How do wings work - Common misconception on lift
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- Опубликовано: 26 июн 2024
- This lecture was recently given by Dr Holger Babinsky, a member of the Department's Aerodynamics Group, to a sixth form audience.
The presentation slides has been converted into a separate video, suggest to view it side by side:
• How Do Wings Work - Sl...
Alternatively, the presentation slides in the video can be found here:
drive.google.com/file/d/0B0JA...
The paper mentioned in the video:
iopscience.iop.org/0031-9120/3...
I believe this lecture was conducted back before 2004 so sorry for the poor video quality.
Video extracted from Cambridge University undergraduate prospectus 2006/2007
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The damage done to this video by not filming what he is showing the class is immeasurable. Breathtakingly stupid camerawork.
Three years after I have watched this lecture the first time,
I come back and watch it again even after I read the paper Dr. Babinsky published on the theory of lift..
I will never forget the first time I watched this..
It shocked me so bad.
All due respect for you.
I just wish I cold be the cameraman on the wedding of whoever shot this video... and just shoot the wedding cake for the ENTIRE time!! Just one, 3 hours long, continuous shot of the wedding cake!
Thanks all for supporting this video, I finally found the presentation and uploaded it here, hope it helps!
drive.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing
Thanks for this video - one of the few cogent descriptions of Bernoulli.
Please note that if you go to the presentation URL (which is the first URL below the video), to get the pdf for your computer, select the *new* "File" menu at the top left, then the Download item in that menu and you get the PDF slides of your own. I repeat the URL here so it is in this same comment.
drive.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing
...
The second link under the video leads here which is an article version of the graphics and talk from: IOP Publishing Ltd PHYSICS EDUCATION 38 (6) :
iopscience.iop.org/0031-9120/38/6/001/pdf/0031-9120_38_6_001.pdf
...
I am disappointed that he didn't take one more step and point out the mass of air "M" that is acellerated "A" downward (behind the wing) by these pressure gradients (a force "F") and the resulting reaction force (Newton #3) that we call lift.
Cheers, ScienceAdvisorSteve
Observ45er NS equation IS 2d Law of Newton for fluids. :-). Not quite sure why you refer to F=ma ( which in fact NOT what Newton said) :-)
Andrew Pa Did I post to the wrong video or something...? [I'll go back and check after posting this] ... back ... No, it's the one I was thinking of for this comment..
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Sorry... What is NS??
...
... I'll clarify my comment...
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RE "F=MA" I use this as a short hand reference to Newton's #2.
...
That is; my short-hand for "Newton's Laws of Motion" [actually nature's laws of motion that Newton is credited to have "revealed"] that I perhaps incorrectly assumed anyone familiar with them would understand:
- Newton #1 describes inertia.
- Newton #2 describes force required for acceleration.
- Newton #3 describes the paired forces concept.
...
Then, I just wanted to point out that lift is not some force that uniquely has no 'opposite and equal' reaction force. A bunch of air is also accelerated downward by the wing's passing. The air is not left undisturbed after the wing passes as I think is implied by the all to common 'incorrect' use of Bernoulli [the faster air causes low pressure & equal transit time version].
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I feel that omitting mention of that effect on the air by a passing wing is omitting, what I consider, a part of the complete explanation of the phenomenon of lift. His full lecture is otherwise, a gold standard as far as I am concerned --- *ESPECIALLY* considering all the misinterpretations of Bernoulli by so many including well known science lecturers and at least one PhD produced series of otherwise good science videos! [of those I've seen]
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That is all I was trying to convey - the well known concept of what I call "paired forces" is present to produce lift.
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... SO... are you saying that what is commonly referred to as "Newton's Second law" does not describe the natural phenomenon relationship between acceleration of a mass and the force causing it?
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So just what did good ole Issac say.? Is that another thing like the all too common "bad Bernoulli" Explanation?
I'm interested in what you have.
...
And, no. I have not read the Principia in its original form... I unfortunately had to rely on a couple of teachers to relay the concepts to me...
Cheers, Steve
Observ45er You did not post anything wrong :-).
NS means Navier Stokes equation ( sorry for using abbreviation).
