Funnily enough I happened to have this video downloaded so I could watch it while on a flight, where I happened to have the window seat above the wing of a Boeing 737-900. Hearing the introduction and realizing I was in that specific situation was a bit of a trip.
equal transit plays a part in particle physics to explain why photons won't accelerate in a gravitational field. they spin to compensate for the field effect, and this distorts momentum to a perceived constant. the particle can't handle anymore acceleration, so to allow this energy it spins. how cute is that?! or it spins in reverse to the curvature of the field..but we don't know if there is gravitational waves, so i can't say if thats right.
why wouldn't they? . how much do you know about physics? all curves are an acceleration, and to maintain a velocity, it must accelerate around a curve, since a photon is a "constant" velocity, it enters a curve but never slows down or accelerates..it contradicts the laws of physics otherwise...so thus it spins to still capacitate energy, but since it can't accelerate or decelerate in an energy field, thus spins in reverse of said field (like a car going too fast, putting its tires in reverse on a nearly frictionless surface per say.) . gravity isn't a resistance force either. and your gravitational field or curvature can be calculated this way, by the projected curvature of a photon from two lengths, one straight and one curved and spin of the photon being proportional to the energy of the field. minus a projected deceleration and acceleration something or another. i'm still working on the theory, but i'd love for you to steal it so i can prove you wrong too. love seeing my stolen work and how off it gets by needy cunts. like my center of mass concept for the shape of a planet. you tools really botched that one
@@treatb09 Wow, you have serious issues, boy. Have you tried seeking professional help? Curves result in acceleration, sure, but going in a straight line through non-euclidean space is still travelling in a straight line.
He’s dedicated his entire life to understanding airfoils in fluid systems. Saying an academic from Princeton got his “hands dirty” in the field is an ironic metaphor that is insulting to actual technicians. Any scars are probably from being hassled for obsessing over the minutiae of fundamentals while the necessary applicable science is well-established. Though, his reverence of engineers’ intuitive understanding of the fundamentals of physics and Boomer-like iconoclasm give me hope that I’ll meet other similar forces in the industry.
@@willloman812 He's served as the lead engineer for many NASA projects, which is without question getting your "hands dirty", and yet you chalk that up to living in an ivory tower just because he has a PhD.
I have seen the common misunderstanding of Bernoulli's equation many times, that velocity causes low pressure; It just causes it for some unknown mysterious reason. That misunderstanding is even written in books! I'm glad to hear Doug come out and say, "it's not a one-way street". Delta pressure cause acceleration, acceleration causes delta velocity, etc. The differential equation is intertwined. The air on the upper wing surface is actually at a lower pressure than the bottom and it's not "just because it's going fast". At 19:40 and 26:00 in the video he describes this pretty clearly.
"The air on the upper wing surface is actually at a lower pressure than the bottom and it's not "just because it's going fast"." Then why don't they fly into the ground when flying upside down? Does the bottom of the wing then have low pressure? Or is it more likely that the wing is just "planing" off of the passing air?
@@rael5469 Your first guess is correct. When flying upside down, you'll have to adjust the angle of attack to still generate lift in the other direction relative to the wing. Changing the angle of attack changes the flow of air on the wing. If you just invert the wing without changing the angle the aircraft will actually fly into the ground.
@@jonasdaverio9369 Then explain how a T-38 (Thunderbirds) flew upside down? It did not generate lift on the "bottom" surface of the wing....it simply skipped off the air on the new-bottom (top) of the wing. No lift on the upper surface, just air piling up on the lower surface. ....like the old Douglas X-3 Stiletto. en.wikipedia.org/wiki/Douglas_X-3_Stiletto Actually....I stand corrected. Even the X-3 Stiletto had full span leading edge devices which changed the curvature of the wing for lower speed flight.
@@rael5469 I only talked about angle of attack. The angle of attack can be changed very easily by pushing on the stick. No need to modify the wing dynamically
Bravo! Been an aero engineer and a pilot, including lots of flight test for the Navy and contractors over a long career. I've been looking for this guy for decades.
@@Valkyrie12124 Thanks. Am 80 years old, done flying after 63 active years as a pilot. Started as a kid at the local airport. Later became a Navy pilot and carried on a good career in the Navy and, later, as a civilian, airlines, etc. Most of career in flight test, Navy and others. Loved it all but don't miss it now. Getting started these days is VERY different from things in my day.
very very educational for those who want a much more in depth understand as to the physical phenomenon behind lift and flow. I feel he could be a bit more thorough about what constitutes a good explanation as opposed to everything that doesn't, but that's just me.
It's because he's a prior Physics major and knows a ton of the advanced computations and principles of general mechanics. I liked how he spoke about biot savart law and understood that the velocity ("Current" in terms of Electro Magnetism) at varying distances contribute to the point in question r-hat, with distance r. Its hard to calculate but he explained the "intuitive" aspect very well. Unfortunately, you need at least advanced vector calculus with various example problems solved by yourself by hand in order to understand what he is talking about to the professional level he is speaking. I'd recommend a good physics program with competent professors to explain Biot-Savart law well (in advanced integral form) to be able to understand the 2nd half of this lecture.
Around @26:17 he did explain lift more or less correctly: it's both Bernoulli flow plus Newton II & III (or vector N-II & III and Euler). But note, that assumes the continuum approximation, which if you want to be pedantic is false. He was also clear about that at the beginning, he is doing the physics correctly for the continuum approximation, which is a fiction, but "good enough". Air (water) is a gas (liquid) of discrete particles. So the true _ultimate_ explanation (of lift) for a purist is molecular collisions. Molecular collision theory (with some adjustments for inter-molecular forces in a real fluid, stronger in liquids, which give more turbulence and drag) explains it all, and there the Bernoulli effect is pure idealization, and it's really all just Newton II & III. That's why the *angle of attack,* not the wing shape, is the dominant factor, and is why you can fly a plane upside down without inverting the wing foil profile.
@bijou smith. Its really true what you have said. The generation of lift is Misconception from beginning well saying pressure difference would actually generate lift but in reality it's much more complicated. Simple Bernoulli equation can't just the lift the sooner you remove Idealisation the clear the picture will be. It's viscous property of flow which generates lift, fluid is one hell of thing, they are freaking intelligent just required a space they shall compress or expand to occupy it. Continues mechanics comes handy here because they explain why we are assuming no slip conditions or neglecting normal velocity for solving navier stokes equations. Molecular Molecular interaction is will give significant understand in unsteady lift distribution.
Hear, hear! I just started re-taking most of the math classes I took in college almost 40 years ago (primarily to re-learn Linear Algebra for various applications). I'm shocked, disappointed, saddened, and (in a way) scared by how math education seems to have degraded since I first learned these topics. There is no time built into the schedule to allow the teacher time to delve deeply into a single topic. The teacher only has enough time to give enough information for us to answer the questions on the homework and exams administered by the computerized learning management system (LMS) we all have to pay an exorbitant price for. More time is devoted to explaining how to properly format answers to the questions in the LMS than lecturing about the WHYs and HOWs (or even the history) of what we're "learning." Everything seems tailored to completing the homework and exams rather than learning how to think like a mathematician. Even worse, there is not enough time for the teacher to stop speaking for even 10 seconds, to allow us to swallow the information that we was just forced down our throats -- let alone process it in our minds. It seems that the teacher is there just to ram as much "stuff" down our throats rather than actually teach. The scariest thing is that nobody asks any questions, either, beyond asking the teacher to repeat something they missed, or can't read on the board. This is all very sad, and makes me worry about the quality of our scientists and mathematicians coming out of school these days and in the future. If this is "education," I'm not sure I want to continue with the traditional lecture format any longer.
I can't believe I stumbled across this video. I am pretty sure I was there live when he spoke - that's the main lecture hall in the FXB. I enjoyed the talk then, and now I get to enjoy it again!
I am not an aeronautical engineer or expert in aerodynamics. However, I have always been interested in aviation in one form or another including model design and building, skydiving, paragliding, hang gliding etc. When I was a kid, for a science project I explained the thrust from a propeller using the "newtonian approach" which the teacher basically scolded me for and said that it was not the way that the thrust was generated. When the Bernoulli explanation was told to me, I didn't understand why the two points of air had to come back together at the same location. I was afraid to ask and I figured I was just missing something. This always bothered me and it is good to hear that I wasn't the only one who didn't get this "explanation". After watching this video, I started to think back to my skydiving days. Skydivers call the low pressure zone behind them the burble. One thing you didn't want to do is get your pilot chute stuck in the burble. It can flop right onto your back and stay there which can be highly inconvenient if you don't know how to deal with the situation. This is just a demonstration of how strong the low pressure can be. Tracking is when you change your body position with your hands and legs pointed back which gives you a significant horizontal velocity. You are changing the position of the burble, which shifts further back towards your legs. The change in the burble position changes the airflow and air pressures around your body. I have been thinking about the burble and how it affects the airflow. When objects are dragged through the air, there is a high pressure zone in the front and a low pressure zone in the back. There is always a loss in energy with time (thrust times velocity, drag times velocity, or for a glider, vertical velocity times weight). Gliders always lose altitude within an airmass, and planes have to be pulled through the air to generate lift. This energy goes into generating the differential air pressure between the front and back of an object. It is the position of the "burble" or low pressure zone that induces the flow pattern around the wing. The flow pattern and burble generate the differential pressure. I don't know if this is correct or not but it appears from this argument that drag induces the lift and not the other way around. You can have drag without lift but you can't have lift without drag. It also seems to me to be a better way of thinking about lift than the old grade-school Bernoulli explanation. I would be interested to hear what people think about this. Thanks.
A problem though. At about 18:09 on the last line of his presentation cell is the item "mass conservation not a direct reason for acceleration." He says according to Newton there has to be a force associated with the acceleration. And claims no one can tell him what the force would be. That kind of ruined it for me. The restriction the asymmetrical geometry presents to the mass flow rate is a hurdle to the free flow of mass supply, thus changing the density profile. This is synonymous with the formation of a pressure gradient. And that pressure gradient is the force he is claiming can't be explained. So, the "law" of mass conservation is itself directly responsible for the force that results in the acceleration. The total mass in must equal total mass out, and any move toward an imbalance creates the pressure gradient force necessary to accomplish sufficient acceleration. I mean, for gosh sakes, the (mass) continuity equation is one of the fundamental Navier-Stokes rules formally describing the interconnected process. He needs to go back to his previous view cell at 16:09 and rethink the "equal transit time" fallacy to bring that dead end into the proper significance of what it was no doubt aiming for in the "collective subconscious" (or whatever), in terms of his "missing force" from the continuity equation that Navier-Stokes take dead aim at.
@@davetime5234 Mass conservation would indeed be a direct reason for acceleration if you could rigorously establish the cause-and-effect for stream tube pinching. As McLean points out, he can't find a validly argued mechanism for stream tube pinching. I agree with you about the pressure gradient. But I can't, for example, explain the upflow well ahead of the wing leading edge, so this whole problem space is riddled with the danger of oversimplification. I would say that McLean is talking and thinking at a level above what we normally see. My brother taught Aeronautical Engineering at the USAF Academy, they relied on F=mA and mass conservation, and that's indeed a much more rigorous way to treat the subject than that equal transit time nonsense. If a section of the flow were actually constrained by a tube, and that tube constricted, then mass conservation would give rise to the exact force we're looking for. But where there is no tube, the problem is more subtle, it seems to me.
@@Tordvergar "danger of oversimplification" NS equations are able to handle extraordinary complexity (to the point of useful solutions being a challenge). But the driving laws of NS are simple in concept: conservation of mass, energy and momentum, each to be enforced separately but with interconnecting consequence. We don't actually need to worry about a constraining tube if we know the entire extended relative flow has to exhibit continuity (without mass flow interruption taken across the entire area of influence), resulting in logical consequences for the other basic properties, of energy and momentum conservation, when that continuity is challenged. "the upflow well ahead of the wing leading edge" The pressure gradient due to the restrictive path to the mass flow, has to settle in some kind of 3D configuration to keep the mass transit rate logjam from stagnating, which would continue to build static pressure (due to the mass accumulation). This obviously has to form in "cooperation" with a flow rate deficit tendency to form at the exit end: the pressure will continue to drop from mass depletion until the acceleration is high enough to maintain the thruput rate. I think it's reasonable to relate that up-flow ahead of the wing as analogous to backed up traffic due to an incident downstream at an intersection, and with vehicles exiting by alternative routes, preserving some of the vehicle thruput rate. But in the case of the airfoil, the continuity equation says, that for the whole system, the traffic rate cannot be impeded after reaching a steady state situation (pathways naturally self-facilitate via the formed pressure distribution to keep the traffic flowing). So, the backed-up traffic of air mass is facilitated by its self-imposed pressure gradient profile, to continuously fully clear according to the continuity rule (a scenario also consistent with conservation of momentum: the quantity of motion cannot be destroyed). edit: The high transport speed at lower pressure (the Bernoulli conservation of energy notion of higher dynamic pressure at the expense of static pressure) has to result from the pressure gradient effectively filtering out the molecular velocities at the higher end of the thermal velocity distribution, in producing an average higher directed speed of flow (consistent with conservation of energy).
