Well done sir! A very thorough and concise presentation of a subject that has baffled brilliant minds for years and even today remains definitively unawnsered.
Condensed math description: real wings create a sheet-vortex at their trailing edge, and if this sheet-vortex is aimed downwards, then it carries significant air-mass with it as it goes. As with jet-pumps and rocket engines, flinging a mass in one direction will create an F=mA force in the opposite direction. Wings use the same physics as outboard motor propellers, helicopter rotors, etc. Insight: the trailing edge of a flat wing must be aimed downwards ...but the trailing edge of a cambered airfoil is already tilted downwards, even at zero AOA. Cambered airfoils are not magic, instead they rely on the rear part of the airfoil, because the front part doesn't shed any vortices, nor produce any downwards reaction-force. Lifting-force is all about the down-motion of that sheet-vortex at the trailing edge. (All wings are like helicopter rotors. Without vortex-shedding and downwash, lifting force must be zero.)
Thank you so much for this video! My head was spinning with all the different explanations of lift and you clarified that for me. Your video was easy to understand and addressed many of my questions including flying upside down and flat wings.
This is great. There is so much misinformation and so many ignorantly oversimplified explanations out there. I was just watching a documentary on Amazon about aircraft wings and the explanation of lift was so misinformed that it was almost embarrassing. Thank you for helping to make us all smarter instead of continuing the spread of ignorance.
A good, well explained, video.There are two more principles in operation of flight, which I'm not sure you mentioned. One is Newton's law of momentum, which is a body's tendency to keep going in a straight path until a force is otherwise acted upon it. Another is a body passing through a medium has pressure exerted equally on all sides which basically causes a straight trajectory, again, unless another force is acted upon it. These are reasons why paper planes fly, since they are not shaped like airfoils nor are they subject to angle of attack. Cheers
In his book, Doug McLean had a problem explaining lift in a way a layman can understand. The reason is that you need a supercomputer to compute lift from a 3D wing. The Navier-Stokes equations are complex, and you need a lot of computations. If you want to explain lift in 10 seconds, you use Newton's third law of motion: The wing pushes the air down, and as a reaction, the air pushes the wing up. In most cases, Bernoulli's principle is used wrong when it comes to explain lift. "Bernoulli lift" is a misleading expression. Bernoulli's principle explains the relation between changes in the velocity and pressure in a stream. And this is important when it comes to lift, but not in the way most people think. This is how I understand lift: 1) When the air meets the wing, it is separated into two flows. The airflow moving over the wing follows a curved path around the leading edge and over the upper surface of the wing. When an air particle changes direction, it is because of an acceleration. (Newton's first law of motion says that an object in motion will continue in a straight path at a constant velocity unless it acted on by a force.) This acceleration is towards the center of the curvature (centripetal force). In accordance with Newton's second law of motion, an acceleration causes a change in velocity. That's why the air acclerates around a curved surface. And in accordance with Bernoulli's equation, when the velocity increases, the static pressure decreases. Since the air particle is accelerating towards the center of the curvature, the static air pressure must be low towards the surface of the wing. (The pressure distitbution is identical to a tornado.) 2) Since the airflow over the top of the wing has less pressure than the atmospheric pressure, the airflow is pushed down towards the top of the wing by the atmospheric pressure acting from above. (This works until you reach the critical angle of attack.) Since the airflow follows the upper surface of the wing, it will continue in a downwards direction aft of the wing. This, together with the airflow from the underside of the wing, is the downwash, which follows Netwon's third law of motion. However, it is the upper surface of the wing that creates most of the lift because the airflow over the wing is much faster than the airflow under the wing. E=mv2. 3) Under the wing, the airflow slows down. And in accordance with Bernoulli's equation, there's an increase in air pressure. This contributes to the lift, but only to a certain degree. That's why an airplane cannot maitain altitude when the wing stalls. 4) The angle of attack plays an important role, as it defines the stagnation point. As the angle of attack increases, the stagnation points moves down and aft along the leading edge. This forces the air to follow a longer curvature, creating a higher lift coefficient. When flying upside-down with an asymmentrical wing profile, the angle of attack is increased to allow for more air to flow along the leading edge, thus maintaining lift. 5) The difference in static air pressure under and over the wing explains lift (conservation of energy). Lift is also explained with Newton's third law (conservation of momentum.) Both are equally correct. They just explain lift from two different angles. (The third principle of lift is conservation of mass.) As you said, model airplanes with flat wings fly because of light weight, large surface and high power. The slipstream from the propeller provides a lot of lift, thanks to the Coanda effect. Without the slipstream, the wing will stall more easily.
Bernoulli's equation says energy will be conserved. In a fluid energy is stored as pressure multiplied by volume and mass multiplied by velocity. Hence Bernoulli's Equation considers momentum + that other form of energy PV.
