21 ms·
The mysteries of aerodynamic lift
- thrustmaster 7y agoI thought it was a combination of newtons third law and Bernoulli's principle, the wings are hitting the air and the air exerts equal force in the opposite direction, Bernoulli's principle allows this equal opposite force to provide easier lift.
- zarmin 7y agoWright you are.
- thrustmaster 7y agoReally? I got a few down-votes... I also know the angle of attack of the wing is important, no angle of attack, no lift?
- redis_mlc 7y agoIn aviation, we consider deflection and Bernoulli's principle as both important. In physics, it's mostly about pressure differentials. When you try to get more specific than that in a forum comment, it means you probably don't really know what you're talking about.
- falcolas 7y agoSo, since the title is a bit baity: On a mathematical level we understand and have consensus; but the "dirtiness" of practical applications of mathematics makes it a bit more complicated to explain fully.
- loeg 7y agoIt's extremely baity.
- falcolas 7y agoI'm not sure if it's because they're trying to break it down for laymen, but there's a lot missing from these explanations and their supposed problems. There's no discussion of boundary layers, turbulent vs laminar flow, the effect of wing textures, nothing. There's also no discussion about what happens when you try and tilt a wing too far upwards - a stall - or why the simple buildup of ice on a wing can cause an otherwise fine wing to lose its ability to produce lift.
- pmoriarty 7y agoWell, the quibble here is whether having equations that are solvable and useful for making predictions is equivalent to having an understanding. If you answer "yes", then the problem with that view is most evident in physics where equations and successfully tested predictions result in counter-intuitive "quantum weirdness" which is hard to reconcile with claims of understanding. As Feynman was supposed to have said, "If you think you understand quantum physics, you don't." Another problem with such a view is it results in descriptions which sound absurd on their face, such as claims that when people look they see photons. But people look they see objects, fields of color, or have other experiences which are irreconcilable with the abstractions or equations created by physicists. This is related to what is known in analytic philosophy circles and cognitive science as "the hard problem of consciousness", which is how one reconciles "scientific" explanations of how the mind works with people's actual experiences.
- falcolas 7y agoIt can be explained, though. I took aerodynamics courses over a decade ago, and they had a decent explanation which covered all of the points brought up in the article, incorporating both Bernoulli's principle and Newton's third principle. The big challenge seems to be making it explainable to someone with no domain knowledge.
- deleted 7y ago[deleted]
- jermaustin1 7y agoI'm tired of this headline, its an oversimplification. We absolutely DO understand how and why they stay in the air, we just don't have the hard numbers behind it.
- FabHK 7y ago> We absolutely DO understand how and why they stay in the air, we just don't have the hard numbers behind it. The article claims the opposite: we do have the hard numbers behind it (we can predict how a wing behaves), but we don't have a good conceptual explanation for it at a layman's level (the how and why, if you so will).
- nimish 7y agoWe have a very good explanation for experts though. It turns out lift is really damn hard to explain since fluids are quite complicated. There's no reason to expect there's a layman's explanation at all, but you can make one from Newton's laws (Navier-Stokes -- conservation of momentum) and conservation of energy (Bernoulli) and conservation of mass (continuity equation) They are very complicated and the complexity is required to understand all the weird edge cases
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- NikolaeVarius 7y agoNeedlessly click-baity article title. TLDR: We don't have a full solution that models flight. We also don't have a full understanding of how bicycles work.
- FabHK 7y ago> TLDR: We don't have a full solution that models flight. We do, actually. It's just hard to explain.
- NikolaeVarius 7y agoThere is a Millennium Challenge problem to provide a solution to the Navier Stokes Equations which are a fundamental component of modeling flight. The entire article about how none of the current models fully explain how a plane stays in the air. So what is this full solution you are talking about because my Aero professors must have done a bad job teaching the topic to me
- FabHK 7y agoI'll let the article (which we are discussing here) speak for itself (my highlighting though): > accounts of lift exist on two separate levels of abstraction: the technical and the nontechnical. [... The former] exists as a strictly mathematical theory, a realm in which the analysis medium consists of equations, symbols, computer simulations and numbers. There is little, if any, serious disagreement as to what the appropriate equations or their solutions are.
