@@gaberatata7156 Yes, the Coanda effect describes how a JET of fluid "attaches" to a nearby surface through entrainment. There's no such jet when a wing moves through still air (or vice versa). This is also contradicted by saying the Bernoulli principle applies, which only applies within a flow field. A jet would not be the same flow field.
I am an Aviation Professor. You have summarized about 2 weeks of my classes in 2.50. Well done. Both are "correct," but not the common "mythconception" of Bernoulli's Principle that does not include the deflection of air downwards. The laws of Physics are not in conflict, and if they appear to be, it is because we misconceive them.
Observ45er I agree with the statement "Each explanation, done correctly, completely accounts for the lift generated by a wing." However, the "done correctly" part is extremely complex. The simple conceptual version of Newton's third law is much closer to correct than the simple conceptual Bernoulli version that shows up in so many "explanations." (NASA calls it the "longer path" theory - see www.grc.nasa.gov/www/k-12/airplane/wrong1.html)
Observ45er - You are correct. Many different explanations are proposed for both systems. The common version of "Bernoulli" that is not correct is the version where an aircraft can fly without creating a downdraft.
Observ45er I must agree that Bernulli principle convinient but confusing idea. People mean 2d law of Newton for fluids or energy conservation principle. But for engineers, educators it is very attractive... I have original book written by Bernulli "Hydrodynamica". Will check...
1donagin Third law can not be used without 2d law in application to fluids flows. Lift is result of fluid flow. When speed is zero no lift is generated. To be honest 2d law gives us the tool to describe 3d and 1st laws as well. To describe lift we need to know 2d law but not enough . We need to look into microworld of fluid atoms to describe friction/diffusion ( i.e. kinetic theory ).
1) Place hand outside the window of a moving car with the thumb facing in the direction of movement. 2) Rotate hand to change its angle of attack. 3) Figure out what angle causes your hand and arm to lift. 4) Find out that your hand has been ripped off by a mailbox. 5) Weep the loss of your dominant hand. 6) Learn to function in daily tasks with your other hand. 7) Forget how lift works. 8) Place hand outside the window of a moving car with the thumb facing in the direction of movement. 9) Rotate hand to change its angle of attack. 10) Find out that your only hand has been ripped off by a passing dump truck. 11) Forget how lift works. 12) Lean out the window of a moving car. 13) Rotate torso to change its angle of attack. 14) Figure out what angle causes your torso to lift. 16) Here lies a dreamer who loved to fly.
FlightChops, Bernoulli's principle isn't wrong, the equal time argument for is wrong, but Bernoulli's principle is the primary component and Newton's component is secondary component, Bernoulli's produces most of the lift, but the Newton component helps the aircraft fly, saying the molecules meet up at the trailing edge though is wrong, the air on the top get to the trailing edge first. But because the top airstream gets their first it creates a low and high pressure, lift.
I ve tried to make some planes fly when i was like 7 so whe i heard that at university I was tottatly not convinced by it so i began searching and found the magnus effect. I believe 90% of current science is right so keep eyes open. There is also some issues with magnetic fields and some other stuff like relativity ( believe on it but it has many stuff not so well explained. Much hard to prove
air changes quite dramatically at high speeds. At low speed, it can be treated as fairly incompressible but if you go past the speed of sound you have to deal with shockwaves - boundaries across which the pressure changes dramatically. I can't speak to the exact wingshapes but that's why one design doesn't work for all regimes.
If you sum the pressures over the top and bottom of the wing, you will get the net force on the wing (which is equal and opposite to the net force on the air). So the point is that a pressure different explanation is also a net force explanation. If a wing didn't deflect the air their would be no pressure difference, and if there were no pressure difference, the air wouldn't deflect.
@@leif1075 apparently because the air above the wing travels a greater distance in less time, to meet the air coming from below on the same side. but I don't get why it should be fast I mean there's this sort of a constriction and shouldn't it slow down the air?
@@kriti522 There's two ways to look at this: you mentioned constriction. The speedup happens due to conservation of energy. Also see Bernoulli's principle. Think about it this way: if you have a pipe with high diameter that connects to a pipe with small diameter, then pushing air down the thick pipe will result in high potential energy (including static pressure) but low kinetic energy (dynamic pressure). As the pipe constricts, potential energy is converted into kinetic energy. Air speeds up. Which also means static pressure drops. The second way to look at it is that curving streamlines always have lower pressure (therefore higher speed) on the inside and higher pressure on the outside of the curve. You could think of it as the difference in pressure pushing the flow around the curve.
+sly1024 well pressure comes from the random motion of particles bouncing off eachother, so I would think if the particles are mostly going the same direction there would be less pressure because there is less random motion
+Nabre Labre That makes sense, thanks. This always puzzled me though: according to relativity it shouldn't matter if you move relative to something or that something moves relative to you. So a moving block of air has higher speed if you look at it from another (non-moving) block of air, but if you sit in the first moving block, then the second has higher speed. I can understand that because speed is relative, but which one has higher pressure then? Is that also relative? Like when you open the window in a moving car. The air inside moves relative to the air outside, but if you look at it from inside then the outside air is moving.
As an aerospace undergrad years back, this is what I took the pains to explain to my mates and each time I was shushed for saying the text books are wrong (or slightly incorrect)! Thanks sir! You are a smart fella. Thank God I'm not alone!
There is a fundamental issue with this explanation and that is the assumption that the Bernoulli theorem (and it is simply a mathematical construct that describes a physical phenomenon) "causes" the lift. No, it does not cause the lift. In a dynamically closed system, a fluid moving into a region of lower pressure must accelerate because it is moving down a pressure gradient. Thus, each fluid parcel is experiencing an unbalanced force, but its resistance to that acceleration "pushes back" at the higher pressure, maintaining that pressure gradient. Now, when the air passes under the wing, the streamlines of fluid parcels are deflected downwards. This is because the underside of the wing directly deflects the adjacent fluid parcels downward. These exert a pressure on incoming parcels that causes them to slow down (accelerate in a forward direction, or against the direction of flow). Their resistance to this acceleration generates the pressure gradient under the wing and the pressure gradient generates the acceleration. Reciprocal cause and effect. Most people can intuitively understand why the air passing under the wing must be deflected downwards and why it must slow down. However, the "cloud" of increased pressure under the wing also extends slightly forward of the wing, as well. Fluid parcels approaching the leading edge that are destined to pass over the wing are initially deflected upwards by that "cloud" of increased pressure extending below and in front of the wing. As they pass over the leading edge and top side of the wing, the individual air molecules would continue in a straight line up and back, but air is a fluid and collisions between air molecules are common. Thus, the air that has been deflected upwards is now being forced by the air above it to accelerate back downwards to follow the contour of the upper surface of the wing. That air's inertial resistance to that downward acceleration causes it to form a "bubble" of low pressure above the wing and that same "bubble" of low pressure causes the acceleration that the air's inertia resists. Again, reciprocal cause-and-effect. The Bernoulli theorem is a mathematical construct that describes the way that fluid parcels must accelerate as they move from high to low pressure (and vice-versa), but it does not, in and of itself, explain *why*
Exactly, after watching this video my thoughts were... So the air does not meet up at the trailing edge of the wing. But WHY does the air over the wing flows faster, so we can apply Bernoulli's Principle to say that it generates a low pressure?
I am starting to wonder if including the Bernoulli component really adds anything to a student's (undergraduate's) learning experience when it comes to explaining how airfoils work.
In a lecture to aerospace engineers, a retired rocket scientist (Doug McLean) handles some common misconceptions about lift and shows how to explain it properly (from about 14:20 to 28:20): ruclips.net/video/QKCK4lJLQHU/видео.html
This is actually an incomplete explanation. The greater velocity along the top, in short, is created by vorticity around the airfoil. The trailing edge of the wing creates a vortex and conservation of amgular momentum dictates that another vortex must be created in the opposite spin. This vortex around the airfoil causes air to move faster along the top. The math is pretty complicated, but there are good walkthroughs online.
There are other ways to include several intuitive concepts that are not incorrect yet do not require advanced math or understanding ... and this one certainly hits the high point(s).
acomputer121 Yes, this one did and I was not disputing that, but supporting it. I was trying to say that the old Bernoulli and equal transit explanation still all over the place is not only incorrect and inadequate, but that a more correct explanatin does not have to include advanced math (or as stated in a recent post the transient portion of lift using Kutta) . There are 3 or 4 easily explained effects that contribute to the downward acceleration of air that produces lift -- and they are each simple and intuitive.... As described in this video.
DaylightDigital I didn't say self evident, just that causes for the turning, or downward acceleration of air can be explained with simple concepts as the video here does without advanced math, circulation concepts or adding Kutta. This takes me too far back and into the area that excites the AEs. The intent is to show on a relatively intuitive level (or at least a level that uses conditions around the airfoil consistent with more common physics) , that first, the old Bernoulli-equal-transit explanation is misleaning since it incorrectly applies Bernoulli and ignores the obvious downwash. Second that the concepts as used in the video are applicable and don't require the AE degree to understand as being significant. In other words, the intent is not to provide a complete, in-depth and advanced study of lift, but using what is relatively common physics, show that downward acceleration of a mass of air provides the F in the F=MA realm. This, of course, assumes that the listener is equipped with at least a reasonable understanding of physics. If not, then tell them Bernoulli and let them go about their ordinary lives not actually needing to have a true understandunbg of lift, nor an advanced degree in aerodynamics...(;-) ... I'm uncertain of your intent. Are you saying that the video is flattly wrong? ... I should go back and view the video to see which effects he used, but I maintain that: the lower surface downward acceleration of air; the upper surface Coanda acceleration (or perhaps better to call it boundary layer attachment); the Bernoulli effect and what I call the "other half venturi concept" (Anderson & Eberhardt call it the virtual scoop, which I like better) can all be understood as contributing to the total downward acceleration of a mass of air producing steady state lift... ... Unfortunately, that page won't display correctly and there appears to be missing content and some is oblitterated by figures. I see where it says:"The condition of finite velocity at the trailing edge is known as the Kutta condition." However it shows me no mention if the infinite velocity concept, nor of the violation of Kutta. I see only the stall videos further down ... Can you summarize the low Re violation? This has all been a long time ago for me. I don't really need to go over this, but a little curiosity is there....so far (;-) btw: this was not my focus, so I don't claim to be an advanced expert, just able to use the easily understood concepts to better the Bernoulli-equal myth. The AE part was interesting, but I focused on electronics.
This videos handles the equal transition theory wonderfully. It really is easy to get down a rabbit hole of misconceptions with lift and this video helps address one of the biggest ones.
You know that was my video right? By in space, I just meant in zero gravity, eg. inside a space ship far away from any masses (but still with air in it).
Very well done video, it was short, concise and to the point. I appreciate how you pointed out the common misconceptions relating to the Equal Time Transit Fallacy and the idea that the top surface has to be longer than the bottom surface immediately and got them out of the way. While I understand this video was made with the purpose of being short and to the point, I would have appreciated if you made it slightly longer in order to explain some of the concepts in more detail. I would have liked it if you went into more detail on the Coanda Effect instead of just briefly mentioning how it's related to the downwards deflection of airflow. Overall great video though.