Here is exact translation of Newton Law "The alteration of motion is ever proportional to the motive force impressed, and is made in the right line in which that force is impressed". Which just principle of equivalence between acceleration and force ( plus definition of inertial mass) :-). 1st and 3d Law can be easily received from 2d Law. N-S equations are in fact 2d law applied to fluid. Reading book of Doug McLean "Understanding aerodynamics" now. Very good book. Recommend it
to you as well :-). Dr Holger Babinsky did a good deal of work with only couple of BUTs. Bernoulli principle ( read equation) does not explain any lift. As per Dr.Babinsky own article "This relationship.... between pressure fields and flow
curvature is very useful for the understanding of fluid dynamics (although it doesn’t have a name)". ( He means it is NOT Bernoulli principle) . I agree with this . But next statement "...we learn that any shape that introduces curvature into the flowfield can
generate lift. Aerofoils work because the flow follows the local surface curvature on the upper and lower surfaces. It is not necessary to consider frictional forces to explain lift, however; it is only due to the action of friction that streamlines take up the pattern we would intuitively expect, so strictly speaking lift would not be possible without friction..." is not correct :-). Without proper understanding WHAT causes curvature no way to explain lift origin.
Cheers, Andrew
Andrew Pa There is curved flow without friction. Caused by electromagnetic field. And it generates lift too. Expensive lift, but efective.
Thank you Dr Babinsky! I finally understand lift! Your explanation is so elegant and beautiful.
Great lecture! Love the fact that he explains the basics between explaining wing lift.
I have always been mistaking the "Coanda effect" phenomenon as a result of surface tension until I see this. Learned something today.
Correct, surface tension is one component, air is 'sticky', as is water.
Dear All, thanks for your comments and sorry about the video quality. I believe the intention of the original video is to show the lecturer on one screen and the slides on another screen.
So I have turned the presentation slides into a separate video, suggest to view it side by side:
ruclips.net/video/Vx_6zhMRFgU/видео.html
if you bend the paper toward you when it is vertical it will have the same reaction as when you are horizontal so you are wrong for this example, try it ..remember the paper is already flat when vertical
that was the point
Actually the reason why the cameraman didn't show the presentation is because his camera cannot lift, as it needs what makes it lifting, and didn't have it back then..
Indeed, to be able to lift the camera needs to have a curvature on the top. This curvature with the air circulating inside the presentation room, will make the pressure on the top of the camera lower, and create a difference between the top and the bottom pressure with the bottom being the high pressure, this phenomenon is called coanda effect. Only by this effect, the camera will lift each time the presenter move to the blackboard creating airflow toward the camera.
😂 🤣😂 🤣😂 🤣
😂🤣😆
Why the heck didn't the cameraman point the camera AT THE SCREEN? It's infuriating!!! How could he possibly not know?
Thanks for posting the slides and the presentation. Beautiful lecture. Playing both make it even easier to watch than all in one vid.
saw this exact lecture a year ago at cambridge by the same guy, thought it sounded very polished haha, he's been doing it 10 years!!
Thanks to this professor helping those who really wants to know this subject but don't have related background.
Nice presentation, closer to truth than many others.
Very nice lecture. Thank you for providing Prof.
Excellent video. Thanks for uploading!
Very illuminating lecture by Prof Babinski. Clearly explained if you can open cyhong2001's slideshow in another tab.
In defence of the video, a couple of things: the Prof mentioned that he was asked to present this lecture earlier _that day_ and presumably the person operating the camera might have been a non-professional volunteer who (thankfully) was able to record the video with little or no notice. This was all a bit last minute in the filming department and the camera operator did a good job. Thanks to cyhong2001 because the slides are invaluable to this lecture.
Also, isn't it quite touching that the (non-professional call-up) camera operator couldn't help themselves following this engaging expert. They were clearly engaged by him!
Theoretically, appreciate the learning procedure about this shows and I like to watch the shows many times I like; thanks.
It's me,
Sule Shangodoyin.
Sule Shangodoyin i
Interesting. I'm going to try to recap the important bits:
- consider a rectangular volume of air (imagine the air is not compressible)
- if there is a higher pressure on the left hand surface than on the right hand surface then the volume will be accelerated to the right due to the force being applied (F-mA)
- so if a volume of air accelerates then, in the direction that it accelerates, there will be a lower pressure on the side that it is accelerating towards
- the streamlines above a wing are curved downward
- this means that there is an acceleration of the air downwards
- this means that the air below the streamline is at a lower pressure
- since there are many layers of streamlines as we approach the wing (with the air pressure "far" above the wing being ambient pressure) this means that the pressure at the top surface of the wing is quite a bit lower than ambient
- this lower pressure will produce an upward pressure on the wind
- apparantly the streamlines below the wing are also curved downward and so produce a higher than ambient pressure at the bottom surface of the wing - forcing it upward
Newton, Bernoulli, Coanda, oh my. And Venturi.
