Great job explaining why a common misconception regarding lift is incorrect. It could have been beneficial as well to include a corrected explanation of how lift is generated to avoid other potentially wrong explanations.
Yes. So many amateurs with yet another video either simply repeating the misconceptions, or explaining they are wrong, but not the real physics. Here is an explanation of the true physics pf one and the hardest part, above a wing: ruclips.net/video/3MSqbnbKDmM/видео.html
So then the air moving over the top of the air foil actually is moving faster than that moving under, ending up further to the rear of the air particles from underneath. Care to tell us why? Seems important to know.
All these amateurs wanting their 15 minutes of You Tube fame don't know. . This is just another one of the videos either simply repeating the misconceptions, or explaining that they are wrong, but not including the real physics. Here is an explanation of the true physics pf ONE and the hardest parts for them to grasp, above a wing: ruclips.net/video/3MSqbnbKDmM/видео.html
Viscosity. The attractive force between molecules means the flow at the trailing edge sheds a bound vortex. The result of this vorticity in the flow (usually called circulation) is that there is up wash inducted in the flow, which accelerates the top flow more. It also produces an area over the upper surface which has a lower pressure for longer also resulting in less deceleration which means more speed.
Many pilots, although capable of piloting airplanes, do not truly understand lift. Simply put, lift is as follows: Assuming our Earth is an ideal sphere with no friction or atmosphere on its surface. We also have an ideal small ball placed on the surface of the Earth, which will exert pressure on the Earth due to gravity. If we move the ball in one direction along the Earth, we will find that the faster the ball moves, the less pressure it exerts on the Earth. When the speed of the ball reaches the appropriate size, the pressure of the ball on the Earth will be equal to zero. Why? This is because the surface of the Earth is curved, and when a small ball moves, it tends to move away from the Earth's surface along the normal direction of the sphere. That means the ball is trying to leave Earth. However, due to gravity, when the speed of the ball is relatively low, it cannot reach Earth. But the pressure of the ball on the Earth will be reduced. Lift is also the same. When air moves along the upper surface of the wing, due to the curved surface of the wing, the air also tends to move away from the upper surface of the wing in the normal direction, so the pressure of the air on the upper surface of the wing is reduced (similar to weightlessness). So there is also lift on the surface of the wing. Of course, the lower surface of the wing also generates lift, but the lower surface is opposite to the upper surface and can cause overweight, resulting in pressure higher than atmospheric pressure. This also contributes to lift.
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.
Actually, since air has inertia, external flow does behave like internal flow. This is a very common misconception in the education literature on the topic. This argument that internal and external flows are not equivalent is used all of the time to argue against Bernoulli based explanations, and they are as wrong as the things they are trying to correct. Everyone can try this, you can use blu tack or playdough to make a venturi, combined with a straw and measure the effect. Like a carburettor or an airbrush, one end of the straw is in the middle of the venturi, and the other is in a liquid (a glass of water). Blow through it and see the reduction in static pressure as the liquid is drawn up the straw. You can then make a "half venturi", or a hump around the same straw, and you can still observe the effect. It is not as significant, but because air has inertia, it still "compresses" around the hump and as such speeds up resulting in a lower static pressure at the top of the hump. People claim Coanda explains this, and that is just wrong. You can do simple CFD and the presence of the hump provides an increase in pressure at the wall, and this in turn gives an acceleration to the flow based on a simple balance of Newton's 2nd law (either Euler or Navier-Stokes). It is common for most aviation and pilot based texts to ignore the pressure on the wall of the venturi, and to only present the static pressure along the centreline. As a result, you never appreciate where the acceleration is coming from.
Video clearly shows common misconceptions, but it would be great if you could briefly explain why lift is generated by the airfoil. In this case it is due to the change in the curvature of the incoming pressure gradient due to the geometry of the airfoil. The top surface of the airfoil has more curvature compared to the bottom surface. An increase in curvature causes an increase in velocity and decrease in pressure of a fluid. This causes the stream at the top of the airfoil to be travelling much faster than the bottom which creates the pressure differential and thus lift.
