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  • #31
    Originally posted by BoeingBobby View Post
    Originally posted by Gabriel
    You are right. The DC-3 is also an airliner after all. Let me correct:

    In all Boeing, Airbus, McDonnell Douglas, Bombardier and Embraer transport category
    Still wrong! Blanket statements will do that to you. Convair 880/990 NO LED's, many EMB's and Bombardier's, NO LED's. So even leaving out all of the older piston engine aircraft, you are still wrong. And Evan, are you EVER going to answer my original question?
    Convair? I said Boeing, Airbus, McDonnell Douglas, Bombardier and Embraer.

    LED's? I said FLAPS (which are TED's).

    Originally posted by Gabriel
    2- Flaps 2: In all airliners the flaps don't go just down, but they extend back
    Is there any Boeing, Airbus, McDonnell Douglas, Bombardier and Embraer transport category jets that don't have flaps that extend back? Not that I know but maybe, in which case I will stand corrected again.

    --- 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


    • #32
      Originally posted by Gabriel View Post
      Convair? I said Boeing, Airbus, McDonnell Douglas, Bombardier and Embraer.

      LED's? I said FLAPS (which are TED's).



      Is there any Boeing, Airbus, McDonnell Douglas, Bombardier and Embraer transport category jets that don't have flaps that extend back? Not that I know but maybe, in which case I will stand corrected again.
      Whatever. I have had about as much fun with you all as I can stand. What is that old saying? No good deed goes unpunished? Think I am going to start to enjoy my retirement. Evan, still waiting for your answer!

      Comment


      • #33
        Originally posted by Evan View Post
        1) Did you mean leading edge there or am I just not getting it?

        3) Are we talking magic salts?
        Fixed both in the original posts. Thanks.

        2) You've given us a nice explanation of leading edge aerodynamics and wing camber and you've already brought Newton into it on the lower wing surface (airflow 'turning'), but... how does the upper surface of the wing contribute to generating lift?
        This is a question that makes no sense four us super-genius-aerofluodynamicist-of-the-millennium (ok, them, not us). There is no "contribution" of one surface vs the other.

        What makes lift is the distribution of pressures around the airfoil, which will depend on the airfoil design and angle of attack.
        You will even find cases where, in the majority of the airfoil, the pressure is lower than the atmospheric pressure, both the upper and lower surface. Just that on the upper surface it is even lower than on the lower surface.

        You will even find cases of similar airfoils that have the same camber geometry and where the thickness distribution of one is just a scale-up of the thickness distribution of the other. For example, NACA 2408 (8% thick) and 2415 (15% thick). Both airfoils have virtually the same lift-to-AoA plot (especially away from the stall zone), meaning that they make the same lift for the same AoA, for any AoA away from the stall.

        Yet, the pressure distributions are different. What you will find is that the pressures are lower in the 2415 all around, both in the upper and lower surface.
        But when you plot the DIFFERENCE between the pressures in the upper and lower surface for each point along the chord, you will see that both plots look almost the same (you'll see, away from the stall, the DIFFERENCE in pressure between both surfaces is more a function of the geometry of the mean line. i.e. the camber, than the thickness distribution).

        In this way, even if you have a "low pressure" in most of the lower surface, you can still have positive lift due to an "even lower pressure" on the upper surface.

        You before "explained" how the airfoil creates a "constriction" on the upper surface which makes the airflow accelerate as it needs to flow through a "narrower" pipe, and how this increases speed means lower pressure due to Bernoulli.

        It can be argued different, we can say that the airflow accelerates the airflow (and the pressure goes down due to Bernoulli) and that acceleration makes the channels to constrict because, due to conservation of mass, more velocity will mean smaller cross section (you don't need a physical barrier that narrows, the same will happen with a stream of water in free fall, the speed will increase due to the gravity and the stream will become narrower, would you say in that case that the water accelerates because of a constriction)?

