I’m an Aerospace Engineer student and we are actually running an experiment like this in my Aerodynamics Lab, except our NACA 0012 has a flap on it. I love your addition of bubbles though! Super cool :)
Bit incorrect with the chord line for the NACA4412. The chord line is a straight line connecting the leading edge and the trailing edge. It's always a straight line. What he drew was the mean camber line. Still, an informative video otherwise!
I'm torn between my affinity for efficiency and my desire to see smoke ;). Maybe a strobe light on the bubble stream. Too bad we can't color bubbles. Good video. I appreciated the explanation of your wind tunnel set-up. Clearly explained 👍
Smoke would be great but for a closed loop-wind tunnel the smoke would just go round-and-round. Which means after about a minute, the whole tunnel is filled with smoke and you can't see anything! I have done it a couple of times. The other downside to smoke is, what is the smoke made of: glycol, glycerin, dry ice? Ideally the smoke should be neutrally buoyant so that it follows the flow and doesn't rise or fall based on a difference in density between the smoke and the air. Think about hot steam from a smoke stack, it rises pretty quickly. Another consideration is what happens to the smoke over time. So if it is a Glycol based smoke, like a lot of theatrical fog machines, it will leave everything in the tunnel a little greasy for a while as it accumulates on your test section and models. I wonder about its effect on hot-wires. A strobe light would be cool to try. Especially if it were synced to something periodic such as a vortex shedding event.
@@marquetteshockphysics5518 Yes, good point about the density difference. I hadn't thought that through. That was my thought on the strobe light as well. It could be variably synched to match flow rates at different points. Then these would appear "frozen" compared to the rest of the flown It would make specific flow rates detectable using vision directly. (Sort of how astronomers use software to reverse moving objects to make them look still, and stationary objects to make them look moving. It helps pick out dwarf planets and asteroids against star fields.) If it doesn't work out, you could have a disco party fundraiser to recoup your costs.
I have been building FPV helicopter aiming at endurance. NACA 0012 and 0015 used to be the standard in the industry, but recent manufacturers/machinists are making NACA 0008 blades, and I am struggling to keep up with them. I am studying NACA 0012 again to see details and try to find solutions.
Try connecting alternate sides of the aerofoil to a multiple tube manometer, and you will get a good approximate view of lift as the area of what you will see. It will be obvious when the aerofoil stalls round about 14 degrees angle of attack.
Except mixing up the chord with the mean chamber line there is another minor inaccuracy. The sensors on the airfoil don`t show you static pressure, but just pressure in particular point. For example, in stagnation point (where V=0, close to leading edge) the measured pressure equals static pressure plus dynamic pressure (0.5*density*velocity^2). So in that formula of pressure coefficient it should be "P" instead of "Ps". And by "P infinity" he means "static far-field pressure". But the video is very informative and useful!
Hi IllIa Thanks for the comment and good point regarding pressure measured by the ports. For sure if a pressure port is oriented parallel with the wind (facing the incoming flow directly) then it would measure the stagnation pressure. In fact that is how one can align the airfoil to the wind, by insuring the leading edge port is measuring stagnation pressure. -jb
Good/informative video. It would be nice to complement it by calculating the induced drag of this profile AND, by using a wing-tipped airfoil, to compare induced drag of the same NACA profile with and without wingtip.
I guess the Static pressure has been measured by the scanivalves to which the tubes are connected from the pressure ports on the surface via the pressure taps
Hey, i'm a student in Switzerland and i am trying to build a windtunnel to measure the dynamic lift. I would like to know more about the manometer you have. How do you know what the diameter of the tubes ought to be? Because with my equations, i would need to measure +/- 0.005 Pascal. Thank you for the video.
how is velocity increasing over free stream velocity? That is happening at the curvature where the pressure gradient is most favorable. The boundary layer is created and It increases with the length of curvature, the upcoming stream of air reacts to the boundary layer as to the psychical surface of the object and thus narrowing the free stream volume. Can we say that the velocity of air is increased because of conservation of momentum, as more mass of air is hitting less mass which is moving through the lower volume at the boundary layer and thus speeding up because it is conserving momentum?