@Tordvergar The stagnation point is the source of the flow pattern, specifically the upwash ahead of the foil. As an airfoil moves through the air, at the stagnation point, it forces air downwards and forward. This force causes a pressure wave in front of the foil as the air just underneath is being accelerated downwards and forwards so it can flow from under the foil, back around the leading edge to the upper suface. This pressure wave, formed on the side of the stagnation point on which air is diverted to flow over the foil, explains the acceleration of air along the upper surface not stream tube pinching. Counterintuitive but this can be visualized in a wind tunnel.
@@singh2702 I wrote “I can’t,” but I meant to write “it can’t.” I think you are correct. It is quite subtle, though, don’t you think? The farther you get ahead of the stagnation point, the harder it is for molecules there to distinguish up from down on the approaching wing.
Stokes's theorem (and Green's functions/theorems in general) are the bit of mathematical physics that most physics/engineering 'enthusiast's would do well to become familiar with. A good reference that I find myself going back to is 'The mathematics of Classical and Quantum Physics' by Byron and Fuller. It builds everything on core theorems of vector space, which after all is the world in which all of physics from hydrodynamics to QED lives. If you are not formally trained, but looking for that extra level of mathematical capability, look no further if your goal is to detect hand-waving in textbooks or lectures.
Any recommendations to what one should be familiar with before reading Byron and Fuller's book? I've got it lying around and am still not sure what the prerequisites are. Maybe single and multi variable real analysis, linear algebra and a bit of ODEs and a bit of complex analysis?
Fascinating lecture! It helps me understand (or question) the experiences I have had sailing a little Laser sail boat. Parcels of air movement (wind) are key to success in racing small boats - but no time to calculate even if we could sense the forces - unless an America's Cup competitor.
I have no answer to this with regards of what's better, but they technically do exist. A lot of WW2 aircraft and even the A10 today kind of achieve this by having a double vertical stabiliser on the edge of the horizontal stabiliser. For military I know that there's radar cross sections that need to be considered which increase drastically with angular planar surfaces, the A10 is an exception because the stabilisers are actually used to hide the hot engine exhaust from IR seekers. With regards to airliners, I think it depends on the results of CFD and wind tunnel tests. I would guess that if rear winglets increased efficiency they would be on there since an airline's goal is to maximise cost. But take this with a grain of salt.
I found this discussion very interesting and informative. I wish he had actually RESOLVED some of the mystery! I would even gladly buy the book (assuming it's available in electronic format - I'm not a Luddite... ;-), if I had ANY confidence it might help to actually EXPLAIN lift, but I have the sneaking suspicion that it would just provide greater detail on what is WRONG with the two prevailing 'pieces of the puzzle' without properly integrating them into a comprehensive all-encompassing DEFINITIVE picture! For now, I'll just continue to use airplanes - though maybe a little more suspiciously...
@@Cheezsoup The problem isn't with the "completeness" of Navier Stokes, it's the existence and smoothness of its solutions, which is inherently a mathematical problem, not a physical one.
I fear that I won't be able to do my job in my later years due to mental decline, but these senior engineers with insanely good intuition give me hope.
I've always intuitively thought that lift was generated from the Newtonian explanation of thrust: particles colliding with the wing at a positive angle of attack, being pushed down, and subsequently the wing being pushed up. (I knew this understanding was incomplete because it couldn't explain how flat bottomed airfoils generated lift at zero angle of attack) I never understood people who only teach the Bernoulli way like it's always been taught to me. Glad to know lift is more complex than what's been taught to me by people who think they are right. I still don't understand lift, but I'm glad I found this video.
The thing is; that particles above the wing are ALSO being 'pushed down' because of the lower pressure above the wing allowing higher pressure far above the wing to push it down. In fact, MORE AIR IS "pushed down" from above the wing than below it. What happens above the wing contributes more to the difference in pressure than the small increase below the wing.
Towed gliders must stay above tow plane ! to avoid the down wash ( displacement of air ) and it is considerable ! a typical C172 displaces 7 tons per second! Bernoulli contributes a lift component , but if you do the arithmetic Bernoulli alone is not sufficient to 'suck' an airplane into the sky !
Air interacting with a space capsule re-entering the atmosphere (aka very thin air at high mach numbers) basically DOSE act like the simple newtonian stream of bullets under thouse conditions, and it's why such vehicles can only generate lift by being tilted to the incoming airstream by dispacing their center of mass.
I'm just a mum staying at home but I found this caught my interest and I understood. I wish though you had explained Newton's second with all the equations and its relation to lift, pressure fields and velocity fields. I really wanted to hear that. Anyway thank you for making this simple to understand. Yeah this covid time broadened my interest. Lol.
Nice presentation. Need to read book. I see some gaps in explaining lift.. great that author mention two ways relationship between pressure and velocity.
You can learn from anyone, don't get caught up in that elitist mentality. I've met plenty of people with decades of experience, that make amateur mistakes. This guy probably isn't the case, but it would be wise of you to take a more humble approach and try to learn from anyone who makes sense.
@@acruzp Theorists with little or no application experience used to be a dime a dozen. With the advent of the Internet, they are now half a cent a hundred, and less on sale. Real humility is in recognizing the difference that practical experience has made in someone else's conceptual understandings relative to one's own.
I think the best way to demonstrate incompleteness of each approach would be to show 2 airfoils: one would be driven solely by Newton's deflection, the other one would be driven only by Bernoulli's pressure difference. otherwise it's unclear how much each of these effects contributes.
It's easy to understand what's going on with a 'lift generating surface' when you look at rotary wings - propellor, helicopters. It sure is windy behind/under them...
Is it true that the vorticity on that capping surface is zero? It seems like we're just assuming that the flow field ahead of the propeller is irrotational, but there must be some because the flow is continuous across the propeller plane.
Reading book. One of the best book about fluid dynamics ( and I already read a lot). Strong points ( so far ) pressure-velocity two way relationship, critics of Reynold number meaning and applicability.
It’s crazy there are so many misunderstood videos on TH-cam regarding lift. I always felt there was something wrong with just saying air travelling faster = lower pressure.
I have my BSc in physics as well and I'm also about to get my private pilots license and every time the explanation of lift came up during ground school it never made any sense to me. Why do air particles HAVE to meet at the other side of the airfoil? They don't. Why is the fluid speed faster over the top surface etc. It's always explained in the pilot community with these naive explanations but this and a couple other videos are gems when it comes to gaining a true understanding of things. This reminds me why I chose physics as my degree!
One thing I'm surprised no one touches on: the contribution of inertia of the contiguous volume of air being accelerated by the angle of attack, the underside of the wing. It's not clear why it's never mentioned that inertia of the air contributes to lift for airplane wings. It is only hinted at when Newton's 3rd law is mentioned. An airplane wing traveling at constant velocity (ie. plane not accelerating) encounters air at neutral (isotropic) pressure and accelerates air below the wing at a magnitude dependent on the angle of attack of the wing. (Extreme example: if the wing's angle of attack were made by turning the wing vertical, the inertia of the air would prevent lift, and the airplane wing would be acting only as an air compressor for the air immediately adjacent to it.) If the air could be accelerated instantly - with no inertia - it would not create lift. The delay in response, caused by inertia, for the air under the wing to 'get out of the way' of the wing's angle of attack is a contribution to lift. The air cannot 'get out of the way' instantly, partly due to inertia (air being matter, and all matter experiences inertia under acceleration). The angle of attack is therefore partially compressing the air immediately adjacent to the (underside of) wing, and the compressed air pushes back against that, creating lift (Newton's 3rd law). This is also why a wing does not 'stall' if its constant velocity is great enough: the angle of attack of the wing accelerates the air underneath, and at great enough velocity, the acceleration of the air under the wing is great enough so that its inertia (inability to instantly accelerate 'out of the way' of the lower part of the wing) is great enough to contribute to lift. If the wing is moving too slowly, inertia of air being accelerated by the angle of attack can no longer contribute to lift. .
The false "equal transit time" is a misstatement of a related requirement: in steady state, rate of mass in has to equal rate of mass out. We know intuitively this has to be true. This more carefully considered truth drives the acceleration of airflow due to the path restriction of the airfoil's asymmetry to be faster than "equal transit time." For the "equal transit time" fallacy people are focusing on too tight a location in space.
Yep, you don’t go into much detail in pilot training, especially for private, primarily because you don’t need to be an aerodynamicist or aeronautical engineer to be a good pilot. Being a good pilot is mostly about situational awareness, adherence to checklists and safety procedures, and some stick and rudder skills. For example you don’t need to know why the boundary layer exists, or why the air molecules do what they do, only things like how an airplane stalls, a general idea of how lift is formed, forces, etc. Everything after that is just extra credit in my opinion because knowing the ladder really won’t make you fly better unless you want to be a Test Pilot or engineer.
10:08 and 11:04 Well what you said is right, I dont see how what they said is "wrong", but rather is incomplete. Its still true that newtons third law (together with his second) implies conservation of momentum, and therefore if you want to design an engine to produce thrust, you must "throw stuff out the back" so to speak. And if you do "throw stuff out the back", then the conservation of momentum requires your rocket move forward. I think the problem is people are confusing the strict statement of the Third law in newtons original formulation (which as you said only talks about forces) with the Conservation of Momentum.
This is why critical thinking and challenging 'authority' is absolutely paramount to progress and ones obtaining of a true understanding in any given topic.
I suspect that the overpressure due to aerodynamic lift never makes it to the ground due to the dissipative action of viscous effects in the atmosphere; this is the same reason why the trailing vortices don't last indefinitely. It seems most plausible that, at least a large distances, a net temperature increase would be only lasting manifestation of lift in the atmosphere.
That addresses the energy portion but not really the force portion of the question. At least I would need to see a more thorough formulation of the concept to convince me.
Easily shown to be false asymptotically. On a sufficiently large planet, with a sufficiently thin atmosphere (so that elevation can be safely ignored in modeling gravitational force) and looking at the equilibrium case, every parcel of mass in the atmosphere has the same downward force no matter where you put it, and the total mass of the atmosphere must be exactly supported by the whole of the planet's surface. When a plane takes off, mass of "atmosphere" increases, hence total projected force onto Earth's surface must also increase, in the static limit. Back in the world of 1/r^2, you can elevate a parcel of mass to reduce its net downward force, thus cancelling out some of the mass of the plane by reshaping the entire atmosphere (possible but implausible). This will be tricky to do while maintaining the criteria of static equilibrium. My own math is not up to the challenge of making any insightful observation about this more complicated problem. Using ballpark parameters for a 747 wing at MTOW, via Google calc: 400 tonne / 6000 sq ft in lb/sq inch = 1.02 pound / (sq inch) The ground support will be _much_ larger than the wing area once you get out of ground effect, and it won't be a pressure we would much notice on the ground. I know this also because many tanks are designed with treads that put no more force on the ground than a man walking, so that either can follow the other onto soft surfaces. What is 6000 sq ft in shoe size? Huge. Not going to leave deep track marks in the sand if the animal is only 400 tonnes.
As a 40 year Boeing aerodynamics engineer, I'm happy to be known as an engineer and not a scientist. Engineers have to make decisions with incomplete data. Scientists generally draw conclusions only after enough data are available that the conclusion is irrefutable.
I, too, am a 40 year Boeing aero engineer and I like the differentiation: a scientist strives to understand the world as it is, an engineer strives to make the world the way we want it to be. (Doug McLean and I worked together for 36 years)
Can anyone help me understand his point made at around 40:00? He says that you can't produce net circulation with a propeller but I can't wrap my head around why. Clearly there is a zone of rotation in the direction I expect, but then in the graph he shows a zone further out (in the 0.5 to 1 region of r/R) that rotates the other way. I'm a bit confused how this counter rotating part comes about, videos showing it happening would be great I think.
I think this could be simplified for a lay audience (people like me) by talking about how a wing interacts with the double vortex in 3D (a helical field), and how wing shapes and velocity affects the interaction - long skinny wings - short fat wings - faster aircraft have swept wings, - winglets - super-critical foil I never thought about the fact that the 3D flow field must also extend forward. I tended to think that the air was still until it met the wing. Another error due to 2D thinking and forgetting about how fast pressure is propagated.
The brilliance of McLean's talk is in how simplified a context subject. I suggest a class in physics for non-science majors. Or, some ground schools in flight training qualify as the aforementioned. Of course, there are probably 'physics for dummies' type books written for the layman. Rather than ask he simplify fuether, you lift your knowledge. I guess that's what torqued me, people wanting to be spoon fed all the while they hardly move a muscle.