The difficulty for initial students of flight is that lift is produced by two or more methods simultaneously and not just by a single force. The lift mechanism is also affected by the speed through the air and compression effects. There is only one important principle that needs to be borne in mind and that is that all wings will stall at a given angle of attack for that wing, no matter what speed the aircraft is flying at. That is the point where the airflow over the top of the wing becomes chaotic and a large element of lift is lost. Tilt the wing up too far into the oncoming airflow and the wing will stop flying. If the aircraft has an excess of thrust over weight, the aircraft will still fly but it is held up in the air by the thrust of the engine against gravity, not because of lift from the wings.
Great video, I appreciate how you talked about some of the fundamental concepts related to lift and gave many different real world examples of mechanical devices that generate lift. I liked that you talked about how Bernoulli's equation doesn't work as a stand alone explanation of lift. I do however wish you would have gone into a bit more detail about both Bernoulli's equation and Newton's 3rd Law explanation of lift. I found it interesting that you referenced Doug McLean's Understanding Aerodynamics textbook which is a textbook used in my mechanical engineering aerodynamics class, however I wish you would have gone into some of the specifics of what McLean talks about in the chapter 7 explanation of lift. Regardless I found your video to be a great introduction to some of the key concepts that relate to how lift is generated.
Extremely well made and presented video. Thank you. I think however, that the major reason for the air foils shape , the reduction of drag caused by turbulent air, was not emphasized enough, especially in conclusion. Thank you again.
I think that the flat wing works because the angle of attack of the wing is causing the air under the wing to be compressed which increases the density of the air while the air above the wing is in turbulence and therefore at a relatively lower pressure, thus the wing is essentially floating on the coloumn of air under it due to the pressure differential.
Tim, you missed the important point from John and from Doug. I have communicated with both. John clearly states "no SIMPLE explanation", and Doug says 16 pages out of 500 were difficult to write, the simple lay person explanation. You have missed the fact that there are 484 other pages explaining it at a university aerospace engineering level. The point here is that there is no debate, we do know; it is the simple explanation that is effectively impossible. As noted by Doug, the Navier-Stokes is what is applicable, and he specifically notes the Reynolds Averaged Navier-Stokes. The Navier-Stokes is Newton's Second Law for fluids with viscosity, and we can use that to determine how much lift is generated. But John also notes that a fluid only acts on a surface via two forces, pressure and viscosity. The asymmetry in the pressure and acceleration is due to the viscosity, in the boundary layer, which results in a difference in pressure acting on the aerofoil. Doug then notes that this, as shown by Prandtl, is equal and opposite to the over pressure on the earth's surface.
AD: Fair enough! But I think the fact alone that it takes up to 500 pages to explain anything pretty much encapsulates the dilemma. Bottomline, engineers can design wings and aircraft for various missions, which is the goal at the end of the day. Tim
Tim, thank you for the excellent content. As a child, paper airplanes made me suspicious of the Bernoulli explanation. When I built a Sig Skyray in 1987, and it flew brilliantly with perfectly flat wings, I knew there had to be more to the story. I find it interesting and somewhat curious that propellers are widely recognized to be airfoils, or “wings” rotating in a vertical plane, yet we commonly invoke Bernoulli to describe the function of wings, and Newton to describe the function of propellers. Could we say that both propellers, and wings produce a force by inducing a flow of air perpendicular to their motion?
BW: Hey, thanks for checking in! As you can see on my channel, I have built and flown a bunch of models with completely flat wings, and they fly well. I do think the action/reaction part of lift explains a lot, although I do not have sufficient knowledge to comment on the props. Tim
The air is static and he wing is the part moving, not the air. The wing pushes the air a little forward the air over the wing is just bumped up a little. (this makes a short vacuum) This also creates a low pressure over the wing and the high pressure under the wing. This will have the same effect on any type of wing shape. So the result is flight. But mostly Newton in play. Bernoulli is more a measure for the effectness of the wing.
I found this amazingly interesting - thank you for the illumination. Isn’t it incredible that lift can’t be explained. I assumed it was just a given - pressure and aerofoils etc. my little boy just made a flat wing f15 and I wondered how it can fly!!
@@TimMcKay56 Hi Tim, my son has made a foam board plane. It's not just flat one - it has a body, front wing and tail wing / rudder. Quite heavy. It's wing span is 34 inches. we got a motor that's - KV : 1000RPM/V. Anyway it doesn't seam to be powerful enough as it looses speed and drops to the ground. I don't know, but I suspect the motor isn't getting full power when the throttle is high? OR - is 1000 just not powerful enough? We've never done this before so haven't a clue what we're doing! So just need a steer on what we should expect from the motors KV or if you have a video you could point us to?
