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#161
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Backwash Causes Lift?
The physicists I know worry about confirming their calculations by
observation. I don't know who MX is referring to. Pure math research doesn't need anything but internal consistancy, but every worthwhile scientist is verifying by measurement, and the measurements are becoming exquisitely accurate. I wish I could be as predictive in my field as those in the hard sciences are in theirs. |
#162
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Backwash Causes Lift?
On Oct 5, 6:32 pm, wrote:
It's familiar because there are many out there who don't understand or don't agree with the textbooks. Even among experts there's disagreement. Every so often one of them makes an issue of it. It's quite normal, especially if they don't use the Google Groups Search function first to see what the previous arguments have been on the subject on a particular newsgroup. I'd like to first note something since I am newly exposed to this field: In electrical engineering, we have our own set of fundamental principles. The "terminal" set of primitives governing electronics (electrostatics and electrodynamics) is Maxwells Equations http://en.wikipedia.org/wiki/Maxwell_equation. [Ironically, during his lifetime, Maxwell was also someone who was a leading expert on aerodynamics. The notions of gradients, the Laplacian, and scalar potentials have strong parallels in both fields.] In EE, we have out own myths, like power lines causing brain cancer, but when they arise, the experts work hard to show indisputable evidence, verifiable, rigorous evidence to the contrary, to nip the non-sense in the bud. We do still have areas of disputes, like what causes shot noise in circuits [http://en.wikipedia.org/wiki/Shot_noise], but on the bread- and-butter basics, you won't find a college-leve textbook speaking untruth. So naturally I am extremely surprised to see this happening in aerodynamics. You are, after all, the rocket scientists. It annoys some of us because the same arguments are put forth repeatedly and we can't figure out why some don't get it. But it's no different than my classroom, in which every new batch of students brings the same misunderstandings and doubts and arguments. We were young once, too, and didn't believe much of what our teachers were trying to tell us. Oh, I certainly don't believe what I wrote in the Jeppensen book. I don't believe what the 3 CFI's told me recently. I don't believe what my friends friend, the pilot, told me three years ago. And though I would be highly honored if I could meet him, I don't believe what Rod Machado, whom I think we would all agree is not exactly dumb nor a bad teacher, nor ignorant in the field, wrote. I don't believe it for two reasons: 1. It's obviously wrong if you read and interpret correctly what Bernoulli wrote. 2. NASA says it's wrong. From Jim Logajan: http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html Bernoulli said that moving air has a lower pressure than static air. The air over the top of the wing is moving considerably faster than that underneath, so it has lower pressure. People are going to yell and boo me for saying this, but after taking a nice long ride tonight on my motorcyle tonight, I thought the venturi/Bernoulli thing through, and I am 95% certain that that is not the reason the pressure is lower. In fact, I could probably provide an experiment showing you a situation where air is moving considerably faster on top than it is on the bottom, with much higher presure on the top. What is ironic is that Bernoulli would still be right, but the interpretation of Bernoulli would fall apart. It's not rarefaction; it's the increase in dynamic pressure (velocity) that subtracts from static pressure, the same phenomenon that makes a turbine engine work so well. Not to nit-pick, but dynamic pressure is p(t), where t is time, and velocity is d/dt R(t), where R is position vector, two totally different things. Newton said that for every action there's an equal and opposite reaction. If you look at the diagrams of airflow here,http://www.av8n.com/how/htm/airfoils.html scrolling down to Figure 3.2, you'll see that there's upwash ahead of the wing as well as downwash behind it. the upwash is generated by the approaching low pressure area above the wing. As the wing passes, the upwash is converted to downwash; if this isn't Newton at work, I don't know what is. Newton would be just another dead guy. Newton did say that. And I looked at that diagram very carefully. [Thanks for link] The upwash is not casued by an approaching low pressure. The upwash is caused by a gradient in pressure, going from high pressure at the leading ede, to low pressure, right above and slightly-back of the wing, due to rarefication of the wing in motion. The area above the rarefication is normal atmosphere that has a propensity to move toward the lower-pressure, rarefied air. The combination of that normal atmosphere air, combine with the high velocity of the molecules from the leading edge of the wing, results in the flow paths (streams) that you see. I haven't looked yet, but I imagine that there are aerodynamicists, all over the world, who, if not for appreciation of the hypothesis I am proposing here, have at least figured this out empircally, and are fretting day and night trying to find the optimal shape of the leading edge of the wing. They have