The pressure changes in air move at the speed of sound. Therefore the effect of the aircraft on the surrounding air reaches out in front of the plane by a distance equal to the time it takes for the plane to get there. As the speed increases the distance to air in front of the plane that is undisturbed is reduced. When the plane is flying at the speed of sound, then air in front of the plane is undisturbed because the change in pressure cannot propagate faster than the plane is flying.
Many years ago in the UK I gained a bachelors degree in aeronautical engineering and followed that up with a master's degree program in aircraft design. I was never satisfied with the explanations given about aerodynamic lift by my teachers so I was keen to watch this video. While I did gain an understanding about why the explanations given by my teachers were so unsatisfying, I still cannot claim to have a complete understanding of the phenomenon. Is it just me?
Indeed no, you aren't alone. And McLean's explanation doesn't help. On the one hand he demolishes the arguments using Bernoulli and turning down momentum, but then at 23:22 he says both are partly right and then at 26:45 asks his audience for assistance to reconcile them.
As a retired naval aviator and graduate of NPGS, it's all done with mirror farms with a sprinkling of Bernoulli's thrown in. Also occasional magic from McBeth.
So everything I've been taught about lift and aerodynamics (which isnt a lot), has just challanged but there has been no real counter explanation that satisfies my understanding.
The answer is that most of the aerodynamics info out there is complete nonsense. Take for example the reason fighter jet wings are swept. You can look far and wide with the only answer you see being the slowing of air over the top delaying the onset of supersonic flow. This is correct for airliners, but the reality for fighter jets, which you will never find, is that the sweeping of the wings keeps the tips out of the supersonic shock cone. That is why faster planes and objects have their wings so far swept and so far back.
@@sheeplord4976 honestly the reason for the wings of fighters jets to be so swept back is all over on the internet... and is an information which is given in every supersonic aerodynamics course. P.S. It is written even on Wikipedia 😅
@@nicolobonaventura5715 It is rather hard to find on the internet and the explanation Wikipedia gives seems incomplete to me (maybe I missed something). Also, of course it is taught in every aerodynamics class, similar to how the way wings actually work is taught in every aerodynamics class.
yes, most basic public information and teaching prior to a university aerodynamics course, is varying shades of wrong. There are two 'true answers'; lift can be explained by a combination of Newton II,III and Euler if you are willing to accept an approximation that fluids are continuous; if you don't, and want to consider individual molecules, then it can be explained by just Newton II,III, and some physics on molecular interaction. Which is a long winded way of saying it can be correctly explained, but that explanation is not intuitive, unless you study hard.
Formula 1 seems to be the epitome of flow and inverse lift (upside down aerofoils) management, etc. I’m wondering if you’ve ever had discussions with the “grand master” of F1 aero design and management, Adrian Newey, to unpack many of the concepts you’ve discussed, Coanda effect, vortex management and many other aerodynamic and flow management concepts. I suspect if not done already, it may be a very interesting and productive engagement! Thank you for a fascinating talk!
Back in the day all we had was ´Enslaved by No Media´. Now ESM is ancient history of the dinosaurs. Doug puts Enslaved finitely to shame with his common sense, logic and reason approach. I wanted to watch the lecture so I would not upload a youtube video trying to explain stuff about aircraft which I know almost nothing about. What we now need, are like 10 hour videos featuring interviews between persons discussing the physics of areodynamics, etc. It would help us greatly to better understand things like airflow, wind impact, etc.
he is the only other person I have ever heard describe the wing shadowgraph at cruise. The only other person I ever knew who knew about it before i told them was Dr. J Polve Col USAF Ret. Who was my Aero instructor in university. So he is making a good start.
To clarify - Dr Polve was my Aero instructor. he was a brilliant man and I learned a ton from him. He told me about the standing shock wave on the top of a wing, and the possibility of seeing the shadow.
According to this site: www.uspto.gov/news/media/ccpubguide.jsp, you wouldn't need permission to publish or use figures or text contained in a patent disclosure. I wonder if the publisher made him ask for permission, or if perhaps the legal situation is more tedious than the site would lead on? --A Michigan Aero grad just thinking out loud...
OK, I am going to stick my neck out here: From around 26:00 he struggles to explain the presence of pressure differences and resorts to “reciprocal cause and effect“, "pressure fields", "diffuse clouds of low pressure" ! Arrant nonsense! And he know it when he says it’s “kind of the weak link” and “the part I'm least satisfied with” and asks his readers for feedback on "how to strengthen this part”. It’s pure fiction!
I like Doug McLean's insistence that you have to understand & explain why some explanations are only partially correct. Feynman was a great believer in that. He showed in some detail one reason why Le Sage's mechanical model of gravitation, although attractive (it does yield the correct force equation between 2 masses), didn't work for other reasons. See "Richard Feynman Messenger Lectures at Cornell The Character of Physical Law Part 2 The Relation of Mathematics to Physics". Also, in AI learning, it is important to present "near misses" in training. If you're trying to get AI to recognize an arch, you have to show it things which are almost arches but not quite. An example of an arch could be a horizontal slab supported by two vertical slabs. But if the horizontal slab is lying on the ground next to the vertical slabs, it's a near miss - it is close to becoming an arch, but it still requires an additional step to achieve.
@@morcogbr True, I am not an engineer, I'm a scientist by profession. My comment was based on my solid scientific study, where I found that the engineers I respect the most use Dells. Both of them.
Question - this is always spoken to in terms of the air, or fluid is “flowing” over or around the foil. But, isn’t it true to say the foil is moving through a fluid not in motion? Is it the same, but different point of view (perspective of foil, or perspective of fluid particle)? Great lecture!
Yes, it is the same. What matters is the relative motion between the fluid and the body. Hence why wind tunnel tests (static body, moving fluid) are representative of real flight scenarios (moving body, static** fluid).
On the Basis of Messrs Dunning and Kruger, I know enough aerodynamics to know, with some certainty that I don't understand it and that all those simplified explanations you find in bools are just "lies we tell to children" or Just-so-stories and in the long run do more harm than good. Having said that this lecture made a lot of sense. See also how transistors work...
Doug, you mentioned "sun shadow graph"? at the start of your talk. An observation I made a couple of times whilst acting as a flight test acceptance engineer, - I have observed "pressure lines" or shadow lines on top of the wing surface during flight (my best description of them was "ghosts" - do you have an explanation for this? I've never been able to work it out. The aircraft in question was an A320 at cruise altitudes. These shadow lines were definite enough to photogrph.
Yes! You're seeing the light bend as it moves through a density jump, also known as the shock wave. It dances around, moving forward and backward, casting a shadow on the wing.
Finally someone I agree with. A plane flies because it pumps air down. Newton’s 2nd Law. Done. You can do this with a flat plywood wing. I knew this as a kid flying my hand outside the car window. The rest of aerodynamics is making that pumping efficient, controlling flight, staying away from stalls.
As a pilot, I have been taught the equal transit explanation. It would have been nice if he explained what the correct idea is as opposed to why it’s wrong lol
I recommend the book series "Fly Better" by Noel Kruse. Freely available online. The first book talks in depth, using simple words, about aerodynamics.
Around @26:17 he did explain lift more or less correctly: it's both Bernoulli flow plus Newton II & III (or vector Newton and Euler). But note, that assumes the continuum approximation, which if you want to be pedantic is false. He was also clear about that at the beginning, he is doing the physics correctly for the continuum approximation, which is a fiction, but "good enough". Air (water) is a gas (liquid) of discrete particles. So the true _ultimate_ explanation (of lift) for a purist is molecular collisions. Molecular collision theory (with some adjustments for inter-molecular forces in a real fluid, stronger in liquids, which give more turbulence and drag) explains it all, and there the Bernoulli effect is pure idealization you do not use it, and it's really all just Newton II & III. That's why the *angle of attack,* not the wing shape, is the dominant factor, and is why you can fly a plane upside down without inverting the wing foil profile. BTW, if you need fine detail currently you need to use a continuum approximation (Navier-Stokes), so it's important to get the continuum theory right if you are in high performance sports like F1 or America's Cup yachting, since (I believe) it's not possible to perform large scale molecular dynamics simulations yet, although computer performance improvements constantly amaze me. On AC75 foils they might be doing some molecular dynamics.
@@Achrononmaster "and is why you can fly a plane upside down without inverting the wing foil profile." I disagree. 1. Not all planes can fly upside down efficiently. Planes that can fly upside down efficiently such as an F18 military jet for example have very different looking wings (looking at cross section they are almost symmetrical) and lift is attained by using angle of attack to create pressure differences when you fly. You'll need to point the nose up towards the sky no matter what if you want to fly upside down.
One reason the equal transit explanation is unsatisfactory is that the acceleration of the fluid across the upper surface starts well before the airfoil. How far? Who knows? It will be a function of the pressure distribution. Also, the top surface distance is defined from the stagnation point, which changes with AOA, not the zero % chord point. But the big problem with pilot training is that it is given by pilots, not scientists or engineers. You don’t want pilots teaching this stuff anymore than you want scientists flying instrument approaches. They don’t have the proper training or technical background. And finally, there is no reason why a pilot needs to understand these phenomena at this level. The famous book stick and rudder states this clearly. It says simply that the wing pushes the air down which keeps the plane up. As an engineer and pilot I can assure you that for piloting purposes this is entirely adequate.
Very good. I would listen to industry experts. Their theories and analyses have to stand the test of actually flying. Thank you Dr McClean. Thank you Michigan Engineering.
34:38 This thing’s pretty funny. Unless the holes in the flow straightener are very small, the vortex is just going to split into a bunch of vortices that are just going to recombine behind it. If the openings in the straightener are small enough, that’s a lot of parasitic drag for one, but he’s essentially built a Dyson vacuum cleaner and the vortices (I think) going to exert a huge amount of skin drag from being de-spun. And I haven’t got through his entire explanation of why it doesn’t work, but if he didn’t mention it, I also imagine whatever vortification it removes is just going to be generated again, meaning even more drag.
People really want simple explanations. Aerodynamics is not simple, so many people cling to simple but wrong explanations, and argue passionately about them. That passion comes from an emotional insecurity and fear that there are things that they can't understand -- things that *cannot* be reduced to a simple explanation. And people with this misconception will deny the reality of *anything* complicated.
My dad always told me to get the seat over the wing... because its the safest location structurally in a crash... I usually get the seat right over the front edge so I can see down, because I'm glued to the window. Maybe not so safe considering I'm near the plane of the spinning turbine blades (but not exactly on it).... but whatever. If they fly off they are going to fly forward, or go back in the engine and detonate that puppy in a mad Star Wars 1 podracer type fireball that I definitely want to have front row seat on to watch...
@ep5 Lol @ seat back home... watching the crash of the flight I didn't get on... I think in a crash, the flames are going to be going rearward... plus in a water crash, you'd be maybe closer to a wing to climb out onto.. be interesting to see sme kind of statistics ... which will probably say, ultimately, it doesn't matter a whole lot.
@ep5 I know right, wehnyou crash, more often than not, it's you in the pilot seat and you never saw it coming. I will say this: my last 3 fatal motorcycle colisions while driving while blind were rendered mute by my 1000 hours spent in a quad copter simulator flying. In all cases I couldn't see the car parked in the road until it was right in my face, and my reaction time was instant knee jerk to swerve around it without thinking. The first, I swerved to the left around a parked van in the road. The second, I immediately swerved back into my lane after passing it, and an on coming car went right on by. THat for sure would of been fatal. The third was a later date where the van parked in the road like a G D idiot happend all over again on the same road. After that I stopped taking that road, then I stopped driving all together as my vision worsened even further. A year earlier with better v\sion but but not 1000 hours of lying in the simulator behind me, I took out 3 construction horses some other id die ots had put on the interstate with no flashing lights, no cones, nothing, just blocking off a lane. I was going 20 miles afster, butstill. I swerved too late to get in the left lane and took out all three construction horses withthe front of my motorcycle like a battering ram and kept going, albeit pissed off. Had to repair all that. So my recomendation... do all your crashing in a simulator. I've basically crashed a million times by now crashing my way upward to being a pro aerobatic pilot. I must crash 30 times a day in the sim..
@ep5 Yep, my neighbor ran a stop sign on a 3 wheel motorcycle and his girlfriend on the back was killed and he lost hi slegs. I've run through intersections once or twice in my life. Simulators are a great way to fly every day, rain or sign. I'm lik 1,200 hours. Way more fun than the real deal, you can do anything in them. Real flying in an airplane in a straight line is now boring to me like a trip to the grocery store. Why fly, when you can frolic in the sky with no G forces and no threat to life or limb. I fly a sim called Liftoff. It took me a long time to tune it from the defaults for the sticks to match my brain, but I finally got it and now my machine flies creamier than ice cream. The real life RC equipment I'm not having so much luck with, I'm sick of fixing broken stuff anymore. My three real people sized airplane projects also probably will never be touched again, they're collecting dust. Now I'm the automated recorded girl that speaks to pilots on their radio. Pull up! Pull up! Pull up!
