I’m an aerospace engineer who graduated from Embry Riddle, the top rated aviation school in the country. And even there, in our early aerodynamics lessons, the equal transit time fallacy was taught. I remember because I asked - Why does the air on the top HAVE TO reach the trailing edge at the same time as the air on the top? And my professor didn’t know… but to his credit, he came back the next week and taught everyone the fallacy of the equal transit time.

@FlywithMagnar

Жыл бұрын

That's a great quality of an instructor.

@jadneves

9 ай бұрын

No aniversário de 100 anos da Aviação eu entrei com essa questão "- Por quê um avião voa?" justamente para abolirem essa falácia que todas escolas ensinam sobre a sustentação e com o mesmo argumento do vôo invertido não aceitei tal resposta;

@markmcgoveran6811

9 ай бұрын

Calm down it's just a math model. Ask any farmer and he will tell you it doesn't have to get there at the same time. It's like permanent magnetism and residual magnetism it's all a personal opinion which one is there. If I like it it's permanent magnetism and I sell it for being a permanent magnet. If I don't like it it's residual magnetism and I don't tell anybody

@SwanOnChips

8 ай бұрын

@jacobstump4414 I have a technical article copied that credits Newton for wing lift, not Bernoulli. Did anyone teach that?

@jean-pierrevandormael5315

8 ай бұрын

Only the second law of Newton related to the variation of momentum : F=d(mV)/dt, describes correctly the wing lift (vector F for the force on an air particle, scalar m for mass of that air particle, vector dV for the variation of velocity and scalar t for time). This law applies to all air particles moved by the plane flying through the air. The wing lift is equal to the vector sum of the forces exerted by all air particles on the wings. The Bernoulli's equation describes only the aerodynamic behaviour of the air due to the movement of the plane. It has noting to do with the lift.

Being a carpenter I remember being taught about Bernoulli's principle and the reason why roof tiles come off a roof during high winds. I have never forgotten about this phenomenon. Love it.

@nathanwoodruff9422

8 ай бұрын

It is the same phenomenon on why people are unable to stand up in a hurricane.

As an instructor, I've been teaching Bernoulli's for straight and level briefs. I tell them it's not a direct translation from venturi tube to an aero foil, but just explain that there is a similar effect of decreasing static pressure above the wing. Didn't realize people were trying to explain the "reason" for it as an equal transit time...

The fact that you can make a flat square fly if you put the centre of gravity in the right place and give it control surfaces and enough thrust and a positive angle of attack tells me that everything else including the aerofoil cross section and other twiddly bits like wingtip vortex generators etc are all about improving efficiency. All you need is enough surface area to direct some air downwards, get the basics right, and it'll fly.

@rdspam

Жыл бұрын

Any supersonic aircraft will demonstrate this.

@FrostCraftedMC

Жыл бұрын

modern wings are mostly working on air pressure differential on top and bottom. the wing moves forward, making high pressure at the bottom, low pressure at the top, sucking the wing upwards while also sucking air over the top

@DietmarSchlager

Жыл бұрын

@@FrostCraftedMC , you are funny.: „modern wings“? And don‘t forget, sucking is only an imagination of the real physics. You only can fix that the side which is turned to the incoming airflow (the bottom) produces more pressure and on the side which is a little bit turned away from incoming flow (upside) decreases the pressure. So it´s clear that there is a difference of pressure that can be seen as generating lift.

@nitramluap

Жыл бұрын

@@FrostCraftedMC Funny... it's pretty windy below a rotary wing aircraft (ie. helicopter). Pretty sure it's not being 'sucked up'.

@JohnDoe-vx3z

Жыл бұрын

@@nitramluap Yep, lift is the opposite reaction to air being pushed down. Helicopter pilots understand that better than their fixed wing counterparts.

I have a private pilot license, but have not flown aircrafts or even being in contact with the world of aviation for about 7 years. Now KZread recommends me this video and it reminded me of when I was taking classes, that one of our textbooks warned against these misconceptions regarding aircraft lift. I also remember the book saying that it is still not completely understood, what makes an aircraft fly. I still have the books with me as well as my (expired) private pilot license.

@FlywithMagnar

Жыл бұрын

Lift is fully understood by aerodynamic specialists. The problem is to explain it to people without an engineering degree without oversimplifying it.

@heathwasson7811

Жыл бұрын

@@FlywithMagnar As an aeronautical engineer (and pilot) I completely understand why the typical example is taught... It's a "good enough" explanation for almost every human on the planet, even for pilots. As you say it's very difficult to explain the totality of what's taking place, without giving a multi-day class on aerodynamics. The funny/sobering thing is... even relatively high levels academics (university science classes not focused on aero/fluid dynamic) are still teaching the incorrect science, because it is good enough most of the time. I only know better because I majored in this specific field. That leaves me to question what I think I "know" about other areas of study.

@johnpipping3848

Жыл бұрын

However hard you try you can’t “fly aircrafts”. The plural of aircraft is……. aircraft.

@motionsic

Жыл бұрын

In the USA, PPL is for life. Just need bi-annual flight review to be current, if I remember correctly.

@NicholasMati

Жыл бұрын

I know what sentence you're referring to. I remember reading it and laughing / cringing. Most of that chapter's explanation for how an airplane flies is either outright wrong or misleading.

I have been dying to find a good video that actually explains lift for pilots in a correct fashion. As an aerospace engineer it's really hard for me when my student pilots tell me about the Equal Transit Time theory for lift. Thank you for this video!

@dougaltolan3017

Жыл бұрын

Show them the wind tunnel video... Not only is equal transit time shown to be wrong, the air over the top of the wing moves even faster than equal transit time would suggest. Note that that video is only valid for that profile, angle of attack and wind speed.

@villiamo3861

Жыл бұрын

Quite right that the equal transit hypothesis is demonstrated as being false. But then it's dismaying to hear him talk about lift almost as though it were purely a function of surface curvature, when even a flat plate tipped at an angle and forced forward at speed will, also very demonstrably, generate lift.

@boeing757pilot

Жыл бұрын

All pilots should look at the book "The Illustrated Guide to Aerodynamics" by Hubert Skip Smith. Excellent conceptual explanations without the math.. Highly recommended..

@boeing757pilot

Жыл бұрын

@@villiamo3861 Good points!

@romanbart5823

Жыл бұрын

The navy had some great demonstrations on lift. This wing that he is showing has such a high angle of attack that he is getting turbulence above the wing that it symbolizes a stall.

Thank you. This was a good explanation and properly addressed the "equal transit time" assertion, which is STILL incorrectly taught in many flight manuals...

When I used to fly RC models, we took a wing on a 3 channel trainer and put it on backwards. It flew just fine

@einherz

8 ай бұрын

because wing was in correct aoa. backwards wing didn't make it broken, it's just make it with worse aerodynamic quality

its was good to see that smoke demonstration clearly showing the air over and under do not get to back of the wing at same time...I've always wondered how people just seemed to conclude it does

You are 100% correct. When I hear people explain this wrong idea I ask them how is it that aerobatic planes can fly and their wings are symmetrical. And how can they fly upside down?

@andyowens5494

Жыл бұрын

Aerobatic aircraft use engine power. The angle of attach of a symmetric wing profile deflects air down, but that flight mechanism creates a lot of drag, which needs more engine power to overcome. Many aircraft can fly upside down, using the control surfaces to deflect the airflow - exactly the same forces as used to change direction, but if the control surface forces exceed the weight of the aircraft, it doesn't fall out of the sky whilst inverted. So, angle of attack, and control surface inputs, which are completely different flight mechanisms from aerofoils.