@@mauriceshapero7200 Maurice: The vast majority of failed designs comes from being overweight. 43" is not much wingspan, and these smaller models are a lot more likely to have flight problems. Maybe try making a larger wing, reducing weight or more power (to include more lipo cell count battery). Tim
A top curve over a wing might reduces the vortexes, a vortex creates drag and slows a plane as it buffets the air, the ideal would be to manage the planes angle so its crossection best manages the vortexes it creates, one can say low pressure lifts a wing but it does so by adding stress onto a wing as the 2 pressures pull and push the wing to create a stable pressure, at low speeds you would want it flezible enough not to be torn between the 2 pressures, at high speeds a flat bottom would create strong vorticies on the top, in this situation you would want equal pressures, probably close to equal arcs on top and bottom to reduce vorticies to managable instances, more speed more lift over smaller angle, idk, its probably why thier are more nose up flips than nose down as the wing naturally wants to exist in the lower pressure area, I feel like the higher pressure is where flight happens and the lower pressure is a byproduct where stress is mitigated, not enough structure or to many vortices can snap a wing
when i grew up i was always told that big flat wing planes could not fly because only the curved wing shape could produce lift. this was obviously not right as paper planes fly just fine and scale them up should not be a problem. actually when you drop a water droplet into a pond there is a rebounce that produce what lift the droplet back into the air. i guess a flat surface just forcing itself against the air also produce a delayed reaction force the pushed the plane up and that this force could be what cause turbulence at the wing tips. in a quad copter drone this delayed reaction force can cause some unwanted air currents that forces the drone to crash forcing it to the ground canceling lift by propellers.
Entire idea behind Bernoulli is the faster air on top of wing creates a lower pressure, thus upwards lift. Inverted, the wing now has the faster air aimed downwards, thus creating lift down, not up. Tim
@@TimMcKay56 hmmm. I stand corrected. Would you then reason that interrupting flow of air at high speeds generates lift. Just the same as water can feel like concrete if collided with at high speeds. Maybe Bernoullli's likely optimizes lift by reducing resistance of air above the wing rather than generating lift?
Yet i can say i understand how wings generate lift when it is curved above so is it compulsory to tilt the flat wing to increase angle of attack because the air pressure of flat is same at the two sides??
Inverted flight does not contradict Bernoulli. If one examines the angle of attack when inverted one finds that the path across the wing is longer on the upside of the surface.
Hi Doug, I wonder if you fully appreciate how revealing your demonstration of flight with flat wings actually is. My brother and I flew flat winged model planes with 3cc diesel motors on control wires 60 years ago and we are still no further to breaking through the aerodynamics madness that requires camber to generate lift. The low pressure above the wing is due to void left behind as the wing sweeps the air in front of it. The high pressure below the wing is caused by the wind sweeping the air into the oncoming air forcing it to compress. MacLean became tangled up with "diffuse clouds of low pressure", Anderson (On P. 21 Fig 1.18) magically reversed the direction of the pressure vector. Babinsky's video clearly demonstrates the air over the top of the wind DOES NOT accelerate. (sure, it goes faster than the air under the wing, but that is because that air goes slower, it doesn't go faster than the "free stream")
@@TimMcKay56 Not even as a retired 777 captain? In fig. 1.15 on p. 19, he shows the pressure arrow pointing towards the surface, and in Fig. 1.19 on p.22, he shows the same pressure arrow pointing away from the surface. There is no explanation for this change of direction. I'm sure you do have the knowledge and background to comment on this anomaly. Please, could I ask you to take a look.
To me lift has always been action/reaction. Bernoulli's principle works great in a wind tunnel because the air is actually moving. What many seem to forget is that in flight air is stationary, it's just sitting there. It's not really flowing and it certainly isn't speeding up. It's the wing that is moving through a medium. So, no curvature is needed as you and others have shown with your flat and symmetrical wings. Nice models and great videos.
Newton vs. Bernoulli is a common debate, argument even. The fundamental physical fact is that a wing must deflect air downwards to generate a lift force. Newton's Third Law applies. Beyond this incontrovertible truth, which answers the 'why?' question, the next question is 'how'? How is the pressure distribution around an aerofoil (or a barn door) generated, which results in that lift force. PS. Too many explanations are led astray by what I characterise as 'The Wind Tunnel Syndrome.' In the real world, it is the wing that is moving, not the air. So you need to think about what the wing does to the air through which it is moving.
Great video. Interesting discussion of lift. I have never understood why it has to be Bernoulli or Newton. Obviously it is both. As you demonstrated the flat wing flies by moving air down but at the cost of high turbulence behind the upper surface. The curve of the airfoil smooths airflow above the wing and reduces this turbulence, making a much more efficient flying surface. Certainly air pressure differences exist above and below the wing and contribute to lift. But your Boeing 777 on the runway would run forever without lifting off if it wasn't rotated to present the bottom of the wing to the relative airflow. That is strictly Newton, pushing masses of airflow down to get the plane off the ground. Once in level flight at altitude, Bernoulli plays a large part in the efficiency of the flying surface. The more interesting situation to me is the case of propellors and helicopter rotors. A helicopter hovering 100 feet above the ground remains in the air only because it is pushing down massive amounts of air, as anyone underneath it would tell you. Bernoulli has no role to play in this situation. Similarly a propellor moves an airplane through the air simply because it pushes air backwards. This is known as mass flow and is the basis for all propellor thrust calculations. A propellor is not being sucked forward by the Bernoulli effect, it is strictly moving forward because of the mass flow it produces opposite the direction of flight.
