6:05 I understand your explanation of the what creates the lift force (i.e. a pressure difference due to velocity difference, according to Bernoulli's Principle) but then... 6:30 I don't see why the fluid flow being "pinched" above the leading edge of the wing results in LOWER density/pressure? Instead, I'd expect this constriction of air molecules to cause HIGHER pressure? 6:42 I also don't see the connection with "Conservation of Mass" which you state, but don't explain. 7:08 Again, you state what the flow would look like without circulation but you don't explain why.
Conservation of mass means that for the same amount of fluid to flow through the constricted section, it's velocity must increase. And Bernoulli's equation tells us that an increase in velocity is accompanied by a reduction in pressure (conservation of energy).
@@TheEfficientEngineer Thanks for replying with an explanation, which helped me understand how Conservation of Mass applies. I also watched another video explaining how wings create lift (by the channel Sixty Symbols) which I found helpful. How circulation is relevant in this case remains a mystery...
@@GonzoTehGreat It's best to think of the air as a fluid. Also whatever the reason, it is the difference in pressure between the top and bottom of the wing that does most of the work. The various reasons, Bernoulli, Coanda or Newton, will have varying input depending on speed and angle of attack. Flaps only work at low speeds. At cruising speed they just add drag. Same with angle of attack. It took until computers became powerful enough to do the calculations for some of this to be unravelled, so its no wonder that it is still being argued about! Edited for spelling.
As a fluid flows around the airfoil, it creates three different kinds of stresses: shear stresses, pressure stresses, and engineering student studying stresses.
Nobody understands why. That’s why it’s called the theory of lift. Even super computers only get close to quantifying it. We only know what conditions need to be satisfied to create it, not the why.
@@Bartonovich52 Oh, I am glad to hear that! I thought it might be a shortage of understanding on my part. So, in essence, we have a description or the ‘what’ of this phenomenon, not the ‘how’ or ‘why.’ Thanks
I've been studying Aeronautical engineering for the last 7 years and I've been playing with some Aerodynamics projects for the last 2 years and I have never found a better explanation of Lift in the entire Internet, amazing job, clean and intuitive speech, wonderful animations and a solid theoretical background. My biggest congratulations for you man! You're Top engineering content creator, keep going!
@@jackz1620 Coanda is just a small part that allows the boundary layer not to detach from the airfoil and produces a bit percentage of the lift with the downwash but lift is based mainly in pressure differencial by bernouilli effect
@@jackz1620 @Ignacio Trueba Coanda does not happen above an airfoil. It is a jet or sheet of air, FORCED into an otherwise still air environment. There is continual entrainment. There is neither of those above an airfoil. . Using the "Bernoulli Effect" as commonly done is an equally incorrect way of explaining lift. *Understanding Lift Correctly:* rxesywwbdscllwpn.quora.com/
2 semesters of advanced aerodynamics and a 4 year aviation degree i learned about lift. This 15 minute video simplified such a complex subject in a way that is easily understood! Phenomenal video... thank you!
Would you comment, or LIKE if appropriate, this short piece of the story for the layman? My 11 yo granddaughter did all the editing. *th-cam.com/video/3MSqbnbKDmM/w-d-xo.html*
@@baloog8 yeah, I agree, I started to learn fluid mechanical to understand exactly how this aerodynamics works, because I learned solid mechanical approach, so it's a little different when you can think a solid as fluid with an extremely high viscosity.
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
Guys that you are making these videos...I am incredibly grateful for your work. I am doing my MSc on Advanced Mechanical Engineering in a great university of UK. Literally, the help that you have provided me is out of this world. I am telling that with all the reality that possesses me. A combination of studies and your videos on Engineering Field have launched my knowledge on many fields. Thank you so so much. Keep working! You are changing the process of studying and unfold the engineering complexity on many fields. Good job!!
Dear The Efficient Engineer, as an Aeronautical Engineer who used to teach Aerodynamics at the uni, and did so proudly, and usually get upset with the poor or directly wrong explanations usually found in youtube, I want to tell you one thing: *CONGRATULATIONS* For a video that scratches the surface and is intended to be accessible to the general public, this is *EXCELLENT*. Yes, concepts were simplified, but all the explanations were CORRECT (unlike most of the videos on the subject). Every time while watching this video that I said "uh-oh" you quickly eliminated any concern that was starting to appear in my head. "Engineers still debate how lift is generated" That is much better than the usual "We still don't fully understand how lift is generated" "Bernoulli and Newton" presented NOT as two contributions to lift, but as 2 ways to approach the explanation of the same phenomena. "Pressure on the top is lower because the air flows faster than on the bottom" Uh-oh, I thought, here comes "equal transit times". Nope. It was so satisfying to see those fluid parcels on the top arrive to the trailing edge before the lines on the bottom. And also, I thought, you were committing the same mistake than many by saying that the lower pressure was caused by the faster speed, when in fact we could also say the faster speed is caused by acceleration that can only be caused by the air parcels running along a path of a negative pressure gradient (or, in another words, the lower pressure causes the faster speed). But then you explained how the three things affect each other and act concurrently, not one causing the other. You were one (or several) steps ahead of me all the time and you won on every thing that I forecasted you were going to say wrong. I am so happy for having been wrong every single time I thought that. It was simply *BRILLIANT*.
@adb012 I'd like your further comments. I have an ulterior motive... As an engineer, I appreciate this is complex and, therefore language is very important. Since I'm critical of words, I'll be very careful with mine... . Example: . What gets me is that while he carefully states Bernoulli's Principle well, at 6:15 he actually says "the increase in air velocity above the airfoil creates an area of lower pressure." [above wing] . A velocity increase is acceleration. It would have been better had he said "the *increased* velocity" or just "speed" it would be accurate. . It isn't the acceleration that causes the transverse gradient, but rather the speed along the curve. . Yes, of course there are tangential speed changes as well along that curved flow, but the transverse gradient is from the air's natural tendency to continue straight. It is the "stretching/swinging/flinging away from the curve's center - what some people consider the inertial force". I think it should be called the centrifugal effect (not force). This is the idea that you feel pulled outward traveling around a curve. Previously called 'centrifugal' force. . Here, we actually do have the case where speed (in the curved flow) actually can be said to "cause" a pressure change. . It causes the *transverse* gradient rather than the more common longitudinal (proverse or adverse) gradient that changes speed. I say that is an unfortunate choice of words in a very technical subject where there are so many misconceptions being spread all the time by so many well meaning amateur scientists. ... .. .. So... My motive is for your comments on this short, simplified video explanation of what I just mentioned. Because my 11 yo granddaughter did the video editing, I would appreciate if you would consider a LIKEit if you feel it appropriate. You should also check my TH-cam About. I'd prefer your comment under the video as threads can get long. *th-cam.com/video/3MSqbnbKDmM/w-d-xo.html* . Regards
@@Observ45er ... I am going to reply to you here since you posted this comment here, and then I am going to copy this reply in your video. The effect that you describe is correct. A parcel of air has to obey Newton's 2nd law (and the others too, of course) that says that F=m*a. The parcel of air has a mass (even if it is a differential mass) so, to be subject to an acceleration, it needs to be subject to a net force (even if it is a differential force). So if the parcel is accelerated, then there must be net force acting on it and, if we neglect viscous drag (say that we are outside the boundary layer), then we are left with pressure only, so an accelerated parcel of air means a pressure gradient. This applies both in the tangential and normal (centripetal) directions. In the tangential direction, the acceleration causes a change in the magnitude of the speed vector of the parcel of air (i.e. the parcel of air will increase or decrease the speed), while in the normal direction it causes a change in the direction of the speed vector. Now, you focus exclusively in the normal direction. Again, that effect exists and your explanation of the effect itself is correct, except that it can't by itself explain the cause of lift. I will start by admitting that I don't remember everything I learnt (and used to teach) about lift. Bute here you have several points to consider: - Why does a flat airfoil (like a piece of balsa board) generate lift, and no only that, but it generates as much lift as any other airfoil at the same incremental angle of attack above the zero-lift angle of attack? (as long as it doesn't stall, which the balsa board will do at a lower angle of attack than a conventional airfoil) - How does a conventional asymmetrical airfoil manage to produce lift when flying upside-down? And why does that hold true even when it is a thin cambered airfoil (one where what would be the upper surface is convex and the lower surface is concave, except that it is upside down so you have the concave side up and the convex side down). - Consider the following 2D Venturi tube. You have 2 lateral walls that parallel are very far away to each other (say 200 meters away). You have a bottom and a top that start parallel to each other with an internal height of 1 meter. Air flows along that tube of rectangular section (1m x 200 m). At some point, the starts a straight ramp up at a shallow angle, at the same point, the top also starts a down slope of the same shallow angle. The lateral walls remain at constant distance to each other. In this way, the section starts to constrict, from 1m x 200m, to 0.8m x 200m, to 0.6m x 200m and so on, in a constant and symmetrical ramp in the top and bottom. Due to continuity (conservation of mass), the flow will gradually accelerate along this upstream side of the venturi, and as it does so, the pressure will go down. Several meters down this double ramp, at the point where the top and bottom are 0.1m away, the flow will be moving 10 times faster and, BY Bernoulli (note I didn't seay BECAUSE of..., that was intentional), the pressure will be much much lower. So you have a constant and gradual decrease in pressure from the point where the constriction started down to this point, yet all the parcels of flow where moving in straight lines. Conclusion? You can (and DO) have changes in pressure even if the flow is moving in a straight line. - I remember there was a "thin airfoils" approximation used to estimate how an airfoil would behave (lift vs angle of attack) that totally neglected the vertical acceleration of the flow, and it was quite accurate for airfoils up to 10 or 12% of thickness at cruise-like angles of attack. - This one is the most crucial one for me: Have you though why the flow NEEDS to curve and follow the airfoil? Typical answer to that question is "because if not it would leave a vacuum behind and that would pull the flow back to the airfoil". That is wrong. You could have a recirculating bubble, like you have at higher angles of attack in a stall. Saying ""the cause of the transverse pressure gradient is that the airflow turns" is more a "political position" that an accurate scientific statement. We could as well say that the cause why the airflow turns is that i flows through a transverse pressure gradient, and in a classical Newtonian view it would be more reasonable to say so: We typically say that a force causes an acceleration, not the other way around. Whether that classical Newtonian view is fair is a different question, I tend to think it is not, that force and acceleration are concurrent and 2 parts of the same phenomena, not one the cause of the other. Let me give you an example. You have a train taking a turn. The lateral normal force between the rails and the flange of the wheel provides the centripetal force that changes the train's direction. How doe the rail know to apply the exact force necessary for the train to keep that exact curve at that speed? The force causes the train to turn or the train turning causes the force? Well, in fluid dynamics it is like this, but worse. Everything is correlated, concurrent, and integrating with everything. You have a pressure field and a velocity field (and a viscos stress field too) and a vorticity field all "conspiring" together to create a solution that meet the 2 boundary conditions: The boundary of the airfoil shall not be penetrated and the flow will separate at the trailing edge. Saying that one thing causes the other is, in my opinion, not real. - Finally, at the end of the day conservation of momentum (or variation of momentum in the presence of a force) does apply. If the air is pushing the wing up, then the wing must be pushing the air down/ That means that the air has to bend its direction from say horizontal far away upstream of the wing to diagonal horizontal and down far away downstream. The turning that you described is PART of this phenomena, but not the that air changes direction long before it reaches the wing, keeps changing direction long after it already passed the wing, and also quite far away above and below the wing. Lift is truly a very complicated phenomena. Any simplistic explanation has to be either wrong or incomplete. Yours in correct but uncomplete.