J.R., Actually, your description has no physics behind it. I am very sorry, but you have thrown words together that actually make no sense. First, "Curvature of pressure gradient" is meaningless. The *flow* is curved. Second, Pressure Gradient is the difference in pressure between two locations. Third, it is the curvature of the *flow* that is important because a flat surface produces a similarly curved and accelerated flow. .. .. There is no physics to explain why a curvature in a flow can directly cause an increase in velocity of a fluid. There are missing steps in that explanation. . A- Fluid has mass and follows Newton's Laws. Therefore, a force is required to accelerate mass and, therefore, fluid. B- In this case, as Euler figured out in the mid 1700s following up on Bernoulli's work, a Pressure Gradient is the source (cause) of the force that accelerates the fluid. Force accelerates an 'object' (having mass). C- It is the pressure reduction that is *caused by* the flow being forced to curve. D- It is the atmospheric pressure far above the wing that provides the centripetal force causing the curved flow: .. .. The true physics of ONE part of lift and the hardest part for people to grasp, is above a wing. The decrease in pressure above a wing is caused as shown in this short video. Once you see that it is the new Pressure Gradient between atmospheric pressure *ahead* of the wing and this lower pressure *above* the wing that is the *cause of* the Acceleration toward the trailing edge: *ruclips.net/video/3MSqbnbKDmM/видео.html*
So what mechanism is producing the pressure distribution around a wing that results in the lift force? And for anyone still clinging to ideas of the upward pressure on the underside of the wing producing most of the the lift force, the greater proportion of that force is actually produced by the reduction in pressure on the upper surface. This has been measured experimentally and demonstrated many times over the years. Essentially, as a wing is speeding through the still air, it’s producing a vortex, and the wingtip vortices are an extension of that mechanism. Aerodynamicists will talk about Circulation Theory, with velocity added to the airflow over the upper surface of the wing and subtracted from the airflow beneath the wing. However, they tend to suffer from Wind Tunnel Syndrome, where the air has velocity, momentum and kinetic energy. In total contrast, still air has none: it is the wing, along with the aircraft, that has velocity, momentum and kinetic energy, some of which is transferred to the air. In a wind tunnel, the air must keep flowing around the wing towards the fan that’s inducing the airflow, whereas in the real world, displacement of the air is produced entirely by the movement of the wing. The downwash decays in seconds and the wingtip vortices in minutes: the energy transferred to the air is soon dissipated. But how can I convince any sceptics that a wing is producing a vortex? Let me start by referring to the Magnus Effect. This is the same aerodynamic effect that causes a spinning baseball to curve, and a spinning soccer ball to bend: the spin produces a lift force. The Magnus Effect is also exploited by a device known as a Flettner Rotor, which is simply a long, rotating cylinder that, with its axis vertical, has been experimented with as a sail on ships. It has even been experimented with as an aircraft wing. So how does a Flettner Rotor produce a lift force? Let’s start by consider it rotating in still air: there’s no lift force generated, but what is happening to the air around it? Because of the viscosity of the air, the rotor develops a forced vortex around it. As disastrously demonstrated by a tornado, the closer to the centre of the vortex, the higher the rotational velocity and the lower the pressure. Didn’t Daniel Bernoulli have something to say about this? When a wind blows across the rotor, the flow is speeded up on one side and slowed down on the other by the vortex. This produces a relative lowering of the pressure on the one side and an increase in pressure on the other. Consequently, the rotor produces a lateral force at right-angles to the airflow: in other words, it’s producing a lift force - but sideways. There is also a displacement of the airflow, the equivalent of the downwash of a wing. I hope that the similarity between the effect on the airflow around a Flettner Rotor and around a lifting aerofoil, otherwise known as a wing, will be obvious. One is producing a vortex, and so is the other: there can be no real difference in the mechanism. Forget the idea of the curvature of the upper surface of the wing increasing the velocity of the airflow over it, relative to the velocity across the flatter lower surface: that same wing; in inverted flight, still produces a lift force. Even a flat plate at an angle of attack to the airflow produces a lift force, with a reduction in pressure on the upper surface and an increase in pressure on the lower. I have one final thought for you: it is the viscosity of the air that results in the production of a lift force - and drag. If air was not viscous, there would be no lift - and no drag.
"it is the viscosity of the air that results in the production of a lift force" This is fairly often stated but is not universally accepted. There are studies and a substantial body of work to the contrary. After all, why would a transverse force not be possible if there is a pressure asymmetry produced from a geometrical asymmetry of the airfoil shape? Where's the proof? The Kutta condition being regularly applied to potential flow? That's no proof of lift being a viscosity phenomenon, it's a technique of mathematical simplification. Again, where is the proof that an asymmetrical solid needs viscosity to produce a transverse force? Most of what you mentioned could be placed under the broad category of "effects of asymmetry," which is fundamentally what causes lift of course: asymmetry of a solid to the relative flow, turns the flow. The pressure asymmetry that results from the conservation fundamentals (mass, momentum and energy) provides the first principle of physics details.