- NikolaeVarius 7y agoYou are misunderstanding what a full solution means and what the article is saying. There are a systems of equations that allow us to model flight. But they are NOT a full model of flight characteristics, as a consequence of, like mentioned, lack of a full solution to the Navier Stokes equations > The solutions of those equations and the output of the CFD simulations yield pressure-distribution predictions, airflow patterns and quantitative results that are the basis for today’s highly advanced aircraft designs. Still, they do not by themselves give a physical, qualitative explanation of lift.
- ethn 7y agoDuring my plane flights I passed the time rediscovering the equations of lift. The physical intuition I’ve found, is for plane flight, the plane must move faster in the direction parallel to the ground than the time it takes for those air molecules under the plane to move away and deform around the wing at some average velocity. In this manner, the plane can push off those air molecules as they’re unable to move out of the way quick enough to escape the force. Similar behavior to skipping a stone on water. For lift, you apply torque on the wing by changing the angle of attack. This also leads to some interesting ideas on wind.
- deleted 7y ago[deleted]
- mech1234 7y agoI suspect if you made a wing out of a flat piece of material, tilted at the appropriate angle of attack, it would be sufficient to fly a plane. It just wouldn't be optimized at all. Really, you need full Navier-Stokes behavior to explain all the forces acting on the wing. Bernoulli doesn't generalize to a full vector field, it's a simplified version of Navier-Stokes. Calling in the big guns doesn't make for an easy discussion. (mechanical engineer, I figure I had like 1/3 of the fluids classes the real aerospace guys get).
- codeduck 7y agoFlat wings work perfectly fine, they just need a higher angle of attack to generate similar lift, and therefore have higher drag.
- exabrial 7y agoAnd have poor stall characteristics because they're more likely to introduce flow separations near the back of the wing.
- jayrot 7y agoWhen you were a kid, did you not ever put your hand out the window on the freeway? You can actually feel the pressure differential lifting your hand up once you get the right angle.
- baroomba 7y agoSame, intuitive way I think of it since learning the school and pop-culture explanations are basically wrong—and for reasons that are unclear to me, because why make up some unintuitive BS when the intuitive and obvious explanation is closer to correct. Stick hand out window, tilt hand, feel wind push hand up. Wind hits bottom of hand, pushes it up. That's the main thing, and everyone already gets that if they've ever, like, experienced wind. Play with it a little and you can feel your hand respond a bit differently based on the kind of "shadow" it's casting in the wind. That's the rest of it, more or less. There, airplanes explained, certainly way better and closer to correct than "well you see the top of the wing is longer than the bottom, so Bernoulli's principle is the reason airplanes can fly..."
- deleted 7y ago[deleted]
- kryogen1c 7y agothis article is so confused and unscientific i have a hard time forming a coherent response. > although bernoulli's theorem is largely correct ... the theorem alone does not explain why this is so or why the higher velocity atop the wing brings lower pressure along with it this blurb is accompanied by an upside down plane with the caption "doesnt explain why planes can fly inverted". this is a "tide goes in, tide goes out, cant explain that" statement [1]. im speechless. some planes can fly upside down, and some cant. its not a mystery we discover through trial and error - theyre designed that way by people who use bernoulli's equations, et al. equations are not explanations. calling a theorem partially correct because you dont know why it works is totally unrelated. either the theorem accurately represents and predicts reality, or it doesnt. no equation says why itself works, thats nonsense talk. [1] https://www.youtube.com/watch?v=_fSlJaZrUhs https://www.youtube.com/watch?v=_fSlJaZrUhs
- FabHK 7y agoI find the article perfectly reasonable. We can model flight quite well, and predict the behaviour of wings quite well, yet it is hard to give an accurate account of it at a layman's level. The article goes on to discuss two accounts that have been given historically, and outlines why they are insufficient. A plane flying upside down is a perfectly fine refutation to the naive Bernoulli "the wing is curved on the upside" explanation. Which parts do you have a problem with? > equations are not explanations. As the article makes painstakingly clear.