@kevinbarry71

Жыл бұрын

@@andyowens5494 yes. Angle of attack is critical. Obviously aerobatic wings are not used on more conventional aircraft for that reason. They are too inefficient. But if the Bernoulli principle was the only thing working, this wouldn't work.

@pk7549

Жыл бұрын

Symmetrical airfoils must always be at a positive angle of attack to produce lift, roughly +4 degrees for unaccelarated flight. Asymmetrical airfoil will still produce significant lift at even zero angle of attack and no lift at roughly -4 degrees under the same condition.

@olddirtbiker5088

Жыл бұрын

@@kevinbarry71 Thank you for pointing out the obvious issues of angle of attack and symmetrical profile wings. If you have ever "flown" your hand out a car window, angle of attack is readily apparent.

@rivernet62

Жыл бұрын

The angle of attack in the smoke demonstration appears to be much more than 4 degrees

Having never heard that hypothesis that the top air would catch up to the bottom air, it was really easy for me to be skeptical about it. In my mind, the speeding up has always been about squeezing the flow to make a fluid go faster, and that applies to a single flow as well. I have no reason to believe there is much of any interaction between the streams once they split between above and below the wing. Anyway, great exploration of the topic.

It’s more important for pilots to understand what causes a wing to stop producing lift, so the passengers don’t get upset.

@FlywithMagnar

Жыл бұрын

It will also be nice if the pilots understand how a wing produces lift.

@rael5469

Жыл бұрын

"It’s more important for pilots to understand what causes a wing to stop producing lift, so the passengers don’t get upset." You mean like when the big fan up front stops cooling the pilots?

@californiadreamin8423

Жыл бұрын

@@rael5469 You got it…..it’s doesn’t do to overheat when the passengers start screaming 😱

@cosmicraysshotsintothelight

9 ай бұрын

As John Wayne would say... "Stop stalling and spit it out..."

@RalphEllis

9 ай бұрын

It has nothing to do with Bernouli. It is action and reaction - it is the deflected downflow of air from under snd over the wing, that provides lift. To make the wing go up, you must deflect molecules of air downwards. No deflection, no lift. The pressure differentials are a product of molecule deflection, not the cause of lift. (ie: more molecules hitting the bottom of the wing than the top.) R.

Two other phenomena need mention: Vortex around the wing caused by viscosity, and simple flat plate lift. The wing's lift is actually a sum of those two, and the latter is still active even when the wing is stalled as long as its AOA remains positive.

@LeoH3L1

Жыл бұрын

The vortex isn't caused by viscosity, it is caused by the pressure differential, and around the wing tip is the only available route the air can move to try to equalise pressure, it can't move against its own flow upstream to come back around the leading edge, or around the trailing edge to do it. You're confusing cause and mechanism. It would be like saying a ball rolls down a hill because it is round, no it rolls down the hill because of gravity, the reason it CAN roll is because it is round. The cause of the vortex is the pressure differential, the mechanism that allows it is the viscosity because without the viscosity it would immediately collapse, but again, that's not the cause.

@Avianthro

Жыл бұрын

@@LeoH3L1 Well, if you want to get really precise, then what's the cause of the pressure differential? The ultimate cause of the wing's lift is the force (thrust) pushing on the wing to accelerate it and then maintain its relative motion with respect to the air. Then there are other co-causes and proximate-intermediary causes-mechanisms. Without the pressure differential along with the air's viscosity (See Prandtl) we would have no vorticity around the wing and it's that vortex's interaction with the air flowing past and through it that's producing the lift, along with a portion (relatively small at low aoa) of lift produced by flat plate drag if angle of attack is positive. We also should mention the shape of the wing, specifically its rounded leading edge and sharp trailing edge. That shape, especially the sharp trailing edge that starts the vortex, also is a cause...can't make lift with a cylinder, unless the cylinder is spinning...Magnus effect used on some "sail" boats. Then there's angle-of-attack...zero angle of attack...zero lift...Want to cause lift, then make the aoa positive but less than 90 degrees. So, we should really say that lift is not caused by any single thing but by a number of factors working in concert, but still the ultimate cause is thrust (from a propulsion unit or from gravity)acting to move the wing relative to the air. So, using your ball rolling downhill analogy: Thrust is gravity. The shape of the airfoil, the vorticity of the air, the aoa of the airfoil...those are the ball's roundness.

@richh1576

Жыл бұрын

@@LeoH3L1 see above response. Recirculation effect on lift was discovered at Boeing Aircraft Research under one Arvel Gentry. The reason for the 'recirculation flow' around a wing/foil/sail is the fundamental viscostiy of the moving fluid. See previous postinjg.

Excellent video, Mrl Magnar! I learned a lot including how many misconceptions I had! Thanks!

There are 12 comments below mine, and they all mirror each other and what I would say. Danke! I'm not sure there's anything else left to say. Science is a process, and you've done it well. As a person studying to be a CFI I think your material would be helpful to future students who care about HOW AND WHY things work. Again, thank you. Ehud Gavron FAA Commercial Helicopter Pilot, Tucson Arizona US. Future CFI because I love to teach. You have helped me today!

As a CFII and someone with an undergraduate degree in Aerospace engineering, the reason it is taught the way it is, is because the students seeking their pilots license would neither understand nor are they interested in fully learning how a wing generates lift. I know, I have tried. What an airfoil really does is to rotate the air in a clockwise manner using the diagram of the airfoil used in the video. This rotation accelerates the air above the airfoil, and retards the air below the airfoil. As mentioned, the total pressure around the airfoil is constant and the same. But with the higher airspeed above the wing, it has a higher dynamic pressure than below the wing, and therefore has a lower static pressure. Lift is generated due to the differences between these static pressures, multiplied by the surface area of the wing. Anything that rotates air, will generate lift.

@royshashibrock3990

Жыл бұрын

Interesting, but incorrect. I am sitting in front of a fan to cool me, which is rotating air...and I assure you it is not producing "lift."

@HH-mw4sq

Жыл бұрын

@@royshashibrock3990 - not that form of rotation. But nice try though. FYI, it is the type of air rotation which causes a golf ball to fly, and the Magnus effect.

@dennispickard7743

Жыл бұрын

@@HH-mw4sq Ahahahahahahaha 😂😂😂

@deang5622

Жыл бұрын

Interesting, looks as if you were taught wrongly in your aerospace engineering degree.

@HH-mw4sq

Жыл бұрын

@@deang5622 - how so? Please elaborate?

Hi Magnar, I am a PPL but more important for this I am an Aeronautical Engineer and also was an Aerodynamics teacher at college. While it is true that Bernoulli's principle applies only to one flow line, it can be also applied to two (or more) flow lines if there is a point where the energy state (speed and pressure) was the same in both flow lines. Sufficiently ahead of the wing, the parcels of air that are going to flow just above the wing and the ones that are going to go just below have the same pressure and speed. So you CAN apply Bernoulli's principle between a point above of the airfoil and another below. Still, transit time is wrong so you can't deduct the speed just by the differences in length. How lift is generated is at the same time more simple, more complicated, and more disappointing (or unsatisfactory explanation) than most people think. Let me know if you want me to expand.

@FlywithMagnar

Жыл бұрын

Thank you for your feedback. Lift can be both easy and complicated to explain. I understand and agree with what your wrote. In this video, I just wanted to address a common misconception.

I'm telling this since decades. Thank you not only to have told, but also to have shown it in practice ❤

@cosmicraysshotsintothelight

9 ай бұрын

The upper surface produces most of it, but "downwash" glancing off the underside also seems to aid/add. Otherwise, helicopter landing zones would not be so breezy. But wait... attach a 25 foot diameter (~8 meter) pan under the helicopter. Is it still able to fly with all the downwash hitting on itself?

@ChrisTietjen_00

8 ай бұрын

@@cosmicraysshotsintothelight If the reaction force off of the blades is greater than the reaction force off of the pan the brick will fly.