        But there is still a third way that it can be argued. We can say that, due to the boundary conditions (explained later), the airfoil forces the air to reduce the pressure, this generates an increase in speed (due to Bernoulli) and the constriction.

        So which of them is correct? It is a little bit of each? No, it's none and and all. There are not "individual contributions" of these effects, are different ways to express the same phenomena.

        It's not that the airfoil does this to the air or that the air does that to the airfoil. There is an interaction between the 2.
        The air will just do what it needs to do.

        That is, the air flowing around the airfoil needs to meet a certain 3 conditions:
        1- Being a continuum, it needs to keep a smooth gradient of speeds and pressures.
        2- It cannot penetrate walls (i.e. the flow that is immediately in contact with the airfoil must be tangent to the airfoil).
        3- It needs to separate at the trailing edge*

        In fact, you can mathematically simulate an airfoil by pacing on the boundary or inside the airflow an infinite number of infinitely small singularities called sources, sinks and rotors Make these sources many but not infinite and small but not infinitely small and you have a numerical model of the style of finite elements that lets you approximate the airfoil, or whole wing, or whole airplane, with an arbitrary accuracy as long as you have sufficient computing power and patience. What you do is set up a number of "checkpoints" on the contour of the airfoil (one of the HAS to be the trailing edge) and calculate the speed field by adding just a constant speed field (that the free stream) to the field generated by each source, sink and rotor. The speed vector of the air at each point of the field (that is, at any point anywhere, including inside the airfoil) will be a function of the intensity of each source, sink and rotor. Then calculate the speed vector at each checkpoint, which, again, each of them will be a function of the intensity of each source, sink and rotor. And finally, you make a quite simple system of linear equations where you FIND the intensity of each source, sink and rotor by making:
        - Component of the speed vector perpendicular to the contour of the airfoil at checkpoint A = 0 (and the same for every checkpoint).
        - Separation happens at the trailing edge.
        - Sum of the intensity of all source and sinks = 0 (i.e. we are not creating or destroying air)

        And then, when you run the simulation of a constant air flow coming from the left and all these sources, sinks and rotors more or less where the airfoil would be, it is amazing to see how the flow flows around an airfoil that doesn't physically exists and how you have a second flows that goes from the sources to the sinks that remains inside the imaginary airfoil and doesn't mix with the external flow.
        The next thing you can do is calculate the pressure of the air at each point in the external flow that is immediately next to where the airfoil would be (i.e. the points where both the external and internal flow are in contact but neither crosses the boundary), and then you can fo further and integrate all the pressures on the top surface on one hand and all the pressures on the bottom surfaces on the other hand. What you will find is that, except in a very narrow zone around the front stagnation point, all the pressures in the contour are lower than the free stream pressure (i.e. atmospheric pressure), but it is even lower on the top surface than in the lower one. Again, it is just what the air NEEDS to do to separate at the trailing edge, avoid penetrating the airfoil, and keep a smooth gradient of pressures and speeds.

        * Condition 3 is is a tricky one, it is something that doesn't come automatically in the equations of potential flow but that you have to "impose" in the model it is called the Kutta condition, super-genius-aerofluodynamicist-of-the-past-millennium took a while to figure this out and, without this condition, lift simply cannot exist. As the stagnation point where the flow splits may not be exactly at the leading edge but a bit behind on the lower surface, the "re-joining" point under potential flow will happen not at the trailing edge but a bit ahead of it on the upper surface, with the air going from below to above around the trailing edge. This led to several super-ge...-past-millennium to assert that heavy-than-air flight was not possible, as if gliding birds did not exist. Also the "no walls penetration" is something that you need to impose in the model otherwise the air would just flow across the airfoil without being disturbed, but this condition is obvious. Remember I said that they were working with the potential flow model, which is an ideal flow with no viscosity. And this trailing edge separation just would not happen in a potential flow, unless you impose it. In reality, the inpentrability of walls happen because, well, walls are impenetrable, and the Kutta condition happens because under the potential flow the air would accelerate to infinite speeds when turning around the sharp trailing edge, which would not only violate Einstein's speed limit but also breaks the approximation of no viscosity. With such huge speed gradients viscosity becomes non-negligible-at-all, the air cannot accelerate to the infinite speed required to turn around the trailing edge, and separates instead. In the potential flow model the Kutta condition is obtained by adding circulation, which is like having the airfoil contour made of "treadmill" and having that band "circulating" around the airfoil. Then you start the treadmill and speed it up more and more until the separation happens at the trailing edge, and now you have a mathematical model that closely matches the flow around the real airfoil. Circulation is what makes lift. Remember the model of the cylinder spinning that I talked before?

