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User talk:Dolphin51/Archive 1
Static marginDear Dolphin51: I like the improvements on center of pressure and static margin. I have one question; why are you distinguishing between neutral point and center of pressure. on the center of pressure page you introduce neutral point but it is not obvious to the non-technical reader what it has to do with the previous discussion on center of pressure. It seems to be an orphaned section. I am an educated reader on the subject and I seem to be missing some subtlety that you are tyring to make.02:22, 3 December 2007 (UTC) —Preceding unsigned comment added by Mangogirl2 (talk • contribs) Dolphin51: Missile people use center of pressure as the stick fixed location (no elevator deflection) of the aero forces on the airframe for epsilon angle of attack. Thus, the center of pressure at zero angle of atttack is defined as a the location of the center of pressure for the resulting pressure field at finite but small angle of attack. The center of pressure cannot be located at an infinite distance since you take the limit. We speak of the center of pressure at very small angle of attack. You calucalte the center of pressue use tail volumes, etc. Saying the neutral point is the definition of static margin is a circular argument for the non-technical reader. It provides no physical explanation. It really has to do with the lift curve slopes and locations of the wing and tail. The aerodynamic prediction code aeroprediction produces a zero angle of attack center of pressure location. Since my explanation is not strictly correct why don't we delete the discussion of static margin and aerodynamic center related to stability. The aerodynamic center is orphaned also. Also we should get rid of the neutral point discussion. Mangogirl2 (talk) 23:05, 4 December 2007 (UTC) Dolphin51:I have trouble following your changes to static margin. I feel that if the cg is ahead of the neutral point this should be call positive static margin. Maybe this is a country difference. Please look at the following link for some slides that I think agree with me.http://ocw.mit.edu/NR/rdonlyres/Aeronautics-and-Astronautics/16-885JFall-2004/6B524E1F-39F5-4E57-9B0E-812B40A21CED/0/aircraft_murman.pdfMangogirl2 (talk) 20:30, 12 December 2007 (UTC) Thanks for your kind invite to have a look at this article as it evolves - I should warn you that I'm not a formally trained aeronautics engineer or fluid dynamicist - just a half-trained planetary radio-astronomer :-). So when faced with questions that need clear thinking on fluids fundamentals, I usually reach for my copy of Batchelor! (I've had an article sketched out in my sandbox entitled 'classical theory of lift', which was also meant to be based on Batchelor's discussion, but which has made little progress in the last year). I'll try and drop by the article over the next few days. Bob aka Linuxlad 15:51, 4 December 2007 (UTC) Thank you for leaving notes on my user page, about your posts on Static pressure, but you don't need to, because that page is already in my watchlist, so that I get notified automatically. Regards. Giuliopp (talk) 23:55, 11 December 2007 (UTC) Dolphin51: looks like you are on top of the issue. I will stay out of it. It does seem to be a cultural practice difference. I have worked with UK folks on the guidance issue to some degree and never notices the difference. In fact we cowrote documents together and I never noticed a problem. I know you know what you are talking about. I will have to rewrite my definition of center of pressure to make more sense to the layman. I just reading an internal document about air vehicle stability and they used center of pressure and static margin consistent with my original use but I believe it is a case of all of us knowing what we mean and the explanation is not strictly corrrect for the unintiated. I will have rewrite missile center of pressure to be more transparent.Mangogirl2 (talk) 15:31, 20 December 2007 (UTC) Here is a link that I believe matcher Mangogirl2's view of center of pressure of an entire vehicle. http://exploration.grc.nasa.gov/education/rocket/rktcp.htmlMangogirl2 (talk) 19:48, 21 December 2007 (UTC) Your concerns regarding the Bernoulli's Principle articleHello! I understand your concerns regarding the section the tries to do away with BP as the main source behind lift. Explaining away one faulty explanation with one a little less faulty but still lacking explanation can certainly put a strain on one's sense of accuracy. I have however argued - on talk:Bernoulli's principle - that we should keep the section mostly intact. For my reasons for feeling this way, please see that page and continue the discussion there. And thank you for the heads up. :) --J-Star (talk) 12:33, 31 December 2007 (UTC)
Static Margindolphin51 -- Just read Static Margin. It is really good now. Good job. This has been an enjoyable experience in that it sharpened my understanding of somtehing I had gotten somewhat blase about. Thanks for challenging me. I have been roving the aerospace topics over the last year. So maybe we meet. I hope you have a good year in 2008. Mangogirl2 (talk) 04:47, 8 January 2008 (UTC) Static PressureLooks really good now. Gman is really belaboring a point that needs no belaboring. Words mean what we choose them to mean. Ever instance I have ever seen in fluid dynamics agrees with you. Gman repeated point about dynamic pressure not being a real pressure is unwarranted. For an isentropic reduction in speed the stagnation pressure is the "static" pressure plus the dynamic pressure (as we all know). Dynamic pressure is as real as any thing else. Way to go.—Preceding unsigned comment added by Mangogirl2 (talk • contribs) 01:53, 16 January 2008 (UTC)
Gman has written (17 Jan 08) Dolphin51 is … wrong about total or - better - stagnation pressure, which is indeed defined as the force per unit area in the fluid, at a stagnation point and can be measured with any Pitot tube. I agree that total pressure and stagnation pressure are identical numerically in incompressible flow, and also in isentropic compressible flow. For that reason we regularly interchange them. However, the two are not synonymous. The concept of total pressure has meaning at every point in a fluid flow field. Stagnation pressure is simply the pressure (aka static pressure) at a stagnation point (and there may be no stagnation point in the flow field.) I maintain that it is not possible to measure total pressure. When people want to know the total pressure along a streamline, or in the efflux from a reservoir, they can be ingenious and artificially create a stagnation point, usually by inserting a Pitot tube in the flow. They can then rely on the fact that stagnation pressure is numerically equal to total pressure and state confidently that the total pressure along the streamline is equal to the pressure measured using the Pitot tube. In supersonic flow the stagnation pressure downstream of a shock is not equal to the total pressure upstream of the shock. As a consequence, a good deal more ingenuity is needed to compute the total pressure. In summary, total pressure is a mathematical concept and is not amenable to measurement, but stagnation pressure, being a pressure (aka static pressure) is readily amenable to measurement. It is meaningful to contemplate the total pressure in the flow in a nozzle or diffuser, but it is not meaningful to contemplate the stagnation pressure in a nozzle of diffuser because clearly there is no stagnation point in such a device. Dolphin51 (talk) 11:30, 20 January 2008 (UTC)
Haven't heard much from you in a while.Mangogirl2 (talk) 01:48, 5 March 2008 (UTC) Dolphin51: I missed the Feb 7 note. Also, I ran out of things that I know enough to write about. Been busy with Science Fairs. Do they have them in your country? Mangogirl2 (talk) 03:25, 7 March 2008 (UTC)