Before getting annoyed by the camera work and then making another comment about it, just go to the link provided to see the slides.
So use 2 computers to watch 1 video.
@@s8bell Jesus. You can open two programs at the same time, can’t you?
Thanks for posting this! Very interesting! I guess the reason that misleading theories are often taught is that these are often the ones that are more easily understood by our brains. It may be that there are too few individuals who are genuinely interested in understanding, and convenient explanations save time right?
camera made me puke. its brilliant lecture ruined by camera
What a pure genuis .. i love this, goddamn what hadn't i that kind of teachers .. they all speak in a boring way with tons of equations when they neglect the vision importance .. experience is worth 1000 equations .. i love this, despite the bad quality but still, a great content. thanks for the uploader.
The explanation was really good.Thank you sir
Thank you, That was amazing :)
Excellent explanation!
I could listen to this guy all day.
the demo before 39:40, that water follows the beaker curve because of surface tension, not because of Coanda Effect. They just look alike.
Initially, upon reading through the comments, I was dismayed. But then I realized that out of nearly 200,000 views, only 500 people (comments at the time) complaining about the camera work self-reportedly didn't read the instructions for viewing this video. That's not a bad ratio, actually! My faith in humanity is more or less restored. (Self reporting doesn't make for great statistics, naturally, but I only needed my faith restored. Not my proof. Har har!)
Excellent video.Thank you Sir.Hope that you will upload many more videos on basics of Aeronautics.
This must be the point of view of a student in love with the professor.
The lecture is excellent however. I have always had a hard time believing the simple "faster means lower pressure" principle very frequently appearing. Curvature flow is much more credible and from a different perspective it also gives another abstract explanation: essentially lift is a type of thrust by creating a downwards flow vector, exactly how thrust is created by a rocket. I am quite sure that if somebody calculated the downward vector of flow of air and carried out change of momentum calculations (based on the principle of retention of momentum), it would pretty much produce the amount of lift created by the wing. I might be wrong but it would be interesting to look into.
Excellent lecture spoiled by dreadful camerawork. The most important part of this presentation is the visual content being projected onto the screen above the lecturer. Didn't anyone explain to the camera operator that it was ok to tilt up to show the viewers that screen? Thankfully there is a link provided to the slide show and it is possible to treat the original RUclips video as a "radio" broadcast and follow the slides from the google-drive webpage. Hardly ideal though!
thank you so much.... that was very helpful
Once the sail (rudder) has an angle of attack, the stagnation point changes and the upper surface has longer distance. When blowing a paper, make sure that you don't add air velocity normal to the surface, otherwise, the boundary condition will never be ideal flow (irrotational, inviscid, & incompressible) over a body like we assume in basic aerodynamics.
Great! Thank you.
that lecture was really good
I enjoyed the presentation its just a pity the cameraman kept following the presenter and not the presentation, it would have been nice to have seen the projector screen.
Tusk Bilasimo did you read the description? The slides are on a 2nd YT film.
The professor gave a very convincing lecture, and explained clearly in sync with sketches and equations, which unfortunately
failed totally to appear in the video.
You must listen very carefully to *See* the acceleration of the "particle" in the streamline with the dropping pressure (from 19:11 to 26:25). In summary, if the pressure is dropping in the direction of travel, there must be more pressure "behind" the particle of air and, therefore, a force accelerating it to a faster speed.
Either that camera can only do horizontal turns or the camera man himself is Darth Vader.
Think of this blurred video as representing the Brownian motion of vorticity which causes a flow separation at the trailing edge of the aerofoil, the dumping of a stopping vortex, and the generation of lift.
Another incomplete explanation of lift to add to the collection, but this one takes an hour to explain instead of 30 seconds.
Have found a lecture on the topic that actually explains the phenomenon? I would appreciate your help!
Honestly there is no easy answer. You need at least 2 semester of thermodynamics and a semester of fluid dynamics before you even get started. Basically lift is created by causing a circulation of air around the wing called a bound vortex. The thermo and fluid dynamics explains why this bound vortex forms. The bound vortex circulates around the wing moving up ant the front rearward over the top, down at the back and forward under the wing. When you add the vectors of the air in the bound vortex to the vectors of the air flowing past the wing you get the air moving over the wing flowing much faster then the air flowing under the wing. This causes a pressure difference between the upper and lower surfaces.