Have you ever opened a learning book for glider pilots? Why are you not explaning what you think causes the lift on the upper side of the wing profile? Until you do that convinsingly, I'll stick to the existing books.
I don't know what is in your books. There are hundreds of incorrect explanations repeated all over by amateur scientists. The true physics of ONE part of lift and the hardest part for people to grasp, is above a wing. The decrease in pressure above a wing is caused as shown in this short video. Once you see that it is the new Pressure Gradient between atmospheric pressure ahead of the wing and this lower pressure above the wing that is the cause of the Acceleration toward the trailing edge: *ruclips.net/video/3MSqbnbKDmM/видео.html*
You obviously haven’t carried a piece of plywood in the wind and it shows lol. You don’t need a wing shape to generate lift all you need is angle of attack.
Yes, plywood in the wind increases your drag, and you can even fly, if you keep it in the right position and run fast enough - preferably let a few people pull you. And yes, there is a reaction from the deflection of the wind on the under side of the wing, but the major lift 3:1 is due to the lowered pressure on the top of the wing. I have been a pilot for decades, began as a glider pilot. Bernoulli is the key word - higher airspeed means lower pressure - or lift in this case. I wish people would stop educating others before they had learned the basics themselves.
@@Eigil_Skovgaard look man I drive cars that doesn’t make me an automotive engineer. Do me a favor type this into RUclips ( doofer 911 how wings actually create lift) the Bernoulli principle is flawed and this video explains what’s actually happening. A wing does create more lift than plywood but not because of the pressure difference like your little book tells you.
@@stuckinthemud4352 Those "little books" are the official law stated by engeneers. If you were the slightest convinced about your new discovery, you would not need to be polemic. I suggest you stay with your car - independent of wings.
The key, here is that air and lower surface is just like wind blowing on you. It pushes on you. This DIRECTLY causes a pressure increase within the air. NOTHING else is needed to explain the physics of that. Air has mass and therefore, inertia, so if pushes more increasing the pressure. .. That pressure ALSO slows down the air. At some points it slows to a stop. It slows BECAUSE that pressure ahead of it is greater than the pressure behind it [atmospheric pressure] . The relative motion of wing and air approaching each other DIRECTLY causes a pressure increase. .. Therefore, the "ricochet" story is kinda' a little in the right direction.. . . It's not a bounce, but there is still an increase of the push. .. If you analyze it correctly, you should be able to reason it out that for the flying, moving wing, the moving wing is directly increasing the air's pressure because it is pushing more on the air when it advances on the air. It has to *PUSH* the air out of its way. THat push is pressure more than ambient. . This is such simple physics. Grade schoolers understand it. - - Cheers. P.S. The converse happens above a wing. . .
Air is not a "liquid" fluid. NASA had it right when they sent the MARS rover. NASA explained that the very thin atmosphere meant it was going to be harder for the propellers to push.
@@Observ45er Yes. And there is one of the problems because they are not the same. A liquid and a gas are different states. The term fluid confuses the matter and creates invalid assumptions.
@@animatem There is no problem, you must simply explain to the student what the terminology means and it is simple. . . In science and engineering we use the terms 'fluid' mechanics and dynamics because the behaviors are very, very similar and we use the same techniques for both liquids and gases. You did not explain why you thought they were different, but if you are thinking about PV=nRt the ideal gas law, and think that air is different because it is compressible, you should know that in normal flight speeds, air acts so close to being incompressible that we consider it as such, just like water. The pressure changes around the wing in normal flight are a very small percentage and the resulting compressibility and, therefore, the density change is insignificant for these common purposes. . And yes, on Mars the atmospheric pressure is similar to what it is on Earth at 100,000 ft. As I recall, that is 0.088 psi, or only 0.6% sea level pressure on Earth. This is easily available on the internet.
@@Observ45er Airplanes, sailboats, etc, do not start at normal flight speeds. An equilibrium obtained in a wind tunnel simulating normal flight speeds with a stationary wing is flawed. My issue started with trying to understand sailboat sails. No sailboat works at those speeds, but this same "wing" process is used to explain sailboats moving in wind. The answer is that seems very unlikely. I am looking for the NASA article, but admit I cannot find it anymore. They were very clear about the push process. That process makes more sense in air.
