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#151
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visualisation of the lift distribution over a wing
In article ,
Beryl wrote: Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. What do you suppose happens to "downwash" when it goes up? Say, pulling positive G force at the top of a loop? Now you lost the surface of the earth, the only thing that, according to you, finally stops it. The earth still stops it: Gravity: perhaps you've heard of it? -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#152
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visualisation of the lift distribution over a wing
Alan Baker wrote:
In article , Beryl wrote: Alan Baker wrote: In article , Jim Logajan wrote: You must have a devil of a time figuring out what keeps balloons afloat, what with no handy downward moving air! I have no trouble figuring that out at all. A gas of a different density within the balloon causes the net upward force on the balloon exerted by the air outside the balloon to be greater than the net downward force on it. Nope! The "gas of a different density" inside does not cause the differential forces exerted by the air outside. Whether the balloon is filled with phlogiston or concrete, the difference between upward and downward forces exerted by the air outside depends on the height of the balloon. That's what my goofy 10,000 foot thick wing was, that would take off with no airspeed or power. A balloon. You're wrong. The "net downward force" includes the force of gravity. Which is lessened because a gas of lower density.. ...I can't believe I have to explain things so basic. I know, but you have to. Your first attempt didn't appear to include unsaid gravity. Gas that you described as "within the balloon" is now treated as "part of" the balloon. |
#153
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visualisation of the lift distribution over a wing
In article ,
Beryl wrote: Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: In article , Jim Logajan wrote: You must have a devil of a time figuring out what keeps balloons afloat, what with no handy downward moving air! I have no trouble figuring that out at all. A gas of a different density within the balloon causes the net upward force on the balloon exerted by the air outside the balloon to be greater than the net downward force on it. Nope! The "gas of a different density" inside does not cause the differential forces exerted by the air outside. Whether the balloon is filled with phlogiston or concrete, the difference between upward and downward forces exerted by the air outside depends on the height of the balloon. That's what my goofy 10,000 foot thick wing was, that would take off with no airspeed or power. A balloon. You're wrong. The "net downward force" includes the force of gravity. Which is lessened because a gas of lower density.. ...I can't believe I have to explain things so basic. I know, but you have to. Your first attempt didn't appear to include unsaid gravity. Gas that you described as "within the balloon" is now treated as "part of" the balloon. Of course gas within the balloon is part of the ballon. Nothing I said ever implied otherwise. -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#154
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visualisation of the lift distribution over a wing
Alan Baker wrote:
In article , Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. Yes, but Newton's laws tell us that there is a net force down on the air. No net force down on the air, no net force up on the plane. Force is change of momentum with respect to time. BTW, the man whom you are contradicting I don't think I contradicted anything there. Point it out. is Scott Eberhardt, Bachelors & Masters Degrees in Aeronautics and Astronautics from MIT, Ph.D. in the same field from Stanford, research scientist at the NASA Ames Research Center, faculty of the University of Washington. But... ...really... http://books.google.com/books?id=wmu...T5&dq=Scott+Eb erhardt+aeronautics+and+astronautics&source=bl&ots =skN-zbDvej&sig=msQ-_Im p6t-P62ehNWIld7RRYWs&hl=en&ei=GgEeS4f4AYzStgPB5eiCCg&s a=X&oi=book_result& ct=result&resnum=6&ved=0CBsQ6AEwBQ#v=onepage&q=dow nwash&f=false ...what would *HE* know about it compared to you? Likely a lot, and possibly nothing. I've encountered more than a couple supposed "authorities" on specific subjects who don't know squat, but they're masters at bull****ting their ways to lofty titles and positions. Did you know that a gas cools as it's compressed? One layer of the atmosphere is called the hemisphere? The stuff in grass that makes it green is chloroform? A jet fighter cruising straight and level at high speed experiences tremendous G forces due to the speed? |
#155
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visualisation of the lift distribution over a wing
Alan Baker wrote:
In article , Beryl wrote: Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. What do you suppose happens to "downwash" when it goes up? Say, pulling positive G force at the top of a loop? Now you lost the surface of the earth, the only thing that, according to you, finally stops it. The earth still stops it: Gravity: perhaps you've heard of it? Gravity is not the earth. |