Don: Great recap of the lift discussion, thanks for sharing! And you are correct on the B-777. We'd be barreling down the runway at 160 kts . . . nothing happens in the lift department until we rotate to around 12 degrees nose up, then off and away! Tim
@@TimMcKay56 Is that actually true? " nothing happens in the lift department until we rotate". Is there really zero (or negative) AoA when accelerating down the runway?
@@alans172 Fair enough. Better to say "not much" happening with lift prior to rotation. I guess an airliner would eventually lift off a runway if no rotation, but it would be several miles and at very high airspeed. Tim
I think that, eventually, aerodynamicists will find that wings actually work because of a combination of both theories much the same as in gas turbines where the princple of operation is a combination of impulse and reaction.
@@TimMcKay56 - I have been thinking about a simple boomerang project for my students. It seems that a boomerang wing works with zero angle of attack. And i have yet to find a boomerang design the works without curvature on the top of the wing. That might just be because it works better that way or everyone thinks it does. And it is hard to add an angle of attack to a boomerang and make it fly. Much more air resistance. It seems though that on first glance, the wing of a boomerang works because of the airfoil shape and not the angle of attack.
The correct explanation of lift does exist. Both what Bernoulli and Newton "say" are correct. Both explain the same phenomenon from different viewpoints. It is even possible to deduce the Bernoulli formula from the third law of Newton. To be honest, I don't understand that explanation because my mathematical skills are poor. Recently, I found a video from somebody who explained why a flat wing can fly but not in a full-scale aircraft. The aircraft you mention don't have 100% flat wings. With model aircraft, it does work because they are hugely overpowered. And rounding the leading edge of a flat wing does improve the flying characteristics significantly. To explain this, he first had to explain what lift is and how it is generated. If you are interested, please look at the video at the link below. It did help me very much. th-cam.com/video/d4w1Iy4vVMg/w-d-xo.html
You lost me when you shown a jet inverted jets can fly without wings they create enough thrust to fly without a wing they are basically rockets show me a Cessna 150 flying inverted with no flaps
Brandon: Based on experience (1,500 hours in the F-4 Phantom), jets use lift from their wings when flying, whether normally or upside down. When inverted, the most is mostly reaction/plate lift, thus not very efficient. But lift. Theoretically, if a jet's thrust exceeds the airplane's weight, the aircraft can "fly" without using lift from wings. But with no relative airflow over the control surfaces, there is no way to maneuver/position the jet. Many fighter aircraft can achieve a 1:1 thrust ratio, but this is more of a stunt to build speed than anything else as the fuel burn is insane (1,000 lbs of fuel per minute in the F-4). And yes, a C-150 can fly inverted . . . if it has sufficient power. The existing 100 HP engine not enough for this to occur, outside of structural concerns. Tim
You can fly a plane with no power you cannot fly your flat wing airplanes without power you are constantly accelerating with a flat wing to stay off the ground. An airplane with an air foil can continue to fly and continue to increase altitude simultaneously decreasing speed
Sure you can, just like sailplanes fly with cambered wings. They rely on rising air, from thermals or ridge lift, so a paper plane, with flat wings, will fly if provided with rising air.
Excellent explanation - you have a wonderful intelligent and easy to listen to manner. Much appreciated!
Nigel: Thanks for stopping by! Tim
Lift is not a complex, all that is to turn the flow of air, low pressure above the wing is due to less momentum of air
Well done sir! A very thorough and concise presentation of a subject that has baffled brilliant minds for years and even today remains definitively unawnsered.
Kevin: Glad it was helpful! Tim
Condensed math description: real wings create a sheet-vortex at their trailing edge, and if this sheet-vortex is aimed downwards, then it carries significant air-mass with it as it goes. As with jet-pumps and rocket engines, flinging a mass in one direction will create an F=mA force in the opposite direction. Wings use the same physics as outboard motor propellers, helicopter rotors, etc.
Insight: the trailing edge of a flat wing must be aimed downwards ...but the trailing edge of a cambered airfoil is already tilted downwards, even at zero AOA. Cambered airfoils are not magic, instead they rely on the rear part of the airfoil, because the front part doesn't shed any vortices, nor produce any downwards reaction-force. Lifting-force is all about the down-motion of that sheet-vortex at the trailing edge. (All wings are like helicopter rotors. Without vortex-shedding and downwash, lifting force must be zero.)
Interesting input, thanks! Tim
Thank you for sharing! It is always good to learn and understand how things work. You did a pretty good summary of a 500 page topic!
DC: Glad it was helpful! Tim
Thank you, I am a new RC plane builder and love trying to understand what make my planes actually work.
Eric: Best of luck with your builds! Tim
I didn't know you flew so many different types of aircraft, Tim. Very cool.
David: Many thanks! Tim
Thank you so much for this video! My head was spinning with all the different explanations of lift and you clarified that for me. Your video was easy to understand and addressed many of my questions including flying upside down and flat wings.
Thanks for tuning in! Tim
Thankyou. What an incredibly well spoken presentation in easy to understand language about a fascinating and important subject.
Thanks!