I agree Nick. This video perfectly summarized the many main contributions of lift as well as the many misconceptions that come with it. I personally believed in the fallacy that the flow on the top of the airfoil must meet with the flow on the bottom of the airfoil at the trailing edge. After learning more about this topic and the physics behind it, it makes sense on why many people fall for that mistake. With the Coanda effect, which is another misconception, only pertains to when the flow is coming from a jet passing over a stationary object. In the case of flight, the wing of the aircraft is passing through the ambient surroundings rather than the flow passing over a stationary object if I'm not mistaken. I hope this helps.
two explanations for one lift force. If you integrate the pressure over the whole surface of the wing, you get the force on the wing, and there is an equal and opposite force on the air.
I remember having a Chem teacher in High school tell me the same thing. I never thought about it much, but after your post, I decided to look it up a bit more. Thanks :3
Funny, I'm studying for my instructor certificate and I was trying to think of what the physical justification was for assuming that two volumes of air separating at the leading edge necessarily join at the trailing edge. I couldn't think of one. Appears that there was a reason for that. Thank you!
YES. They are optimized for flying right side up! The shape is all about reducing drag, the optimum shape will vary depending on the intended use, since the design AOA and speed range will vary for different aircraft.
This is a better explanation that I was taught at school. However low pressure is created over a curved surface and it also partially contributes to lifts. See video - "How do Wings work - common misconception on lift." This is one of the best explanations on lift I came across. Still thuumbs of to this video for presenting a difficult concept in a way that everybody can understand.
at the very end, there's a graphic that hints at it - the wings need to be angled so they have an appropriate angle of attack such that they deflect air down.
Aaaaah. This is such a releaf. After so much videos on youtube going wirh supercomplicated, but wrong explanations, someone finally got it right. So good feeling, thank you
Veritasium: We will answer the question in this video: "How does a wing actually work?" *Veritasium 2 minutes later* Veritasium: We did not actually answer how wings work.
This is a great, concise video that refutes what is likely the biggest misconception about lift force on airfoils. I also appreciated that you looked at the theory of lift from multiple perspectives (both Newton’s Laws and the Bernoulli equation), and would have loved for you to take it even farther than that. There are a lot of things that go into lift forces, and many many theories surrounding these things. Thank you for correcting some of the misconceptions so well!
I read a really long and detailed explanation of how airplanes fly once. There are several things going on with the wing which create lift and contributed to flight being possible. Some of them seem to be quite minor effects, but apparently its difficult to account for where 100% of the lift comes from.
It is due to the Coanda effect, which is caused by entrainment. Essentially, a streamline passing over the top of the wing entrans air creating a region of low pressure directly above the wing. This creates a pressure gradient over the wing that pushes the streamline down and causes it to follow the curvature of the wing (this is the Coanda effect). The force from the pressure gradient not only changes the direction of the streamline but it also increases the speed of the streamline.
the truth is that as air passes over the wing it strips electrons off the molecules, creating a wing that has a positive charge. As the earth is also positively charged it repels the wing away from it!! Problem solved. That's why Dennis Lillee would rub the ball on his pants before bowling and thereby give the ball more lift. Genius! That is also why all you people that produce negative comments on YT will never go places....
Unfortunately not- as you'd have to be shuffling along at approx 50km/hr... not humanely possible. Although I did see someone take off momentarily when after shuffling they got a nasty static shock in the butt.
I would tell you what is the reality Listen carefully.... actually according to bernoulli's principle law the airfoil does not create lift but it helps the airfoil or other shape (it does not matter that have leading and trailing edge) to fly in straight direction because of beneath and up pressure passing through the wing, so the bernoulli's explanation about generating lift and low pressure over the wing is completely wrong and useless and according to the Newton law the deflection of the downward air generates lift and push the wing up, and fast pressure moving through the beneath and up side of the wing keep the plan stable in straight direction.... thanks hope you enjoyed and no need to know more
I think the misconception is that air flow needs to be horizontal to create lift. The amount of lift created is partly due the AoA (Angle between relative airflow and the chord line of the wing). this relative airflow can be completely vertical e.g. when the aircraft is climbing straight up as you said, but it is still creating lift. But you are correct in saying that the limitation now is the engine as the only component that will keep it going up when vertical is thrust
+Mike Cammiso Why-oh-why do so many feel compelled to go to so much trouble to spread so many longstanding misconceptions....? Prandtl and Bernoulli have spun their way through the globe many times...(;-)...I'd appreciate a *brief* summary of the major points you follow.
+Mike Cammiso If the textbooks are wrong, people tend to make wrong conclusions. I have a question to you that I hope you will answer. I'm reading the book "Fundamentals of Aerodynamics" by John D. Anderson, Jr. (as a hobby, not for professional use - I'm a glider pilot just student wanting to know more about aerodynamics). I suppose you as a professor know this book. On page 74 he has a figure (1.53) showing the velocity profiles in the laminar and turbulent boundary layers, This fígure indicates that the laminar velocity profile is mostly linear and the turbulent velocity profile is strongly unlinear, having a much higher shear stress on the surface. I feel confortable that this is right because it explains to me that the viscosity in the laminar flow is uniform, yielding a uniform flow speed (hence laminar). But searching the internet, I haven't found another figure showing the same. Confused? I am! Is Mr. Anderson wrong? If you answer my question, and I would ask another professor in aerodynamics the same question, then would I get the same answer from both of you? If no, why shouldn't I be confused?
The air streams (above and below the wing) do not need to meet up simultaneously at the trailing edge. The air above the wing reaches the trailing edge first than the air below. I think the correct explanation is the air stream above the wing near the front edge is squeezed more than the below stream. Using conservation of mass, the speed of the upper stream is higher due to the small cross-sectional area
Pressure is just force over a surface area. you can describe lift as a result of force pushing up, or pressure "pushing up". ps: pushing up is in quotation because it not the best terminology when we talk about pressure. think of it more as a combination of push from below and suction from above. atmospheric pressure is constant it pushes everything in all direction. so in order to move something in one direction you have to speed up air on that side which reduce pressure (or creates suction)
***** RE: "less time for the air particles to impact the upper surface due to speed past the steel plate." "due to speed" is not correct. ... Though your written explanation attempts to be saying much the same as the video and what is actually happening, that part is incorrect. Speed does not cause lower pressure. It is the other way around. A lower pressure in one region is the cause of air accelerating toward that region. The upper, convex curve creates a lower pressure in a way your words are trying to explain, for sure. To use words more like you are using: The upper surface curve's change in direction away from the airflow's original direction creates a lower pressure region along the surface that causes the air to follow the curve This is what Derek in the video calls Coanda, but is not what Coanda is considered to be. Coanda has a very specific description requiring a *forced* stream of air. ... Many also fail to consider that the lower pressure along the upper airfoil surface has an effect on a considerable amount air further above the wing that is also part of the air that is accelerated downward behind the wing. Cheers
I have tried fling even in F16 jets and i can say the video missing a lot,the wing will generate the lift due to its shape first which delays the separation point and reduced form drag which is generated from the shapes. the principle of lift generation is proved and we did many experiments using different shapes from ball to awkward shapes in a wind tunnel. I will answer his question about flying with flat wings, do you know that this wing can fly ? yes it can if you increase AOA but how efficient ? it is low and need long runs to take off, look at missiles what wing shape they have? it is an awkward triangular shape, how can that fly then? and about the flying upside down dude you cant fly A320 upside down or you die the jets can fly like that because the thickness to chord ratio is so small and the wing chambers has slight difference which allow the jet to reach mach speed and fly inversely. but have you ever tried inverse flying ? if you fly F16 and inverse fly it you will notice that altitude will start to decrease why? because the wing is cambered more in the upper side. the force he talked about is the force produced from the downwash which generates SOME lift and another type of drag but flying straight and level has nothing to do with downwash. Aerodynamics is a very complex subject and defeating its principles needs more that a short video.
Trust me your video is missing a lot, The wind tunnel equipped with accurate static and dynamic pressure sensors which shows you graphs of every single point in the cambered wing with zero AOA and we tried to defeat Bernoulli's principal like you but the experiments proved it, it proves that in a single inch of a wing you can get a lot of lift and by calculations of C 17 wing you can get a massive amount of force capable of carrying tons. All aircraft you see now calculated using 1/2 (density)(velocity square)(coefficient of lift)(wing area)
I think that answer is a bit general... In particular: The answer is CENTRIFUGAL FORCE, because airflow at the top of the wing has to turn rapidly when it reaches max camber, and the force required to make that change in direction is a centripetal force actuated in the mass of air. Because of Newton's 3rd law (one force actuates in conjunction with another one, with same direction and intensity, however different way) there is another, centrifugal force, that actuates on the wing. This force is, in most part, the source for lift. This theory explains the fact why airplanes DO fly inverted, as long as they fly with a positive angle of attack in relation to the ground... There is a number of ways to increase lift (in many cases, the lift coefficient L=0.5*rho*V^2*A*C_L): -Increase speed, because the centripetal force and centrifugal force will be greater; -Increase the density of the mass of air (basically, fly lower and in colder temperatures); -use high-lift devices such as flaps and slats, which increase the curvature of the wing, although creating more drag; -increase the curvature of the wing profile itself; -etc
This was a great video, I liked how you pointed out the common misconceptions of lift and explained why they are incorrect. Using flat wings and airplanes flying upside down was a great response to the equal transit time fallacy and the video you showed proving that certain the top and bottom airflows do not reach the trailing edge at the same time was very helpful to those who might be caught up on this notion. I also liked how you mentioned how there are multiple explanations of lift that when used together can better explain lift. It is very important to acknowledge that both Newton's theory and Bernoulli's theory are necessary to explain what causes lift and that neither theory can stand by themselves.
pressure at the top of the wing is generally lower, so air is accelerated when moving towards it pressure at the bottom of the wing is generally greater, so air is decelerated when moving towards it the part I don't understand is if air pressure caused the speed difference, then there is no way that the speed difference is the cause of air pressure, and the misconception is completely wrong. But what caused the difference in air pressure then?
It's relative to the shape, the particles try to remain in the same place because of inertia, and both sides of the wing move at the same speed, the difference is that the upper side is a larger way to go.
+Hector Palacios The part about inertia is part of the true science. However, it is a very common misconception that "the upper side is a larger way to go" . A sail or a flat wing has the same distance on both surfaces; an inverted wing has the greater distance below; and they all generates lift, so this shows that this is false science. ... The important thing is the path that the air is forced to take by the wing. .... The pressure above a wing is lower because the air and wing are, in essence, moving away from each other and the air's inertia then is responsible for lowering the pressure. ... By observing a real wing, we find that as wing goes past the still air, it is the air under the wing that is moved along at the highst speed. THe air above the wing is hardly moved along at ll and is only accelerated downward. ... It is not clear what you intend with this "...both sides of the wing move at the same speed,..." --- Regards, ScienceAdvisorSteve
Observ45er Thanks. I tried to specify that the upper and lower side are part of the same structure and move at the same speed. If the upper part is a longer trajectory, the particle moves relatively faster above than below because it is forced by geometry and inertia, although it is not the whole reason of flying as you say. As shown in the video, geometry also slows down the wind below and makes it go down, and that creates an opposite force. A question, the air also speed up in the upper side of other wings, or just the aire below is slowed down?
