used, now some boats use a solid 'wing' larger than a A380 wing.

                    While the Newtonian - action/reaction is true with the wind from behind for a boat, the quickest speed a boat can reach is when the wind is from 45* from the front - some Newtonian and some pressure differential 'lift' that allows the boat to travel FASTER THAN THE WIND TRAVELLING

                    Comment


                    • #85
                      Originally posted by Gabriel View Post
                      That didn't work either.
                      So I stopped trying,
                      Evanie made one valuable point: That there’s much, varied, and somewhat questionable information out there on how wings work- CONVERSELY - given the predominance of fuel injection we don’t hear much about that carburetor part called the Venturi.
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #86
                        Originally posted by Gabriel View Post
                        Well, I tried Lift = k * r *V^2 * AoA.
                        It can't be a technical equation.

                        Originally posted by Gabriel View Post
                        I also tried "Wing pushes air down, air reacts pushing wing up".
                        The problem with this is that it is too simple. Too vague. Therefore, it is wide open to misintepretation.

                        A better 'simple' version would be: "The wing, interacting with the surrounding airstream, produces a lower pressure above the wing than below it, which causes the wing to lift upward."

                        But, that is still too simple and open to misinterpretation and erroneous understanding of the 'whys' involved.

                        Originally posted by Gabriel View Post
                        But that didn't work.
                        Then I tried with #23, #33, #62 and others.
                        #23 was an explanation of wing shape, not lift itself (but very informative on that subject).
                        #62 was a list of misconceptions.
                        #33 was very helpful but too detailed and tooooo looong for most non-aeroengineers.

                        So, continuing to build on:

                        The wing produces circulation in proportion to its angle of attack (and its airspeed). This circulation means the air above the wing is moving faster. This in turn produces low pressure in accordance with Bernoulli’s principle. The low pressure pulls up on the wing and pulls down on the air in accordance with all of Newton’s laws. This causes the wing to lift upward.
                        1) Circulation cannot be explained simply, but the reason for it can be included (as a 'convenience').
                        2) We don't need to name-drop. We can omit Bernoulli and replace him with the general theorum.
                        3) Same goes for Newton.

                        So, let's try this:

                        As the wing begins to move forward, the interaction of the wing and the surrounding air produce an initial air disturbance called a vortex, and this vortex, in turn, produces an opposite 'bound' vortex, or 'circulation', which flows around the entire wing shape, moving from front to back across the top of the wing and back to front along the bottom of the wing. This force of this circulation causes the air travelling above the wing to move faster and the air travelling below the wing to slow down. Since a faster-moving parcel of air has a lower pressure than a slower-moving parcel of air, this creates an area of lower pressure above the wing which pulls up on the wing and pulls down on the air. This, along with some other contributing factors, causes the wing to lift upward. The amount of lift = airspeed × circulation × air density × wingspan.

                        Now, keep in mind that this is an explanation for a general audience intended to replace the equally brief erroneous explanations that currently pervade everything from the internet to actual piloting manuals. This requires it to be brief and succinct. If anyone wants to know about the Kutta condition and Navier–Stokes equations and viscosity and the Magnus effect and Newton and Bernoulli and all the actual mechanisms and physics involved in detail, they can dive down that rabbit-hole to their heart's content.

                        Would you disagree with that general explanation?

                        Comment


                        • #87
                          Originally posted by 3WE
                          I too cringe that you continue to say “we don’t know how lift is generated”.
                          Did I say that?

                          I'm saying two things:

                          - Many, many people (if not most people) who know a thing or two about aviation, some of whom are pilots, have a false understanding of how lift is generated.
                          - Hydrodynamics, aerodynamics and thus the nature of lift are observed phenomena, for which the mechanics are empirically observed and theoretically deduced to form a single universally-accepted theory.

                          On the first point:

                          Originally posted by John S Denker
                          This may come as a shock to many readers, because all sorts of standard references claim that the air is somehow required to pass above and below the wing in the same amount of time. I have seen this erroneous statement in elementary-school textbooks, advanced physics textbooks, encyclopedias, and well-regarded pilot training handbooks.
                          Or...

                          Originally posted by 3WE
                          The lower stream is SLOWED because this board is plowing through it and PUSHING it down (and forward just a tad).
                          The upper stream is accelerated because a 'vacuum' PULLS it down and back and into the low pressure area that even goes behind the wing.
                          And...