Which means the particle will move in a straight line at constant speed (or not move at all?)
Well done sir.
I agree with most of the statements. But, as for the setting of the experiment, where the flow from above moves significantly faster than the flow from below (14: 17), it seems to me there is some distortion in the sense that the influence of the walls of the air tube in the test area is not taken into account. And there is a significant overlap of the flow passage section from the bottom of the wing, which means that there is a very noticeable additional braking of this underwing flow.
you are amaziiiiiiing. thaaaanks. stupid professors always were wrong and confused mee. thanks for beautiful explanation.
I use to curse on Discovery and those channels when they start with their wrong explenation. They should see this and learn!
Great lecture but so wished you could view the graphics that were referred too.
Was this filmed on a VHS? I can barely see "the erofoil".
I think Dr Babinsky should reconsider his use of the glass beaker and water to show the Coanda Effect. There may be some push back if people argue the fact that the glass beaker is hydrophilic, and generally attracts polar water anyway. The effect will still hold, but how much of the turning is happening because of water's attraction to glass vs the Coanda Effect. Perhaps a non-polar liquid? Because the surface tension from water's capillary action on glass can be used to explain the water turning over the edge of a container.
I'm sure it would work just fine with other material, and would help you avoid confusion about fluid cohesion of polar water molecules.
The Coanda effect is irrelevant to aerodynamics. It exists, but doesn't affect wings.
explain your reasoning. Why is it irrelevant?
Invisiblejihadi Air pressure pushes air particles down above the wing and the Coanda effect is not necessary.
Googelplus Sucksys That’s correct . The average speed of air molecules at ground level is about 500 m/s , far faster than speed of sound ( ~ 340 m/s ) or a subsonic aircraft ( ~ 100 m/s ) . The random velocity of these molecules in a streamline exceeds the flow velocity by far . The latter is almost a drift velocity . So this is why the air ‘ bends around ‘ a surface curving away from it . No need to give this effect a fancy name
It's important to note that Dr. Babinsky's vortex theory only applies when using a curved surface to generate lift, specifically in the Bernoulli and Circulation theories of lift which he demonstrates so well. It does not apply to the Momentum theory of lift when using a flat plate wing which creates lift by downward deflection of air.
The coefficient of lift is much lower with a flat plate wing (or sail: remember that Chinese junks had flat rigid sails) but it will still fly given enough thrust (velocity). Airfoils and sails are curved for a reason.
An excellent lecture though it was a bitch going back and forth to see his slides on the other link.
I think it still holds for a flat plate- it still causes the curved streamlines, albeit not as well as a curved shape?
Oh my God !! however the video is, this lecture helped me to clear my whole damn conception about lift. well if you know aerodynamics and physics quite well then this video is just enough i guess. Thanks to the people behind this, thanks a lot :)
Please explain why you would have the camera on the professor when the professor is trying to communicate using a overhead, you might as well faced the camera to the back wall.
What has not been explained is why the streamline acting parallel to gravity on a wing aligned with gravity does not create a sideways "lift".
This is really nice! Unfortunately, it does not have the projections above.
I'm not sure we need the "coanda effect" for lift. Boundary layer interactions between inertia of the fluid and velocity of the slipstream explain this. Also, once the flow curve is established, pressure gradients with the surrounding air will keep it going that direction
Good presentation. (Graphics?)
CY Hong, why was you camera keep locked onto the lecturer? You should show the projector screen when he is writing on the screen.
Good to see someone knows how it works.Just remember pressure came from Gravity & high pressure at the nose helps make a higher speed over the top & this helps made a stronger vacuum.In the end its all about Pressures.
Gravity is actually quite irrelevant.
Without it the plane would fall out of the sky.
chris lomas Ahem... without _gravity_ the airplane would fall out of the sky? Without gravity, exactly what would make the airplane fall out of the sky? Without gravity, the airplane might float freely into space and while relevant to flying it is irrelevant to the explanation of aerodynamic lifting forces.
OK.It would not fall out of the sky but without gravity the air pressure would drop from 14.5psi to O so there would not be any air to work on the wing or prop or Engine.It would I suppose just keep going in a straight direction like a Comet.
Without gravity we wouldn't need the wing - just jump up and keep going! But what he meant is that the H (potential energy due to elevation) component in Bernoulli was so small that it can be ignored. You still need the Pa = 14.7 or so psi to make this work.