Nope. It's actually referred to as the equal transit fallacy in most aerodynamic text books. If you want to spend about 4 hours on wiki, check out the airfoil page and go to the various linked pages. The math gets pretty intense fast, but if you like vector calculus you'll be ok.
A normal wing section will also fly upside down...badly... and in a wind tunnel with puffs of oil smoke injected so you can track air speed, you will find that the air going over the upper part of the wing (The flat bit) will be much faster than the air under the wing (The curved bit)..
lift has two reasons : 1- Bernoulli pressure difference due to shape (the small partial lift part No1 ). 2- wind inclination to lift airfoils two components ( impacting drag ,and impacting lift perpendicular to it ) Part No 2
wooten cleng Best and most honest comment! Do not worry you are in good company. Simplest analogy can be pendulum,. kinetic energy goes up, potential goes down and vice versa. Same here - speed up , pressure down. this pressure difference works against gravity... :-)
+LS DO - It is very easy. A wing works the same way as a ceiling fan, a kite, or a paper plane. If you have ever stuck your hand out of a car window while moving and inclined it to the airflow you have made lift. Lift is a simple Newtonian reaction force. You bend the air downwards and the wing goes up. Thinking of is like you hand, the palm of you hand is facing the oncoming air. You will bend the air through an angle that is equal to the angle of your hand to the oncoming air. The force on your palm is part on of lift. Part two is the air bending around the back of your hand. Since there are no vaccums in normal space, the air has to follow the angle of the back of your hand as well. Both surfaces of your hand bend the air downwards and the equal and opposite force is that your hand goes up. It's is pretty much that simple. Sit under a ceiling fan and that you feel is the result of lift production. If you could measure the force on the as shaft that attaches it to the ceiling you would measure the lift it is creating.
+Complete Aerogeek Despite of my deep respect to your comments I cannot agree with this description. Even if the 3d Law is applicable here , which is not fully justified, your explanation replaced cause with effect. Downstream as result of redirection of flow plays minimal if any role in lift explanation. - looks like polished but still incorrect Newton explanation. Main contributor to downstream flow is pressure difference.
+auletes Bernoulli's principle... the air above the wing isn't as dense as the air below and air molecules, which means the air molecules above move quicker.
+Gavanization Not necessarily. Air molecules don't care about meeting at the trailing edge so surface are above and below don't really play too big of a key role in the bigger picture.
When air molecules separate at the leading edge, the air over the top of the wing is compressed. Google stream tubes around an airfoil and you will understand. Now let's take the continuity equation (google) and disregard the density (because it will be equal throughout the airflow), you will notice that if there is a drop in area, it will result in a rise in velocity. Due to the compressed stream tubes above the airfoil, area within the tubes are decreased, thus velocity of the air molecules increase.
+Googelplus Sucksys Density and Pressure are completely different. In the case of lift production, atmospheric density remains the same through the airflow above and below the wing.
Great work starting with the commonly perpetuated myth and following it up with a debunk and more complete explanation. Very quick and concise collection of counterexamples that help people ask questions about what they've heard before. The deflection of air/momentum concept is an important contributor, so it's good that it was mentioned. However, the Coanda Effect applies to jet flows, which is not applicable in regular flow over an airfoil. A good explanation given such a short time frame. Other important contributors to lift like circulation could have been described, but the information presented was mostly correct and serves as a good basis to start from in a little over 2 minutes. The part at the end talking about how these differing theories can coexist and explain the same phenomenon was also great for sparking more curiosity.
I agree, Matt. The Coanda effect is only applicable to a jet flow. As a result, the external flow over an airfoil would not be a proper place to apply that concept. I think a better way to describe the flow over the upper surface would be that the deflection of the streamlines is caused by the change in geometry the flow sees (i.e. the airfoil) or the pressure field. This would generally cause the deflection over BOTH the upper AND lower surface to be downward. This is a great video by the way, Veritasium!
If I say 'centrifugal force' everyone will get very upset because the acutal force is not centrifugal, the force is centripetal, the reaction is centrifugal. However, if I say 'lift force' nobody has a problem... except I do, you should too! Lift is a reaction, an equibrant of the force that an aerofoil imparts onto the air. To be even more precise, lift is a vector component of the total reaction of an aerofoil interacting with the air. The aerofoil has kinetic energy, it imparts that energy onto the air; the force is generated by the aerofoil interacting with the air as it moves through it. This video describes the air having kinetic energy and acting on the aerofoil, which is incorrect unless you are in a wind tunnel. The force is produced by the aerofoil moving through the air and it has an equal and opposite reaction, the total reaction, the 'vertical' vector component of the total reaction we call lift (although, lift may not always act vertically - another simplification, I'm not going there today). This is never described very well in any text book, it is always "simplified" to the point that it doesn't describe reality and causes unnecessary confusion.
Malevolent Prophecies Oh, and because I just now actually read the latter half of what you were saying, lol, no, because you're privileging a reference frame.
Malevolent Prophecies My points were exceptionally clear. Kindly respond to them, be silent, or find a way to take your head out of your ass so you can proceed with screwing yourself.
Newton's 3rd law of motion informally states: Every action has an equal and opposite reaction. So if the wings push the air molecules down and left, the air molecules must push the wings (and the plane) up and right, which is lift and air-resistance respectively. That's one of the 2 explanations offered in this video to explain flight. I'm not entirely sure if I understand the other one though.
To expand on that, textbooks generally quote around 0.3Ma, above which compressibility effects begin to become noticeable, with indeed a sharp change at Mach 1. The actual craft need only fly close to the speed of sound like 0.9 (transonic), where local flows across the tops of wings exceed Mach 1.
I just realized I wrote an entire research paper on this (Newton vs Bernoulli) back in my sophomore year of high school... and my thesis was apparently correct. God things have changed in the past 2 years.
+Ghassen Mez when inverted, the air over the wing is made to follow a convex curve ( by the increased angle of attack). When upright, the upper camber shape does this also, just at a lower angle of attack. It's the same when upright. One explanation (when done correctly) works for BOTH!
that was explained so well even i understood that and im not very smart at all.you always make things easy to understand and that's why im a subscriber.no need to make things so complicated like some youtubers do.nice work bro
According to the comments, noone really understood this video nor knows how "it really works". still it has only 221 thumbs down? I like veritasium, but this video is just terrible.
It does. That's what causes wake turbulence behind an aircraft. It has to move an equivalent mass of air downwards to counteract the lift coefficient. What's often neglected about the discussion is AoA (Angle of Attack) -- the airplane is in a slightly nose-high orientation during cruise in an optimum equilibrium of not being so high to increase drag under the wing too much to deflect downwards vs the beneficial lift from the overwing low-pressure. It's a combination of forces, not just one.
the faster velocity air on top of the wing, does lower the pressure.... it has NO bearing on the air traveling under the wing. in fact, if you blow over a balloon, the balloon will rise... proof of Bernoulli's principles.. if you defect air by pointing air underneath a wing, it will lift too... both Newtonian and Bernoulli's principles are correct and work in concert with each other. the air doesn't have to meet.. that's why there is wing tip vortexs and drag flow curls at the trailing edges of wings. air moves to differential pressure and that's what happens as a wing passes through the air.... this video is silly as it talks about flat wings.... flat wings make no lift(non air foils) but, when you tilt the surface, it becomes a surface with lift and drag coefficients. Most importantly, why does an airplane have the ability to fly upside down??? simple.... it is the angle of attack of the wing that determines its lift/drag characteristics, and in what direction that force is generated. NOT the shape.
After the HP and TQ video, I clicked your google account to see what your other interests are. Man! I'm kind of excited to see someone else who gets it! I've argued this with my teachers, and others for years. Awesome to see someone else who actually understands physics.
zanick2 You've got the right idea, but a few misconceptions. ... 1) RE: "Faster velocity" The lower pressure bove the wing is what accelerates the mass of air (Newton#1) to a higher tangential speed and radially around the curve. ... 2) RE: "no bearing" Correct. I think you mean that the upper air and lower air cannot be compared with Bernoulli's Equation, no? I've seen that done ! And in a prep school course video on TeacherTube. 3) The rising balloon is due to (summarizing) the ...a) air being accelerated *Newton #1) around the curve by a lowered pressure @ the surface (Bernoulli), then ...b) the resulting reactive force on the balloon lifting it...> Air down > balloon up (Newton #3)... ... Flat wings do the same thing. ... Simply saying that AOA creates lift completely ignores the physics going on around the wing to create that lift. AOA controls the amount of lift created by the phenomena around the wing.-- .... thought I already commeted on this.
No they aren't. They are both used improperly. The simple fact is that the wing must push air around to move through it. This alone creates the pressure changes around it. These pressure changes then cause all the air accelerations we see around the wing. THAT is why it is Newton, not the way most people explain it as a "reaction' to the downwash. Angle of attack is the factor that a wing-like shape needs to create these pressure differences around the wing.
+I No, the video is not 'fine'.. Derek states one of the most common misconceptions, that fast air over the wing *_creates_* a lowered pressure - false science. Fast air having a lower pressure than nearby still air is well known to be false and it is not just another fundamental law of physics to be memorized, Like Newton's Laws. The most common demonstrations "proving it" ignore the fact that there is a curved flow causing the pressure change. Prevent the curved flow and the demo falls apart. I've done it just to prove out a demo I developed myself. ... He also does not specify just what the "correct" version of Bernoulli is. It appears to involve only the upper surface. Is it the use of Bernoulli's Equation equating the upper velocity to the lower velocity (which is flat bad science and math)? He then, does not explain just what the correct explanation of the "Newton" version is. That appears to involve only the lower surface. This is the "hail of bullets concepr actually posed BY Newton and is also incorrect. ... He is much too vague about what the two things are that are two ways to look at the same thing. He did himself a great disservice with this video. ... Once you have the pressures, you can show how they produce all the air movements around the wing: below, above, off the ends, behind and ahead of the wing. This means that the down wash is just another necessary part (due to Newton #3) of the WHOLE story, not ANOTHER "parallel" explanation. ... Calculating the pressures on the wing gives the lift force. Calculating the momentum transfer of the downwash also gives the lift force. These are indeed two ways to *_CALCULATE_* lift because of Newton #3. However, they BOTH are part of the whole explanation of lift. People confuse describing the phenomenon with calculating the force. -- Cheers
Bernoulli explanation is not bad in understanding the flow over an aerofoil and giving an introductory over view of the flow but for detailed flow, we need to use a state space representation of the Navier Stokes equations using the solutions from the Laplace.
Yep, they fly at an increased angle of attack in inverted flight to compensate for the inefficiencies, although if you think about it it is really everything else that is at the wrong angle, since as you say angle of attack is relative to the air, but they have a built in angle of attack which is relative to the tailplane and fuselage and optimized for normal flight.
Dilip Tien Thank you for bothering in commenting my comment, It reflects my opinion only, which I believe this space is meant for. Your assertion about my confusion (sorry) is quite hollow. I perfectly understand the forces involved in the process of lifting an airplane, thought I expected a little more from this channel in clarifying the misconception surrounding this subject, and not this taste of “both are correct, both are wrong”. The major reason that lead me to subscribe this channel is that the author (which deserves big credits for his work) separates facts from fiction in a very entertaining way, to a very comprehensive audience while being very “Veritas” (Latin for truth) , which sometimes, I believe must be very hard to maintain (the balance between entertainment and factuality). My expectations with this video were that it could come to a final conclusion for the wing phenomena. I’m pretty sure it’s heavily Newton’s third law, while Bernoulli’s theory participation is quite humble. It is not accurate to say that both are right, and both are wrong... we are not talking quantum mechanics here…so remember the principium tertii exclusi ou tertium non datur.
