Hi Everyone! Here is the link to the article that prompted the title: www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/ Let me know what you think in the comments. I'll try and answer any questions as always. Thanks, Chris
Hi Chris, I find the more I read of this subject, the more I don't know. I found this helpful th-cam.com/video/QKCK4lJLQHU/w-d-xo.html Thanks for your quality content, I'm almost done with my AOS5.
It's fascinating that Chris can always dive deep into the physics of FPV related topics. Here's an idea of another topic. I'm always curious on how heat is generated in motor, why a badly tuned PID / noisy gyro generate so much heat, and how does the wasted heat affect the efficiency and flight time of the quads.
I graduated from an aviation college... with a degree in Aviation Science/Professional Pilot. Had to take several classes on aerodynamics. My roommate was an Aeronautical Engineer. Your explanations at times had me shaking my head "NO".... at times had me shaking my head "YES..." the rest of the time had me scratching my head "What the hell is he talking about...???". In the end, we know and have known for a very very long time that the production of lift is a combination of Newton's 3rd law of motion, and Bernoulli's principle. Neither alone explains the total lift produced, but when both are considered, it all comes together-- Overly simplified, Bernoulli is at work on the top surface and Newton is at work on the bottom. You touched on drag a bit... the first type of drag you showed with the vector diagram is called "Induced Drag"... it is the drag caused solely by the production of lift. The second drag type that you called "skin drag" is properly termed "Parasite drag"... I kinda think you got form drag right, sort of...
Sounds like you had all the possible reactions! I would agree that this is a classic case of Newton's 3rd law in action. Bernoulli applies to the whole air flow field so it is acting on the top and bottom surface and doesn't directly contribute to lift (it rather describes the link between the flow and pressure fields). The top surface creates lift by deflecting flow downwards, just like the bottom surface. Air pressure is the effect that keeps flow attached to the top of the aerofoil and allows that to happen.
@@ChrisRosser Well.... I don't really know about that. I'm going to say "not exactly". Bernoulli is working on the top. The upper curvature of the wing is a half section of your venturi example. You don't need the full venturi cross section to be there for the effect to exist. How would you explain then, the fact that an airfoil stalls at the same angle of attack regardless of the true airspeed, and regardless of the altitude (pressure)? An airfoil at just below critical angle of attack will experience wildly different air pressures on the top of the airfoil vs. the bottom at let's say 50 KTAS vs 500KTAS. Yet the static pressure is the same. So, If I understand your argument correctly, the 500KTAS airfoil should stall much sooner (lower angle of attack) because the air pressure (due to high velocity, again, bernoulli...)would not be there to keep the flow attached to the top of the airfoil. Yet we know that this does not happen. In fact, at higher airspeeds, the air pressure on the top of the airfoil at high angles of attack can drop so low that it causes the temperature of that air to drop to the point where the moisture condenses out and becomes visible... approaching zero psi... a truly LARGE change in pressure!! But it still remains attached. And under the wing, at the same moment, the air pressure would be dramatically higher than at the upper surface of the wing I've never heard anyone explain it as you have... maybe I'm just not grasping your explanation and we're both seeing the same thing, but I don't think so... This is one of those discussion topics that requires a LOT of beer.
@@ChrisRosser Coanda effect is what keeps flow attached to the top of airfoil. Bernoulli indeed acts on both top and bottom surface, but the speed of the fluid attached to the top is faster and bottom slower due to airfoil, so it creates difference in preassure between them, add Newton's 3rd law and there you have it - lift. The lift is the trio - Bernouli, Newton, Coanda. Theres also Raynolds and other factors lift depends on, so yeah - a lot of beers talk :D BTW, if noone could explain lift, then there would be no CFD software :)
@@Демократът Coanda effect only applies to jets of air into a slower moving fluid. Because all the air incident on the aerofoil is moving at the same speed there is no speed difference, no entrainment and therefore no Coanda effect acting on a simple aerofoil. This is a very common misexplanation of why the flow attaches to the surface. The real reason is simply air pressure. Some advanced aerofoil designs bleed air from below the wing and inject it as a jet into the boundary layer above the wing (using slats) to keep the boundary layer attached at high AOA. Locally that is Coanda effect because you have a jet of fast moving air entering a region of slower moving air.