@@adb012 .. For readability, TH-cam accepts ENTER for paragraphs. You can paste paragraph marks into Quora from another document such as a Word doc. I compose in Word then Paste. Double marks with a period between works better.. .. In your order… .. First, you think you have a gotcha, but you haven’t. This is not a subject I embarked upon within the last few weeks. Read my About for my TH-cam account. .. You repeat what I summarize in the video, Newton’s #1: “Acceleration requires a force.” .. The video title and the description below it clearly say that the video is about the upper pressure reduction and ONLY the upper pressure reduction. The primary goal is to refute all the common misconceptions in so many amateur videos and papers that claim things like the venturi effect (pinching) and a misunderstanding of Bernoulli’s Principle and Equation. .. .. This ‘around the bend, over the top’ explanation covers all the wing types you mention; flat; symmetric; cambered; normal and inverted ‘thin’ camber (Wright’s); boat sail and keel. It also figures into the Coanda Effect, Magnus Effect and Fletner wing as well as the self-centering ball on a column of air (not the Bernoulli nonsense so often claimed). .. I note that the very similar flow around a flat wing at 5 degrees AoA is shown in: Introduction to John D. Anderson Fund of aero 5th Edition. Flat plate flow Figure 4.52 Page 391. .. .. Note that in my first airflow diagram I have a semicircle. The key point that needs understanding is that it is the flow path/shape that it significant, NOT simply the surface shape. All the ‘normal’ wings have this same phenomenon above them - curved flow affected by the same “inertial force” (as some folks like to call it these days). On ALL these wings, the air goes around that upper bend, one way or another - Bending or turning the air…. .. .. .. .. .. RE: Gradual venturi. That is a longitudinal Pressure Gradient; along the flow. .. The one formed by the curved flow, the main topic in my video, is transverse; across the existing flow. You seem to be implying that having the transverse Pressure Gradient somehow negates the possibility of a longitudinal one and I see no such logic. .. In fact, above the wing from the LE stagnation line back, there is both longitudinal and transverse Pressure Gradients. .. So, I don’t see any problem it introduces. .. .. Pressure Gradient across a flow that curves it. .. This is where Boeing’s Doug McLean likes to say that it is a two way street. A transverse Pressure Gradient that is there before the flow moves is enhanced by the moving flow’s curved path. The two-way path is not simply both ways because the reverse path you have the surface providing the boundary condition that mandates the curved flow. .. In addition, that the air would ‘go straight’ has two conditions and I challenge you to examine both the moving air (wind tunnel) frames and the moving wing (flying) reference frames. These two cases have different values of momentum. .. I also point out that viewing a wing flying by shows what seems to contradict this common misunderstanding that says that faster air has a lower pressure. With the flying wing, still air frame-of-reference, the upper air actually has a slower speed than the lower air, but it has completely reversed direction; a high acceleration caused by the mostly longitudinal Gradient. This is real data from a lift generating wing shows this and all fundamental principles apply. .. I don’t understand the intent of that “thin airfoil - ignore the vertical”. All I can think is that if you can calculate the surface pressures, ignoring momentum transfer, you have the lift. In fact a paper by Charles Eastlake describes just that. He described how lift can be CALCULATED by either of two methods. 1) Surface pressure calculation using as I recall Bernoulli and. 2) Momentum change of surrounding air. I spoke with him about it. .. wiki.mattrude.com/images/4/44/Bernoulli_Newton_Lift.pdf .. Re: The NEED to turn and ‘vacuum’. The flat plate flow in Anderson shows that ‘bubble’ above the LE allowing a flow virtually identical to the common asymmetrical cambered wing. This easily reinforces the concept that we need to focus on the flow, not simply the detailed shape. The flows are ALL similar and are compatible with the video’s description. .. Yes you can say that the curve is caused by the transverse gradient, but the flow then clearly enhances that gradient. If we set up the initial gradient, then start the flow, that gradient is increase with the speed of the flow due to the inertia effect. You can’t maintain the original Gradient once the flow moves without changing mass and that it off the table, right?. .. I don’t consider that Political. .. The curved flow clearly enhances the transverse Gradient. This situation is clearly NOT one of simple speed causing a gradient. A pressure Gradient causes a linear, or tangential acceleration, but a curved speed causes a transverse Gradient. This is not a simple bidirectional A< - > B thing. It is not simply reversed in both directions. .. The transverse Gradient is indeed something that sounds like the Bernoulli misconception of speed causing a pressure reduction; Just not like so many characterize it as a longitudinal gradient. This causes a gradient across the flow, not downstream pressure reduction. The problem here is that they are orthogonal gradients in play. This is where McLean says that one “supports” the other rather than “causes” it and I think that is fair. .. I don’t know if that comes across well in text like this. .. RE Train: First, the flange does not come into play on a train curve. Rail wheels are conical (cones) because they are on a solid shaft and need to cover different distances around the curve. .. “lateral normal” is an oxymoron, but I think I know what you mean, just lateral. .. Regardless we can use an auto on a curve just as well for what I think you are getting at. .. You are on acceleration and Newton’s Third Law. What is the cause of the two forces ? Is it the “action”? Or is it the “reaction” that causes things to happen. By the way, this (radial acceleration commonly called centripetal) is no different from linear acceleration. Whether you speed up, slow down or curve, it is acceleration. We must still have the action and reaction to satisfy Newton-3. .. The train’s motion / inertia is the cause and I maintain that these are NOT two separate and distinct forces as implied by Newton’s original wording. Rather there are two “parts” to a force. A force, ALL forces act in two opposite directions at once. There is no unidirectional force. That is a long-standing illusion imprinted in our brains by that original wording. .. It is the same if we are skateboards and I push you, it is my arm muscles that apply an outward force between us, pushing us away from each other. One force, two “parts”, two moving objects. .. Likewise, taking this high level view with a wing, the pressure pushes both up on the wing and own on some air --- Newton is happy and other things happen - covered elsewhere… Because: Again, my explanation is NOT EXPLAINING LIFT and does NOT claim to be. It is a ONE MINUTE explanation of ONE difficult aspect of lift. BTW: it also ignores up-wash, down-wash, speed variations, below wing phenomenon and tip-spill. .. Regards
one of the best videos about lift, often when they want to build an intuition they state the Bernoulli Principle or Newton's Third Law but Never the Circulation and Kutta theory these we studied only at university and they always focus more on the math and calculation than on understanding, your video has a nice balance between the two.
Watch large jets taking off or landing in the rain sometime. You can sometimes catch a glimpse that the air and water spray over the top surface is moving substantially faster than the jet is even travelling down the runway, and the air is actually accelerating over the wing, past the flaps and then downward.
The explanation with potential flows (uniform+circulatory) is actually more practical as they are used in many preliminary design tools like xflr,xfoil etc
Yes. The textbooks approach the problem in a piecemeal yet detailed fashion. And in the end, you are either completely confused, or the lightbulb goes off in your head. What is funny about the Kutta condition and Circulation is that you can see these first hand by doing an almost childlike experiment in the bathtub with a model airplane wing , and pepper sprinkled on the surface of the water. In effect a 2D wind tunnel, where you move the wing through it instead of the water moving. The pepper particles show the startup vortex off the trailing edge of the wing (Kutta Condition), and when you move the wing from right to left through the water then suddenly remove it, you see a ghostly slow clockwise motion (Circulation) of the area where you removed the wing. Got this little experiment from a book called Aerodynamics for Engineers. So I guess its college level.😜
Amazing explanation as always. I loved that you touched on the circulation aspect, because it often is not explained or mentioned as a reason of the velocity increase. Super thankful and so happy to see the extended version on Nebula! Thanks mate!
hey man, uni student here and im always confused abt what circulation is. yes , there is a mathematical definition abt it but what is the physical meaning on it?
@ David Davids Pressure difference would not exist without circulation. A tiny spoiler on top of the wing is very good at stopping circulation and instantly destroying lift.
Current aerospace senior, I have “learned”(the best a struggling engineering student can), and seeing your video helped me understand how all these concepts tie together. Learning everything in detail was a headache and stress inducer, but taking step back and seeing the broader picture has made me realized I actually learned a lot. Great job keep up the awesome work
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
@@RalphEllisto get to the action ur describing is through out the differential pressure caused by the airfoil. With no action there’s no reaction 3rd newtons law 😂
wrong. 1) lift occurs BENEATH a wing. 2) a major Source of lift is the presence of a Persistent Zone of Reduced pressure (eg, a specific pattern of TURBULENCE.) ABOVE a wing. 3) not circulation
@ David davids Wrong. The lower surface of the wing not only has almost nothing to do with lift creation... but there is actually low pressure under most wings. The only wings that create high pressure underneath them are supercritical airfoils which still need the low pressure on the upper surface for a lot of the lift and most lift at higher angles of attack and lift coefficients... and the few fighter aircraft that can do high alpha maneuvers at which point the drag coefficient is about ten times as high as it would be to create the same lift coefficient in at a lower angle of attack. If your theory is true, explain how a tiny spoiler or a layer of hoar frost on top of a wing can be so effective at destroying lift.
@@Bartonovich52 'there is actually low pressure under most wings' ????? jeezuss. that massively incorrect statement tells us all that, we can IGNORE anything else that you might say. out
@@daviddavids2884 I am not sure whether you couldn't comprehend whatever is depicted in the video or just needlessly trying to be a moron by just completely ignoring what is being explained. 1) True , there is lift below the wing.2) True, the cause of the lift is presence of reduced air pressure above the wing.3) But the video addresses why is there such a pressure distribution...that is a level deeper in explaining the cause of lift than what you know or think...that specific pressure distribution is in part attributed to a mathematical equivalency of circulation
Probably the best video on this topic I have ever seen, and I have watched a few over there years because I come back for a refresher now and then. This one is top notch.
I am a US Navy Veteran Aircraft Mechanic specialized training in Aircraft Metals / Structures, Hydraulics/Pneumatics/Flight Controls, Landing Gear/Brakes Systems Technician/Maintenance and I did it for 8 years, learned all the basics. It is always great to know the DEEP ADVANCED PHYSICS and Mathematics how Airplanes fly, and what Aerospace/Aeronautical Engineers know and do.
This has been the most enjoyable channel I have ever seen! “I have never had a class that I enjoyed quite as much as this one. Thank you so much for this wonderful channel!
I'm doing an Aviation Specialist degree to become a commercial pilot and this vid has just explained in 15 mins most of what I've been studying for a month
Finally found a single youtube video on this which is actually correct about the basic mechanism of lift generation. It's a little sad how unique that actually is, but for some reason it seems to be just about the single topic with the most pervasive misconceptions circulating about it.