I at least found "who" talked about the flight but not the full NASA explanation of flight: One of the biggest engineering challenges is getting the Mars Helicopter’s blades just right. They need to push enough air downward to receive an upward force that allows for thrust and controlled flight - a big concern on a planet where the atmosphere is only one percent as dense as Earth’s. “No helicopter has flown in those flight conditions - equivalent to 100,000 feet (30,000 meters) on Earth,” said Bob Balaram, chief engineer for the project at NASA’s Jet Propulsion Laboratory.
Incorrect. There was never any need for the air to "meet" at the end, that is just an additional reason the lift would be greater. That doesn't refute the transit time being roughly equal. The skipping stone explanation also only spies in certain cases like flaps. I'm sure this account will be deleted though.
As I understand this video you are only saying the two air particles do not and cannot meet up at the same time where the airflow again meets trailing edge. The airflow over the upper surface is still traveling faster, Which should still mean a lower pressure area above the aerofoil.
The particles above the wing travel *even faster* than they would had the "equal transit" theory been true. So the speed and pressure difference is true, Bernoulli is true, but the magical equal transit time is not. An important part is that air is deflected downwards behind the wing, which is the "opposite reaction" to the wing being lifted upwards.
In a 2D wind tunnel there is no downwash. Before you quote Understand Flight by Anderson and Eberhard, lift in 2D is real, every old school lift and drag curve for a NACA aerofoil you have looked at came from the NACA 2D wind tunnel. So, sorry, no air deflected downwards. Those measurements in those wind tunnels were all down with pressure taps, and that was good enough until the 1980s when the first action reaction explanation appeared in the literature.
If you want to know where the equal transit time came from I have an article on arXiv, On the Origins and Relevance of the Equal Transit Time Fallacy to Explain Lift. Sorry can't post URLs.
@@davetime5234 It is a result of not including viscosity. Without a non-conservative force, every path (streamline) around an aerofoil is like every other potential (hiking around a mountain), where the path does not affect the balance of energy. However, when you add a non-conservative force (in the case of aerodynamics that is viscosity, or friction when hiking around the mountain) then the path taken means there will be an overall effect, and not all streamlines will now be traversed in equal time. I note in my paper that D'Alembert assumed equal transit, but both he and Euler calculated it to be true, hence giving D'Alembert's paradox. The common misconception is that equal transit time can be used to explain lift, where it was non lifting flows that give equal transit (and hence D'Alembert's paradox).
@@aerospacedoctor I don't quite understand this in relation to the mass flow continuity issue. A moving reference frame without the airfoil, but centered on where the airfoil will be, has a rate of mass flow traversing the region. When the airfoil is there, the same mass flow rate must be maintained. This must be accounted for by the combined mass transit speed above and below the airfoil. Because there is less available space, the average particle transit speed should be higher than before to keep the mass flow rate constant (for constant density). So, the asymmetry should result in yet even more speed above the wing than the already increased average particle speed (from the imposed transit space restriction), with the slow down below the wing being sufficient to keep the combined mass transit rate the same as in the case without the foil in the moving reference frame. Aren't these separate transit times affected by the need to have the composite mass transit time avoiding flow stagnation? How is this connected to viscosity?
@@davetime5234 Let me ask you a question. You note the keyword, "asymmetry". Fundamentally, and I mean very fundamental physics, what causes the asymmetry? You are correct in everything you say in the last paragraph, but what is the physical mechanism that results in asymmetry? I noted D'Alembert's paradox which was also the solution from Euler; they both predicted a symmetric flow, and hence no drag (or lift).
@@aerospacedoctor "I mean very fundamental physics, what causes the asymmetry...what is the physical mechanism that results in asymmetry? ?" Asymmetrical geometry of the solid to the relative wind (from the combined asymmetry of AoA plus any asymmetry of camber) resulting in an asymmetrical transit passage presented to the relative wind's dynamic pressure in the cross-sectional area of influence, which results in an asymmetrical pressure response necessary to maintain the prior existing mass flow rate in the that area of influence, is the best I can come up with at the moment.
We still don't know. We have developed piles of models that give us very good approximations of what would happen, but we still don't really know why wings have the extreme lift we observe. You will see explanations that talk like they have all the answers, but actually, they don't.
Great job explaining why a common misconception regarding lift is incorrect. It could have been beneficial as well to include a corrected explanation of how lift is generated to avoid other potentially wrong explanations.
Yes. So many amateurs with yet another video either simply repeating the misconceptions, or explaining they are wrong, but not the real physics.
Here is an explanation of the true physics pf one and the hardest part, above a wing: ruclips.net/video/3MSqbnbKDmM/видео.html
As a Lockheed Martin dev engineer told me. “We don’t know how exactly lift comes about but our computers find a good shape that does”
So then the air moving over the top of the air foil actually is moving faster than that moving under, ending up further to the rear of the air particles from underneath. Care to tell us why? Seems important to know.