The simplest way I understand what happens at the topside is that the top of the wing sweeping through airflow creates vacuum volume behind it so the higher pressure air above it pushes air molecules to fill that space. Works with flat planes and symmetrical airfoils too, only the angle of attack matters in the direction of the lift. But a gradual curving shape helps keeping the flow attached to the surface and prevent turbulentic flow separation. I think this is the basics of Coanda effect.
Absolutely spot on with everything except the effect is simple air pressure not coanda effect. Coanda effect is only applicable to jets of air not a bulk flow like you get over a wing. 👍
Great explanation. Would love to see part 2 on how propwash is caused by flow separation, and why modern props have near zero AoA at tips to help recover from stalls.
the twist in modern props is there to create a constant distribution of the lift coefficient along the diameter the tip of the prop moves faster than the center therefore, it can be at a smaller angle of attack the most efficient shape for a normal wing is an ellipse (not quite) and because of the same reason as before, the most efficient shape for a prop is a towards the tip slighly tapered ellipse
This explanation is also quite handy at explaining what happens during a stall. As the static pressure right on top of the surface of the wing approaches 0, the pressure differential that causes the airstream to follow the wing curvature can't get any higher. Any further increase in the angle of attack has the airstream detaching from the wing. This increases pressure at the wing surface at first, but it gets lowered again as the airstream is again deflected by the pressure differential to follow the curvature. As the cycle repeats, the airstream oscillates between these two states causing vortices to form.
This is a great explanation with great visuals, a lot of the misconceptions were cleared up correctly. Only suggestion I would add is that the pressure gradient at the top of the airfoil will have usually traveled a much farther distance than the lower stream. It would be great if you could accurately represent this in some of your graphics to further drive home the point of the difference in velocity between the upper and lower surfaces, as well as how far out the geometry of the airfoil affects the incoming pressure gradient
When I studied for my license there was a question in regards to propellers and why they are the shape they are, I took quite some time writing the answer because as you go out from the centre well you know all the changes to everything... and no one in the course got it right except me, because information on the internet was vague to say the least, no one explains why the pitch decreases as it goes away from the hub correctly, anyway, good video.
So nice to hear the term Bernoulli again. My first time encountering it was 1995. I was a pc support at that time. I got assigned to do a review of Iomega Bernoulli Drive. :)
I think you do. An aerospike engines uses atmospheric pressure to hold the exhasut against the spike but there is no cross sectional area reduction achieved. The venturi explanation is a very common incorrect explanation of lift, covered in more detail here: www.grc.nasa.gov/www/k-12/airplane/wrong3.html
Doesn’t form drag for a streamlined aerofoil become abruptly significant at a stalling angle of something like 12-15 degrees? I’ve tried this with NACA 0012 in a wind tunnel. I had alternate sides of the aerofoil connected up to a multiple manometer and it’s pretty obvious when stalling occurs.
Thanks for the efforts you went into researching and explaining this intriguing topic. In the derivative form of Bernoulli's equation, the variable of the differentiation is the position variable, but you still have performed differentiation of the V^2 term?
This is an elaboration on the very basic explanation of how lift is generated often used by Don Stackhouse. His usual simplification of the process is "a wing generates lift by grabbing chunks of air and shoving them downward". He too could go into the details of how this is done but most often, for the purposes of his comments this elaboration is not necessary. Truth is that I would love to hear his detailed explanation and compare it to Chris Rosser's. No doubt there would be some differences in how it is explained but the overall conclusion would be much the same.
Exactly right, the control volume explanation is literally just Newton's 3rd Law. The second half of the explanantion really just expands on that by describing the method by which the aerofoil grabs hold of the air (air pressure holding the flow against the surface) and how the deflection of the flow creates the pressure difference on the wing that forces it upwards.
Navier-Stokes :) The derivation of Bernouili's equation assumes irrotational and/or invisicid flow and/or movement along streamlines. Those assumptions are not always satisfied. A turbulent (non-strealine) flow over a wing can still generate lift (many wings are not laminar... especially when looking at flow near the trailing edge).
please, make some more aerodynamics talks man. i love it!!! Also, what do you think about the hydrofoils recently used in the america`s cup sail boats?!
Excellent stuff Chris, maybe in a future video you could touch on prop/blade twist and the effects of airflow through them at different RPM and angle of attack including autorotation.
I know this video is a year old but just curious if you could explain lift without using an airfoil. Example a foam profile rc airplane. Symmetrical and flat surfaces but yet it still flies very good
I don't think the au fits in the 3.5 and it would be very heavy for smaller props. I think the vista is the way to go. You get 50mbps with the vista and equal range. Twin antennas only helps in strong multipath environments.