        --- 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


        • #34
          Originally posted by BoeingBobby View Post
          Evan, still waiting for your answer!
          You'll be waiting a while. He's still to answer the much more benign question of what airlines he rides on as a passenger. In all these years he made one peep about being on Air Berlin (RIP) once.

          Comment


          • #35
            Originally posted by Gabriel View Post
            Foxed both in the original posts. Thanks.
            Outfoxed, you might say.

            Comment


            • #36
              Originally posted by Evan View Post
              Outfoxed, you might say.
              Shot!!! (see? another typo)

              --- 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


              • #37
                Originally posted by Gabriel
                So which of them is correct? It is a little bit of each? No, it's none and and all. There are not "individual contributions" of these effects, are different ways to express the same phenomena.
                I do appreciate the technical lessons you provide, but I'm afraid I'm finding this one as impenetrable as an LH-B747 post. Is it possible to give a layman's answer to how the entirety of factors introduced by an airfoil create lift?

                Let me put this to you as a multiple choice question. Which of the following is true?:

                [a] Lift is a known science, the mechanics of which are absolutely proven to be known.

                [b] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a single universally-accepted* theory.

                [c] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a number of competing theories.

                * By the super-geniuses of aerofluodynamics

                Comment


                • #38
                  Originally posted by Evan View Post
                  I do appreciate the technical lessons you provide, but I'm afraid I'm finding this one as impenetrable as an LH-B747 post. Is it possible to give a layman's answer to how the entirety of factors introduced by an airfoil create lift?

                  Let me put this to you as a multiple choice question. Which of the following is true?:

                  [a] Lift is a known science, the mechanics of which are absolutely proven to be known.

                  [b] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a single universally-accepted* theory.

                  [c] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a number of competing theories.

                  * By the super-geniuses of aerofluodynamics
                  It's all PFM.

                  Comment


                  • #39
                    Originally posted by Evan View Post
                    I do appreciate the technical lessons you provide, but I'm afraid I'm finding this one as impenetrable as an LH-B747 post. Is it possible to give a layman's answer to how the entirety of factors introduced by an airfoil create lift?

                    Let me put this to you as a multiple choice question. Which of the following is true?:

                    [a] Lift is a known science, the mechanics of which are absolutely proven to be known.

                    [b] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a single universally-accepted* theory.

                    [c] Lift is an observed phenomenon, for which the mechanics are empirically observed and theoretically deduced to form a number of competing theories.

                    * By the super-geniuses of aerofluodynamics
                    It is definitively not [c]

                    It's almost like [a], except that the science is not Lift but Mechanics of Fluids.
                    And I am not sure what is the difference with [b]. Science IS basically empirical observation, theoretically modeling these observations, confirming with more observation, making predictions with the model, and then testing to confirm if the predictions hold true.

                    We have a full physical and mathematical model of how fluids work. The model is found to work (it closely matches reality). And generation of lift is just part of that.