According to the normalization, isn't C=0.1524m = 6" ? 9:27 In the data sheet, the chord length is 1.969 mm = 0.075", which is too small and coincides with the first step.
A good reference is a book entitled "Theory of wing sections", www.amazon.com/Theory-Wing-Sections-Aeronautical-Engineering/dp/0486605868 The book contains lots and lots of dimensionless data for many of the 4 and 5 digit NACA airfoils.
Excuse me sir, how can you obtain the lift and moment coefficient at quarter chord length? i am walking on a similar projet and do not know how to go about it, thank you.
Hi Armel, to get lift you can integrate the pressure profile over the area. The resulting force will act at the center of pressure. For more details seek out reference materials in a textbook or a reliable web-source like www.grc.nasa.gov/www/k-12/airplane/cp.htm To get a moment relative to a given location, it is a similar process: integrate the pressure distribution times a moment arm.
Super interesting!! I am not sure where in the video you are referring to but there are regions of the flow where the pressure isless than atmospheric pressure (ie a vacuum pressure). But the pressure never goes to absolute zero (like a hard vacuum). In regions of the flow where the air is moving faster the pressure is low, lower than atmospheric pressure. So it is a vacuum pressure in the sense that it is slightly lower than atmospheric. This is due to the Bernoulli effect, which for incompressible fluid behavior (as is reasonable to assume here) states that as the pressure and velocity are inversely proposal: if pressure goes up, then velocity goes down and if velocity goes up then pressure goes down.
Good job! I am a student from SJTU and I am trying to do flow visualization in an open wind tunnel. Can you share more visualization techniques in wind tunnel? It seems a little more diffcult to performe PIV in a wind tunnel than in water. Thanks advance!
No idea! I suppose you are talking about a wind turbine, whether it be horizontal or vertical (more like a water wheel type). The tunnel cross-section at the test section is 2 feet x 2 feet, so the wheel would have to be small. As a rule of thumb, anything you place in the tunnel should have a projected area less than 10% of the test section area.
Excuse me, how can you obtain lift and drag from the results? Me and some friends are working in a similar project, but we don't know how to obtain this data (L & D), thank you
There are several ways to get the lift and drag. One way is to measure the pressure on the surface of the airfoil and then integrate that pressure over the area, force=pressure*area. Another way is to measure the velocity profile behind the airfoil and calculate the momentum loss, that will be equivalent to the drag. Then perhaps the best way is to directly measure it with a force balance. If you are interested in learning more you can check out a nice fluids text book, such as Frank White's "Fluid Mechanics" or there are lots of resources on line such as www.grc.nasa.gov/www/k-12/airplane/right1.html
At 10:24 you deduce the velocity from the pressure using Bernoulli! Why didn't you measure the velocity? You have bubbles (beautiful bubbles - brilliant innovation.) You could get a high-speed camera to measure the speed of the air? We know there is a pressure difference... the only way a fluid can impart force to a body is via pressure. You measuring that pressure difference. Where does that pressure come from? You assume Bernoulli. But that may not be true. There are a lot of reasons it may not be: Air IS compressible, the fluid is NOT flowing in a tube, and more. With a high speed camera you could validate the theory.
What is nice about reporting non-dimensional numbers is that two data sets (collected at two different free stream velocities) can be compared. If the non-dimensional data matches for these two data sets then we know we have dimensional similarity. Thus we need not data data for every free stream velocity we might be interested in.
@@marquetteshockphysics5518 sir, the idea you're expressing is that while comparing data between 2 models of a body, it is much more convenient to predict Aerodynamic forces if we make use of non-dimensional numbers correct?
@@akarshshetty9262 Absolutely. Making use of non-dimensional data not only reduces the amount of data we have to take but it can also indicate when there are major changes in the physics. For example, if comparing two data sets it might be easier to spot when separation of boundary layer transition occurs.