All these amateurs wanting their 15 minutes of You Tube fame don't know.
.
This is just another one of the videos either simply repeating the misconceptions, or explaining that they are wrong, but not including the real physics.
Here is an explanation of the true physics pf ONE and the hardest parts for them to grasp, above a wing: ruclips.net/video/3MSqbnbKDmM/видео.html
Viscosity. The attractive force between molecules means the flow at the trailing edge sheds a bound vortex. The result of this vorticity in the flow (usually called circulation) is that there is up wash inducted in the flow, which accelerates the top flow more. It also produces an area over the upper surface which has a lower pressure for longer also resulting in less deceleration which means more speed.
Many pilots, although capable of piloting airplanes, do not truly understand lift. Simply put, lift is as follows:
Assuming our Earth is an ideal sphere with no friction or atmosphere on its surface. We also have an ideal small ball placed on the surface of the Earth, which will exert pressure on the Earth due to gravity.
If we move the ball in one direction along the Earth, we will find that the faster the ball moves, the less pressure it exerts on the Earth. When the speed of the ball reaches the appropriate size, the pressure of the ball on the Earth will be equal to zero.
Why?
This is because the surface of the Earth is curved, and when a small ball moves, it tends to move away from the Earth's surface along the normal direction of the sphere. That means the ball is trying to leave Earth. However, due to gravity, when the speed of the ball is relatively low, it cannot reach Earth. But the pressure of the ball on the Earth will be reduced.
Lift is also the same. When air moves along the upper surface of the wing, due to the curved surface of the wing, the air also tends to move away from the upper surface of the wing in the normal direction, so the pressure of the air on the upper surface of the wing is reduced (similar to weightlessness). So there is also lift on the surface of the wing.
Of course, the lower surface of the wing also generates lift, but the lower surface is opposite to the upper surface and can cause overweight, resulting in pressure higher than atmospheric pressure. This also contributes to lift.
please keep going to publish new lessons, you are amazing, It is easy and enjoyable to understand from your explenation
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.
Actually, since air has inertia, external flow does behave like internal flow. This is a very common misconception in the education literature on the topic. This argument that internal and external flows are not equivalent is used all of the time to argue against Bernoulli based explanations, and they are as wrong as the things they are trying to correct. Everyone can try this, you can use blu tack or playdough to make a venturi, combined with a straw and measure the effect. Like a carburettor or an airbrush, one end of the straw is in the middle of the venturi, and the other is in a liquid (a glass of water). Blow through it and see the reduction in static pressure as the liquid is drawn up the straw. You can then make a "half venturi", or a hump around the same straw, and you can still observe the effect. It is not as significant, but because air has inertia, it still "compresses" around the hump and as such speeds up resulting in a lower static pressure at the top of the hump. People claim Coanda explains this, and that is just wrong. You can do simple CFD and the presence of the hump provides an increase in pressure at the wall, and this in turn gives an acceleration to the flow based on a simple balance of Newton's 2nd law (either Euler or Navier-Stokes). It is common for most aviation and pilot based texts to ignore the pressure on the wall of the venturi, and to only present the static pressure along the centreline. As a result, you never appreciate where the acceleration is coming from.
Video clearly shows common misconceptions, but it would be great if you could briefly explain why lift is generated by the airfoil. In this case it is due to the change in the curvature of the incoming pressure gradient due to the geometry of the airfoil. The top surface of the airfoil has more curvature compared to the bottom surface. An increase in curvature causes an increase in velocity and decrease in pressure of a fluid. This causes the stream at the top of the airfoil to be travelling much faster than the bottom which creates the pressure differential and thus lift.
J.R.,
Actually, your description has no physics behind it. I am very sorry, but you have thrown words together that actually make no sense.
First, "Curvature of pressure gradient" is meaningless. The *flow* is curved.
Second, Pressure Gradient is the difference in pressure between two locations.
Third, it is the curvature of the *flow* that is important because a flat surface produces a similarly curved and accelerated flow.
.. ..
There is no physics to explain why a curvature in a flow can directly cause an increase in velocity of a fluid. There are missing steps in that explanation.
.
A- Fluid has mass and follows Newton's Laws. Therefore, a force is required to accelerate mass and, therefore, fluid.
B- In this case, as Euler figured out in the mid 1700s following up on Bernoulli's work, a Pressure Gradient is the source (cause) of the force that accelerates the fluid. Force accelerates an 'object' (having mass).