19:00 LOL... excellent statement. So lets assume time is the force, or connected to it.... do we see an increase or a decrease in time, and if time is a constant where does it get the time needed to create a change in the transition state? And what happens to space if space is relative to time? 23:00 Ahha... the information frame we live in where phase provides the correct answer of the moment and everything is made out of contradiction. Some say the electron moves... and some same say the "hole" moves. But what if time has a reverse arrow connected to the "missing" graviton and they both move connected to "something" stationary... say a true inertial frame of reference they are both relative to... just not at the same exact time because there is a wait state involved separating the phase timing? Is Bernoulli dealing more with the concept of space, and Newton more with the concept of time, and both showing the same cause of force? 27:14 Sounds more like he is talking about the strong force... more accurately than in any book. The strong force keeps two protons from pushing each other away... but what if the proton's phase timing is connected to a true inertial frame of reference. Is a wall a force because it refuses to move and a ball bounces off of it? 30:49 What if it takes the time (and space) of two Mass oscillations to create one observed instance in 3D? Will we see gravity move sideways? How about light moving through in a slit in 3D... if we divide the phase timing in half will we see the effect turn sideways? 36:36 Ouch.... OK so lesson learned but what do I call it if not induced drag? We are left hanging here. I guess when you get the name correct you'll have answered the question. Maybe the question is wrong... great video, makes you think.
Maybe another misconception is describing the "wingtip vortex" which might be a misnomer. I would think it is realistically a product of the whole aircraft rather than the wingtip alone. Any attempt to counter the vortex pair would require a device the size of the aircraft itself (admittedly with diminishing returns as device size increases). Is there a possibility that wingtip devices are a marketing ploy (Star Wars) and not a real improvement? After all, a small increase of wing span should do the same thing, and as the wing tip devices produce perhaps the same wing root cranked in moment as a wing extension (for the same improvement) and the devices just add complexity, why use them? As an aerodynamics mechanical engineer I tried to get into Boeing aerodynamics but maybe they found that my birth date was the same year the Hindenburg crashed, a bad omen, so they put me to work--on boats.
Well, the wingtip vortex is due to the circulation theory about the airfoil. You can have a flying wing and still have wingtips vortices. What also helps create wingtip vortices is the difference in pressure between the upper and lower panels of the airfoil. Wing tip devices come with their own cons. They are a benefit at full TO weight, but become more of a detriment towards the middle to the end of the flight. I had to look it up after a discussion in an aero group. And it is hard to get in as an aerodynamicist. Not as many jobs in the field. Some of it expanded into wind turbines. Not exactly what I would call interesting stuff.
The reality is that much of aerodynamics is done, leaving the aerodynamicists to work on the crumbs. After all, while the work still continues (maybe not) with the mathematics, they still wind tunnel test their ideas. That is, except me, where I built the first "Trike" that I know of, using other peoples numbers, and I survived the first test flights.
Many people don’t realize that there are symmetric airfoils, such as in RC helicopter blades. This is so they can generate the same amount of lift when flying inverted (upside down). The Bernoulli/Equal Time explanation falls flat for these from the start, as lift is generated only when the blade pitch is changed, and thus there has to be a different explanation.
@conacal rubdur I'm not an engineer, just an interested middle-aged geek. I do, though, share your concerns regarding the aerospace industry. How much of aerospace engineering is transferable to other engineering disciplines in the job market? (That's something to ask your adviser or the website of some Society of Engineers.) And how much would your graduation be delayed if you changed majors in a couple of years? (Also something to ask your adviser.) Good luck with this important choice!!
@conacal rubdur Go for It! Otherwise, as an old mechanical engineer you will ask yourself why didn't make aerospace. You will find jobs in both of them, but you will love the job if you do what you like the most. Regards
YEP ! 26:00 to 28:00 are the deepest keys to apprehend this fascinating result (instinct make me think of a sort of succion, caused by gradient and sustained by fluid's inertia , countr acting gravity for gliders, thrust etc...) . He should have made some // with swim too...
I am not entirely sure this video really did clarify and explain how lift is generated. it started off pretty good to debunk the wrong ways of thinking how lift is explain, but at the end I am still not sure if it did much to explain how it's generated. Perhaps I missed something, which is possible.
@William Buckley; Mankinds Great Intellectual! Mr Buckley, I believe we understand how an airplane flies and how lift is generated. We know lift is the resultant of differential pressures around the wing. That much is clear to a lot of people. I think the problem is how we explain it and your statement above is a good example, which is what the video debunks. We know Bernoulli law explains that increase in velocity of an air molecule on the same streamline decreases pressure and slow air molecule increases pressure and the resultants of imbalance pressures keeps planes in the air so that's not the issue. The issue is often times, the explanation as to why the velocity increases at the wing top and decrease at the bottom of the wing is where people explain with haste. And you made the same mistake in your replay. As the video debunks, what is the physics behind the claim that the air molecule at the top and bottom has to meet? Did they decided at the leading edge that "hey meet me at some time at the tail end of the wing and let's have pizza and beer?" That's the issue with such explanation--there is no basis for that logic in physics and that's where people confuses the issues. I think the video did a good job debunking that explanation, but my problem with the video is I didn't understand the replacement of the physics explanation as to why the velocity increases at the top and lower at the bottom. That's what I was asking about. Thank you for trying to help, but I think like me, you also didn't get the physics explanation of the why the velocity increases at the top. I would like someone to explain to me as to what the physics explanation is that causes the velocity to go up .
The quickest and simplest way to destroy misconceptions in aerodynamics is to first give a visual example and experiment not an explanation. This experiment requires 3 items. 1. A average sized screwdriver with a smooth round head on the handle end. 2. Air compressor capable of 90-120 psi. 3. Air blower. Hold screw driver by its shank so the head of the handle is vertical up. Blow air from air blower across smooth head of screwdriver at about 3-5 inches away and about 45 degrees pointing vertical. The screwdriver will suspend in mid air. The air flowing across the smooth round head of the screwdriver is creating lift by creating low pressure just above the head of the screw driver. I used this example in the hangar teaching student pilots and it always creates the eureka moment of aerodynamics.
one of the biggest problems explaining lift starts with using molecules with momentum instead of at rest with the object having momentum. A wing moves out from under molecules that are weighted down from above and as long as the pressure differential is great enough, the weight of the object is negated. Take scales on to an elevator and weigh yourself as the floor moves down as opposed to being stationary. The top of the wing is constantly moving out from under the pressure of the molecules directly in contact with it.
The wind tunnel is the most practical way to study lift. The reality is of course that the air is still and the wing comes along and slices through it. The wind tunnel encourages concentration on near field effects while seeing the aircraft approach and fly past gives you an appreciation of the far field effects, which also exist. This is especially striking when there is smoke to help you visualize the effects on the air, such as in the NASA vortex studies.
I am not sure but my first impression is that he elaborates the things, which are indeed straightforward, more than necessary and makes them seem incomprehensible. i would suggest students to stick to anderson's book in order not to get lost in details which are not really details. he speaks as if he was talking on a subject related to quantum mechanics.
it is i believ really that deep.i have had some "expansion" of my thoughts just as he had.i suspect that people are takeing somethings for granted which are "obvious" but not easily vocalized.or simply put,a not knowing.
You can´t be serious? It´s clear as water what the lecture is all about and you have obviously not been reading that. What you want the lecture to be is something else - isn´t it?
+norton noble, which of the two Andersons? There are two different guys with two different books and views. If you are talking about the Andersons that proposes the "scoop" allegory to explain lift, you do need to pay more attention to what Mr. Lean is explaining!
A "no-slip condition at the surface." What is the effect of this assumption? What is "slip." An extremely valuable perspective from the real side of math and physics. Doug McLean is assuredly an aerospace scientist.
No slip is assuming that there is non-flowinf air right at the surface of the wing on a very tiny molecular distance, which is largelt why a boundary layer forms. Little friction on the wing surface doesnt allow the air to perfectly slip.
Me being an Accounting Major. I would say no. Only forward momentum with the help of gravitational pull and fluid propagation difference caused by the mass behind the leading edge.
To this day, I remember explaining the forward thrust of a propeller using the Bernoulli airfoil theory in my undergraduate physics test and it not feeling right. Little did I know, how little I knew 😄
The equivalence with electric and magnetic fields clicked it a lot for me, because we have the same exact confusions, to the point that he claims “in electromagnetism that is a causal relation, the induction law”, but that’s mostly a historical artifact of how we discovered these phenomena.
What an intelligent human being. These are the real unsung heroes of our modern word I swear.
>Intelligent
>hero
Pick one
@@RakedLeaf Why do I have to "pick one" when I think he is both intelligent and a hero? A person can be both in my opinion.
@@r3ttgaming177 he's not a hero
@@RakedLeaf well, certainly he is for r3ttgaming177, stop being so charismatic
@@RakedLeaf Maybe he's not a hero for you, and that's fine... However, he is a hero in my eyes.
This is the best title for a presentation ever.
Funnily enough I happened to have this video downloaded so I could watch it while on a flight, where I happened to have the window seat above the wing of a Boeing 737-900. Hearing the introduction and realizing I was in that specific situation was a bit of a trip.
"Equal transit time is wrong" good never made sense to me
equal transit plays a part in particle physics to explain why photons won't accelerate in a gravitational field. they spin to compensate for the field effect, and this distorts momentum to a perceived constant. the particle can't handle anymore acceleration, so to allow this energy it spins. how cute is that?! or it spins in reverse to the curvature of the field..but we don't know if there is gravitational waves, so i can't say if thats right.
@@treatb09 Why would photons accelerate, even in a gravitational field? That makes no sense. Speed of light is constant.
why wouldn't they? . how much do you know about physics? all curves are an acceleration, and to maintain a velocity, it must accelerate around a curve, since a photon is a "constant" velocity, it enters a curve but never slows down or accelerates..it contradicts the laws of physics otherwise...so thus it spins to still capacitate energy, but since it can't accelerate or decelerate in an energy field, thus spins in reverse of said field (like a car going too fast, putting its tires in reverse on a nearly frictionless surface per say.) . gravity isn't a resistance force either. and your gravitational field or curvature can be calculated this way, by the projected curvature of a photon from two lengths, one straight and one curved and spin of the photon being proportional to the energy of the field. minus a projected deceleration and acceleration something or another. i'm still working on the theory, but i'd love for you to steal it so i can prove you wrong too. love seeing my stolen work and how off it gets by needy cunts. like my center of mass concept for the shape of a planet. you tools really botched that one
@@treatb09 Wow, you have serious issues, boy. Have you tried seeking professional help?
Curves result in acceleration, sure, but going in a straight line through non-euclidean space is still travelling in a straight line.
@@treatb09 irrelevant to the topic here innit ?
Ex industry professionals make the best lecturers. They have got their hands dirty and have the battle scars to prove it.
He’s dedicated his entire life to understanding airfoils in fluid systems. Saying an academic from Princeton got his “hands dirty” in the field is an ironic metaphor that is insulting to actual technicians. Any scars are probably from being hassled for obsessing over the minutiae of fundamentals while the necessary applicable science is well-established.
Though, his reverence of engineers’ intuitive understanding of the fundamentals of physics and Boomer-like iconoclasm give me hope that I’ll meet other similar forces in the industry.
@@willloman812 He's served as the lead engineer for many NASA projects, which is without question getting your "hands dirty", and yet you chalk that up to living in an ivory tower just because he has a PhD.
I have seen the common misunderstanding of Bernoulli's equation many times, that velocity causes low pressure; It just causes it for some unknown mysterious reason. That misunderstanding is even written in books!
I'm glad to hear Doug come out and say, "it's not a one-way street".
Delta pressure cause acceleration, acceleration causes delta velocity, etc. The differential equation is intertwined.
The air on the upper wing surface is actually at a lower pressure than the bottom and it's not "just because it's going fast".
At 19:40 and 26:00 in the video he describes this pretty clearly.
There’s even a MIT video on aerodynamic with this misunderstanding.
"The air on the upper wing surface is actually at a lower pressure than the bottom and it's not "just because it's going fast"."
Then why don't they fly into the ground when flying upside down? Does the bottom of the wing then have low pressure?
Or is it more likely that the wing is just "planing" off of the passing air?
@@rael5469 Your first guess is correct. When flying upside down, you'll have to adjust the angle of attack to still generate lift in the other direction relative to the wing. Changing the angle of attack changes the flow of air on the wing. If you just invert the wing without changing the angle the aircraft will actually fly into the ground.
