Who says the separated air must meet at the trailing edge at the same time? Bernoulli didn't say that! Definitely Bernoulli's principle is true, but everyone is using this principle based on a wrong premise.
Thats to make the air wind in the same pattern, (laminar flow). If the air wind doesnt meet at the same time the air will become (turbulent flow) which will make the air behind not good as it was. Making it impossible for other planes to travel at the same direction after a while.
The only way in which the wing surface can feel forces is either through tangential or normal forces, with tangential forces being viscous shear forces, and normal forces being pressure. The air cannot impart force on the wing surface accept through these means. What this means is that a pressure difference IS the reason a wing generates lift. Experimentation shows clearly that an airfoil shape creates differences in pressure all along the surface and when you integrate the pressure over the whole curve of the airfoil shape, the net force has some component in the normal direction to the freestream, and some component parallel to the freestream, with the normal component being what we call lift. The net result of causing this pressure difference is a turning of the flow, since the only way the flow can be turned is through the pressure gradients within it. So, from a mathematical standpoint, you are correct, the flow is turned by an amount exactly required to generate the amount of lift that is generated, but to say that lift is not actually caused by a pressure difference is incorrect, because again, the only way the wing surface can feel force is through the pressure and viscous forces acting on it directly (viscous forces barely contribute to lift, but rather contribute mostly to drag). The turning of the flow is just another result of the pressure differences within the flow field. The reason, then, that the Equal Transit Time theory is wrong, is not because it explains that pressure differences cause lift, but instead because of HOW it explains the pressure difference is created in the first place, which is admittedly much more complicated than can be explained without some very complicated math and physical principles. Equal Transit theory is not based on Bernoulli's Principle, it just uses Bernoulli's Principle to explain the result in change of pressure from the false premise it starts with. Don't equate the Equal Transit time fallacy with Bernoulli's Principle because there are plenty of valid uses of Bernoulli's equation.
correct! F1 cars use a diffuser for that reason, speeding up airflow beneath the vehicle and creating low pressure air underneath, effectively sucking the car to the ground.
Good comment, but I'm surprised you didn't comment on the completely false and incorrect graphic shown in the video at 2:50. That downdraft shows something that wind tunnels never show for such an angle of attack. Case in point, for planes cruising at constant altitude there is *no* net vertical momentum and therefore *no* net downdraft. Instead there is displacement up and down and then relaxation back to original level. Very disappointing that engineers keep repeating this mistake that flight is due to air mass being "pushed down". It's true only when a plane is ascending or rapidly accelerating.qph.fs.quoracdn.net/main-qimg-cdba626b7a727d8315c1514104ab99bb
Please check your references, the air DOES NOT join at the SAME TIME at the trailing edge of the wing, “same time” is simply a totally WRONG statement.
The equal transit theory is false. Lift creation is very complex but it’s mainly caused by the pressure differential between the top and bottom of the wing and the downward deflection at the trailing edge. So it’s a combination of Bernoulli’s principle and the third law of motion.
3:38 unless I'm mistaken a wing in stall still produces lift, it's just that it's overcome by drag so not very practical, and uncontrollable due to no flow over control surfaces.
While it is true that the flow tends to remain attached to the surface of the airfoil, it is not because of the Coanda effect. This effect specifically applies to jet flow, which an airfoil would not experience. The equal transit time theory is wrong as you stated, but the relative pressure fields between the top and bottom surfaces of the wing would play a role in generating lift. Pressure and velocity changes are coupled when looking at a flow like you displayed, meaning they change continuously with each other. This is a big misconception when it comes to explaining lift.
Coanda Effect and flow-attachment involve the same physics. (Simply make the diameter of the jet be wider, and the connection becomes obvious.) Attacking the term "Coanda Effect" is misguided, smacking of one-upmanship, rather than pointing out a significant error. Yes, the proper term here is Flow Attachment. But Coanda Effect is an example of flow-attachment. If you believe that the two of them employ two different kinds of physics, then you need to explain the details. Coanda Effect becomes Flow-Attachment in the limit of increasing the jet-diameter. In 1999 I saw the very first use of this same misguided attack, this "it's not Coanda Effect." The person using it insisted that Coanda Effect only involved liquid jets in air, such as water flowing over the back of a teaspoon. Why would he say this? It was quite obviously a well-poisoning fallacy. He had just been caught (in a very public situation) believing and supporting "transit-time fallacy," Rather than publicly admitting error, was trying to avoid embarrassment, by attacking his attackers, pointing out their "huge error," suggesting that they weren't competent, because Coanda Effect only involved water-jets ...the tea sticking to the teapot spout, etc. Henri Coanda didn't discover his named effect by launching any water-jets. The phenomenon appeared with air-jets coming too close to a parallel fuselage surface, where they'd unexpectedly exhibit flow-attachment. (But how wide must the "jet" become, before it's simply flow-attachment, and not Coanda Effect? Answer that, and you'll have a perhaps valid point.)
I don’t get why most descriptions focus on the low pressure above the wing, instead of the high pressure beneath the wing. The high pressure is what creates the lift after all.