C- It is the pressure reduction that is *caused by* the flow being forced to curve.
D- It is the atmospheric pressure far above the wing that provides the centripetal force causing the curved flow:
.. ..
The true physics of ONE part of lift and the hardest part for people to grasp, is above a wing.
The decrease in pressure above a wing is caused as shown in this short video. Once you see that it is the new Pressure Gradient between atmospheric pressure *ahead* of the wing and this lower pressure *above* the wing that is the *cause of* the Acceleration toward the trailing edge:
*ruclips.net/video/3MSqbnbKDmM/видео.html*
So what mechanism is producing the pressure distribution around a wing that results in the lift force? And for anyone still clinging to ideas of the upward pressure on the underside of the wing producing most of the the lift force, the greater proportion of that force is actually produced by the reduction in pressure on the upper surface. This has been measured experimentally and demonstrated many times over the years.
Essentially, as a wing is speeding through the still air, it’s producing a vortex, and the wingtip vortices are an extension of that mechanism. Aerodynamicists will talk about Circulation Theory, with velocity added to the airflow over the upper surface of the wing and subtracted from the airflow beneath the wing. However, they tend to suffer from Wind Tunnel Syndrome, where the air has velocity, momentum and kinetic energy. In total contrast, still air has none: it is the wing, along with the aircraft, that has velocity, momentum and kinetic energy, some of which is transferred to the air.
In a wind tunnel, the air must keep flowing around the wing towards the fan that’s inducing the airflow, whereas in the real world, displacement of the air is produced entirely by the movement of the wing. The downwash decays in seconds and the wingtip vortices in minutes: the energy transferred to the air is soon dissipated.
But how can I convince any sceptics that a wing is producing a vortex? Let me start by referring to the Magnus Effect. This is the same aerodynamic effect that causes a spinning baseball to curve, and a spinning soccer ball to bend: the spin produces a lift force. The Magnus Effect is also exploited by a device known as a Flettner Rotor, which is simply a long, rotating cylinder that, with its axis vertical, has been experimented with as a sail on ships. It has even been experimented with as an aircraft wing.
So how does a Flettner Rotor produce a lift force? Let’s start by consider it rotating in still air: there’s no lift force generated, but what is happening to the air around it? Because of the viscosity of the air, the rotor develops a forced vortex around it. As disastrously demonstrated by a tornado, the closer to the centre of the vortex, the higher the rotational velocity and the lower the pressure. Didn’t Daniel Bernoulli have something to say about this?
When a wind blows across the rotor, the flow is speeded up on one side and slowed down on the other by the vortex. This produces a relative lowering of the pressure on the one side and an increase in pressure on the other. Consequently, the rotor produces a lateral force at right-angles to the airflow: in other words, it’s producing a lift force - but sideways. There is also a displacement of the airflow, the equivalent of the downwash of a wing.
I hope that the similarity between the effect on the airflow around a Flettner Rotor and around a lifting aerofoil, otherwise known as a wing, will be obvious. One is producing a vortex, and so is the other: there can be no real difference in the mechanism. Forget the idea of the curvature of the upper surface of the wing increasing the velocity of the airflow over it, relative to the velocity across the flatter lower surface: that same wing; in inverted flight, still produces a lift force. Even a flat plate at an angle of attack to the airflow produces a lift force, with a reduction in pressure on the upper surface and an increase in pressure on the lower.
I have one final thought for you: it is the viscosity of the air that results in the production of a lift force - and drag. If air was not viscous, there would be no lift - and no drag.
"it is the viscosity of the air that results in the production of a lift force"
This is fairly often stated but is not universally accepted. There are studies and a substantial body of work to the contrary. After all, why would a transverse force not be possible if there is a pressure asymmetry produced from a geometrical asymmetry of the airfoil shape?
Where's the proof? The Kutta condition being regularly applied to potential flow? That's no proof of lift being a viscosity phenomenon, it's a technique of mathematical simplification. Again, where is the proof that an asymmetrical solid needs viscosity to produce a transverse force?
Most of what you mentioned could be placed under the broad category of "effects of asymmetry," which is fundamentally what causes lift of course: asymmetry of a solid to the relative flow, turns the flow.
The pressure asymmetry that results from the conservation fundamentals (mass, momentum and energy) provides the first principle of physics details.
Have you ever opened a learning book for glider pilots? Why are you not explaning what you think causes the lift on the upper side of the wing profile? Until you do that convinsingly, I'll stick to the existing books.