And I have to point out that pressure and flow are not "fields". The vector of a field, namely its strength and direction, is insensitive to the chosen (inertial) frame of reference (FoR). For example, magnetism always has its direction along the field line leading to the N pole. Its strength is irrespective whether the magnet is stationary wrt the observer or moving. The same is true for an electric field and gravity , the only other naturally occurring fields that I am aware of. On the other hand, the vector of flow, namely its speed, and direction is quite different if you change your FoR from the foil, where the flow speed is the speed of the foil, to the ambient air, where the flow speed is zero. I'm not sure who is responsible for the introduction of fields into fluid dynamics, but I'm pretty sure it was current at the early part of the 20th Century. Certainly Prandtl in the '20s was (mis)using the term. It's a pretty deep question that casts serious doubt on a helluva lot of fluid dynamics.
Aerodynamics ehh?…..okay “Clever Trousers” now you’re in my house Sir. 😄 POST VIEWING EDIT: Very nice, comprehensive video, interesting, accurate and the potato gun analogy almost justified the invocation of the “Bernoulli effect” 😉 (As if Chris Rosser requires my personal scientific validation 😆)
It's hard to tell when you cease debunking the false explanation and start with your explanation. But I guess it was at round 7:00 when you choose the differential of the Bernoulli equation and the potato gun. It doesn't need Bernoulli to explain that air moves from high to low pressure, potato guns notwithstanding. Atmospheric air is moving from a high to low pressure BUT IT IS NOT ACCELERATING! Pressure and flow are not coupled fields like electricity and magnetism. You (and MacLean) have invented this myth! It's much simpler, as I explain in the paper linked in the description of th-cam.com/video/dgE9xhIjTOU/w-d-xo.html
Maybe one day. But don't worry, there's plenty of exciting AOS stuff in the works. Ultralight 5", Cinewhoop, Cinelifter and a revolutionary (pun intended) line of motors.
Chris, Chris, Chris ... you relatively correctly pointed out that the "usual" explanations have flaws, but your explanation is as much flawed as these are ... the "100% Explained" is a massive overstatement - Bernoulli is a fact, the problem is that it is for conditions which do not fully apply to an airfoil - Newton is a fact, but again the problem is that one can't apply it that naively, since air is a gas and not a solid body - you are incorrect in saying that the airfoil must have a particular upper shape, see collective pitch helicopters, or just take a plank and hold it outside of your car's window - you are incorrect in saying that you can think it either way. It's like Ohm's law, then you know I you can get U, and if you know U you can get I, but physically it is absolutely clear that it is a U which drives the I, and not vice versa. Similarly so with F and a, F results in a, and not vice versa, and similarly so with v and dP/dx, dP/dx results in v, and not vice versa. it is also not difficult to see that your two explanations are equally bad or good as the flawed ones - your flow vector model obviously violates vector field equations (divergence). Air needs to come from somewhere and needs to go to somewhere - your 2nd explanation is even more obviously wrong, and in fact suffers from exactly the same flaw as the Bernoulli, Newton & Venturi explanations: The velocity of the air at the surface of the airfoil is ZERO! This is known as no-slip condition and is an extremely good and universally accepted assumption in aerodynamics. Ironically, in your (wrong) drag explanation you show indications of that the velocity on the surface gets smaller. But it in fact goes to zero everywhere on the airfoil surface. Therefore, it is simply not possible to talk of a velocity of an air stream. There is a one-line correct explanation for why airfoils create lift: Flow is a continuous vector field. Admittedly this is not so easy to understand what this is and what it implies. None of what I say is in contradiction to the article you refer to, to the contrary, the article concludes exactly the same. The video by Doug McLean is in fact excellent, absolutely excellent, and explains it all quite nicely, a must watch. You should consider removing the claim that you have now finally given a better explanation. Sorry mate, no offense. :)
Let me take each of your points in turn: Bernoulli is a fact, and it is often used to explain why faster flow is at lower pressure. However, it doesn't explain why the flow should acclerate in the first place. As an analogy: conservation of energy explains why an apple accelerates as it falls. but it doesn't explain why it falls in the first place. Newton's laws apply to solids, liquids, and gases in exactly the same way. I actually stated that the upper shape of an aerofoil matters for calculating its lift generation (not that it must have any particular shape to generate lift). In a motor the current created by wires moving through a magnetic field generates voltage. Electromagnetism is a coupled field so you can find examples where voltage seems to generate current and vice versa. There is no correct way round, anything that can be explained by one way of thinking can be explained equally well the other way round. I'm well aware of the no slip condition in the boundary layer. It doesn't stop us calculating the average velocity change of the air. The average is a little less because of skin friction but we can still calculate the number just fine. Stating that flow is a continuous vector field doesn't constitute much of an explanation in my book. If I asked you how wings generate lift and you said "flow is a continuous vector field" I don't think I would walk away with a better understanding of the physics involved.