                    But there are no competing theories. What we have is akin to asking "Why does an object accelerate when it falls down? Because it converts potential gravitational energy into kinetic energy so 1/2*m*v^2=m*g*h or because the force of the weight imposes an acceleration given by F=m*g=m*a?" It's not one or the other. It is both. "Ok, so how much is the contribution of each of these effects? Or are they different competing theories and we don't know which of the 2 is the correct one?" Nonsensical question, they are not different contributions or theories, they are different ways to view the same thing. In fact one equation can be mathematically derived from the other.

                    The governing theory is the Navier Stokes equation, which is basically F=m*a applied to an infinitesimal element of fluid, and where the forces are normal forces (pressure), share forces (viscosity), inertial forces (depending the frame of reference you choose) and external forces (like gravity or those made on the elementary volume of fluid by the walls of a container).

                    The full Navier Stokes equation has very few assumptions (like assuming that the fluid is a continuum, which it is not, and that the Newton equations are correct, which they are not, but both are damn good approximations), and no known solution (there is a 1 million dollar for whomever finds a solution to the full Navier Stokes equation).
                    However, do not dismay, because it can be tackled numerically and specific cases can be simulated and solved with arbitrary precision.

                    Also, the Navier Stokes equations have known closed solutions if you add more assumptions (things like incompressibility, no or constant viscosity, laminar flow, etc...)

                    For example, the Bernoulli and hydrostatic equations, for example, were conceived long before the Navier Stokes equation. But they can also be derived from the full Navier Stokes equations by adding assumptions (line all speeds and accelerations are zero for Hydrostatics, or laminar non-viscous and constant speed flow for Bernoulli, which is called potential flow).

                    The generation of lift can also be derived from the Navier Stokes equations taking the same assumptions than for Bernoulli and adding the boundary conditions (cannot penetrate the airfoil and must separate at the trailing edge). The assumptions are very good away from the stall and out of the boundary layer (where the flow is viscous it is typically turbulent too so bye-bye Bernulli), yet luckily the boundary layer is a very thin layer around the airfoil, so the shape of the airfoil+boundary layer is basically the shape of the airfoil. The Kutta condition (separation at the trailing edge) was added first empirically, based on observations that the flow does separate at the trailing edge (something that the potential flow equations did not predict), but then it was understood when it was seen that the assumptions of the potential flow equations predicted an impossible infinite-speed singularity at the trailing edge (if you don't force the separation there) and that the boundary layer that was being neglected (where the viscous processes take place) could not theoretically sustain that and it would separate, as it does in practice as the boundary layer theory predicts.

                    This simplified theory of potential flow with no flow separation except at the trailing edge is capable of explaining lift, pressure drag and induced drag. But not parasite drag. The boundary layer theory can predict the parasite drag, however it needs some numbers to be "forced" from outside, like where the transition from a laminar boundary layer to a turbulent boundary layer happens. There are theories to predict that too on a perfect surface. Add rivers, bugs, paint texture etc and it becomes quite unpredictable, so you "force" it by hand (like the Kutta condition).

                    There are better models based on finite elements that can predict virtually anything by using fewer assumptions and dividing the "space" into a lot of little (but not infinitesimal) volumes and "checkpoints" at the boundaries to enforce the boundary conditions. These equations are so good that, with current computer power, the test pilots of a new transport category jet can fly it in the simulator in all the envelope before the first flight takes place, and even before wind tunnel testing. And the results are not perfect but very close.

                    So, like every science, Mechanics of Fluids is based on observations, the observations are transformed into laws of equations with assumptions, and the equations are then used to make predictions, that are then tested and found to hold true confirming the power of the theory.

                    As said: We have a full physical and mathematical model of how fluids work. The model is found to work (it closely matches reality). And generation of lift is just part of that.

                    --- 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


                    • #40
                      Originally posted by ATLcrew View Post
                      It's all PFM.
                      No magico.

                      The lift comes from the pilot pulling on the stick or yoke, and then the engines pull/push the plane up.