I don't know what is in your books. There are hundreds of incorrect explanations repeated all over by amateur scientists.
The true physics of ONE part of lift and the hardest part for people to grasp, is above a wing.
The decrease in pressure above a wing is caused as shown in this short video. Once you see that it is the new Pressure Gradient between atmospheric pressure ahead of the wing and this lower pressure above the wing that is the cause of the Acceleration toward the trailing edge:
*ruclips.net/video/3MSqbnbKDmM/видео.html*
You obviously haven’t carried a piece of plywood in the wind and it shows lol. You don’t need a wing shape to generate lift all you need is angle of attack.
Yes, plywood in the wind increases your drag, and you can even fly, if you keep it in the right position and run fast enough - preferably let a few people pull you. And yes, there is a reaction from the deflection of the wind on the under side of the wing, but the major lift 3:1 is due to the lowered pressure on the top of the wing. I have been a pilot for decades, began as a glider pilot. Bernoulli is the key word - higher airspeed means lower pressure - or lift in this case. I wish people would stop educating others before they had learned the basics themselves.
@@Eigil_Skovgaard look man I drive cars that doesn’t make me an automotive engineer. Do me a favor type this into RUclips ( doofer 911 how wings actually create lift) the Bernoulli principle is flawed and this video explains what’s actually happening. A wing does create more lift than plywood but not because of the pressure difference like your little book tells you.
@@stuckinthemud4352 Those "little books" are the official law stated by engeneers. If you were the slightest convinced about your new discovery, you would not need to be polemic. I suggest you stay with your car - independent of wings.
The key, here is that air and lower surface is just like wind blowing on you. It pushes on you. This DIRECTLY causes a pressure increase within the air.
NOTHING else is needed to explain the physics of that.
Air has mass and therefore, inertia, so if pushes more increasing the pressure.
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That pressure ALSO slows down the air. At some points it slows to a stop. It slows BECAUSE that pressure ahead of it is greater than the pressure behind it [atmospheric pressure]
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The relative motion of wing and air approaching each other DIRECTLY causes a pressure increase.
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Therefore, the "ricochet" story is kinda' a little in the right direction.. . .
It's not a bounce, but there is still an increase of the push.
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If you analyze it correctly, you should be able to reason it out that for the flying, moving wing, the moving wing is directly increasing the air's pressure because it is pushing more on the air when it advances on the air. It has to *PUSH* the air out of its way. THat push is pressure more than ambient.
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This is such simple physics. Grade schoolers understand it.
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Cheers.
P.S. The converse happens above a wing. . .
Air is not a "liquid" fluid. NASA had it right when they sent the MARS rover. NASA explained that the very thin atmosphere meant it was going to be harder for the propellers to push.
The term fluid is the general term for both liquids and gases.
@@Observ45er Yes. And there is one of the problems because they are not the same. A liquid and a gas are different states. The term fluid confuses the matter and creates invalid assumptions.
@@animatem There is no problem, you must simply explain to the student what the terminology means and it is simple.
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In science and engineering we use the terms 'fluid' mechanics and dynamics because the behaviors are very, very similar and we use the same techniques for both liquids and gases.
You did not explain why you thought they were different, but if you are thinking about PV=nRt the ideal gas law, and think that air is different because it is compressible, you should know that in normal flight speeds, air acts so close to being incompressible that we consider it as such, just like water.
The pressure changes around the wing in normal flight are a very small percentage and the resulting compressibility and, therefore, the density change is insignificant for these common purposes.
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And yes, on Mars the atmospheric pressure is similar to what it is on Earth at 100,000 ft. As I recall, that is 0.088 psi, or only 0.6% sea level pressure on Earth. This is easily available on the internet.
@@Observ45er Airplanes, sailboats, etc, do not start at normal flight speeds. An equilibrium obtained in a wind tunnel simulating normal flight speeds with a stationary wing is flawed. My issue started with trying to understand sailboat sails. No sailboat works at those speeds, but this same "wing" process is used to explain sailboats moving in wind. The answer is that seems very unlikely. I am looking for the NASA article, but admit I cannot find it anymore. They were very clear about the push process. That process makes more sense in air.
I at least found "who" talked about the flight but not the full NASA explanation of flight: One of the biggest engineering challenges is getting the Mars Helicopter’s blades just right. They need to push enough air downward to receive an upward force that allows for thrust and controlled flight - a big concern on a planet where the atmosphere is only one percent as dense as Earth’s. “No helicopter has flown in those flight conditions - equivalent to 100,000 feet (30,000 meters) on Earth,” said Bob Balaram, chief engineer for the project at NASA’s Jet Propulsion Laboratory.