Antonio Lucena when did I ever say that you couldn't put your opinions anywhere? Whether you expected something different or not is irrelevant. He is still correct. And it definitely wasn't confusing. Nothing he said was hard to understand. You're "pretty sure", whereas Derek is sure. If you have nothing to show that he's wrong, then don't try and say that he's wrong.
Dilip Tien well... You didn't get it, did you? Read it again :) PS I love this channel and have lots of respect for the author's work. Please don't bother in guessing my intentions. Best regards
Nicely done and a neat separation of the micro and macro (or local and global) views of the generation of lift. As noted, Bernoulli is correct - but I don't believe Bernoulli ever anticipated that someone would invent a wing and then argue that the upper and lower flows reached the trailing edge at the same time. My quals for saying this: aeronautical engineer for the last 30 years, glider pilot for longer and just plain interested in understanding stuff.
A wing works by "twisting" the airflow around it. This causes the air over the wing to flow faster and air below to flow slower. The rest you should know
Brendan Raymond Guess I made the classic mistake of commenting before watching the whole video lol. Although he was still wrong. Yes there is pressure difference happening on a wing, but not because of Bernoullis principle. It only works on a single streamline, not on a two separate flows.
I enjoyed this video and like how you mentioned the misconception of equal time transit fallacy. I think how you mentioned how Bernoulli and Newton's third law apply to lift was well done. However it is a misconception that Bernoulli and Newton's third law are two different explanations of lift, when in reality they are both equally important and should be used at the same time when explaining lift as they influence each other. Also as mentioned in another comment, the Coanda effect is only applicable for jet flow and not normal flow an airfoil will usually see. Hope this information helps!
One of the reasons (as far as we know, there are 4 reasons, all helping to create Lift upwards, but the exact % of each of these reasons in the creation of Lift is today unknown) that the Airfoil creates Lift is the pressure difference between the top and bottom of the airfoil and this pressure difference is created when the air above the airfoil must speed up due to the Ventouri effect. It does NOT speed up in order to reach the end of the airfoil at the same time as the air flowing beneath. The air that goes above the airfoil reaches the end of the airfoil faster than the air that travels below it. Look up the Ventouri effect and Bernoullis theorem for a better understanding of this.
Thank you for this explanation. I never really understood why the air should "reconnect" at the end of the wing. There just doesn't seem to be any good reason for that. This makes a lot more sense.
Oh this is great!!! For years I was confused as to why helicopters would stir up dust with the old simple explanation of a wing this makes perfect sense now!!!
what about that: i was told, that the difference in speed comes from conservation of angular momentum. the upper stream of air must travel further than the stream of air underneath, so when both meet, they swirl at the end of the wing (delay). that causes an a. m. (ccw if the wing flyes left). because of the law of c. o. a. m., another a. m. occurs that spins in the opposite direction and around the whole wing, which causes the upper stream to get faster than the one underneath. then bernoulli.
Watching this video after 9 years in 2021. And, surprise to know Veritasium, Smarter everyday, minute physics, How ridiculous, all these were internet friends 😍😍 You salute u all to give us inspiration to be great RUclipsr
...{continue} Now if you want to mantain level flight, Lift must equal Weight. Lift is 1/2ρ*v^2*A*Cl. So if weight increases we must either increase density ρ, speed V or Cl (assuming we cannot increase wing area). If we dont change altitude/temperature (ρ) if we dont change V, CL must increase (and CL is based on the AOA). And there is a point where, by increasing the AOA to increase CL, we reach the critical AOA and the wing stalls. {continue}...
If you are having confusion, just remember that the first theory is correct in that there is less pressure over the top due to a faster speed of air, pushing it upward, and the second theory is correct in that the deflection of air due to the angle causes the air below the wing to move slower, increasing the pressure and generating lift. In conclusion, what this video is trying to say is that both the ANGLE and the SHAPE of the wing matters in the lift.
If you wanted to go into even more detail, you could describe the necessity of circulation for lift. If anyone want's a mathematical perspective, you could look into the principle of potential flows and super position. What Veritasium posted in the video was correct, but there are certainly more ways to look at it. -An Aerospace Engineering Student
To anyone who doesn’t understand this, I was in the exact same scenario just a week ago so listen up. So air moves over and around the plane as it flies. (You already understand this, when you put your hand out of the window of a moving car, it’s the same thing.) As that air moves along the back-end of the wing, (the air is sticking to the wing, and moving along with the shape of the wing.) The air is then pushed downward because of the shape of the wing. (The back-end of the wing is pointed downward.) All of that downward air then thrusts the plane upward, “lifting” the plane, which is why this is called “lift.” I really hope I didn’t over complicate that more than I had to, but if it helps at least one fella out there then it was worth it.
thank you for putting this information out there, i mean REALLY THANK YOU!!!!! I'm a baby boomer and when i was in school they taught us great deal of things that agreed with science at the time and that turned out to be incorrect. they taught us that light can only travel in a straight line, for example. little inaccuracies that added up to handicapping many. if you see some of this bad information please, please, please put out the word! like this thing that they taught us where electrons circle a nucleus in rings and now-a-days we find out that it's a cloud. i'd love to discuss if light is a particle or an electromagnet field etc...
i think gunny just wanted to add that this whole "angle of attack" thing only works to a certain limit. if the angle get's to big the flow of air will disconnect from the wing and you will end up with turbolant flow on the wings top side. those turbolent flows are slower so that the pressure gets higher again.
my take on this matter is, that in a commercial airplane, you want the most lift you can get out of a wing, and the maximum speed isn't too important, so you have maximum lift, but also quite a lot of drag. In a supersonic airplane, lift isn't too important anymore, because at the speed there is a lot more air travelling by, creating lift. Drag is also increased. But here you want minimal drag, and just enough lift to keep it airborne. The different shapes are a compromise between drag and lift.
to explain how planes fly upside down: Planes that fly upside down have laminar flow aerofoils. Meaning they are less cambered. flipping the plane over wont affect the lift too much as long as the angle of attack it adjusted accordingly (pushing forward on the stick which moves the nose up). This creates lift as he says in the video. Besides that, planes that do aerobatics generally have enough power to do alot more and other factors should be considered.
Wake turbulence is caused by the air from beneath the wing wanting to travel too the low pressure area on top of the wing via the wingtips. And so creating vortices which travel downwards and causing induced drag. the downward deflected air along the wing is called downwash. As of your explanation about the optimum AoA during cruise. The optimum AoA is that which gives the best Lift/Drag ratio. But alot more forces come to mind such as velocity, wingsurface, wing design, air density, etc.
I'm not an aerospace engineer, but I did take physics in college. The concept isn't complicated. Note, the Wright brothers did not use a tear shaped wing cross section. They simply bent the wings of their experimental fabric bi-plane to generate the lift. The point is that it's not Bernoulli's principle (which is of course a real thing, don't get me wrong) that generates most of the lift. It's simply the angle of attack forcing the air down. Upside down, you just gotta keep your nose up.
Yes thats right. The wing on F1 cars are set with a very specific negative angle of attack or negative incidence relative to the centerline of the car. Cessna horizontal stabilizers work the same way by being set to a negative angle of incidence
I've wondered this for a long time and never really found a proper answer, but this explains it perfectly. Also, as it turns out, my assumption to how it works was correct!
If you put an airfoil and move it you will see it has lift and drag. Water cannot be compressed to any degree with the motions of your hand and an airfoil, the water will just displace and gain volume. Therefore pressure differences have very little to do with it, it's merely the leading surface is contacting more matter, creating an opposite and equal reaction dependent on the orientation of the wing and the direction of the flow.
Fantastic video. Equal transit time explained away quickly and simply.
Hi Destin, how are you?
👍
Hellllloooo destin
Isn't the Coanda effect explanation wrong?
@@gaberatata7156 Yes, the Coanda effect describes how a JET of fluid "attaches" to a nearby surface through entrainment.
There's no such jet when a wing moves through still air (or vice versa).
This is also contradicted by saying the Bernoulli principle applies, which only applies within a flow field. A jet would not be the same flow field.
I am an Aviation Professor. You have summarized about 2 weeks of my classes in 2.50. Well done. Both are "correct," but not the common "mythconception" of Bernoulli's Principle that does not include the deflection of air downwards. The laws of Physics are not in conflict, and if they appear to be, it is because we misconceive them.
Bernulli principle can not explain lift. It is just energy conservation law.
Observ45er I agree with the statement "Each explanation, done correctly, completely accounts for the lift generated by a wing." However, the "done correctly" part is extremely complex. The simple conceptual version of Newton's third law is much closer to correct than the simple conceptual Bernoulli version that shows up in so many "explanations." (NASA calls it the "longer path" theory - see www.grc.nasa.gov/www/k-12/airplane/wrong1.html)
Observ45er - You are correct. Many different explanations are proposed for both systems. The common version of "Bernoulli" that is not correct is the version where an aircraft can fly without creating a downdraft.
Observ45er I must agree that Bernulli principle convinient but confusing idea. People mean 2d law of Newton for fluids or energy conservation principle. But for engineers, educators it is very attractive... I have original book written by Bernulli "Hydrodynamica". Will check...
1donagin Third law can not be used without 2d law in application to fluids flows. Lift is result of fluid flow. When speed is zero no lift is generated. To be honest 2d law gives us the tool to describe 3d and 1st laws as well. To describe lift we need to know 2d law but not enough . We need to look into microworld of fluid atoms to describe friction/diffusion ( i.e. kinetic theory ).
1) Place hand outside the window of a moving car with the thumb facing in the direction of movement.
2) Rotate hand to change its angle of attack.
3) Figure out what angle causes your hand and arm to lift.
4) Find out that your hand has been ripped off by a mailbox.
5) Weep the loss of your dominant hand.
6) Learn to function in daily tasks with your other hand.
7) Forget how lift works.
8) Place hand outside the window of a moving car with the thumb facing in the direction of movement.
9) Rotate hand to change its angle of attack.
10) Find out that your only hand has been ripped off by a passing dump truck.
11) Forget how lift works.
12) Lean out the window of a moving car.
13) Rotate torso to change its angle of attack.
14) Figure out what angle causes your torso to lift.
16) Here lies a dreamer who loved to fly.
Bold of you to assume I live in a country with roads on the right and my dominant hand is right
What's 15 though?
SW "Had us in the first half, not gonna lie."
@@KougaJ7 Number 15 has been censored due to graphic material.
dark
My grade 7 self who did his science fair experiment on Bernoulli's Principle just had his mind blown :)
looooool
Nice to see you here Flightchops :) I'm a subscriber of both this and your channel. Nice to know you watch Veritasium too.
FlightChops, Bernoulli's principle isn't wrong, the equal time argument for is wrong, but Bernoulli's principle is the primary component and Newton's component is secondary component, Bernoulli's produces most of the lift, but the Newton component helps the aircraft fly, saying the molecules meet up at the trailing edge though is wrong, the air on the top get to the trailing edge first. But because the top airstream gets their first it creates a low and high pressure, lift.