Did anyone else realise that Bernoulli's theorum as is often applied to a wing contradicts Newton. It has the increased velocity causing the pressure drop when in fact it must be the pressure drop increasing the velocity as only an outside force can cause an acceleration!
The best way to understand lift is as action/reaction as described by Newton. The moving wing imparts a downward velocity to the air, (downwash). Lift is merely the upward, or opposite reaction force to the force that is accelerating the air downward. Simple, isn't it?
In Russian! Круто. Теперь можно обойтись без циркуляции, комплексных чисел и конформных преобразований. Теория Н.Е.Жуковского теперь просто математическая модель, а физика объяснена здесь. Просто и понятно даже старшекласнику. Добавим вязкость и можно объяснить турбулентность и срыв...
А кинооператор редкостный Дегенерат!
I tried to calculate lift according to FL=m*V^2/R. But here is problem how to define mass of gas. While area of a wing is known, thickness of gas layer that is involved is unknown. Strictly speaking it is infinite, but mass involvement depends on a distance. Could you tell how to get proper gas mass for a known wing area?
It's a shame some of the commenters have ignored what you put in the description.
Great lecture, but can someone explain this: When we take two sheets of paper, place them vertically next to each other(similar experiment like in the video on 15:00 just with two papers next to each other) and blow between them. What happens? The two papers come close together. Why? I assume that there is formed a low pressure region because of speed of air going between them, decreasing the pressure, but experiment done in the video on 15:00 is saying exactly the opposite. How come? I think that experiment in the video wasn't done properly, I tried it and when you blow a little away from a paper(not so close as in the video) it actually goes in the way of speeding air! Interesting... any thoughts?
That wings produce lift through relative motion with the air is known to all. Why and how they do so is still debated
Damn, my bet was on "Magic".
(Would be nice if they interlaced the graphics into this talk.)
I was given that speed difference above / below the wing as an undergraduate.
and now we know why 'fighter jets' have such uniformly thin wings!!! It' called the
4'x8' plywood-wing theory ! and it's true.. The camber of airfoils can not possibly sustain any idea that Bernoullli has any thing at all to do with lift < at high speeds of course!>
You can find the paper mentioned at the following link. The one provided in the description requires a subscription.
www3.eng.cam.ac.uk/outreach/Project-resources/Wind-turbine/howwingswork.pdf
Logical False Dichotomy: If this lecture isn’t any good, the article also isn’t any good. NOW: I will watch the presentation AND read the article and decide if either one or both are excellent or rubbish or something else.
24:39 I dont see why the pressure needs to decrease when its going faster, since the pressure above the wing and above the flow that is flowing along the top surface of the airfoil, is still pushing the flowing air with the same atmospheric pressure as it did when the flowing air did not pick up the large speed.
I only see that working if it was in a pipe (since the fluid will be enclosed from the outside air pressure) with a constant flow rate, and changing the area results in a greater speed and a decrease in pressure.
And I get it, the airfoil does have a decreasing area as you go along the shape from the front to the tail. But that would still yield the same pressure force above the airfoil as it does under the airfoil.
35:30 Shouldn't the cow be sucked into the ground since high pressure always go to low pressure? With that being said, shouldnt the hurricance suck into itself, because of the high pressure at the top?
hi im trying to understand what happens to a single air particle as it move across the raduis of the airofoil
( centripitle force acting on the particle moving over the top of the wing )
is it like this??
because theres a centriplitle force acting on the particle (towards the radius centre) then there is then a equal and opposite force ( centrifugal)
acting outwards from the centre ??
air is not attached by a piece of string to the centre so would really want to fly outwards from the raduis
Jim Hedger Yes a centripetal force. The wing's shape moving through the air causes a lower pressure along the upper surface. The (higher) atmospheric pressure further above the surface and this lowered pressure together provide the net radial force toward the center of curvature (inward toward the wing)....I do notunderstnd your point about the string...Cheers
Observ45er would you be able to link me a website or a short video with just the basics of lift that are correct, cheers :)
One minor iversight in an otherwise excellent talk is at 41:08. The wind tunnel does indeed distort the streamlines making this a little misleading. On the right, streamlines in actual flight will have a downward component of velocity. The streamlines leaving the trailing edge will be angled somewhat downward as they leave to the right.
This, Prof Babinsky fails to mention, is the result of the downward force exerted on the air as the wing passes. This, then is the opposite and equal (downward) force to the force (lift) on the wing. A significant amount of air is not undisturbed after the wing passes, but has been accelerated downward with a force equal to the lift.