@@marquetteshockphysics5518 yeah! Sir, here you hav made use of pressure ports to measure the normal pressure loads... Is there any way to measure the Tangential Shear loads experimentally other than methods like CFD? Edit1: *other than non-experimental methods like CFD
The general rule of thumb for blockage is that the frontal projected area of the test article should not exceed 10% of the total cross-section of the tunnel. The total cross section of the wind tunnel is 2ft x 2ft. Thus the frontal projected area should not exceed 0.4 ft^2. This is of course just a general rule.
Excellent stuff! Long time aviator,theories have been changing.Can you approximate the ratio of lift that top surface(low press,bernoulli) does as opposed to bottom surface,(hi press,Newtonian) for a GA aircraft?Irealise it will vary,but Im guessing 25% Bern and 75% Newtonian.Cheers and thanks
Good question! Not sure I could answer that. I think of it more like there are two simple theories that do a good job of describing the same complicated physics. Both theories have their advantages and disadvantages but neither can describe everything that is happening: laminar-turbulent boundary layer transitions, wing-tip vortex rollup, flow separation. So in a way they are both just models (ideas) of what is happening to the flow along the wing. Sorry that got a little existential for a moment... :)
Even in a "pure" Newtonian sense the lift doesn't only come from the bottom surface / high-pressure. The air that travels over the top surface is deflected downwards as well too which by Newton's second law means it also contributes to the lift force.
@@marquetteshockphysics5518 If Bernoulli's equation is just an equation that calculates the conservation of energy, why is it so often assumed that the increase speed over the top of the airfoil then must have lower pressure, instead of the other way 'round. If the high pressure at the leading edge and slightly the lower surface (assuming an angle of attack), wouldn't this create a low pressure behind this pressure buildup (which also causes the updraft), leading to the fluid speeding up? I don't understand how if a vacuum on the top of the wing lifts the entire gross weight of an aircraft, fuel, passengers, and cargo, how could, say, a fabric coated wing be held together by glue. Seems more intuitive to me that the low pressure causes a high speed, which spills off the trailing edge downward, pushing the wing up. No?
@@BrentDanley Bernoulli just tells you the numbers. It doesn't explain why it happens. In fact, it is the lower pressure which pulls the air in (accelerates it). Your intuition about vacuum is correct. Take a container with a vacuum inside. There is (literally) nothing inside which "pulls" on the wall. Even just a tiny bit of air inside will always PUSH against the wall. But the outside (atmospheric) pressure will press a lot more against the walls. But there is nothing inside to hold back. Same with the wing. The lower the pressure on the upper side, the more the pressure on the under side can push the wing up. (At least as far as i understand)
@@BrentDanley re: "why is it so often assumed that the increase speed over the top of the airfoil then must have lower pressure" Correct me if I'm wrong, but his plotted data near the end of this video **shows** just that, increased velocity and __lower__ pressure ...
See the following webpage for the definition of the center of pressure (cp): www.grc.nasa.gov/www/k-12/airplane/cp.html So you could perform numeric integration for cp using something as simple as the trapezoid rule
@@marquetteshockphysics5518 amazing setup sir. I was wodering about putting naca duct in a long wing where the air detaches at the rear end of the wing. I believe that naca ducts on such wing will suck the air from the bottom of the wing. 1) improving the downforce 2) forcing the air to remain attached to the bottom side of the wing making it more efficient. Please let me know what you think and if you could experiment such setup.
I am not familiar with NASA ducts. But there is a wiki page:en.wikipedia.org/wiki/NACA_duct separationopeningbleeding-off pressure, aeffectivenessopportunemaneuversseparation or transition could be suppressed or enhancedNeat idea! application
Sorry to nitpick, but you drew the mean camber line and not the airfoil chord. The chord is always a straight line while the camber line follows the average of the upper and lower surface heights. en.wikipedia.org/wiki/Chord_%28aeronautics%29#%3A%7E%3Atext%3DIn_aeronautics%2C_a_chord_is%2Ctrailing_edge_of_an_aerofoil.%26text%3DThe_wing%2C_horizontal_stabilizer%2C_vertical%2Cused_to_describe_their_width.?wprov=sfla1
But the point is ...airfoil moving in static air and....air moving over a static airfoil...are two completely different paradigms...no streamlines are present in actual airspace around a moving wing since all air is static... Lift is a mystery and there's no scientific explanation for it's origin and cause.