Overall very great video! However, one thing that is important to mention is that the lower air pressure does not "suck" on the airfoil as is implied by your pressure distribution illustration, but rather that the lower pressure on the top surface is pushing less on the body than the higher pressure along the lower surface.
While technically true, it's not uncommon to refer to the "suction side" and the "pressure side" of an airfoil, and it's fine to think of them that way in the context of gauge pressure. Sure, the reality is a reduced inwards pressure, but mathematically and even conceptually, it works just fine either way.
Why is there so much emphasis placed on suction and pressure differences when explaining lift?Pressure differences are more important to lighter than air flight (Hot air Ballons and Blimps). Lighter-than-air flight is achieved through buoyancy. Heavier than air flight is based on the reaction of accelerating air. The primary source of lift in aircraft that utilize airfoils is the downward deflection of air. Deflecting the air downward creates and opposite and equal reaction upward. I consider the pressure differences as the engine that accelerates air downward. The reaction principle of lift creates a unified theory of flight that also applies to rockets. Keep in mind that I am not putting forth that aircraft fly just because they accelerate air downward. The amount of force generated by the downward acceleration of air equals the weight of the aircraft .This alone will not cause an aircraft to climb. The vertical component of thrust from a propeller or a jet causes an aircraft to climb. Once the pilot reaches the desired altitude the upward and downward forces are balanced. Once balanced an increase in thrust will create a climb and a decrease in thrust will create a descent.
This is one of the best videos on YT about airfoil lift. You have provided a useful introduction whilst ackowledging the shortcomings which come with oversimplification. Most importantly, you have avoided being wrong, which is the problem with a lot of videos on this..
Unfortunately, you have been mislead. As I previously posted: . It's rather disappointing to see, while this engineer have good intentions, He uses poor wording in several places. . I see the following problems here. . The graph at the left at 4:14 shows the change from ambient, or gage pressures. Saying that pressure above “is greater”, as you do, is misleading and confusing. . It is more correct to say that the *change or difference from ambient* is larger above. You do refer to it as "suction pressure" which sort of says it, but we must remember that you don't actually suck or pull on a fluid, but suction is an accepted term short for “lowering the pressure so a higher pressure can push toward it." .. Unfortunately, he also repeats the big fallacy at 6:15, that the "increase in air velocity creates an area of lower pressure." This directly violates Newton’s Laws. Acceleration does not cause a force. Force causes acceleration. He also states the equally incorrect converse about the lower air "decrease in velocity creates a higher pressure." It is exactly the opposite. Air has mass and a force is required to accelerate any mass. It is a pressure difference that provides this accelerating force to slow it. . The fact that the velocity increase is accompanied by the pressure decrease (and visa-versa) IS CONSISTENT WITH Bernoulli's Principle. However, Bernoulli's Principle DOES NOT assign a cause and effect! It only says that a pressure changes and velocity changes *accompany each other.* . In the mid 1700s it was Euler, following up on Bernoulli's work, that determined that it is a Pressure Gradient that Accelerates fluid. This is Newton's Laws operating in fluids. When there is a pressure difference between two locations, the higher pressure pushes more and accelerates the fluid toward the lower pressure. This is simple and intuitive IF you understand what Newton was supposed to teach you. . Pressures are the cause! . At least he correctly states that the top/bottom pressure difference _is_ the lift. . Then, using Kutta as the cause is equally poor. It still does not explain what the force is accelerating (or decelerating) the air above (below). Kutta is something that had to be added because the initial mathematical calculations failed to correctly model the actual flow - to correct the math, not to make the flow correct. . The circulation story is also backwards. Yes, we can *deconstruct" the flow into two components; one unidirectional and one circulating. BUT what is it precisely that causes this circulation? This story says it is because the air can't make that turn around the trailing edge, but this still does NOT explain the force causing the accelerations we see. We can directly observe the air NOT curving backwards around the trailing edge. Why would it want to do this swirl-around stunt? . As @icojb25 explains so well in another comment: “In terms of the circulation, I guess one needs to understand "circulation" is actually a mathematical concept (ie not real) - used by physicists and engineers in the 1920's when trying to come up with the first aerodynamic theories (like thin airfoil, LLT etc). So remember, there is no magical vorticity "circulating" around the airfoil generating lift. Its a very elegant concept though, and great for many simpler explanations. One just has to decide if you want to explain a physical phenomenon using a non-physical (abstract) concept like circulation, however elegant.” . The pinching above is not just "incomplete", but completely false idea because there is no wall further above ...AND...AND there is another “Pinch Point" right below the wing (time 6:43), where it is "pinched" from above by the wing bottom BUT with NO speed increase, nor pressure reduction!! In fact, the pressure is higher and flow slower.!.!.!. Therefore, serious problem with "pinching". BAD SCIENCE. . Yes, That "Newton Action / Reaction" thing does occur! It must! However, it is the (net) pressure that pushes up on the wing (AS you correctly state with the pressure difference talk) BUT those VERY SAME pressures also cause ALL accelerations of air around the wing. . Bottom line: Once you understand the most fundamental principle, that cannot be violated that: Pressure Gradients CAUSE Acceleration, then everything is easily explained -- cause and effect included.!. See *Understanding Lift Correctly:*. ***rxesywwbdscllwpn.quora.com/*
Nope it is not. Another non-physical explanation . Nothing said about origin of FORCE. Not Energy conservation and not 3d law of Newton can explain FORCE
This video is a good introduction that does not overstate the completeness of any one approach. It gives an idea of the different approaches and an idea that all the approaches are intertwined in a complicated way.
Bernoulli's principle only works for incompressible and inviscid fluids (air moving below Mach=0.3). Instead of Bernoulli, we use isentropic relations, the energy equation, mach number, and the equation of state. Not that Bernoulli is wrong, but the idea can be generalized purely by energy conversion, which you did. The random internal KE (static pressure) converts to bulk KE (flow velocity) because it needs to move around the airfoil (otherwise the flow would clump together in space which is non-physical). Splitting it over an airfoil causes the upper flow to speed up more than the lower flow, taking away more of the internal KE, thereby decreasing the static pressure much more over the top, creating lift. This is quantified explained by the other equations I mentioned, the catch is that we assume it is isentropically converted, which agrees well with experiment unless there are shockwaves. Other techniques analyze that.
As a person who wants to study aeronautical engineering i am so thankfull for this explanation. Thanks to the animation of newton's third law i have finally been able to intuitively comprehend what creates lift. Amazing video and simply amazing content
Nice video. I'd like to clarify the purpose of flaps and slats: 11:36 Partial flaps/slats are sometimes used for takeoffs, but generally full use is reserved only for landings. Flaps: 1) Increase camber 2) Increase angle of attack 3) Increase chord length (some designs only) Slats 1) Increase camber 2) Decrease angle of attack 3) Increase chord length In the case of flaps, all three effects tend to increase lift and drag. The increase in lift allows landing at lower speeds, and the increase in drag helps slow the aircraft after touching down. This shortens the landing distance. For slats, effect #2 decreases angle of attack (relative to fuselage longitudinal axis), so this would tend to decrease lift and drag for a given aircraft pitch. Slats further complicate the aircraft design, so deeper examination is needed to explain the utility of flaps+slats vs. flaps alone. Increased angle-of-attack (relative to fuselage), reduces aircraft pitch during landing approach. This improves runway visibility for the pilot, and increases ground clearance for the tail during landing. However, it detrimentally results in reduced ground clearance for the wing trailing edge, increases the likelihood of propeller/nose-wheel strikes, and reduces tire traction and rolling resistance while rolling level on the runway, on all gear wheels. The reduced traction (from lift) reduces the effectiveness of wheel brakes and nose-wheel steering, but the increased drag means the wheel brakes don't have to work as hard after landing. We can conclude that the addition of slats allows the wing to be highly cambered, without excessive angle-of-attack that might result from using flaps alone.
Nice! and just to add a little: Higher pitch attitude on landing also increases landing run on nose wheeled aircraft as the maximum application of brakes requires the nose wheel to be on the ground. This nose lowering time is limited by the aircraft structure. Thus in the case of flap failures it is often the case that the use of slats is limited to some intermediate position.
this is the only correct simple explanation of lift i have seen on youtube because it's the only one i've seen that has talked about circulation/the kutta condition
Thank you! This is the most complete and intuitive explanation of lift that I have ever seen! I've been searching for years but every video only had pieces of the explanation. Might I suggest a part 2 of this that delves into airfoils and their uses? Maybe an explanation for supersonic airfoils? Thanks again!
I am in class 11 and i've been watching these videos for a while. I just love how he explains in a simple manner by breaking down complex topics into simpler ones. Although there are meant for mechanical and civil engineers, it also helps us slot. Keep posting these type of educational videos in an animated manner. Love from India❤❤
I have only one minor nitpick at the very end. Pilots generally do not want higher lift for takeoff and landing. They generally want the same lift capability (enough to lift the aircraft) at a lower airspeed. The reason we want a lower airspeed is usually to allow a takeoff in a shorter distance and land either in a shorter distance or minimize the energy at landing to minimize wear on the tires or in case there is an accident, a lower speed is less dangerous. With high winds, we may want to keep our speed up for better control so we often don't use as much flaps. Other than that, I loved the video!
But why does the faster velocity occur? And why is air deflected downwards? A faster velocity on top and slower on bottom is the definition of having circulation
The best and comprehensive explanation is the mathematical one. But we need this simplified and still very good explanation. I am happy to see you bring both, Bernoulli and Newton instead of already choosing one. It is complicated! Great video!
I think the explanation at time14:18 of the video says that the "low pressure" on the top surface is larger in magnitude than the "high pressure" on the bottom surface. This is maybe a mistake because the pressure at the top is less than that at the bottom. I would prefer also to replace the "low pressure" with negative pressure and "high pressure" with positive pressure to avoid confusion !!
I bestow the highest honor i could award to an youtube channel, all notifications had been turned on!! Next time you post something, I will be there in seconds.
The stagnation point is BELOW the wing not at the tip of the nose. The greater the angle of attack the further it moves underneath the wing. This is due to circulation around the wing.
I am not from aerospace engineering background but i want to say that whenever i travel by plane i am always curious about how aeroplane is taking-off and landing. You have explained this concept in a very easy way and also the animations you used. Now i got to know why aeroplane have airfoils of particular shapes. Thanks for your great explanation
Good video, but "this bullet" *shows entire cartridge as example* lol. I get your point, but it's not exactly accurate. For those reading this, the bullet is only the projectile loaded into the front of the brass casing and NOT the entire assembly pictured.
A very good video with graphical visuals rather than only mathematical formulae and text in books. It helps to understand the concept thousand times better.