                      By the way- as to the most recent exchange. Evan seems unable to comprehend that wings “grab” passing air and shove it down...which creates a reaction called lift.
                      Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

                      Comment


                      • #41
                        It's almost like [a], except that the science is not Lift but Mechanics of Fluids.
                        And I am not sure what is the difference with [b]. Science IS basically empirical observation, theoretically modeling these observations, confirming with more observation, making predictions with the model, and then testing to confirm if the predictions hold true.
                        I guess I would say that known science (meaning scientifically "proven" fact) has withstood all reasonable scepticism. Is there room for doubt or scepticism in the prevailing explanation of airfoil-induced lift? If not, then I would consider it a known science. But I get the impression that there is room, and that the explanations for lift are very scientific postulations conceived to explain an observed phenomena—that they are the product of abductive reasoning—(that lift was discovered by physical experimentation long before the postulation was deduced (or induced?) to explain it).

                        But this is what I'm asking you, because I really don't know the answer.

                        I also really don't know that I could accurately explain how a wing creates lift to a five-year-old. I could say it's due to the plane of the wing deflecting the air downward and Sir Newton requiring an equal but opposite upward force. I could explain that the airfoil creates an area of lower pressure above the wing also resulting in an upward force.

                        But this is how a five-year-old (god bless them) would have me:

                        Me: The airfoil creates an area of reduced pressure above the wing, so the higher pressure below the wing pushes it upward (Bernoulli).

                        Kid: Why?

                        Me: Because the airstream above the wing is induced by the airfoil to accelerate and this reduces the local air pressure.

                        Kid: Why?

                        Me: I don't know kid... I think I hear your mother calling you.

                        So what would you tell a (relatively smart but pre-Gabriellian) five-year-old to answer that question?

                        Comment


                        • #42
                          Originally posted by Evan View Post
                          I guess I would say that known science (meaning scientifically "proven" fact) has withstood all reasonable scepticism. Is there room for doubt or scepticism in the prevailing explanation of airfoil-induced lift? If not, then I would consider it a known science. But I get the impression that there is room, and that the explanations for lift are very scientific postulations conceived to explain an observed phenomena—that they are the product of abductive reasoning—(that lift was discovered by physical experimentation long before the postulation was deduced (or induced?) to explain it).
                          Are you serious or you forgot the blue font? That's how Science works!!! Did Newton came up with the General Theory of Gravity before it Gravity was observed? No, Newton observed Gravity, modeled it, and that's the General Theory of Gravity (and, basically, all Newtonian Mechanics). Did Einstein come up with the Theory of Relativity and concluded that the speed of light was constant? No, he modeled it around the discovered fact that the speed of light is constant. Now, the good thing about Science is that the models and theories developed to explain nature often make predictions of things that had not been observed so far, and by testing them you can strengthen the theory or destroy it. To name only 2 examples, gravitational waves (Relativity) and winglets (Aerodynamics). Winglets were not observed in nature, they were reasoned out from the ramifications of the theory/model and THEN created, tested and found to work as predicted.

                          A Theory is NEVER "true". It is just a better (or worse, or useless) approximation to nature.
                          You can put the explanation of airfoil-induced lift right there with evolution, germ theory of disease, relativity, gravity, and quantum mechanics. None of them are perfect of the ultimate truth. But that is how much doubt or skepticism there is around it.

                          Now, in fact, in the very end, everything is particles Physics modeled under Quantum Mechanics and General Relativity (still lacking a unified theory). But I am not going to explain how lift works at that level because I don't know how, and nobody knows how. So we have macroscopic models that assume, for example, that the air is acontinuum instead of a bunch of sub-atomic particles and quantum fields. And because we do the same when we talk about biology, chemistry, car dynamics or whatever a little more complex that a few sub-atomic particles.

                          If that's not "proven enough science" for you, I can't help you.

                          But this is what I'm asking you, because I really don't know the answer.