Dolph51: There is a good description on Wikipedia under science fair I have changed my name to skimaniac. —Preceding unsigned comment added by Skimaniac (talk • contribs) 18:23, 13 March 2008 (UTC) Load factor (aerodynamics)I had to cut a major part out of Load factor (aerodynamics) because of copyright violations. Now the article has no introduction. If you have time, can you give it an introduction? Cheers, Kingturtle (talk) 13:22, 12 March 2008 (UTC) Thanks Kingturtle. I have posted a reply on your User talk page. I have also initiated a discussion on the Talk:Load factor page. Dolphin51 (talk) 00:34, 13 March 2008 (UTC) Thanks for your recent edits to Vortex generator. Your info there looks pretty accurate and reasonable, but other than citing two FAR/air regs, you haven't provided any refs for the information. My own experience suggests that your info is right, but I don't have a ref to back it it. All factual edits in Wikipedia must be supported by references see WP:citing sources. Lately Wikipedia has been under the gun in the general press for doing damage with unreferenced articles. For anyone who doesn't think it is important for Wikipedia to be scrupulously referenced, I suggest that you read this CBC article. A lack of references can cause real damage in some cases. Obviously your edit on vortex generators isn't going to get anyone labeled a terrorist, but refs are still needed! - Ahunt (talk) 11:13, 14 March 2008 (UTC)
Edit of 203.218.190.157 on Bernoulli's principleHi Dolphin51. It is very well possible that 203.218.190.157, who seems to be new to WP, did his removal of this example in good faith. The example is quite dubious, given all discussions about "misunderstandings" on lift. Crowsnest (talk) 11:38, 25 March 2008 (UTC) Hi Crowsnest. I see that you and the special contributor have deleted the description of lift and Bernoulli's principle. You will notice that the text you deleted contained a reference: When a stream of air flows past an airfoil, there are local changes in velocity round the airfoil, and consequently changes in static pressure, in accordance with Bernoulli’s Theorem. The distribution of pressure determines the lift, pitching moment and form drag of the airfoil, and the position of its centre of pressure.” Clancy, L.J., Aerodynamics , Section 5.5 This is a very, very powerful reference. Very powerful indeed. This book is very comprehensive in the field on aerodynamics, and its author L.J. Clancy is one of the doyens of aerodynamics, at least in Europe. In contrast, the Bernoulli Sceptics (you are one of these) never, never quote a reference of any kind when you do your work. The threshold for inclusion in Wikipedia is verifiability, not truth. See WP:Verifiability. Whether your deletion is true or not is of secondary importance. Verifiability is paramount and I have provided the reference to Clancy's words on the matter. What do you have to say about verifiability of your point of view? If you have a reference, please reveal what it is. If you don't, please immediately re-instate the text you have deleted. It is not sufficient to say "see the discussions on lift". There is a lot of material on the Talk:Lift page. I don't intent to wade through it to find what you have in mind, or to find a reference for you. Dolphin51 (talk) 11:51, 25 March 2008 (UTC)
Troll? Is it possible that Rcgldr/203.218.190.157 is a troll? Based on this entry:
I'm beginning to have my suspicions... ComputerGeezer (talk) 22:50, 1 April 2008 (UTC) Hi ComputerGeezer. I don't think he is a troll. I think his enthusiasm for participating on matters of aviation greatly exceeds his expertise. So far his efforts have been harmless because he has not edited the main article, only the Talk page. He only started contributing to Wikipedia on 31 March, and everything he has contributed has been on the Bernoulli Talk page. He displays a high degree of self-confidence but his writings don't warrant that self-confidence. He mostly writes nonsense. I am about to comment on his latest contribution. Best regards. Dolphin51 (talk) 11:03, 2 April 2008 (UTC)
Hi. Thanks for your message and its "heads up". Maybe one day Wikipedia will include an Automated Edit Warning System that features a "LINK UP!" alert... Sardanaphalus (talk) 12:12, 30 March 2008 (UTC) PS The way in which creatures such as dolphins move so rapidly through water with such seemingly work-defying ease is one of those natural wonders I'm particularly impressed by. Thanks for the reminder on your userpage. thanks: wing WarpingI added references explicitly. Since I had linked to the Wright Brothers Page and to the wing warping page that had references to authoritative sources, i thought I didn't have to insert them in the section I added. The Wright Bros page talks extensively about the lack of realization of the need for aircraft control before the Wrights. The other big contribution of the Wrights was the wind tunnel for scale model testing. Saltysailor (talk) 02:35, 9 May 2008 (UTC) AfD nomination of Laurence ClancyI have nominated Laurence Clancy, an article you created, for deletion. I do not feel that this article satisfies Wikipedia's criteria for inclusion, and have explained why at Wikipedia:Articles for deletion/Laurence Clancy. Your opinions on the matter are welcome at that same discussion page; also, you are welcome to edit the article to address these concerns. Thank you for your time. Do you want to opt out of receiving this notice? RolandR (talk) 12:44, 11 May 2008 (UTC)
Talk:Spin (flight)I have never flown an aircraft as Pilot In Command but I grew up on a airport and had AvGas in my blood for most of my younger years. I just never went as far as to get flight training. Therefore, I'm surprised that you, as a trained pilot, disputed the validity of the term "flat spin". Before taking this as another personal attack, please read on. Over the last couple of years, I have seen a great deal of accurate and useful information disputed or even excised from Wikipedia by know-nothing buttinskis who have nothing better to do with their time than peruse Wikipedia for unreferenced statements to dispute. Those who believe that Wikipedia should err on the side of exclusion have won-out over those of us who believe that it should err on the side of inclusion. Your suggestion that the term "flat spin" should be removed--a term that is used in countles books, manuals, official accident reports and published scientific research--made you look like one of the above. The last thing I expected was to find out that you have experience in aviation. So, my question to you now is, as a trained pilot, why do you think "flat spin" is a colloquialism? Is there a school of thought, that I'm unaware of, that says "a spin is a spin, there is no 'flat spin'"? —Preceding unsigned comment added by Rsduhamel on June 5, 2008. Hi again Rsduhamel! Thanks for explaining your viewpoint. It gives me the opportunity to explain mine. As a pilot, flying instructor and aeronautical engineer I have carried out a lot of spins and read quite a few books on the subject. I am very respectful of all spins, including those regarded as steep spins (alpha less than 45 degrees). It is not only flat spins (alpha more than 45 degrees) that are potentially hazardous. Flying instructors regularly demonstrate to their students the way their airplane spins, and also the recovery procedure. They don’t demonstrate steep and flat spins. In my (general aviation) experience, single-engine airplanes have one spin mode only. It is not possible to choose whether to put these airplanes into a steep spin or a flat spin. It is only possible to put them into a spin and then accept whatever angle of attack is the result.