... Note:
When an airfoil passes, the air that was motionless before the wing arrived; after the wing passes will be moving downward and slightly forward. These motions will be proportional to the lift and drag respectively.
...
This 'bunch' if air will then mix with the other air around it forming the well known wing tip vortices, downwash and and turbulance as it eventually comes to rest mixed with the atmosphere. This, of course, causes a little heating as the energy used to propell the plane and produce this the is transferred to the atmosphere.
Cheers
I could have received all the information by radio, the camera work is unacceptable, he is either on drugs or alcohol.Great lecture on important subject.
Thank you so much for this amazing video!
The problem is that if you insist on using this (the correct) explanation on the FAA's private pilot exam rather than the Bernoulli/greater distance explanation, it'll be marked wrong, and you'll fail the test.
Imagination is greater than knowledge...
I now understand undercamber. However the pressure gradient effect is only a part of the reason there is lift. The main cause of lift is the upward vector of the forward force caused by the angle of attack. The source of this force is the motor which both advances the wing and makes it move upwards when it is greater than gravitational force downwards. I’m not sure how this fits in with the concept of space time!
When Dr. Babinsky blows across the paper hanging vertically the weight of the paper tends to straighten the curvature. Flow is not made to curve so there is little pressure depression developed thus the paper does not move....
To Expand on a wing or prop or fan pushing air down. When you stand under a helicopter the air is coming straight down from the rotating blades much like when you stand behind a airplane that is running up its engine. Both are airfoils that push air at a 90 degree angle from the direction of contact the under side of the blade. That is lift.
terry wayne Hamilton Prof Babinski does not include the downwash in this lecture, it is true. Downward moving air is not the lift. The down-wash/prop-wash is the *result* of the pressure differences on the airfoil. The perssure difference he details *IS* the net upward force on the wing that*IS* the lift force on the wing. ...The downwash/propwash is the result of the pressure difference (force) around the wing and is the reaction referred to by Newton in the "Equal and Opposite" part called Newton's Third :aw of Motion.The air is pushing up on the wing. lifting it, therefore the air experiences the equal and opposite force which accelerates a bunch of air downward. ...The downward moving air did not start this whole thing going.-- Cheers
About 29:30,
So, Bernoulli's equation only works in the same stream line. But, before reaching the airfoil, the streamlines that are next to each other don't present any difference because of negligible potential energy variation due to to closeness, right? Let's call it C1. When one stream reaches the upper surface (point 1), and the other one reaches de bottom (point 2), why couldn't we call both points C1, if they didn't show any difference before?
39:42 n.b. Coanda effect, is the phenomena in which a jet flow attaches itself to a nearby surface (round or STRAIGHT) and remains attached EVEN when the surface CURVES away from the initial jet direction. This is the the fact!!
Yes, it is the the fact. He's just explaining it.
One thing most people forget when they are demonstrating lift with a wind tunnel is that the air is moving over the wing. This does not reflect what is actually happening in a real flight scenario where the wing is MOVING through the air not the other way around. When the air is moving it has inertia and I believe that must have some adverse effect or influence on their tests. Also if you want to send a staunch Bernoulli principle believer into outer orbit, ask them why an aerobatic airplane can fly upside down all day with fully a symmetrical wing. Check this article out about the long distance record for inverted flight, (650 miles): articles.latimes.com/1991-08-01/local/me-200_1_pilot-sets
Okay, this is first quarter physics: when objects are not being accelerated, it doesn't matter which object is considered the "fixed" object. It's only the relative motion that matters. So a fixed wing in moving air behaves exactly like a moving wing in fixed air. That's a whole different lecture if you need to have it proved to you. The inertia of the air RELATIVE TO THE WING does not change.
Also, I believe he covered the symmetrical wing case quite well in the lecture.
Having used tell tales and sailed correctly. I can assure you the wind is faster on the forward side of the sails and slower on the aft side of the sails. That is the aim of keeling and sail handling. The boat sails much faster flying with lift on the sails.
So, by this explanation, air flow parallel to a flat plate will not cause a pressure drop on that surface. I'm not arguing the theory; I'm only wondering if that's been shown empirically. Something a little more controlled than blowing across a vertical piece of paper.
Surely a Venturi tube would indicate something.
Jeez, it would’ve been nice to point the camera at the diagrams❗️
Explanation was a brilliant, if only I could have seen the illustrations to understand it better. Please redo this presentation with a camera person of equal intelligence. Thanks!