                          I also really don't know that I could accurately explain how a wing creates lift to a five-year-old. I could say it's due to the plane of the wing deflecting the air downward and Sir Newton requiring an equal but opposite upward force. I could explain that the airfoil creates an area of lower pressure above the wing also resulting in an upward force.

                          But this is how a five-year-old (god bless them) would have me:

                          Me: The airfoil creates an area of reduced pressure above the wing, so the higher pressure below the wing pushes it upward (Bernoulli).

                          Kid: Why?

                          Me: Because the airstream above the wing is induced by the airfoil to accelerate and this reduces the local air pressure.

                          Kid: Why?

                          Me: I don't know kid... I think I hear your mother calling you.

                          So what would you tell a (relatively smart but pre-Gabriellian) five-year-old to answer that question?
                          I guess that if a kid asks you how clouds are formed you are going to start to explain how the air is a mixture of gases, gaseous water being one of them, and how the solubility of the water in air depends on the temperature so when the temperature goes down to a point called "dew point" it can't hold the water dissolved anymore and, since the temperature is less than that needed to keep the water gaseous by itself, it will form little droplets that is what we see as clouds. I, instead, will show him water vapor coming from bathtub filled with water and make a nice analogy with the sea and the clouds.

                          No, I would not go the way you did for lift. I would say:

                          Put your rollers on and I will put mine. Ok now push me hard. Hey, why did you move back? Push me hard but avoid moving back. No, grabbing the chair or using the brake is cheating. Come on, push me. Why why are you moving back again? You can't help it? That's fine. You'll see, you cannot push something without being pushed yourself in the opposite direction.
                          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. Now kid, get in the car.
                          Ok, we are doing 60 miles per hour in this solitary highway and we are in the 1st lane next to the shoulder so go ahead and stick your hand out of the window. Extend your hand and put it horizontal, like this. Now tilt it a little bit up, like this? Fell the force pushing your hand up? Want to guess what is happening? Correct! Wile we cannot see it, the air is being deviated, pushed down by your hand in that angle, same that happened with the water and the spoon. And since your hand is pushing the air down, the air is pushing your hand up, just like when we pushed each other with the rollers. And that is the same way how the wing pushed the air down, so the air pushes the wing up, and planes can fly.


                          The problem is that you want a 5-years-old-friendly explanation as to how lift is produced an the intimate level of the interaction of the the infinitesimal elemental volumes of air between themselves and with the airfoil. I don't know how to do that but that is MY fault, not that the theory is not there, is not fully understood, there are doubts or skepticism, ambiguity, lack of consensus among experts about it or whatever. The theory is and works perfectly fine, whether I can explain it to a 5-years-old kid or not.

                          --- 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


                          • #43
                            Originally posted by Gabriel
                            That's how Science works!!!
                            To varying degrees. I guess the issue will always be an epistomological one, but I'm not trying to go that far for the sake of argument here. You can ask me what causes a rainbow and I can give you the answer in one or two sentences using science that is very nearly beyond any scepticism. You can ask me what the nature of gravity is and I will need to give a more equivocal answer that still includes a significant degree of scepticism.

                            I'm under the (perhaps false) impression that 'air-turning' aspect of lift does not account for the total lift generated by the airfoil, and that the entire understanding of causal factors behind an airfoil creating lift is not as agreed upon and beyond scepticism as, for instance, the science of optical refraction. That is not to say that 'known science' demands absolute certainty (which may not be possible in anything), but to inquire as to whether the entire theory of lift is considered 'known science' on the level of things that are universally considered to be resolved as factual by the scientific community. Is the current prevailing explanation of the mechanics of lift at that level of factual resolution or do problems remain that leave it open to scepticism and thus alternate theories and relegate it to the theoretical realm rather than the factual one?

                            The theory is and works perfectly fine, whether I can explain it to a 5-years-old kid or not.
                            The fact that a simple enough explanation cannot be given for the non-obvious part of the equation (the part that doesn't involve sticking your hand out the car window), that even I can understand, causes me to become sceptical...