I have in front of me the excellent book Aerodynamics for Naval Aviators by H.H. Hurt Jr. It contains comprehensive information about spins. The terms flat spin and steep spin are not used anywhere in the book. Every reference is about spins in general without regard to whether the angle of attack is less than, or greater than, 45 degrees. In my experience, professional aviation books talk inclusively about spins without attempting to differentiate them into steep and flat spins. The av8n web site is generally very good, but it does misuse the notion of the “flat spin”. NASA distinguishes between steep and flat by arbitrarily using an angle of attack of 45 degrees. NASA does not claim there is a significant change in the character of spins at the 45 degree point. I intend to use the comment facility on the av8n web site and draw the misuse of "flat spin" to the attention of the authors. Under Steep spin it says:
Under Flat spin it says:
I understand your frustration at seeing Wiki editors deleting information they disagree with. However, be aware of this guidance: WP:BeBold More on flat spinsOkay, you subscribe to a school of thought that says "a spin is a spin". Your arguments have merit and my first impression is to agree. If you can cite independent research that agrees with your point of view then, by all means, put it in the article. However, even if the overwhelming scientific consensus is that all spins are varying degrees of the same event, the term "flat spin" should not be removed from the article. "Flat spin" means something to many people. Many pilots use the term, NTSB investigators use the term, NASA has defined the term. The article should then explain why many people differentiate between steep spins and flat spins and why the differentiation is not scientifically useful. That will educate people rather that leaving them high and dry if they want to learn what a flat spin is. In fact, if you had said something to the effect of "There is debate as to whether the term 'flat spin' is scientifically useful. The term 'unrecoverable spin' is often preferred (or whatever you would say).", I would have had no problem. But, then, I wouldn't have been prompted to do some research and add to the article. As far as NASAs definition being arbitrary is concerned, it certainly is. Nothing new about that in science. If a tropical cyclone has sustained winds speeds of at least 74 MPH (and it's in the Atlantic or eastern Pacific Oceans), it's officially a hurricane. If the winds are less, it's a tropical storm or tropical depression. There is no significant change in the storm's characteristics at 74 MPH. But it is universally accepted as the dividing line between a tropical storm and a hurricane. The NASA definition of a flat spin seems unlikely to coincide with the point where a spin becomes unrecoverable. That would need to be covered in the article. As far as the guideline WP:BeBold. Great idea but often abused. In my observation this abuse has often led to the people with the strongest opinions controlling the content. I have cut my editing back, perhaps, 80 percent. This is mainly because I spent too much time fighting to keep material from being deleted (mine as well as other's). So, the next time someone wants to delete the article about Dmitri Maksutov, because inventing an important type of telescope isn't notable enough to to warrant an article in Wikipedia, more power to them (That was someone else's article, not mine, I just saved it). Rsduhamel (talk) 05:30, 6 June 2008 (UTC)
ThanksThanks for your input at Talk:Siphon! Third-party reviews help in these debates.--Yannick (talk) 13:53, 8 June 2008 (UTC) Re: Adidiabatic processI agree that adiabatic is also widely used for irreversible process in which no heat is transferred. However, in theoretical physics, we tend avoid using the word adiabatic for such irreversible processes. I can't really point to a source that says this, because it is just a custom that theoretical physics professors stick to when they teach to students. The reason why we do this is because we base thermal and statistical physics on fundamental physics, in particular quantum mechanics. So, when we explain what "work" is we consider some isolated system which is in some energy level. We slowly change an external variable (e.g. volume) and the value of that energy level changes. The "adiabatic theorem" of quantum mechanics guarantees that the system stays in that energy level. So, it would be confusing to use the same word "adiabatic" later on in the course to describe e.g. the free expansion process, which is precisely not adiabatic in the sense used earlier in the course. I agree that everything has to be sourced in wikipedia, so I don't mind if my comment in the article is removed. But it would be a good idea to point out the apparent contradiction between "adiabatic" as used in quantum mechanics as that contradiction is very relevant for theoretical physics students. Count Iblis (talk) 14:44, 16 June 2008 (UTC)
Re: Isenthalpic processThe previous version suggested that enthalpy stays constant in an isolated system. But in a completely isolated system (kept at cnstant volume) the internal energy will stay the same. So, if we want to mention a generic class of insenthalpic processes, then we should point to adiabatic processes that happen under constant pressure (change in E + P V = absorbed heat = zero). Of course, this does not mean that the reverse is true, i.e. an isenthalpic process is not necessarily a process that takes place under constant pressure. Just like energy can be conserved in an open system too (if as much energy flows into the system as flows out). Count Iblis (talk) 15:00, 16 June 2008 (UTC) Re: VandalismSorry, but you don't understand your own sources. I'm going to revert you every time you make nonsensical statements in wikipedia articles. What you are doing is writing something like: 1 + 1 = 0 See source X when source X talks about artithmetic modulo 2. You are insisting on keeping that sentence in the article when it is clear that for an isolated system with fixed volume H = E + P V is not conserved, only E is conserved. Your source says H is conserved, but then the meaning of that is in a completely different setting. And the article doesn't talk about that at all. You are talking about a system in which you define some system boundaries, you have a generator that can extract work and only that work counts as work done by the gas. But where in the aticle are these details mentioned? Nowhere! Count Iblis (talk) 23:30, 17 June 2008 (UTC)
Article Joule–Thomson effect vandalized by me!Check it out. I'm sure that your sources say that the gas does no work here (because it should be obvious that there is a generator somewhere that is supposed to extract work and the gas moving through the valve is not letting a turbine spin) :) Count Iblis (talk) 23:41, 17 June 2008 (UTC) Bernoulli Principle and liftLooking at the discussion thread and at several web sites, I have questions rather than suggestions for changes, I'm posting these here, since I assume it's inapropriate to post questions in the discussion threads on articles (would be nice if wiki articles had a seperate page for questions). It might help if I start with Newton stuff first. My simplified version of newton explanation of lift: air is accelerated downwards and slightly forwards, resulting in reactive lift and drag forces. Work is done on the air in the process of producing lift and/or drag, resulting in a change of the total energy of the air. One question about terminology. Induced drag is defined as the drag associated with producing lift. Does induced drag times distance equal the component of work required to produce lift? Does parasitic drag times distance equal the component of work required to produce the remaining drag (not sure if friction is included as part of parastitic drag)? I'm am having problem understanding Bernoulli Principle and lift as described in the discussion thread on Bernoulli principle. I don't understand why near horizontal air flow relative to a wing, results in a vertical force reaction. I understand the concept that pressure and airspeed have an inverse relationship in a closed system (such as Venturi effect used in caurberators). Getting back to wings, it's an open system, and air is accelerated towards lower pressure areas, and away from higher pressure areas from all directions (almost, air can't flow through the solid wing). I read that streamlines can be considered "closed" systems, but wouldn't low pressure areas draw air from outside the streamline as well as from the streamline itself? Take the case of a wing where almost all the lift effect occurs from above the wing, which was mentioned in the discussion. If Bernoulli principle is about the near horizontal air flow over such a wing, so that the air is accelerated horizontally backwards relative to the wing, then it seems the result would be thrust and not drag. Where is the source of drag in this case? I've seen wind tunnel videos, and it's clear that the pulsed smoke stream above a wing ends up well ahead of the pulsed smoke stream below the wing. The only thing that would make sense here is that almost all the drag would occur from below the wing, but it would seem that the primary method of creating drag below a wing would be to increase the pressure below the wing, and this would conflict with the concept that all of the lift effect occurred from above a wing. What am I getting wrong here? It was mentioned that airfoil simulation programs calculate pressures, lift, and drag, from air speeds, but aren't those air speeds also just calculated values? What was the point of that statement? From my point of view, if it was simply stated that wings produce lower pressure areas above and/or higher pressures below, causing a net downwards acceleration of air, where the accelerations correspond to the transitions in pressure areas, and that for all of the air affected by a wing, speed^2 corresponded inversely with pressure I wouldn't have a problem (I'm guessing that there is some slight mistmatch in speed versus pressure due to work being done and a change in total energy of the air). It's the apparent emphasis on the horizontal flow across a wing that has me confused, since if using the air itself as the frame of reference, then the flow (and acceleration) of air corresponding to lift is downwards. Lastly, how would Bernoulli Principle be modified to calculate (predict) the net work done on the air? Jeffareid (talk) 21:58, 20 June 2008 (UTC)
Reply to JeffareidJeff Here are my thoughts on the first of your questions. Your words are in bold. I will provide more information in the next day or two. Work is done on the air in the process of producing lift. Lift is defined to be perpendicular to the airfoil’s velocity through the atmosphere so you might expect lift to do no work on the air. However, the downwash associated with the airfoil’s trailing vortices causes the air close to the airfoil to be moving in a slightly different direction to the airfoil’s velocity through the atmosphere. (This small difference in direction is called the induced angle of attack.) Consequently, lift does a small amount of work and this causes some of the air to have kinetic energy associated with its downward motion. The airfoil constantly has to provide this kinetic energy and this is one explanation of induced drag. The greater the induced drag the greater the kinetic energy of the air moving in the downward direction. Work is done on the air in the process of producing drag. Does induced drag times distance equal the component of work required to produce lift? Does parasitic drag times distance equal the component of work required to produce the remaining drag (not sure if friction is included as part of parastitic drag)? … wouldn't low pressure areas draw air from outside the streamline as well as from the streamline itself? Imagine some particles of air being given a pencil so each one can draw a line as they move. The result of all those pencil lines is a number of streamlines. When you ask whether air is drawn from outside the streamlines you are thinking of isobars (lines of constant pressure). Streamlines are not isobars. Think of the weather map – the wind is shown by small arrows. At ground level the wind blows across the isobars but it doesn’t blow across the arrows – the arrows show the wind’s actual direction. Each arrow is parallel to the local streamline. Take the case of a wing where almost all the lift effect occurs from above the wing … It is a bit like talking about a child’s toy balloon. The size of the inflated balloon depends on the difference in pressure between the interior of the balloon and the atmosphere. It would not be reasonable to say the interior of the balloon contributes more to the size of the balloon than the exterior. It is reasonable to say the pressure in the interior is greater than the pressure in the atmosphere. Dolphin51 (talk) 03:42, 24 June 2008 (UTC)
A typical airfoil section has its maximum thickness at about 25% of the chord (distance from leading to trailing edge.) So from the leading edge to the 25% point the air accelerates spectacularly. Then from the 25% point to the trailing edge (ie 100%) it decelerates to roughly the same speed at which it approached the airfoil, and the same speed as the air coming from the lower surface. In contrast, air passing via the lower surface of the wing does not undergo any acceleration. It simply passes from the leading to the trailing edge at roughly constant speed. Because of the spectacular acceleration and then deceleration the air travelling via the upper surface arrives at the trailing edge long before its partner arriving via the lower surface. The two partners never meet again, not even long after the wing has passed. This is known as cleavage.
