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#281
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OK, IF Backwash Causes Lift then...
Bertie the Bunyip wrote:
wrote in : Bertie the Bunyip wrote: "Gig 601XL Builder" wrDOTgiaconaATsuddenlink.net wrote in : How does a gyrocopter fly because the airflow over it's "wing" is going up. They're gliders. The same rules apply. Bertie I agree the same rules apply, but they aren't gliders unless the engine craps out. Fair enough, but the wing is behaving in exactly the same way. Bertie Of course. -- Jim Pennino Remove .spam.sux to reply. |
#282
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Backwash Causes Lift?
Jim Logajan wrote:
wrote: Mxsmanic wrote: How do you accelerate an aircraft without accelerating anything downward? [ ... ] An aircraft in straight and level flight is not accelerated. Cute - classic Usenet response. Simultaneously correct, but not really addressing the original issue. The point is that talking about aircraft acceleration in straight and level flight when discussing lift is irrelevant as the aircraft is not accelerating. -- Jim Pennino Remove .spam.sux to reply. |
#283
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Backwash Causes Lift?
On Oct 8, 1:37 am, Jim Logajan wrote:
Le Chaud Lapin wrote: It's what gases do. The particles are constantly bouncing away from each other. This is pretty simple physics - something that should almost be intuitive. If you have a cylinder of gas with an air-tight piston and pull back on the piston and double the size of the volume do you seriously think the gas will not expand into the other half as fast as it can to try and stay in contact with the piston? The gas will stay in contact with the piston. But the gas will not stay in contact because of the piston head. It will stay in contact because of the fixed cylinder wall and the molecules of the gas itself. To take your example further, let us suppose that you pop the top of the cylinder so that the fixed head is no longer present. Let pressure on inside equalize to pressure on outside. Now pull the piston head again to increase the volume. The gas will follow the piston head, but not because of the piston head. It will follow because of the pressure of the molecules in the air bombarding each other, causes some of the molecules to race toward the moving piston head. In other words, the piston head is not capable of exerting a force on the air molecules that is in the direction that you just moved the piston head. In order for it to be able to do that, there would have to be an attractive force between the piston head and the molecules that follow it. But there is no attractive force. The gas expands because of intermolecular bombardment, and because of richochet from the cylinder walls. So one can say that, if you increased the volume in the chamber by moving the piston head downward, the piston head does not exert a downward force on any molecule that hits it. If you are having this much trouble on a basic concept of gases, then I see no value in you or anyone else investing time in dealing with your questions, which you chose to post to an inappropriate newsgroup anyway. Grumble. Now I recall why I had established a personal policy to stay away from discussions of aerodynamics on this newsgroup: futility avoidance. No trouble at all. -Le Chaud Lapin- |
#284
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Backwash Causes Lift?
flightoffancy wrote:
In article , says... Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis sayonara, Good lucko, NASA doesn't agree with you. Not knowing what your qualifications are I'll favor NASA's explanation of a combination of Newtonian / Bernoulli as described in part by Euler's equations, the idea being that the airfoil turns the airflow to generate lift. NASA's done a lot of experiments & measurements and have a long publication history dating back to the NACA days let alone an astonishing track record in flying high and low performance aircraft. I don't think there's any single person out there that can beat the combined knowledge of NASA's decades of experience. NASA doesn't say or even imply that Bernoulli and Newton COMBINE to create lift because they don't combine to create a total. Each is a complete explanation and can stand alone one without the other, which BTW is exactly what NASA says. DH -- Dudley Henriques |
#285
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Backwash Causes Lift?
flightoffancy wrote in news:MPG.217387a97cce62d3989691
@news-server.hot.rr.com: In article , says... Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis sayonara, Good lucko, NASA doesn't agree with you. They do, actually. Not knowing what your qualifications are I'll favor NASA's explanation of a combination of Newtonian / Bernoulli as described in part by Euler's equations, the idea being that the airfoil turns the airflow to generate lift. NASA's done a lot of experiments & measurements and have a long publication history dating back to the NACA days let alone an astonishing track record in flying high and low performance aircraft. I don't think there's any single person out there that can beat the combined knowledge of NASA's decades of experience. I don't think so either. Bertie |
#286
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Backwash Causes Lift?
Dudley Henriques wrote in
: flightoffancy wrote: In article , says... Bernoulli, Period, Full stop, end of story, finito, spaghettio, Finis sayonara, Good lucko, NASA doesn't agree with you. Not knowing what your qualifications are I'll favor NASA's explanation of a combination of Newtonian / Bernoulli as described in part by Euler's equations, the idea being that the airfoil turns the airflow to generate lift. NASA's done a lot of experiments & measurements and have a long publication history dating back to the NACA days let alone an astonishing track record in flying high and low performance aircraft. I don't think there's any single person out there that can beat the combined knowledge of NASA's decades of experience. NASA doesn't say or even imply that Bernoulli and Newton COMBINE to create lift because they don't combine to create a total. Each is a complete explanation and can stand alone one without the other, which BTW is exactly what NASA says. Yep Bertie |
#287
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Backwash Causes Lift?
