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#41
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Backwash Causes Lift?
On Oct 3, 10:34 am, wrote:
Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. -Le Chaud Lapin- |
#42
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Backwash Causes Lift?
Le Chaud Lapin writes:
For example, as I mentioned earlier, I am reading Jeppesens Private Pilot manual, and there are clearly errors in concept the manual (energy being created by engine, for example), even though Jeppensen probably has access to as many Ph.D. laureates as they want. Describe the errors in a letter and send it to them. Good technical publishers are always willing to accept corrections. |
#43
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Backwash Causes Lift?
Le Chaud Lapin wrote in
oups.com: On Oct 3, 10:34 am, wrote: On Oct 3, 8:15 am, Le Chaud Lapin wrote: Actually I did because every book I read about flying skimped on the subject. I'm going to hop over to MIT's OpenCourseWare later this week and download their most basic course on aero/astro. Benoulli's principle is toss around as if it were facecloth, but I'm getting the feeling that no one is really doing the physics. Lemme see: People have been building flying machines since the late 1800's, about 125 years now, and none of them have been interested enough in the phenomenon of lift to do the physics? How old are you, anyway? Many of the contributors here have been flying much longer than you have likely been alive and have studied this in detail, and some of them might even have doctorates in the subject. The subject of lift has been beaten to death on this forum and if you Googled it you'd find some good information. I want to be clear. I did not me to say "no one" is doing the physics. Obviously there are aero/astro scientists all over the world. What I mean to say is that there seems to be a lot of *pilots* who are using Bernoulli's principle somewhat carelessly, IMO. Some of these people are CFI's. Please don't ask me to name individuals, but I know with certainty that there are at least 2 living, breathing CFI's who do not understand where 29.92 Hg comes from, or does not understand it well enough to make it make sense to a student. The might have understood it at one point, but they don't now. I know because I asked them. My feelings about teaching is that if you are not very certain about something, you do more damage than talking about it. Of course, this leads to the conundrum of having to explain to a student why a plane stays in the air without providing erroneous information. If I were a CFI, I would simply say that the aerodynamics result in pressure below plane is sufficient to counteract pressure above planes for force of gravity. That's not enough either. you need to know how and why lift varies throughot the flight envelope, but after th ebook learning, it's mostly intuitive and the intuition comes from experience. Bertie |
#45
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Backwash Causes Lift?
Le Chaud Lapin wrote in
ups.com: On Oct 3, 10:34 am, wrote: Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. Couldn't be clearer and it's really all you need to know. Go out and fly now. If you ask any more questions I'l just hand you over to Anthony from now on. Tough love. Bertie |
#46
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Backwash Causes Lift?
On Oct 3, 12:05 pm, Bertie the Bunyip wrote:
Le Chaud Lapin wrote roups.com: On Oct 3, 10:34 am, wrote: Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. Couldn't be clearer and it's really all you need to know. Go out and fly now. If you ask any more questions I'l just hand you over to Anthony from now on. I don't think actually flying an airplane will explain the aerodynamics of lift any more than driving a car will help with understanding of rack-and-pinion. Yes, there will be an an intuition that will develop, but that's going to happen anyway, and that would have happened even if I were a 16-year-old sitting in pilot's seat. Doesn't mean that 16-year-old is going to understand aerodynamics. Let's face it. A large pecentage of people walking this planet think there is a "suction" force. I was watching the History Channel one day, and the narrator actually used that term - a "suction" force, and he did not mean the force that is on the other side of the barrier where the "suction" force was being applied. I've also seen countless erroneous explantions on the same channel about electronics which I do know about. Typically the narrator will say voltage when he meant current, or energy when he meant power. I'm more of a mind-over-matter type. I'll get my license and fly around and develop the intuition that you mention, certainly, but that's not enough. -Le Chaud Lapin- |
#47
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Backwash Causes Lift?
Le Chaud Lapin wrote in
ups.com: On Oct 3, 12:05 pm, Bertie the Bunyip wrote: Le Chaud Lapin wrote roups.com: On Oct 3, 10:34 am, wrote: Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. Couldn't be clearer and it's really all you need to know. Go out and fly now. If you ask any more questions I'l just hand you over to Anthony from now on. I don't think actually flying an airplane will explain the aerodynamics of lift any more than driving a car will help with understanding of rack-and-pinion. Well, then you're a lost cause. Ask Anthony and be damned, then Bertie |
#48
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Backwash Causes Lift?