@@jonasdaverio9369 Then explain how a T-38 (Thunderbirds) flew upside down? It did not generate lift on the "bottom" surface of the wing....it simply skipped off the air on the new-bottom (top) of the wing. No lift on the upper surface, just air piling up on the lower surface. ....like the old Douglas X-3 Stiletto.
en.wikipedia.org/wiki/Douglas_X-3_Stiletto
Actually....I stand corrected. Even the X-3 Stiletto had full span leading edge devices which changed the curvature of the wing for lower speed flight.
@@rael5469 I only talked about angle of attack. The angle of attack can be changed very easily by pushing on the stick. No need to modify the wing dynamically
Bravo! Been an aero engineer and a pilot, including lots of flight test for the Navy and contractors over a long career. I've been looking for this guy for decades.
How did you become a pilot, that’s my dream
@@Valkyrie12124 Thanks. Am 80 years old, done flying after 63 active years as a pilot. Started as a kid at the local airport. Later became a Navy pilot and carried on a good career in the Navy and, later, as a civilian, airlines, etc. Most of career in flight test, Navy and others. Loved it all but don't miss it now. Getting started these days is VERY different from things in my day.
Definitely one of best talks on aerodynamics on TH-cam. Thank you!!!!
very very educational for those who want a much more in depth understand as to the physical phenomenon behind lift and flow. I feel he could be a bit more thorough about what constitutes a good explanation as opposed to everything that doesn't, but that's just me.
It's because he's a prior Physics major and knows a ton of the advanced computations and principles of general mechanics. I liked how he spoke about biot savart law and understood that the velocity ("Current" in terms of Electro Magnetism) at varying distances contribute to the point in question r-hat, with distance r. Its hard to calculate but he explained the "intuitive" aspect very well. Unfortunately, you need at least advanced vector calculus with various example problems solved by yourself by hand in order to understand what he is talking about to the professional level he is speaking. I'd recommend a good physics program with competent professors to explain Biot-Savart law well (in advanced integral form) to be able to understand the 2nd half of this lecture.
Around @26:17 he did explain lift more or less correctly: it's both Bernoulli flow plus Newton II & III (or vector N-II & III and Euler). But note, that assumes the continuum approximation, which if you want to be pedantic is false. He was also clear about that at the beginning, he is doing the physics correctly for the continuum approximation, which is a fiction, but "good enough". Air (water) is a gas (liquid) of discrete particles. So the true _ultimate_ explanation (of lift) for a purist is molecular collisions. Molecular collision theory (with some adjustments for inter-molecular forces in a real fluid, stronger in liquids, which give more turbulence and drag) explains it all, and there the Bernoulli effect is pure idealization, and it's really all just Newton II & III. That's why the *angle of attack,* not the wing shape, is the dominant factor, and is why you can fly a plane upside down without inverting the wing foil profile.
@@Achrononmaster yesss....!!
@@Achrononmaster Can you recommend any books which explains this topic in right way.
@bijou smith.
Its really true what you have said. The generation of lift is Misconception from beginning well saying pressure difference would actually generate lift but in reality it's much more complicated. Simple Bernoulli equation can't just the lift the sooner you remove Idealisation the clear the picture will be. It's viscous property of flow which generates lift, fluid is one hell of thing, they are freaking intelligent just required a space they shall compress or expand to occupy it. Continues mechanics comes handy here because they explain why we are assuming no slip conditions or neglecting normal velocity for solving navier stokes equations. Molecular Molecular interaction is will give significant understand in unsteady lift distribution.
Good stuff to feed my brain. The art of understanding and not merely regurgitating answers while learning.
Hear, hear! I just started re-taking most of the math classes I took in college almost 40 years ago (primarily to re-learn Linear Algebra for various applications). I'm shocked, disappointed, saddened, and (in a way) scared by how math education seems to have degraded since I first learned these topics.
There is no time built into the schedule to allow the teacher time to delve deeply into a single topic. The teacher only has enough time to give enough information for us to answer the questions on the homework and exams administered by the computerized learning management system (LMS) we all have to pay an exorbitant price for. More time is devoted to explaining how to properly format answers to the questions in the LMS than lecturing about the WHYs and HOWs (or even the history) of what we're "learning." Everything seems tailored to completing the homework and exams rather than learning how to think like a mathematician.
Even worse, there is not enough time for the teacher to stop speaking for even 10 seconds, to allow us to swallow the information that we was just forced down our throats -- let alone process it in our minds. It seems that the teacher is there just to ram as much "stuff" down our throats rather than actually teach. The scariest thing is that nobody asks any questions, either, beyond asking the teacher to repeat something they missed, or can't read on the board.
This is all very sad, and makes me worry about the quality of our scientists and mathematicians coming out of school these days and in the future. If this is "education," I'm not sure I want to continue with the traditional lecture format any longer.
Thank you Mr. McLean for your passion and expertise.
He has doctor rate. So His title is Dr. McLean.
Mr. McLean would be interesting to have a discussion about common misconceptions about presentations. His presentation is nicely done.
I can't believe I stumbled across this video. I am pretty sure I was there live when he spoke - that's the main lecture hall in the FXB. I enjoyed the talk then, and now I get to enjoy it again!
Thanks to my old friend, Al Zheimer!
@@robbmain3030 oof
I am not an aeronautical engineer or expert in aerodynamics. However, I have always been interested in aviation in one form or another including model design and building, skydiving, paragliding, hang gliding etc. When I was a kid, for a science project I explained the thrust from a propeller using the "newtonian approach" which the teacher basically scolded me for and said that it was not the way that the thrust was generated. When the Bernoulli explanation was told to me, I didn't understand why the two points of air had to come back together at the same location. I was afraid to ask and I figured I was just missing something. This always bothered me and it is good to hear that I wasn't the only one who didn't get this "explanation".
After watching this video, I started to think back to my skydiving days. Skydivers call the low pressure zone behind them the burble. One thing you didn't want to do is get your pilot chute stuck in the burble. It can flop right onto your back and stay there which can be highly inconvenient if you don't know how to deal with the situation. This is just a demonstration of how strong the low pressure can be.
Tracking is when you change your body position with your hands and legs pointed back which gives you a significant horizontal velocity. You are changing the position of the burble, which shifts further back towards your legs. The change in the burble position changes the airflow and air pressures around your body.
I have been thinking about the burble and how it affects the airflow. When objects are dragged through the air, there is a high pressure zone in the front and a low pressure zone in the back. There is always a loss in energy with time (thrust times velocity, drag times velocity, or for a glider, vertical velocity times weight). Gliders always lose altitude within an airmass, and planes have to be pulled through the air to generate lift. This energy goes into generating the differential air pressure between the front and back of an object. It is the position of the "burble" or low pressure zone that induces the flow pattern around the wing. The flow pattern and burble generate the differential pressure. I don't know if this is correct or not but it appears from this argument that drag induces the lift and not the other way around. You can have drag without lift but you can't have lift without drag. It also seems to me to be a better way of thinking about lift than the old grade-school Bernoulli explanation.
I would be interested to hear what people think about this. Thanks.
Two flows of air do not get back together. Difference is drag.
Top flow gets to trailing edge first.
I can relate to the first paragraph of this comment.
can you make vedio on your topic some points are really intresting
How rare on TH-cam to hear someone burble coherently.
This lecture is very impressive, it should recommended for all new pilots..
These are not for pilots. They can't understand these theoretical facts. These are for scientists and engineers. Cheers !
I think this is the single best engineering lecture I've ever seen. Powerhouse.
A problem though. At about 18:09 on the last line of his presentation cell is the item "mass conservation not a direct reason for acceleration." He says according to Newton there has to be a force associated with the acceleration. And claims no one can tell him what the force would be.
That kind of ruined it for me. The restriction the asymmetrical geometry presents to the mass flow rate is a hurdle to the free flow of mass supply, thus changing the density profile. This is synonymous with the formation of a pressure gradient. And that pressure gradient is the force he is claiming can't be explained.
So, the "law" of mass conservation is itself directly responsible for the force that results in the acceleration. The total mass in must equal total mass out, and any move toward an imbalance creates the pressure gradient force necessary to accomplish sufficient acceleration.
I mean, for gosh sakes, the (mass) continuity equation is one of the fundamental Navier-Stokes rules formally describing the interconnected process.
He needs to go back to his previous view cell at 16:09 and rethink the "equal transit time" fallacy to bring that dead end into the proper significance of what it was no doubt aiming for in the "collective subconscious" (or whatever), in terms of his "missing force" from the continuity equation that Navier-Stokes take dead aim at.
@@davetime5234 Mass conservation would indeed be a direct reason for acceleration if you could rigorously establish the cause-and-effect for stream tube pinching. As McLean points out, he can't find a validly argued mechanism for stream tube pinching. I agree with you about the pressure gradient. But I can't, for example, explain the upflow well ahead of the wing leading edge, so this whole problem space is riddled with the danger of oversimplification.
I would say that McLean is talking and thinking at a level above what we normally see. My brother taught Aeronautical Engineering at the USAF Academy, they relied on F=mA and mass conservation, and that's indeed a much more rigorous way to treat the subject than that equal transit time nonsense. If a section of the flow were actually constrained by a tube, and that tube constricted, then mass conservation would give rise to the exact force we're looking for. But where there is no tube, the problem is more subtle, it seems to me.
@@Tordvergar "danger of oversimplification"
NS equations are able to handle extraordinary complexity (to the point of useful solutions being a challenge). But the driving laws of NS are simple in concept: conservation of mass, energy and momentum, each to be enforced separately but with interconnecting consequence.
We don't actually need to worry about a constraining tube if we know the entire extended relative flow has to exhibit continuity (without mass flow interruption taken across the entire area of influence), resulting in logical consequences for the other basic properties, of energy and momentum conservation, when that continuity is challenged.
"the upflow well ahead of the wing leading edge"
The pressure gradient due to the restrictive path to the mass flow, has to settle in some kind of 3D configuration to keep the mass transit rate logjam from stagnating, which would continue to build static pressure (due to the mass accumulation). This obviously has to form in "cooperation" with a flow rate deficit tendency to form at the exit end: the pressure will continue to drop from mass depletion until the acceleration is high enough to maintain the thruput rate.
I think it's reasonable to relate that up-flow ahead of the wing as analogous to backed up traffic due to an incident downstream at an intersection, and with vehicles exiting by alternative routes, preserving some of the vehicle thruput rate.
But in the case of the airfoil, the continuity equation says, that for the whole system, the traffic rate cannot be impeded after reaching a steady state situation (pathways naturally self-facilitate via the formed pressure distribution to keep the traffic flowing).
So, the backed-up traffic of air mass is facilitated by its self-imposed pressure gradient profile, to continuously fully clear according to the continuity rule (a scenario also consistent with conservation of momentum: the quantity of motion cannot be destroyed).
edit: The high transport speed at lower pressure (the Bernoulli conservation of energy notion of higher dynamic pressure at the expense of static pressure) has to result from the pressure gradient effectively filtering out the molecular velocities at the higher end of the thermal velocity distribution, in producing an average higher directed speed of flow (consistent with conservation of energy).
@Tordvergar The stagnation point is the source of the flow pattern, specifically the upwash ahead of the foil.
As an airfoil moves through the air, at the stagnation point, it forces air downwards and forward. This force causes a pressure wave in front of the foil as the air just underneath is being accelerated downwards and forwards so it can flow from under the foil, back around the leading edge to the upper suface. This pressure wave, formed on the side of the stagnation point on which air is diverted to flow over the foil, explains the acceleration of air along the upper surface not stream tube pinching. Counterintuitive but this can be visualized in a wind tunnel.
@@singh2702 I wrote “I can’t,” but I meant to write “it can’t.” I think you are correct. It is quite subtle, though, don’t you think? The farther you get ahead of the stagnation point, the harder it is for molecules there to distinguish up from down on the approaching wing.
Dudes face even looks aerodynamic
🤣🤣
Yeah but that's kinda rude :(
Lmao
@@briancaguirre tu
😂
Stokes's theorem (and Green's functions/theorems in general) are the bit of mathematical physics that most physics/engineering 'enthusiast's would do well to become familiar with. A good reference that I find myself going back to is 'The mathematics of Classical and Quantum Physics' by Byron and Fuller. It builds everything on core theorems of vector space, which after all is the world in which all of physics from hydrodynamics to QED lives. If you are not formally trained, but looking for that extra level of mathematical capability, look no further if your goal is to detect hand-waving in textbooks or lectures.
Any recommendations to what one should be familiar with before reading Byron and Fuller's book? I've got it lying around and am still not sure what the prerequisites are. Maybe single and multi variable real analysis, linear algebra and a bit of ODEs and a bit of complex analysis?
@@OttzelTV Just look up the pre-req's for a 4th year Modern Physics course at any major university.
Fascinating lecture! It helps me understand (or question) the experiences I have had sailing a little Laser sail boat. Parcels of air movement (wind) are key to success in racing small boats - but no time to calculate even if we could sense the forces - unless an America's Cup competitor.