- pmoriarty 7y ago"We can model flight quite well, and predict the behaviour of wings quite well, yet it is hard to give an accurate account of it at a layman's level." The problem in that statement is an implied equivalence between having a good model and having a good understanding of the phenomena in question. It's not so much a layman's understanding that's at issue, but having what's often called an "intuitive understanding" that doesn't resort to the model. Sure, it's easy to plug in numbers in to a computerized model, and get answers back about the behavior, as from a black box, but it's quite a different thing to oneself have an intuitive understanding of what's going on. It's often useful to have visualizations of mathematical models and equations precisely because complex models and equations are so difficult to understand, and this difficulty in understanding them highlights that models and equations are not the understanding itself.
- Isamu 7y agoSo this is about intuitive explanations of flight. The complaint about using Newton's law is that it doesn't readily explain the low-pressure region above the wing. Let me give it a try. Intuitively, all the forces on the wing are manifest as air pressure measured the wing surface and expressed as a force normal to the surface at that point. There are no other forces from the air. You sum them over the wing and the net force upward is called lift, the net force backward is call drag. If there is net lift, that means the net normal forces summed over the wing are upward, implying that the pressure is low above the wing relative to below the wing. The Newtonian explanation is that a force must be exerted to change the direction of the air. The net force on the air is in the direction that the air turns, and the reaction force on the wing is in the opposite direction. On the underside of the wing the air is diverted downward and the reaction force on the wing is upward, and this is measured by the air pressure on underside of the wing. On the top of the wing the air is again diverted downward and the reaction force on the top of the wing is again upward, and this is measured by a lowered air pressure, giving a net upward force.
- munificent 7y agoThis is a somewhat confusingly written article about a famously confusing topic. It directly parallels arguments about how sailboats are able to sail. Sails are also airfoils so similar mechanics come into play. Interestingly, because a sail has effectively no thickness, both sides of the sail always have the same length, which immediately calls the Bernoulli argument into question. Sailboats are also interesting because they generate all their power from the wind and yet can also sail faster than the wind at times. As far as I understand it, the fundamental reason airfoils in boats and places work the way they do requires viscosity. Without that, the math falls apart and the ship doesn't move. It is not enough to treat air as a bunch of tiny billiard balls bouncing off the bottom of the wing (the Newton's third law argument). Likewise, you can't pretend the air above and below the wing are each confined to their own perfectly frictionless tubes with different velocities (the Bernoulli argument), since the air moving over the wing is part of a continuous whole extending out arbitrarily far. In order to explain how fabric-thin sails are able to generate lift, how planes with curved wings can fly upside down, and how the ground effect comes into play, you have to treat the surrounding fluid as a continuous medium with viscosity. That's how the math works. Unfortunately, we don't seem to have a good intuition for how that feels so it's hard to treat that as a satisfactory explanation.
- starpilot 7y agoWhat you're getting at is the Kutta condition: https://physics.stackexchange.com/questions/135707/what-is-a-physically-accurate-explanation-for-the-kutta-condition https://physics.stackexchange.com/questions/135707/what-is-a.... This only arises in viscous flow and ensures that the upper and lower flows leave the trailing edge smoothly. Without this, the flow would not be turned.
- simonebrunozzi 7y ago> can also sail faster than the wind at times. Really? Can you elaborate?
- trhway 7y agoyou can look at kiters and windsurfers - even on a mild wind they glide very fast - orthogonal to the wind you get constant ( i.e. practically independent of your speed) force driving you forward, and it accelerates you until it matches the force of the water and air resistance to your movement which grows with your speed. And of course here comes that: https://newatlas.com/wind-powered-car-world-record/11346/ https://newatlas.com/wind-powered-car-world-record/11346/ "March 29, 2009 With a wind speed of just 30mph (48kmh), British engineer Richard Jenkins has set a new land speed record for a wind-powered vehicle at blistering 126.1mph. "
- zkms 7y agoDoug McLean (Boeing Technical Fellow) has a quite decent talk about the question of intuitive explanations for aerodynamic lift: https://www.youtube.com/watch?v=QKCK4lJLQHU https://www.youtube.com/watch?v=QKCK4lJLQHU Also Philippe Spalart's quote is right on the money: "It's easy to explain how a rocket works, but explaining how a wing works takes a rocket scientist".