The angle of attack has an impact on the lift as well. It correlates to the under the wing lift.

@shi01

Жыл бұрын

There's no such thing as "under the wing lift" The lift a wing generates is the result of the pressure difference between the air over the wing and under the wing. By increasing the angle of attack you increase the pressure difference, which in turn results in more lift. That by the way also explains the wingtip vortices. Because all that is, is air trying to flow from the higher pressure area under the wing to the lower pressure area above the wing. At the inside of the wing generally the fuselage of the aircraft prevents this movement, but on the outside there's nothing that prevents this from happening if you don't add things like winglets.

@rykehuss3435

Жыл бұрын

@@shi01 Have you ever held a piece of flat cardboard (or something similar) against the wind? Tell us you feel nothing pushing against you. Its not "air trying to flow", its literally physical mass of air pushing you. So you can call it "under the wing lift", which it is. Same exact principle if I shot you with a water cannon, you'd go flying yourself momentarily, and not because the water is trying to go around you to reach lower pressure area lol. Air is a fluid too.

@shi01

Жыл бұрын

@@rykehuss3435 If it would be only reaction force, explain the stall effect. If you increase Aoa, yes the pressure under the wing will increase slightly, but the pressure over the wing drops even further. The the flow over the wing "stalls" the higher pressure under the wing isn't nearly big enough to provide any meaningful lift. The aircraft will drop like a stone regardless of it's speed.

I still don't get it.

Thank you sir! As an Aerospace Enginnering student, in 1976, and a student pilot in 1980 I was tought this principle, exactly the way you explain it and show it. What has been happening to teaching this principle since those old times?

Great explanation, I like the intermittent smoke air flow

Thank you. Beautifully demonstrated!

I’ve had this argument with CFIs and FAA examiners more than once. Myths are hard to overcome.

@boeing757pilot

Жыл бұрын

Yes.. And "equal transit time" is still the explanation written into many flight manuals..

@erickborling1302

Жыл бұрын

CFI's should not be deficient in this fact! Really.

Glad to hear you explain the real science behind lift. In the early70's I was taught in junior high science that lift was not created by increase pressure under the wing but decreased pressure above it. I was always interested in flying but this explanation always left a question in my mind because it didn't make sense that enough negative pressure alone could create enough lift. With my education with internal combustion engines, hydraulics and other machines operating on the laws of physics I began to realize that it is the pressure differential that causes lift. Lower pressure above and higher pressure below do to Bernoulli's law creating differential pressure is the cause of lift.

@shi01

Жыл бұрын

What is also importent to know though, Bernoulli alone does only explain why the pressure drops over the wing. But another interesting question is why does the air follow the upper wing profile. Why doesn't it simply get pushed aside by the leading edge and create a turbulent void? And that's where the coanda effect comes in.

@jsquared1013

Жыл бұрын

The decreased pressure on the top side is still of a greater magnitude than the increased pressure on the bottom. I'm no aerodynamicist but I have seen quite a few diagrams of wing profiles showing the pressure gradients along the surfaces (granted it is for racecar wings, so the airfoils are inverted compared to an airplane, but the idea is the same).

This has created great discussion! The wind tunnel test could do with more examples. For example an asymmetric wing and different AOA. More importantly 'zooming out' and visualisation of air much higher and lower from the wing. The example shown seems to result in the upper surface air (close to the wing) having the same speed as the air above. The lower surface in contrast, has markedly slower air (close to the wing) than the air below. In this specific example you could argue that lift is caused by high pressure below the wing and not low pressure above. It does easily disprove the equal transit time hypothesis however.

Thank you. Like so many others I had to "learn" the wrong explanation for lift when I learned to fly. It's good to hear someone debunking it.

@einherz

8 ай бұрын

there nothing wrong with this explanation, it's just not complete

@nikthefix8918

8 ай бұрын

@@einherz In electronics (my field) plumbing analogies are often used as teaching aids. They work fine until they don't. The model of the atom taught in school physics is utterly wrong but conceptually useful - until it isn't. I suspect that the newton / bernoulli lift contribution ratio and their respective real world inticasies are revealed on a need-to-know basis (so to speak). I have commercial pilot friends who claim that it's 2/3 bernoulli and 1/3 newton, but a quantum physicist would say that it's ultimately neither of these things!:)

@einherz

8 ай бұрын

@@nikthefix8918 sure it's all about wing form direction aoa. some forms will use more time bernoulli, some forms - newton. but both will used all time, even flat wing with 90* aoa will forced by bernoulli too, same as laminar symmetric wing at 0* aoa will use newton force too. flight is dynamic aircraft is dynamic, air is dynamic environment. engine above wing more bernoulli, engine under wing - less bernoulli, but if imagine all airflows around there newton and bernoulli everywhere:)

Good explanation. I knew Bernoulli's didn't explain it all. RC pilots have made flat boards fly (not efficient, but they fly)

When i was told the faster air stream at the top meet the slower air at the bottom on trailing edge, i was confused, thinking the faster air must be waiting for the slower one at the end....until you come along saying it is just a hypothesis , not a proven theory. I 'm feeling relief. 🤗

I'm not sure what's being said here. It seems to be a criticism of pilot education, but what is the specific criticism? Bernoulli only holds true when there's non-turbulent flow and when laminar flow starts to break down the forces on a wing (or anything else for that matter) become a far more complicated proposition. It's fine to tell pilots about lift generated by laminar flow around an aerofoil but I'd be surprised if they don't cotton on very quickly, maybe around the time of their first stall, that there's a lot more to the fluid dynamics of lift than just what Bernoulli said.

You can also take the opposite of a flat wing and use a round rod shaped wing but add a little wingtip votrix by spinning the rod. All you need is to direct more of the air down than up and it will fly. Note that the wing shown in the KZread thumbnail for this clip will not generate lift because it does not direct or pust the air down so the air will not push the wing up.

In that particular demonstration, not only was equal transit time wrong, the air over the wing went even faster than equal transit time would suggest. Meaning that lift due to Bernouli's Principal is even greater than equal transit time would predict.

Very simple and concise explanation, however I would add why the velocity increases over the top surface of the airfoil. This is actually due to curvature of the airfoil, which causes a curvature in the streamline due to the coanda effect. An increase in curvature of a streamline causes an increase in velocity. Hence why the top surface of the airfoil has a larger velocity than the bottom due to it being curved more.

Good explanation. Especially at 3:04 where the velocity of air over the wing is shown. Someone should make that venturi apparatus with only one side pinched to model air flow over an airfoil. * Of course now you have the problem of showing the tube of liquid which shows the pressure differential. But this isn't difficult to over come. *The demonstrator as it now is shows two wings mirrored with the liquid filled tubes modeling the pressure above the air foil against the pressure in front of the 'wing'. You actually want three measuring tubes. One on the 'airfoil' (at the venturi), one before the venturi and the third under the 'wing'. These could work if you just have a reservoir of liquid feeding all three tubes, then each tube would show the air pressure before the wing, on top of the wing and under the wing (which might be made to show how angle of attack increases air pressure.)

Nothing can be accelerated instantly. Because it has inertia. That is why air molecules are literally forced apart at the top faster than it can accelerate toward the wing, becoming less dense (lower pressure), by a wing at speed. The air at the bottom of a wing is forced by the wing so fast it becomes compressed faster than it can accelerate away from the wing. (Higher pressure)

The wings are pulled up mainly because the wing is tilted up in front. The air hitting under the tilted wing is lifting up the wing. Play with your palm pulled out of a running car. Tilt the palm. The lift of the palm is because the air hiting under. The Bernoully applies too, but the main force is from under the wing. Increasing the tilt will increase the loft force until at near 90 degrees there will be no lifting force.