I ve tried to make some planes fly when i was like 7 so whe i heard that at university I was tottatly not convinced by it so i began searching and found the magnus effect. I believe 90% of current science is right so keep eyes open. There is also some issues with magnetic fields and some other stuff like relativity ( believe on it but it has many stuff not so well explained. Much hard to prove
i am in grade 7 and my mind is blown
air changes quite dramatically at high speeds. At low speed, it can be treated as fairly incompressible but if you go past the speed of sound you have to deal with shockwaves - boundaries across which the pressure changes dramatically. I can't speak to the exact wingshapes but that's why one design doesn't work for all regimes.
"Wings move air downward, and react by being pushed upward. That's what makes lift. All the rest is just interesting details." - Roger Long
Great vid Veritasium/MinutePhysics! Can't wait to do a vid with you guys!
How Ridiculous
If you sum the pressures over the top and bottom of the wing, you will get the net force on the wing (which is equal and opposite to the net force on the air). So the point is that a pressure different explanation is also a net force explanation. If a wing didn't deflect the air their would be no pressure difference, and if there were no pressure difference, the air wouldn't deflect.
So you're saying it's either, or, or neither? :D
BTW, there*
confusion is good - it's the start of learning!
Why donyoubassume air travels faster over top of wing? Why not the same ifn the same shape?
@@leif1075 apparently because the air above the wing travels a greater distance in less time, to meet the air coming from below on the same side. but I don't get why it should be fast I mean there's this sort of a constriction and shouldn't it slow down the air?
@@kriti522 yea so you see my point..
Your Coanda effect explanation is indeed doo doo sir
@@kriti522 There's two ways to look at this: you mentioned constriction. The speedup happens due to conservation of energy. Also see Bernoulli's principle.
Think about it this way: if you have a pipe with high diameter that connects to a pipe with small diameter, then pushing air down the thick pipe will result in high potential energy (including static pressure) but low kinetic energy (dynamic pressure).
As the pipe constricts, potential energy is converted into kinetic energy. Air speeds up. Which also means static pressure drops.
The second way to look at it is that curving streamlines always have lower pressure (therefore higher speed) on the inside and higher pressure on the outside of the curve. You could think of it as the difference in pressure pushing the flow around the curve.
I always hated the explanation that the air meets back up at the back of the wing. It's seems to imply magic, or that the air is alive
Why is there less pressure on the top??
+ByteMe the air on top moves faster, faster air has lower pressure
+Nabre Labre
Yeah, but why? :) really!
+sly1024 well pressure comes from the random motion of particles bouncing off eachother, so I would think if the particles are mostly going the same direction there would be less pressure because there is less random motion
+Nabre Labre
That makes sense, thanks. This always puzzled me though: according to relativity it shouldn't matter if you move relative to something or that something moves relative to you. So a moving block of air has higher speed if you look at it from another (non-moving) block of air, but if you sit in the first moving block, then the second has higher speed. I can understand that because speed is relative, but which one has higher pressure then? Is that also relative? Like when you open the window in a moving car. The air inside moves relative to the air outside, but if you look at it from inside then the outside air is moving.
As an aerospace undergrad years back, this is what I took the pains to explain to my mates and each time I was shushed for saying the text books are wrong (or slightly incorrect)!
Thanks sir! You are a smart fella. Thank God I'm not alone!
I love how you always stick to your teaching philosophy of introducing misconceptions first, you don't just say it, you do it.
There is a fundamental issue with this explanation and that is the assumption that the Bernoulli theorem (and it is simply a mathematical construct that describes a physical phenomenon) "causes" the lift. No, it does not cause the lift. In a dynamically closed system, a fluid moving into a region of lower pressure must accelerate because it is moving down a pressure gradient. Thus, each fluid parcel is experiencing an unbalanced force, but its resistance to that acceleration "pushes back" at the higher pressure, maintaining that pressure gradient.
Now, when the air passes under the wing, the streamlines of fluid parcels are deflected downwards. This is because the underside of the wing directly deflects the adjacent fluid parcels downward. These exert a pressure on incoming parcels that causes them to slow down (accelerate in a forward direction, or against the direction of flow). Their resistance to this acceleration generates the pressure gradient under the wing and the pressure gradient generates the acceleration. Reciprocal cause and effect. Most people can intuitively understand why the air passing under the wing must be deflected downwards and why it must slow down.
However, the "cloud" of increased pressure under the wing also extends slightly forward of the wing, as well. Fluid parcels approaching the leading edge that are destined to pass over the wing are initially deflected upwards by that "cloud" of increased pressure extending below and in front of the wing. As they pass over the leading edge and top side of the wing, the individual air molecules would continue in a straight line up and back, but air is a fluid and collisions between air molecules are common. Thus, the air that has been deflected upwards is now being forced by the air above it to accelerate back downwards to follow the contour of the upper surface of the wing. That air's inertial resistance to that downward acceleration causes it to form a "bubble" of low pressure above the wing and that same "bubble" of low pressure causes the acceleration that the air's inertia resists. Again, reciprocal cause-and-effect.
The Bernoulli theorem is a mathematical construct that describes the way that fluid parcels must accelerate as they move from high to low pressure (and vice-versa), but it does not, in and of itself, explain *why*
Intuitive explanation.
Exactly, after watching this video my thoughts were... So the air does not meet up at the trailing edge of the wing. But WHY does the air over the wing flows faster, so we can apply Bernoulli's Principle to say that it generates a low pressure?
I am starting to wonder if including the Bernoulli component really adds anything to a student's (undergraduate's) learning experience when it comes to explaining how airfoils work.
In a lecture to aerospace engineers, a retired rocket scientist (Doug McLean) handles some common misconceptions about lift and shows how to explain it properly (from about 14:20 to 28:20): ruclips.net/video/QKCK4lJLQHU/видео.html
+
This is actually an incomplete explanation. The greater velocity along the top, in short, is created by vorticity around the airfoil. The trailing edge of the wing creates a vortex and conservation of amgular momentum dictates that another vortex must be created in the opposite spin. This vortex around the airfoil causes air to move faster along the top.
The math is pretty complicated, but there are good walkthroughs online.
John C. Ellis - this is called circulation theory. And is the cornerstone to thin airfoil theory.
Correct
thank you man someone speaking facts
+
This is kelvin's circulation theorm.
But if you fly upside down, even with a symmetrical wing, you need to make sure you have an appropriate angle of attack right?
According to my rc airplane yes need a positive angle of attack
I am sooo glad to hear someone finally mention the Coanda effect and not base lift solely on Bernoulli.
No discussion of lift makes sense without discussing the Kutta Condition and the effects of viscosity...
There are other ways to include several intuitive concepts that are not incorrect yet do not require advanced math or understanding ... and this one certainly hits the high point(s).
Well, this one did.
acomputer121 Yes, this one did and I was not disputing that, but supporting it. I was trying to say that the old Bernoulli and equal transit explanation still all over the place is not only incorrect and inadequate, but that a more correct explanatin does not have to include advanced math (or as stated in a recent post the transient portion of lift using Kutta) . There are 3 or 4 easily explained effects that contribute to the downward acceleration of air that produces lift -- and they are each simple and intuitive.... As described in this video.
If all this is so easy and self-evident then can you explain why the exact same airfoil makes zero lift AND violates the Kutta Condition for Re
DaylightDigital I didn't say self evident, just that causes for the turning, or downward acceleration of air can be explained with simple concepts as the video here does without advanced math, circulation concepts or adding Kutta. This takes me too far back and into the area that excites the AEs. The intent is to show on a relatively intuitive level (or at least a level that uses conditions around the airfoil consistent with more common physics) , that first, the old Bernoulli-equal-transit explanation is misleaning since it incorrectly applies Bernoulli and ignores the obvious downwash. Second that the concepts as used in the video are applicable and don't require the AE degree to understand as being significant. In other words, the intent is not to provide a complete, in-depth and advanced study of lift, but using what is relatively common physics, show that downward acceleration of a mass of air provides the F in the F=MA realm. This, of course, assumes that the listener is equipped with at least a reasonable understanding of physics. If not, then tell them Bernoulli and let them go about their ordinary lives not actually needing to have a true understandunbg of lift, nor an advanced degree in aerodynamics...(;-)
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I'm uncertain of your intent. Are you saying that the video is flattly wrong?
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I should go back and view the video to see which effects he used, but I maintain that: the lower surface downward acceleration of air; the upper surface Coanda acceleration (or perhaps better to call it boundary layer attachment); the Bernoulli effect and what I call the "other half venturi concept" (Anderson & Eberhardt call it the virtual scoop, which I like better) can all be understood as contributing to the total downward acceleration of a mass of air producing steady state lift...
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Unfortunately, that page won't display correctly and there appears to be missing content and some is oblitterated by figures.
I see where it says:"The condition of finite velocity at the trailing edge is known as the Kutta condition." However it shows me no mention if the infinite velocity concept, nor of the violation of Kutta. I see only the stall videos further down
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Can you summarize the low Re violation? This has all been a long time ago for me. I don't really need to go over this, but a little curiosity is there....so far (;-) btw: this was not my focus, so I don't claim to be an advanced expert, just able to use the easily understood concepts to better the Bernoulli-equal myth. The AE part was interesting, but I focused on electronics.
This videos handles the equal transition theory wonderfully. It really is easy to get down a rabbit hole of misconceptions with lift and this video helps address one of the biggest ones.
Finally! Someone that can actually explain it. Thank you.
You know that was my video right? By in space, I just meant in zero gravity, eg. inside a space ship far away from any masses (but still with air in it).
Does this mean that the song "Wind Beneath My Wings" is aerodynamically incorrect?
No. As long as the song is referring to a glider in a thermal updraft. "You are the updraft beneath my wings." LOL
In as much sense as Aerosmith is physically correct.
Air can't be smelted.
I don't think.
Anthony Khodanian LOL, smelted no. Bent yes, by a bender.
Very well done video, it was short, concise and to the point. I appreciate how you pointed out the common misconceptions relating to the Equal Time Transit Fallacy and the idea that the top surface has to be longer than the bottom surface immediately and got them out of the way. While I understand this video was made with the purpose of being short and to the point, I would have appreciated if you made it slightly longer in order to explain some of the concepts in more detail. I would have liked it if you went into more detail on the Coanda Effect instead of just briefly mentioning how it's related to the downwards deflection of airflow. Overall great video though.
I agree Nick. This video perfectly summarized the many main contributions of lift as well as the many misconceptions that come with it. I personally believed in the fallacy that the flow on the top of the airfoil must meet with the flow on the bottom of the airfoil at the trailing edge. After learning more about this topic and the physics behind it, it makes sense on why many people fall for that mistake. With the Coanda effect, which is another misconception, only pertains to when the flow is coming from a jet passing over a stationary object. In the case of flight, the wing of the aircraft is passing through the ambient surroundings rather than the flow passing over a stationary object if I'm not mistaken. I hope this helps.
two explanations for one lift force. If you integrate the pressure over the whole surface of the wing, you get the force on the wing, and there is an equal and opposite force on the air.
thanks Derek
this was the shocker explained to me in the first lesson at uni
0:52 "That's not Wright!" hahahahahahaha
I remember having a Chem teacher in High school tell me the same thing. I never thought about it much, but after your post, I decided to look it up a bit more.