Вот мужик молодец! Сам наверно того не понимая разоблачит теоретическую аэродинамику. Посмотрите внимательно куда летят снежинки над крылом на 7:10 по 7:25? Они летят снизу на верх и вперед по ходу полета крыла, т.е. поток не то что ускоряется над крылом, а летит в противоположном направлении, т.е. "за крылом". При этом угол атаки у него где-то +15...+20°. А как известно в аэротрубе максимальная подъемная сила возникает на угле атаки +45°. Эх жаль перевода нет!
Cпасибо за комментарии! Крыло меняет направление импульса ветра. Это то, что создает подъемную силу на крыле. Пузырьки гелия показывают, как меняется направление ветра.
@@marquetteshockphysics5518 Пузырьки показывают что воздух который находится над крылом в реальном полете будет лететь за крылом, т.к. над крылом создается разрежение, а основной закон физики и природы звучит так: "Вещество всегда перемещается из области высокого давления в область низкого." Поэтому в реальном полете никакого обтекания крыла потоком не будет. Воздух вокруг крыла летит вместе с крылом в том же направлении что и крыло и с той же скоростью что и крыло из за того что имеет ВЯЗКОСТЬ. А воздух над крылом летит еще быстрей чем крыло в том же направлении что и крыло. А из этого следует, что всю теоретическую аэродинамику, с ее обтеканием и потоком и ускорением потока над крылом, можно спустить в унитаз как лженауку!
The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force.
Aerodynamic force is the wind force, stands for relative wind. Further, in physics, wind force and aerodynamic force are different. The wind force strikes the object, and the aerodynamic force is which the object receives at right angle to the contact surface.
The force object receives is always normal to the contact surface and (static) air pressure always acts normal to the surface of the body. This has long been well known, and I don't know why in flight theories and aerodynamics books this is (mostly) omitted.
@@vlatkopopovski2685 The resultant vector of the lifting force isn’t always perpendicular to the chord line. We can see this from pressure measurements along the surface of the wing.
Fantastic demonstration! I’d love to see pictures of the bubbles in a strobe light so we can see the change in the bubbles over time.
As a former wind tunnel researcher, I loved watching this video. We used Scanivalves too, but they were much more cumbersome back in the 1990's.
I’m an Aerospace Engineer student and we are actually running an experiment like this in my Aerodynamics Lab, except our NACA 0012 has a flap on it. I love your addition of bubbles though! Super cool :)
Thanks!
The bubbles are unique feature never seen before. I just want to own this wind tunnel setup. Highly fascinating and excellent demonstration, doc.
Thank you for very interesting presentation Dr. Borg.
You are very welcome
This is a really cool setup!
Thanks!
You are an amazing teacher. I loved this video. Thank you!
Great video! a long exposure photo showing the paths of many bubbles over the airfoil would be interesting.
Thanks! Very informative, demonstrated and illustrated..
Glad it was helpful!
Bit incorrect with the chord line for the NACA4412. The chord line is a straight line connecting the leading edge and the trailing edge. It's always a straight line. What he drew was the mean camber line. Still, an informative video otherwise!
Good point! Thanks for the comment!!
I'm torn between my affinity for efficiency and my desire to see smoke ;).
Maybe a strobe light on the bubble stream. Too bad we can't color bubbles. Good video. I appreciated the explanation of your wind tunnel set-up. Clearly explained 👍
Smoke would be great but for a closed loop-wind tunnel the smoke would just go round-and-round. Which means after about a minute, the whole tunnel is filled with smoke and you can't see anything! I have done it a couple of times. The other downside to smoke is, what is the smoke made of: glycol, glycerin, dry ice? Ideally the smoke should be neutrally buoyant so that it follows the flow and doesn't rise or fall based on a difference in density between the smoke and the air. Think about hot steam from a smoke stack, it rises pretty quickly. Another consideration is what happens to the smoke over time. So if it is a Glycol based smoke, like a lot of theatrical fog machines, it will leave everything in the tunnel a little greasy for a while as it accumulates on your test section and models. I wonder about its effect on hot-wires.