- starpilot 7y agoWe have trouble explaining it at a lay level, but we can solve the entire time-varying (for unsteady cases) 3d flow field around a wing to very high accuracy. Lift seems like it should be intuitive because we've experienced the force of wind and see birds flying, but therein lies the rub. Straightforward results arise from a series of complex, interacting phenomena. Another example might be explaining why sticky tape is sticky.
- H8crilA 7y agoI'm surprised people don't start with the basics on this confusing topic. The third law of Newton's mechanics tells us that for the plane to get an up force to counteract the gravity, the air must receive and equal amount of down force. Therefore what planes must be doing is deflect air masses down. A plane must be applying a downward force to air masses, with total force value of "mass * g", i.e. supply "mass * g * 1second" worth of downward momentum per second. As simple as that.
- jvanderbot 7y agoYes, and in rotating-wing configurations (e.g., helicopters), the lift is basically calculated using the momentum of the column of air being forced downward + the momentum of the chassis. By accelerating air downward in a column below the rotating wingspan, the column of air gains a net negative momentum (downward), necessitating a net positive (upward) momentum to the chassis to keep the system's momentum conserved. This principle seems to work just fine for me w.r.t. fixed wings.
- lutorm 7y agoSure, that's just momentum conservation. But how do you know how much downward momentum the column of air has?
- H8crilA 7y agoAirplane/helicopter mass * g * time Assuming the plane/helicopter didn't accelerate up or down and assuming there's no wind.
- lutorm 7y agoSure, that has to be true if the helicopter can hover. But how do you know that's possible? You can't postulate that something flies as part of an explanation why it can fly...
- 7y ago
- opwieurposiu 7y agoA wing is a device that pumps air downward, which in turn pushes the wing upward, by newton's third law. For a large plane, the wing will be pumping many tons of air per second. Start with a cube of still air, with zero mean velocity. Fly a plane through it, and that cube will have a mean downward velocity. http://www.aviation-history.com/theory/lift.htm http://www.aviation-history.com/theory/lift.htm
- eganist 7y agoWait a second. Are you saying if I have a cube suspended in space, and I put e.g. a drone inside it that just flies around in a circle inside the cube, the cube will start to move down? What then? Will the drone crash into the ceiling of the cube because it's independent from the cube itself? My brain disagrees with this, but I'm a hacker, not a physicist.
- _whiteCaps_ 7y agohttps://www.newscientist.com/article/dn26807-if-birds-in-a-truck-fly-does-the-truck-get-lighter/ https://www.newscientist.com/article/dn26807-if-birds-in-a-t...
- czinck 7y agoI think the parent poster means a "cube of air" as in a region of air, not something bounded on all 6 sides by glass walls. But to your question, if it was a glass cube, I'm pretty sure the drone would hover in the middle of the cube while gravity pulls it down exactly like if the drone was turned off, based on conservation of momentum. Sure the drone is pushing the air down, but then the air hits the bottom, bounces up to the top, and then gets pushed by the drone again. It's (very literally) a closed system, so nothing happening inside is really noticeable outside, and vice-versa (steady state, if you smack the box the drone will notice).
- leetcrew 7y agothe interior of the cube in your example is a closed system, so ultimately there is no net force in any direction. if the cube is large, the drone might create a slight pressure differential accelerating the cube downwards, but it would eventually be canceled out when the drone hits the top of the cube (I'm assuming zero g, so the drone immediately starts accelerating when it turns on its props). if the cube is sufficiently small, the drone might immediately create too much turbulence to generate sustained thrust in any particular direction.
- pdonis 7y agoI've found the discussion in the following article (which is a chapter in a much larger online treatment of all aspects of flying) to be quite clear and easy to follow: https://www.av8n.com/how/htm/airfoils.html https://www.av8n.com/how/htm/airfoils.html
- phendrenad2 7y agoStart by understanding why paper airplanes "glide", then you can introduce downward thrust from plane wings.