Wow, this is one of the most beautiful videos I’ve seen! Thank you.

I remember going to a Physics teachers workshop and Bernoulli's Principle came up. So, I asked a few Physics Teachers how it worked. I got the standard answer you heard here; pressure is reduced. When I probed further and asked about the actual physical phenomenon causing this drop in pressure, I got one of two answers, "I don't know," or "because Bernoulli's Principle says so." Teaching Physics is about imparting an understanding about how the physical world operates, not teaching students to memorize laws and equations with no understanding about the underlying phenomena. So, how does Bernoulli's Principle work, in other words, why is the pressure reduced on a surface when air flows over it? Air pressure is the result of molecules of air molecules impacting the surface. Air pressure decreases for two reasons, fewer molecules strike the surface, and the speed with which they strike the surface is reduced. If air is flowing over the surface, fewer molecules will strike the surface because they are being dragged along the surface by the air stream flowing over the surface. Greater speed of the air stream, results in fewer molecules striking the surface resulting in lower pressure. That's it, it is no more complicated than that.

@FlywithMagnar

9 ай бұрын

You are absolutely right!

When an aerofoil at a small angle of attack starts from rest, it dumps a starting vortex in the flow which would be anti-clockwise in the example shown. If it is then stopped, it dumps a stopping vortex of clockwise rotation. While the stopping vortex is associated with the aerofoil, it generates lift by the Magnus effect. These vortices can be visualised. I can explain about non-superfluidity, the Kutta condition and the Kutta-Joukowski circulation theorem if you like, but here I have given the basics which are not difficult to see and to understand. Bernoulli’s Theorem is a secondary explanation. It doesn’t work in liquid helium.

@rael5469

Жыл бұрын

What about inverted flight? How does the aircraft stay up during inverted flight? Why doesn't the wing "lift" right into the ground?

@FlywithMagnar

Жыл бұрын

When you fly upside down, you fly with the nose above the horizon. Then, the lift acts towards the sky. Many aerobatic aircraft have symmetrical airfoil, which makes this easier.

@rael5469

Жыл бұрын

@@FlywithMagnar Thanks for replying !

@user-yc7sg7xj4f

9 ай бұрын

@@FlywithMagnar Very simple: Airfoils can optimice the stall point or airflow. LIFT is created by a moving mass being deflated. End of discussion..:-D This is why planes fly upside down, stones can skip over water and if you hold your hand out of the car window at 60 mph, it will fly...

I used to be a flying instructor in the late 80's. We would explain this to our students and the easy way to confirm it was the propellor wash you could feel behind an aircraft. If Bernoullie was the reason for lift a propellor would produce no wash and a helicopter would not create any downwash. (That would be nice - I flew rescue helicopters for years and the downwash was always an issue during a winch rescue)

Thank you for finally stating this. The pressure under the wing is FAR greater than the negative pressure about the wing. If the wing was nothing but a flat surface, it would still work just fine.

@Quraishy

9 ай бұрын

Indeed this has been my intuitive thought for 2 decades, but scientists always talking to the wing lift due to lower pressure at the top always bothered me. If there is more pressure at the bottom, its enough to cause lift. when you hold you hand out of the car slightly tiling up wards, you feel the lift, and the wind pressure on the underside or inside of your hand, a lot more then the any pull force you feel at the top of your hand.

@batmandeltaforce

9 ай бұрын

@@Quraishy The shape is more to avoid stall:)

The main reason of lift generation is down deflection of flow due to the angle of attack. There are airfoils with more curvature on the bottom than the top (for instance ) and they provide ample lift provided there is enough AA. Besides, pilots generally don't understand aerodynamics past very basic level. They understand and follow rules and procedures.

The same thing that causes the drag causes the lift, the wing vortex. It produces upwash at the tip, lowering lift, because it blocks the suction surface, but when it reverses direction it produces downwash which then blocks and slows flow on the pressure surface side, and draws air across the suction surface accelerating it. Winglets just move the tip vortex exposing more surface area to air flow, allowing slightly lower AOA, thus improving fuel efficiency. The vortex strength remains the same, ie proportional to lift. Extending flaps just increases and strengthens the vortex sheet. There's a reason Prandtl equated downwash with lift.

@FlywithMagnar

3 ай бұрын

The wing tip vortex is an unwanted side-effect of lift. The swirl does not contribute to lift, but is known as induced drag. To reduce the vortex, the designers can increase the aspect ratio of the wing (gliders are good examples.) Another technique is to taper the wing towards the tip. Winglets reduce the vortex, and hence drag, especially at high angles of attack. When Prandtl equated downwash with lift, he ment the downwash inboard of the vortex. He also concluded that the most effective lift distribution is bell-shaped. You can learn more about Prandtl and how NASA developed the Prandtl wing here: Al Bowers - Prandtl wing update: kzread.info/dash/bejne/qWGYzZOHoLm0fqw.html

As you mentioned, the wing's curvature causes the acceleration of the air over it. I'd like to add that this acceleration is further enhanced by the suction effect, drawing air towards the area of lower pressure. This pressure difference is influenced by the angle of attack, not just the air's acceleration due to the wing's curvature.

@KajolKhan-qj5ne

5 ай бұрын

Yes but before this suction could be possible, the speed had to be increased, hence the curvature, which provoked the acceleration, then the low pressure and from that comes what you just explained.

@BState

5 ай бұрын

@@KajolKhan-qj5ne I agree that the wing's curvature is the initial factor that accelerates the air, leading to the subsequent low-pressure area. My point was to highlight the combined effects of this acceleration and the suction effect it creates, along with the role of the angle of attack.

At 2.39 notice how the air is being forced downwards. The lift can can also be determined using this. A wing works in the same as a propeller. Stand behind a propeller at full thrust and you will get the idea.

@jayreiter268

Жыл бұрын

Static thrust is a special case. I had not seen that slow motion before. I only saw the old spark stop motion. That explained turbulent flow.

@deang5622

Жыл бұрын

I think the explanation you are looking for is Newton's Third Law of motion.

@dwmac2010

Жыл бұрын

Mark, I was going to make the same point you make, except with a helicopter "Rotary Wing". A helicopter rotor is also shaped the same way as an airplane wing. Its motion with rotor angle of attack create a tremendous movement of air downward. It is F=MA. The Mass of the air times the Acceleration of that air creates the Force upward, which lifts the copter. It is "For every Force, there is an equal and opposite Reaction." Air downward/Helicopter upward. Same with an airplane wing. Thank you for mentioning your point about the propeller. Propellers also have the same airfoil shape. I agree with you 100%.

@mikekelly5869

Жыл бұрын

A wing doesn't work the same way as a propellor but most rotors work the same way as a wing, at least to some extent.

@jayreiter268

Жыл бұрын

@@mikekelly5869 They all work the same way.. We just view the effect differently. With a fan or propeller stationary we feel the blast of air because the blade is drawing in air one blade at a time in the same place. When the airplane is in motion the blade describes a spiral. The British word for propeller is Aero Screw. Many propellers have Clark Y airfoil. I never worked on helicopters so do not have a full understanding. The larger the rotor "disk" the more it can lift. The same as wing span. It all has to do with Mass Airflow.

That makes so much sense in contrary what we see always explained the wrong way. This is a great video, thank you.

@thomasmaughan4798

Жыл бұрын

So why do you believe THIS video but not others? I find it interesting.

@hugobloemers4425

Жыл бұрын

@@thomasmaughan4798 Because the other more common explanation never resonated with me and I always felt I did not understand it. With this explanation I feel like I understand the physics behind it. My back ground is in the semiconductor industry, so I may be a layman at fluid-dynamics but from a technical perspective.