Not really, its the relative difference between the top and the bottom of the wing. There is no entity called "high pressure" under the wing. There wouldnt be any difference between lowering the pressure above the wing or increasing the pressure below it.
Good video for the shortness of it. You are correct- exactly! Basically, the various "theories" of why wings work to create lift all say the same thing, but in different ways. The idea of alerting the airflow to create lift, is best explained with your explanation. Air has mass- quite a lot of mass, actually. Anytime you move mass, there is an equal and opposite force created. In order to get any aircraft off the ground, you must move (at velocity) a mass (or weight) of air equal to the mass (or weight) of the aircraft in the opposite direction in which you want the aircraft to move. Any given volume of air (a "slug") has specific weight. You can calculate what amount of force is being generated by centripetal force of moving that weight. So, basically, the wing lifts for the same reason a weight being slung around a center point get's "heavier"- the faster the weight is slung, the "heavier" it gets. the redirection of the air slugs by the wings angle of attack, eventually is going fast enough to literally force the wing upward against the weight holding it down. this is why even a flat, angular board held at an angle to the direction of flow will cause lift- the rectangular wing will fly (though with higher drag) without the curvature (I've proven this to the vast chagrin of "Bernoulli" adherents with RC airplane models. The advantage of a curved or "Bernoulli" wing is a reduction in drag AND and enhancement of more easily redirecting the airflow in a different and downward direction, thus causing more efficient lift. The fundamentalist Bernoulli people have a hard time explaining why properly curved wings can fly (still generate lift) when flying upside down...and don't even get them going on the symmetrical (curved the same on both sides of the wing surface) fly better, with less drag and more lift at higher speed than the traditional "Bernoulli" models - that is the "flat bottom" wings. It is merely the re-direction of mass that causes airplane wings to create lift- that's the whole bottom line. All the other aspects of a wings design are for reducing drag while enhancing that re-direction of mass. Excellent video. Excellent explanation of why wings create lift.
Centrifugal or Centripetal force has nothing to do with an air wing generating lift. Other than that you are mostly correct that Newtons 3rd law of motion is what provides the lift. You are incorrect though to say the poster of the video is correct in that regard because that is not what he said. He said something completely different and believes a downdraft creates lift which makes no sense whatsoever.
@@lxdimension What SHOULD have he said? What part did he say that was 'completely different'? 'Newton's 3rd law of motion' doesn't make planes fly.. More words, please. (Seen Kooper, above?)
@@lxdimension I agree re: centripetal force, that made no sense to me at all. However, in terms of the video, what do you think a "downdraft" is, if it isn't literally the "opposite" aspect of Newton's 3rd law? The air has shifted direction, due to a force being applied to it by the wing moving through it, there's an opposite force... hello lift!
The Bernoulli/Newton dispute is a false dichotomy. They are simply different ways of describing the same phenomonem. Newtonian mechanics is arguably the more fundamental explanation, but the proximal cause of the lift (the only thing the wing feels) is the pressure differential that is a resultant of that Newtonian action/reaction. And that pressure drop is known as the Bernoulli effect, although Newton himself had observed the effect in tennis balls and concluded correctly (of course,) that it was due to action/reaction with the passing air. So, probably go with Newton since he was a couple of centuries earlier than Bernoulli.
A basic symmetrical airfoil shape is a flat sheet wing with a shape added around it to allow thickness for spars, and to improve aerodynamics at different angles of attack. A flat bottom airfoil is really a cambered sheet wing with an airfoil added around it. So if you look at the centerline of that flat bottom airfoil, you can see that when the flat bottom is parallel with the direction of travel, the wing itself really has a slight positive angle of attack. Hence lift at what seems like a neutral angle of attack, but which is really slightly positive.
Maule aircraft have a flat bottom wing, the flaps can be set to negative angle to improve cruise. Other than that pretty horrible aircraft to fly in tricycle gear form.
what you should have mentioned as main reason why the incorrect theory is wrong, is, that the assumption that air fom upper and lower side will NEVER EVER meet again: commons.wikimedia.org/wiki/File:Karman_trefftz.gif I also would rather call it "accelerating air downwards instead of "turning" it. but nice video tho.
1:56 Correct, The wing is indeed turning the airflow downward. But there is also a pressure difference between the top and bottom of the wing! The lift force is literally equal to the average pressure difference between. The bottom and top of the wing times the surface area of the wing! And it is in fact the pressure gradient formed arround the wing that turns the airflow downward! Please correct your mistake!
First off I enjoyed your visual representation of how flow goes around the airfoil. You were mentioning Newton's third law when you said the airfoil turns the fluid flow downward applying equal and opposite forces lifting the airfoil, which is a part of how lift works. However when flow is curved there is a pressure gradient. This gradient forms a pressure and velocity field around the airfoil that affects a wide area in the fluid. As you said the pressure above is lower and the velocity is faster, while below the pressure is high and the velocity is low. The pressure and velocity affect each other simultaneously and the pressure difference drives the lift force as well. Also the Coanda effect only applies to jet flow and not for ordinary flow airfoils are usually in, so it is not a factor in lift.