Change in pressure causes fluid to move not the opposite. Air is faster above the wing because of a favourable pressure gradient along the flow direction on the suction side and an adverse pressure gradient on the pressure side. This is due to the curvature in the flow as the wing passes through the air due to the way a wing is designed. Newton's second law. Wings are also designed in a way to produce downwash. Newton's third law. Newton's second and third Laws explain lift completely and correctly. Consider two particles in the stagnation region. At the suction side, the streamlines are curved in a way that there is low pressure on the suction side as compared to the stagnation pressure. Therefore the prticle at the suction side get accelerated. At the pressure side, the stream line curvature is in a the way that pressure gradient is adverse as compared to the suction side. Apply 2nd law to both fluid particles or to a small control volume of particles at suction or pressure sides. This is why speeds re different. This is well underattod in case specially of flow through pipes and cyclones etc. It happens due to centrifugal force. Whenever there is a bend in a pipe i.e. streamlines change direction/bend etc. there is change in pressure gradient across the streamlines. Same is the case with typhoons, cyclones etc. Also, when there is high curvature of the stremline, there is high pressure gradient between successive streamlines and low absolute pressure like in the center of the typhoon has high speed and low pressure. There is a lecture of Dr. Holger Babinsky in which he explains it very clearly what I am trying to say...
A question about the Bernoulli principle. If the lift is really explained by Bernoulli, why does the stall of the airfoil automatically lead to a sudden reduction of the lift? Assuming that the flow separation occurs (initially) beyond 3/4 of the chord, the main contribution to lift, according to Bernoulli, would remain unchanged. Resulting therefore in a lift that is, if not equal, very similar. Personally, I'm with Newton.
No, it would not remain unchanged. With significant flow separation at the trailing edge the Kutta condition no longer holds, which leads to a great reduction (and sometimes even total reduction) in circulation. Circulation is the cause of acceleration on the top surface. Less circulation -> less acceleration -> less reduction in pressure on top (Bernoulli) -> less lift. It is not Newton or Bernoulli, it is both, and by exactly the same amount. They are equivalent. Two sides of the same coin.
THANK YOU SO MUCH SIR.PLEASE ACCEPT MY RESPECT FROM INDIA.THESE VIDEOS ARE SUCH A BLESSING...WHAT I COULDNT UNDERSTAND IN 3 HOUR LECTURES YOU TAUGHT ME WITH 15 MIN VIDEO. THANK YOU SO MUCH.
7:14 The flow tendency to round the trailing edge creates separated vortices left in the wake, the sum of the vortex strength is precisely the opposite of the circulation , due to angular momentum conservation.
Newton’s 2nd Law is why a wing generates lift. The wing changes the momentum of the air by pumping it down. This results in a force up. The engineering part is how do you do this to minimize drag so you don’t need monster thrust to weight to plow your flat wings through the air. But if you aren’t pumping air down you aren’t generating lift.
You are talking about the 3rd law by the way. Anyway, you are partially correct, Newton's downwash is one reason, pressure difference is another though. You need both on planes like a 747. But no sane person is arguing about that. The only thing that is hard to explain is why the air travels faster at the top. Everything else is trivial.
You mentioned how airfoils are used in wings, propellers, and so forth. So am I to assume that propellers suck an airplane forward? And the huge volume (and mass) of a prop blast being thrust rearward is of little consequence? You show the airflow passing an airfoil blissfully trailing aftward, not being deflected downward. Why, then, do downwash and wingtip vortexes travel downward at astonishing rates? Seems you are ignoring the role of a wing as an air pump, and relying on Bernoulli's modest principle to explain lift. Perpetuating the old CFI tale. Read Stick and Rudder. Wings do not suck a plane into the sky.
The propeller blades are clearly curved as to incline the airflow backwards, the direction the trailling edge is pointing is something a 2 year old would realize so I'm not gonna spare you for that, and they do essentially the same thing, low pressure area in front of the blade. And wingtip vortexes don't travel downwards, wtf, you can see planes flying through smoke, the votexes grow bigger over time, but they stay in the same general area. I am only finding it now that there's the equivalent of Flat-Earthers for fluid dynamics, I thought it was too smart of a field for you guys to bother.
OOOOHHHHhhhhh! I’m a just layperson who happens to be fascinated by aviation and I LOVE this explanation for flaps and slats that even *I* could understand! Very cool. Thanks!
I just stop the video on 0:16 to remember everyone that Alberto Santos Dumond, a brasilian, made the first self propelled airplane that flighted without being thrown through a catalpult.
Awesome explanation ! Currently finishing the bachelor in aeronautics and it is great to have such a channel that refreshes my memory on the basis of aerodynamics!
Thank you so much for this video. Making something like this requires several things. Firstly, an understanding itself of the subject topic. Then, thinking through how better to present it and, then, maybe finally, doing all of the work to make the video itself with plots, etc. again, thank you. This is informative.
I know nothing about aerodynamics or even engineering. I just got curious to try to underestand how we actually can fly on a multi tons aircraft. And this video just made it so simple to understand, or at least the basic principle behind it. This is how grterat your video is! Thank you so much, and keep on the great work
I appreciate how you acknowledged the complexity of the topic and that there can sometimes be a clear cause-and-effect relationship between the different phenomena involved in generating lift. Your exploration of both Bernoulli's Principle and Newton's Third Law as valuable insights into the understanding lift, while also pointing out their limitations, helps avoid falling into the pitfalls of common misconceptions. I suggest briefly mentioning the common misconceptions about lift, even though your video does not rely on them. This would further educate the audience on the subject and create a more comprehensive understanding of lift. Overall, great job! Your video is accurate and informative and offers a balanced explanation of lift generation. Keep up the excellent work!
This is the best presentation I have seen for lift so far! I really appreciate you emphasizing that this is only a very small portion of the physics of lift, there is much to be learned.
Thank you for the quality of the video, that is one of the few that introduce (quickly though) the notion of "suction" (4:18). And Yes, ALL wings, those of propellers or foils used for water sport for instance do not move the medium (air o water) backwards or downwards, they are sucked by the lower pressure zones created by the movement within that medium.
I wish the full explanation wasn't paywalled since I can't afford it and your explanations seem manageable - or at least more manageable than what I got from lectures of my professor. Also, thanks for not perpetuating the equal-transit time myth. Screwed my head for many years.
Whoa, that was an excellent video! I just took a course on "Advanced Fluid Dynamics" and the effect of circulation generated by airfoils didn't click until I watched this video. You did a better job explaining this then my professor or my textbook. And I asked my prof like 3 times to explain it and read through the text sections a few times... Turns out I fell into the fairly common pitfall of "Equal Transit" theory (AKA longer path theory). I swear my prof taught me that false theory when I asked the first time
Excellent video. The best summary of how lift works I have seen. There are a lot of videos out there that take such a simplistic view that they end up being wrong, or at least misleading. [Edited for content]
Thank you so much for this amazing explanation! Although I had an outstanding Aerodynamics Professor back in the days when I was taking my Aerospace engineering degree, visualizing this “basic” principles for the second time helps to understand the topic even further.
The video explains lift generation very well! But on a completely unrelated note, I must say that I appreciate the use of the ScoutCond font. It's one of my favourite fonts and I am happy to see it being used ahaha
Great job explaining the background information relevant to the generation of lift. I liked that it was mentioned that a flat plate could also generate lift, hopefully dispelling misconceptions that the shape of airfoils uniquely generates lift. I don't believe the pinching of streamlines is able to explain pressure differences over the top & bottom surfaces, as that's an effect caused by the geometry of internal flows. Good exploration of the parts that the relationship between pressure & velocity, circulation, and momentum all play in generating lift. Mentioning the limitations of different theories is incredibly important as well, along with the mutual interaction between the explanations.
A frisbee has a curved upper surface and a flat or hollow lower surface, so it is like a circular wing. Now try throwing it upside down and see if it flies - best demo of how wings work!
A lot of people struggle with Newton or Bernouli. If you think of Bernouli as a more detailed description of Newton, then it all becomes much clearer. Following is a very simplified description of the basic components of lift, approximately 1/3rd of lift is pressure under the wing, and 2/3rd suction above the wing as it flows through the air at a positive angle of attack. This can vary considerably with different shapes. But I hope it makes it a bit clearer for those struggling with understanding what is happening.
🎁 Get access to my extended and bonus videos on Nebula - nebula.tv/videos/the-efficient-engineer-understanding-aerodynamic-lift-extended-version.
Thank you so much (I already own curiosity though, lol)
6:05 I understand your explanation of the what creates the lift force (i.e. a pressure difference due to velocity difference, according to Bernoulli's Principle)
but then...
6:30 I don't see why the fluid flow being "pinched" above the leading edge of the wing results in LOWER density/pressure? Instead, I'd expect this constriction of air molecules to cause HIGHER pressure?
6:42 I also don't see the connection with "Conservation of Mass" which you state, but don't explain.
7:08 Again, you state what the flow would look like without circulation but you don't explain why.
Conservation of mass means that for the same amount of fluid to flow through the constricted section, it's velocity must increase. And Bernoulli's equation tells us that an increase in velocity is accompanied by a reduction in pressure (conservation of energy).
@@TheEfficientEngineer Thanks for replying with an explanation, which helped me understand how Conservation of Mass applies.
I also watched another video explaining how wings create lift (by the channel Sixty Symbols) which I found helpful.
How circulation is relevant in this case remains a mystery...
@@GonzoTehGreat It's best to think of the air as a fluid. Also whatever the reason, it is the difference in pressure between the top and bottom of the wing that does most of the work. The various reasons, Bernoulli, Coanda or Newton, will have varying input depending on speed and angle of attack. Flaps only work at low speeds. At cruising speed they just add drag. Same with angle of attack. It took until computers became powerful enough to do the calculations for some of this to be unravelled, so its no wonder that it is still being argued about!
Edited for spelling.
As a fluid flows around the airfoil, it creates three different kinds of stresses: shear stresses, pressure stresses, and engineering student studying stresses.
I’m going to shamelessly steal this pun
Just the third one 😄
It also stresses laymen like me. I know that wings create lift. I still don’t understand why, though sometimes I think I do
Nobody understands why.
That’s why it’s called the theory of lift.
Even super computers only get close to quantifying it.
We only know what conditions need to be satisfied to create it, not the why.
@@Bartonovich52 Oh, I am glad to hear that! I thought it might be a shortage of understanding on my part. So, in essence, we have a description or the ‘what’ of this phenomenon, not the ‘how’ or ‘why.’ Thanks
I've been studying Aeronautical engineering for the last 7 years and I've been playing with some Aerodynamics projects for the last 2 years and I have never found a better explanation of Lift in the entire Internet, amazing job, clean and intuitive speech, wonderful animations and a solid theoretical background. My biggest congratulations for you man! You're Top engineering content creator, keep going!
Really? I thought we have proved that the lift is caused by the Coanda effect not the Bernoulli effect.
@@jackz1620 Coanda is just a small part that allows the boundary layer not to detach from the airfoil and produces a bit percentage of the lift with the downwash but lift is based mainly in pressure differencial by bernouilli effect
pitty it is not based on physics for all the benoulli version. See my comments above.
@@jackz1620 @Ignacio Trueba
Coanda does not happen above an airfoil. It is a jet or sheet of air, FORCED into an otherwise still air environment. There is continual entrainment. There is neither of those above an airfoil.
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Using the "Bernoulli Effect" as commonly done is an equally incorrect way of explaining lift.
*Understanding Lift Correctly:* rxesywwbdscllwpn.quora.com/
Totally agree!
2 semesters of advanced aerodynamics and a 4 year aviation degree i learned about lift. This 15 minute video simplified such a complex subject in a way that is easily understood! Phenomenal video... thank you!