two conflicting objectives: 1. Make the shape in such a way so as to minimize drag. 2. Make the shape in such a way so as to increase pressure to impart high velocity to air molecules moving up/backwards. I'll be the first to admit that i don't have the capacity to do so at this moment, but imagine that that one shape of the leading edge is not appropriate for all speeds of the aircraft. For a given set of context variables like density, temperature, pressure, angle-of- attack, airspeed, what-the-plane-was-doing-20-milliseconds-ago, turbulences...wind, etc...there is an optimal shape for that leading edge, depending on what you are trying to do. It would be quite wild if someone were to design a wing that could morph, dynamically by control of a computer, into an instaneously-optimal shape. For the average PPL or CPL this should be sufficient. It's true enough, even if it doesn't give the detail that the physicist would like. As I said, most pilots have other careers and interests and they find that Newton and Bernoulli jibe with what they experience in the air, so they're satisfied. Making textbooks thicker or filling them with competing theories does nothing but confuse these people. I believe it should be possible to explain a venturi tube, Bernoulli's principle, and a decent part of why a wing has lift, in about 2-3 pages of written text, with pictures, using no formulas, not even grade-school mathematics. If a student wants to argue that the physics as presented are all wrong he should do extensive research and publish a book on the subject, not argue with pilots who have been trusting their soft pink bodies to Bernoulli and Newton for decades. I definitely agree a paper should be written, and there should be an element of rigor, obviously lacking in my posts. However, I honestly think pilot's have been trusting neither Bernoulli nor Newton. They are dead. But they each left a legacy, which, according to the NASA links, have been misinterpreted and abused by countless theoritsts and educators in this field. So one could say that the pilots have been trusting these theorists and educators, but perhaps not even that is the case. I think what Ron hinted at is most- likely the case, that there is a phenomenon that would allow even a Neanderthal to achieve technical advancement: The Neanderthal starts with a contraption that works, and through much trial-and-error, finds better and better rendentions of that same contraption. Eventually, he will have something that works so well, that the question of "Why" would hardly need be asked. Naturally, theorists will tag along and try to explain with rigorous scientific principles what he has accomplished with only raw will of spirit, but the theory does not necessarily have to be right or complete get the thing in the air. Of course, the Wright Brothers were high-minded individuals, but I think you get the point. One might ask, "Well if that is the case, then what is the point of nit-picking with theory?" It is because a theory that correctly explains observed phenomenon generally opens up an entirely new world of order and efficiency. -Le Chaud Lapin- |
#163
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Backwash Causes Lift?
Mxsmanic wrote in
: Dudley Henriques writes: AOA actually can be defined relative to any given reference datum, but normally it's considered in the industry as being the angle formed between the chord line of the wing and the relative wind as you have correctly stated. The angle of attack is the angle between the forward stagnation point and the trailing stagnation point. The points of intersection of the chord line with the airfoil surface are static, but the stagnation points can change, altering the angle of attack. If the angle of attack is not positive, there is no lift. You cannot have lift at negative angles of attack because that is not symmetric. If a negative angle of attack can produce positive lift, what happens when you turn the airfoil upside down? Logically that would mean that even a positive angle of attack would force the wing down, which makes no sense. Nope Bertie |
#164
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Backwash Causes Lift?
Mxsmanic wrote in
: Bertie the Bunyip writes: Really_ i´ve nly seen you trying to explain it for a few months now. Many books explain it incorrectly. So do you dip****. Bertie |
#165
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Backwash Causes Lift?
Mxsmanic wrote in
: Crash Lander writes: And we all know math has absolutely nothing to do with physical reality eh? Modern physicists tend to understand math but not physics. They develop their theories in mathematical terms, and explain them in mathematical terms, but when asked to explain them in physical terms are unable to do so. This makes them different from their more illustrious predecessors. For these modern physicists, math has replaced reality, because they don't really understand reality. They believe that if the math works, that's reality. Unfortunately, there are infinitely many mathematical models that will work, but they don't necessarily have anything to do with reality. You won't be able to find anyone who can explain string theory without using math. But Einstein could explain physics without math. Wrong again. First thing he would have said after talking to you is "You are one dumb mother****er" That's math. Bertie |
#166
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Backwash Causes Lift?