On Oct 3, 10:56 am, Le Chaud Lapin wrote:
On Oct 3, 10:34 am, wrote: Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. -Le Chaud Lapin- See http://www.petester.com/html/bachap02.html or Google yourself using terms like static, dynamic pressures, kinetic energy, converging or diverging ducts, net energy, and so on. If we have gas flow in a pipe, and if we had a static gauge and a dynamic pressure gauge (airspeed), we would see the static pressure fall as the airspeed rose. If the no-movement static pressure was 29.92" hg, the dynamic pressure would be zero. As the speed comes up to, say, 10" hg on the dynamic, the static will fall 10" to 19.92. There is no free lunch. The static and dynamic always add up to the same figure as speed increases or decreases, unless there is further energy input as in a turbine combustion section. As I said, it's not intuitive. Converging and diverging ducts do different things than you'd expect, but we know they work because the turbine engine uses their principles, and wouldn't work without them. Dan |
#49
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Backwash Causes Lift?
On Oct 3, 1:33 pm, wrote:
On Oct 3, 10:56 am, Le Chaud Lapin wrote: On Oct 3, 10:34 am, wrote: Both Newton and Bernoulli are correct. Even inside a pipe the static pressure drops as velocity increases. That's why your bottom table jumps as you yank off the top one: you accelerated an airflow. And in generating lift there's a displacement of air. Can't escape that at all. Also, if you don't mind, I would like to understand what you mean here. It's not clear to me. [explanation of Bernoulli's principle clipped]. I did not mean that I did not understand Bernoulli's principle. What I am saying is that I do not believe that the bottom table jumps because of airflow acceleration. In fact, if I were to use tables with circular faces, and put the entire apparatus in a giant cylindrical tube, and pull up on the top table, assuming that the very bottom of the tube were open-ended, the bottom table would follow the top table upward, no matter how fast any air inside the tube were moving. I could move the top table one molecular diameter every 10,000,000 years, and after the top table has moved, say, 0.5 meters, the bottom table will follow. This assumes, of course, that the appartus is airtight, that no air from outside the tube can squeeze in between the walls of table and tube to fill the void that was created. There are 14.7 lbs per square inch of pressure pressing upward against the underside of the bottom table. The yanking of the top table creates a vacuum between the two faces of the table. The lack of pressure on the top of the bottom table leaves nothing to counteract the pressure pressing upward on the underside of the bottom table. Then the only thing holding the bottom table on the floor is gravity. Assuming that the table is a typical table of typical weight and size, one is guranteed that the impulse net pressure of 14.7lbs / in^2 is enough to overcome gravity and lift the bottom table off the floor. Note that this really has nothing to do with Bernoulli's principle or dynamic pressures. If it is still not clear, put the assembly in a tube again, anchor the bottom table with a tie wire so it cannot move upward, and using a hydraulic jack, pull the top table upward, then stop, wait a minute, have a Coke (sipping with a straw of course), then take cutters and snap the wire holding the bottom table to the floor. At the precise moment that the wire is snapped, there is no movement of anthing at all. There is no Bernoulli action. The bottom table will rush up toward the top table, even slamming against it quite hard if the coefficient of sliding friction between table-side and tube wall is low enough. -Le Chaud Lapin- |
#50
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Backwash Causes Lift?
"Le Chaud Lapin" wrote in message I'm saying that, if you take a plane with certain critical angle, throw away engine, put on an engine that can generate 10x the thrust, the plane should still fly, even if you exceed critical angle. These books imply that the critical angle is angle at with bad things happen above the wing, and because of that, the plane will fall. I'm saying that, you can have all the bad things happen above the wing and still be able to keep the plane aloft due to compression that occurs beneath the wing. Of course, I have only been doing this officially 7 weeks, so I might be wrong. You are. With a stronger engine, the wing would still be stalled. You would be flying on the thrust of the engine. Disruption of the flow on the top side of the wing is what defines a stall. The wing would create only a fraction of the list that it would, unstalled. -- Jim in NC |
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