A strobe light would be cool to try. Especially if it were synced to something periodic such as a vortex shedding event.
@@marquetteshockphysics5518
Yes, good point about the density difference. I hadn't thought that through.
That was my thought on the strobe light as well. It could be variably synched to match flow rates at different points. Then these would appear "frozen" compared to the rest of the flown It would make specific flow rates detectable using vision directly.
(Sort of how astronomers use software to reverse moving objects to make them look still, and stationary objects to make them look moving. It helps pick out dwarf planets and asteroids against star fields.)
If it doesn't work out, you could have a disco party fundraiser to recoup your costs.
Thanks for making and sharing this video showing a very interesting and informative demonstration.
Best regards
For beginner, it is useful content. Thanks.
Thank you for sharing this amazing experiment 😀
Thank you!
Loved it. Easy to follow. Thanks
Tremendous!
I have been building FPV helicopter aiming at endurance. NACA 0012 and 0015 used to be the standard in the industry, but recent manufacturers/machinists are making NACA 0008 blades, and I am struggling to keep up with them. I am studying NACA 0012 again to see details and try to find solutions.
Try connecting alternate sides of the aerofoil to a multiple tube manometer, and you will get a good approximate view of lift as the area of what you will see. It will be obvious when the aerofoil stalls round about 14 degrees angle of attack.
Interesting Video! Thanks for sharing!
Great Video! Thank you!
This was great! Thanks.
Except mixing up the chord with the mean chamber line there is another minor inaccuracy. The sensors on the airfoil don`t show you static pressure, but just pressure in particular point. For example, in stagnation point (where V=0, close to leading edge) the measured pressure equals static pressure plus dynamic pressure (0.5*density*velocity^2). So in that formula of pressure coefficient it should be "P" instead of "Ps". And by "P infinity" he means "static far-field pressure". But the video is very informative and useful!
Hi IllIa
Thanks for the comment and good point regarding pressure measured by the ports. For sure if a pressure port is oriented parallel with the wind (facing the incoming flow directly) then it would measure the stagnation pressure. In fact that is how one can align the airfoil to the wind, by insuring the leading edge port is measuring stagnation pressure.
-jb
do u know what total pressure is for the experiment??
even for a layman this video is great.
I've been just doing research for 2 days and i know the chord is a straight line always
Good/informative video. It would be nice to complement it by calculating the induced drag of this profile AND, by using a wing-tipped airfoil, to compare induced drag of the same NACA profile with and without wingtip.
sorry do u know how he worked out static pressure?
for I do not know total pressure
I guess the Static pressure has been measured by the scanivalves to which the tubes are connected from the pressure ports on the surface via the pressure taps
What is power requirement of this closed loop wind tunnel? My calculation for 45 m/s 0.372 sqm open tunnel is about 21 kW + losses...
Thank you
Hey, i'm a student in Switzerland and i am trying to build a windtunnel to measure the dynamic lift. I would like to know more about the manometer you have. How do you know what the diameter of the tubes ought to be? Because with my equations, i would need to measure +/- 0.005 Pascal. Thank you for the video.
good job
how is velocity increasing over free stream velocity? That is happening at the curvature where the pressure gradient is most favorable. The boundary layer is created and It increases with the length of curvature, the upcoming stream of air reacts to the boundary layer as to the psychical surface of the object and thus narrowing the free stream volume. Can we say that the velocity of air is increased because of conservation of momentum, as more mass of air is hitting less mass which is moving through the lower volume at the boundary layer and thus speeding up because it is conserving momentum?
According to the normalization, isn't C=0.1524m = 6" ?
9:27 In the data sheet, the chord length is 1.969 mm = 0.075", which is too small and coincides with the first step.
Loved the video. Where can these type of dimensionless data be found for different airfoils?