Mxsmanic wrote in
: Jim Logajan writes: Then you should have no problem naming a few who exhibit this problem. The ones who have the problem are unimportant, as they don't really understand physics, anyway. I do and you do not. Waht's more, I can make fizziks dance at m fingertiips. We al know waht dances at the end of your fingertips. Bertie |
#167
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Backwash Causes Lift?
Tina wrote in news:1191642553.306168.208000@
22g2000hsm.googlegroups.com: The physicists I know worry about confirming their calculations by observation. I don't know who MX is referring to. The little "Famous physicists " pics he had on his jammies. Pure math research doesn't need anything but internal consistancy, but every worthwhile scientist is verifying by measurement, and the measurements are becoming exquisitely accurate. I wish I could be as predictive in my field as those in the hard sciences are in theirs. What's the deal with infinitely dividing the time it takes for a quarter to hit the floor anyway? Actually, I might have more insight into that than most in that lab we like to cal "the last sector" Bertie |
#168
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Backwash Causes Lift?
Mxsmanic wrote in
: Gatt writes: I SWEAR to you guys, somebody sounding conspicuously like him was out here within the last couple of months refuting Bournoulli and referring to pressure under the wing, making plywood fly, etc. Sounds awful familiar. It's entirely possible for an opinion to be shared by several people, even if that opinion is not shared by the president of the treehouse club. If there was any doubt before... Bertie |
#169
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Backwash Causes Lift?
Le Chaud Lapin wrote in
ps.com: On Oct 5, 6:32 pm, wrote: It's familiar because there are many out there who don't understand or don't agree with the textbooks. Even among experts there's disagreement. Every so often one of them makes an issue of it. It's quite normal, especially if they don't use the Google Groups Search function first to see what the previous arguments have been on the subject on a particular newsgroup. I'd like to first note something since I am newly exposed to this field: In electrical engineering, we have our own set of fundamental principles. The "terminal" set of primitives governing electronics (electrostatics and electrodynamics) is Maxwells Equations http://en.wikipedia.org/wiki/Maxwell_equation. [Ironically, during his lifetime, Maxwell was also someone who was a leading expert on aerodynamics. The notions of gradients, the Laplacian, and scalar potentials have strong parallels in both fields.] In EE, we have out own myths, like power lines causing brain cancer, but when they arise, the experts work hard to show indisputable evidence, verifiable, rigorous evidence to the contrary, to nip the non-sense in the bud. We do still have areas of disputes, like what causes shot noise in circuits [http://en.wikipedia.org/wiki/Shot_noise], but on the bread- and-butter basics, you won't find a college-leve textbook speaking untruth. So naturally I am extremely surprised to see this happening in aerodynamics. You are, after all, the rocket scientists. It annoys some of us because the same arguments are put forth repeatedly and we can't figure out why some don't get it. But it's no different than my classroom, in which every new batch of students brings the same misunderstandings and doubts and arguments. We were young once, too, and didn't believe much of what our teachers were trying to tell us. Oh, I certainly don't believe what I wrote in the Jeppensen book. I don't believe what the 3 CFI's told me recently. I don't believe what my friends friend, the pilot, told me three years ago. And though I would be highly honored if I could meet him, I don't believe what Rod Machado, whom I think we would all agree is not exactly dumb nor a bad teacher, nor ignorant in the field, wrote. I don't believe it for two reasons: 1. It's obviously wrong if you read and interpret correctly what Bernoulli wrote. 2. NASA says it's wrong. From Jim Logajan: http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html Bernoulli said that moving air has a lower pressure than static air. The air over the top of the wing is moving considerably faster than that underneath, so it has lower pressure. People are going to yell and boo me for saying this, but after taking a nice long ride tonight on my motorcyle tonight, I thought the venturi/Bernoulli thing through, and I am 95% certain that that is not the reason the pressure is lower. In fact, I could probably provide an experiment showing you a situation where air is moving considerably faster on top than it is on the bottom, with much higher presure on the top. What is ironic is that Bernoulli would still be right, but the interpretation of Bernoulli would fall apart. It's not rarefaction; it's the increase in dynamic pressure (velocity) that subtracts from static pressure, the same phenomenon that makes a turbine engine work so well. Not to nit-pick, but dynamic pressure is p(t), where t is time, and velocity