@thomasmaughan4798

Жыл бұрын

@@hugobloemers4425 I admit that the usual explanations of Bernoulli effect are incomplete and don't really explain the region of low pressure directly above the wing; the missing element is *inertia* . Air, being viscous, has inertia. So the leading edge rams into the air in a non-symmetrical way. Under the leading edge is relatively flat; the air gets sliced. The part above the leading edge is rounded, but in a very specific way. A short radius, sharp rounding starts upward and the air has high pressure and low velocity. As the air starts to gain vertical velocity it reduces its pressure in the immediate vicinity, the *venturi effect* but since it is close to the surface of the wing, this venturi effect causes the air to cling to, and follow, the curvature. It has inertia and it is that inertia that is trying to pull the airflow away from the wing; but the venturi effect is creating suction. The air is rapidly gaining velocity, which lowers the pressure even more, and because of this increase in velocity, you simply cannot curve the wing as much or it will detach from the suction with a lot of turbulence. That's called a "stall" if this airflow has such inertia that it overcomes the venturi effect; the suction is not sufficient to keep the airflow attached to the wing. And finally, you let the airflow gradually rejoin the airflow that went under the wing. This reduces or eliminates turbulence and the energy robbing effect of turbulence. At the most efficient, you don't need an engine at all; gliders in other words, and they operate entirely on the Bernoulli principle and keep their airfoils straight into the wind. Getting a glider down can sometimes be a challenge. Summarize: The wing does not know or care what the wind is doing. It knows only that the air pressure under the wing is higher than the air pressure above the wing, and while many approaches exist to make it so, a wing with a rounded upper surface will cause air to try to pull away from it creating a suction, and that's where you get lift. If the wing was simply convex, then you would have an area of pushing down, and an area of lift, more or less cancel. So the abrupt convex area and long gentle curve after that eliminates the down-pushing aspect; the drag vector is to the rear instead of down. The engine is overcoming forward drag and not much needed for staying in the air. (and a glider has no engine). A helicopter in hover, meanwhile, uses enormous power just to stay in the air, but even then, the blades are shaped as airfoils to increase efficiency and stability.

@hugobloemers4425

Жыл бұрын

@@thomasmaughan4798 Thanks for taking the time to write this reply :)

@ Kevin Barry symmetrical wings do have lift coefficient and it is incidentally more than a flat plate (flat plate has only reactionary lift) Planes with cambered aerofoil also can fly inverted. Symmetrical aerofoil for that. Symmetrical aerofoils are used for high speed flight (transonic and supersonic)

Thank you for this video, I like the way you explained this concept, can you please expand upon this and how this applies to exceeding the critical angle of attack which causes a stall, more specifically why does the lift drop so rapidly. Thank you! Waiting for your next video :)

Why can't people get this right? 1. Bernoulli is only valid along a stream tube in an inviscid flow. The inviscid flow part is usually pretty valid for high Reynolds number flows outside of the boundary layer and shear layer trailing the wing. The stream tube is much more restrictive except when you assume that the far field has a uniform velocity and static pressure. Under this assumption (which is usually pretty good), all fluid starts with the same total pressure and thus has the same total pressure around the wing. Your statement about how Bernoulli isn't valid because the wing divides the airflow into two parts is wrong. 2. Curvature in the wing is important for keeping the adverse pressure gradient under control and keeping flow attached at high angles of attack, but it still misses the point. Just as the symmetric airfoil befuddles the equal transit time nonsense, the flat plate airfoil (commonly found on small RC foam models) and the supersonic diamond airfoil (with a sharp leading edge) befuddle curvature as the source of lift. IMHO, the best conceptual explanations don't even mention Bernoulli, but instead focus on what the forces are doing to individual masses of fluid. Air is under pressure and will expand when given the chance. As it passes over the top of the wing and the upper surface deflects down, air accelerates into what would otherwise be a void behind the wing. This is accomplished through a vertical pressure gradient resulting in reduced pressure on the upper surface. However, pressure is a scalar and the reduced pressure also corresponds to a horizontal pressure gradient which first acts to speed up and then slow down the flow. At the same time, the bottom of the airfoil has to deflect flow away from it which has the opposite effect and produces a high pressure region which slows flow down and then speeds it up. This is why the transit time over the suction side is faster than the transit time over the pressure side. The exact geometry determines where the peak pressures occur. On most subsonic airfoils, fluid begins to be deflected from the pressure side to the suction side a short distance ahead of the airfoil. Because it already has an "up" component (or down component for negative lift), it has to expand around part of the leading edge resulting in much higher normal accelerations (from the high curvature) and lower pressures which move the location of the minimum pressure forward. In a completely inviscid flow, this perfectly balances out the normal force experienced over most of the wing (which is tilted back towards the trailing edge) and results in no drag. In a real flow, there is some pressure drag, but most drag comes from viscous forces in the boundary layer. I suspect someone will mention circulation. There are enough people who view circulation as fundamental that I won't completely dismiss it, but I personally view it as a convenient mathematical relationship derived from complex analysis (one derivation literally just uses a conformal map of a complex valued function) that is largely divorced from what is actually happening.

Instead of equal transit time, think of conservation of mass. You can draw a control volume around the wing and show that mass entering and exiting are equal. From there you can derive L/D from Bernoulli

Nice experiment! Thanks!

Spot on and well done. Thanks greatly.

When I was doing my physics teachers degree I heard my teacher say that the air particles reached the end at the same time. I immediately knew this was wrong and exclamated: "Why, they don't have a date, do they?" I still have much respect for that teacher but that day learned me never trust anybodies word for it.

I did watched all your videos all your videos about secret of lift. Great explanation ! My favourite videos which I watched is from professor Alexander Lippisch. Can I post a link for KZread video here ?

As an Instructor Pilot for 20 yrs I couldn't agree more. Very misunderstood concept. Bravo! Lift is Bernoulli living on top of the wing while Newton lives on the bottom. Two separate operations but both must work together or.... Bernulli, on it's own, would never make enough lift for flight.

I believe your wind tunnel example may be slightly misleading with what is causing the change in airspeed around the airfoil. I looks to me that the AoA of the foil is deflecting air down slowing all of the air in the lower portion of the demonstration making it harder to determine if the air over the top of the airfoil is actually speeding up as you mentioned in the video or is actually remaining constant. Would a more cambered airfoil with a flat bottom parallel with the relative be better conditions to demonstrate how the shape effects the airspeed?

Using Bernoulli to explain wing lift is only partially correct but is easy for students to understand. A flat plate will develop lift as its incidence is increased, it's just that it's not very efficient and stalls at low incidence. A sailboat sail develops lift even though it has no thickness (between upper and lower surfaces), only camber. It's very easy to do a calculation of the pressure difference created by a notional aerofoil in accordance with Bernoulli but you will soon find out that the lift generated is nowhere near that actually generated by a real wing. The full description of the generation of lift is best explained by newton's Third Law. Lift is the reaction to the motion of the wing deflecting the air downwards as it passes through it. Lift is equal and opposite to the vertical component of the algebraic sum of the rate of change of momentum of all the air as the aircraft passes through it. In the horizontal direction it is induced drag.

The problem with the video shown at 2:36 is that that is not what happens with the wing at that angle of attack (other than in a headwind situation). Since it is the wing that is moving through the air. So in this situation the air should be hitting the wing at the same angle that the wing is at (other than in a head wind situation), The air is accelerated at the leading edge of the wing, because the air is being pulled down by gravity, The leading edge pushes the air up causing a squeezing effect of the air, which then accelerates the air relative to the air below the wing.