Incorrect. There was never any need for the air to "meet" at the end, that is just an additional reason the lift would be greater. That doesn't refute the transit time being roughly equal.
The skipping stone explanation also only spies in certain cases like flaps.
I'm sure this account will be deleted though.
Bernoulli is not wrong, it sounds like it's even more true than true: it's faster than fast!
As I understand this video you are only saying the two air particles do not and cannot meet up at the same time where the airflow again meets trailing edge. The airflow over the upper surface is still traveling faster, Which should still mean a lower pressure area above the aerofoil.
The particles above the wing travel *even faster* than they would had the "equal transit" theory been true. So the speed and pressure difference is true, Bernoulli is true, but the magical equal transit time is not. An important part is that air is deflected downwards behind the wing, which is the "opposite reaction" to the wing being lifted upwards.
In a 2D wind tunnel there is no downwash. Before you quote Understand Flight by Anderson and Eberhard, lift in 2D is real, every old school lift and drag curve for a NACA aerofoil you have looked at came from the NACA 2D wind tunnel. So, sorry, no air deflected downwards. Those measurements in those wind tunnels were all down with pressure taps, and that was good enough until the 1980s when the first action reaction explanation appeared in the literature.
You probably believe in the Easter Bunny.
Useful
doesn't explain the correct reason for lift
If you want to know where the equal transit time came from I have an article on arXiv, On the Origins and Relevance of the Equal Transit Time Fallacy to Explain Lift. Sorry can't post URLs.
I assume it's an oversimplification of mass flow continuity, which is a very real constraint driving the creation of lift.
@@davetime5234 It is a result of not including viscosity. Without a non-conservative force, every path (streamline) around an aerofoil is like every other potential (hiking around a mountain), where the path does not affect the balance of energy. However, when you add a non-conservative force (in the case of aerodynamics that is viscosity, or friction when hiking around the mountain) then the path taken means there will be an overall effect, and not all streamlines will now be traversed in equal time. I note in my paper that D'Alembert assumed equal transit, but both he and Euler calculated it to be true, hence giving D'Alembert's paradox. The common misconception is that equal transit time can be used to explain lift, where it was non lifting flows that give equal transit (and hence D'Alembert's paradox).
@@aerospacedoctor I don't quite understand this in relation to the mass flow continuity issue.
A moving reference frame without the airfoil, but centered on where the airfoil will be, has a rate of mass flow traversing the region. When the airfoil is there, the same mass flow rate must be maintained.
This must be accounted for by the combined mass transit speed above and below the airfoil. Because there is less available space, the average particle transit speed should be higher than before to keep the mass flow rate constant (for constant density).
So, the asymmetry should result in yet even more speed above the wing than the already increased average particle speed (from the imposed transit space restriction), with the slow down below the wing being sufficient to keep the combined mass transit rate the same as in the case without the foil in the moving reference frame.
Aren't these separate transit times affected by the need to have the composite mass transit time avoiding flow stagnation?
How is this connected to viscosity?
@@davetime5234 Let me ask you a question. You note the keyword, "asymmetry". Fundamentally, and I mean very fundamental physics, what causes the asymmetry? You are correct in everything you say in the last paragraph, but what is the physical mechanism that results in asymmetry? I noted D'Alembert's paradox which was also the solution from Euler; they both predicted a symmetric flow, and hence no drag (or lift).
@@aerospacedoctor "I mean very fundamental physics, what causes the asymmetry...what is the physical mechanism that results in asymmetry? ?"
Asymmetrical geometry of the solid to the relative wind (from the combined asymmetry of AoA plus any asymmetry of camber) resulting in an asymmetrical transit passage presented to the relative wind's dynamic pressure in the cross-sectional area of influence, which results in an asymmetrical pressure response necessary to maintain the prior existing mass flow rate in the that area of influence, is the best I can come up with at the moment.
So what's right? You could've elaborated on what's right... Nevertheless dank vdo
We still don't know. We have developed piles of models that give us very good approximations of what would happen, but we still don't really know why wings have the extreme lift we observe. You will see explanations that talk like they have all the answers, but actually, they don't.
@@douggale5962best statement
@@douggale5962why airfoil work then?😅
coanda effect proves the skipping stone one wrong
Importantly the Coanda effect has NOTHING to do with conventional lift production. It doesn't even exist around a conventional low speed aerofoil.