The parasitic drag on the wing is partly due to the viscous nature of the air flowing past the upper and lower surfaces of the wing. (This is called surface-friction drag or skin-friction drag. It is just like trying to pull a knife quickly through a viscous liquid like honey or oil.) The air passing over the upper surface is travelling faster than the air passing over the lower surface so the drag on the upper surface is higher than the drag on the lower surface. (Any attempt to measure the drag simply measures the total drag. It is not possible to measure the drag on upper and lower surfaces separately.) The other part of the parasitic drag on the wing is due to the lower pressure in the wake. (This is called form drag.) Near the leading edge of the wing the pressure is high – it is called stagnation pressure because the air is stopped against the solid surface. In contrast, in the wake at the trailing edge of the wing the air is not stopped and so the air in the wake has a pressure less than stagnation pressure. With higher pressure pushing backwards on the leading edge of the wing; and lower pressure pushing forwards on the trailing edge of the wing, the net result is a backwards force opposing the forward motion of the wing. This is usually called form drag and it is a component of parasitic drag. What am I getting wrong here? It was mentioned that airfoil simulation programs calculate pressures, lift, and drag, from air speeds, but aren't those air speeds also just calculated values? What was the point of that statement? The point of the statement is that it isn’t possible to take a particular airfoil, angle of attack and airspeed and directly calculate lift and form drag. It is necessary to first calculate the airspeed distribution around the airfoil. When we have the airspeed distribution all that is necessary is to apply Bernoulli’s principle to convert the airspeed distribution into a pressure distribution. (When people say Bernoulli’s principle is not applicable to lift on an airfoil they are completely wrong.) Lastly, how would Bernoulli’s principle be modified to calculate (predict) the net work done on the air? The motion of that small parcel of air will be downwards and forwards (in the same direction as the wing). The downwards component is a result of having exerted induced drag on the wing; and the forwards component is a result of having exerted parasitic drag on the wing. I will deal with your remaining questions in a day or two. Cheers. Dolphin51 (talk) 12:31, 24 June 2008 (UTC)
However, the Newtonian explanation of lift doesn’t explain why airfoils always have thin, sharp trailing edges. Nor does it explain such things as trailing vortices and wake turbulence. When you want to understand why airfoils have sharp trailing edges it is time to move on to grasp the Kutta condition. When you want to understand trailing vortices it is time to move on to the circulation theory of lift (see Kutta-Joukowski theorem.) But if those things never bother you there is no reason to grapple with them, and no reason to go beyond the Newtonian explanation. I'm guessing that there is some slight mismatch in speed versus pressure due to work being done and a change in total energy of the air. Is the total energy of this air (pressure + kinetic) changed by the wing, or is all the increase in speed offset by a decrease in pressure? Some of the air passes the upper surface of the wing. Its speed increases significantly as it passes the first quarter of the upper surface of the wing. As it does so, its pressure falls significantly. (That is why the lift experiences lift.) By the time it has reached about the end of the first quarter it begins to decelerate until it reaches the trailing edge. As its speed reduces its pressure increases. At the trailing edge the stream from the upper and lower surfaces join up. They are both moving at about the same speed and have the same pressure. Even though the air passing the upper surface increases in speed, and its pressure reduces, the total pressure (dynamic pressure plus pressure) remains constant throughout the whole flow field (except in the boundary layer and the core of vortices.) Assuming that a wing does peform work on the air, which seems to be implied by the term induced drag, is all of the work done related to drag only, or is work also peformed related to lift? Assuming that work related to lift is peformed, then how is this accomplished? Most of the lift performs no work because the lift vector is almost perpendicular to the direction of motion. I say almost perpendicular because it is ninety degrees minus a small angle called the induced angle of attack. The component of angle of attack called the induced angle is the small component due to downwash related to the trailing vortices. This violates the Bernoulli principle in that the air ends up with a higher velocity, but not a corresponding decrease in pressure.
The newton approach is so much simpler as it just leaves out the nasty details. I'm not an aerodynamics engineer (which doesn't seem to help since they can't agree either). I hope this helps. If it doesn’t, don’t hesitate to ask more questions. I will do what I can to explain. Happy editing! Dolphin51 (talk) 04:15, 27 June 2008 (UTC)
strange request...Hey, I am currently a pilot and a 4th year aero student and I will be taking a flight controls/dynamics class in the fall. I'm studying for the class now and I'm struggling with arriving at the closed loop state equations and the transfer functions from the short-period perturbation dynamics diff eqs. I have no idea what to do because all I learned in my diff eq class was how to solve standard laplace transforms and things with the famous tables. I don't know whats going on. (btw.. I'm one of these "learn everything intuitively" people because I will probably forget the mathematics eventually and will only remember what things "feel" like...this is half the reason I became a pilot so that I could feel the equations instead of just writing numbers down.) Sorry to bother you and any help would be GREATLY appreciated! Katanada (talk) 19:47, 24 June 2008 (UTC) Hi Katanada. You have my sympathy! Like you, I'm a pilot (but not current), and an aeronautical engineer. The subjective elements of flight dynamics we retain readily, and for a long time, but the advanced math takes a lot, lot longer to become intuitive. My advice is that there is no alternative to working carefully through the text-book and doing a few example problems along the way. (If your prescribed text-book doesn't inspire you as much as you would like, don't hesitate to search out a better book.) Nothing helps grasp new ideas in math as much as doing a few example problems, preferably where you can find the correct answer so you can keep at it until you get it right. Also it is my experience that in classes with a lot of intimidating math, they don't really expect students to be able to regurgitate the high-level stuff in the exam - they usually set an exam that assesses whether each student has grasped the important basics and is able to use that to handle some of the basic math. So don't study the high-level math with the objective of committing it to memory - memorise the fundamentals, and get a feel for where the fundamentals lead to, but it would not be an efficient use of your time to try to memorise the high-level stuff. Good luck in the fall! Dolphin51 (talk) 03:13, 27 June 2008 (UTC) re: center of liftRereading my references (see the talk page) I've determined that way back when I should have simply worked on the aerodynamic center article rather than starting one on center of lift. The term is often used, but it's synonymous with AC, rather than CP. Hopefully this is a satisfactory solution to the issue! ericg ✈ 01:07, 28 June 2008 (UTC) re: Ashes articlesI didn't vandalise English cricket team in Australia in 1994-95. I have been seperating the tour articles and the Ashes articles, as the Ashes have notoriety in their own right, but the tour match information does not belong in the Ashes article. Therefore the material related to the Ashes can be found in 1994-95 Ashes series, and the rest of the tour matches are at English cricket team in Australia in 1994-95, as is the case with all of the other editions I have completed. It is a large project, but i have done most of the 90's and created many of the early series already... Robert Fleming (talk) 13:10, 9 July 2008 (UTC) Hi, thanks for your kind note. You are quite right, in interleaving my edits in between yours I screwed up. Let me reinstate the text and ref that you noted that I deleted and then you can see if that fixes it. - Ahunt (talk) 21:11, 24 July 2008 (UTC) Flight MechanicsYour discussion of steady state climb and dive is quite correct but you might want to mention unsteady climb (and dive) achieved by lift greater than weight. A glider can make loops by pulling an angle of attack where lift is greater than weight. As you point out this does not change the total potential energy (except for the drag losses of course) but you can climb without thrust. My poorly trimmed hand launched gliders do it all the time (at least until they reach zero speed and plumment to the ground)Skimaniac (talk) 04:59, 27 July 2008 (UTC) Thanks for the Welcome back. It means a lot.Skimaniac (talk) 02:29, 29 July 2008 (UTC) WelcomeI received your welcome notice on my user talk page. Given that you didn't respond to my question as to why I'd been welcomed some years after my first posting, I took it as condescending ... that aside from the redundance of such a late "welcome". I've also seen other users' "welcome" graffiti on other users' talk pages, and every one is different. Surely the best way to accomplish this would be to create a welcome package for "new" users and then post a simple message, such as "