3:18 This is the main point. The curvature leads to a change in direction of the air molecules creating a centripetal acceleration speeding up the airflow on the top of the wing. (velocity being a vector having both magnitude and direction)

The smoke "bursts" show that the airflow is not speeding up over the top of the wing - it is continuing at the same speed it was before encountering the wing. On the other hand, the airflow under the wing slows down.

The air at the leading edge is not accelerated directly by the curve, the bottom is also curved and there the air decelerates. It is accelerated by a difference in pressure(force), the pressure gradient is created by the overall wing profile. Even adding a tiny 90 degree flap to the trailing edge will change the gradient and flow near the leading edge.

Wow! So the top air stream actually arrives at the trailing edge *sooner!* This phenomenon is *more* than equal transit time: the lower air stream x velocity is slowed more than the upper air stream (which is perhaps sped up). The problem with equal transit time for pilots is they might assume an inverted (fixed wing) aircraft will inherently produce a lift that pushes them toward the ground. No lift would produce a "zero gravity" experience, so negative Gs indicate that negative angle of attack can overcome airfoil effects to produce negative lift.

[Another perspective] Here is how I see it, the upper part of the aerofoil has a longer distance as it is curved, the lower part has a shorter distance. Now let's stream an imaginary 100 molecules of air to the tip of the aerofoil, 50 molecules go up and 50 go down. The shorter part (lower) has more molecules per distance than the upper part where the molecules are less dense. Now we know denser particle have more pressure compared to lower, this is why the molecules below try to push upward, Hence, lift. I completely agree with everything else.

Most lift is produced by angle of attack: The airfoil shape allows for the same lift at a lower angle of attack, presenting less frontal area or lower coefficient of drag and less turbulence, thus increasing efficiency.

I believe the Bernoulli principal work for super lightweight aircraft that can take off and land at almost zero speed, but when a plane is in the air flying, it acts just like a fish in water. It slices through the medium, in this case air, and that is what keep sit afloat.

If you get tangled in velocity and pressure try the Newton alternative. For an aircraft in level flight and slow, so at high angle of attack, the wing moves a relatively small mass of air with a large downward component of the subsequent velocity. The resulting force has a reaction equal to the mass of the aircraft. At high speed, hence lower angle of attack the mass of air increases and the downward velocity component reduces giving the same effect. It is not rocket science but both flying vehicles use action and reaction. Alas the best demonstration is given by contrails of an approaching aircraft at a close level, preferably as dawn is breaking behind the trails The downward deflection of air is apparent in a fashion that is not as easy to show as blowing over a sheet of paper hanging from one's fingers and watching the trailing edge rise. Propellers and the blades of turbine engines have a strong connection to wings but as devices to provide thrust the reaction connection is apparently more obvious. As indicated at the begining, this is an alternative perspective of the process that makes a wing work and alters none of Bernoulli's work. Blinkers work well on a horse but are a disaster in crowded airspace.

I believe this misconception comes from the effects of a venturi. In the Pilots Handbook of Aeronautical Knowledge, concerning explaining Bernoulli's principle, it says that for a venturi tube "The mass of the air entering the tube must exactly equal the mass exiting the tube. At the constriction, the speed must also increase to allow the same amount of air to pass in the same amount of time as in all other parts of the tube." In a constricted environment like the tube, this would apply, however in the open space an airfoil operates in, this is not the case and thus two particles flowing over and under an airfoil do not meet at the same time.

Hi Magnar. Many have an issue with Bernoulli, and they are mistaken. As long as you are outside the boundary layer Bernoulli's principle applies. In fact, when most engineers use the pressure coefficient it is directly related to Bernoulli, as the ratio of the change in static pressure to the dynamic pressure. The ETT was initially a hypothesis of D'Alembert, and is a result of potential flow, the first real attempt to apply Newton's laws of motion to a fluid. In this situation the curvature of the streamlines at the training edge and leading edge are symmetric, and you get no resultant lift force. As such, saying that the curvature is responsible for the acceleration (while true), neglects the resolution to D'Alembert's paradox which resulted because viscosity was not understood until Navier and Stokes 100 years later. So, the asymmetric acceleration around an aerofoil is due to viscosity. There are two specific effects, the Kutta condition, which moves the rear stagnation point to the TE. and the induction of more flow upwards ahead of the wing. The end result is an asymmetric velocity of the flow (circulation) which at the surface of the wing is given as a pressure force, which will also be asymmetric, with lower pressure above and relatively speaking higher pressure below.

@FlywithMagnar

Жыл бұрын

Thank you for your contribution!

It is not that the air moves faster over the top, but that the air flows more slowly under the wing, with the net effect that the air over the wing is faster when compared with the air underneath, so ... what pilots are taught is actually correct, it is just not due to distance travelled. Also, not mush mention is made of the trailing edge actually redirecting the airflow downwards, resulting in additional lift.

I liked this demonstration. What about the Coanda Effect? The fluid flowing over the top of the airfoil clings to the wing surface, and as it follows the trailing edge, it is directed (accelerated) downwards. Following Newton's Third Law, the mass of the air flowing downwards exerts an equal force in the opposite direction: upwards. This is how most of the lift is generated. If the angle of attack becomes too great, the fluid cannot adhere to the trailing edge and the lift ceases. The flow along the bottom of the wing, can also be diverted by flaps or ailerons, and this directs even more air, or water, downwards, generating even more lift. Also, because the airflow (mass) is taking place along the trailing edge, it exerts a rotational force the wants to pitch the airframe downwards. The elevators counteract this by directing air leaving the trailing edge of the tail upwards to maintain level flight, or whatever pitch the pilot wants. Without that counteracting force, the craft would do a somersault and tumble over itself and out of the sky, like a leaf blowing in the wind. Please tell me if I'm completely wrong here.

@cowboybob7093

Жыл бұрын

KZread title: _Doug McLean | Common Misconceptions in Aerodynamics_ puts much less emphasis on the Coanda Effect. The clip has some chapters. Lift has not been defined. So far I'm in the "it's mainly like a rock skipping on water" - And if one can't generalize that to a steady flow model then one can't criticize it.

@FlywithMagnar

Жыл бұрын

The Coanda effect is used to blow air over the wing's upper surface and/or flaps to control the boundary layer. Lift is not Bernoulli or Newton. They both describe the same thing. Please watch this video: kzread.info/dash/bejne/opxlqtOrmdKygNY.html The bottom of the wing produces only a small portion of the lift. That's why a wing stalls when the angle of attack is too large and the airflow over the wing is disturbed. The downwash behind the wing is balanced by an upwash ahead of the wing, which is also part of the lift. www.av8n.com/how/htm/airfoils.html#sec-upwash-downwash The rotational force is created by the fact that the lift center is behind the center of gravity. It is balanced withe the horizontal stabilizer (and elevator). If you move the center of gravity the the location of the center of lift, the aircraft will be unstable like the F-16, which can only maitain flight with the aid of computers.

@cowboybob7093

Жыл бұрын

@@FlywithMagnar With all due respect to you, an industry professional who is captivated by the subject, your demonstration of the Coanda effect at three minutes into the clip you linked: _"Forget Bernoulli and Newton | The easy way to explain lift"_ is misleading. The leading edge of the paper device is different in the two orientations you demonstrate. While it's tempting to address the airstream and leading edge curl, the major force difference in that specific demonstration is the natural springiness of the paper pulp matrix. That springiness assists the success of horizontal demonstration by amplifying the effect. In the vertical demonstration it contributes to stiffness which resists the effect but contributes to flutter. Held horizontally as shown, the leading edge curl imparts forces, pressure and tension on the whole matrix, including the trailing edge. Those forming forces are from within the paper matrix and would be present to form the paper to the same shape even in a vacuum. Vertically held the paper's shape is maintained by the matrix' springiness and produces flutter where the trailing edge is not assisted. Again, in a vacuum any vertical paper would conform the same vertical shape. I am not convinced you watched the clip I posted the title of. Perhaps you did. It is of a Boeing Technical Fellow's lecture at U. Michigan, it lasts about 45 minutes and presents the non-matrix factors you and I cite, and more. As I wrote before, it recognizes the Coanda effect as integral to the phenomenon of lift but does not predominate the phenomenon. However I find Doug McLean's multi-force harmony approach to be more comprehensive than yours. Ultimately though I believe _LIFT_ has not been fully defined due to the inability of real-world observations to be made. My statement is not meant to discount the importance of wind tunnels, it is simply to state that measuring aerodynamic changes at some fixed points in space relative to the moving aircraft is extremely difficult. That last point in mind, from the reference of an aircraft moving at 200 knots at an altitude 1000m above the ground plane, to discover where air initially is disturbed by the oncoming aircraft, for instance, is a challenge. Perhaps flying through a hectare large array of smoke trailing rockets would help, but I haven't seen such footage.