A good reference is a book entitled "Theory of wing sections",
www.amazon.com/Theory-Wing-Sections-Aeronautical-Engineering/dp/0486605868
The book contains lots and lots of dimensionless data for many of the 4 and 5 digit NACA airfoils.
@@marquetteshockphysics5518 thank you very much. I really appreciate the prompt response
Thanks! Very informative . please could you mention the name of your scanivalve or datasheet.
Excuse me sir, how can you obtain the lift and moment coefficient at quarter chord length? i am walking on a similar projet and do not know how to go about it, thank you.
Hi Armel, to get lift you can integrate the pressure profile over the area. The resulting force will act at the center of pressure. For more details seek out reference materials in a textbook or a reliable web-source like www.grc.nasa.gov/www/k-12/airplane/cp.htm
To get a moment relative to a given location, it is a similar process: integrate the pressure distribution times a moment arm.
The chord length in column D is not correct. It can’t be 1.9 mm.
Great job. Do you have any research on water tunnels?
I do not. I wanted to build a water tunnel but it is still on my to-do list!
What happends if we have water and not air
?
Great video... are there any simulators that could give this kind of data?
XFLR5
Designfoil is a shareware tool you can use for this. It has the NACA airfoil generators in it along with a 2D wind tunnel.
That is NOT the chord line for the 4412. What he draws is the Mean Chamber Line!
Good point!
So is that dead zone a vacuum. So interesting .
Super interesting!! I am not sure where in the video you are referring to but there are regions of the flow where the pressure isless than atmospheric pressure (ie a vacuum pressure). But the pressure never goes to absolute zero (like a hard vacuum). In regions of the flow where the air is moving faster the pressure is low, lower than atmospheric pressure. So it is a vacuum pressure in the sense that it is slightly lower than atmospheric. This is due to the Bernoulli effect, which for incompressible fluid behavior (as is reasonable to assume here) states that as the pressure and velocity are inversely proposal: if pressure goes up, then velocity goes down and if velocity goes up then pressure goes down.
Good job! I am a student from SJTU and I am trying to do flow visualization in an open wind tunnel. Can you share more visualization techniques in wind tunnel? It seems a little more diffcult to performe PIV in a wind tunnel than in water. Thanks advance!
you have any idea how many rotating water wheel type generator/alternators you could attach to that to produce energy?
No idea! I suppose you are talking about a wind turbine, whether it be horizontal or vertical (more like a water wheel type). The tunnel cross-section at the test section is 2 feet x 2 feet, so the wheel would have to be small. As a rule of thumb, anything you place in the tunnel should have a projected area less than 10% of the test section area.
Excuse me, how can you obtain lift and drag from the results? Me and some friends are working in a similar project, but we don't know how to obtain this data (L & D), thank you
There are several ways to get the lift and drag. One way is to measure the pressure on the surface of the airfoil and then integrate that pressure over the area, force=pressure*area. Another way is to measure the velocity profile behind the airfoil and calculate the momentum loss, that will be equivalent to the drag. Then perhaps the best way is to directly measure it with a force balance. If you are interested in learning more you can check out a nice fluids text book, such as Frank White's "Fluid Mechanics" or there are lots of resources on line such as www.grc.nasa.gov/www/k-12/airplane/right1.html
At 10:24 you deduce the velocity from the pressure using Bernoulli! Why didn't you measure the velocity? You have bubbles (beautiful bubbles - brilliant innovation.) You could get a high-speed camera to measure the speed of the air?
We know there is a pressure difference... the only way a fluid can impart force to a body is via pressure. You measuring that pressure difference. Where does that pressure come from? You assume Bernoulli. But that may not be true. There are a lot of reasons it may not be: Air IS compressible, the fluid is NOT flowing in a tube, and more. With a high speed camera you could validate the theory.
Sir, what's the purpose of non dimensionalizing the velocity with the free stream velocity?
What is nice about reporting non-dimensional numbers is that two data sets (collected at two different free stream velocities) can be compared. If the non-dimensional data matches for these two data sets then we know we have dimensional similarity. Thus we need not data data for every free stream velocity we might be interested in.