Le Chaud Lapin wrote in
ups.com: On Oct 8, 1:37 am, Jim Logajan wrote: Le Chaud Lapin wrote: It's what gases do. The particles are constantly bouncing away from each other. This is pretty simple physics - something that should almost be intuitive. If you have a cylinder of gas with an air-tight piston and pull back on the piston and double the size of the volume do you seriously think the gas will not expand into the other half as fast as it can to try and stay in contact with the piston? The gas will stay in contact with the piston. But the gas will not stay in contact because of the piston head. It will stay in contact because of the fixed cylinder wall and the molecules of the gas itself. To take your example further, let us suppose that you pop the top of the cylinder so that the fixed head is no longer present. Let pressure on inside equalize to pressure on outside. Now pull the piston head again to increase the volume. The gas will follow the piston head, but not because of the piston head. It will follow because of the pressure of the molecules in the air bombarding each other, causes some of the molecules to race toward the moving piston head. In other words, the piston head is not capable of exerting a force on the air molecules that is in the direction that you just moved the piston head. In order for it to be able to do that, there would have to be an attractive force between the piston head and the molecules that follow it. But there is no attractive force. The gas expands because of intermolecular bombardment, and because of richochet from the cylinder walls. So one can say that, if you increased the volume in the chamber by moving the piston head downward, the piston head does not exert a downward force on any molecule that hits it. If you are having this much trouble on a basic concept of gases, then I see no value in you or anyone else investing time in dealing with your questions, which you chose to post to an inappropriate newsgroup anyway. Grumble. Now I recall why I had established a personal policy to stay away from discussions of aerodynamics on this newsgroup: futility avoidance. No trouble at all. "My point is that you should strive to keep your instructions simple and to the point. The people that come to an instructor for training are not in the least bit interested in leaning th emathemaical equation that keeps the airplane in an inverted turn. there only concern should be in how to use the controls to get it there" Bertie |
#288
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Backwash Causes Lift?
On Oct 8, 11:38 am, Phil wrote:
First, I would like to point out that your post is interesting because it implies at first something which I disagree with, but then at the very end of the post, what you say is exactly true. Let me try to explain: If the airflow on top of the wing doesn't contribute to lift, then how can we explain the phenomenon of the wing stalling? When the wing stalls, it is the airflow over the top of the wing that detaches from the curve of the wing and becomes turbulent. This causes a radical loss of lift. To me, this indicates that the airflow over the top of the wing plays an essential role in providing lift. What I am saying is that Newton's law is not at play with downwash, not in the "uppper surface of wing pull down on molecules" sense. Yes, there is downwash. Yes, the camber of the wing will influence the net force exerted on the wing. Yes, there will be stalling, turbulence, etc. all these things will happen. The key here is that the air molecules that are above the wing cannot be pulled down by the wing more can they pull up on the wing. Those air molecules can only causes the lateral forces of friction (laminar drag), and a perpendicular downward force on the wing which aircraft designers obviously want to keep from happening. I know the Bernoulli effect has been invoked historically to (at least partially) explain the lift produced by the top surface of a wing. I think another way to look at it is the Coanda effect (http://en.wikipedia.org/wiki/Coand%C4%83_effect). The airflow tends to follow the curve of the top of the wing, and is displaced downward. As long as the air flow follows the curve faithfully, you have good lift. When the airflow detaches in a stall, you lose most of your lift. This top surface lift is combined with the downward displacement of air by the bottom of the wing. The wing is essentially throwing air downward using both the top and bottom surfaces. This is why a curved wing is a better lift producer than a simple flat wing. The top surface curve helps contribute to the lift. I agree that air is being thrown downward by the bottom surface. I do not think a top surfaces throws air downward. Even this Coanda effect says that contact, at least initially, is caused by a pressure differential. From your link above: "As a gas flows over an airfoil, the gas is drawn down to adhere to the airfoil by a combination of the greater pressure above the gas flow and the lower pressure below the flow caused by an evacuating effect of the flow itself, which as a result of shear, entrains the slow-moving fluid trapped between the flow and the down-stream end of the upper surface of the airfoil. The effect of a spoon apparently attracting a flow of water is caused by this effect as well, since the flow of water entrains gases to flow down along the stream, and these gases are then pulled, along with the flow of water, in towards the spoon, as a result of the pressure differential. Supersonic flows have a different response." "greater pressure above the gas flow and the lower pressure below the flow caused by an evacuating effect..." This is what I keep saying. I have been using the words "rarefication and rarefaction" and instead of "evacuating effect", but this is essentially what I mean. Now, how does the wing feel the lift? It feels high pressure on its bottom surface, and it feels low pressure on its upper surface. It is pushed up from below, and sucked up from above. That is how the airplane experiences the effects of the downward displacement of air. I agree with the downward force. I do not agree that there is a sucking force above, any more than I agree that there is a sucking force when a purpose sucks on a straw. Given that the bottom surfaces of the wing is already 14.7lbs/in^2, one simply needs to reduce the pressure above the wing to cause lift. This is what I tried to illustrate with my two-pieces-of-paper- superposed demonstration. But in many cases the bottom surface has even more than 14.7lbs/^2. -Le Chaud Lapin- |
#289
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Backwash Causes Lift?