Why dont we see swept up wingtips on rear horizontal stabilizers? Only on maing wings?
Wouldnt adding this also reduce drag?
I have no answer to this with regards of what's better, but they technically do exist. A lot of WW2 aircraft and even the A10 today kind of achieve this by having a double vertical stabiliser on the edge of the horizontal stabiliser. For military I know that there's radar cross sections that need to be considered which increase drastically with angular planar surfaces, the A10 is an exception because the stabilisers are actually used to hide the hot engine exhaust from IR seekers.
With regards to airliners, I think it depends on the results of CFD and wind tunnel tests. I would guess that if rear winglets increased efficiency they would be on there since an airline's goal is to maximise cost. But take this with a grain of salt.
I found this discussion very interesting and informative. I wish he had actually RESOLVED some of the mystery! I would even gladly buy the book (assuming it's available in electronic format - I'm not a Luddite... ;-), if I had ANY confidence it might help to actually EXPLAIN lift, but I have the sneaking suspicion that it would just provide greater detail on what is WRONG with the two prevailing 'pieces of the puzzle' without properly integrating them into a comprehensive all-encompassing DEFINITIVE picture!
For now, I'll just continue to use airplanes - though maybe a little more suspiciously...
AFAIK There is NO COMPLETE theory of lift . Aerodynamists use various theories depending on what they are looking for .
@@Cheezsoup well there is navier-stokes which is pretty much complete, but yeah maybe that's just renaming the problem
@@screwhalunderhill885
If you know Navier-Stokes to be complete and can show same there is a MILLIOM dollars waiting for you.
@@Cheezsoup lol
@@Cheezsoup The problem isn't with the "completeness" of Navier Stokes, it's the existence and smoothness of its solutions, which is inherently a mathematical problem, not a physical one.
I fear that I won't be able to do my job in my later years due to mental decline, but these senior engineers with insanely good intuition give me hope.
Apparently the brain is the only organ in the human body that doesn’t age, if kept exercise. Amazing creation
Hey, I’m in school now for mechanical after working coast guard(have experience). Do you have any advice as to what to expect?
I've always intuitively thought that lift was generated from the Newtonian explanation of thrust: particles colliding with the wing at a positive angle of attack, being pushed down, and subsequently the wing being pushed up. (I knew this understanding was incomplete because it couldn't explain how flat bottomed airfoils generated lift at zero angle of attack) I never understood people who only teach the Bernoulli way like it's always been taught to me. Glad to know lift is more complex than what's been taught to me by people who think they are right. I still don't understand lift, but I'm glad I found this video.
The thing is; that particles above the wing are ALSO being 'pushed down' because of the lower pressure above the wing allowing higher pressure far above the wing to push it down. In fact, MORE AIR IS "pushed down" from above the wing than below it.
What happens above the wing contributes more to the difference in pressure than the small increase below the wing.
Towed gliders must stay above tow plane ! to avoid the down wash ( displacement of air ) and it is considerable ! a typical C172 displaces 7 tons per second! Bernoulli contributes a lift component , but if you do the arithmetic Bernoulli alone is not sufficient to 'suck' an airplane into the sky !
Air interacting with a space capsule re-entering the atmosphere (aka very thin air at high mach numbers) basically DOSE act like the simple newtonian stream of bullets under thouse conditions, and it's why such vehicles can only generate lift by being tilted to the incoming airstream by dispacing their center of mass.
I'm just a mum staying at home but I found this caught my interest and I understood. I wish though you had explained Newton's second with all the equations and its relation to lift, pressure fields and velocity fields. I really wanted to hear that. Anyway thank you for making this simple to understand. Yeah this covid time broadened my interest. Lol.
Nice presentation. Need to read book. I see some gaps in explaining lift.. great that author mention two ways relationship between pressure and velocity.
This dude is the real deal. You can only learn from people who have been there and done it.
You can learn from anyone, don't get caught up in that elitist mentality. I've met plenty of people with decades of experience, that make amateur mistakes. This guy probably isn't the case, but it would be wise of you to take a more humble approach and try to learn from anyone who makes sense.
@@acruzp Theorists with little or no application experience used to be a dime a dozen. With the advent of the Internet, they are now half a cent a hundred, and less on sale. Real humility is in recognizing the difference that practical experience has made in someone else's conceptual understandings relative to one's own.
I always attributes lift to coanda effect… thank you so much for clearing the concepts!!!
I think the best way to demonstrate incompleteness of each approach would be to show 2 airfoils: one would be driven solely by Newton's deflection, the other one would be driven only by Bernoulli's pressure difference. otherwise it's unclear how much each of these effects contributes.
It's easy to understand what's going on with a 'lift generating surface' when you look at rotary wings - propellor, helicopters. It sure is windy behind/under them...
He addressed this reason @20:40
Is it true that the vorticity on that capping surface is zero? It seems like we're just assuming that the flow field ahead of the propeller is irrotational, but there must be some because the flow is continuous across the propeller plane.
Reading book. One of the best book about fluid dynamics ( and I already read a lot). Strong points ( so far ) pressure-velocity two way relationship, critics of Reynold number meaning and applicability.
Andrew Pawhat book ?
Thanks I will check it out. I'm sure it will be helpful and ofcourse interesting
Hello, can you suggest a couple of other good books on lift?
I'm feeling like I dont have clear concepts regading lift
What is the critique of the meaning of the Reynold's number?
It’s crazy there are so many misunderstood videos on TH-cam regarding lift. I always felt there was something wrong with just saying air travelling faster = lower pressure.
But air is NOT travelling faster: th-cam.com/video/rHidaQgBb-Y/w-d-xo.html
Hey Doug McLean
you are the man !
That is exactly I have been dealing and feeling too !
Thank you for the explanation
I have my BSc in physics as well and I'm also about to get my private pilots license and every time the explanation of lift came up during ground school it never made any sense to me. Why do air particles HAVE to meet at the other side of the airfoil? They don't. Why is the fluid speed faster over the top surface etc. It's always explained in the pilot community with these naive explanations but this and a couple other videos are gems when it comes to gaining a true understanding of things. This reminds me why I chose physics as my degree!
One thing I'm surprised no one touches on: the contribution of inertia of the contiguous volume of air being accelerated by the angle of attack, the underside of the wing.
It's not clear why it's never mentioned that inertia of the air contributes to lift for airplane wings. It is only hinted at when Newton's 3rd law is mentioned. An airplane wing traveling at constant velocity (ie. plane not accelerating) encounters air at neutral (isotropic) pressure and accelerates air below the wing at a magnitude dependent on the angle of attack of the wing.
(Extreme example: if the wing's angle of attack were made by turning the wing vertical, the inertia of the air would prevent lift, and the airplane wing would be acting only as an air compressor for the air immediately adjacent to it.)
If the air could be accelerated instantly - with no inertia - it would not create lift. The delay in response, caused by inertia, for the air under the wing to 'get out of the way' of the wing's angle of attack is a contribution to lift. The air cannot 'get out of the way' instantly, partly due to inertia (air being matter, and all matter experiences inertia under acceleration). The angle of attack is therefore partially compressing the air immediately adjacent to the (underside of) wing, and the compressed air pushes back against that, creating lift (Newton's 3rd law).
This is also why a wing does not 'stall' if its constant velocity is great enough: the angle of attack of the wing accelerates the air underneath, and at great enough velocity, the acceleration of the air under the wing is great enough so that its inertia (inability to instantly accelerate 'out of the way' of the lower part of the wing) is great enough to contribute to lift.
If the wing is moving too slowly, inertia of air being accelerated by the angle of attack can no longer contribute to lift.
.
The false "equal transit time" is a misstatement of a related requirement: in steady state, rate of mass in has to equal rate of mass out. We know intuitively this has to be true. This more carefully considered truth drives the acceleration of airflow due to the path restriction of the airfoil's asymmetry to be faster than "equal transit time."
For the "equal transit time" fallacy people are focusing on too tight a location in space.
Yep, you don’t go into much detail in pilot training, especially for private, primarily because you don’t need to be an aerodynamicist or aeronautical engineer to be a good pilot. Being a good pilot is mostly about situational awareness, adherence to checklists and safety procedures, and some stick and rudder skills. For example you don’t need to know why the boundary layer exists, or why the air molecules do what they do, only things like how an airplane stalls, a general idea of how lift is formed, forces, etc. Everything after that is just extra credit in my opinion because knowing the ladder really won’t make you fly better unless you want to be a Test Pilot or engineer.
The Maxwell X-57 aircraft, currently in development, is about to relearn some stuff talked about at 37:30.
10:08 and 11:04
Well what you said is right, I dont see how what they said is "wrong", but rather is incomplete.
Its still true that newtons third law (together with his second) implies conservation of momentum, and therefore if you want to design an engine to produce thrust, you must "throw stuff out the back" so to speak. And if you do "throw stuff out the back", then the conservation of momentum requires your rocket move forward.
I think the problem is people are confusing the strict statement of the Third law in newtons original formulation (which as you said only talks about forces) with the Conservation of Momentum.
Absolutely fantastic lecture. Thank you so much!!!
Amazing level of detail and insight.
This is why critical thinking and challenging 'authority' is absolutely paramount to progress and ones obtaining of a true understanding in any given topic.
I suspect that the overpressure due to aerodynamic lift never makes it to the ground due to the dissipative action of viscous effects in the atmosphere; this is the same reason why the trailing vortices don't last indefinitely. It seems most plausible that, at least a large distances, a net temperature increase would be only lasting manifestation of lift in the atmosphere.
That addresses the energy portion but not really the force portion of the question. At least I would need to see a more thorough formulation of the concept to convince me.
Easily shown to be false asymptotically. On a sufficiently large planet, with a sufficiently thin atmosphere (so that elevation can be safely ignored in modeling gravitational force) and looking at the equilibrium case, every parcel of mass in the atmosphere has the same downward force no matter where you put it, and the total mass of the atmosphere must be exactly supported by the whole of the planet's surface.
When a plane takes off, mass of "atmosphere" increases, hence total projected force onto Earth's surface must also increase, in the static limit.
Back in the world of 1/r^2, you can elevate a parcel of mass to reduce its net downward force, thus cancelling out some of the mass of the plane by reshaping the entire atmosphere (possible but implausible). This will be tricky to do while maintaining the criteria of static equilibrium. My own math is not up to the challenge of making any insightful observation about this more complicated problem.
Using ballpark parameters for a 747 wing at MTOW, via Google calc:
400 tonne / 6000 sq ft in lb/sq inch = 1.02 pound / (sq inch)
The ground support will be _much_ larger than the wing area once you get out of ground effect, and it won't be a pressure we would much notice on the ground.
I know this also because many tanks are designed with treads that put no more force on the ground than a man walking, so that either can follow the other onto soft surfaces.
What is 6000 sq ft in shoe size? Huge. Not going to leave deep track marks in the sand if the animal is only 400 tonnes.
As a 40 year Boeing aerodynamics engineer, I'm happy to be known as an engineer and not a scientist. Engineers have to make decisions with incomplete data. Scientists generally draw conclusions only after enough data are available that the conclusion is irrefutable.
I, too, am a 40 year Boeing aero engineer and I like the differentiation: a scientist strives to understand the world as it is, an engineer strives to make the world the way we want it to be. (Doug McLean and I worked together for 36 years)
@@dougball328 I assume that you have an autographed copy of his book.
@@dougball328 I recall that you retired to Greater Phoenix. Hope you are enjoying retirement.
@@engineeringoyster6243 I do not have a copy of his book. Not sure how that happened. Retirement in AZ is nice, but would love to see some rain here !
My God how video examples would have helped with this lecture.
One of my favorite “EXPLAINER” videos of all time.
Can anyone help me understand his point made at around 40:00? He says that you can't produce net circulation with a propeller but I can't wrap my head around why. Clearly there is a zone of rotation in the direction I expect, but then in the graph he shows a zone further out (in the 0.5 to 1 region of r/R) that rotates the other way. I'm a bit confused how this counter rotating part comes about, videos showing it happening would be great I think.
@@willaware3583 So would that be from the air flows coming off the ailerons counteracting the rolling torque then?
I think this could be simplified for a lay audience (people like me) by talking about how a wing interacts with the double vortex in 3D (a helical field), and how wing shapes and velocity affects the interaction
- long skinny wings
- short fat wings
- faster aircraft have swept wings,
- winglets
- super-critical foil
I never thought about the fact that the 3D flow field must also extend forward. I tended to think that the air was still until it met the wing. Another error due to 2D thinking and forgetting about how fast pressure is propagated.
The brilliance of McLean's talk is in how simplified a context subject.
I suggest a class in physics for non-science majors. Or, some ground schools in flight training qualify as the aforementioned. Of
course, there are probably 'physics for dummies' type books written for the layman.
Rather than ask he simplify fuether, you lift your knowledge. I guess that's what torqued me, people wanting to be spoon fed all the while they hardly move a muscle.