                            Comment


                            • #44
                              Originally posted by Evan View Post
                              To varying degrees. I guess the issue will always be an epistomological one, but I'm not trying to go that far for the sake of argument here. You can ask me what causes a rainbow and I can give you the answer in one or two sentences using science that is very nearly beyond any scepticism.
                              Are you sure of that? Do you want to see who many steps down the WHY ladder we can go before you face skepticism? Because sooner rather than later we are going to reach the point of "why does the light travel slower in water than in the air?" And good luck with that. Sooner or later, with anything, you are going to reach the point where you will be faced with 2 options: a) Because God did it this way and don't ask me why again, the Lord works in mysterious ways" or b) "There is no why, that is HOW it works, and there is no hidden will or intention behind it. Get over it".

                              Science explains HOW nature works not why.

                              I'm under the (perhaps false) impression that 'air-turning' aspect of lift does not account for the total lift generated by the airfoil,
                              Yes, that's a false impression. The shoving of the air down (if that's what you mean by the "air-turning" explains 100% of the lift, and it could not be in any other way unless there was something else beyond the air generating the lift, which there isn't. Any force that the air makes on the wing will be accompanied bu an equal and opposite force that the wing makes on the air. If the force on the wing is up, the force on the air is down. And because the air was happily at rest in equilibrium buoyancy in air, the sum of forces was already zero before the wing came by, so whatever force the wing makes on the air will cause an acceleration in the same direction.

                              and that the entire understanding of causal factors behind an airfoil creating lift is not as agreed upon and beyond scepticism as, for instance, the science of optical refraction.
                              Again, false.

                              That is not to say that 'known science' demands absolute certainty (which may not be possible in anything), but to inquire as to whether the entire theory of lift is considered 'known science' on the level of things that are universally considered to be resolved as factual by the scientific community.
                              Yes, it is resolved, except that we are waiting for the winner of the million dollars who discovers a closed solution for the Navier Stokes equation. But the concepts behind the most complete and universal Mechanics of Fluids theory is in fact quite straight forward. We do know all the forces that act on an infinitesimal volume of air. Pressure, fiction, inertial forces and external forces. We know how much is the mass of an infinitesimal volume of air (volume times density). We know how the density, volume and temperature interact (Pv=nRT, does it sound familiar?) That's it. End of the theory. Yes, we are assuming that the air is continuum and a perfect gas. These are approximations. Where these approximations break down, the theory breaks down. As does the refraction of photons on water if you shoot one photon on one molecule of water.

                              Is the current prevailing explanation of the mechanics of lift at that level of factual resolution or do problems remain that leave it open to scepticism and thus alternate theories and relegate it to the theoretical realm rather than the factual one?
                              It is as factual as any scientific theory. As factual as what causes a rainbow if you like.

                              The fact that a simple enough explanation cannot be given for the non-obvious part of the equation (the part that doesn't involve sticking your hand out the car window), that even I can understand, causes me to become sceptical...
                              There is no non-obvious part that is not at play when you stick your hand out of the car. 100% of the lift is wing shoves air down so air reacts pushing wing up. Get over it.

                              --- 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


                              • #45
                                F.A.O.: Gabriel

                                I know I enjoy the debate and learning and razzing and am sometimes "part of the problem".

                                BUT...

                                ...when you have significant training in aerodynamics, and you go to some effort to explain things, but someone argues incessantly...and I really mean incessantly

                                Do you feel the need to ask if they have any demonstrable training or experience or credentials in aerodynamics?, or even physics?...Not that you are "asserting" your qualifications, but maybe a "reminder" that you might have some valid insight that should be considered instead of incessantly dismissed...because of your qualifications?

                                (PS: I also enjoy ironing and seeing the foot on the other hand (as they say in Airplane!)).
                                Les règles de l'aviation de base découragent de longues périodes de dur tirer vers le haut.

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