@@marquetteshockphysics5518 sir, the idea you're expressing is that while comparing data between 2 models of a body, it is much more convenient to predict Aerodynamic forces if we make use of non-dimensional numbers correct?
@@akarshshetty9262 Absolutely. Making use of non-dimensional data not only reduces the amount of data we have to take but it can also indicate when there are major changes in the physics. For example, if comparing two data sets it might be easier to spot when separation of boundary layer transition occurs.
@@marquetteshockphysics5518 yeah! Sir, here you hav made use of pressure ports to measure the normal pressure loads... Is there any way to measure the Tangential Shear loads experimentally other than methods like CFD?
Edit1: *other than non-experimental methods like CFD
@@akarshshetty9262 Sure. Look up hot-film anemometers. You can purchase or make these. They are attached directly to the surface of the body.
Sir what was the maximum blockage ratio in this wind tunnel
The general rule of thumb for blockage is that the frontal projected area of the test article should not exceed 10% of the total cross-section of the tunnel. The total cross section of the wind tunnel is 2ft x 2ft. Thus the frontal projected area should not exceed 0.4 ft^2. This is of course just a general rule.
Excellent stuff! Long time aviator,theories have been changing.Can you approximate the ratio of lift that top surface(low press,bernoulli) does as opposed to bottom surface,(hi press,Newtonian) for a GA aircraft?Irealise it will vary,but Im guessing 25% Bern and 75% Newtonian.Cheers and thanks
Good question! Not sure I could answer that. I think of it more like there are two simple theories that do a good job of describing the same complicated physics. Both theories have their advantages and disadvantages but neither can describe everything that is happening: laminar-turbulent boundary layer transitions, wing-tip vortex rollup, flow separation. So in a way they are both just models (ideas) of what is happening to the flow along the wing. Sorry that got a little existential for a moment... :)
Even in a "pure" Newtonian sense the lift doesn't only come from the bottom surface / high-pressure. The air that travels over the top surface is deflected downwards as well too which by Newton's second law means it also contributes to the lift force.
@@marquetteshockphysics5518 If Bernoulli's equation is just an equation that calculates the conservation of energy, why is it so often assumed that the increase speed over the top of the airfoil then must have lower pressure, instead of the other way 'round. If the high pressure at the leading edge and slightly the lower surface (assuming an angle of attack), wouldn't this create a low pressure behind this pressure buildup (which also causes the updraft), leading to the fluid speeding up?
I don't understand how if a vacuum on the top of the wing lifts the entire gross weight of an aircraft, fuel, passengers, and cargo, how could, say, a fabric coated wing be held together by glue.
Seems more intuitive to me that the low pressure causes a high speed, which spills off the trailing edge downward, pushing the wing up. No?
@@BrentDanley Bernoulli just tells you the numbers. It doesn't explain why it happens. In fact, it is the lower pressure which pulls the air in (accelerates it).
Your intuition about vacuum is correct. Take a container with a vacuum inside. There is (literally) nothing inside which "pulls" on the wall. Even just a tiny bit of air inside will always PUSH against the wall. But the outside (atmospheric) pressure will press a lot more against the walls. But there is nothing inside to hold back.
Same with the wing. The lower the pressure on the upper side, the more the pressure on the under side can push the wing up. (At least as far as i understand)
@@BrentDanley re: "why is it so often assumed that the increase speed over the top of the airfoil then must have lower pressure"
Correct me if I'm wrong, but his plotted data near the end of this video **shows** just that, increased velocity and __lower__ pressure ...
Sir how do we calculate the centre of pressure from the data in the excel ?
See the following webpage for the definition of the center of pressure (cp): www.grc.nasa.gov/www/k-12/airplane/cp.html
So you could perform numeric integration for cp using something as simple as the trapezoid rule
@@marquetteshockphysics5518 amazing setup sir.
I was wodering about putting naca duct in a long wing where the air detaches at the rear end of the wing.
I believe that naca ducts on such wing will suck the air from the bottom of the wing.