I have the same question for the same reason. In particular, is the list of suggested reading simply pro-forma or because you have specific areas of concern and believe that my work is not up to snuff? If the former, then perhaps your welcome notice should say so; if the latter, given the variety of my editing over the last six months or so, it would be far more helpful if you pointed to specifics. While I have absolutely no illusions that I am a perfect writer or everyone's cup of tea, I write a great deal in a variety of contexts, paid, pro-bono, and avocational and would like to believe that the very limited work (mostly minor edits) that I have done on Wiki is done to a reasonable standard.Jameslwoodward (talk) 14:07, 27 January 2009 (UTC) Thanks for your quick and thoughtful response. Certainly Wiki can be intimidating -- some of the help pages are not as clear as they might be -- and having an actual human take an interest in my work feels good. I will take you up on your offer of help at some point. I might suggest that since your initial welcome raised much the same question in me and in Rfsmit, that you might consider modifying it a bit, perhaps something along these lines (using mostly your words), "Hello XXXX and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. In Wikipedia, new Users do not automatically receive a machine-generated welcome. Welcome messages come from individuals so they are personal and genuine. They contain an offer of assistance if such assistance is ever desired. I suggest to everyone that I welcome that they may find some of the following helpful -- there’s nothing personal in my suggestion and you may not need any of these: Introduction The five pillars of Wikipedia How to edit a page Help pages Tutorial How to write a great article Manual of Style I hope you enjoy editing here and being a Wikipedian! Please sign your name on talk pages using four tildes (Jameslwoodward (talk) 13:02, 28 January 2009 (UTC)); this will automatically produce your name and the date. If you need help, check out Wikipedia:Questions, ask me on my talk page, or place {{helpme}} on your talk page and ask your question there. Again, welcome! "
Looks good -- we make a good edit team. Jameslwoodward (talk) 22:13, 30 January 2009 (UTC) 'SupOh hay look here. Benshi (talk) 06:48, 4 August 2008 (UTC) And here! Benshi (talk) 08:39, 11 August 2008 (UTC) Well? Did you look at it! —Preceding unsigned comment added by Benshi (talk • contribs) 06:07, 12 August 2008 (UTC)
Hay I was wondering, what's an aeronautical engineer? What do you do? 58.179.51.127 (talk) 09:43, 14 August 2008 (UTC) Don't mention it!I am glad to be of help. :) --PeaceNT (talk) 12:12, 12 August 2008 (UTC) Need help pleaseHello again Dolphin. I would appreciate constructive help with how to proceed with my first page the http://en.wikipedia.org/wiki/Jen_Delyth I have registered my complaint at the slamming I have taken from the RHowarth editor, who had no appreciation for the difficulties a new user may experience. However, I would like to move on with a different editor, as the personal conflict I am experiencing is stressful. I don't know if that would be you, or what the procedure is, but appreciate your help. I have (after the rough start) done my best to study the Wikipedia regulations and to change and update the page accordingly. I"ve worked pretty hard on the page, refined the language to be more "enclylopedic", added some outside sources, formated and referenced and added several reputable Wikipedia links with Jen to show connections with other noteable artists/authors. I understand that this would all have been better submitted through someone who was not connected with the subject. (which I did not initially understand when first posting the page). But I have now done the work, and set up the page, I am sincerely trying to present an unbiased, clear, objective summary of the facts. If I understand the regulations, they are guidelines, and have flexibility. I am being open and transparant, and want to continue in this way. For the record, this (page creation) is not an attempt for self promotion. Jen Delyth is well known in her field to have made significant contribution to the contemporary Celtic Art genre, and in fact was at the forefront of the revivial of this popular folk art style in this country. The only way to show that, is through her work. It is difficult to discuss the time frame, and an understanding of the style that she began, that has been emulated (yet not as well as the originator) since. Within both the Celtic arts community, and fast spreading beyond it, Jen's original "Celtic Tree of Life' design has become an iconographic symbol, that is considered "THE" Celtic Tree of life, misinterpreted as an actual ancient Celtic symbol, and spreading throughout the world as a major archetype. Its difficult to show the importance of this creation, or the artist who is behind it (except through google searches etc). Certainly worthy of a Wikipedia reference, and of interest to your community. I would appreciate help in this. How to proceed, with integrity, and get this page worked out. Is the page as it has been edited now editorially ok? Can you suggest any changes or ways to show this is a good solid contribution? Also I don't know how to "hide" (blank?) the page whilst its worked on. (It is an embarressment having those messages and tags on there in full public view, when Jen Delyth gets over 600 views a day on her website). Also, would it help to have just one basic line about the artist and not all the other info, so that others (not myself) can add to the site? (we noticed the Amy Brown site was like that.. She is a contemporary peer artist of Jen Delyth, linked on same Faerieworlds site (which is what brought me to create this page in the first place.. as Jen Delyth is listed as a guest artist there) I appreciate your help and advice. Thanks, Scott Silverberg 66.117.128.94 (talk) 17:34, 12 August 2008 (UTC)
Jen delyth EDIT S. SilverbergDolphin... Appreciating your help as I noted on my talk page. From now on will address comments here. The "EDIT" button has dissapeared from the top of JEN DELYTH page... so I can't edit it and add the inline citations you reccomended. Appreciate your help in getting that EDIT access back. Also, can i request an extention in time to get the page updated? Also, someone (not me) has added to the page, and given no sources. should I delete that contribution even though it came from an independant source? thanks a lot, scottSSilverberg (talk) 04:58, 13 August 2008 (UTC)
Thanks a lot Dolphin.. Very relieved that the editorial work so far has helped. Still a ways to go.. And still don't see the "edit" button at top of page for main intro section in Firefox (mac) or Safari (mac os x). However, I now understand the use of the sand box. (apologies for not before). So am doing all main edits on this page, until updating on main page. http://en.wikipedia.org/wiki/User:SSilverberg/Sandbox Would appreciate a quick look to see if this is much more Wiki compatible. Adding quotes and references for all statements whenever possible. Not easy to do when "evidence" is not quoted but is found easily on google searches.. which I'm hoping will be valid (to show widespread use of Celtic Tree of Life design and widespread publication of Jen's work..) How does one mention "best selling"?? Her Celtic Mandala Calendar has sold over 100,000 copies.. through her publisher Amber Lotus. How do we express that? And her images are extremely popular out in the world. And it sounds so commercial to say anyway. But if we must show notablity, we need to show popularity as well? Atlhough I think the article you said made it clear that was not altogether the point, but contribution.(I notice other artist pages mention popularity and don't give any sources etc.. Such as the Amy Brown page. and many others.) Jen's contribution is on such a grass roots level, its hard to get the wikipedia standard. But nonetheless, Jen's work has contributed in a big way to a style and spread of Celtic art in this country, starting when she did. But how to show or verify that? I respect and understand this need though.. just a challenge is all. Well doing my best, and enjoying learning now that things are less emotionally conflicting. any help and advice, please let me know. thanks again, Scott —Preceding unsigned comment added by SSilverberg (talk • contribs) 06:45, 13 August 2008 (UTC)
Thanks Dolphin... I could not have worked that out.. even though that button was kind of obvious at the top of the page.. since it was different before. This is better though, because I had to edit each section individually before.. Its 3.34am, and another long night of referencing etc. I have added inline citations as you requested, even though I think it reads a bit strangely to do that rather than footnote references.. However, I found some that directly related to the "notability" topic. And more references and ISBN numbers etc. also someone has added something again, another user - so I'm not touching those. So 2 outside sources now (although how does the Wikipedia know I didn't add them?? The references are quite long at times, and has been quite complicated to construct. Please let me know if its getting close now. I need help at this point - All is uploaded to the Jen delyth page (not the sandbox anymore). thanks. scott SSilverberg (talk) 10:40, 13 August 2008 (UTC)