Thanks :3
yes meeting at the trailing edge and no air deflection down are parts of the standard misconception
Funny, I'm studying for my instructor certificate and I was trying to think of what the physical justification was for assuming that two volumes of air separating at the leading edge necessarily join at the trailing edge. I couldn't think of one. Appears that there was a reason for that. Thank you!
But why is air over the wing faster than air under the wing?
Because it needs more "speed" to climb over and above the wing.
Centripetal acceleration
My guess is the force from the air is getting redirected up and over the wind while the force from below remains steady and stronger
YES. They are optimized for flying right side up!
The shape is all about reducing drag, the optimum shape will vary depending on the intended use, since the design AOA and speed range will vary for different aircraft.
nope, the streams don't meet with incompressible fluids - for this case air is fairly incompressible, that's an assumption of Bernoulli's Principle
This is a better explanation that I was taught at school. However low pressure is created over a curved surface and it also partially contributes to lifts. See video - "How do Wings work - common misconception on lift." This is one of the best explanations on lift I came across. Still thuumbs of to this video for presenting a difficult concept in a way that everybody can understand.
+greysponge66 If you mean 99% under "partial" than I will agree with you
at the very end, there's a graphic that hints at it - the wings need to be angled so they have an appropriate angle of attack such that they deflect air down.
Aaaaah. This is such a releaf. After so much videos on youtube going wirh supercomplicated, but wrong explanations, someone finally got it right. So good feeling, thank you
Veritasium: We will answer the question in this video: "How does a wing actually work?"
*Veritasium 2 minutes later*
Veritasium: We did not actually answer how wings work.
did you not watch it or something?
Are you high? This completely explained it in so many ways lmao
This is a great, concise video that refutes what is likely the biggest misconception about lift force on airfoils. I also appreciated that you looked at the theory of lift from multiple perspectives (both Newton’s Laws and the Bernoulli equation), and would have loved for you to take it even farther than that. There are a lot of things that go into lift forces, and many many theories surrounding these things. Thank you for correcting some of the misconceptions so well!
I read a really long and detailed explanation of how airplanes fly once. There are several things going on with the wing which create lift and contributed to flight being possible. Some of them seem to be quite minor effects, but apparently its difficult to account for where 100% of the lift comes from.
It is due to the Coanda effect, which is caused by entrainment. Essentially, a streamline passing over the top of the wing entrans air creating a region of low pressure directly above the wing. This creates a pressure gradient over the wing that pushes the streamline down and causes it to follow the curvature of the wing (this is the Coanda effect). The force from the pressure gradient not only changes the direction of the streamline but it also increases the speed of the streamline.
the truth is that as air passes over the wing it strips electrons off the molecules, creating a wing that has a positive charge. As the earth is also positively charged it repels the wing away from it!! Problem solved. That's why Dennis Lillee would rub the ball on his pants before bowling and thereby give the ball more lift. Genius! That is also why all you people that produce negative comments on YT will never go places....
mike mason are you saying if i shuffle on a carpet with socks on i will fly
Unfortunately not- as you'd have to be shuffling along at approx 50km/hr... not humanely possible. Although I did see someone take off momentarily when after shuffling they got a nasty static shock in the butt.
I would tell you what is the reality Listen carefully.... actually according to bernoulli's principle law the airfoil does not create lift but it helps the airfoil or other shape (it does not matter that have leading and trailing edge) to fly in straight direction because of beneath and up pressure passing through the wing, so the bernoulli's explanation about generating lift and low pressure over the wing is completely wrong and useless and according to the Newton law the deflection of the downward air generates lift and push the wing up, and fast pressure moving through the beneath and up side of the wing keep the plan stable in straight direction.... thanks hope you enjoyed and no need to know more
I think the misconception is that air flow needs to be horizontal to create lift. The amount of lift created is partly due the AoA (Angle between relative airflow and the chord line of the wing). this relative airflow can be completely vertical e.g. when the aircraft is climbing straight up as you said, but it is still creating lift. But you are correct in saying that the limitation now is the engine as the only component that will keep it going up when vertical is thrust
I am too an aerodynamics professor, and I must say that this video has got it all wrong.
+Mike Cammiso Why-oh-why do so many feel compelled to go to so much trouble to spread so many longstanding misconceptions....? Prandtl and Bernoulli have spun their way through the globe many times...(;-)...I'd appreciate a *brief* summary of the major points you follow.
+Mike Cammiso Would you care to summarize (please) the error(s) as you see them ?? I've already posted mine.-- Regards
+Mike Cammiso
Then share your view on the subject.
+Mike Cammiso thats not a helpful comment. tell us why it is wrong
+Mike Cammiso If the textbooks are wrong, people tend to make wrong conclusions. I have a question to you that I hope you will answer. I'm reading the book "Fundamentals of Aerodynamics" by John D. Anderson, Jr. (as a hobby, not for professional use - I'm a glider pilot just student wanting to know more about aerodynamics). I suppose you as a professor know this book.
On page 74 he has a figure (1.53) showing the velocity profiles in the laminar and turbulent boundary layers, This fígure indicates that the laminar velocity profile is mostly linear and the turbulent velocity profile is strongly unlinear, having a much higher shear stress on the surface. I feel confortable that this is right because it explains to me that the viscosity in the laminar flow is uniform, yielding a uniform flow speed (hence laminar). But searching the internet, I haven't found another figure showing the same. Confused? I am! Is Mr. Anderson wrong?
If you answer my question, and I would ask another professor in aerodynamics the same question, then would I get the same answer from both of you? If no, why shouldn't I be confused?
The air streams (above and below the wing) do not need to meet up simultaneously at the trailing edge. The air above the wing reaches the trailing edge first than the air below.
I think the correct explanation is the air stream above the wing near the front edge is squeezed more than the below stream. Using conservation of mass, the speed of the upper stream is higher due to the small cross-sectional area
Right here after that pinned comment.
Pressure is just force over a surface area. you can describe lift as a result of force pushing up, or pressure "pushing up".
ps: pushing up is in quotation because it not the best terminology when we talk about pressure. think of it more as a combination of push from below and suction from above.
atmospheric pressure is constant it pushes everything in all direction. so in order to move something in one direction you have to speed up air on that side which reduce pressure (or creates suction)
I am studying aerodynamics for years and I can see a lot of crap in the comment section
*****
you nailed it 100%, any way I was talking about some people who create their own theories .
***** RE: "less time for the air particles to impact the upper surface due to speed past the steel plate." "due to speed" is not correct.
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Though your written explanation attempts to be saying much the same as the video and what is actually happening, that part is incorrect. Speed does not cause lower pressure. It is the other way around. A lower pressure in one region is the cause of air accelerating toward that region. The upper, convex curve creates a lower pressure in a way your words are trying to explain, for sure. To use words more like you are using: The upper surface curve's change in direction away from the airflow's original direction creates a lower pressure region along the surface that causes the air to follow the curve This is what Derek in the video calls Coanda, but is not what Coanda is considered to be. Coanda has a very specific description requiring a *forced* stream of air.
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Many also fail to consider that the lower pressure along the upper airfoil surface has an effect on a considerable amount air further above the wing that is also part of the air that is accelerated downward behind the wing.
Cheers
I have tried fling even in F16 jets and i can say the video missing a lot,the wing will generate the lift due to its shape first which delays the separation point and reduced form drag which is generated from the shapes. the principle of lift generation is proved and we did many experiments using different shapes from ball to awkward shapes in a wind tunnel. I will answer his question about flying with flat wings, do you know that this wing can fly ? yes it can if you increase AOA but how efficient ? it is low and need long runs to take off, look at missiles what wing shape they have? it is an awkward triangular shape, how can that fly then? and about the flying upside down dude you cant fly A320 upside down or you die the jets can fly like that because the thickness to chord ratio is so small and the wing chambers has slight difference which allow the jet to reach mach speed and fly inversely. but have you ever tried inverse flying ?
if you fly F16 and inverse fly it you will notice that altitude will start to decrease why?
because the wing is cambered more in the upper side.
the force he talked about is the force produced from the downwash which generates SOME lift and another type of drag but flying straight and level has nothing to do with downwash. Aerodynamics is a very complex subject and defeating its principles needs more that a short video.
Trust me your video is missing a lot, The wind tunnel equipped with accurate static and dynamic pressure sensors which shows you graphs of every single point in the cambered wing with zero AOA and we tried to defeat Bernoulli's principal like you but the experiments proved it, it proves that in a single inch of a wing you can get a lot of lift and by calculations of C 17 wing you can get a massive amount of force capable of carrying tons. All aircraft you see now calculated using
1/2 (density)(velocity square)(coefficient of lift)(wing area)
Observ45er i see your points, thank you
I think that answer is a bit general... In particular:
The answer is CENTRIFUGAL FORCE, because airflow at the top of the wing has to turn rapidly when it reaches max camber, and the force required to make that change in direction is a centripetal force actuated in the mass of air. Because of Newton's 3rd law (one force actuates in conjunction with another one, with same direction and intensity, however different way) there is another, centrifugal force, that actuates on the wing. This force is, in most part, the source for lift. This theory explains the fact why airplanes DO fly inverted, as long as they fly with a positive angle of attack in relation to the ground... There is a number of ways to increase lift (in many cases, the lift coefficient L=0.5*rho*V^2*A*C_L):
-Increase speed, because the centripetal force and centrifugal force will be greater;
-Increase the density of the mass of air (basically, fly lower and in colder temperatures);
-use high-lift devices such as flaps and slats, which increase the curvature of the wing, although creating more drag;
-increase the curvature of the wing profile itself;
-etc
SUCTION!!!!
Rexy!
STAT!!!! 10 CC'S OF EPI!!! CLOSE HIM UP!!!
This was a great video, I liked how you pointed out the common misconceptions of lift and explained why they are incorrect. Using flat wings and airplanes flying upside down was a great response to the equal transit time fallacy and the video you showed proving that certain the top and bottom airflows do not reach the trailing edge at the same time was very helpful to those who might be caught up on this notion. I also liked how you mentioned how there are multiple explanations of lift that when used together can better explain lift. It is very important to acknowledge that both Newton's theory and Bernoulli's theory are necessary to explain what causes lift and that neither theory can stand by themselves.
hmm yes so why does the air above speed up?
pressure at the top of the wing is generally lower, so air is accelerated when moving towards it
pressure at the bottom of the wing is generally greater, so air is decelerated when moving towards it
the part I don't understand is if air pressure caused the speed difference, then there is no way that the speed difference is the cause of air pressure, and the misconception is completely wrong. But what caused the difference in air pressure then?
i AFJ i
It's relative to the shape, the particles try to remain in the same place because of inertia, and both sides of the wing move at the same speed, the difference is that the upper side is a larger way to go.
+Hector Palacios The part about inertia is part of the true science. However, it is a very common misconception that "the upper side is a larger way to go" . A sail or a flat wing has the same distance on both surfaces; an inverted wing has the greater distance below; and they all generates lift, so this shows that this is false science.
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The important thing is the path that the air is forced to take by the wing. ....
The pressure above a wing is lower because the air and wing are, in essence, moving away from each other and the air's inertia then is responsible for lowering the pressure.