                          There is a widely-held misconception that it is the velocity relative to the skin of the wing that produces lift. This causes no end of confusion.
                          Bernoulli’s principle is very easy to understand provided the principle is correctly stated. However, we must be careful, because seemingly-small changes in the wording can lead to completely wrong conclusions.
                          On the second point:

                          Originally posted by John S Denker
                          Kutta condition- It is a bit of a mystery why the air hates turning a corner at the trailing edge, and doesn’t mind so much turning a sharp corner at the leading edge — but that’s the way it is.
                          A full discussion of turbulence and/or separated flow is beyond the scope of this book; indeed, trying to really understand and control these phenomena is a topic of current research.
                          Etc. Yes, aerodynamic predictions are largely accure these days. Yes, I overstated it for effect, and you, of course, recreated it as a black-and-white statement, but, while aerodynamics are very well-understood by aeroengineers, I contend that their mathematical predictions are less reliable than those of other areas of science and engineering because of the phenomena involved. Some of the 'whys' are still open to debate.

                          And there even seems to be argument here:

                          Originally posted by Gabriel
                          Now, air is difficult to see, so let's play with water. Take that spoon and hold it hanging lightly from the tip of the handle, now put the round part under this stream of water from the tap. Slowly. SO what did you see? Correct! The shape of the spoon gets the water is deviated, pushed to one side, and the spoon is pushed to the other side.
                          Originally posted by John S Denker
                          You may have heard stories saying that the Coandǎ effect explains how a wing works. Alas, these are just fairy tales. They are worse than useless.

                          Comment


                          • #88
                            Originally posted by Evan View Post
                            It can't be a technical equation.



                            The problem with this is that it is too simple. Too vague. Therefore, it is wide open to misintepretation.

                            A better 'simple' version would be: "The wing, interacting with the surrounding airstream, produces a lower pressure above the wing than below it, which causes the wing to lift upward."

                            But, that is still too simple and open to misinterpretation and erroneous understanding of the 'whys' involved.



                            #23 was an explanation of wing shape, not lift itself (but very informative on that subject).
                            #62 was a list of misconceptions.
                            #33 was very helpful but too detailed and tooooo looong for most non-aeroengineers.

                            So, continuing to build on:


                            1) Circulation cannot be explained simply, but the reason for it can be included (as a 'convenience').
                            2) We don't need to name-drop. We can omit Bernoulli and replace him with the general theorum.
                            3) Same goes for Newton.

                            So, let's try this:

                            As the wing begins to move forward, the interaction of the wing and the surrounding air produce an initial air disturbance called a vortex
                            Why? How?
                            and this vortex, in turn, produces an opposite 'bound' vortex
                            Why? How?

                            , or 'circulation', which flows around the entire wing shape, moving from front to back across the top of the wing and back to front along the bottom of the wing.
                            Forget abotu why and how... Whaaaaat?

                            his force of this circulation causes the air travelling above the wing to move faster and the air travelling below the wing to slow down. Since a faster-moving parcel of air has a lower pressure than a slower-moving parcel of air,
                            Why

                            this creates an area of lower pressure above the wing which pulls up on the wing and pulls down on the air. This, along with some other contributing factors, causes the wing to lift upward. The amount of lift = airspeed × circulation × air density × wingspan.
                            Do you mean that the angle of attack and the chord or area of the wing doesn't have anything to do with the generation of lift?
                            And that there are other contributor factors other than the pressure differential above vs below the wing?

                            Now, keep in mind that this is an explanation for a general audience intended to replace the equally brief erroneous explanations that currently pervade everything from the internet to actual piloting manuals. This requires it to be brief and succinct. If anyone wants to know about the Kutta condition and Navier–Stokes equations and viscosity and the Magnus effect and Newton and Bernoulli and all the actual mechanisms and physics involved in detail, they can dive down that rabbit-hole to their heart's content.

                            Would you disagree with that general explanation?
                            If you find it useful, I am happy for you. I see it as very complicated. The reduction of air pressure with increased speed is Bernoulli. The circulation is the Kutta condition which I find much more simple, understandable and intuitive than the circulation. And the circulation, Kutta condition and the Magnus effect exist because of viscosity.

                            And in any event, why is the circulation the magnitude it is so the speeds above and below are what they are and not something else (for example not something that would make the parcels above and below arrive together at the trailing edge)? I don't think that your explanation fixes any of the objections or complaints that you had with the other explanations, rather the opposite, and it is much more complicated and difficult to understand.

                            --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                            --- Defend what you say with arguments, not by imposing your credentials ---

                            Comment


                            • #89
                              Originally posted by Gabriel View Post
                              Why? How?
                              It has to be a summary of the hows and whys, but it's balance of how much understanding you can provide in a summary. As I said...