- kyuudou 7y agoSomething to consider: http://milesmathis.com/lift.pdf http://milesmathis.com/lift.pdf
- Geee 7y agoI think it's quite easy to understand how planes fly. I figured out this as a kid when I pushed my hand out of a car window and tilted it at different angles. This way you can feel the pressure differential and the how the air pushes the hand upwards or downwards.
- o_nate 7y agoA scientific explanation though would explain why those regions of high and low pressure get created.
- baq 7y agoDepends. Newton’s third law is scientific enough to explain what’s going on. Bernoulli and Navier-Stokes and all the hard equations are needed when you need to optimize the system or understand the micro scale, but they’ll simplify into conservation of energy or momentum in the macro limit.
- o_nate 7y agoNewton's law doesn't do a good job of explaining why airplane wings have the shape they do. Why not just use a flat wing at a 45 degree angle?
- baq 7y agoExactly what I had in mind when I said Navier-Stokes. It isn't the job of Newton's third law to explain that. It's job is to say that if you have 200 ton aircraft and want to keep it in the air, it has to push 200 tons of air down no matter if it does that with a carbon-fiber CFD-optimized wing or a barn door nailed to the airframe.
- copperx 7y agoSo, if a plane wing is like a tilted hand pushing air down, how come a plane can fly upside down with no change to its wings?
- SubuSS 7y agoProbably a very dumb attempt but Doesn't the leading edge being thick and rounded up top deflect away air from getting to the slant-plane right behind it creating a low pressure zone above the wing? Same will apply in flat-wing cases because angle of attack will cause same effect. What am I missing?
- lutorm 7y agoThe best intuitive discussion about lift that I've come across is John Denker's "See How It Flies": https://www.av8n.com/how/ https://www.av8n.com/how/ The key ingredients that I took away from the above are that circulation and the Kutta condition are fundamental to explaining lift. I think people's confusion with this situation is that there's no simple cause and effect. It's just that the fluid equations have a solution that has circulation and that gives lift, but you can't solve for it like you can with most mechanics problems, because you need a global solution that satisfies the fluid equations.
- lmilcin 7y agoI don't think there is anything mysterious about lift. We can model it very well, we have precise equations that predict the exact results (though we can't solve them) and we know where these equations come from. The fact that I do not understand the equations doesn't mean there is anything mysterious behind it. There might be some artistry with regards to actually designing the aerodynamic shapes. We have no way of finding the best possible shape yet, this is largely a process of trial and error (though nowadays it can be automated with simulation without actually having to go through building physical model).
- minblaster 7y agoWouldn’t you say something that has an equation that works but no theory of why is mysterious? Mysterious doesn’t mean magical, it just means there’s an unexplained gap in what we understand, which is the case.
- lmilcin 7y agoBut there is no unexplained gap. This might only be "mysterious" to somebody, but not in general. When you decide to title your article telling something is "mysterious" it suggests it is mysterious in general. Anything could be said to be mysterious to somebody, there will always be somebody that has no knowledge to somebody. This way you can title anything as "mysterious" but it is not very useful (unless you count to bait clicks).
- namirez 7y ago"We have no way of finding the best possible shape yet" In general, you're right but for certain class of problems we absolutely have solutions. Just look up inverse methods whereby the input is a pressure distribution and the output is a shape. This is used often for designing airfoils, ducts, and other simple geometries.
- mannykannot 7y ago"The third problem provides the most decisive argument against regarding Bernoulli’s theorem as a complete account of lift: An airplane with a curved upper surface is capable of flying inverted." Unfortunately, the author has fallen into the very trap that he is trying to explain. If you were to measure the velocity and pressure fields around the wing of an airplane flying inverted, you would find that they conform to Bernoulli (so long as the airplane is flying slowly enough that compressibility is not an issue, which is another source of complication.) What the author is doing here is to accept some bogus, hand-waving arguments for why the airflow velocity changes around the wing, such as the equal transit-time 'theory', which is, quite simply, false. To answer that question, you need the Navier-Stokes equations (which are the application of Newton's laws to a viscous fluid), or some realistic approximation. You may find this more informative: https://fermatslibrary.com/s/how-airplanes-fly-a-physical-description-of-lift https://fermatslibrary.com/s/how-airplanes-fly-a-physical-de...