is d/dt R(t), where R is position vector, two totally different things. Newton said that for every action there's an equal and opposite reaction. If you look at the diagrams of airflow here,http://www.av8n.com/how/htm/airfoils.html scrolling down to Figure 3.2, you'll see that there's upwash ahead of the wing as well as downwash behind it. the upwash is generated by the approaching low pressure area above the wing. As the wing passes, the upwash is converted to downwash; if this isn't Newton at work, I don't know what is. Newton would be just another dead guy. Newton did say that. And I looked at that diagram very carefully. [Thanks for link] The upwash is not casued by an approaching low pressure. The upwash is caused by a gradient in pressure, going from high pressure at the leading ede, to low pressure, right above and slightly-back of the wing, due to rarefication of the wing in motion. The area above the rarefication is normal atmosphere that has a propensity to move toward the lower-pressure, rarefied air. The combination of that normal atmosphere air, combine with the high velocity of the molecules from the leading edge of the wing, results in the flow paths (streams) that you see. I haven't looked yet, but I imagine that there are aerodynamicists, all over the world, who, if not for appreciation of the hypothesis I am proposing here, have at least figured this out empircally, and are fretting day and night trying to find the optimal shape of the leading edge of the wing. They have two conflicting objectives: 1. Make the shape in such a way so as to minimize drag. 2. Make the shape in such a way so as to increase pressure to impart high velocity to air molecules moving up/backwards. I'll be the first to admit that i don't have the capacity to do so at this moment, but imagine that that one shape of the leading edge is not appropriate for all speeds of the aircraft. For a given set of context variables like density, temperature, pressure, angle-of- attack, airspeed, what-the-plane-was-doing-20-milliseconds-ago, turbulences...wind, etc...there is an optimal shape for that leading edge, depending on what you are trying to do. It would be quite wild if someone were to design a wing that could morph, dynamically by control of a computer, into an instaneously-optimal shape. For the average PPL or CPL this should be sufficient. It's true enough, even if it doesn't give the detail that the physicist would like. As I said, most pilots have other careers and interests and they find that Newton and Bernoulli jibe with what they experience in the air, so they're satisfied. Making textbooks thicker or filling them with competing theories does nothing but confuse these people. I believe it should be possible to explain a venturi tube, Bernoulli's principle, and a decent part of why a wing has lift, in about 2-3 pages of written text, with pictures, using no formulas, not even grade-school mathematics. If a student wants to argue that the physics as presented are all wrong he should do extensive research and publish a book on the subject, not argue with pilots who have been trusting their soft pink bodies to Bernoulli and Newton for decades. I definitely agree a paper should be written, and there should be an element of rigor, obviously lacking in my posts. However, I honestly think pilot's have been trusting neither Bernoulli nor Newton. They are dead. But they each left a legacy, which, according to the NASA links, have been misinterpreted and abused by countless theoritsts and educators in this field. So one could say that the pilots have been trusting these theorists and educators, but perhaps not even that is the case. I think what Ron hinted at is most- likely the case, that there is a phenomenon that would allow even a Neanderthal to achieve technical advancement: The Neanderthal starts with a contraption that works, and through much trial-and-error, finds better and better rendentions of that same contraption. Eventually, he will have something that works so well, that the question of "Why" would hardly need be asked. Naturally, theorists will tag along and try to explain with rigorous scientific principles what he has accomplished with only raw will of spirit, but the theory does not necessarily have to be right or complete get the thing in the air. Of course, the Wright Brothers were high-minded individuals, but I think you get the point. One might ask, "Well if that is the case, then what is the point of nit-picking with theory?" It is because a theory that correctly explains observed phenomenon generally opens up an entirely new world of order and efficiency. -Le Chaud Lapin- Wanna make a bet about how long it takes you to get your licence? Let's have a pool! I got never! Bertie |
#170
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Backwash Causes Lift?
"Bertie the Bunyip" wrote: The physicists I know worry about confirming their calculations by observation. I don't know who MX is referring to. The little "Famous physicists " pics he had on his jammies. Haw! You're on a hot streak, Bertie. -- Dan T-182T at BFM |
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