1) improving the downforce
2) forcing the air to remain attached to the bottom side of the wing making it more efficient.
Please let me know what you think and if you could experiment such setup.
I am not familiar with NASA ducts. But there is a wiki page:en.wikipedia.org/wiki/NACA_duct
separationopeningbleeding-off pressure, aeffectivenessopportunemaneuversseparation or transition could be suppressed or enhancedNeat idea!
application
Sorry to nitpick, but you drew the mean camber line and not the airfoil chord. The chord is always a straight line while the camber line follows the average of the upper and lower surface heights. en.wikipedia.org/wiki/Chord_%28aeronautics%29#%3A%7E%3Atext%3DIn_aeronautics%2C_a_chord_is%2Ctrailing_edge_of_an_aerofoil.%26text%3DThe_wing%2C_horizontal_stabilizer%2C_vertical%2Cused_to_describe_their_width.?wprov=sfla1
Good point!! Thanks for pointing that out!! :)
At 9:26 Chord Length in the table is 1.969 mm. Why??? Bad for Mr. Reynolds... LOL
Hi Danko, yikes that does seem small! I just went down in the lab and remeasured the chord length of that airfoil to be 6 inches (0.1524 m).
i like more smoke. i can see it better
But the point is ...airfoil moving in static air and....air moving over a static airfoil...are two completely different paradigms...no streamlines are present in actual airspace around a moving wing since all air is static...
Lift is a mystery and there's no scientific explanation for it's origin and cause.
sir we want to find momentum loss "'wake survey of an aerofoil'' we want to contact you can you pass your email
john.borg@mu.edu
Вот мужик молодец! Сам наверно того не понимая разоблачит теоретическую аэродинамику.
Посмотрите внимательно куда летят снежинки над крылом на 7:10 по 7:25? Они летят снизу на верх и вперед по ходу полета крыла, т.е. поток не то что ускоряется над крылом, а летит в противоположном направлении, т.е. "за крылом".
При этом угол атаки у него где-то +15...+20°. А как известно в аэротрубе максимальная подъемная сила возникает на угле атаки +45°.
Эх жаль перевода нет!
Cпасибо за комментарии! Крыло меняет направление импульса ветра. Это то, что создает подъемную силу на крыле. Пузырьки гелия показывают, как меняется направление ветра.
@@marquetteshockphysics5518 Пузырьки показывают что воздух который находится над крылом в реальном полете будет лететь за крылом, т.к. над крылом создается разрежение, а основной закон физики и природы звучит так: "Вещество всегда перемещается из области высокого давления в область низкого." Поэтому в реальном полете никакого обтекания крыла потоком не будет. Воздух вокруг крыла летит вместе с крылом в том же направлении что и крыло и с той же скоростью что и крыло из за того что имеет ВЯЗКОСТЬ. А воздух над крылом летит еще быстрей чем крыло в том же направлении что и крыло. А из этого следует, что всю теоретическую аэродинамику, с ее обтеканием и потоком и ускорением потока над крылом, можно спустить в унитаз как лженауку!
The authors have two wrong scientific approaches: researching the creation of Lift force and Low pressure at upper side of the wing, relative to the ground surface and Earth. I explain the aerodynamic cavitation and existence of Lee side aerocavern, and creation of Aerodynamic force.
What are you talking about? Where do you explain lift?
@@Talon19 In my book "Drowned in the air"
Aerodynamic force is the wind force, stands for relative wind. Further, in physics, wind force and aerodynamic force are different. The wind force strikes the object, and the aerodynamic force is which the object receives at right angle to the contact surface.
The force object receives is always normal to the contact surface and (static) air pressure always acts normal to the surface of the body. This has long been well known, and I don't know why in flight theories and aerodynamics books this is (mostly) omitted.
@@vlatkopopovski2685
The resultant vector of the lifting force isn’t always perpendicular to the chord line. We can see this from pressure measurements along the surface of the wing.
Cord in inches....the rest in SI units......😩
Yes, I know mixed units.... what can you do? I love them both!! :)
@@marquetteshockphysics5518 I can cry....