This is great. There is so much misinformation and so many ignorantly oversimplified explanations out there. I was just watching a documentary on Amazon about aircraft wings and the explanation of lift was so misinformed that it was almost embarrassing. Thank you for helping to make us all smarter instead of continuing the spread of ignorance.
Thanks for checking in! Tim
A good, well explained, video.There are two more principles in operation of flight, which I'm not sure you mentioned. One is Newton's law of momentum, which is a body's tendency to keep going in a straight path until a force is otherwise acted upon it. Another is a body passing through a medium has pressure exerted equally on all sides which basically causes a straight trajectory, again, unless another force is acted upon it. These are reasons why paper planes fly, since they are not shaped like airfoils nor are they subject to angle of attack. Cheers
Good points! Tim
In his book, Doug McLean had a problem explaining lift in a way a layman can understand. The reason is that you need a supercomputer to compute lift from a 3D wing. The Navier-Stokes equations are complex, and you need a lot of computations. If you want to explain lift in 10 seconds, you use Newton's third law of motion: The wing pushes the air down, and as a reaction, the air pushes the wing up.
In most cases, Bernoulli's principle is used wrong when it comes to explain lift. "Bernoulli lift" is a misleading expression. Bernoulli's principle explains the relation between changes in the velocity and pressure in a stream. And this is important when it comes to lift, but not in the way most people think.
This is how I understand lift:
1) When the air meets the wing, it is separated into two flows. The airflow moving over the wing follows a curved path around the leading edge and over the upper surface of the wing. When an air particle changes direction, it is because of an acceleration. (Newton's first law of motion says that an object in motion will continue in a straight path at a constant velocity unless it acted on by a force.) This acceleration is towards the center of the curvature (centripetal force). In accordance with Newton's second law of motion, an acceleration causes a change in velocity. That's why the air acclerates around a curved surface. And in accordance with Bernoulli's equation, when the velocity increases, the static pressure decreases. Since the air particle is accelerating towards the center of the curvature, the static air pressure must be low towards the surface of the wing. (The pressure distitbution is identical to a tornado.)
2) Since the airflow over the top of the wing has less pressure than the atmospheric pressure, the airflow is pushed down towards the top of the wing by the atmospheric pressure acting from above. (This works until you reach the critical angle of attack.) Since the airflow follows the upper surface of the wing, it will continue in a downwards direction aft of the wing. This, together with the airflow from the underside of the wing, is the downwash, which follows Netwon's third law of motion. However, it is the upper surface of the wing that creates most of the lift because the airflow over the wing is much faster than the airflow under the wing. E=mv2.
3) Under the wing, the airflow slows down. And in accordance with Bernoulli's equation, there's an increase in air pressure. This contributes to the lift, but only to a certain degree. That's why an airplane cannot maitain altitude when the wing stalls.
4) The angle of attack plays an important role, as it defines the stagnation point. As the angle of attack increases, the stagnation points moves down and aft along the leading edge. This forces the air to follow a longer curvature, creating a higher lift coefficient. When flying upside-down with an asymmentrical wing profile, the angle of attack is increased to allow for more air to flow along the leading edge, thus maintaining lift.
5) The difference in static air pressure under and over the wing explains lift (conservation of energy). Lift is also explained with Newton's third law (conservation of momentum.) Both are equally correct. They just explain lift from two different angles. (The third principle of lift is conservation of mass.)
As you said, model airplanes with flat wings fly because of light weight, large surface and high power. The slipstream from the propeller provides a lot of lift, thanks to the Coanda effect. Without the slipstream, the wing will stall more easily.
FM: Great update, many thanks! Tim
Bernoulli's equation says energy will be conserved. In a fluid energy is stored as pressure multiplied by volume and mass multiplied by velocity. Hence Bernoulli's Equation considers momentum + that other form of energy PV.
Very good, thanks! Tim
Excellent presentation and explanation!
JS: Many thanks! Tim
Thanks Tim ..... All your videos are so interesting I look forward to the next one .
Randall: Glad you like them! Tim
The difficulty for initial students of flight is that lift is produced by two or more methods simultaneously and not just by a single force. The lift mechanism is also affected by the speed through the air and compression effects. There is only one important principle that needs to be borne in mind and that is that all wings will stall at a given angle of attack for that wing, no matter what speed the aircraft is flying at. That is the point where the airflow over the top of the wing becomes chaotic and a large element of lift is lost. Tilt the wing up too far into the oncoming airflow and the wing will stop flying. If the aircraft has an excess of thrust over weight, the aircraft will still fly but it is held up in the air by the thrust of the engine against gravity, not because of lift from the wings.
Good discussion!
Fascinating explanation! I had wondered about your flat wing designs. Thanks Tim
Tim: Glad it was helpful! Tim
Great video, I appreciate how you talked about some of the fundamental concepts related to lift and gave many different real world examples of mechanical devices that generate lift. I liked that you talked about how Bernoulli's equation doesn't work as a stand alone explanation of lift. I do however wish you would have gone into a bit more detail about both Bernoulli's equation and Newton's 3rd Law explanation of lift. I found it interesting that you referenced Doug McLean's Understanding Aerodynamics textbook which is a textbook used in my mechanical engineering aerodynamics class, however I wish you would have gone into some of the specifics of what McLean talks about in the chapter 7 explanation of lift. Regardless I found your video to be a great introduction to some of the key concepts that relate to how lift is generated.