Would you comment, or LIKE if appropriate, this short piece of the story for the layman? My 11 yo granddaughter did all the editing. *th-cam.com/video/3MSqbnbKDmM/w-d-xo.html*
It's not totally correct
@@baloog8 yeah, I agree, I started to learn fluid mechanical to understand exactly how this aerodynamics works, because I learned solid mechanical approach, so it's a little different when you can think a solid as fluid with an extremely high viscosity.
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
Life is not totally correct, but we can enjoy it.@@baloog8
You always happen to upload the topics my uni projects are on at the time and i love it
Absolutely insane how I’m in the last 2 weeks of fluid mechanics and we’re doing external flow now, and this guy uploads precisely on lift 😂
be careful, physics and engineering are two different things! Still no one is certain on how an airplane flies!
@@rogerdodger8813 I would say people are certain on how airplanes fly, just lacking in certainty regarding deeper issues relating to CFD.
@@rogerdodger8813 That information has the value of zero.
Guys that you are making these videos...I am incredibly grateful for your work. I am doing my MSc on Advanced Mechanical Engineering in a great university of UK. Literally, the help that you have provided me is out of this world. I am telling that with all the reality that possesses me. A combination of studies and your videos on Engineering Field have launched my knowledge on many fields. Thank you so so much. Keep working! You are changing the process of studying and unfold the engineering complexity on many fields. Good job!!
Glad to hear it - thank you!
Go Cranfield! Maybe! 🤓
Aren’t you lucky to go to school with White people?
Dear The Efficient Engineer, as an Aeronautical Engineer who used to teach Aerodynamics at the uni, and did so proudly, and usually get upset with the poor or directly wrong explanations usually found in youtube, I want to tell you one thing:
*CONGRATULATIONS*
For a video that scratches the surface and is intended to be accessible to the general public, this is *EXCELLENT*.
Yes, concepts were simplified, but all the explanations were CORRECT (unlike most of the videos on the subject).
Every time while watching this video that I said "uh-oh" you quickly eliminated any concern that was starting to appear in my head.
"Engineers still debate how lift is generated" That is much better than the usual "We still don't fully understand how lift is generated"
"Bernoulli and Newton" presented NOT as two contributions to lift, but as 2 ways to approach the explanation of the same phenomena.
"Pressure on the top is lower because the air flows faster than on the bottom" Uh-oh, I thought, here comes "equal transit times". Nope. It was so satisfying to see those fluid parcels on the top arrive to the trailing edge before the lines on the bottom.
And also, I thought, you were committing the same mistake than many by saying that the lower pressure was caused by the faster speed, when in fact we could also say the faster speed is caused by acceleration that can only be caused by the air parcels running along a path of a negative pressure gradient (or, in another words, the lower pressure causes the faster speed). But then you explained how the three things affect each other and act concurrently, not one causing the other.
You were one (or several) steps ahead of me all the time and you won on every thing that I forecasted you were going to say wrong.
I am so happy for having been wrong every single time I thought that.
It was simply *BRILLIANT*.
@adb012
I'd like your further comments. I have an ulterior motive...
As an engineer, I appreciate this is complex and, therefore language is very important. Since I'm critical of words, I'll be very careful with mine...
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Example:
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What gets me is that while he carefully states Bernoulli's Principle well, at 6:15 he actually says "the increase in air velocity above the airfoil creates an area of lower pressure." [above wing]
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A velocity increase is acceleration. It would have been better had he said "the *increased* velocity" or just "speed" it would be accurate.
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It isn't the acceleration that causes the transverse gradient, but rather the speed along the curve.
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Yes, of course there are tangential speed changes as well along that curved flow, but the transverse gradient is from the air's natural tendency to continue straight.
It is the "stretching/swinging/flinging away from the curve's center - what some people consider the inertial force". I think it should be called the centrifugal effect (not force). This is the idea that you feel pulled outward traveling around a curve. Previously called 'centrifugal' force.
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Here, we actually do have the case where speed (in the curved flow) actually can be said to "cause" a pressure change.
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It causes the *transverse* gradient rather than the more common longitudinal (proverse or adverse) gradient that changes speed.
I say that is an unfortunate choice of words in a very technical subject where there are so many misconceptions being spread all the time by so many well meaning amateur scientists.
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So...
My motive is for your comments on this short, simplified video explanation of what I just mentioned.
Because my 11 yo granddaughter did the video editing, I would appreciate if you would consider a LIKEit if you feel it appropriate. You should also check my TH-cam About.
I'd prefer your comment under the video as threads can get long.
*th-cam.com/video/3MSqbnbKDmM/w-d-xo.html*
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Regards
@@Observ45er ... I am going to reply to you here since you posted this comment here, and then I am going to copy this reply in your video.
The effect that you describe is correct. A parcel of air has to obey Newton's 2nd law (and the others too, of course) that says that F=m*a. The parcel of air has a mass (even if it is a differential mass) so, to be subject to an acceleration, it needs to be subject to a net force (even if it is a differential force). So if the parcel is accelerated, then there must be net force acting on it and, if we neglect viscous drag (say that we are outside the boundary layer), then we are left with pressure only, so an accelerated parcel of air means a pressure gradient. This applies both in the tangential and normal (centripetal) directions. In the tangential direction, the acceleration causes a change in the magnitude of the speed vector of the parcel of air (i.e. the parcel of air will increase or decrease the speed), while in the normal direction it causes a change in the direction of the speed vector.
Now, you focus exclusively in the normal direction. Again, that effect exists and your explanation of the effect itself is correct, except that it can't by itself explain the cause of lift.
I will start by admitting that I don't remember everything I learnt (and used to teach) about lift. Bute here you have several points to consider:
- Why does a flat airfoil (like a piece of balsa board) generate lift, and no only that, but it generates as much lift as any other airfoil at the same incremental angle of attack above the zero-lift angle of attack? (as long as it doesn't stall, which the balsa board will do at a lower angle of attack than a conventional airfoil)
- How does a conventional asymmetrical airfoil manage to produce lift when flying upside-down? And why does that hold true even when it is a thin cambered airfoil (one where what would be the upper surface is convex and the lower surface is concave, except that it is upside down so you have the concave side up and the convex side down).
- Consider the following 2D Venturi tube. You have 2 lateral walls that parallel are very far away to each other (say 200 meters away). You have a bottom and a top that start parallel to each other with an internal height of 1 meter. Air flows along that tube of rectangular section (1m x 200 m). At some point, the starts a straight ramp up at a shallow angle, at the same point, the top also starts a down slope of the same shallow angle. The lateral walls remain at constant distance to each other. In this way, the section starts to constrict, from 1m x 200m, to 0.8m x 200m, to 0.6m x 200m and so on, in a constant and symmetrical ramp in the top and bottom. Due to continuity (conservation of mass), the flow will gradually accelerate along this upstream side of the venturi, and as it does so, the pressure will go down. Several meters down this double ramp, at the point where the top and bottom are 0.1m away, the flow will be moving 10 times faster and, BY Bernoulli (note I didn't seay BECAUSE of..., that was intentional), the pressure will be much much lower. So you have a constant and gradual decrease in pressure from the point where the constriction started down to this point, yet all the parcels of flow where moving in straight lines. Conclusion? You can (and DO) have changes in pressure even if the flow is moving in a straight line.
- I remember there was a "thin airfoils" approximation used to estimate how an airfoil would behave (lift vs angle of attack) that totally neglected the vertical acceleration of the flow, and it was quite accurate for airfoils up to 10 or 12% of thickness at cruise-like angles of attack.
- This one is the most crucial one for me: Have you though why the flow NEEDS to curve and follow the airfoil? Typical answer to that question is "because if not it would leave a vacuum behind and that would pull the flow back to the airfoil". That is wrong. You could have a recirculating bubble, like you have at higher angles of attack in a stall. Saying ""the cause of the transverse pressure gradient is that the airflow turns" is more a "political position" that an accurate scientific statement. We could as well say that the cause why the airflow turns is that i flows through a transverse pressure gradient, and in a classical Newtonian view it would be more reasonable to say so: We typically say that a force causes an acceleration, not the other way around. Whether that classical Newtonian view is fair is a different question, I tend to think it is not, that force and acceleration are concurrent and 2 parts of the same phenomena, not one the cause of the other. Let me give you an example. You have a train taking a turn. The lateral normal force between the rails and the flange of the wheel provides the centripetal force that changes the train's direction. How doe the rail know to apply the exact force necessary for the train to keep that exact curve at that speed? The force causes the train to turn or the train turning causes the force? Well, in fluid dynamics it is like this, but worse. Everything is correlated, concurrent, and integrating with everything. You have a pressure field and a velocity field (and a viscos stress field too) and a vorticity field all "conspiring" together to create a solution that meet the 2 boundary conditions: The boundary of the airfoil shall not be penetrated and the flow will separate at the trailing edge. Saying that one thing causes the other is, in my opinion, not real.
- Finally, at the end of the day conservation of momentum (or variation of momentum in the presence of a force) does apply. If the air is pushing the wing up, then the wing must be pushing the air down/ That means that the air has to bend its direction from say horizontal far away upstream of the wing to diagonal horizontal and down far away downstream. The turning that you described is PART of this phenomena, but not the that air changes direction long before it reaches the wing, keeps changing direction long after it already passed the wing, and also quite far away above and below the wing. Lift is truly a very complicated phenomena. Any simplistic explanation has to be either wrong or incomplete. Yours in correct but uncomplete.
@@adb012 ..
For readability, TH-cam accepts ENTER for paragraphs. You can paste paragraph marks into Quora from another document such as a Word doc. I compose in Word then Paste. Double marks with a period between works better..
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In your order…
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First, you think you have a gotcha, but you haven’t. This is not a subject I embarked upon within the last few weeks. Read my About for my TH-cam account.
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You repeat what I summarize in the video, Newton’s #1: “Acceleration requires a force.”
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The video title and the description below it clearly say that the video is about the upper pressure reduction and ONLY the upper pressure reduction. The primary goal is to refute all the common misconceptions in so many amateur videos and papers that claim things like the venturi effect (pinching) and a misunderstanding of Bernoulli’s Principle and Equation.
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This ‘around the bend, over the top’ explanation covers all the wing types you mention; flat; symmetric; cambered; normal and inverted ‘thin’ camber (Wright’s); boat sail and keel. It also figures into the Coanda Effect, Magnus Effect and Fletner wing as well as the self-centering ball on a column of air (not the Bernoulli nonsense so often claimed).
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I note that the very similar flow around a flat wing at 5 degrees AoA is shown in: Introduction to John D. Anderson Fund of aero 5th Edition.
Flat plate flow Figure 4.52 Page 391.
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Note that in my first airflow diagram I have a semicircle. The key point that needs understanding is that it is the flow path/shape that it significant, NOT simply the surface shape. All the ‘normal’ wings have this same phenomenon above them - curved flow affected by the same “inertial force” (as some folks like to call it these days). On ALL these wings, the air goes around that upper bend, one way or another - Bending or turning the air….
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RE: Gradual venturi. That is a longitudinal Pressure Gradient; along the flow.