#156
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visualisation of the lift distribution over a wing
Alan Baker wrote:
In article , Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. Yes, but Newton's laws tell us that there is a net force down on the air. No net force down on the air, no net force up on the plane. Force is change of momentum with respect to time. BTW, the man whom you are contradicting is Scott Eberhardt, Bachelors & I wasn't, but I will now. "...the wing then throws the air downwards" is just plain wrong. "Downwards" is not a direction that the air was *ever* thrown. |
#157
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visualisation of the lift distribution over a wing
In article ,
Beryl wrote: Alan Baker wrote: In article , Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. Yes, but Newton's laws tell us that there is a net force down on the air. No net force down on the air, no net force up on the plane. Force is change of momentum with respect to time. BTW, the man whom you are contradicting I don't think I contradicted anything there. Point it out. is Scott Eberhardt, Bachelors & Masters Degrees in Aeronautics and Astronautics from MIT, Ph.D. in the same field from Stanford, research scientist at the NASA Ames Research Center, faculty of the University of Washington. But... ...really... http://books.google.com/books?id=wmu...T5&dq=Scott+Eb erhardt+aeronautics+and+astronautics&source=bl&ots =skN-zbDvej&sig=msQ-_Im p6t-P62ehNWIld7RRYWs&hl=en&ei=GgEeS4f4AYzStgPB5eiCCg&s a=X&oi=book_result& ct=result&resnum=6&ved=0CBsQ6AEwBQ#v=onepage&q=dow nwash&f=false ...what would *HE* know about it compared to you? Likely a lot, and possibly nothing. I've encountered more than a couple supposed "authorities" on specific subjects who don't know squat, but they're masters at bull****ting their ways to lofty titles and positions. Did you know that a gas cools as it's compressed? One layer of the atmosphere is called the hemisphere? The stuff in grass that makes it green is chloroform? A jet fighter cruising straight and level at high speed experiences tremendous G forces due to the speed? Sorry, but if I have to trust what you understand versus what he understands, it isn't even a contest. And I'd like to see you show just *who* is supposed to have said those things and whether they are actually educated in the appropriate fields. -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#158
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visualisation of the lift distribution over a wing
In article ,
Beryl wrote: Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. What do you suppose happens to "downwash" when it goes up? Say, pulling positive G force at the top of a loop? Now you lost the surface of the earth, the only thing that, according to you, finally stops it. The earth still stops it: Gravity: perhaps you've heard of it? Gravity is not the earth. LOL -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#159
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visualisation of the lift distribution over a wing
In article ,
Beryl wrote: Alan Baker wrote: In article , Alan Baker wrote: In article , Beryl wrote: Alan Baker wrote: It's true that the exhaust stream doesn't directly push on the inner surface of a rocket engine. Yeah, I like that aerospike design, the inside-out nozzle thing. wing encounters some unmoving air, and the wing then throws the air downwards, the velocity of the air has been changed, and the wing will experience an upwards reaction force. At the same time, a downwash- flow is created. The wing, remember, is moving forward. "Downwards" is one component of circulation. Those weren't my words. Yes, but Newton's laws tell us that there is a net force down on the air. No net force down on the air, no net force up on the plane. Force is change of momentum with respect to time. BTW, the man whom you are contradicting is Scott Eberhardt, Bachelors & I wasn't, but I will now. "...the wing then throws the air downwards" is just plain wrong. "Downwards" is not a direction that the air was *ever* thrown. You are incorrect. The plane experiences a force upwards from the air, therefore (and this is inescapable basic Newtonian physics) the air experiences a force downward from the aircraft. Bachelors and Masters from MIT, Ph.D. from Stanford, all in Aeronautics and Astronautics, but you know better! LOL -- Alan Baker Vancouver, British Columbia http://gallery.me.com/alangbaker/100008/DSCF0162/web.jpg |
#160
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visualisation of the lift distribution over a wing
Alan Baker wrote:
Jim Logajan wrote: Alan Baker wrote: Look if you think that conservation of *mass* plays any role in this, you're missing out from the start. It's conservation of *momentum* that's in play here. It appears you have never studied fluid dynamics (maybe elementary fluid statics?) and I doubt that you own any books on the subject. Sorry, lad, but conservation of mass is a principle that comes up mostly in *chemistry*. Please don't patronize when you've never studied a subject. A moment's research would have prevented you from posting something that incredibly ignorant. You might want to look up the "axioms of fluid dynamics" before you further add to your public embarrassment. The aircraft has a force exerted on it equal to its weight. That means that the aircraft must be exerting a force on the air in the opposite direction. In other news, 1 + 1 = 2. What a pity then that you don't understand it. Shrug - your insults are lame and tiresome, but I will admit you're patronization is irritating. I do make mistakes about things I was taught, but I should point out to you that I did well enough in college physics to earn an undergraduate degree in the subject. Unlike you, I have had to solve a **** load of problems involving conservation of momentum to prove I understood the basics - including conservation of momentum in quantum mechanical systems. So far as I know, you HAVEN'T had to prove your mastery of the subject with ANYONE. (Just FYI, imagine a ~957 kg (Fg ~= 9379 N) helicopter dropped from a balloon from 3,000 m altitude (rho ~= 0.83 kg/m^3) and it's engine immediately started. After a small drop it levels out and maintains a downwash of air moving through its 6 m diameter disk (A ~= 28 m^2) at, say, 20 m/s. (So m_dot ~= 469 kg/s and hence Fe = Fg.) It would take ~150 s for that downwash to reach the ground if it maintained that speed. In the mean time, once the helicopter stopped descending, conservation of mass in an incompressible fluid seems to require an equal volume of air to have an upward vector of 20 m/s. So the surface of earth appears to be irrelevant for over two minutes.) Nope. Dang - I try to use real numbers to establish a baseline example, and you manage to use a single word to demolish my attempts! Really helpful mathematical counter-example you produced - not. No math is necessary for this. Look up "qualitative analysis". Well that probably explains your problem - you don't know how to set up the math properly, so you have no way to validate whether your "qualitative analysis" is correct. Ironically, all your posts contain the same violation of conservation of momentum - and yet you keep pointing to that concept as vindication. I don't know what your problem is - maybe you are thinking this is a rocket problem where no external fluids are involved and you can't get your mind around the fact that THIS ISN'T A BLOODY ROCKET PROBLEM. Whatever the case, you seem to be fixated on applying one conservation law to one element in the entire system to the exclusion of everything else. The law I'm focussed on is the one that counts. It doesn't matter whether the fluid is expelled from inside or whether it's an external fluid diverted down by the surfaces of the craft. You can't "focus" on one conservation law because the number of constraining equations has to equal the number of variables. Doing so simply leads to an infinite number of bogus results. In order for there to be a continuous force W equaling the weight of the craft acting on it, the craft must exert a force -W on the fluid. That -W means that there is a downward change of momentum in the fluid. Sigh. This is a case where a little knowledge is a dangerous thing. It would take a book to explain the problem with your conceptual view of fluid dynamics. I don't have that sort of patience. Since the fluid is no accelerated indefinitely, there must be a continuous flow (mass per unit time M/t) of the fluid accelerated to a velocity V where the equation looks like: -W = M/t * V Of course if you had read my earlier post you'd see I'd ALREADY USED THAT EQUATION. But you obviously aren't familiar with the conventions used in fluid dynamics, so you probably had no clue what my "m_dot" meant or how I got the figures I did. The velocity of the fluid will be: V = -W/(M/t) That is inescapable. If the craft weighs 9800N (newtons), and it moves 100kg of air every second, then the air must be moving downward (net, now!) at 98 m/s. You math is correct and no one has denied there is a downwash (why you think otherwise continues to baffle me) yet your "net, now" comment violates conservation of momentum. Here's why: If we choose a reference frame so that at T=0 everything in the system is stationary with respect to that frame, we set the net momentum of the system to 0. Then, so long as the system remains closed, at all other times the conservation of momentum must yield 0. But according to your "qualitative analysis" the net vertical momentum P_net_z increases with time T, like so: P_net_z(T) = (100 kg/s)*T*V That's because the earth and the airplane maintain zero vertical momentums (P_earth_z(T) = 0, P_plane_z(T) = 0,) and there appears to be nothing in your conceptual view of the situation to correct that violation of conservation of momentum. I'm sorry if you don't get this, but it is very simple and absolutely irrefutable. It appears to salve your ego to ascribe assertions to me that I never made and then tell the world that those falsehoods prove I don't "get it." Probably because you've grown so much hubris and so little humility. |
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