Sixty Symbols - 2017-09-11
Featuring Professor Mike Merrifield. Animation by Pete McPartlan. More links and info below ↓ ↓ ↓ Discuss on Brady's subreddit: https://redd.it/6zenc6 Visit our website at http://www.sixtysymbols.com/ We're on Facebook at http://www.facebook.com/sixtysymbols And Twitter at http://twitter.com/sixtysymbols This project features scientists from The University of Nottingham http://bit.ly/NottsPhysics Patreon: https://www.patreon.com/sixtysymbols Sixty Symbols videos by Brady Haran http://www.bradyharanblog.com Email list: http://eepurl.com/YdjL9
What didn't Euler do?
Phonetic spelling?
Euler was the father of engineering! Legend!
about half of all math
Mack Martin And Gauss did the other half .
@David White And he did phonetic spelling
This video has a lift-wing bias.
Arrrgg! Groan !! [Wouldn't it be a lift-wing angle of an attack on Bernoulli...?
mad cobra... so you had to make 3 additional accounts to like your comment. amazing...
It's p-factor mate ;)
gold!
@Arseboth No, the Greeks created 'Democracy', which has nothing whatever to do with modern Politics, which is basically an Oligarchy masquerading as Democracy.
Nothing better than having something you firmly believed you understood shown to be significantly mistaken. Excellent, thank you.
Aircraft mechanic here, teachers explained Bernoulli effect and conservation of momentum and then basically said it's complicated and were not engineers. Basic aerodynamics class was just to explain the function of winglets vortex generators and the fact that different wing shapes do different things. Now shush and go turn a wrench.
Yeah, it's not like the air molecules are quantum entangled!
Nothing better than having something you firmly believed you understood shown to be slightly underexplained
I just wish all those who believe in pseudoscience would have the same attitude..
More people need to have this attitude towards life.
Euler looks super smug about the underwear he's wearing on his head
One of his greatest unsung discoveries was he invented a way to avoid folding laundry by wearing it on your head.
How about analyzing how bicycles work? There are lots of false ideas there.
Can confirm. Own a bike in a one-dimensional frictionless environment.
Bicycle's stability is fundamentally tied to relativity. For example, a bicycle escaping from the temporally decreasing gravitational influence of a pub might lose stability for the observer travelling at b (speed of bicycle). Within that system, the curvature of spacetime fluctuates as well, so it's basically proven by Einstein already.
University of Delft proved that angular momentum is not sufficient to explain why a bike does not fall over. There are more factors involved. The human factor (constantly adjusting) is the most important.
The bike itself and/or the rider have a tendency to steer into a lean. Other effects, like the gyroscopic effect of the wheels also improve stability if they are present. But those effects aren't absolutely required because evidently it can be sufficient for stability just for the bike to have a tendency to steer into a lean.
When the wheels turn, the bycicle moves. Simple
Now we just have to wait for professor Philips Moriarty telling us that professors Merrifield's explanation is wrong on so many levels. ;)
Aerospace engineer here. I really like the explanations and the video, but I would like to mention that the explanation of the air being 'squeezed in' near the leading edge as if there was a wall is also kind of 'fallacious' (at least from the point of view of my teachers). The real reason why the air goes faster in the upper side is because of the Kutta condition (https://en.wikipedia.org/wiki/Kutta_condition) which I would have liked to be mentioned here. This condition states that a body such as an airfoil, with a thin trailing edge, will create circulation around it (air rotating basically) so that an stagnation point (this means, a point where the air speed is 0) can exist at the trailing edge. The explanation for this condition is the fact that the air coming from the upper and the lower sides, when they meet, has to have the same speed vector, otherwise the conservation of mass equation does not hold, and it has to be at the trailing edge because this is where the geometry suddenly changes, and the air can be properly separated from the surface. A deeper explanation for this point involves the existance of a viscous bondary layer near the surface, and how it follows the shape of the airfoil. Actually, the reason why an airfoil 'stalls' is because the air suddenly does not follow the shape of the airfoil when the angle of attack is too steep, and decides to separate from it, causing the destruction of the circulation, the bernoulli effect and the momentum change in the air.
And as for what is the real contribution to the lift, either momentum equation or bernoulli, as Prof Merrifield says, it's actually a combination of everything :), but I just like to explain to people the more simpler conservation of momentum (that is, the fact that the air gets turned down by the shape of the airfoil an the angle of attack).
Also, as someone pointed out somewhere in the comments, the animation of the wingtip vortices at around 9:20 is the other way round :), air has more pressure on the lower surface so it will go upwards at the wingtips, causing a vortex going clockwise in the left wing when viewing the aircraft from behind (and also causing a type aerodynamic drag called induced drag).