- learn_more 7y agohttps://en.wikipedia.org/wiki/coanda_effect https://en.wikipedia.org/wiki/coanda_effect
- namirez 7y agoThis is a confusing take on lift. To explain lift intuitively we need two ingredients: the Laplace equation and the Kutta condition. Most people have an intuitive understanding of the Laplace equation. For example lightning usually hits the peak of mountains. The reason is that in solutions of Laplace equations, field gradient is proportional to curvature. In fluid dynamics, this field is called the stream function. The top of airfoil is more curved than the bottom so the stream function gradient is higher on top which results in higher wind speeds over airfoil. But the second ingredient is the Kutta condition which represents viscosity. If there were no viscosity, there would be no lift. The Kutta condition is applied to the tail (trailing edge) of airfoil. Without Kutta condition, the speed at the trailing edge would be infinity (because of Laplace equations. Speed around sharp corners is inevitably infinite). Viscosity prevents infinite velocities so we apply another condition at the trailing edge to make the air velocity smooth. It's kind of complicated and I agree that there is no simple explanation to lift, but if you think about it for a little while, it's not that hard to grasp.
- lutorm 7y agoA flat plate generates lift, though, so the curvature is incidental.
- namirez 7y agoThat's in interesting observation. Yes, the same thing happens at the leading edge of a flat plate due to curvature resulting in flow separation and a vortex bubble on the top surface. If the flow doesn't separate, the velocity at the front (leading) edge of the plate will be infinity. The result is a vortex bubble over the flat surface which effectively changes its geometry and aerodynamic behavior. See figure 2-12 in the following link: http://heli-air.net/2016/02/13/inclined-flat-plate/ http://heli-air.net/2016/02/13/inclined-flat-plate/
- jb775 7y agoRecently saw this crazy video of planes being lifted into the air during a microburst. At the time I wondered what caused the lift...food for thought for this discussion. https://www.youtube.com/watch?v=b_WmjWAGkLI https://www.youtube.com/watch?v=b_WmjWAGkLI A microburst is a rare weather event where a cloud basically shoots air downwards up to 100mph: https://www.weather.gov/bmx/outreach_microbursts https://www.weather.gov/bmx/outreach_microbursts
- knolan 7y agoI lecture fluid mechanics. There are actually two Bernoulli equations. Remember that Bernoulli’s work is derived for and is only valid along a streamline. A streamline is an imaginary curve that is tangent to the flow field. It’s not some invisible tube, it’s a mathematical representation of a vector field. The first one is the well known one mentioned in the article. It relates pressure and velocity tangent to a streamline. So if the velocity is somehow increased the pressure drops. The second equation deals with pressure changes due to curvature, i.e. force normal to a curving streamline. On an airfoil there is an effective reduction in the area through which the air passes between the surface of the airfoil and a far field streamline unaffected by the airfoil. This increases the velocity (via the continuity equation) which in turn reduces the pressure. The curvature of the airfoil also curves the streamline close to the surface resulting in an additional pressure reduction normal to the surface. You can imagine how this affects a highly cambered airfoil. If anyone is interested here are my lecture notes on the derivation. https://nbviewer.jupyter.org/github/nolankucd/MEEN20010/blob/master/3.2%20Derivation%20of%20Bernoulli%27s%20Equation.ipynb https://nbviewer.jupyter.org/github/nolankucd/MEEN20010/blob...
- mhh__ 7y agoIf you want to see something really mysterious yet mathematically modellable (ish) then look between your car and the road. Tyres are hard.