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By observing a real wing, we find that as wing goes past the still air, it is the air under the wing that is moved along at the highst speed. THe air above the wing is hardly moved along at ll and is only accelerated downward.
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It is not clear what you intend with this "...both sides of the wing move at the same speed,..."
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Regards, ScienceAdvisorSteve
Observ45er Thanks. I tried to specify that the upper and lower side are part of the same structure and move at the same speed. If the upper part is a longer trajectory, the particle moves relatively faster above than below because it is forced by geometry and inertia, although it is not the whole reason of flying as you say.
As shown in the video, geometry also slows down the wind below and makes it go down, and that creates an opposite force.
A question, the air also speed up in the upper side of other wings, or just the aire below is slowed down?
This was the first topic on our physics class that didn´t make complete sense as the teacher explained it, I´m glad to see it confuses others as well.
Snap!
finally a video that explains it correctly unlike 99% of all the youtube videos!
So Equal transit time isn't true after all?
Nope. It's actually referred to as the equal transit fallacy in most aerodynamic text books. If you want to spend about 4 hours on wiki, check out the airfoil page and go to the various linked pages. The math gets pretty intense fast, but if you like vector calculus you'll be ok.
A normal wing section will also fly upside down...badly... and in a wind tunnel with puffs of oil smoke injected so you can track air speed, you will find that the air going over the upper part of the wing (The flat bit) will be much faster than the air under the wing (The curved bit)..
lift has two reasons :
1- Bernoulli pressure difference due to shape (the small partial lift part No1 ).
2- wind inclination to lift airfoils two components ( impacting drag ,and impacting lift perpendicular to it ) Part No 2
still dont get how a wing works
wooten cleng Best and most honest comment! Do not worry you are in good company. Simplest analogy can be pendulum,. kinetic energy goes up, potential goes down and vice versa. Same here - speed up , pressure down. this pressure difference works against gravity... :-)
+LS DO - Same.
+LS DO - It is very easy. A wing works the same way as a ceiling fan, a kite, or a paper plane. If you have ever stuck your hand out of a car window while moving and inclined it to the airflow you have made lift.
Lift is a simple Newtonian reaction force. You bend the air downwards and the wing goes up. Thinking of is like you hand, the palm of you hand is facing the oncoming air. You will bend the air through an angle that is equal to the angle of your hand to the oncoming air. The force on your palm is part on of lift.
Part two is the air bending around the back of your hand. Since there are no vaccums in normal space, the air has to follow the angle of the back of your hand as well.
Both surfaces of your hand bend the air downwards and the equal and opposite force is that your hand goes up.
It's is pretty much that simple.
Sit under a ceiling fan and that you feel is the result of lift production.
If you could measure the force on the as shaft that attaches it to the ceiling you would measure the lift it is creating.
+Complete Aerogeek Despite of my deep respect to your comments I cannot agree with this description. Even if the 3d Law is applicable here , which is not fully justified, your explanation replaced cause with effect. Downstream as result of redirection of flow plays minimal if any role in lift explanation. - looks like polished but still incorrect Newton explanation. Main contributor to downstream flow is pressure difference.
LSDO like a rocket
I love how you educators at youtube are working together to make people "smarter everyday" ^_^
The Air above the wing MUST go faster? Why?
There's less surface area for the air particles to move over than the bottom
+auletes Bernoulli's principle... the air above the wing isn't as dense as the air below and air molecules, which means the air molecules above move quicker.
+Gavanization Not necessarily. Air molecules don't care about meeting at the trailing edge so surface are above and below don't really play too big of a key role in the bigger picture.
When air molecules separate at the leading edge, the air over the top of the wing is compressed. Google stream tubes around an airfoil and you will understand. Now let's take the continuity equation (google) and disregard the density (because it will be equal throughout the airflow), you will notice that if there is a drop in area, it will result in a rise in velocity. Due to the compressed stream tubes above the airfoil, area within the tubes are decreased, thus velocity of the air molecules increase.
+Googelplus Sucksys Density and Pressure are completely different. In the case of lift production, atmospheric density remains the same through the airflow above and below the wing.
Great work starting with the commonly perpetuated myth and following it up with a debunk and more complete explanation. Very quick and concise collection of counterexamples that help people ask questions about what they've heard before. The deflection of air/momentum concept is an important contributor, so it's good that it was mentioned. However, the Coanda Effect applies to jet flows, which is not applicable in regular flow over an airfoil. A good explanation given such a short time frame. Other important contributors to lift like circulation could have been described, but the information presented was mostly correct and serves as a good basis to start from in a little over 2 minutes. The part at the end talking about how these differing theories can coexist and explain the same phenomenon was also great for sparking more curiosity.
I agree, Matt. The Coanda effect is only applicable to a jet flow. As a result, the external flow over an airfoil would not be a proper place to apply that concept. I think a better way to describe the flow over the upper surface would be that the deflection of the streamlines is caused by the change in geometry the flow sees (i.e. the airfoil) or the pressure field. This would generally cause the deflection over BOTH the upper AND lower surface to be downward. This is a great video by the way, Veritasium!
If I say 'centrifugal force' everyone will get very upset because the acutal force is not centrifugal, the force is centripetal, the reaction is centrifugal. However, if I say 'lift force' nobody has a problem... except I do, you should too! Lift is a reaction, an equibrant of the force that an aerofoil imparts onto the air. To be even more precise, lift is a vector component of the total reaction of an aerofoil interacting with the air.
The aerofoil has kinetic energy, it imparts that energy onto the air; the force is generated by the aerofoil interacting with the air as it moves through it. This video describes the air having kinetic energy and acting on the aerofoil, which is incorrect unless you are in a wind tunnel. The force is produced by the aerofoil moving through the air and it has an equal and opposite reaction, the total reaction, the 'vertical' vector component of the total reaction we call lift (although, lift may not always act vertically - another simplification, I'm not going there today). This is never described very well in any text book, it is always "simplified" to the point that it doesn't describe reality and causes unnecessary confusion.
Malevolent Prophecies Actually, what everyone should do is stop being a bunch of whiny pedants.
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Malevolent Prophecies Oh, and because I just now actually read the latter half of what you were saying, lol, no, because you're privileging a reference frame.
seigeengine Do you have a point? Because I don't see it and I'm all for discussion on the matter.
Malevolent Prophecies My points were exceptionally clear.
Kindly respond to them, be silent, or find a way to take your head out of your ass so you can proceed with screwing yourself.
Newton's 3rd law of motion informally states: Every action has an equal and opposite reaction. So if the wings push the air molecules down and left, the air molecules must push the wings (and the plane) up and right, which is lift and air-resistance respectively. That's one of the 2 explanations offered in this video to explain flight. I'm not entirely sure if I understand the other one though.
Well. That was a little confusing
To expand on that, textbooks generally quote around 0.3Ma, above which compressibility effects begin to become noticeable, with indeed a sharp change at Mach 1. The actual craft need only fly close to the speed of sound like 0.9 (transonic), where local flows across the tops of wings exceed Mach 1.
2:08 I have been diagnosed with cancer
i'm sorry for that
At that point in the video, your doctor kicks down your door, runs into your room and screams "YOU HAVE CANCER".
+Dramawind eeuumm ok
sorry to hear about that.
I just realized I wrote an entire research paper on this (Newton vs Bernoulli) back in my sophomore year of high school... and my thesis was apparently correct. God things have changed in the past 2 years.
you still didn't explain how aireplanes fly upside down or how nearly flat wings can fly a plane
+Ghassen Mez airplanes fly upside by changing the angle of attack. This is done by controlling the elevators in the tail.
+Ghassen Mez when inverted, the air over the wing is made to follow a convex curve ( by the increased angle of attack). When upright, the upper camber shape does this also, just at a lower angle of attack. It's the same when upright. One explanation (when done correctly) works for BOTH!
Did you even watched the video? 2:41
that was explained so well even i understood that and im not very smart at all.you always make things easy to understand and that's why im a subscriber.no need to make things so complicated like some youtubers do.nice work bro
According to the comments, noone really understood this video nor knows how "it really works". still it has only 221 thumbs down? I like veritasium, but this video is just terrible.
It does. That's what causes wake turbulence behind an aircraft. It has to move an equivalent mass of air downwards to counteract the lift coefficient. What's often neglected about the discussion is AoA (Angle of Attack) -- the airplane is in a slightly nose-high orientation during cruise in an optimum equilibrium of not being so high to increase drag under the wing too much to deflect downwards vs the beneficial lift from the overwing low-pressure. It's a combination of forces, not just one.
the faster velocity air on top of the wing, does lower the pressure.... it has NO bearing on the air traveling under the wing. in fact, if you blow over a balloon, the balloon will rise... proof of Bernoulli's principles.. if you defect air by pointing air underneath a wing, it will lift too... both Newtonian and Bernoulli's principles are correct and work in concert with each other. the air doesn't have to meet.. that's why there is wing tip vortexs and drag flow curls at the trailing edges of wings. air moves to differential pressure and that's what happens as a wing passes through the air.... this video is silly as it talks about flat wings.... flat wings make no lift(non air foils) but, when you tilt the surface, it becomes a surface with lift and drag coefficients. Most importantly, why does an airplane have the ability to fly upside down??? simple.... it is the angle of attack of the wing that determines its lift/drag characteristics, and in what direction that force is generated. NOT the shape.
After the HP and TQ video, I clicked your google account to see what your other interests are. Man! I'm kind of excited to see someone else who gets it! I've argued this with my teachers, and others for years. Awesome to see someone else who actually understands physics.
Chris Arnold Who you referring to...?
zanick2 I responded on his google+ page. I thought it would end up as a direct reply to him. Apologies
zanick2 the shape is a really big factor for the lift/drag ... the angle of attack is important but the shape also
zanick2 You've got the right idea, but a few misconceptions.
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1) RE: "Faster velocity" The lower pressure bove the wing is what accelerates the mass of air (Newton#1) to a higher tangential speed and radially around the curve.
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2) RE: "no bearing" Correct. I think you mean that the upper air and lower air cannot be compared with Bernoulli's Equation, no? I've seen that done ! And in a prep school course video on TeacherTube.
3) The rising balloon is due to (summarizing) the
...a) air being accelerated *Newton #1) around the curve by a lowered pressure @ the surface (Bernoulli), then
...b) the resulting reactive force on the balloon lifting it...> Air down > balloon up (Newton #3)...
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Flat wings do the same thing.
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Simply saying that AOA creates lift completely ignores the physics going on around the wing to create that lift. AOA controls the amount of lift created by the phenomena around the wing.--
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thought I already commeted on this.
so both are correct? im confused its bc of pressure difference and angle of attack?
No they aren't. They are both used improperly.
The simple fact is that the wing must push air around to move through it. This alone creates the pressure changes around it. These pressure changes then cause all the air accelerations we see around the wing. THAT is why it is Newton, not the way most people explain it as a "reaction' to the downwash.
Angle of attack is the factor that a wing-like shape needs to create these pressure differences around the wing.
The Bernoulli explaination sucks.
+I Cute. I like that. Yes. Bernoulli is the wrong way to explain it. ...DEREK !! PLEASE RE-DO THIS VIDEO CORRECTLY !!
No, the video is fine. I just wanted to state what needed to be stated.