Nick: Thanks for checking in, will add to a future video! Tim
Thank you for a helpful educational video on lift!🙂
👍🏻😊 Tim
Thank you
You're welcome! Tim
Extremely well made and presented video. Thank you.
I think however, that the major reason for the air foils shape , the reduction of drag caused by turbulent air, was not emphasized enough, especially in conclusion. Thank you again.
KW: Thanks for checking in! Tim
I think that the flat wing works because the angle of attack of the wing is causing the air under the wing to be compressed which increases the density of the air while the air above the wing is in turbulence and therefore at a relatively lower pressure, thus the wing is essentially floating on the coloumn of air under it due to the pressure differential.
Interesting point! Tim
Very interesting video, Tim.
David: Glad you enjoyed it! Tim
Tim, you missed the important point from John and from Doug. I have communicated with both. John clearly states "no SIMPLE explanation", and Doug says 16 pages out of 500 were difficult to write, the simple lay person explanation. You have missed the fact that there are 484 other pages explaining it at a university aerospace engineering level.
The point here is that there is no debate, we do know; it is the simple explanation that is effectively impossible. As noted by Doug, the Navier-Stokes is what is applicable, and he specifically notes the Reynolds Averaged Navier-Stokes. The Navier-Stokes is Newton's Second Law for fluids with viscosity, and we can use that to determine how much lift is generated.
But John also notes that a fluid only acts on a surface via two forces, pressure and viscosity. The asymmetry in the pressure and acceleration is due to the viscosity, in the boundary layer, which results in a difference in pressure acting on the aerofoil. Doug then notes that this, as shown by Prandtl, is equal and opposite to the over pressure on the earth's surface.
AD: Fair enough! But I think the fact alone that it takes up to 500 pages to explain anything pretty much encapsulates the dilemma. Bottomline, engineers can design wings and aircraft for various missions, which is the goal at the end of the day. Tim
I like your builds, I'm working on a few myself.
Skyart: Many thanks! Tim
great video
Glad you enjoyed it! Tim
@@TimMcKay56 where can i read up more about drag coefficient and aspect ratio, im in the design stages of a solar powered powered rc plane
@@urmum8540 Seriously, best to do a Google search and see what comes up, as well as books at Amazon. Tim
Great video for novice people like myself .
👍🏻😊 Tim
Great article, could you make a video explaining dehydral,polyhedral etc.
A.Arenas.
AA: Working on a dihedral video now. 😁👍 Tim
Thanks, for the information..
Perry: You bet! Tim
Tim, thank you for the excellent content.
As a child, paper airplanes made me suspicious of the Bernoulli explanation. When I built a Sig Skyray in 1987, and it flew brilliantly with perfectly flat wings, I knew there had to be more to the story.
I find it interesting and somewhat curious that propellers are widely recognized to be airfoils, or “wings” rotating in a vertical plane, yet we commonly invoke Bernoulli to describe the function of wings, and Newton to describe the function of propellers.
Could we say that both propellers, and wings produce a force by inducing a flow of air perpendicular to their motion?
BW: Hey, thanks for checking in! As you can see on my channel, I have built and flown a bunch of models with completely flat wings, and they fly well. I do think the action/reaction part of lift explains a lot, although I do not have sufficient knowledge to comment on the props. Tim
The air is static and he wing is the part moving, not the air. The wing pushes the air a little forward the air over the wing is just bumped up a little. (this makes a short vacuum) This also creates a low pressure over the wing and the high pressure under the wing. This will have the same effect on any type of wing shape. So the result is flight. But mostly Newton in play. Bernoulli is more a measure for the effectness of the wing.
Great points, thanks! Tim
I found this amazingly interesting - thank you for the illumination. Isn’t it incredible that lift can’t be explained. I assumed it was just a given - pressure and aerofoils etc. my little boy just made a flat wing f15 and I wondered how it can fly!!
Maurice: Thanks for this feedback and glad you enjoyed the video! Tim
@@TimMcKay56 Hi Tim, my son has made a foam board plane. It's not just flat one - it has a body, front wing and tail wing / rudder. Quite heavy. It's wing span is 34 inches. we got a motor that's - KV : 1000RPM/V. Anyway it doesn't seam to be powerful enough as it looses speed and drops to the ground. I don't know, but I suspect the motor isn't getting full power when the throttle is high? OR - is 1000 just not powerful enough? We've never done this before so haven't a clue what we're doing! So just need a steer on what we should expect from the motors KV or if you have a video you could point us to?
@@mauriceshapero7200 Maurice: The vast majority of failed designs comes from being overweight. 43" is not much wingspan, and these smaller models are a lot more likely to have flight problems. Maybe try making a larger wing, reducing weight or more power (to include more lipo cell count battery). Tim
@@TimMcKay56 thanks Tim….it’s all part of journey!