As an aerospace engineer, this is a useful explanation for the average person to understand what creates lift, but we can’t totally disregard the fact that there is a pressure difference. I disagree with you when you say that a pressure difference is not what creates lift. In fact, there are many times where we can actually compute the lift force (or lift coefficient) on an airfoil WITH the pressure distribution and using calculus to integrate the difference in pressure acting on the top and bottom. At the end end of the day, there are two natural sources that cause for all aerodynamic forces and they are none other than the pressure distribution and the viscous shear stress. I’m not saying you’re wrong for thinking this (although I am saying you’re wrong for saying the pressure theory is wrong), but I think they go hand in hand. You can’t have one without the other. To say one idea is more correct than the other would be ignorance. I appreciate the video though and it helped me deepen my understanding a bit because I had never heard it explained this way. Thanks! 👍🏼
I hate to argue with an aerospace engineer, and I'm also 4 years late to this party, but I do have some questions. First, take a situation where you are in a moving car and you put your hand out of the window. Where there is no AoA, there is no lift generated. There is some drag, but it's manageable. However, if you turn your hand into a slightly positive AoA, you simultaneously feel a substantial increase in drag and your hand flies upwards. If you're not prepared, it basically goes up and back as both drag and lift are generated. When I started considering lift, it seemed easy. I thought - "this has got to be because of the equal and opposite reaction of dumping flowing air downward, changing its direction by providing a force that changes its vector". Newton's 3rd law - the same force that your hand is applying to the airflow to change its direction (created by the car's engine and your muscles pushing your hand against the pressure of the airflow to overcome drag) is also applied via to your hand, causing it to want to go up. The effect is so strong and so instantaneous that I found it extremely difficult to believe that it can be caused by the development of a pressure differential above and below the "wing" of your hand. But that feeling is not scientific in nature. After all, I caution myself that an explosive decompression event causes substantial forces very quickly. And the moment you unscrew a bottle which contained a carbonated drink, the top wants to fly off as the pressure tries to equalise with the room you're in. It doesn't have to "build"... so pressure differentials can create forces quickly. So I guess the challenge in answering this question to everyone's satisfaction is that it seems hard to imagine circumstances where you can impart downward motion to air meeting an aerofoil where you're not also creating a pressure differential below and above the wing, so it feels like the Newtonian approach and one based on pressure differences seem to "come up with the same answer" and everyone is shouting about which one is right, based on the answer that feels better to them. I don't know how to bridge the gap and I don't have enough scientific understanding to try and do so - I fly planes rather than design them. But I do know that explanations of lift forces have been plagued by bad and poorly explained answers for a long, long time - it's remarkable to me that we can go to the moon, explore the wreck of the Titanic, do AI facial recognition, connect all the computers around the world, search deep space for answers to whether we're alone and image amazing parts of the universe the naked eye can't see.. to say nothing of achieving net positive energy fusion reaction. Yet a single unified and sensible theory of aerodynamic lift continues to be a challenge to describe in a way that people accept and understand. (and yes, everyone thinks their answer is right - I am not inviting more of that, just saying that there do still seem to be challenges in describing the lift forces). However, I found this quote useful, from good old Wikipedia... "A serious flaw common to all the Bernoulli-based explanations is that they imply that a speed difference can arise from causes other than a pressure difference, and that the speed difference then leads to a pressure difference, by Bernoulli's principle. This implied one-way causation is a misconception. The real relationship between pressure and flow speed is a mutual interaction." Yes. That feels right. So I think we are saying that when the air flows around (meets) the wing, all kinds of pressure differentials are created in the local atmosphere of the wing, the net result of which is upward lift. The laws of conservation still apply (it's not an either / or) because the net overall force lifting the wing is equal to, and opposite, the net overall force exerted downward on the rest of the localised atmosphere. It's just that the net overall forces are created by / are a symptom of the pressure differential.
@@cjad100 Woah, I barely remember even making this comment haha! It’s been a while so I had to rewatch the video. The main problem with the video is that he is marrying the “equal transit time” (an incorrect theory) with Bernoulli’s principle and dismisses the pressure difference idea because the equal transit theory is wrong. Newton’s law can be an explanation for how lift is created. Bernoulli’s principle and Newton’s laws suffice to explain what creates lift. But at the end of the day, you are absolutely correct. We actually do not fundamentally understand why there is pressure difference. We know the pressure decreases on the top of the wing and the pressure increases on the bottom, due to a lower velocity. However, we cannot answer the question of “Does the pressure decrease because the flow increases, or does the flow increase because the pressure decreases?” It’s basically the chicken or the egg debate.