Chris, thanks for sharing your explanations :D, hey i do not know if you have seen it but, will you make an analysis and maybe some upgrade mods to the following DIY quad frame th-cam.com/video/1FsyVs9F5as/w-d-xo.html Happy New Year !
@@ChrisRosser i have not tested one myself yet, i forgot to ask the author about the specs of the fiber tubes, what is the inside and outer diameter so to know the wall thickness, what type of fiber is also do a graph to see where you minimize weight and maximize the damping, what if you use semi hollow tubes or solid tubes. what you think
Hi Everyone!
Here is the link to the article that prompted the title: www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/
Let me know what you think in the comments. I'll try and answer any questions as always.
Thanks, Chris
Hi Chris, I find the more I read of this subject, the more I don't know. I found this helpful th-cam.com/video/QKCK4lJLQHU/w-d-xo.html
Thanks for your quality content, I'm almost done with my AOS5.
The terminology "Suck" is incorrect
It's fascinating that Chris can always dive deep into the physics of FPV related topics. Here's an idea of another topic. I'm always curious on how heat is generated in motor, why a badly tuned PID / noisy gyro generate so much heat, and how does the wasted heat affect the efficiency and flight time of the quads.
That's a great topic for a future video thank you!
That's a great question. Looking forward to Chris' video!
I just learned english to understand your videos 👌
I graduated from an aviation college... with a degree in Aviation Science/Professional Pilot. Had to take several classes on aerodynamics. My roommate was an Aeronautical Engineer. Your explanations at times had me shaking my head "NO".... at times had me shaking my head "YES..." the rest of the time had me scratching my head "What the hell is he talking about...???". In the end, we know and have known for a very very long time that the production of lift is a combination of Newton's 3rd law of motion, and Bernoulli's principle. Neither alone explains the total lift produced, but when both are considered, it all comes together-- Overly simplified, Bernoulli is at work on the top surface and Newton is at work on the bottom. You touched on drag a bit... the first type of drag you showed with the vector diagram is called "Induced Drag"... it is the drag caused solely by the production of lift. The second drag type that you called "skin drag" is properly termed "Parasite drag"... I kinda think you got form drag right, sort of...
Sounds like you had all the possible reactions! I would agree that this is a classic case of Newton's 3rd law in action. Bernoulli applies to the whole air flow field so it is acting on the top and bottom surface and doesn't directly contribute to lift (it rather describes the link between the flow and pressure fields). The top surface creates lift by deflecting flow downwards, just like the bottom surface. Air pressure is the effect that keeps flow attached to the top of the aerofoil and allows that to happen.
bernoulli works on both top and bottom, but the top is shaded from the airstream and the bottom is exposed?
@@ChrisRosser Well.... I don't really know about that. I'm going to say "not exactly". Bernoulli is working on the top. The upper curvature of the wing is a half section of your venturi example. You don't need the full venturi cross section to be there for the effect to exist.
How would you explain then, the fact that an airfoil stalls at the same angle of attack regardless of the true airspeed, and regardless of the altitude (pressure)? An airfoil at just below critical angle of attack will experience wildly different air pressures on the top of the airfoil vs. the bottom at let's say 50 KTAS vs 500KTAS. Yet the static pressure is the same. So, If I understand your argument correctly, the 500KTAS airfoil should stall much sooner (lower angle of attack) because the air pressure (due to high velocity, again, bernoulli...)would not be there to keep the flow attached to the top of the airfoil. Yet we know that this does not happen. In fact, at higher airspeeds, the air pressure on the top of the airfoil at high angles of attack can drop so low that it causes the temperature of that air to drop to the point where the moisture condenses out and becomes visible... approaching zero psi... a truly LARGE change in pressure!! But it still remains attached. And under the wing, at the same moment, the air pressure would be dramatically higher than at the upper surface of the wing
I've never heard anyone explain it as you have... maybe I'm just not grasping your explanation and we're both seeing the same thing, but I don't think so...