+I No, the video is not 'fine'.. Derek states one of the most common misconceptions, that fast air over the wing *_creates_* a lowered pressure - false science. Fast air having a lower pressure than nearby still air is well known to be false and it is not just another fundamental law of physics to be memorized, Like Newton's Laws. The most common demonstrations "proving it" ignore the fact that there is a curved flow causing the pressure change. Prevent the curved flow and the demo falls apart. I've done it just to prove out a demo I developed myself.
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He also does not specify just what the "correct" version of Bernoulli is. It appears to involve only the upper surface. Is it the use of Bernoulli's Equation equating the upper velocity to the lower velocity (which is flat bad science and math)? He then, does not explain just what the correct explanation of the "Newton" version is. That appears to involve only the lower surface. This is the "hail of bullets concepr actually posed BY Newton and is also incorrect.
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He is much too vague about what the two things are that are two ways to look at the same thing. He did himself a great disservice with this video.
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Once you have the pressures, you can show how they produce all the air movements around the wing: below, above, off the ends, behind and ahead of the wing. This means that the down wash is just another necessary part (due to Newton #3) of the WHOLE story, not ANOTHER "parallel" explanation.
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Calculating the pressures on the wing gives the lift force. Calculating the momentum transfer of the downwash also gives the lift force. These are indeed two ways to *_CALCULATE_* lift because of Newton #3. However, they BOTH are part of the whole explanation of lift. People confuse describing the phenomenon with calculating the force.
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Cheers
Bernoulli explanation is not bad in understanding the flow over an aerofoil and giving an introductory over view of the flow but for detailed flow, we need to use a state space representation of the Navier Stokes equations using the solutions from the Laplace.
Give me a video that properly explains this
Yep, they fly at an increased angle of attack in inverted flight to compensate for the inefficiencies, although if you think about it it is really everything else that is at the wrong angle, since as you say angle of attack is relative to the air, but they have a built in angle of attack which is relative to the tailplane and fuselage and optimized for normal flight.
A bit confusing and not that acurate! Sorry.
Keep on the great work with your videos.
Antonio Lucena it is accurate. Your confusion probably led to you thinking that it's inaccurate.
Dilip Tien Thank you for bothering in commenting my comment, It reflects my opinion only, which I believe this space is meant for.
Your assertion about my confusion (sorry) is quite hollow. I perfectly understand the forces involved in the process of lifting an airplane, thought I expected a little more from this channel in clarifying the misconception surrounding this subject, and not this taste of “both are correct, both are wrong”.
The major reason that lead me to subscribe this channel is that the author (which deserves big credits for his work) separates facts from fiction in a very entertaining way, to a very comprehensive audience while being very “Veritas” (Latin for truth) , which sometimes, I believe must be very hard to maintain (the balance between entertainment and factuality).
My expectations with this video were that it could come to a final conclusion for the wing phenomena. I’m pretty sure it’s heavily Newton’s third law, while Bernoulli’s theory participation is quite humble.
It is not accurate to say that both are right, and both are wrong... we are not talking quantum mechanics here…so remember the principium tertii exclusi ou tertium non datur.
Antonio Lucena when did I ever say that you couldn't put your opinions anywhere? Whether you expected something different or not is irrelevant. He is still correct. And it definitely wasn't confusing. Nothing he said was hard to understand. You're "pretty sure", whereas Derek is sure. If you have nothing to show that he's wrong, then don't try and say that he's wrong.
Dilip Tien well... You didn't get it, did you? Read it again :)
PS I love this channel and have lots of respect for the author's work. Please don't bother in guessing my intentions. Best regards
Nicely done and a neat separation of the micro and macro (or local and global) views of the generation of lift. As noted, Bernoulli is correct - but I don't believe Bernoulli ever anticipated that someone would invent a wing and then argue that the upper and lower flows reached the trailing edge at the same time. My quals for saying this: aeronautical engineer for the last 30 years, glider pilot for longer and just plain interested in understanding stuff.
There is no venturi occurring above the wing.
wroooooooooooooong. sigh
+jiunn wong
Why?
+Jonas Bové Mørk (Protoxus) Pretty much everything he said at the beginning was wrong. Rest I didn't even listen...
+SingleTurboSupra That's not what I asked. I asked why it was wrong.
A wing works by "twisting" the airflow around it. This causes the air over the wing to flow faster and air below to flow slower. The rest you should know
Brendan Raymond
Guess I made the classic mistake of commenting before watching the whole video lol.
Although he was still wrong. Yes there is pressure difference happening on a wing, but not because of Bernoullis principle. It only works on a single streamline, not on a two separate flows.
I liked the style he was talking in which Henry does.Good explaination.
For an efficient wing the both the principle must work on same object well with any single one any one can fly also. Thanks for nice video.
I enjoyed this video and like how you mentioned the misconception of equal time transit fallacy. I think how you mentioned how Bernoulli and Newton's third law apply to lift was well done. However it is a misconception that Bernoulli and Newton's third law are two different explanations of lift, when in reality they are both equally important and should be used at the same time when explaining lift as they influence each other. Also as mentioned in another comment, the Coanda effect is only applicable for jet flow and not normal flow an airfoil will usually see. Hope this information helps!
One of the reasons (as far as we know, there are 4 reasons, all helping to create Lift upwards, but the exact % of each of these reasons in the creation of Lift is today unknown) that the Airfoil creates Lift is the pressure difference between the top and bottom of the airfoil and this pressure difference is created when the air above the airfoil must speed up due to the Ventouri effect.
It does NOT speed up in order to reach the end of the airfoil at the same time as the air flowing beneath. The air that goes above the airfoil reaches the end of the airfoil faster than the air that travels below it.
Look up the Ventouri effect and Bernoullis theorem for a better understanding of this.
Thank you for this explanation. I never really understood why the air should "reconnect" at the end of the wing. There just doesn't seem to be any good reason for that. This makes a lot more sense.
Oh this is great!!! For years I was confused as to why helicopters would stir up dust with the old simple explanation of a wing this makes perfect sense now!!!
I learned more about planes in this 2:50 video than I did in 2 weeks of learning about planes at school.
what about that: i was told, that the difference in speed comes from conservation of angular momentum. the upper stream of air must travel further than the stream of air underneath, so when both meet, they swirl at the end of the wing (delay). that causes an a. m. (ccw if the wing flyes left). because of the law of c. o. a. m., another a. m. occurs that spins in the opposite direction and around the whole wing, which causes the upper stream to get faster than the one underneath. then bernoulli.
Watching this video after 9 years in 2021.
And, surprise to know Veritasium, Smarter everyday, minute physics, How ridiculous, all these were internet friends 😍😍 You salute u all to give us inspiration to be great RUclipsr
...{continue} Now if you want to mantain level flight, Lift must equal Weight. Lift is 1/2ρ*v^2*A*Cl. So if weight increases we must either increase density ρ, speed V or Cl (assuming we cannot increase wing area). If we dont change altitude/temperature (ρ) if we dont change V, CL must increase (and CL is based on the AOA). And there is a point where, by increasing the AOA to increase CL, we reach the critical AOA and the wing stalls. {continue}...
If you are having confusion, just remember that the first theory is correct in that there is less pressure over the top due to a faster speed of air, pushing it upward, and the second theory is correct in that the deflection of air due to the angle causes the air below the wing to move slower, increasing the pressure and generating lift. In conclusion, what this video is trying to say is that both the ANGLE and the SHAPE of the wing matters in the lift.
If you wanted to go into even more detail, you could describe the necessity of circulation for lift.
If anyone want's a mathematical perspective, you could look into the principle of potential flows and super position. What Veritasium posted in the video was correct, but there are certainly more ways to look at it.
-An Aerospace Engineering Student
To anyone who doesn’t understand this, I was in the exact same scenario just a week ago so listen up.
So air moves over and around the plane as it flies. (You already understand this, when you put your hand out of the window of a moving car, it’s the same thing.)
As that air moves along the back-end of the wing, (the air is sticking to the wing, and moving along with the shape of the wing.) The air is then pushed downward because of the shape of the wing. (The back-end of the wing is pointed downward.) All of that downward air then thrusts the plane upward, “lifting” the plane, which is why this is called “lift.”
I really hope I didn’t over complicate that more than I had to, but if it helps at least one fella out there then it was worth it.
Best and precise explanation video.
thank you for putting this information out there, i mean REALLY THANK YOU!!!!!
I'm a baby boomer and when i was in school they taught us great deal of things that agreed with science at the time and that turned out to be incorrect. they taught us that light can only travel in a straight line, for example. little inaccuracies that added up to handicapping many.
if you see some of this bad information please, please, please put out the word!
like this thing that they taught us where electrons circle a nucleus in rings and now-a-days we find out that it's a cloud.
i'd love to discuss if light is a particle or an electromagnet field etc...
i think gunny just wanted to add that this whole "angle of attack" thing only works to a certain limit. if the angle get's to big the flow of air will disconnect from the wing and you will end up with turbolant flow on the wings top side. those turbolent flows are slower so that the pressure gets higher again.
my take on this matter is, that in a commercial airplane, you want the most lift you can get out of a wing, and the maximum speed isn't too important, so you have maximum lift, but also quite a lot of drag.
In a supersonic airplane, lift isn't too important anymore, because at the speed there is a lot more air travelling by, creating lift. Drag is also increased. But here you want minimal drag, and just enough lift to keep it airborne. The different shapes are a compromise between drag and lift.
Great video. Best explanation on RUclips
to explain how planes fly upside down: Planes that fly upside down have laminar flow aerofoils. Meaning they are less cambered. flipping the plane over wont affect the lift too much as long as the angle of attack it adjusted accordingly (pushing forward on the stick which moves the nose up). This creates lift as he says in the video. Besides that, planes that do aerobatics generally have enough power to do alot more and other factors should be considered.
Wake turbulence is caused by the air from beneath the wing wanting to travel too the low pressure area on top of the wing via the wingtips. And so creating vortices which travel downwards and causing induced drag. the downward deflected air along the wing is called downwash. As of your explanation about the optimum AoA during cruise. The optimum AoA is that which gives the best Lift/Drag ratio. But alot more forces come to mind such as velocity, wingsurface, wing design, air density, etc.
I'm not an aerospace engineer, but I did take physics in college. The concept isn't complicated.
Note, the Wright brothers did not use a tear shaped wing cross section. They simply bent the wings of their experimental fabric bi-plane to generate the lift. The point is that it's not Bernoulli's principle (which is of course a real thing, don't get me wrong) that generates most of the lift. It's simply the angle of attack forcing the air down. Upside down, you just gotta keep your nose up.
Yes thats right. The wing on F1 cars are set with a very specific negative angle of attack or negative incidence relative to the centerline of the car. Cessna horizontal stabilizers work the same way by being set to a negative angle of incidence
I've wondered this for a long time and never really found a proper answer, but this explains it perfectly. Also, as it turns out, my assumption to how it works was correct!
2.50 minutes video but explained really good and clear.
If you put an airfoil and move it you will see it has lift and drag. Water cannot be compressed to any degree with the motions of your hand and an airfoil, the water will just displace and gain volume. Therefore pressure differences have very little to do with it, it's merely the leading surface is contacting more matter, creating an opposite and equal reaction dependent on the orientation of the wing and the direction of the flow.