A top curve over a wing might reduces the vortexes, a vortex creates drag and slows a plane as it buffets the air, the ideal would be to manage the planes angle so its crossection best manages the vortexes it creates, one can say low pressure lifts a wing but it does so by adding stress onto a wing as the 2 pressures pull and push the wing to create a stable pressure, at low speeds you would want it flezible enough not to be torn between the 2 pressures, at high speeds a flat bottom would create strong vorticies on the top, in this situation you would want equal pressures, probably close to equal arcs on top and bottom to reduce vorticies to managable instances, more speed more lift over smaller angle, idk, its probably why thier are more nose up flips than nose down as the wing naturally wants to exist in the lower pressure area, I feel like the higher pressure is where flight happens and the lower pressure is a byproduct where stress is mitigated, not enough structure or to many vortices can snap a wing
Good stuff, thanks! Tim
@@TimMcKay56 I am just guessing here, I'm a trained graphic designer, just got a really good mind for visualizing things, have fun with that hobby 👍
@@proven22x52 All good! Tim
when i grew up i was always told that big flat wing planes could not fly because only the curved wing shape could produce lift. this was obviously not right as paper planes fly just fine and scale them up should not be a problem. actually when you drop a water droplet into a pond there is a rebounce that produce what lift the droplet back into the air. i guess a flat surface just forcing itself against the air also produce a delayed reaction force the pushed the plane up and that this force could be what cause turbulence at the wing tips. in a quad copter drone this delayed reaction force can cause some unwanted air currents that forces the drone to crash forcing it to the ground canceling lift by propellers.
Great analysis, thanks! Tim
Why would an inverted plane negate Bernoulli's explanation? Do you assume air pressure changes with air speed only when the plane is right side up?
Entire idea behind Bernoulli is the faster air on top of wing creates a lower pressure, thus upwards lift. Inverted, the wing now has the faster air aimed downwards, thus creating lift down, not up. Tim
@@TimMcKay56 hmmm. I stand corrected. Would you then reason that interrupting flow of air at high speeds generates lift. Just the same as water can feel like concrete if collided with at high speeds. Maybe Bernoullli's likely optimizes lift by reducing resistance of air above the wing rather than generating lift?
Yet i can say i understand how wings generate lift when it is curved above so is it compulsory to tilt the flat wing to increase angle of attack because the air pressure of flat is same at the two sides??
Correct! Tim
Inverted flight does not contradict Bernoulli. If one examines the angle of attack when inverted one finds that the path across the wing is longer on the upside of the surface.
😊👍🏻 Tim
Hi Doug, I wonder if you fully appreciate how revealing your demonstration of flight with flat wings actually is. My brother and I flew flat winged model planes with 3cc diesel motors on control wires 60 years ago and we are still no further to breaking through the aerodynamics madness that requires camber to generate lift. The low pressure above the wing is due to void left behind as the wing sweeps the air in front of it. The high pressure below the wing is caused by the wind sweeping the air into the oncoming air forcing it to compress.
MacLean became tangled up with "diffuse clouds of low pressure",
Anderson (On P. 21 Fig 1.18) magically reversed the direction of the pressure vector.
Babinsky's video clearly demonstrates the air over the top of the wind DOES NOT accelerate. (sure, it goes faster than the air under the wing, but that is because that air goes slower, it doesn't go faster than the "free stream")
Good stuff! Tim
@@TimMcKay56 What do you think about Anderson's reversed pressure vector?
@@alans172 O do not really have enough knowledge or background to properly comment. : ) Tim
@@TimMcKay56 Not even as a retired 777 captain?
In fig. 1.15 on p. 19, he shows the pressure arrow pointing towards the surface, and in Fig. 1.19 on p.22, he shows the same pressure arrow pointing away from the surface. There is no explanation for this change of direction. I'm sure you do have the knowledge and background to comment on this anomaly. Please, could I ask you to take a look.
@@alans172 Will take a look! Tim
you left out the navier stokes equations and used a lifting body as an example of a flatwing design
Great point! Tim
@@TimMcKay56 Only pointed it out after doing a lot of finite model analysis
@@leonmusk1040 😊👍🏻 Tim
To me lift has always been action/reaction. Bernoulli's principle works great in a wind tunnel because the air is actually moving. What many seem to forget is that in flight air is stationary, it's just sitting there. It's not really flowing and it certainly isn't speeding up. It's the wing that is moving through a medium. So, no curvature is needed as you and others have shown with your flat and symmetrical wings. Nice models and great videos.
Rob: Many thanks for your input! Tim
Newton vs. Bernoulli is a common debate, argument even. The fundamental physical fact is that a wing must deflect air downwards to generate a lift force. Newton's Third Law applies. Beyond this incontrovertible truth, which answers the 'why?' question, the next question is 'how'? How is the pressure distribution around an aerofoil (or a barn door) generated, which results in that lift force.
PS. Too many explanations are led astray by what I characterise as 'The Wind Tunnel Syndrome.' In the real world, it is the wing that is moving, not the air. So you need to think about what the wing does to the air through which it is moving.