The pressure changes in air move at the speed of sound. Therefore the effect of the aircraft on the surrounding air reaches out in front of the plane by a distance equal to the time it takes for the plane to get there. As the speed increases the distance to air in front of the plane that is undisturbed is reduced. When the plane is flying at the speed of sound, then air in front of the plane is undisturbed because the change in pressure cannot propagate faster than the plane is flying.
Wanted to see laminar flow discussion. Missed efficiency discussion. What is the efficiency of flight?
It was pretty efficient, until they put the TSA in the way . . .
Many years ago in the UK I gained a bachelors degree in aeronautical engineering and followed that up with a master's degree program in aircraft design. I was never satisfied with the explanations given about aerodynamic lift by my teachers so I was keen to watch this video. While I did gain an understanding about why the explanations given by my teachers were so unsatisfying, I still cannot claim to have a complete understanding of the phenomenon. Is it just me?
Indeed no, you aren't alone. And McLean's explanation doesn't help. On the one hand he demolishes the arguments using Bernoulli and turning down momentum, but then at 23:22 he says both are partly right and then at 26:45 asks his audience for assistance to reconcile them.
Does 46:15 imply that you can fly with a completely flat symmetrical wing?
Yes, you can.
As a retired naval aviator and graduate of NPGS, it's all done with mirror farms with a sprinkling of Bernoulli's thrown in. Also occasional magic from McBeth.
What do they use for helo aerodynamics, Señor Shmuckatelli? All that and a dose of Icarus?
Lift demons and thrust pixies.
36:04 Could someone explain that kinematic requirement?
So everything I've been taught about lift and aerodynamics (which isnt a lot), has just challanged but there has been no real counter explanation that satisfies my understanding.
The answer is that most of the aerodynamics info out there is complete nonsense. Take for example the reason fighter jet wings are swept. You can look far and wide with the only answer you see being the slowing of air over the top delaying the onset of supersonic flow. This is correct for airliners, but the reality for fighter jets, which you will never find, is that the sweeping of the wings keeps the tips out of the supersonic shock cone. That is why faster planes and objects have their wings so far swept and so far back.
@@sheeplord4976 honestly the reason for the wings of fighters jets to be so swept back is all over on the internet... and is an information which is given in every supersonic aerodynamics course.
P.S. It is written even on Wikipedia 😅
@@nicolobonaventura5715 It is rather hard to find on the internet and the explanation Wikipedia gives seems incomplete to me (maybe I missed something).
Also, of course it is taught in every aerodynamics class, similar to how the way wings actually work is taught in every aerodynamics class.
yes, most basic public information and teaching prior to a university aerodynamics course, is varying shades of wrong.
There are two 'true answers'; lift can be explained by a combination of Newton II,III and Euler if you are willing to accept an approximation that fluids are continuous; if you don't, and want to consider individual molecules, then it can be explained by just Newton II,III, and some physics on molecular interaction.
Which is a long winded way of saying it can be correctly explained, but that explanation is not intuitive, unless you study hard.
Formula 1 seems to be the epitome of flow and inverse lift (upside down aerofoils) management, etc. I’m wondering if you’ve ever had discussions with the “grand master” of F1 aero design and management, Adrian Newey, to unpack many of the concepts you’ve discussed, Coanda effect, vortex management and many other aerodynamic and flow management concepts. I suspect if not done already, it may be a very interesting and productive engagement! Thank you for a fascinating talk!
Upwash is necessary for lift or downforce, providing the camber transitions into a slope so the flow can reattach after low pressure region.
When I heard him say ''My undergraduate degree is in physics'', I immediately thought ''This is going to be good''
Back in the day all we had was ´Enslaved by No Media´. Now ESM is ancient history of the dinosaurs. Doug puts Enslaved finitely to shame with his common sense, logic and reason approach. I wanted to watch the lecture so I would not upload a youtube video trying to explain stuff about aircraft which I know almost nothing about. What we now need, are like 10 hour videos featuring interviews between persons discussing the physics of areodynamics, etc. It would help us greatly to better understand things like airflow, wind impact, etc.
he is the only other person I have ever heard describe the wing shadowgraph at cruise. The only other person I ever knew who knew about it before i told them was Dr. J Polve Col USAF Ret. Who was my Aero instructor in university. So he is making a good start.
To clarify - Dr Polve was my Aero instructor. he was a brilliant man and I learned a ton from him. He told me about the standing shock wave on the top of a wing, and the possibility of seeing the shadow.
fuck me ... an actual professor , thank you sir , we have been waiting for you for a long time
Can the Q & A be posted please?
According to this site: www.uspto.gov/news/media/ccpubguide.jsp, you wouldn't need permission to publish or use figures or text contained in a patent disclosure. I wonder if the publisher made him ask for permission, or if perhaps the legal situation is more tedious than the site would lead on? --A Michigan Aero grad just thinking out loud...
OK, I am going to stick my neck out here: From around 26:00 he struggles to explain the presence of pressure differences and resorts to “reciprocal cause and effect“, "pressure fields", "diffuse clouds of low pressure" ! Arrant nonsense! And he know it when he says it’s “kind of the weak link” and “the part I'm least satisfied with” and asks his readers for feedback on "how to strengthen this part”. It’s pure fiction!
11:35 - Thank you, thank you, THANK YOU for giving F=ma, the most beautiful equation in the world, the top position it deserves also here.
I like Doug McLean's insistence that you have to understand & explain why some explanations are only partially correct. Feynman was a great believer in that. He showed in some detail one reason why Le Sage's mechanical model of gravitation, although attractive (it does yield the correct force equation between 2 masses), didn't work for other reasons. See "Richard Feynman Messenger Lectures at Cornell The Character of Physical Law Part 2 The Relation of Mathematics to Physics". Also, in AI learning, it is important to present "near misses" in training. If you're trying to get AI to recognize an arch, you have to show it things which are almost arches but not quite. An example of an arch could be a horizontal slab supported by two vertical slabs. But if the horizontal slab is lying on the ground next to the vertical slabs, it's a near miss - it is close to becoming an arch, but it still requires an additional step to achieve.
He is using a Dell, not Apple. A sign of a solid engineer!
You are judging an engineer from the laptop he uses, not a sign of a solid engineer
@Thomas Jones in the making, hopefully
@@morcogbr True, I am not an engineer, I'm a scientist by profession. My comment was based on my solid scientific study, where I found that the engineers I respect the most use Dells. Both of them.
That is not a personal computer, it was given by his employer.
Question - this is always spoken to in terms of the air, or fluid is “flowing” over or around the foil. But, isn’t it true to say the foil is moving through a fluid not in motion? Is it the same, but different point of view (perspective of foil, or perspective of fluid particle)?
Great lecture!
Yes, it is the same. What matters is the relative motion between the fluid and the body. Hence why wind tunnel tests (static body, moving fluid) are representative of real flight scenarios (moving body, static** fluid).
“If you can't explain it to a six year old, you don't understand it yourself.”
― Albert Einstein
and Feynman, about explaining to a college freshman.
On the Basis of Messrs Dunning and Kruger, I know enough aerodynamics to know, with some certainty that I don't understand it and that all those simplified explanations you find in bools are just "lies we tell to children" or Just-so-stories and in the long run do more harm than good.
Having said that this lecture made a lot of sense.
See also how transistors work...
I hate pop-science and 10 minutes videos
I study accountancy what the hell I am even doing here?I am so confused.
It was a good talk though.
Figuring out life choices ;D
He did mention double book-keeping
Biology pre-med, same boat as you - I go to a school in a completely different timezone than this U of M
i study arts xD
Doug, you mentioned "sun shadow graph"? at the start of your talk. An observation I made a couple of times whilst acting as a flight test acceptance engineer, - I have observed "pressure lines" or shadow lines on top of the wing surface during flight (my best description of them was "ghosts" - do you have an explanation for this? I've never been able to work it out. The aircraft in question was an A320 at cruise altitudes. These shadow lines were definite enough to photogrph.
Yes! You're seeing the light bend as it moves through a density jump, also known as the shock wave. It dances around, moving forward and backward, casting a shadow on the wing.
Finally someone I agree with. A plane flies because it pumps air down. Newton’s 2nd Law. Done. You can do this with a flat plywood wing. I knew this as a kid flying my hand outside the car window.
The rest of aerodynamics is making that pumping efficient, controlling flight, staying away from stalls.
Great, and interesting insights. Is there another video where he gets into the next parts he announced?
As a pilot, I have been taught the equal transit explanation. It would have been nice if he explained what the correct idea is as opposed to why it’s wrong lol
I recommend the book series "Fly Better" by Noel Kruse. Freely available online. The first book talks in depth, using simple words, about aerodynamics.
Around @26:17 he did explain lift more or less correctly: it's both Bernoulli flow plus Newton II & III (or vector Newton and Euler). But note, that assumes the continuum approximation, which if you want to be pedantic is false. He was also clear about that at the beginning, he is doing the physics correctly for the continuum approximation, which is a fiction, but "good enough". Air (water) is a gas (liquid) of discrete particles. So the true _ultimate_ explanation (of lift) for a purist is molecular collisions. Molecular collision theory (with some adjustments for inter-molecular forces in a real fluid, stronger in liquids, which give more turbulence and drag) explains it all, and there the Bernoulli effect is pure idealization you do not use it, and it's really all just Newton II & III. That's why the *angle of attack,* not the wing shape, is the dominant factor, and is why you can fly a plane upside down without inverting the wing foil profile.
BTW, if you need fine detail currently you need to use a continuum approximation (Navier-Stokes), so it's important to get the continuum theory right if you are in high performance sports like F1 or America's Cup yachting, since (I believe) it's not possible to perform large scale molecular dynamics simulations yet, although computer performance improvements constantly amaze me. On AC75 foils they might be doing some molecular dynamics.
@@Achrononmaster Yes! Have been trying to explain this to people for 20 years.😂
@@Achrononmaster "and is why you can fly a plane upside down without inverting the wing foil profile." I disagree. 1. Not all planes can fly upside down efficiently. Planes that can fly upside down efficiently such as an F18 military jet for example have very different looking wings (looking at cross section they are almost symmetrical) and lift is attained by using angle of attack to create pressure differences when you fly. You'll need to point the nose up towards the sky no matter what if you want to fly upside down.
One reason the equal transit explanation is unsatisfactory is that the acceleration of the fluid across the upper surface starts well before the airfoil. How far? Who knows? It will be a function of the pressure distribution. Also, the top surface distance is defined from the stagnation point, which changes with AOA, not the zero % chord point. But the big problem with pilot training is that it is given by pilots, not scientists or engineers. You don’t want pilots teaching this stuff anymore than you want scientists flying instrument approaches. They don’t have the proper training or technical background. And finally, there is no reason why a pilot needs to understand these phenomena at this level. The famous book stick and rudder states this clearly. It says simply that the wing pushes the air down which keeps the plane up. As an engineer and pilot I can assure you that for piloting purposes this is entirely adequate.
Very good. I would listen to industry experts. Their theories and analyses have to stand the test of actually flying.
Thank you Dr McClean. Thank you Michigan Engineering.
"people with inventive minds" - love the euphemism for "crackpots" ;)
34:38 This thing’s pretty funny. Unless the holes in the flow straightener are very small, the vortex is just going to split into a bunch of vortices that are just going to recombine behind it. If the openings in the straightener are small enough, that’s a lot of parasitic drag for one, but he’s essentially built a Dyson vacuum cleaner and the vortices (I think) going to exert a huge amount of skin drag from being de-spun.
And I haven’t got through his entire explanation of why it doesn’t work, but if he didn’t mention it, I also imagine whatever vortification it removes is just going to be generated again, meaning even more drag.
Yep, basically what you said.
ahhhhhhhhhh I need him to finish his talk, too important to cut for time.
17:35 I don't understand why he has the air travelling faster over the top of the wing than the bottom.
And you're right to wonder: th-cam.com/video/rHidaQgBb-Y/w-d-xo.html
This guy took literally everything we got told about lift in collage and wipes his butt with it. Freakin legend
You made a collage about lift? Cool!
So, vorticity is the "Failure mode", the way we see or observer the "failure". In that case, the phenomenon of tip vortices?
People really want simple explanations. Aerodynamics is not simple, so many people cling to simple but wrong explanations, and argue passionately about them. That passion comes from an emotional insecurity and fear that there are things that they can't understand -- things that *cannot* be reduced to a simple explanation. And people with this misconception will deny the reality of *anything* complicated.
I really enjoyed listening to him! Thanks for sharing this video!
My dad always told me to get the seat over the wing... because its the safest location structurally in a crash... I usually get the seat right over the front edge so I can see down, because I'm glued to the window. Maybe not so safe considering I'm near the plane of the spinning turbine blades (but not exactly on it).... but whatever. If they fly off they are going to fly forward, or go back in the engine and detonate that puppy in a mad Star Wars 1 podracer type fireball that I definitely want to have front row seat on to watch...