Thanks.. I'm glad its starting to look more editorial. I can see why it was not ok in the beginning, although I did follow the example of other artist and musician pages on Wikipedia.. Nonetheless, I understand the need for references and so on, its been a good excercise. I have run out of things to add/change for now I think. So do I leave it alone? What is the process of asking for a review to keep the page? Didn't know you're in Australia. Wikipedia is amazing how everyone is all over the world. Best wishes, Scott —Preceding unsigned comment added by SSilverberg (talk • contribs) 00:01, 14 August 2008 (UTC) Dolphin, I need your help/advise with RHaworth's posting of the "conflict of interest" tag. I have responded on the Jen delyth talk page. [[1]]. Please advise.. thanks, ScottSSilverberg (talk) 19:30, 14 August 2008 (UTC) Dolphin, As you requested on my user page, I have responded to you on the Jen delyth page. and here.. (in response to comment on my user page..) Thanks Dolphin, I didn't see those comments (regarding making CTofL be main focus). Very helpful.. I'll get on with responding to them, although its worrying that all the work may be for nothing.. But keeping my fingers crossed, and either way have learned much of interest, and all will not be lost whatever the outcome. Thanks for your time, much appreciation across the world - ScottSSilverberg (talk) 00:16, 15 August 2008 (UTC) Scott SSilverberg (talk) 02:01, 15 August 2008 (UTC) Just to say thanks again for your generous advice and support. I think I must let things go as they will now. I suppose it could take some time? much appreciation for some sanity in all this.. Scott —Preceding unsigned comment added by SSilverberg (talk • contribs) 00:07, 16 August 2008 (UTC) Review & StatusHello Dolphin. I would like to know what the process for review is, how long it could take to remove the tags on the page. Jen Delyth is a featured artist at a large upcoming conference, with a main stage presentation and featuring of her new work. The tags are not exactly positive. Can the page be taken down until the review is done? What is the procedure? thanks, Scott SSilverberg (talk) 03:36, 20 August 2008 (UTC) Thanks again Dolphin for helping get this page appropriately edited and acceptable to Wikipedia. Could not have managed this without your support. And have learned how articles are written now, and what is considered a positive contribution. Thanks... Scott —Preceding unsigned comment added by SSilverberg (talk • contribs) 20:54, 3 September 2008 (UTC) Bernoulli and lift #2OK, much simpler thoughts this time. Newton - A wing produces lift by applying a downwards force on the air, via a combination of forwards speed and effective angle of attack. This downward force results in a downwards acceleration of air, which responds with an equal and opposing force (Newton's 3rd law). Bernoulli - The downwards acceleration of air results in an increase in kinetic energy of the air. Most (or almost all) of this increase in kinetic energy occurs via a Bernoulli like transition where the pressure energy is decreased by the increase in kinetic energy. Wings are not 100% efficient, so there is drag, which occurs whenever a solid passes through a gas of fluid. I'm not interested that much in distinguishing between parasitic and induced drag, partly because induced drag has multiple definitions, and since parasitic drag can be reduced, but not eliminated. The efficiency is pretty good in the case of high end, 80 foot or more (some 100 foot) wingspan, gliders with glide ratios of 60:1 at around 60 knots. My main question is about high force situations, such as a propellor or turbine (non-combustion, such as electric powered ducted fan turbines used on radio control models). The increase in kinetic energy in these situations is well beyond the total pressure energy of the air, negative pressure doesn't exist, so it would appear there has to be a very significant non-Bernoulli like transition in these cases. There's a huge increase in kinetic energy in the direction of "lift", which seems like a conflict because how can work be done if the force is perpendicular to the direction of travel? The answer seems to be that there is a force applied in the direction of travel, if you take into account the perpendicular component of distance from the leading edge to the trailing edge of the airfoil used, the sin of the angle of attack times chord length. The work done for lift would be the integral of the force over the perpendicular component of the distance from leading to trailing edge of the wing, propellor, or turbine, plus possibly some "effective" perpendicular distance due to coanda like or similar effects. I assume that a wing is behaving in the same manner, the main difference being that a lot of the work done in the direction of lift is conversion from pressure energy into kinetic energy, until the speed and angle of attack reach a point where there's a significant increase in total energy, both pressure and kinetic. I assume that a wing under a high load factor, such as a 9 g turn in a F16, or a 40 g turn in a radio control model (like rc gliders dynamic soaring) would result in a significant increase in total energy of the air. Assuming all of this is correct, then is there a way to "describe" when producing lift transitions from a mostly pressure to kinetic energy conversion into an overall increase in total energy of the air (a conversion of energy from the source of power for an aircraft)? Jeffareid (talk) 13:48, 16 August 2008 (UTC)
Total energy is constant along a streamline, but only providing there is no energy added from an external source. In the cases you mention - a propeller (or turbine), significant energy is added to the fluid as it flows through the disc of the propeller. As fluid ahead of the propeller accelerates towards the propeller its speed increases and its pressure decreases so that its total pressure remains constant in accordance with Bernoulli. As this fluid emerges out the downstream side of the propeller disc its speed is about the same as on the upstream side of the disc but its pressure has increased significantly and so has the total pressure. The pressure difference across the propeller disc is the source of the thrust generated by the propeller. As the fluid flows away from the propeller disc its speed increases as the pressure falls towards atmospheric but total pressure remains constant at the value throughout the plume exiting the propeller disc. When the pressure falls to that of the surrounding atmosphere the plume exiting the propeller ceases to accelerate further. (The energy acquired by the plume as it flows through the propeller disc is ultimately dissipated by the action of viscosity and is manifest as a very small rise in temperature of the air.) Bernoulli’s principle applies upstream of the propeller disc, and also downstream of the disc, but there is a significant increase in total pressure (ie total energy) as the fluid passes the propeller disc and acquires extra energy from the propeller. This is often explained using simple momentum theory. My favourite book is Aerodynamics (by L.J. Clancy) and it is explained in section 17.4 The Rankine-Froude Momentum Theory of Propulsion. The lift on an airfoil is defined to be perpendicular to the vector representing the airfoil’s velocity relative to the stationary atmosphere, so lift does no work on the air although it does alter the direction of movement of the air close to the airfoil. (The change of direction of the air leads to the Newtonian explanation of lift.) However, in the case of a propeller (or turbine) it is as though there are multiple airfoils following one behind the other. Each blade is constantly moving through the downwash caused by the blade ahead of it. As a wing approaches a parcel of air the parcel accelerates and rises to meet the wing (this is called the upwash, ahead of the wing). After the wing has passed, the parcel is decelerating downwards (this is downwash behind the wing, but not the full downwash caused by the trailing vortices) and eventually returns to the stationary state it had before the wing arrived. In the case of a propeller or turbine, there is not sufficient time or distance for the air to return to the stationary state before the next blade arrives. So each blade of a propeller or turbine is not meeting stationary air. Each blade is operating in air that is still moving “downwards” as a result of its interaction with the preceding blade. The lift force on each blade is perpendicular to the direction of flow of air past the blade, but that direction is different to the direction of the blade relative to the atmosphere remote from the blade. As a result, the lift on the blade does work on the air, and the kinetic energy of the blade increases as it passes through the propeller disc. (It is similar to lift generated by a three-dimensional airfoil. The trailing vortices cause an induced-component of angle of attack and the lift vector is rotated by an angle equal to the induced-component of angle of attack. The lift does negative work on the air, resulting in what we call induced drag.) I hope this helps. Cheers! Dolphin51 (talk) 03:02, 30 August 2008 (UTC) Dolphin, Jeffareid writes:
My question is: Doesn't only half the wing's surface produce an downwards force on the air, and doesn't the other half produce an upward force?