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The one formed by the curved flow, the main topic in my video, is transverse; across the existing flow. You seem to be implying that having the transverse Pressure Gradient somehow negates the possibility of a longitudinal one and I see no such logic.
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In fact, above the wing from the LE stagnation line back, there is both longitudinal and transverse Pressure Gradients.
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So, I don’t see any problem it introduces.
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Pressure Gradient across a flow that curves it.
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This is where Boeing’s Doug McLean likes to say that it is a two way street. A transverse Pressure Gradient that is there before the flow moves is enhanced by the moving flow’s curved path. The two-way path is not simply both ways because the reverse path you have the surface providing the boundary condition that mandates the curved flow.
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In addition, that the air would ‘go straight’ has two conditions and I challenge you to examine both the moving air (wind tunnel) frames and the moving wing (flying) reference frames. These two cases have different values of momentum.
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I also point out that viewing a wing flying by shows what seems to contradict this common misunderstanding that says that faster air has a lower pressure. With the flying wing, still air frame-of-reference, the upper air actually has a slower speed than the lower air, but it has completely reversed direction; a high acceleration caused by the mostly longitudinal Gradient. This is real data from a lift generating wing shows this and all fundamental principles apply.
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I don’t understand the intent of that “thin airfoil - ignore the vertical”. All I can think is that if you can calculate the surface pressures, ignoring momentum transfer, you have the lift. In fact a paper by Charles Eastlake describes just that. He described how lift can be CALCULATED by either of two methods. 1) Surface pressure calculation using as I recall Bernoulli and. 2) Momentum change of surrounding air. I spoke with him about it.
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wiki.mattrude.com/images/4/44/Bernoulli_Newton_Lift.pdf
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Re: The NEED to turn and ‘vacuum’. The flat plate flow in Anderson shows that ‘bubble’ above the LE allowing a flow virtually identical to the common asymmetrical cambered wing. This easily reinforces the concept that we need to focus on the flow, not simply the detailed shape. The flows are ALL similar and are compatible with the video’s description.
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Yes you can say that the curve is caused by the transverse gradient, but the flow then clearly enhances that gradient. If we set up the initial gradient, then start the flow, that gradient is increase with the speed of the flow due to the inertia effect. You can’t maintain the original Gradient once the flow moves without changing mass and that it off the table, right?.
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I don’t consider that Political.
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The curved flow clearly enhances the transverse Gradient. This situation is clearly NOT one of simple speed causing a gradient. A pressure Gradient causes a linear, or tangential acceleration, but a curved speed causes a transverse Gradient. This is not a simple bidirectional A< - > B thing. It is not simply reversed in both directions.
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The transverse Gradient is indeed something that sounds like the Bernoulli misconception of speed causing a pressure reduction; Just not like so many characterize it as a longitudinal gradient. This causes a gradient across the flow, not downstream pressure reduction. The problem here is that they are orthogonal gradients in play. This is where McLean says that one “supports” the other rather than “causes” it and I think that is fair.
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I don’t know if that comes across well in text like this.
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RE Train: First, the flange does not come into play on a train curve. Rail wheels are conical (cones) because they are on a solid shaft and need to cover different distances around the curve.
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“lateral normal” is an oxymoron, but I think I know what you mean, just lateral.
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Regardless we can use an auto on a curve just as well for what I think you are getting at.
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You are on acceleration and Newton’s Third Law. What is the cause of the two forces ? Is it the “action”? Or is it the “reaction” that causes things to happen. By the way, this (radial acceleration commonly called centripetal) is no different from linear acceleration. Whether you speed up, slow down or curve, it is acceleration. We must still have the action and reaction to satisfy Newton-3.
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The train’s motion / inertia is the cause and I maintain that these are NOT two separate and distinct forces as implied by Newton’s original wording. Rather there are two “parts” to a force. A force, ALL forces act in two opposite directions at once. There is no unidirectional force. That is a long-standing illusion imprinted in our brains by that original wording.
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It is the same if we are skateboards and I push you, it is my arm muscles that apply an outward force between us, pushing us away from each other. One force, two “parts”, two moving objects.
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Likewise, taking this high level view with a wing, the pressure pushes both up on the wing and own on some air --- Newton is happy and other things happen - covered elsewhere… Because:
Again, my explanation is NOT EXPLAINING LIFT and does NOT claim to be. It is a ONE MINUTE explanation of ONE difficult aspect of lift.
BTW: it also ignores up-wash, down-wash, speed variations, below wing phenomenon and tip-spill.
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Regards
I'm an A&P mechanic and engineer and this is the BEST explanation of how lift works on an airfoil. Thank you for this video.
no, it's not.
Yes, it is @@SoloRenegade
one of the best videos about lift, often when they want to build an intuition they state the Bernoulli Principle or Newton's Third Law but Never the Circulation and Kutta theory these we studied only at university and they always focus more on the math and calculation than on understanding, your video has a nice balance between the two.
Watch large jets taking off or landing in the rain sometime. You can sometimes catch a glimpse that the air and water spray over the top surface is moving substantially faster than the jet is even travelling down the runway, and the air is actually accelerating over the wing, past the flaps and then downward.
The explanation with potential flows (uniform+circulatory) is actually more practical as they are used in many preliminary design tools like xflr,xfoil etc
Yes. The textbooks approach the problem in a piecemeal yet detailed fashion. And in the end, you are either completely confused, or the lightbulb goes off in your head.
What is funny about the Kutta condition and Circulation is that you can see these first hand by doing an almost childlike experiment in the bathtub with a model airplane wing , and pepper sprinkled on the surface of the water.
In effect a 2D wind tunnel, where you move the wing through it instead of the water moving.
The pepper particles show the startup vortex off the trailing edge of the wing (Kutta Condition), and when you move the wing from right to left through the water then suddenly remove it, you see a ghostly slow clockwise motion (Circulation) of the area where you removed the wing.
Got this little experiment from a book called Aerodynamics for Engineers. So I guess its college level.😜
good video with wrong explanation
Amazing explanation as always. I loved that you touched on the circulation aspect, because it often is not explained or mentioned as a reason of the velocity increase. Super thankful and so happy to see the extended version on Nebula! Thanks mate!
Thanks. :) Agreed, circulation is often not discussed which is a shame!
hey man, uni student here and im always confused abt what circulation is. yes , there is a mathematical definition abt it but what is the physical meaning on it?
at 3:53, the secret to lift is Persistent zones of PRESSURE difference.!!!. not circulation
@ David Davids
Pressure difference would not exist without circulation.
A tiny spoiler on top of the wing is very good at stopping circulation and instantly destroying lift.
@ ileonlite
Circulation is what you are left with after you subtract the free steam vectors from the airflow around a wing.
That subtle background music, please don't dump it. Dont ever stop using it. Makes the videos doper🥺
I love your videos and please keep it up!
والله انك زلمة كفو قعد المهندس ٤ محاضرات وهو بشرح فيه عالفاضي ما فهمتو بس بفيديو ربع ساعه فهمتو منيح
جد شكرا عالفيديو الرائع عراسي استمر😍
Current aerospace senior, I have “learned”(the best a struggling engineering student can), and seeing your video helped me understand how all these concepts tie together. Learning everything in detail was a headache and stress inducer, but taking step back and seeing the broader picture has made me realized I actually learned a lot. Great job keep up the awesome work
Taking an aerodynamics course currently and this summed up everything covered thus far perfectly!
same here
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
@@RalphEllisto get to the action ur describing is through out the differential pressure caused by the airfoil. With no action there’s no reaction 3rd newtons law 😂
YES!! THANK YOU. Finally someone who knows what they’re talking about. Circulation is the correct explanation for lift
And also mentioning Newton's law too. A big plus there
wrong. 1) lift occurs BENEATH a wing. 2) a major Source of lift is the presence of a Persistent Zone of Reduced pressure (eg, a specific pattern of TURBULENCE.) ABOVE a wing. 3) not circulation
@ David davids
Wrong.
The lower surface of the wing not only has almost nothing to do with lift creation... but there is actually low pressure under most wings.
The only wings that create high pressure underneath them are supercritical airfoils which still need the low pressure on the upper surface for a lot of the lift and most lift at higher angles of attack and lift coefficients... and the few fighter aircraft that can do high alpha maneuvers at which point the drag coefficient is about ten times as high as it would be to create the same lift coefficient in at a lower angle of attack.
If your theory is true, explain how a tiny spoiler or a layer of hoar frost on top of a wing can be so effective at destroying lift.
@@Bartonovich52 'there is actually low pressure under most wings' ?????
jeezuss. that massively incorrect statement tells us all that, we can IGNORE anything else that you might say. out
@@daviddavids2884 I am not sure whether you couldn't comprehend whatever is depicted in the video or just needlessly trying to be a moron by just completely ignoring what is being explained. 1) True , there is lift below the wing.2) True, the cause of the lift is presence of reduced air pressure above the wing.3) But the video addresses why is there such a pressure distribution...that is a level deeper in explaining the cause of lift than what you know or think...that specific pressure distribution is in part attributed to a mathematical equivalency of circulation
Probably the best and only video online that actually explains this topic in an intelligent and complete way. This is pure gold!
Probably the best video on this topic I have ever seen, and I have watched a few over there years because I come back for a refresher now and then. This one is top notch.
Im studying flight principles for my ATPL rn so this video came out at a pretty perfect time!
I am a US Navy Veteran Aircraft Mechanic specialized training in Aircraft Metals / Structures, Hydraulics/Pneumatics/Flight Controls, Landing Gear/Brakes Systems Technician/Maintenance and I did it for 8 years, learned all the basics. It is always great to know the DEEP ADVANCED PHYSICS and Mathematics how Airplanes fly, and what Aerospace/Aeronautical Engineers know and do.
This has been the most enjoyable channel I have ever seen!
“I have never had a class that I enjoyed quite as much as this one.
Thank you so much for this wonderful channel!
I'm doing an Aviation Specialist degree to become a commercial pilot and this vid has just explained in 15 mins most of what I've been studying for a month
Wow! I think it is the most complete lift explanation on TH-cam! Very helpful and useful for engineers in Universities. Thanks!
no, it's not.
I teach aerobatics for a living - this is the most concise video explaining lift than any other I've found in years.
this channel is gold
Finally found a single youtube video on this which is actually correct about the basic mechanism of lift generation.
It's a little sad how unique that actually is, but for some reason it seems to be just about the single topic with the most pervasive misconceptions circulating about it.
Overall very great video! However, one thing that is important to mention is that the lower air pressure does not "suck" on the airfoil as is implied by your pressure distribution illustration, but rather that the lower pressure on the top surface is pushing less on the body than the higher pressure along the lower surface.
While technically true, it's not uncommon to refer to the "suction side" and the "pressure side" of an airfoil, and it's fine to think of them that way in the context of gauge pressure. Sure, the reality is a reduced inwards pressure, but mathematically and even conceptually, it works just fine either way.
Why is there so much emphasis placed on suction and pressure differences when explaining lift?Pressure differences are more important to lighter than air flight (Hot air Ballons and Blimps). Lighter-than-air flight is achieved through buoyancy. Heavier than air flight is based on the reaction of accelerating air. The primary source of lift in aircraft that utilize airfoils is the downward deflection of air. Deflecting the air downward creates and opposite and equal reaction upward.