@Observ45er it doesn't. I was responding to the statement that kutta-joukowski represents the true physics of fluid flow. The most simplistic answer and the one that is true is that aircrafts fly due to more force below the wing than on top. This is directly due to more pressure on the lower surface of the wing than on the top.
+Rickrollingman,
OK. Thanks
@Rickrollingman The sad thing is, many people, even aerospace engineers, think that Kutta-Joukowski theorem, or Coanda effect, or downwash is the primary source of the lift, but they are just the effect of lift.
@Leidan Wing Obviously you would know more than me about this, but isnt induced drag created because the lift vector is perpendicular to the flow LEAVING the trailing edge of the wing, which is slightly angled down, thus the true lift vector is up, but with a slight aft component?
Thanks for the clarification!
Well, I too learned the venturi effect of air acceleration near the leading edge because of the constriction--airfoil on bottom; layers of air above. It is this constriction that accelerates the airflow. And that seems to be supported based on wind tunnel tests. I'm not saying you're wrong. Likely, there are conflicting schools of thought, both of which can be successfully argued.
Ahhh Euler, the source of countless nightmares of engineering students
The false explanations are conspiracies propagated by the Airlluminati
your wingtip vorticies in the animation at 9:21 appear to be moving in the wrong direction
You're right.
Yep, I spotted that too. "Parker Vortex" maybe?
Graphics guy error !
when you analyze it, the first argument is actually the same as the first
+palmomki Yeah, it was just a bad joke or something.
No !
Noooooo
Well you know what they say, the first rule of tautology is the first rule of tautology.
But if A is A and B is B then the sea is cold around the poles.
@magnushman wtf kind of words are that
Just wanted to share that due mostly to people like Professor Mike Merrifield (and Poliakov and... ) from these channels, I'm now enrolled in a degree in Physics, at age 46. I don't know if it will take me anywhere but I'm enjoying the way :) So thank you, I'll hug you if I could.
This was probably the best video on YouTube I've ever seen for this material.
Something I have always wanted to know: What is that thing on Leonhard Euler's head and why is it there?
Flying will get easier since we are running out of gravity.
A stream of ping pong balls aimed at a wall would also splay sideways because the balls heading toward the wall would collide with the ones bouncing back
Nilguiri I bet that was some show.
That is what he is saying: you also have to consider the interaction between the particles
+Francois,
I also thought that was poor to say. I suspect he was trying to discount Newton's "hail of bullets" concept and went a bit off track.
I was thinking the same thing.
Exactly, which means all of aerodynamic can be explained with Newtons law, assuming you had a computer powerful enough to calculate these paths, you'd be able to predict everything about your model to a very high accuracy.
Obviously before the age of computer, that would never work, which is why we have all these different theories, which act as shortcuts to some behaviors we see in aerodynamics.
As an aerospace engineer I'd say that at low velocities the energy equation stops being useful, since density tends to be constant and the mass and momentum equations form a determinate system by themselves, so I'd say the momentum equation is more useful than the energy.
I am a fluid dynamics PhD student doing 3D aerodynamic simulations, and I approve this message. Fluid dynamics on YouTube can be really cringe-worthy, but leave it to sixty symbols to do it exactly right... Well done, more please
TheNightWatch001 Where are you doing your Phd from?
TheNightWatch001 I’ve always been a bit suspicious about fluid dynamics ( which includes liquids as well as gases) being applied to aerodynamics, because liquids can sustain an internal tension and gases can’t . Molecules in liquids are in direct contact with each other and gas molecules are about ten diameters apart at STP , and the mean free path of gas molecules under these conditions is closer to a hundred diameters.
To take just one example——the viscosity of liquids generally decreases with temperature, but that of gases increases. Ouch!
@David White fluid dynamics and aerodynamics is literally the same thing?! aerodynamic is, if you really wanted to called it that, an under-category of fluid dynamics. The same laws apply. Yes in your everyday experience water and air behave very differently, but from a fundamental stand point they can be described with the same PDEs, the navier-stokes equations.
You know, an airplane would also work under water (tbh even better due to the much higher density).
this is the best video about lift on YouTube because it explains all the partially true theories separately and then combines it to show the more complete truth!
@4:45 "How does an airplane fly?"
I'm so happy that your voice expressed the incredulity that I was feeling.
From what I understand, the Coanda effect, the ability of a fluid to attach to a surface, also plays a large part in providing lift for the wing.
Nope, it is incorrect, pls watch the youtube video "Common misconception of lift "by Cambridge's proff Doug Mclean.
"It is not needed for viscosity or Coanda effect for the flow to follow convex surface."