My question: On the upper half the wing, isn't the force unsuccessfully opposing, rather than 'resulting in' the downwards acceleration of the air? Mark.camp (talk) 23:11, 6 February 2009 (UTC)
Center of pressureDear Dolphin51 : Thank you for your comments. Is it possible to have a discussion outside this page ? What I need to discuss may not be quite relevant for this page. may I request you send me your e-mail address where i can communicate withyou direct. My e-mail addreess is cgibwn@gmail.com. After we communicate, if you think it is ok, we could shift the entire conversation here for the benefit of all. Thanking you, regards,CGI BWN (talk) 14:43, 17 August 2008 (UTC) Dear Dolphin51 : Can you please explain what will happen if the CofG of an aircraft and its CofP were co-located by design ? There will be no nose up / down moments. Then what will be the function of the tailplane ? What would happend when the weight of an aircraft reduces due to consumption of fuel, external or internal stores carried in / on the aircarfat ? Or if the engine fails during flight ? Will the tail plane be able to control / stabilize the aircraft in level flight ?CGI BWN (talk) 07:20, 10 August 2008 (UTC)
Starting vortexHello. I noticed that you moved the Spanish text out to the talk page. Have you contacted the author Hazebrouck about transwikiing it to the Spanish Wiki? He seems best suited to insert it over there. Have a look at the entry at "Pages needing translation into English", we've been discussing the general matter over there. De728631 (talk) 20:01, 27 August 2008 (UTC)
Bernoulli and lift #3Thanks for the previous response, continuing from #2, I think I have an idea here: "The lift force on each blade is perpendicular to the direction of flow of air past the blade". Wings and propellors do have an effective angle of attack, so there is a direct mechanical force applied to the air by a wing or propellor over a small perpendicular component of distance, approximately the sin(angle of attack) times chord distance, so although the force is perpendicular to the direction of the overall wing, it's not perpendicular to the direction of the surface of the wing, so a significant amount of work can be done in the direction of "lift". A wing or propellor is literally pushing the air (via collisions with the surface), on the downflow surface. On the upflow side, it's possible that Coanada like effect could allow for some mechanical interaction via friction and viscosity, but most of this is the production of a low pressure area which accelerates air in a Bernoulli like fashion (conversion of pressure energy into kinetic energy with virtually no increase in total energy). On the upflow side of an airfoil, the pressure energy can't be reduced below zero, but on the downflow side, there's no such limiting factor. Even in the case of a wing, a very high g-force turn or loop could probably create a similar situation where the total energy increase of air is very large. I've read that radio control gliders pull about 40g's while dynamic soaring (link to video of a 333mph run 333mph dynamic soaring, a 357mph run done later that day. Last I read was the record was 365mph. What started me thinking about this was reading that sound waves in the air are limited to about 190db. Above that, the pressure peaks are more than double atmospheric pressure, while the valleys can't be less than zero pressure, and these higher energy, imbalanced waves are shock waves. It's not possible to produce such waves without a non-Bernoulli like mechanical interaction, like a supersonic aircraft, or an explosion. A more common experience that triggered this in my mind is that prop wash is easily felt in comparason to any air flow in front of a prop (at a reasonably safe distance). Jeffareid (talk) 06:03, 31 August 2008 (UTC)
Also, somewhere along the line I confused a pressure differential of 1 psi with 1 atm. Some eletric ducted fans (turbines) get a bit over 1 psi jump, like a 120mm screw type propeller in a tube, generating 19 lbs of thrust across 17.5 in^2 of area. A F-16 has 77 lbs / ft^2 wing loading at 1 g, or .5347 psi and can pull 9 g's for about 4.8 psi of pressure differential. Jeffareid (talk) 07:18, 5 September 2008 (UTC) Balanced FlightDolphin51: I am not a pilot (but an aero engineer). While your physics seem to be correct, I do not enough about the pilot term for balanced flight to comment. I recently was traveling and read severl books on flying (for pilots). It seems that pilots must think of things in the steady-state. So my earlier comment about flight mechanics and the gliders might not be appropriate for a general audience. I spend most on my time thinking about things that are not in a steady condition. Skimaniac (talk) 13:42, 2 September 2008 (UTC)
Nice work fixing up this article, including refs, it makes good sense now! - Ahunt (talk) 11:30, 12 September 2008 (UTC) Turning flight stallHi there. The rework of the accelerated stall section makes sense to me, although I think the followings should be addressed:
I'm happy to work on these points - when I have a minute - if there are no objections. Giuliopp (talk) 00:48, 7 October 2008 (UTC)
Flight DynamicsHi Dolphin51. Yes I had put 'three axis control' as it is a term coined by the Wrights themselves. But basically I made the amendment because the article accurately describes the three axis' of which a fixed wing aircraft must be controlled. 'Three Axis Control' is somewhat of an archaic term but accurate and to the point of fixed wing aircraft controle.Im okay with the deletion as it may confuse people. So, you have it from me, it's okay. Thanks Koplimek (talk) 07:41, 16 October 2008 (UTC) BernoulliThanks for the help on the Bernoulli page I'll read over the Kutta conditions. It just feels like the explanations I've heard for lifts are snow jobs. When I think of things like aspirators I don't imagine the Bernoullie principle; I think of molecules being stripped out of an atmosphere and into the liquids flow. If this wasn't the case then an aspirator would quickly reach an equilibrium when attached to a closed container. I realize I'm probably missing something there... My point is thanks for suggestions at an appropriate level.--OMCV (talk) 05:00, 14 December 2008 (UTC)
Lift doing workI am sometimes unclear on what is meant by statements about work done on "the air", or changes in momentum or energy of "the air", which speak of "the air" as if it were a single body with a single momentum, position, or energy, or of the wing as if every part of it were doing the same work or subject to the same pressure. Example, you wrote above "Consequently, lift does a small amount of work". (1) Does work on what body, what parcel? In which cases of a parcel undergoing a change in kinetic energy does the lift do work and in which does it not? For example, (2) a parcel in a lower streamtube moving from one place in front of the wing to another in front of the wing and increasing in kinetic energy as it becomes part of upwash? (3) A parcel moving over the high point of the wing, whose acceleration is down, but with that acceleration being opposed by the force from the wing? (4) A parcel above the wing which has no contact with the wing (does Newton's second law about two bodies exerting a direct force on each other also apply when the two bodies exert no direct force on each other?) (5) A parcel which was accelerated downward in the trailing vortex and is now moving vertically upward and thus accelerating laterally? Mark.camp (talk) 03:36, 13 January 2009 (UTC)