This is one of those discussion topics that requires a LOT of beer.
@@ChrisRosser Coanda effect is what keeps flow attached to the top of airfoil.
Bernoulli indeed acts on both top and bottom surface, but the speed of the fluid attached to the top is faster and bottom slower due to airfoil, so it creates difference in preassure between them, add Newton's 3rd law and there you have it - lift.
The lift is the trio - Bernouli, Newton, Coanda. Theres also Raynolds and other factors lift depends on, so yeah - a lot of beers talk :D
BTW, if noone could explain lift, then there would be no CFD software :)
@@Демократът Coanda effect only applies to jets of air into a slower moving fluid. Because all the air incident on the aerofoil is moving at the same speed there is no speed difference, no entrainment and therefore no Coanda effect acting on a simple aerofoil. This is a very common misexplanation of why the flow attaches to the surface. The real reason is simply air pressure. Some advanced aerofoil designs bleed air from below the wing and inject it as a jet into the boundary layer above the wing (using slats) to keep the boundary layer attached at high AOA. Locally that is Coanda effect because you have a jet of fast moving air entering a region of slower moving air.
As an engineer, I love these explanations. Your channel is just brilliant, thank you and keep it up.
Thank you very much!
The simplest way I understand what happens at the topside is that the top of the wing sweeping through airflow creates vacuum volume behind it so the higher pressure air above it pushes air molecules to fill that space. Works with flat planes and symmetrical airfoils too, only the angle of attack matters in the direction of the lift. But a gradual curving shape helps keeping the flow attached to the surface and prevent turbulentic flow separation. I think this is the basics of Coanda effect.
Absolutely spot on with everything except the effect is simple air pressure not coanda effect. Coanda effect is only applicable to jets of air not a bulk flow like you get over a wing. 👍
Great explanation. Would love to see part 2 on how propwash is caused by flow separation, and why modern props have near zero AoA at tips to help recover from stalls.
the twist in modern props is there to create a constant distribution of the lift coefficient along the diameter
the tip of the prop moves faster than the center
therefore, it can be at a smaller angle of attack
the most efficient shape for a normal wing is an ellipse (not quite) and because of the same reason as before, the most efficient shape for a prop is a towards the tip slighly tapered ellipse
Great info thanks for sharing!
This explanation is also quite handy at explaining what happens during a stall.
As the static pressure right on top of the surface of the wing approaches 0, the pressure differential that causes the airstream to follow the wing curvature can't get any higher. Any further increase in the angle of attack has the airstream detaching from the wing. This increases pressure at the wing surface at first, but it gets lowered again as the airstream is again deflected by the pressure differential to follow the curvature. As the cycle repeats, the airstream oscillates between these two states causing vortices to form.
Hapy new year Chris.
Thank you for your effort educating the community.
My pleasure!
Thank you Chris. Happy New year my friend.
Happy new year!
This is a great explanation with great visuals, a lot of the misconceptions were cleared up correctly. Only suggestion I would add is that the pressure gradient at the top of the airfoil will have usually traveled a much farther distance than the lower stream. It would be great if you could accurately represent this in some of your graphics to further drive home the point of the difference in velocity between the upper and lower surfaces, as well as how far out the geometry of the airfoil affects the incoming pressure gradient
When I studied for my license there was a question in regards to propellers and why they are the shape they are, I took quite some time writing the answer because as you go out from the centre well you know all the changes to everything... and no one in the course got it right except me, because information on the internet was vague to say the least, no one explains why the pitch decreases as it goes away from the hub correctly, anyway, good video.
Fantastic job explaining this topic Chris!
Excellent explanation!
So nice to hear the term Bernoulli again. My first time encountering it was 1995. I was a pc support at that time. I got assigned to do a review of Iomega Bernoulli Drive. :)
LOL!
Interesting! Same name in completely different fields 😁
@@ChrisRosser I remember it utilizes the Bernoulli's principle on the rotating media. That's what I remember.
great content , thanks ,Happy new year and happy flying Chris
Happy new year!
For Venturi effect to work you do not need 2 surfaces, point in case aerospike engine where second surface is "virtual" formed by ambient pressure.