@Lewis And indeed viscosity is what allows flow to detach. Inviscid flow (in thin airfoil theory) doesn't ever separate.
Great explanation other than one thing which I have to disagree with, you can absolutely separate the bernoulli and momentum effects.
Simply by creating a symmetrical wing, symmetrical wings work and are used vastly for military fighter jets, this is because at extreme speeds, a small angle of attack is more than enough to create the desired lift and aerofoil lift becomes miniscule in comparison, so to amend the final part, lift has a larger effect at slower speeds, and AOA is more important at higher speeds, aswell as allowing no change in control during inverted flight.
Yes but the Prof also showed (in the upside down section of the video) that no matter the wing cross-section , the angle of attack creates the bernoulli effect so it's still there.
Those two are one and the same. Momentum change in air is caused by pressure difference, which is caused by Bernoulli effect. Prof makes it sound like those are separate for some reason. They aren't.
Yeah, as soon as you change the angle of attack Bernoulli is now involved due to the "stagnation area" moving off center as the Prof points out. You've made it an airfoil shape by not directing the air along the longitudinal axis (wing chord) of the symmetrical airfoil -- making it unsymmetrical, at least as far as the airflow is concerned.
Also, take a look at the cross section of the wingtip of an F-15 or F-35. Not only is the airfoil not symmetrical but, at least at the point of the wingtip, there's an under-camber like an old fabric covered plane (it doesn't carry through the whole wing, it's more like the leading edge twists down as you move toward the wingtip -- this gives you a wing that's not doing the same thing through its whole length, exactly because different areas are specialized for different speeds and angles of attack).
That's assuming that the stagnation point remains at the same location on the symmetric airfoil as the angle of attack changes. At a = 0, the front stagnation point will obviously be at the nose, but this will change as the angle of attack increases.
"So maybe everyone should be happy" <3
Came for Euler, stayed for Prof. Merrifield.
Before I watched this video: I know how airplanes are flying.
After I watched this video: I don't even think I'm close to understand how airplanes are flying.
Wow!!! This is the most accurate and thorough explanation of how an aircraft wing (or rather wing profile) actually works I've ever seen!
This is a really great video!!!
Wonderfully perfect implementation of exactly this today: check out the "Illium" project...!
I would personally start with conservation of momentum (a sort of distant view of the system) and work backwards into smaller details like bernoulli which is more about minimizing drag for the amount of lift. After all even a flat, infinitely thin wing can still fly.
Another thing that often trips people up is the angle of attack of a wing is usually just seen as the chord line - a straight line between the bottom two points on a wing. However, since most wings are designed to minimize drag with the same side facing the ground they get quite a substantial tilt which gets hidden by their curve. Stunt planes are designed to flip over though and as such often have completely symmetric wings - without altering their angle of attack they'd have zero lift.
Hmm... But even the flat wing needs an angle of attack, and with increased angle the Bernoulli effect increases.
0:25 everyone always cites Bernoulli...
THANK YOU!!!!! I always kinda knew this simple explanations cant be the whole story. Now i finally know 😎👍🏻
Thank you! Always heard that argument that air travelling over the wing had to meet up with air travelling under the wing and thought why, (or BS)
What a fantastic professor! And what a great explanation!
Great video! Glad to know my IB Physics teacher got his explanation correct!
4:44
Brady asks the best questions! No joke.
Navier-Stokes Equations <3
It’s amazing to see all the different professors from Brady’s videos age. Then I go look in the mirror and I can’t remember how I looked all those years ago.
I finally feel like I understand this. Finally! Thanks!
Loved the graphics for this one. Great as usual!
Hey Ethan! Keep up the great work, proud of you!
Thank you for this thorough explanation. Or at least, much more satisfyingly thorough explanation than is commonly given.
Thank you sir. you're my lifesaver
Is he doing ok? this dude is one of my favorite in your videos
As Aviation Engineering student I approve this video
Another awesome video, thank you! :)
I want real measurements from each part of a real wing!
0:17 lol
I'd be curious to see this same discussion extended to talk about what happens when a wing stalls.
You can make a brick fly if you can keep its velocity up and find a way to control its attitude to maintain the needed angle of attack.
thanks for making this- clears things up for me a lot💛
Roboterize - 2017-09-11
What an uplifting video.
Objects in Motion - 2017-09-12
I'd like to keep this chain going, but I'd rudder not.
ZK-BEE Poorboy PB1 - 2017-09-16
Foiled again!
Starknife Z - 2018-01-15
I’m glad they streamlined their target audience to get the most out of the video
lukewingman007 - 2018-01-17
Roboterize get out.
Admiral Stukov - 2018-03-18
This channel will always be on my radar.