Hi Mark. Thanks for sending me your questions. When a solid body is moving in a straight line, without rotating, it is easy to calculate, and visualise, its kinetic energy and momentum. Every gram (or ounce) of material in the body has the same kinetic energy and momentum. I agree it is not so easy with a fluid because, in most fluid flow situations of interest to us, every gram of fluid has a different kinetic energy and momentum. It might make it easier to begin the transition from a solid body to a fluid by considering a solid body that rotates, such as the propeller on a stationary airplane. The kinetic energy and linear momentum of a gram of material at the outer tip of the propeller is very high. The kinetic energy and linear momentum of a gram of material at mid-radius is only half that at the tip. The kinetic energy and linear momentum of a gram of material at the center of the propeller is zero. With a fluid, the kinetic energy and linear momentum are likely to vary around the flow field, not with a simple mathematical relationship like the various positions on a propeller, but in a more complex fashion. With a solid body it is easy to see that the work performed on the body by the resultant force acting on the body exactly equals the change in kinetic energy (KE) of the body. (Positive work causes an increase in KE; and negative work causes a decrease.) With a fluid the same principle applies, but it is usually not possible to identify any boundary to the part of the fluid whose kinetic energy has changed – in one region of the fluid the KE changes significantly; surrounding that region is another region where the KE changes a smaller amount; surrounding that region is another region where the KE changes only a little; and surrounding that region is another region where the KE barely changes at all. When a propeller is generating significant thrust it is causing major increases in the KE of each gram of air close to the propeller. Several propeller diameters away the increase in KE of each gram of air is much less. Theoretically, the propeller is increasing the KE of each gram of air in the entire atmosphere! User:Jeffareid wrote about the lift force doing work on the air. My view is that, when we are viewing an airplane in flight from the inertial reference frame attached to the atmosphere, lift never does work because it is, by definition, the component of the aerodynamic force perpendicular to the velocity of the airplane. (Work is only done by a force when that force has a component in the direction of movement. A force that is perpendicular to the displacement vector, such as a centripetal force, does no work and hence causes no change in kinetic energy.) Seeing Jeffareid held the view that a lift force does work on the air, I conceded that lift can do a small amount of work. What I had in mind was that the induced drag is actually a component of lift. Induced drag certainly does work because it is parallel to the velocity vector. Therefore it is reasonable to say that the component of lift that is the induced drag does work. (However, it is simpler to avoid this complexity and say that lift never does any work when viewed from the inertial reference frame attached to the atmosphere.) Drag does work on the atmosphere. Consider a stationary atmosphere, and an airplane flying from right to left. The drag force acts on the airplane, in a direction from left to right, retarding its motion. The reciprocal force (the equal and opposite force) is the force on the air, in a direction from right to left. This latter force on the air does positive work on the air and causes its KE to increase as some of the air begins to move from right to left. After the airplane has passed (and disappeared to the left) the wake remains, moving from right to left as though it is trying to follow the airplane. The work done on the air by the reciprocal of drag exactly equals the increase in KE of the air in the wake. There is KE in the wake, but the remainder of the atmosphere is unaffected by the passage of the airplane, and its KE remains zero. The reason the air moves through a complex path around an airfoil – such as first moving upwards in the upwash, then in a circular path around the nose of an airfoil, then downwards in the downwash, is all caused by the varying pressure around the airfoil. Air near the nose of the airfoil is strongly influenced by the pressure gradient near the nose, but much less influenced by the pressure further away near other parts of the airfoil. Similarly, air near the trailing edge of the airfoil is strongly influenced by the pressure gradient near the trailing edge but much less influenced by the pressure near the nose. The vector sum of all these small pressure forces on the airfoil is the aerodynamic force on the airfoil. Lift is the component of aerodynamic force perpendicular to the velocity vector, and drag is the component parallel to the velocity vector. Finally, some ideas on the important question of the reference frame. When thinking about aviation there are three obvious reference frames.
I have rambled quite a bit here, and I probably haven’t answered all your questions. Don’t hesitate to ask some more and I will try my best to give a satisfactory answer. Dolphin51 (talk) 00:20, 14 January 2009 (UTC)
Transparent materialsDear Dolphin51: I recently submitted a new article on "Transparent Materials". While I was in the process of edting it, I was interrupted by an Editing Conflict which redirected my page to the page entitled "Transparency (optics)". I wasn't sure what to do, so I copied the majority of my material on light transmission over to the page "Transparency (optics)" where it is now firmly in place. My concern is for the material on light transmission in glasses and ceramics which was also on the original page. It has apprently disappeared altogether (?) I would like to know how to retrieve that information for the purpose of building a new page on Transparent Ceramics. Please advise...and thanks for your time and energy ! logger9 (talk) 20:08, 20 January 2009 (UTC)
Invite to Canberra Meetup #2--.../Nemo (talk • Contributions) 14:28, 22 January 2009 (UTC)
_ Bernoulli "demonstration", straw versus static portI've found several examples of Bernoulli princicple being "demonstrated" by having a stream of air blow across the top of straw with the other end drawing up water from glass implying that the pressure in the stream of air is below ambient. Realizing that aircraft use static ports to sense the pressure of moving air, I decided to create my own static port using by inserting the end of the straw through a spool of thread and attaching it to a piece of carboard. Links to pictures of my "static port": If the breeze is strong, then you'd want to cut down the size of the cardboard, or use wood. However at this point, note that real static ports can be purchased for less than $20 (USA): I then repeated the pressure measurement test using a blow dryer and a straw in water. With just the straw, the water rises indicating lower pressure in the straw. With the static port there was virtually no movment of the water. I then noted a surface tension and friction effect was resisting vertical movement within the straw, so I mixed in a small amount of liquid soap into the water. This changed the surface within the straw from convex to concave, and for some reason raised the water a slight amount (capillary like effect?). Retesting with the "static port" the water receded a small amount, indicating a slighly higher than ambient pressure in the output stream of the blow dryer. The blow dryer source is also problematic, because it has a tapered nozzle, acting as a venturi to cause a Bernoulli type exchange of speed for pressure. If the nozzle wasn't tapered, then the wash from the fan would have higher than ambient pressure, unless there is some special design of fan or propeller that reduces pressure fore of the prop more than than it increases pressure across the prop disc. This Nasa link explains what I'm getting at (prop increases pressure, air continues to accelerate after the prop as it's pressure returns to ambient): I'm not sure what is going on with the exposed end of the straw in a stream other than it interferes with the stream while the static port doesn't (apparently it's "hiding" in the boundary layer of air near the surface around the port). It's how the exposed end of the straw inteferes with the stream that has me puzzled, does it generate a vortice with corresponding low pressure? Jeffareid (talk) 04:11, 26 January 2009 (UTC)
Much AppreciatedDear Dolphin51, Thanks mate. Of all the Gin Joints in all the places... who should i meet but a fellow Aussie! I wholeheartedly agree with your intro and truly believe there is more to what's going on here at Wiki than meets the eye. It truly is a brave new world now that the shackles to knowledge have been so thoroughly loosened at last. Knowledge needs to be free if the human race is to reach it's full potential, i believe. Thanks for all the advise and your kind offer re Wikipedia usage also. I will look it up post haste and familiarize myself better with Wiki protocol. Will stay in touch and let you know if my 'thought experiment' goes anywhere interesting. TTFN, Walt Outofthewoods (talk) 22:25, 26 January 2009 (UTC)
New Article Advice
Thanks for your contributions
--Bl00513 (talk) 03:24, 29 January 2009 (UTC) Welcome!Thanks for the welcome. keeping to jets etc. ghostshipred is a craft much slower to what I'm use to. Lack of thrust!--GhostShipRed (talk) 12:11, 1 February 2009 (UTC)
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