On Oct 8, 12:32 pm, Phil wrote:
There isn't any debate about what a wing stall is, and what causes it. It has been well-explored in wind tunnel testing. The phenomenon of wing stall is real-world evidence that the top surface of the wing is a large contributor to lift. The Bernoulli effect and the associated Coanda effect are well-understood scientific phenomena. They explain how the curved top surface of the wing displaces air downward. Unless someone can come up with a better explanation for the fact that wing stall destroys lift, I think the only debate is by people who are determined to ignore the scientific evidence. On Oct 8, 12:32 pm, Phil wrote: On Oct 8, 11:46 am, Mxsmanic wrote: There isn't any debate about what a wing stall is, and what causes it. It has been well-explored in wind tunnel testing. The phenomenon of wing stall is real-world evidence that the top surface of the wing is a large contributor to lift. The Bernoulli effect and the associated Coanda effect are well-understood scientific phenomena. They explain how the curved top surface of the wing displaces air downward. Unless someone can come up with a better explanation for the fact that wing stall destroys lift, I think the only debate is by people who are determined to ignore the scientific evidence. What's wrong with the supposition that, all other things being equal, the configuration of the fluid in a smooth stream results in less pressure on the upper surface than the configuration of the fluid in turbulence? In other words, one could argue that the fluid above the wing, during streaming (sorry for terminology), no longer exerts its full 14.7lbs/ in^2, but during a stall, even though there is still is some reduction from the full 14.7lbs/in^2, the reduction is not as complete as it would have been had there been a nice stream... -Le Chaud Lapin- |
#290
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Backwash Causes Lift?
Le Chaud Lapin wrote in
ups.com: On Oct 8, 11:38 am, Phil wrote: First, I would like to point out that your post is interesting because it implies at first something which I disagree with, but then at the very end of the post, what you say is exactly true. Let me try to explain: If the airflow on top of the wing doesn't contribute to lift, then how can we explain the phenomenon of the wing stalling? When the wing stalls, it is the airflow over the top of the wing that detaches from the curve of the wing and becomes turbulent. This causes a radical loss of lift. To me, this indicates that the airflow over the top of the wing plays an essential role in providing lift. What I am saying is that Newton's law is not at play with downwash, not in the "uppper surface of wing pull down on molecules" sense. Yes, there is downwash. Yes, the camber of the wing will influence the net force exerted on the wing. Yes, there will be stalling, turbulence, etc. all these things will happen. The key here is that the air molecules that are above the wing cannot be pulled down by the wing more can they pull up on the wing. Those air molecules can only causes the lateral forces of friction (laminar drag), and a perpendicular downward force on the wing which aircraft designers obviously want to keep from happening. I know the Bernoulli effect has been invoked historically to (at least partially) explain the lift produced by the top surface of a wing. I think another way to look at it is the Coanda effect (http://en.wikipedia.org/wiki/Coand%C4%83_effect). The airflow tends to follow the curve of the top of the wing, and is displaced downward. As long as the air flow follows the curve faithfully, you have good lift. When the airflow detaches in a stall, you lose most of your lift. This top surface lift is combined with the downward displacement of air by the bottom of the wing. The wing is essentially throwing air downward using both the top and bottom surfaces. This is why a curved wing is a better lift producer than a simple flat wing. The top surface curve helps contribute to the lift. I agree that air is being thrown downward by the bottom surface. I do not think a top surfaces throws air downward. Even this Coanda effect says that contact, at least initially, is caused by a pressure differential. From your link above: "As a gas flows over an airfoil, the gas is drawn down to adhere to the airfoil by a combination of the greater pressure above the gas flow and the lower pressure below the flow caused by an evacuating effect of the flow itself, which as a result of shear, entrains the slow-moving fluid trapped between the flow and the down-stream end of the upper surface of the airfoil. The effect of a spoon apparently attracting a flow of water is caused by this effect as well, since the flow of water entrains gases to flow down along the stream, and these gases are then pulled, along with the flow of water, in towards the spoon, as a result of the pressure differential. Supersonic flows have a different response." "greater pressure above the gas flow and the lower pressure below the flow caused by an evacuating effect..." This is what I keep saying. I have been using the words "rarefication and rarefaction" and instead of "evacuating effect", but this is essentially what I mean. Now, how does the wing feel the lift? It feels high pressure on its bottom surface, and it feels low pressure on its upper surface. It is pushed up from below, and sucked up from above. That is how the airplane experiences the effects of the downward displacement of air. I agree with the downward force. I do not agree that there is a sucking force above, any more than I agree that there is a sucking force when a purpose sucks on a straw. Given that the bottom surfaces of the wing is already 14.7lbs/in^2, one simply needs to reduce the pressure above the wing to cause lift. This is what I tried to illustrate with my two-pieces-of-paper- superposed demonstration. But in many cases the bottom surface has even more than 14.7lbs/^2. Meanwhile your airplane is tearing along and you don't have a notion what to do with it. Bertie |
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