I consider the pressure differences as the engine that accelerates air downward.
The reaction principle of lift creates a unified theory of flight that also applies to rockets.
Keep in mind that I am not putting forth that aircraft fly just because they accelerate air downward.
The amount of force generated by the downward acceleration of air equals the weight of the aircraft .This alone will not cause an aircraft to climb. The vertical component of thrust from a propeller or a jet causes an aircraft to climb. Once the pilot reaches the desired altitude the upward and downward forces are balanced. Once balanced an increase in thrust will create a climb and a decrease in thrust will create a descent.
Well, because the guy is clearly a Bernoulli believer.
@@omarjones1460 Agreed. Nature doesn't suck.
This is one of the best videos on YT about airfoil lift. You have provided a useful introduction whilst ackowledging the shortcomings which come with oversimplification. Most importantly, you have avoided being wrong, which is the problem with a lot of videos on this..
Unfortunately, you have been mislead. As I previously posted:
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It's rather disappointing to see, while this engineer have good intentions, He uses poor wording in several places.
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I see the following problems here.
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The graph at the left at 4:14 shows the change from ambient, or gage pressures.
Saying that pressure above “is greater”, as you do, is misleading and confusing.
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It is more correct to say that the *change or difference from ambient* is larger above. You do refer to it as "suction pressure" which sort of says it, but we must remember that you don't actually suck or pull on a fluid, but suction is an accepted term short for “lowering the pressure so a higher pressure can push toward it."
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Unfortunately, he also repeats the big fallacy at 6:15, that the "increase in air velocity creates an area of lower pressure." This directly violates Newton’s Laws. Acceleration does not cause a force. Force causes acceleration.
He also states the equally incorrect converse about the lower air "decrease in velocity creates a higher pressure."
It is exactly the opposite. Air has mass and a force is required to accelerate any mass. It is a pressure difference that provides this accelerating force to slow it.
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The fact that the velocity increase is accompanied by the pressure decrease (and visa-versa) IS CONSISTENT WITH Bernoulli's Principle. However, Bernoulli's Principle DOES NOT assign a cause and effect! It only says that a pressure changes and velocity changes *accompany each other.*
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In the mid 1700s it was Euler, following up on Bernoulli's work, that determined that it is a Pressure Gradient that Accelerates fluid. This is Newton's Laws operating in fluids. When there is a pressure difference between two locations, the higher pressure pushes more and accelerates the fluid toward the lower pressure. This is simple and intuitive IF you understand what Newton was supposed to teach you.
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Pressures are the cause!
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At least he correctly states that the top/bottom pressure difference _is_ the lift.
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Then, using Kutta as the cause is equally poor. It still does not explain what the force is accelerating (or decelerating) the air above (below). Kutta is something that had to be added because the initial mathematical calculations failed to correctly model the actual flow - to correct the math, not to make the flow correct.
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The circulation story is also backwards. Yes, we can *deconstruct" the flow into two components; one unidirectional and one circulating. BUT what is it precisely that causes this circulation? This story says it is because the air can't make that turn around the trailing edge, but this still does NOT explain the force causing the accelerations we see. We can directly observe the air NOT curving backwards around the trailing edge. Why would it want to do this swirl-around stunt?
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As @icojb25 explains so well in another comment: “In terms of the circulation, I guess one needs to understand "circulation" is actually a mathematical concept (ie not real) - used by physicists and engineers in the 1920's when trying to come up with the first aerodynamic theories (like thin airfoil, LLT etc). So remember, there is no magical vorticity "circulating" around the airfoil generating lift. Its a very elegant concept though, and great for many simpler explanations. One just has to decide if you want to explain a physical phenomenon using a non-physical (abstract) concept like circulation, however elegant.”
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The pinching above is not just "incomplete", but completely false idea because there is no wall further above ...AND...AND there is another “Pinch Point" right below the wing (time 6:43), where it is "pinched" from above by the wing bottom BUT with NO speed increase, nor pressure reduction!! In fact, the pressure is higher and flow slower.!.!.!.
Therefore, serious problem with "pinching". BAD SCIENCE.
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Yes, That "Newton Action / Reaction" thing does occur! It must! However, it is the (net) pressure that pushes up on the wing (AS you correctly state with the pressure difference talk) BUT those VERY SAME pressures also cause ALL accelerations of air around the wing.
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Bottom line:
Once you understand the most fundamental principle, that cannot be violated that: Pressure Gradients CAUSE Acceleration, then everything is easily explained -- cause and effect included.!.
See *Understanding Lift Correctly:*. ***rxesywwbdscllwpn.quora.com/*
@@Observ45er I read your previous post, and have responded directly to it, as it is riddled with errors.
@@XPLAlN I'll stay in the other thread to avoid confusion and have answered there.
THE best explanation I have found yet on YT. Even after 3 years of looking arround. Keep up the good work!
Keep looking, there are far better and more accurate explanations of lift on TH-cam. This video is full of misconceptions and inaccuracies.
@@SoloRenegade Would you mind linking one?
@@dundun92 search Holger Babinsky and watch his lecture/slides. His explanation is the right explanation. Babinsky Principle.
This is literally the most complete and best explanation I’ve found of Lift presented in an easy way.
Nope it is not. Another non-physical explanation . Nothing said about origin of FORCE. Not Energy conservation and not 3d law of Newton can explain FORCE
@@AndrewPa do you have a link to a description or a description of your own?
By far the best video on aerodynamic lift available on YT. Thank you for this great content!
no it's not.
This video is a good introduction that does not overstate the completeness of any one approach. It gives an idea of the different approaches and an idea that all the approaches are intertwined in a complicated way.
Bernoulli's principle only works for incompressible and inviscid fluids (air moving below Mach=0.3). Instead of Bernoulli, we use isentropic relations, the energy equation, mach number, and the equation of state. Not that Bernoulli is wrong, but the idea can be generalized purely by energy conversion, which you did. The random internal KE (static pressure) converts to bulk KE (flow velocity) because it needs to move around the airfoil (otherwise the flow would clump together in space which is non-physical). Splitting it over an airfoil causes the upper flow to speed up more than the lower flow, taking away more of the internal KE, thereby decreasing the static pressure much more over the top, creating lift. This is quantified explained by the other equations I mentioned, the catch is that we assume it is isentropically converted, which agrees well with experiment unless there are shockwaves. Other techniques analyze that.
Yes but that is annoying and incompressible flow is so pretty!
As a person who wants to study aeronautical engineering i am so thankfull for this explanation. Thanks to the animation of newton's third law i have finally been able to intuitively comprehend what creates lift. Amazing video and simply amazing content
Nice video. I'd like to clarify the purpose of flaps and slats: 11:36
Partial flaps/slats are sometimes used for takeoffs, but generally full use is reserved only for landings.
Flaps:
1) Increase camber
2) Increase angle of attack
3) Increase chord length (some designs only)
Slats
1) Increase camber
2) Decrease angle of attack
3) Increase chord length
In the case of flaps, all three effects tend to increase lift and drag. The increase in lift allows landing at lower speeds, and the increase in drag helps slow the aircraft after touching down. This shortens the landing distance. For slats, effect #2 decreases angle of attack (relative to fuselage longitudinal axis), so this would tend to decrease lift and drag for a given aircraft pitch. Slats further complicate the aircraft design, so deeper examination is needed to explain the utility of flaps+slats vs. flaps alone.
Increased angle-of-attack (relative to fuselage), reduces aircraft pitch during landing approach. This improves runway visibility for the pilot, and increases ground clearance for the tail during landing. However, it detrimentally results in reduced ground clearance for the wing trailing edge, increases the likelihood of propeller/nose-wheel strikes, and reduces tire traction and rolling resistance while rolling level on the runway, on all gear wheels. The reduced traction (from lift) reduces the effectiveness of wheel brakes and nose-wheel steering, but the increased drag means the wheel brakes don't have to work as hard after landing.
We can conclude that the addition of slats allows the wing to be highly cambered, without excessive angle-of-attack that might result from using flaps alone.
Nice! and just to add a little: Higher pitch attitude on landing also increases landing run on nose wheeled aircraft as the maximum application of brakes requires the nose wheel to be on the ground. This nose lowering time is limited by the aircraft structure. Thus in the case of flap failures it is often the case that the use of slats is limited to some intermediate position.
this is the only correct simple explanation of lift i have seen on youtube because it's the only one i've seen that has talked about circulation/the kutta condition
Thank you! This is the most complete and intuitive explanation of lift that I have ever seen! I've been searching for years but every video only had pieces of the explanation. Might I suggest a part 2 of this that delves into airfoils and their uses? Maybe an explanation for supersonic airfoils? Thanks again!
Most exhaustive and complete explanation till date!
Your videos are so concise and incredibly well mad!. They are definitely helping many people out there, and teaching many more. Keep up the good work!
I am in class 11 and i've been watching these videos for a while. I just love how he explains in a simple manner by breaking down complex topics into simpler ones. Although there are meant for mechanical and civil engineers, it also helps us slot. Keep posting these type of educational videos in an animated manner. Love from India❤❤
I am from India but now in Canada. Have you mastered the concept of potential vortices, if so we can discuss
Yet another masterpiece! Well done!
I have only one minor nitpick at the very end. Pilots generally do not want higher lift for takeoff and landing. They generally want the same lift capability (enough to lift the aircraft) at a lower airspeed. The reason we want a lower airspeed is usually to allow a takeoff in a shorter distance and land either in a shorter distance or minimize the energy at landing to minimize wear on the tires or in case there is an accident, a lower speed is less dangerous. With high winds, we may want to keep our speed up for better control so we often don't use as much flaps.
Other than that, I loved the video!
This is a masterclass! Thanks man! Keep up the great work!
Alas! First a video on aerodynamics drag and now lift....... Love your content.... And the way you've explained them.... Keep it up man!
Hey nigga
*Principle of lift:* Bernoulli's, Newton's 3rd law, coanda effect, circulation of air into effect.
*Factors affecting lift:* angle of attack, camber.
flat piece of plywood produces the same lift when tilted..
so youve proved nothing..sorry..dr johnny
But why does the faster velocity occur? And why is air deflected downwards? A faster velocity on top and slower on bottom is the definition of having circulation
My man, these videos are beautiful! Really making up for all the professors who don't know how to teach online.
Omg, thank you so much for this video. It really helped me as an aspiring flight instructor so that I have the ability to explain lift to my students.
The best and comprehensive explanation is the mathematical one. But we need this simplified and still very good explanation. I am happy to see you bring both, Bernoulli and Newton instead of already choosing one. It is complicated! Great video!
I think the explanation at time14:18 of the video says that the "low pressure" on the top surface is larger in magnitude than the "high pressure" on the bottom surface. This is maybe a mistake because the pressure at the top is less than that at the bottom. I would prefer also to replace the "low pressure" with negative pressure and "high pressure" with positive pressure to avoid confusion !!
I bestow the highest honor i could award to an youtube channel, all notifications had been turned on!! Next time you post something, I will be there in seconds.
The stagnation point is BELOW the wing not at the tip of the nose. The greater the angle of attack the further it moves underneath the wing. This is due to circulation around the wing.