- averros 7y agoThe article is pretty much junk because it completely misses the fact that the very existence of aerodynamic lift relies on Coandă effect (i.e. airflow "sticking" to a smooth surface) which in turn is the consequence of viscosity (very close to surface air molecules aren't moving relative to the surface, and far they're moving fast, so viscosity creates a transition layer with different speeds, which creates the force pushing the molecules towards the surface, which results in vertical motion of air downwards, which creates the opposite force (i.e. the lift) on the surface by Newton's 3rd law). The very same effect can be seen as air being pulled down above the wing, resulting in smaller pressure which "sucks" the wing up. Oh, and because air molecules need to fill the space they need to accelerate horizontally - thus resulting in behavior seen as Bernoulli's law. The two basic explanations of lift are not alternatives; they're simply the different aspects of the same process. It's just that Bernoulli's law is not fundamental, it's a consequence of viscosity and Newton's laws of motion. A propos: there are fluids which have zero viscosity. Wings do not generate lift in them. See also: https://en.wikipedia.org/wiki/D%27Alembert%27s_paradox https://en.wikipedia.org/wiki/D%27Alembert%27s_paradox
- Dansvidania 7y agoI could not find sources quoted for the controversy and doubt regarding the physics behind lift in this article? As a sailor with an amateur-ish passion for physics, the dynamics of lift are clear to me for years (Dunning Kruger?) and I would love to read about where the doubts regarding each of the theories lie. The doubts reported in the info-graphics are really confusing, because both the increased speed and the low pressure area above the wing are easily explainable with vector arithmetic and fluid dynamic respectively. The statement that Bernoulli's principle does not explain planes flying upside down seems also very naive.
- savrajsingh 7y agoThe way I think about lift is that at a certain point, the air can’t get out of the way fast enough, so lift is created. If you’ve ever skydived, you know the air at high speeds feels thick —- slight deflections and imbalances produce drastic movements.
- mikorym 7y ago> There is little, if any, serious disagreement as to what the appropriate equations or their solutions are. The objective of technical mathematical theory is to make accurate predictions and to project results that are useful to aeronautical engineers engaged in the complex business of designing aircraft. > But by themselves, equations are not explanations, and neither are their solutions. There is a second, nontechnical level of analysis that is intended to provide us with a physical, commonsense explanation of lift. The objective of the nontechnical approach is to give us an intuitive understanding of the actual forces and factors that are at work in holding an airplane aloft. This approach exists not on the level of numbers and equations but rather on the level of concepts and principles that are familiar and intelligible to nonspecialists. It's funny to read this after many years of teaching myself to think "mathematically". The situation described above is in some ways the true mathematical ideal: to be able to describe our surroundings so precisely that intuition and perception blurs away, giving way instead to something stronger than what we can describe in human words. When you describe something to two different people, the objective is to adapt each explanation to their personal framework, much in the way an artist or musician would adapt to their audience. However, the objective of mathematics is to take away exactly that: the variability in perhaps equally valid social or human explanations. I do think that intuition and perception is a very important of mathematics, but I think it forms the first steps of the scientific method behind mathematics. Identify perceptions and intuitions and after that try to get to precision and rigour. Mathematics aims not to be intelligible, but it is in fact a fortunate state of affairs that mathematics is intelligible to humans at all! It reminds me of what Eugene Wigner wrote about mathematics, titled The Unreasonable Effectiveness of Mathematics in the Natural Sciences. [1] One thing that should be more clearly stated in the article is that it esentially claims that the mathematical descriptions themselves seem somewhat incomplete, the explanation of which I don't know, as the article tries to avoid mathematics in the first place. [1] http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html
- p_l 7y agoThe article is... bad. Very bad. Doubleplusungood bad, in fact. I recommend checking out https://www.grc.nasa.gov/www/k-12/airplane/lift1.html https://www.grc.nasa.gov/www/k-12/airplane/lift1.html which is much more complete explanation, and written for school age children - without the usual "lie to children" part that is common till you hit fluid dynamics at university level.
- james-imitative 7y agoAnyway, the point is that aeroplanes _do_ fly. I have been in an aeroplane that flew, and it flew using wings that had engines attached to them. I have also seen a variety of planes fly through the sky, and they have all had either engines or propellors propelling them. Wings alone are not enough. An aeroplane that only has wings does not have enough "thrust" to continue flying. It's as simple as that.