@ep5 Lol @ seat back home... watching the crash of the flight I didn't get on...
I think in a crash, the flames are going to be going rearward... plus in a water crash, you'd be maybe closer to a wing to climb out onto.. be interesting to see sme kind of statistics ... which will probably say, ultimately, it doesn't matter a whole lot.
@ep5 I know right, wehnyou crash, more often than not, it's you in the pilot seat and you never saw it coming.
I will say this: my last 3 fatal motorcycle colisions while driving while blind were rendered mute by my 1000 hours spent in a quad copter simulator flying. In all cases I couldn't see the car parked in the road until it was right in my face, and my reaction time was instant knee jerk to swerve around it without thinking.
The first, I swerved to the left around a parked van in the road. The second, I immediately swerved back into my lane after passing it, and an on coming car went right on by. THat for sure would of been fatal. The third was a later date where the van parked in the road like a G D idiot happend all over again on the same road. After that I stopped taking that road, then I stopped driving all together as my vision worsened even further.
A year earlier with better v\sion but but not 1000 hours of lying in the simulator behind me, I took out 3 construction horses some other id die ots had put on the interstate with no flashing lights, no cones, nothing, just blocking off a lane. I was going 20 miles afster, butstill. I swerved too late to get in the left lane and took out all three construction horses withthe front of my motorcycle like a battering ram and kept going, albeit pissed off. Had to repair all that.
So my recomendation... do all your crashing in a simulator. I've basically crashed a million times by now crashing my way upward to being a pro aerobatic pilot. I must crash 30 times a day in the sim..
@ep5 Yep, my neighbor ran a stop sign on a 3 wheel motorcycle and his girlfriend on the back was killed and he lost hi slegs. I've run through intersections once or twice in my life.
Simulators are a great way to fly every day, rain or sign. I'm lik 1,200 hours. Way more fun than the real deal, you can do anything in them. Real flying in an airplane in a straight line is now boring to me like a trip to the grocery store. Why fly, when you can frolic in the sky with no G forces and no threat to life or limb.
I fly a sim called Liftoff. It took me a long time to tune it from the defaults for the sticks to match my brain, but I finally got it and now my machine flies creamier than ice cream.
The real life RC equipment I'm not having so much luck with, I'm sick of fixing broken stuff anymore. My three real people sized airplane projects also probably will never be touched again, they're collecting dust.
Now I'm the automated recorded girl that speaks to pilots on their radio. Pull up! Pull up! Pull up!
@ep5 SPoken like a true barnstormer.
You should join my Flying Circus... Google me.
How bout making laminar flow propulsion?
19:00 LOL... excellent statement. So lets assume time is the force, or connected to it.... do we see an increase or a decrease in time, and if time is a constant where does it get the time needed to create a change in the transition state? And what happens to space if space is relative to time? 23:00 Ahha... the information frame we live in where phase provides the correct answer of the moment and everything is made out of contradiction. Some say the electron moves... and some same say the "hole" moves. But what if time has a reverse arrow connected to the "missing" graviton and they both move connected to "something" stationary... say a true inertial frame of reference they are both relative to... just not at the same exact time because there is a wait state involved separating the phase timing? Is Bernoulli dealing more with the concept of space, and Newton more with the concept of time, and both showing the same cause of force? 27:14 Sounds more like he is talking about the strong force... more accurately than in any book. The strong force keeps two protons from pushing each other away... but what if the proton's phase timing is connected to a true inertial frame of reference. Is a wall a force because it refuses to move and a ball bounces off of it? 30:49 What if it takes the time (and space) of two Mass oscillations to create one observed instance in 3D? Will we see gravity move sideways? How about light moving through in a slit in 3D... if we divide the phase timing in half will we see the effect turn sideways? 36:36 Ouch.... OK so lesson learned but what do I call it if not induced drag? We are left hanging here. I guess when you get the name correct you'll have answered the question. Maybe the question is wrong... great video, makes you think.
+John F Hendry Please explain to me what is time?
zeogiannes Take your pick: Mass oscillation, the speed of light created by Mass oscillation, or E-motion.
John F Hendry Thank you for the reply. The selection list, does not help me to understand what is time in the real, physical Cosmos.
zeogiannes Some things cannot be understood without experiencing it. Even having the math skills to paint a picture is not enough to "see" it.
The physical manifestation and measurement of the delta between then and now... :o)
Why I am watching this at 3 AM in the morning in my bed? And I like it.
Maybe another misconception is describing the "wingtip vortex" which might be a misnomer. I would think it is realistically a product of the whole aircraft rather than the wingtip alone. Any attempt to counter the vortex pair would require a device the size of the aircraft itself (admittedly with diminishing returns as device size increases). Is there a possibility that wingtip devices are a marketing ploy (Star Wars) and not a real improvement? After all, a small increase of wing span should do the same thing, and as the wing tip devices produce perhaps the same wing root cranked in moment as a wing extension (for the same improvement) and the devices just add complexity, why use them?
As an aerodynamics mechanical engineer I tried to get into Boeing aerodynamics but maybe they found that my birth date was the same year the Hindenburg crashed, a bad omen, so they put me to work--on boats.
Well, the wingtip vortex is due to the circulation theory about the airfoil. You can have a flying wing and still have wingtips vortices. What also helps create wingtip vortices is the difference in pressure between the upper and lower panels of the airfoil.
Wing tip devices come with their own cons. They are a benefit at full TO weight, but become more of a detriment towards the middle to the end of the flight. I had to look it up after a discussion in an aero group.
And it is hard to get in as an aerodynamicist. Not as many jobs in the field. Some of it expanded into wind turbines. Not exactly what I would call interesting stuff.
The reality is that much of aerodynamics is done, leaving the aerodynamicists to work on the crumbs. After all, while the work still continues (maybe not) with the mathematics, they still wind tunnel test their ideas. That is, except me, where I built the first "Trike" that I know of, using other peoples numbers, and I survived the first test flights.
Tell me more about your trike.
Many people don’t realize that there are symmetric airfoils, such as in RC helicopter blades. This is so they can generate the same amount of lift when flying inverted (upside down). The Bernoulli/Equal Time explanation falls flat for these from the start, as lift is generated only when the blade pitch is changed, and thus there has to be a different explanation.
15:54 "Longer path length" is what I was taught in the 1970s.
@conacal rubdur Who knows what evil lurks in the hearts of YT? The Shadow knows!
@conacal rubdur no. Why do you ask?
@conacal rubdur I'm not an engineer, just an interested middle-aged geek.
I do, though, share your concerns regarding the aerospace industry. How much of aerospace engineering is transferable to other engineering disciplines in the job market? (That's something to ask your adviser or the website of some Society of Engineers.) And how much would your graduation be delayed if you changed majors in a couple of years? (Also something to ask your adviser.)
Good luck with this important choice!!
@conacal rubdur Go for It! Otherwise, as an old mechanical engineer you will ask yourself why didn't make aerospace. You will find jobs in both of them, but you will love the job if you do what you like the most. Regards
If you haven't sorted it out in half a century, shame on you.
YEP ! 26:00 to 28:00 are the deepest keys to apprehend this fascinating result (instinct make me think of a sort of succion, caused by gradient and sustained by fluid's inertia , countr acting gravity for gliders, thrust etc...) . He should have made some // with swim too...
I like the book almost no formulas, just explanation of physics)
I am not entirely sure this video really did clarify and explain how lift is generated. it started off pretty good to debunk the wrong ways of thinking how lift is explain, but at the end I am still not sure if it did much to explain how it's generated. Perhaps I missed something, which is possible.
@William Buckley; Mankinds Great Intellectual! Mr Buckley, I believe we understand how an airplane flies and how lift is generated. We know lift is the resultant of differential pressures around the wing. That much is clear to a lot of people. I think the problem is how we explain it and your statement above is a good example, which is what the video debunks. We know Bernoulli law explains that increase in velocity of an air molecule on the same streamline decreases pressure and slow air molecule increases pressure and the resultants of imbalance pressures keeps planes in the air so that's not the issue. The issue is often times, the explanation as to why the velocity increases at the wing top and decrease at the bottom of the wing is where people explain with haste. And you made the same mistake in your replay. As the video debunks, what is the physics behind the claim that the air molecule at the top and bottom has to meet? Did they decided at the leading edge that "hey meet me at some time at the tail end of the wing and let's have pizza and beer?" That's the issue with such explanation--there is no basis for that logic in physics and that's where people confuses the issues. I think the video did a good job debunking that explanation, but my problem with the video is I didn't understand the replacement of the physics explanation as to why the velocity increases at the top and lower at the bottom. That's what I was asking about. Thank you for trying to help, but I think like me, you also didn't get the physics explanation of the why the velocity increases at the top. I would like someone to explain to me as to what the physics explanation is that causes the velocity to go up .
The quickest and simplest way to destroy misconceptions in aerodynamics is to first give a visual example and experiment not an explanation. This experiment requires 3 items. 1. A average sized screwdriver with a smooth round head on the handle end. 2. Air compressor capable of 90-120 psi. 3. Air blower. Hold screw driver by its shank so the head of the handle is vertical up. Blow air from air blower across smooth head of screwdriver at about 3-5 inches away and about 45 degrees pointing vertical. The screwdriver will suspend in mid air. The air flowing across the smooth round head of the screwdriver is creating lift by creating low pressure just above the head of the screw driver. I used this example in the hangar teaching student pilots and it always creates the eureka moment of aerodynamics.
+Curtis fen 14:49
a parachute in water travels along the flow..a piece of plywood can fly in water or air... a screwdriver can fly with enough force...case closed
Provably false...
one of the biggest problems explaining lift starts with using molecules with momentum instead of at rest with the object having momentum. A wing moves out from under molecules that are weighted down from above and as long as the pressure differential is great enough, the weight of the object is negated. Take scales on to an elevator and weigh yourself as the floor moves down as opposed to being stationary. The top of the wing is constantly moving out from under the pressure of the molecules directly in contact with it.
Jon Miller as Galeleo pointed out the it doesn't matter if the air is moving over a stationary body or the body is moving through stationary air.
The wind tunnel is the most practical way to study lift. The reality is of course that the air is still and the wing comes along and slices through it. The wind tunnel encourages concentration on near field effects while seeing the aircraft approach and fly past gives you an appreciation of the far field effects, which also exist. This is especially striking when there is smoke to help you visualize the effects on the air, such as in the NASA vortex studies.
I am not sure but my first impression is that he elaborates the things, which are indeed straightforward, more than necessary and makes them seem incomprehensible. i would suggest students to stick to anderson's book in order not to get lost in details which are not really details. he speaks as if he was talking on a subject related to quantum mechanics.
it is i believ really that deep.i have had some "expansion" of my thoughts just as he had.i suspect that people are takeing somethings for granted which are "obvious" but not easily vocalized.or simply put,a not knowing.
You can´t be serious? It´s clear as water what the lecture is all about and you have obviously not been reading that. What you want the lecture to be is something else - isn´t it?
+norton noble, which of the two Andersons? There are two different guys with two different books and views. If you are talking about the Andersons that proposes the "scoop" allegory to explain lift, you do need to pay more attention to what Mr. Lean is explaining!
norton noble, that is just why this is called "Common Misconceptions in Aerodynamics"...
When learning to fly how is Lift explained? Is how a wing creates lift dumbed down for learning?
Superkudos. I think everbody should undergrad physics before going into engineering.
A "no-slip condition at the surface." What is the effect of this assumption? What is "slip."
An extremely valuable perspective from the real side of math and physics. Doug McLean is assuredly an aerospace scientist.
No slip is assuming that there is non-flowinf air right at the surface of the wing on a very tiny molecular distance, which is largelt why a boundary layer forms. Little friction on the wing surface doesnt allow the air to perfectly slip.
"I'll take trailing vortices for 200, Alex." Ha, rocket scientist humor.
So do gliders produce thrust. I.e move forward by pushing air backwards?
Me being an Accounting Major. I would say no. Only forward momentum with the help of gravitational pull and fluid propagation difference caused by the mass behind the leading edge.
Omg......I did it.
Bottom line is that 2 guys from a bicycle shop managed to get into the air before all the engineers in the world.
I would argue that they were engineers, as long as you define "engineer" by their actions and not by their certifications.
I have his Understanding Aerodynamics book. Does anyone know where to send errata?
To the publisher.
To this day, I remember explaining the forward thrust of a propeller using the Bernoulli airfoil theory in my undergraduate physics test and it not feeling right.
Little did I know, how little I knew 😄
Moog dal
Moog sprotous
The equivalence with electric and magnetic fields clicked it a lot for me, because we have the same exact confusions, to the point that he claims “in electromagnetism that is a causal relation, the induction law”, but that’s mostly a historical artifact of how we discovered these phenomena.