You missed a step by saying the turning of the flow is what causes lift, turning the flow creates regions of high and low pressure simply due to the flow being directed away from it's "intended/original" path. These differences in pressure is what creates the Lift force, or more specifically: the surface integral of all the vectors normal to the surface multiplied by their associated pressure value over the entire surface area of the body (airfoil in our case). Creates a resultant force, of which the Y component is LIFT and the x component is DRAG. What this means in practice is that there are some vectors pointing upwards(ish) above the airfoil which are "sucking" it up into the rest of the atmospheric pressure field, and some areas below where it is being "pushed" upwards away from the atmospheric pressure field. (The front of the airfoil actually tends to be pushed downwards in the majority of cambered airfoils, due to the region of high pressure at the leading edge) For anyone who's actually read this I'll assume you know at least a little about aerodynamics, so if I've made a mistake, feel free to correct me, I am only a 3rd year student lol.
His explanation was simple and made for the average RU-vidr. Who knows nothing about lift, drag, and much more. Not good to give TMI to people that just want the basics. Notice how he didn't get into ailerons and about nine other basic things I believe not to confuse people.
THANK YOU for confirming my belief that Bernoulli is BS in terms of its overall impact on lift. Sure there is some, but that's NOT the major source of the lift! BTW, there are a lot of folks saying the lift for DRONES comes from Bernoulli's Principle...even though the propeller blades are virtually flat. I point them to ceiling fans and ask them to explain THEM! LOL. Anyways, thanks for the clear and no BS video.
Mmmmmm........Sort of correct..... but the statement that air HAS to travel faster over the top of the wing so it meets at the trailing edge is wrong. There are lots of videos from wind tunnels where you can see that sometimes the airflow on top of the wing travels that fast that in gets to the trailing edge before its lower surface counterpart. Why is this ???? Think of Air as a multilayer fluid. The air layers close to the top of the wing are being compressed due to it passing over the curve of the upper surface, and this compression causes the layers to "squash" together and form a Venturi. Thats why the airflow speeds up on the upper, curved surface and therefore a resultant decrease in pressure. Rest of your presentation is brill .....
But if the air below the wing is being pushed downward, wouldn’t it get squashed with the air below and create the same effect as the air above the wing?
Amazing how people are not satisfied with a simple answer to a complicated situation there are many factors involved in flight I think you did a great job and just pulling up a couple of basics unfortunately there are those who have more questions instead of bashing you they should do research on the internet that is in their hands if they really want to know
Indulge an old fitter please. When I was a kid more than six five years ago, I built a flew model aircraft with completely flat wings. as long as these were angled upwards against the line of thrust, the models achieved lift. I figured it was like a boats rudder. Barry
It's all Newton's Third Law - the mass of air pushed down offsets the mass of the aircraft. This is so obvious when you think about a rotary wing aircraft (ie. helicopter). It's very windy underneath there. The airfoil is only important for maximising air deflection while minimising drag. It's not the upper surface separating that CAUSES the lift to fail, but the increase in DRAG which decreases the forward movement, thus impacting the air deflected downwards (ie. lift).
Thx for the vid! But I still don't get it why the upper stream just speeds up by itself oO can it be that it travels with its normal speed whereas the lower stream is being slowed by the curvature of the wing?
There are no airstreams in flight. Air is mostly stationary, and the wing is moving through it, forcing the airmolecules apart in a mostly vertical movement pattern.
At time 1:58 you state: "it's NOT a pressure difference that creates lift". This statement is WRONG. It IS the pressure difference that creates the largest part of a wing's lift. Of course the downward accelleration of the air mass (deflection of the airstream that passes around the wing in a downward direction) is also part of the lift that is generated by the wing. But if your "theory" of the wing that is not related to a pressure differential between the upper side and the lower side of the wing would be correct, you could minimize the wing area by having only very minimal chord length - a profile that only deflects the air downward. But the force of the lift is clearly the mean pressure differential over the entire wing area multiplied by the wing area. If the lift would not be caused by the pressure differential then increasing the wing area would not increase lift as long as chamber (downward bending of airstream) would not be increased. But any wind tunnel experiment will show you that a longer wing chord with the same chamber will result in a greater lift. I agree with you that there are many wrong theories about how a wing generates lift - but it seems that your video is also falling into that category.
Pressure differential and downward displacement of air are in a causative relationship and not separable. A larger wing area will displace more airover a given time, and the effectiveness of wing length and width on lift varies with lreasure, airspeed and air viscosity. Air on earth is generally not very viscous, and usual airspeeds are below the speed of sound, so while the pressure wave created will dissipate relatively quickly, the air will displace faster than the wing moves through it. At speeds above the sound barrier you get the wing cutting through the medium faster than it can displace, and so a wider wing, allowing for a longer contact time becomes more drag efficient, whilst in a higher viscosity flud, such as say water, a much thinner foil suffices to produce similar lift.
To delay a stall you can also use vortex generators on top surface of wing. Vortices tend to "stick" to the wing better than regular air, so the separation occurs at higher AoA.
@@Wrtvrxgvcf55 The F-18 uses a different principle. It uses vortices, which can be created at high angles of attack by wings with more than 45 degrees of sweep. Vortices are not the same as generic turbulent flow. They are their own phenomena. This is also used by most true delta winged aircraft.
@@HarwinSingh If I remember correctly, stall strips are intended for the opposite purpose - to initiate flow separation earlier. You place them on the root of the wing and you get pitch down instead of a spin when the aircraft is stalled.