Many illustrations of air flowing around a wing have an error. Some of them show the air continuing to flow horizontally after it has left the wing. That does not happen! Any time a wing is producing lift, it is also causing a downdraft behind the wing! There is a loss of lift when the airflow separates from the top surface of the wing. Then the air DOES continue horizontally after it has left the wing. Drag also increases sharply. The aluminum overcast turns into aluminum precipitation!

Boyles law I think also applies i.e. Pressure x volume = a constant. Comparing the still air just before the impact of the leading edge of the wing. The volume of air flowing over the top surface of the wing is larger so the pressure reduces as the leading edge strikes the still air. Conversely the volume of air passing under the wing is lower so the pressure increases. As folk rightly observe this effect (high and lower volumes - a volume differential) is caused by the angle of attack of the wing, and holds true for the aerobatic plane flying upside down, as long as that low pressure is on the heavens side you get to see the stars and live to tell the tale…..else take a dive to the ground.

Bernoulli's principle is often (and mistakenly) used by sailing instructors to try to explain how a sail propels a a boat despite the fact that a sail is a sheet of zero thickness and therefore has exactly equal distance on each of its sides. A sail works because it deflects the airstream. Newton's law: an action results in a reaction. Deflecting the airstream results in an equal and opposite reaction.

@davidg4288

9 ай бұрын

The rubber band powered toy balsa wood planes we had as kids did actually fly a short distance from a flat surface. The wings were flat. Of course more sophisticated models did have airfoils and flew better.

@jeffreyerwin3665

9 ай бұрын

@@davidg4288 In the Fall on 1962 I was attending some kind of introductory forum at MIT. The new students there knew how to construct super-light balsa planes that seemed to stay up forever on rubber band power.

That is a great demonstration. The 'meets at the tail of the wing at the same time' explanation has always troubled me. Another thing that nobody seems to consider is the change in direction. Clearly the air leaving the tail side is moving downward to some degree and that means a force was applied by the wing.

@blusheep2

Жыл бұрын

Why would that mean a force was applied by the wing? Wouldn't that have something to do with the fact that the bottom air is lagging behind the upper air? The downward movement of air is more about induced drag I believe.

@mikefochtman7164

Жыл бұрын

@@blusheep2 Well from a simplistic analysis, let's assume at first the air was not moving (assuming no wind at all), and then the air is accelerated downward as the wing slices through it. The underside of the wing is at a slight angle and deflects some air downward (angle of attack). The air over the wing flows over the curved surface and exits the back side in a smooth flow line along that surface (assuming the angle of attack is not so steep that the wing 'stalls'), which is slanting downward even further. Sure, AFTER the wing passes there are all sorts of eddys / whorls and turbulence in the air. But before that the air is being accelerated downward as the wing slices through. Hence, I believe, the wing is acting to push the air downward and an opposite reaction force pushing the wing up.

@blusheep2

Жыл бұрын

@@mikefochtman7164 OK, I see. The deflection of the bottom air down demonstrates an earlier force on the bottom of the wing. Its a Newton's 3rd law thing as opposed to a Bernoullie principle thing.

@dougaltolan3017

Жыл бұрын

@@mikefochtman7164 Absolutely this! Treat the wing as a black box. Before the wing, the air is static, after the wing the air is moving downwards. Whatever accelerates that ir must exert a force on it and experience an equal and opposite force. Only if you need to design a wing and present its characteristics do you need to know HOW it works. Which makes me wonder, why teach pilots this anyway? There are shed loads of systems on aircraft that pilots, aren't taught.

@mikekelly5869

Жыл бұрын

@@blusheep2 Exactly. Coanda effect due to surface resistance slows the layer in immediate contact with the wing and causes the air avove to curve downwards due to velocity transfer to the slowed air below

Civil Engineer here. Lift has always conceptually made sense from observation. But, being familiar with hydraulic behaviors, the explanations by PPL instructors and videos have always left me incredibly dissatisfied. Thank you for correctly explaining this concept. It's unnerving to see the perpetuation of such a large fallacy!

I thought that lift is achieved by the momentum created by the downward air mass acceleration by the wing. This effect can be visualized by the huge air vortex following a plane. The shape of the wing helps to minimize the disturbances and losses and increase the flow stability. I must be wrong somewhere.

Great thank you for effforts

The Bernoulli effect arguments the lift created by an airfoil. A flat wing, or fully symmetrical airfoil, or semi symmetrical airfoil will all generate lift due to dynamic forces striking the bottom of the wing. The higher the angle of incidence and/or angle of attack (to the point of stall), the higher that dynamic force and subsequent lift. At an equivalent angle of attack, a semi symmetrical airfoil will be more efficient as it will generate lift both from dynamic forces and Bernoulli effect. Hold a piece of paper by the edges and blow over the top of it. The paper will lift up because of Bernoulli forces….no dynamic forces present. The wind tunnel test in this video is interesting. Thanks for posting it.

I agree with commenters below, angle of incidence is a much-underestimated factor in lift. The wing is like a propeller blade that isn't spun but instead pushed or pulled through the air, it's not complicated. Tizzying it up with a lot of theorising about airflow is great for fine improvements in efficiency, but the main thing is using the angle of incidence of the wing to constantly push down the equivalent of the plane's weight worth of air so that the plane stays aloft.

Differential pressure is only one part of the story. There are other components such as reactionary lift and konda effect. Equal transit time theory has long been discarded, as far as I remember from my flying training days around forty years ago, it has always been differential pressure to explain lift off a cambered aerofoil, and coefficient of lift obtained as a result of various factors affecting the aerofoil. This includes downwash at trailing edge.

Regarding molecules at the surface of a wing, the velocity of the wing, and the vektor components of the impact of the air molecules, you will recognize that this also explain very good the lift at the wing. Pressure is the number of impact of the molecules on a surface. At the nose of the wing, and with wingspeed, the impact will be higher (max speed vector component of molecule plus speed of wing against molecule). If the curve goes down, the vektor of molecules impact (x direction) is less, and reduced by the wing surface velocity. Result is a lower pressure. With same reason the pressure increases at the underside. Regarding all movements of the molecules you will have macroscopic the Bernoulli as well as Newton. Sign it with vector components in a drawing, it will become clear. And apologize my bad english.

Yes, you can fly with air-dams or sails but fuel costs are much higher. Minimize drag by using less angle of attack and more Bernoulli lift.

A great demo. It has always bugged me how people parrot this lift principle, as if it's very simple, without really thinking about it, and without understanding Bernouilli's principle.

I never got how Bernoulli works and this is a step in the right direction in disproving equal transit time. But it still doesn't explicitly say wy the pressures are different. I believe the answer is shown by the greater distances between the air molecules above the wing; the density and therefore pressure is lower.