I think you do. An aerospike engines uses atmospheric pressure to hold the exhasut against the spike but there is no cross sectional area reduction achieved. The venturi explanation is a very common incorrect explanation of lift, covered in more detail here: www.grc.nasa.gov/www/k-12/airplane/wrong3.html
Can you recommend beginner or academic books which explain this topic?
Excellent work! I wish you could have been my fluid dynamics prof in college. So intuitive
Doesn’t form drag for a streamlined aerofoil become abruptly significant at a stalling angle of something like 12-15 degrees? I’ve tried this with NACA 0012 in a wind tunnel. I had alternate sides of the aerofoil connected up to a multiple manometer and it’s pretty obvious when stalling occurs.
Thanks for the efforts you went into researching and explaining this intriguing topic. In the derivative form of Bernoulli's equation, the variable of the differentiation is the position variable, but you still have performed differentiation of the V^2 term?
This is an elaboration on the very basic explanation of how lift is generated often used by Don Stackhouse. His usual simplification of the process is "a wing generates lift by grabbing chunks of air and shoving them downward". He too could go into the details of how this is done but most often, for the purposes of his comments this elaboration is not necessary. Truth is that I would love to hear his detailed explanation and compare it to Chris Rosser's. No doubt there would be some differences in how it is explained but the overall conclusion would be much the same.
Exactly right, the control volume explanation is literally just Newton's 3rd Law. The second half of the explanantion really just expands on that by describing the method by which the aerofoil grabs hold of the air (air pressure holding the flow against the surface) and how the deflection of the flow creates the pressure difference on the wing that forces it upwards.
Navier-Stokes :)
The derivation of Bernouili's equation assumes irrotational and/or invisicid flow and/or movement along streamlines. Those assumptions are not always satisfied. A turbulent (non-strealine) flow over a wing can still generate lift (many wings are not laminar... especially when looking at flow near the trailing edge).
Absolutely right, and that is why the correct explanation of lift for a wing doesn't rely on bernoulli. Only the false ones do 👍
please, make some more aerodynamics talks man. i love it!!!
Also, what do you think about the hydrofoils recently used in the america`s cup sail boats?!
What's going on with that machine over your shoulder? It has a quad mounted to it? I'm curious.
Thrust test stand. Working on some motor testing.
Excellent stuff Chris, maybe in a future video you could touch on prop/blade twist and the effects of airflow through them at different RPM and angle of attack including autorotation.
I know this video is a year old but just curious if you could explain lift without using an airfoil. Example a foam profile rc airplane. Symmetrical and flat surfaces but yet it still flies very good
Hello Chris, I've just ordered your AOS 3.5 frame to copy your
I don't think the au fits in the 3.5 and it would be very heavy for smaller props. I think the vista is the way to go. You get 50mbps with the vista and equal range. Twin antennas only helps in strong multipath environments.
And I have to point out that pressure and flow are not "fields".
The vector of a field, namely its strength and direction, is insensitive to the chosen (inertial) frame of reference (FoR). For example, magnetism always has its direction along the field line leading to the N pole. Its strength is irrespective whether the magnet is stationary wrt the observer or moving. The same is true for an electric field and gravity , the only other naturally occurring fields that I am aware of.
On the other hand, the vector of flow, namely its speed, and direction is quite different if you change your FoR from the foil, where the flow speed is the speed of the foil, to the ambient air, where the flow speed is zero.
I'm not sure who is responsible for the introduction of fields into fluid dynamics, but I'm pretty sure it was current at the early part of the 20th Century. Certainly Prandtl in the '20s was (mis)using the term.
It's a pretty deep question that casts serious doubt on a helluva lot of fluid dynamics.
Aerodynamics ehh?…..okay “Clever Trousers” now you’re in my house Sir. 😄 POST VIEWING EDIT: Very nice, comprehensive video, interesting, accurate and the potato gun analogy almost justified the invocation of the “Bernoulli effect” 😉
(As if Chris Rosser requires my personal scientific validation 😆)
It is a very positive feeling to get a positive comment from another skilled in the art! Thank you Sir!
It's hard to tell when you cease debunking the false explanation and start with your explanation. But I guess it was at round 7:00 when you choose the differential of the Bernoulli equation and the potato gun. It doesn't need Bernoulli to explain that air moves from high to low pressure, potato guns notwithstanding. Atmospheric air is moving from a high to low pressure BUT IT IS NOT ACCELERATING! Pressure and flow are not coupled fields like electricity and magnetism. You (and MacLean) have invented this myth!