Thanks I needed this. I didn't even know what aerofoils were before this and now I understand Bernoulli's principle over it. That's some big brain time
Fun Video!! Thanks for posting! Question?.....I know nothing about nothing (no degree, not in the field), but in general it seems like Bernoulli is more accurate. For someone who knows maybe explain for me....if the opposite of Bernoulli is true and the air going over the wing is hitting the air going under the wind and firing downward....isn't ALL of that taking place AFTER the wing has left that pocket of air? If so how can that downward collision have effect on the wing that is front of it? Isn't it Bernoulli's pressure difference that form the "clouds" we sometime see around wings?
This "correct" explanation was given in 1944 (possibly earlier?) by Wolfgang Langewiesche in his book "Stick and Rudder" and rubbished (at the time). It is now known that BOTH principles are involved, it's just that the Bernoulli principle was incorrect regarding the speed at which air travels over the top of the airfoil..
Bernoulli Principle is not incorrect. Bernoulli Principle says nothing about the velocity profile of two adjacent streamlines, it strictly deals with flow along a single streamline.
Stop talking about "air flowing over a wing", Air flows over a wing only in a wind tunnel when the wing is stationary. In real aircraft the air does not flow much horizontally but it is ACCELERATED vertically DOWNWARDS ( eventually) .This downwards acceleration originates for different reasons above and below the wing. In fact if one has to be accurate, the air mass particles around the wing move forwards a little . I shall let the readers deduce why that happens. . As the wing moves forwards, it SHAVES and accelerate the mass of air downwards. The SHAVING starts at the leading edge and below the wing by compressing the viscous fluid to ACCELERATE IT DOWN, Above the wing the SHAVING of the mass of air is done by first accelerating the air fluid upwards above the leading edge and then causing the tension in the fluid at a later stage to the trailing edge . The CONTINUOUS downwards ACCELERATION of the masses of air above and below the wing results in an opposite reaction to lift the wing. It is these acceleration at various locations that cause the Bernoulli, the Newton and the Coanda effect, and it is thee fluid accelerations around bird wings, fish flukes, and all the flying surfaces that exist in insects aircraft and helicopters and rockets and missiles, .
Had balsa winged wind-up planes as a kid. Wings as flat as a credit card and they flew quite nicely. Seen plenty of planar, flat winged foam RC planes here on the site, both screamin at world record top speed and gliding leisurely at slow speed. lol
Lift is action and reaction. The action is the deflection of air molecules downwards, the reaction is the wing being pushed upwards. Pressure differences are secondary. If there is no downflow of air from the wing, there is no lift. R
Burnoulli never stated anything about "airflow over a wing".... he made his findings public in his book published in 1738.....more than a century before there were any wings.
I'm confused. This video tells us that it's not the pressure difference, but the deflected air that creates the lift (according to Newton's principle of action and reaction, I'd assume). Another video I've just watched tells me that it is mainly the pressure difference according to Bernoulli that creates lift, while the deflected air just creates a small percentage of the lift. Whitch is it? Or is that question still the object of brawls between physicists?
As often happens, the same phisical phenomena can be explained under differect aspects, all true. For example, I could explain that a pendulum works by the force of gravity slowing down and accelerating the ball back and forth, while you could explain it saying that it trades potential energy for kinetic energy ciclically. Both explanation would be valid. While we all agree that the "same time" explanation is wrong, lift can indeed be explained (and calculated) by the pressure differential between lower and upper faces of the wing, which in turn are caused by profile shape and incidence. At the same time, you can also explain lift by saying that the wing pushes air downwards, creating a force upwards. Both are true at the same time.
The way l see it is aircraft extend leading edge flaps on their wings at takeoff which have the effect of thickening them. A thick wing generates more lift. At V1 the air can't get out of the way quickly enough and gets bounced upwards but immediately comes down again with the weight of the atmosphere pushing down on it. This has the effect of creating a vacuum above the wing otherwise known as a shock wave. But vacuums have to go where vacuums belong, to the top of the atmosphere (equilibrium law). The atmosphere, all trillions of tons of it, detect a vacuum and push it upwards. But practically it's only the air around the plane which does the job. The A380 weighs 560 tons app. at take-off and flies! At higher speeds say north of 400 knots or so the shock wave has difficulty keeping up with the plane and tends to drag back on it. The engineers get around this by angling the wing back into the shock wave reducing its drag effect. This 'sweep' angle gives an idea of the operational speed of the plane. The bang one hears when the plane breaks the sound barrier is the shock wave, no longer able to keep up with the plane, collapsing explosively. I've seen these shock waves above planes' wings landing at airports as condensation formed along them. In fact, you could say aircraft fly by using the earth's gravity, reversing its effect of a downward force to one of lift. Aircraft fly by gravity.
To me, the explanation concerning Newton’s 3rd law always seemed more intuitive and easier to understand than Bernoulli’s. Especially observing how sharply the trailing edge of an airfoil tapers off like that. But in my simpleton brain, I just conclude that it’s a combination of the two and leave it there. I’m no engineer.