How do planes fly upside down? How does the little wind-up balsa-wood toy plane fly when it has no wing shape. What about paragliders? Is it possible that the air is being pushed down (notice that it moves down relative to the direction of travel in the flow), on the underside by impact with the wing surfaces and Newton is simply in charge as the action (air being pushed down) is offset by an equal and opposite reaction (wing being pushed up?)

As someone else commented- the wind tunnel demonstration is misleading because the wing is inclined at a steep angle. Like every other video that I have viewed about 'lift' this video debunks the common Bernoulli explanation yet doesn't give an alternative explanation for lift. A diagram and a few hurried equations with P and PA is all we get.

Where does the thrust from the engine(s) come into play. You can take a hollow tube and put a powerful enough engine in it and make it "fly", I am visualizing children's toy rockets. If you put flat wings, angled up slightly, on an aircraft and engine(s) to produce just the right amount of thrust to push the assembly through the air with just a little extra wouldn't it keep the assembly "flying"?

There are so many ways at explaining lift or movement. When a vehicle traveling at a high rate of speed collides at an oblique angle with a stationary vehicle, it moves the stationary vehicle because of impact and not Bernouli"s Principle. Call it what you want, but the wing is colliding with a mass of air.

@FlywithMagnar

8 ай бұрын

The only place where the wing is colliding with a mas of air, is at the stagnation point.

So is there any lift from a wing if it is at 0° AOA? What is the purpose of asymmetrical camber of the wing ?

@FlywithMagnar

Жыл бұрын

Yes, an asymmetrical wing will procedue lift at 0 AOA because of the greater camber. No, a symmetrical wing will not produce lift at 0 AOA. The purpose of the camber is to increase the curvature over the wing, which in turn increases lift. On fast aircraft, the curvature is reduced as this reduces drag at high speeds. Fast aircraft rely on flaps and slats to increase the wing's curvature for slow flight.

excellent information

Isn't the the wind acting on the wing and wing gliding through the air different....? cuz when wing glides through the air inertia acts on the particle of air and makes the particles at the top and bottom reach at the same time..... don't know if what I said is correct... 😅

Now I’ve retired, it’s fantastic to know after 35 years and 20,000 hours of flying jets (mostly in command) without accident or incident. Is this an example of what they call a ”firm grasp of the non essentials”?

@mmichaeldonavon

Жыл бұрын

I love that statement. :-) As a 40 year flyer - of meager hours - I honestly have always been in awe of you, the airline pilots, with 20 plus thousands of hours. As a student pilot in 1980, we students thought that a guy with 250hrs was a GOD! True. :-) I know you are still flying on the weekends. God bless you - you ARE "da man." Thanks. N6395T (but the Piper Arrow was my favorite - until the wings started falling off. . :-)

@markmcgoveran6811

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Well I'm glad your comment was 99% about how wonderful you are a wonderful your experiences are and kind of 1% of a dig at the contents of the video. Understanding anything is not important for a pilot it's all monkey see monkey do train responses regulated you don't have to understand anything you just kind of point it where the instructor told you and do what the instructor told you to do and that's how it works for you. Then arrogant pilot that you are you call this a non-essential. This is essential and it's a fundamentally simple essential thing for a person who understands airplanes enough to design one for you to fly. I had a pilot friend like you one time I found a book about engineering and airplane design in the thrift store. I told my pilot friend that if an f-15 tomcat had a thousand less horsepower The minimum turn radius at 300 miles an hour went up by 50%. He was sure his pilot experience made him absolutely correct about airplanes and me not owning an airplane made me incorrect. Next time I saw him I got out the textbook from the college and I showed him the f-15 problem and I walked him through those calculations and I said imagine that. I didn't write this book but I understand it do you understand it now?

@mmichaeldonavon

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@@markmcgoveran6811 Was that "put down" comment for me? I was just commenting on the Airline Pilot's exploits. Quite a career, IMHO. My meager manipulation of the controls was given as a "contrast" to his exploits. How do you fit in? Thanks for commenting. p.s. I thought we had just about beat Mr. Bernoulli to death.

@markmcgoveran6811

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@@mmichaeldonavon not really a put down. Everybody needs a different version of an airplane. The pilot needs one thing the engineer needs another. It's a very handy thing to grab as big a piece of knowledge in your version of an airplane or anything else. Bernoulli may have been beat to death for you because you lack mathematical sophistication. A big airplane manufacturer will cut out an airfoil. They fly it in a wind tunnel and they take a lot of measurements wetted area velocity direction I mean they do a lot of measuring. Then these measurements are sealed in a vault and our top secret no one can see them. Then some extremely powerful mathematicians compete at this it's called a benchmark. They use Bernoulli's principle and partial differentiation differential equations and a bunch of other miserable math stuff and they predict the behavior of the air flowing around the airfoil and the forces generated by the airfoil. Of course you just look on a chart and it tells you everything you need to know about launching it at altitude landing in an altitude loads under certain altitudes. That was written by somebody who's very well versed in Bernoulli's principle. Did you use a checklist when you were a pilot? When the first multi engine bombers came out pilots flew up in the air and crashed on takeoff the airplane was worthless, the engineers are idiots they build something that can't fly. The engineer said you guys can't remember everything you need to do to launch this multi-engine aircraft. Here's a checklist. The pilots didn't think they needed a checklist. The general thought they needed a checklist and ordered the pilots to roll down the checklist every time they launched a multi-engine airplane and they quit crashing on takeoff.

@mmichaeldonavon

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@@markmcgoveran6811 Thank you for your in-depth comments. I really liked your comment that: "... because you lack mathematical sophistication." I'll bet you are fun at parties. Thanks. E=Mc2

I like your video. However another way to demonstrate the increased force on the underside of the wing is to simply rotate the section further clockwise. As we do so becomes clear that the wing will be forced to the right . .

Nice explanation.

Thank you very much, I have been thinking about this for a long time that air must not reach at the end at the same time, and you described it with visualisation of smoke, that's the most important thing as ९९ percent people don't know how Bernoulli theorem actually lifting the plane

Delighted that Magnar clearly lays out that "theory" and "hypothesis" are not the same thing.

So, if the air flowing over the top of the wing creates a "low" pressure. And the high pressure is under the wing. |A low pressure will seek a "high" or higher pressure. that would mean the higher pressure under the wing is pushing UP on the wing to help the top of the wing (low pressure) find it's "higher" pressure that is called lift. a Mooney's wing is asymmetrical (equal top and bottom) gets it lift from the angle of incidence. the way the wing is attached to the body.

What is the meaning of that? Anything similar to a sheet having sufficient speed flies. Even that wing when upside down. That is just a profile that can fly and have a small air drag.

What would happen, if the air below the wing gets stopped at the end of the wing? Like with full flaps down, does it negate the lift and at how much percentage?

@screenname8267

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The air doesn't really get "stopped", as it will find a way around just like when a big boxy tractor trailer goes down the highway; but you get a massive amount of drag that can cause you to suddenly drop in speed and stall, not to mention the counteracting motion of a huge drag behind the center of lift is the nose will come down. Basically pitching up and dropping flaps makes crashing easy and acceleration or climbing difficult.

A wing causes differential pressure on one side or the other (typically) of its 2 surfaces (if and only if) it is placed in fluid flow of some sort. Without fluid flow a wing produces no lift. The wings of an airplane will not produce lift setting in the hanger with the doors closed and the engine off. Unless there is fluid flow around the wings no lift is produced. So its the fluid flow that provides the energy (does the work) for lift...not the wing. The amount of differential lift (pressure) is directly proportional to the rate of fluid flow around it and the pressure differential between the two sides of the wing. Fluid flow and differential pressure around the wing produces lift. A wing is just a device that allows differential pressure to take place when in a free flowing fluid.