A cameraman for a lecture surely doesn´t have to be of "equal intelligence" to a university professor. He has to be just smart enough, to make a 2nd video of exact same duration, with all the illustrations, and link this 2nd video in the description of this video here... 😀
I would like to understand what is the nature of the centripetal force you are talking about( in case of the curved streamline). You said you have ignored all the forces. Therefore it must be a pressure difference which must be giving rise to this centripetal force. My question is, fundamentally what causes this pressure difference? In case of a stone attached to a string, the centripetal force is provided by the tension in the string, in case of planets moving around the sun, this centripetal force is Gravitational force. Similarly in case of curved streams (I agree that there is a pressure difference) what exact forces are involved?
Now we are flying off keel. The curl que is more important than Bernoulli is this true?
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. This is the principle of stable flight. I used this example in the hangar teaching student pilots and it always creates the eureka moment of aerodynamics.
+Curtis fen It may not be creating low pressure but diverting air downwards creating an equal and opposite reaction. The very first problem with aerodynamics is the word "lift". It implies a force pushing upwards, whereas reaction is simply what it says. Thrust, in a vector presentation shows a force pointing forwards yet, in reality, all aircraft propulsion, excluding gliders, is rearwards. The resultant is forwards, not the force. When my car accelerates it actually tries to push the road backwards. The road stays where it is, so my car travels forwards. Question: what is the direction of the tyre on the road when my car travels forwards? What is the direction of air after being accelerated by a propeller or jet engine?
Curtis fen: you believe that a single demonstration will eliminate misconceptions. This is very, very far from true. The pursuit of science has been a continuous battle of "but that doesn't explain ... ", and "but what about the case of the ... ?" So, great, you have a demonstration that worked for you. The professor has an explanation that works to disprove some other misconceptions.
You'll need his MISSING SLIDES from HERE (Click the Download Icon for the complete set of slides):
docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing
Or here:
docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit
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His equivalent article from PHYSICS EDUCATION magazine "How do wings work?", Holger Babinsky:
www.prirodopolis.hr/daily_phy/pdf/How%20do%20wings%20hork.pdf
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PLEASE NOTE
1) When Prof Babinsky says "Coanda" he technically misspoke. The term "Coanda Effect" is defined for high speed jets or sheets of air FORCED over a curved, convex surface into an _otherwise still environment_, NOT for a wing moving through air. It simply states that a forced jet or sheet follows the surface. Coanda did note the pressure reduction. While the two may be due to similar physics a definition is a definition.
2) YES, he stops short of describing the downwash, but that is a result of the pressures, so it is not a contributor to lift as commonly described.
the cameraman was totally unprepared for this lecture and had no initiative at all to point the camera at the point of interest.
Pressure is force divided by area, so not a force itself. Pressure is not in Newtons alone
The Lecture was great, super awesome!!! However, ... oh, the camera man, ... not only not pointing the camera to the screen, but 144p too... and here i thought, that there couldn't be anything worse than 240p :D
Well, luckily the uploader gave the link to the slides in the description, if not for those, the lecture would have been only half as useful.
"There is no reason why two persons walking around a building would meet at the same time"?`What😯
This is currently (Oct 2015) a *direct* link to all 25 lecture slides:
docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit
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Cheers
truly a wonderful presentation! I'd admonish the vidiographer for concentration on the professor rather than his 'slides' or 'video' elements of his presentation.. We know he's an interesting fellow, extremely competent and likable .. but show what he wants his audience to see!!! ..it would have been much more an 'emphatic' display of his very sound ideas!!
(j.a. , mech.eng., m.d. , aeronautical engineer)
when the lecturer put the paper across and blew it, the paper reacted bcos of the pressure gradient, and note that was a downward gravitational force or atmospheric pressure acting on both sides. However, when he place the paper downwards and blew it, there was no reaction. Now, the question is, why was there no reaction? Is it bcos there was no downward gravitational force as the thin paper was also placed pointing down, where there was no atmospheric pressure acting along the thin edges of the paper?
No.
Great Lecture! +cyhong2001, If the curving of the streamlines is what causes the lift, then wings with rectangular cross section cannot generate lift? If I am not wrong, the first flight did not have a curved wing cross section. Please explain. Thank you!