Good start by debunking one of the common myths about lift generation. Unfortunately I think too much was thrown out with that theory. Pressure does indeed play a part in lift generation, but it's only part of the larger puzzle. To say that the pressure difference doesn't create lift is incorrect. The Coanda Effect also only applies to fluid jet flows, which is not descriptive of a fluid flowing over an airfoil. The turning of the airflow, or momentum, theory is definitely one of the ways that lift is generated. Circulation is a more complex concept, but including it would have resulted in a much more complete explanation of what causes lift.
Some fighter aircraft have a symmetric wing shape, same on top and on the bottom. They can fly upright or upside-down. Their wing is an inclined plain to the airflow that produces lift. The angle of attack is very critical. For the traditional wing shape, the angle of attack is much less critical. QED
Well the actual force of the lift is created by the pressure difference between the upper and lower side of the wing. The air directed downwards is basically just the result of that. Most simply explained by newtons first law that an action must have an equal oppsite reaction. We push the plane up so the air must get pushed down as a result.
Seeking causality makes everything complicated. Ultimately, lift requires a pressure difference and requires a change in momentum, and it's hard to separate those.
@@AmbientMorality Pressure preempts movement. Its a state that begets a force, which in turn begets movement. Confusing the direction of this causal relationship is probably because the bernaulli principle is also sometimes involved, in which a change in fluid velocity begets a change in its pressure. That is not the mechamism, however, by which air compressed by a wing at high AoA gains its momentum.
@@AmbientMorality Correct. Horizontal movement of the aerofoil relative to the medium compresses the medium (or indeed vica versa), which in turn creates the vertical air movement. Neither movement however acts as a vertical force on the wing.
That depends on many factors. The size and weight of the aeroplane whether it's a prop or jet whether it's made for one passenger or 300 this is something that is not a one word answer
An oblique hydrofoil dragged slowly through liquid helium will not generate any transverse force. Fluid flows round the trailing edge of the aerofoil and doubles back towards the rear stagnation point. As the hydrofoil speeds up, we are putting in enough energy to warm up the helium and destroy superfluidity. Then all the vorticity is concentrated in boundary layers around the hydrofoil. As the fluid warms up, a thickening boundary layer is unable to negotiate the trailing edge and so vorticity is dumped as a starting vortex in the flow. This establishes a Kutta condition at the trailing edge, and there is residual circulation around the hydrofoil opposite in sense to the starting vortex, which generates a transverse force. This can be explained in terms of Bernoulli's Principle as well once things get going, but the formation of the starting vortex is the thing to look at. It won't happen without viscosity.
The lift generated by a wing is due to the pressure difference between the upper and lower surface. The question is WHY is this pressure difference created. Physical testing shows that the speed of the air over the top surface IS faster than the flow over the bottom surface. There are mathamatical formulas for calulating lift that are accurate. Aircraft designers use them! The amount of lift depends on the density of the air, the coefficient of lift (determined by the cross section shape of the airfoil), the angle of attack of the airfoil, the area of the wing and the speed of the wing through the air squared. There are various sections that have been tested, the NACA sections and the coefficient of lift at various angles of attack and can been looked up for each section. The "Downwash" theory sound convincing but it forgets the "Upwash" that occurrs in front of the wing as the air rises ahead of the wing to enter the low pressure area above the wing. The "Creation of lift" is obviously far more complicated than a simple bernoulli or downward deflection explanation. The fact is lift IS created by a combination of the factors listed above and explanation involve deflection of air and the speeding up of air over the top and slowing of the air on the bottom. The pressure differences have been maesured and the force from the lower pressure on top is greater than the force from the increased pressure on the bottom. So the statement that lift is not reliant on the pressure differences above and below the wing is clearly NOT correxct.
Try throwing a frsibee upside down. Then try throwing a flat disk of plastic or wood and see if it flies like a frisbee. A frisbee has a curved upper surface and that is what makes wings fly.
3:45 So if the airflow on the top of the wing stops there will be no lift generated as you say. But earlier you said that top of the wing airflow was not what generated lift. So I am confused now!
It always amuses me when I think of mans earliest attepmts to fly, becuase they didn't study the birds in any great depth, particularly wing shape and even after they discovered that they still didn't consider how a birds head and beak are shaped so that it reduces drag in flight and how they tuck their legs under thier bellies. Admittedly, they didn't undestand the effects of drag and air flow etc in the beginning but they still should of followed the birds example in design because they are natural flying creatures and so they are designed for optimal flight even if you don't understand how.
Coanda effect, Bernoulli's principle and newton's laws of motion all work together to produce lift. This simple explanation given here is flawed in my opinion.
Here's a link to a NASA article about why this explanation is wrong. www.grc.nasa.gov/www/k-12/airplane/wrong1.html If you do not trust clicking the attached link just google search "can a symmetric airfoil produce lift" and the first option should be the article I am referencing. An excellent point in the article is that if the air passing over the top wings is what creates the lift, then a plane flying inverted would be pulled straight to the ground. But planes can fly inverted, because lift is created by pushing air down from the angle of the wing.
some much half understood information .Equal transit is not a consequence of Bernoulli law . Bernoulli does not in any way contradict newtons laws . low speed aircraft in a non turbulent air flow obey both newton and Bernoulli principles
I never took physics and still don't understand all these "principles" and "theories." All I grasp is high pressure under the wings, lower pressure on top. No idea why or how.