I am not from aerospace engineering background but i want to say that whenever i travel by plane i am always curious about how aeroplane is taking-off and landing. You have explained this concept in a very easy way and also the animations you used. Now i got to know why aeroplane have airfoils of particular shapes. Thanks for your great explanation
Do you also find this stunning ?
I have always found aeronautics fascinating and interesting ❤️
Yes
Just a regular person and this is the best explanation of lift I have seen. Thanks
Good video, but "this bullet" *shows entire cartridge as example* lol. I get your point, but it's not exactly accurate. For those reading this, the bullet is only the projectile loaded into the front of the brass casing and NOT the entire assembly pictured.
A very good video with graphical visuals rather than only mathematical formulae and text in books. It helps to understand the concept thousand times better.
Change in pressure causes fluid to move not the opposite.
Air is faster above the wing because of a favourable pressure gradient along the flow direction on the suction side and an adverse pressure gradient on the pressure side. This is due to the curvature in the flow as the wing passes through the air due to the way a wing is designed. Newton's second law.
Wings are also designed in a way to produce downwash. Newton's third law.
Newton's second and third Laws explain lift completely and correctly.
Consider two particles in the stagnation region.
At the suction side, the streamlines are curved in a way that there is low pressure on the suction side as compared to the stagnation pressure. Therefore the prticle at the suction side get accelerated.
At the pressure side, the stream line curvature is in a the way that pressure gradient is adverse as compared to the suction side.
Apply 2nd law to both fluid particles or to a small control volume of particles at suction or pressure sides. This is why speeds re different.
This is well underattod in case specially of flow through pipes and cyclones etc. It happens due to centrifugal force.
Whenever there is a bend in a pipe i.e. streamlines change direction/bend etc. there is change in pressure gradient across the streamlines. Same is the case with typhoons, cyclones etc. Also, when there is high curvature of the stremline, there is high pressure gradient between successive streamlines and low absolute pressure like in the center of the typhoon has high speed and low pressure.
There is a lecture of Dr. Holger Babinsky in which he explains it very clearly what I am trying to say...
This is just wow!!! I am running out of words to describe this video because it’s purely perfection ❤️❤️❤️
Bernoulli's Principle: I am why planes fly.
Newton's Third Law: No, I am.
*_Circulation enters the chat_*
what if both theories are applied at the same time
Bernoulli is just a rewrite/application of Newton. Look at how the Bernoulli principle is derived if you don't believe me.
This is a reliable introduction to lift, and the best I have seen.
A question about the Bernoulli principle. If the lift is really explained by Bernoulli, why does the stall of the airfoil automatically lead to a sudden reduction of the lift?
Assuming that the flow separation occurs (initially) beyond 3/4 of the chord, the main contribution to lift, according to Bernoulli, would remain unchanged. Resulting therefore in a lift that is, if not equal, very similar.
Personally, I'm with Newton.
No, it would not remain unchanged. With significant flow separation at the trailing edge the Kutta condition no longer holds, which leads to a great reduction (and sometimes even total reduction) in circulation. Circulation is the cause of acceleration on the top surface. Less circulation -> less acceleration -> less reduction in pressure on top (Bernoulli) -> less lift.
It is not Newton or Bernoulli, it is both, and by exactly the same amount. They are equivalent. Two sides of the same coin.
THANK YOU SO MUCH SIR.PLEASE ACCEPT MY RESPECT FROM INDIA.THESE VIDEOS ARE SUCH A BLESSING...WHAT I COULDNT UNDERSTAND IN 3 HOUR LECTURES YOU TAUGHT ME WITH 15 MIN VIDEO. THANK YOU SO MUCH.
7:14 The flow tendency to round the trailing edge creates separated vortices left in the wake, the sum of the vortex strength is precisely the opposite of the circulation , due to angular momentum conservation.
Newton’s 2nd Law is why a wing generates lift. The wing changes the momentum of the air by pumping it down. This results in a force up. The engineering part is how do you do this to minimize drag so you don’t need monster thrust to weight to plow your flat wings through the air.
But if you aren’t pumping air down you aren’t generating lift.
Finally, someone who knows lift has nothing to do with Bernoulli and everything to do with Newton.
@@P13586 For the life of me I don't see why this is so difficult to understand.
You are talking about the 3rd law by the way.
Anyway, you are partially correct, Newton's downwash is one reason, pressure difference is another though. You need both on planes like a 747.
But no sane person is arguing about that. The only thing that is hard to explain is why the air travels faster at the top. Everything else is trivial.
This is by far the best explanation I've ever seen how airfoils generate lift.
You mentioned how airfoils are used in wings, propellers, and so forth. So am I to assume that propellers suck an airplane forward? And the huge volume (and mass) of a prop blast being thrust rearward is of little consequence? You show the airflow passing an airfoil blissfully trailing aftward, not being deflected downward. Why, then, do downwash and wingtip vortexes travel downward at astonishing rates? Seems you are ignoring the role of a wing as an air pump, and relying on Bernoulli's modest principle to explain lift. Perpetuating the old CFI tale. Read Stick and Rudder. Wings do not suck a plane into the sky.
Thank you
The propeller blades are clearly curved as to incline the airflow backwards, the direction the trailling edge is pointing is something a 2 year old would realize so I'm not gonna spare you for that, and they do essentially the same thing, low pressure area in front of the blade.
And wingtip vortexes don't travel downwards, wtf, you can see planes flying through smoke, the votexes grow bigger over time, but they stay in the same general area.
I am only finding it now that there's the equivalent of Flat-Earthers for fluid dynamics, I thought it was too smart of a field for you guys to bother.
Hands down the best explanation on the topic that I have come across.
Others came here for the semesters, I came here for the curiousity.
Same lol
I came here for beyblades😂
@@UwUJayUwU what does that have to do with lift and aero dynamics 😭🙏
@@MotionX_Studios trying to think of a way to optimize the speed
OOOOHHHHhhhhh! I’m a just layperson who happens to be fascinated by aviation and I LOVE this explanation for flaps and slats that even *I* could understand! Very cool. Thanks!
I just stop the video on 0:16 to remember everyone that Alberto Santos Dumond, a brasilian, made the first self propelled airplane that flighted without being thrown through a catalpult.
YES!
Awesome explanation ! Currently finishing the bachelor in aeronautics and it is great to have such a channel that refreshes my memory on the basis of aerodynamics!
Thank you so much for this video. Making something like this requires several things. Firstly, an understanding itself of the subject topic. Then, thinking through how better to present it and, then, maybe finally, doing all of the work to make the video itself with plots, etc. again, thank you. This is informative.
I know nothing about aerodynamics or even engineering. I just got curious to try to underestand how we actually can fly on a multi tons aircraft. And this video just made it so simple to understand, or at least the basic principle behind it. This is how grterat your video is! Thank you so much, and keep on the great work
I appreciate how you acknowledged the complexity of the topic and that there can sometimes be a clear cause-and-effect relationship between the different phenomena involved in generating lift.
Your exploration of both Bernoulli's Principle and Newton's Third Law as valuable insights into the understanding lift, while also pointing out their limitations, helps avoid falling into the pitfalls of common misconceptions.
I suggest briefly mentioning the common misconceptions about lift, even though your video does not rely on them. This would further educate the audience on the subject and create a more comprehensive understanding of lift.
Overall, great job! Your video is accurate and informative and offers a balanced explanation of lift generation. Keep up the excellent work!
this might be the best video I saw so far on TH-cam!
How this worked has bothered me for over 25 years. Thanks for setting my mind at peace :)
One of the best channel for mechanical engineering.
Amazing work. This 14mins video reminded me what i studied before 14 Years and how I ended up in totally different field for work. 😀
This is the best presentation I have seen for lift so far! I really appreciate you emphasizing that this is only a very small portion of the physics of lift, there is much to be learned.
Thank you for combining concept of circulation with Bernoulli and Newton in your explanation. By far the best video on this topic I have seen.
Isn't it assumptions, imputation, and estimations at this point?
Thank you for the quality of the video, that is one of the few that introduce (quickly though) the notion of "suction" (4:18). And Yes, ALL wings, those of propellers or foils used for water sport for instance do not move the medium (air o water) backwards or downwards, they are sucked by the lower pressure zones created by the movement within that medium.
Best, nuanced but simple video. 👊
I wish the full explanation wasn't paywalled since I can't afford it and your explanations seem manageable - or at least more manageable than what I got from lectures of my professor.
Also, thanks for not perpetuating the equal-transit time myth. Screwed my head for many years.
This is very well done. The best explanation possible in less than 15 minutes!
Concise, complete and elegant!
Whoa, that was an excellent video! I just took a course on "Advanced Fluid Dynamics" and the effect of circulation generated by airfoils didn't click until I watched this video. You did a better job explaining this then my professor or my textbook. And I asked my prof like 3 times to explain it and read through the text sections a few times... Turns out I fell into the fairly common pitfall of "Equal Transit" theory (AKA longer path theory). I swear my prof taught me that false theory when I asked the first time
Excellent video. The best summary of how lift works I have seen. There are a lot of videos out there that take such a simplistic view that they end up being wrong, or at least misleading. [Edited for content]
Much more easier to understand than those Wikipedia articles. Thanks!
Thank you so much for this amazing explanation! Although I had an outstanding Aerodynamics Professor back in the days when I was taking my Aerospace engineering degree, visualizing this “basic” principles for the second time helps to understand the topic even further.
The video explains lift generation very well! But on a completely unrelated note, I must say that I appreciate the use of the ScoutCond font. It's one of my favourite fonts and I am happy to see it being used ahaha
Amaaaaaaazing! Please upload the extended versions on a second youtube channel, would love to see that content for free :)
I have to say this is one of the best if not the best video about the subject that I have ever seen! You got a new subscriber!
I used this video for a High school english project, hope i get an A
Great job explaining the background information relevant to the generation of lift. I liked that it was mentioned that a flat plate could also generate lift, hopefully dispelling misconceptions that the shape of airfoils uniquely generates lift. I don't believe the pinching of streamlines is able to explain pressure differences over the top & bottom surfaces, as that's an effect caused by the geometry of internal flows. Good exploration of the parts that the relationship between pressure & velocity, circulation, and momentum all play in generating lift. Mentioning the limitations of different theories is incredibly important as well, along with the mutual interaction between the explanations.
A frisbee has a curved upper surface and a flat or hollow lower surface, so it is like a circular wing. Now try throwing it upside down and see if it flies - best demo of how wings work!
Best video on the topic i've seen so far!
Best explanation and video, thanks!
By far the best video I have ever seen discussing the topic of lift! The visual representation was amazing! Keep it up!
there is far better on youtube, and that are actually correct, unlike this video.
The best explanation I found on the net
Best concise explanation of lift I have ever seen
A lot of people struggle with Newton or Bernouli.
If you think of Bernouli as a more detailed description of Newton, then it all becomes much clearer.
Following is a very simplified description of the basic components of lift, approximately 1/3rd of lift is pressure under the wing, and 2/3rd suction above the wing as it flows through the air at a positive angle of attack.
This can vary considerably with different shapes.
But I hope it makes it a bit clearer for those struggling with understanding what is happening.