Good points!
Great video. Interesting discussion of lift. I have never understood why it has to be Bernoulli or Newton. Obviously it is both. As you demonstrated the flat wing flies by moving air down but at the cost of high turbulence behind the upper surface. The curve of the airfoil smooths airflow above the wing and reduces this turbulence, making a much more efficient flying surface. Certainly air pressure differences exist above and below the wing and contribute to lift. But your Boeing 777 on the runway would run forever without lifting off if it wasn't rotated to present the bottom of the wing to the relative airflow. That is strictly Newton, pushing masses of airflow down to get the plane off the ground. Once in level flight at altitude, Bernoulli plays a large part in the efficiency of the flying surface. The more interesting situation to me is the case of propellors and helicopter rotors. A helicopter hovering 100 feet above the ground remains in the air only because it is pushing down massive amounts of air, as anyone underneath it would tell you. Bernoulli has no role to play in this situation. Similarly a propellor moves an airplane through the air simply because it pushes air backwards. This is known as mass flow and is the basis for all propellor thrust calculations. A propellor is not being sucked forward by the Bernoulli effect, it is strictly moving forward because of the mass flow it produces opposite the direction of flight.
Don: Great recap of the lift discussion, thanks for sharing! And you are correct on the B-777. We'd be barreling down the runway at 160 kts . . . nothing happens in the lift department until we rotate to around 12 degrees nose up, then off and away! Tim
@@TimMcKay56 Is that actually true? " nothing happens in the lift department until we rotate". Is there really zero (or negative) AoA when accelerating down the runway?
@@alans172 Fair enough. Better to say "not much" happening with lift prior to rotation. I guess an airliner would eventually lift off a runway if no rotation, but it would be several miles and at very high airspeed. Tim
I think that, eventually, aerodynamicists will find that wings actually work because of a combination of both theories much the same as in gas turbines where the princple of operation is a combination of impulse and reaction.
Sounds good! Tim
I wonder if there is a wing shape that creates a lifting force with zero angle of attack.
Good question! Tim
@@TimMcKay56 - I have been thinking about a simple boomerang project for my students. It seems that a boomerang wing works with zero angle of attack. And i have yet to find a boomerang design the works without curvature on the top of the wing. That might just be because it works better that way or everyone thinks it does. And it is hard to add an angle of attack to a boomerang and make it fly. Much more air resistance.
It seems though that on first glance, the wing of a boomerang works because of the airfoil shape and not the angle of attack.
@@my_dear_friend_ No experience with this. 😟
The correct explanation of lift does exist. Both what Bernoulli and Newton "say" are correct. Both explain the same phenomenon from different viewpoints. It is even possible to deduce the Bernoulli formula from the third law of Newton.
To be honest, I don't understand that explanation because my mathematical skills are poor.
Recently, I found a video from somebody who explained why a flat wing can fly but not in a full-scale aircraft. The aircraft you mention don't have 100% flat wings.
With model aircraft, it does work because they are hugely overpowered. And rounding the leading edge of a flat wing does improve the flying characteristics significantly.
To explain this, he first had to explain what lift is and how it is generated.
If you are interested, please look at the video at the link below. It did help me very much.
th-cam.com/video/d4w1Iy4vVMg/w-d-xo.html
Great inputs, thanks! Tim
You lost me when you shown a jet inverted jets can fly without wings they create enough thrust to fly without a wing they are basically rockets show me a Cessna 150 flying inverted with no flaps
Brandon: Based on experience (1,500 hours in the F-4 Phantom), jets use lift from their wings when flying, whether normally or upside down. When inverted, the most is mostly reaction/plate lift, thus not very efficient. But lift. Theoretically, if a jet's thrust exceeds the airplane's weight, the aircraft can "fly" without using lift from wings. But with no relative airflow over the control surfaces, there is no way to maneuver/position the jet. Many fighter aircraft can achieve a 1:1 thrust ratio, but this is more of a stunt to build speed than anything else as the fuel burn is insane (1,000 lbs of fuel per minute in the F-4). And yes, a C-150 can fly inverted . . . if it has sufficient power. The existing 100 HP engine not enough for this to occur, outside of structural concerns. Tim
You can fly a plane with no power you cannot fly your flat wing airplanes without power you are constantly accelerating with a flat wing to stay off the ground. An airplane with an air foil can continue to fly and continue to increase altitude simultaneously decreasing speed
👍🏻 Tim
Sure you can, just like sailplanes fly with cambered wings. They rely on rising air, from thermals or ridge lift, so a paper plane, with flat wings, will fly if provided with rising air.
So how flat wing foam gliders fly so well?
I'm sure you heard this one. With enough power, you can make a brick fly.
David: Otherwise known as the "McDonnell-Douglas Theory of Flight." Tim
You can fly a brick if you have enough power!
Otherwise known as an Apollo Saturn 5 moon rocket launch. 😳😊
This explains why pilots shouldn't try to explain lift. Leave it to engineers who know what they are talking about.
👍🏻 Tim
The same engineers who can't explain it either.