Why would a plane stall just because the air doesn't "connect" at the rear? There's is the equivalent displacement of air which would result in consequent lift.
"The air that goes above the wing has to travel further distance therefore it moves faster" This is total rubbish. First of all, it doesn't HAVE TO move faster. There's no police that DEMANDS the air ABOVE the wing to arrive at the back of the wing at the same time as the air below the wing. Second. if just longer path ABOVE the wing was causing the air to move faster, why not making the path arbitrary longer. The longer the path, the quicker the air will have to go, right? So why not making it EVEN MORE longer, like INSANELY longer. These are the two obvious arguments that the proponents of "air above the wing has to move faster" are intentionally ignoring
A wing, flat on the bottom, curved on the top, with the bottom parallel to the airflow, lifts some. There is no angle of attack in such a case. (In that case it lifts because of Bernoulis principle). But that does not cause enough lift to support the plane. It makes the airplane more efficient though. The vast, vast majority of lift is actually caused by AoA. Many, many airplane wings are symmetrical, i.e. they are curved exactly the same on the top and bottom. So ....??? EVERY airplane you see flying has serious AoA. Look at how airplanes are built. The wing is always at and angle to the body. It has been traditional thru the 20th century to proclaim that the difference in curve of the top and bottom causes the lift. Even the airforce taught that. They should have been ashamed of themselves and many told them so.
Other than pressure difference and AoA, i never realized that the airflow above the wing goes down to generate lift! great vid to understand the basics of the wings.
+Thanatos if lift was explained only by reaction forces from the deflection of incoming air, then only planes with a thrust-to-weight ratio above 1.0 could take off. Also, once the upper surface flow detaches from the wing the airfoil becomes stalled. Which is why fighter jets implement Leading Edge Root Extensions (LERX), slats, chines, etc to preserve the upper flow of air during high AoA maneuvers. History of aircraft design itself debunks the theory that airfoils only generate lift through deflection. Your hand doesn't try to fly up in a moving car because it's not a well designed airfoil. If you designed an airfoil just the right size for your hand and which could generate lift at low speeds, you'd feel it pull up when outside a car window.
I'm sure Thanatos is an aerodynamics expert, and all these other people who build and design planes are just cretins compared to his massive intellect. He called it, you guys. We're done here. From now on, all planes will be designed with giant hands on the sides.
No it's because the air going over the top is deflected up and thus creates a pull on the front of the wing. Additionally the air going below the wing pushes because of the low angle of deflection. It has nothing to do with air speeding up, the air isn't joined at the hip and the longer distance the air has to travel is a coincidence and is a miss applied term..
No Conda effect is involved in flow curvature or wing attachemnt, . Coanda installed a jet engine at the fusiform end of a fuselage and noticed the jetstream curved toward the fuselage. The air in between the jet and the fuselage is in fact entrapped more quickly than other air can replace it, so there is a local decrease of pressure in that "triangle", The higher pressure around the jetstream push the stream toward the area at lower pressure.Coanda effect describes the interaction of a static fluid sourrounding a jetstream, static fuid that is entrapped in the stream by viscosity and turbolence. It does'nt have anything to do with flow curvature or attachement over a wing. The explanations that uses Coanda effect to describe the flow curvature of a water jetstream around a curve surface are wrong. The wing airflow works the way we see because it flows as a continuous material and because every air particle in a streamline, forced to change direction by a solid object , must develop an acceleration toward the centre of curvature. That is the reason for the attachement, and the curvature, the centripetal force that ovverride the centrifugal. See Holger Babinsky, professor of fluidodinamic at Cambridge or Doug McLean (Boeing) Understanding Aerodinamics. Or, simply, F=ma. No viscous forces are involved in wing attachement, neither can explain flow curvature. Flow curvature and wing attachement works in the same way with or without viscous shear forces. To have lift, the first necessary condition is flow curvature by a solid object, and the second is to have different speed over the two wing surfaces, the upper and the lower. See also the NASA pages on aerodinamic.