Easy. A flat airfoil can still curve flow with angle of attack. It doesn't work as well as a nicely curved asymmetrical airfoil, but it will curve the flow
@@GZA036 Exactly, curvature is all one needs. Best shown with the display of the firstly still and then turning cylinder, showing some Magnus-effect. When turning, takes advantage of the coanda-effect, I guess, and prolongs the curvature, generating much more lift, than if the air blows on half the cylinder, which cylinder now stands still... Lift, for cylinders or airfoils, is always lift, and Magnus-effect is called like than, cause back then, none has figured out yet, that it´s one and the same phenomenon...
Half of the explanations say that flow over the top is faster, because it's lower pressure. Other half of them say the pressure over the top is lower because it's moving faster.
So is it the chicken or the egg?
Is it the chicken or the egg? It's both. A pressure differential accelerates air. Moving air which encounters an obstacle and thus changes velocity results in a pressure differential. The key fact which every text book author seems to not realize is that, when reversing a differential to form an integral the initial condition of the integral has to be included. For moving air, pressure is proportional to the rate of velocity change or,
P = K*dV/dt.
Reversing this differential to an integral you get velocity change is proportional to the integral of acceleration over time or,
delta V = K* INT(a).
But see there? That was delta V, not actual V.
One must include the initial condition in an integral so:
V = Vinit + delta V or,
V = Vinit + K * INT(a)
The fact that air is only moving does not in itself cause a pressure differential. The acceleration or de-acceleration of that air in the first place causes a pressure differential.
John Frazer. We call chicken-egg problems differential equations: one thing depends on another that depends on the first. They can be solved with a huge load of maths
+Darrell Hambley,
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That's not exactly correct. It can get confusing, but viewed carefully it's understandable
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Air has mass and we know it takes a force to accelerate a mass, ANY MASS at ALL times. Newton #1.
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That force in a fluid comes from a pressure difference between two regions also called pressure gradient.
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When a flow encounters an object that it is generally moving toward it (as under a wing) in essence it "impacts" the surface which increases the pressure. It is then this increased pressure which slows (negative acceleration) the air.
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If air and surface are trying to move away from each other, as over a wing, the pressure is reduced.
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Pressure drives acceleration, but a curved flow maintains the pressure difference due to its *acceleration*, not speed.
Above the wing the curved path is caused because viscosity prevents the air from going straight and "sliding along" some air 'inside the curve".
You can view it as the air's inertia is trying to go straight, and, therefore "swing out, away from the curved surface" lowering the pressure.
Chicken. Curving the flow over the top surface of the wing creates angular acceleration (centrifugal force trying to fling it away from the surface of the wing) causing decreased pressure, resulting in increased velocity
user.uni-frankfurt.de/~weltner/Physics%20of%20Flight%20internet%202011.pdf
also
what causes the pressure gradient above the wing??
(at the atomic scale - attraction / repultion of electrons in air atoms) ???
I understood the bit about (a hurricans centre)
where near the centre of the radius pressure is just lower compared to further out you get
Jim Hedger While the fundamental phenomenon is that an object moving through a fluid creates pressure differences in order to move the air around so it may pass, more informatoin on this is in the resources I linko to below. ...I've posted this several times before and PLEASE NOTE that the owner HAS include this in the description above:His missing slides are HERE (Click the Download Icon for the complete set of slides):
docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit?usp=sharing ...
This is the 2003 article he mentions in the video. It is little better than the iop version above in the description:
www3.eng.cam.ac.uk/outreach/Project-resources/Senior-glider/howwingswork.pdf
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Other articles to get more info:
Weltner in PDF - "Misinterpretations of Bernoulli's Law":
user.uni-frankfurt.de/~weltner/Misinterpretations%20of%20Bernoullis%20Law%202011%20internet.pdf Weltner as a web page:
www-stud.rbi.informatik.uni-frankfurt.de/~plass/MIS/mis6.html
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Dave Bentley Wings Don't Suck 2015
219sqn.aafc.org.au/Flight/Wings%20don't%20suck-How%20planes%20really%20fly.pdf
David Bentley Australian Air Force Cadets 2013:
219sqn.aafc.org.au/Flight/Principles%20of%20Flight%20-%20web.pdf
Dave Bentley shows slowing of upper air & other misconceptions 2012:
219sqn.aafc.org.au/Flight/Simple%20Aerodynamics-How%20planes%20fly.pdf
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Peter Eastwell Bernoulli?
www.scienceeducationreview.com/open_access/eastwell-bernoulli.pdf
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John S. Denker www.av8n.com/
Contents: www.av8n.com/how/
I'd just like to point out, among all the other negative points about the camera operator, is that the person behind that camera is very likely a student of one of the best universities in the world. Oh dear.