                              If anyone wants to know about the Kutta condition and Navier–Stokes equations and viscosity and the Magnus effect and Newton and Bernoulli and all the actual mechanisms and physics involved in detail, they can dive down that rabbit-hole to their heart's content.

                              Forget abotu why and how... Whaaaaat?
                              Do you mean that the angle of attack and the chord or area of the wing doesn't have anything to do with the generation of lift?
                              And that there are other contributor factors other than the pressure differential above vs below the wing?
                              The way I currently understand it from reading the link you provided, the chicken-and-egg question of airspeed and pressure differentials can be explained as follows:
                              The circulation (the span-wise 'bound' vortex) is responsible for acceleration of airflow adjacent to the wing by imparting an opposing force against the lower airflow and an additive force to the upper airflow, and that THIS is what results, thanks to Bernoulli, in the areas of pressure differential that give the wing its lift. Any change in AoA will have the effect of increasing or decreasing circulation, so AoA is included within the equation as 'circulation'. Other contributing factors are the air being turned by the wing volume (or impenetrability) and deflected down by the lower wing surface in a positive angle of attack. Do you agree with that?

                              I didn't think we should include AoA in the general explanation of lift, because it would become, once again, too complicated, and isn't necessary to the basic understanding.

                              I see it as very complicated.
                              I know, but everybody can't be Gabriel. You are assuming certain a priori knowledge of concepts that most people lack.

                              Comment


                              • #90
                                Originally posted by John S Denker
                                Kutta condition- It is a bit of a mystery why the air hates turning a corner at the trailing edge, and doesn’t mind so much turning a sharp corner at the leading edge — but that’s the way it is.
                                I disagree with that part. Air (or any fluid) hates turning any sharp edge anywhere, so it doesn't. The leading edge is not sharp in most cases and if it is, there will be separation there too unless the AoA is such that the stagnation point is exactly at the leading edge. Now, if the AoA is not too big, the separated air can form a bubble and re-adhere on the upper surface later on. But now the air is going around the bubble, not the sharp leading edge.

                                And the reason for the Kutta condition is not a mitsery. The centripetal acceleration is V^2/R. On a sharp edge R->0 so for any non-zero speed the normal acceleration is infinite. It gets paradoxical because an infinite acceleration requires an infinite force on the parcel of air turning the sharp edge, which in turn would require infinite low pressure and hence infinite high speed. In other words, the potential flow model predicts a singularity in the trailing edge, a singularity that would put the flow out of the scope of the model (potential flow = no viscosity and there is no way that you can neglect the viscosity wen you have infinite speed). It is quite obvious that a real flow will not be able to achieve the conditions needed to turn around a sharp edge.

                                It is true that, in the early ages of mechanics of fluids, when they were working with the potential flow model, it eventually became apparent (intuitive, obvious and also observed) that the flow would separate at the trailing edge but there was no model to explain that. So it was an external condition imposed to the model (together with "the flow will not penetrate the airfoil", which is something that no model "predicts", it is a condition imposed from outside of the model, in the same way that "the train will follow the tracks" in an example I gave in a previous post).

                                Now, model a boundary layer (for which you need to take viscosity into account) and now the model predicts the Kutta condition.

                                Now, air is difficult to see, so let's play with water. Take that spoon and hold it hanging lightly from the tip of the handle, now put the round part under this stream of water from the tap. Slowly. SO what did you see? Correct! The shape of the spoon gets the water is deviated, pushed to one side, and the spoon is pushed to the other side.
                                Ok, that's a bit of out-of-context and a bunch of my bad. I thought of adding a clarification but remember it was an explanation for a 5-years-old.

                                The Coanda effect (the tendency of a stream of flow to remain attached to the surface of an object) is not how a wing creates lift because, simply, there is no "one jet of flow".
                                The stream of water surrounded by air or a jet of air surrounded by static air would be Coanda effect.

                                My intention was related to explaining the action-reaction. The spoon pushes the water and the water pushes the spoon. It is noice because you can SEE the water being displaced in one direction and you can SEE the spoon displaced in the opposite direction and defeating gravity (it is not hanging vertically). And when you stick your hand out of the window at an angle of attack, you hand pushes the air and the air pushes your hand. I hoped it would be intuitive that a thing at an AoA would push the fluid. But the reason why the hand pushes the air is not the same than the reason why the spoon deviates the water.

                                --- Judge what is said by the merits of what is said, not by the credentials of who said it. ---
                                --- Defend what you say with arguments, not by imposing your credentials ---

                                Comment

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