@@AmbientMorality a change in flow speed requires a pressure difference. We can say the same thing about a change in flow direction: The only thing that can cause a change in the velocity vector is a pressure gradient. Thus for the normal acceleration to happen, the normal pressure gradient must already be there. And then if we incorrectly limit ourselves to one-way causation, we leave unanswered the question of what causes the pressure gradient. A correct explanation must acknowledge circular causation between the pressure and velocity fields.(McLean, uderstanfing aerodinamycs)
@@AmbientMorality it is depending by the solid object that change the flow direction. In a steady flow , if the object is a wing, a flat panel moving ahead with an angle of attack is a good basic wing, indeed the flow curvature brings different speeds above and below (the so called circulation) and this brings the pressure conditions along the streamlines that at its own time generates a new set of different speeds station by station. Speed and pressure changes sustain each other in a circular reciprocal relationships which we can look at with the bernoulli principle along each stremline. Ia a particle accelerates in a direction along a streamline pushed by pressure, the increased speed brings lower local pressure. Conservation of energy. The change in direction , the curvature, is also due to pressure and the acceleration across the streamlines is normal toward the centre of curvature. The object (flat panel with an angle of attack) moving ahead pushes air in front of it ad this does create the diffuse clouds of pressure gradients that makes air accelerate from higher to lower pressure zones, giving raise to circulation. Once circulation is set, we have lift and a newer condition of diffuse pressure gradients is created arond the wing. Nothing fancy as the so called starting vortex is required to activate circulation. That vortex exist but is a consequence of circulation and lift
nevertheless the theory in this video doesn't explain how the paper planes fly (they have flat wings) or can an aircraft fly upside-down that can be seen in airshows or air to air combats. it seems to me that the lift cannot be explained with one theory, there are other aspects to it
Motion is due to wind deflection to the stern (sails) / to down (wings). This ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-jhem8Z9ujPE.html shows that close-hauled motion with no wind on leeward side is possible.
This explanation has some issues. Bernoulli's principle and Newton's third law are both at work. Equal transit (which is separate from Bernoulli's principle) has been disproven, but airflow over the top does move faster and creates a lower pressure area above the airfoil while the air traveling beneath, moves slower creating a higher pressure area generating some lift.
I fully agree with what's happening here, but I don't understand a stall. A stall happens when the air over the top of the wing separates from the wing itself, but how does this cause a stall if the the air moving over the wing has no relevance to the lift produced. Can anyone help? I'm happy to explain further if that wasn't enough, thanks.
Lift is created by pushing air down, and thus the air pushing back upwards against you. The explanation in the video is incorrect. If the explanation in the video was correct, and inverted plane could not fly and would just fall straight out of the sky. A stall is induced when the angle of attack is too great for the speed of the airplane. For example a aircraft that is powerful enough to climb at a 90 upward angle to the earth, will not stall until it reaches the point that the air has become too thin for the motor/engine to produce more thrust than the weight of the aircraft. That is basically how a helicopter works. So if you have a large commercial jet fully loaded, it is extremely heavy, even with big engines, it is not a high performance aircraft, and it can not climb at as steep of an angle of attack as a small, light, fast plane. Think of it like a car driving up a hill, a sports car can drive up a really steep hill because its engine is powerful, and the car is lightweight, so it can drive up the hill with ease. But if a heavy vehicle with a less powerful engine tries, the hill may be too steep, and the vehicle will either stop, or roll/slide back down the hill. So for every aircraft there is a speed+weight+wing area+altitude combination that will decide the limit of the angle of attack that it can continue flying level, or climbing. Essentially if you increase the angle of attack too much, the bottom of the wing begins to face forward, and air is just running into the bottom of the wing. So now your wing is just pushing air forward instead of down. This will create way too much drag, no lift, and slow the aircraft. I know this explanation is not very good or understandable but I hope it helps.
In a stall its because the push up under the wing, not the lift thats on top , becomes more and more of a push back. Lift is on the top, like a vacuum, and when air is no longer going over the top there is no vacuum..all you have is push back by the air underneath.
@@Rickie53 An aircraft stall and a wing stall are not the same. An aircraft can still fly with stalled wings, which specifically refers to the cessation of laminar flow of air around the wing.
While it is true that the longer path theory is incorrect, it is also incorrect to assume that the pressure difference across the wing has nothing to do with the creation of lift. Circulation plays a role in creating lift, but there are other factors at play as well.
I think I’m right in saying drag is a good thing caused by flaps and not a bad thing, as drag is the opposing force to thrust therefore the flaps are keeping the plane slow whilst still maintaining lift.
Why does the stall configuration cause the aircraft to fall? You’d think having really low pressure on top and same amount of high pressure on the bottom would be better?
In a stall air stops flowing smoothly over the top surface - higher angles of attack lead to larger pressure gradients that try to force airflow to separate. The airflow after that separation point is recirculating, low velocity air so it’s no longer very low pressure
As a flying aerobatics pilot I have 2 questions: 1) I fly Extra 300 and Extra 330. How the hell am I flying if these planes have... symmetrical airfoils? 2) I also fly RV-7. How am I able to fly inverted over runway and not smash into it?
hey doofer, I'm a huge fan, yes, the equal transit theory is totally incorrect, but you've missed a few things out here 1. the camber on an airfoil produces lift mainly by the curvature of the streamline and the euler equation, When a streamline is curved, the air loses its pressure 2. Another thing to take into account is streamtubes, as the air meets the cambered portion of the airfoil the "Streamtubes" are slightly squished, following the venturi theorum Yes, Wings do indeed create lift by downwash too although Edit: Also the downwash eventually levels out due to its inertia
The equal transit time hypothesis does not explain lift. It says that a pressure differential causes lift. However a pressure differential does not cause lift. It is lift. "A pressure differential causes lift"? Makes no sence to begin with.