It's much simpler, as I explain in the paper linked in the description of th-cam.com/video/dgE9xhIjTOU/w-d-xo.html
....for the algorythm :)
This one gets it! Thank you!
So soon we'll have AOS props won't we 😅
Maybe one day. But don't worry, there's plenty of exciting AOS stuff in the works. Ultralight 5", Cinewhoop, Cinelifter and a revolutionary (pun intended) line of motors.
Chris, Chris, Chris ... you relatively correctly pointed out that the "usual" explanations have flaws, but your explanation is as much flawed as these are ... the "100% Explained" is a massive overstatement
- Bernoulli is a fact, the problem is that it is for conditions which do not fully apply to an airfoil
- Newton is a fact, but again the problem is that one can't apply it that naively, since air is a gas and not a solid body
- you are incorrect in saying that the airfoil must have a particular upper shape, see collective pitch helicopters, or just take a plank and hold it outside of your car's window
- you are incorrect in saying that you can think it either way. It's like Ohm's law, then you know I you can get U, and if you know U you can get I, but physically it is absolutely clear that it is a U which drives the I, and not vice versa. Similarly so with F and a, F results in a, and not vice versa, and similarly so with v and dP/dx, dP/dx results in v, and not vice versa.
it is also not difficult to see that your two explanations are equally bad or good as the flawed ones
- your flow vector model obviously violates vector field equations (divergence). Air needs to come from somewhere and needs to go to somewhere
- your 2nd explanation is even more obviously wrong, and in fact suffers from exactly the same flaw as the Bernoulli, Newton & Venturi explanations: The velocity of the air at the surface of the airfoil is ZERO! This is known as no-slip condition and is an extremely good and universally accepted assumption in aerodynamics. Ironically, in your (wrong) drag explanation you show indications of that the velocity on the surface gets smaller. But it in fact goes to zero everywhere on the airfoil surface. Therefore, it is simply not possible to talk of a velocity of an air stream.
There is a one-line correct explanation for why airfoils create lift: Flow is a continuous vector field. Admittedly this is not so easy to understand what this is and what it implies.
None of what I say is in contradiction to the article you refer to, to the contrary, the article concludes exactly the same. The video by Doug McLean is in fact excellent, absolutely excellent, and explains it all quite nicely, a must watch.
You should consider removing the claim that you have now finally given a better explanation. Sorry mate, no offense. :)
Let me take each of your points in turn:
Bernoulli is a fact, and it is often used to explain why faster flow is at lower pressure. However, it doesn't explain why the flow should acclerate in the first place. As an analogy: conservation of energy explains why an apple accelerates as it falls. but it doesn't explain why it falls in the first place.
Newton's laws apply to solids, liquids, and gases in exactly the same way.
I actually stated that the upper shape of an aerofoil matters for calculating its lift generation (not that it must have any particular shape to generate lift).
In a motor the current created by wires moving through a magnetic field generates voltage. Electromagnetism is a coupled field so you can find examples where voltage seems to generate current and vice versa. There is no correct way round, anything that can be explained by one way of thinking can be explained equally well the other way round.
I'm well aware of the no slip condition in the boundary layer. It doesn't stop us calculating the average velocity change of the air. The average is a little less because of skin friction but we can still calculate the number just fine.
Stating that flow is a continuous vector field doesn't constitute much of an explanation in my book. If I asked you how wings generate lift and you said "flow is a continuous vector field" I don't think I would walk away with a better understanding of the physics involved.
Chris, thanks for sharing your explanations :D, hey i do not know if you have seen it but, will you make an analysis and maybe some upgrade mods to the following DIY quad frame th-cam.com/video/1FsyVs9F5as/w-d-xo.html Happy New Year !
Hey! I like the tubular concept certainly it'll be very very stiff for its weight. How do you find the durability with thin walled tube?
@@ChrisRosser i have not tested one myself yet, i forgot to ask the author about the specs of the fiber tubes, what is the inside and outer diameter so to know the wall thickness, what type of fiber is also do a graph to see where you minimize weight and maximize the damping, what if you use semi hollow tubes or solid tubes. what you think
Fixed wing vs propelling wing unexplained... 🤦♂️
good lord Chris don't you know they fly using will power see TH-camr Lee Evans, he explains it in great detail. your welcome :)
Ha!
Haha I love Lee Evans!