Talk:Foil (fluid mechanics)

NACA 00xx foil formula
I believe that the "y" in the shape formula is the half-thickness (to surface from the centerline) rather than the thickness, as stated. Maybe someone more familiar with this can check; I am hesitant to change anything, but my other research finds the formula written "±y = ... etc..." GinSTexas 00:53, 13 April 2007 (UTC)


 * You're right, you reflect the formula across the centerline (which in the 00xx series is the axis) to get the full shape. scot 14:08, 13 April 2007 (UTC)

Dispute : Physics of foils
The section Physics of foils promotes some points of view that appear to be popular at present, but in my view are not soundly based on science. This section contains no in-line citations or references so it is impossible for any reader to check the validity of the presentation. WP:Verifiability says The threshhold for inclusion in Wikipedia is verifiability, not truth.

Here is my dissection of this disputed section:
 * Foil design is strongly influenced by Bernoulli's principle. It is good to see Bernoulli's principle given such prominence at this point in the section!  It is true that B's principle is pre-eminent in explaining the origin of lift on a foil, but I doubt this principle is used in the design of foils.  The primary task of foil design is accounting for the behaviour((("accounting" for the behavior of the boundary layer--don't you mean "controlling the behavior of the boundary layer?"--"The difference between the right word and the wrong one is the difference between lightning and a lightning bug."--Mark Twain)))  of the boundary layer but B's principle is not applicable in the boundary layer.(((Regarding your overall point here, and the original statement, not to get lost in your "dissection," as you put it, B's principle being a key to LIFT, a main target of exploitation, the design of a foil is of course influenced by it-- "Foil design is strongly influenced by Bernoulli's Principle.")))
 * which states that high speed fluid flow results in lower pressure on surfaces parallel to the flow B's principle addresses the pressure at all points in the fluid flow (except the boundary layer), not just on surfaces ((BUT it does result in lower pressure on the surfaces in the statement, that is, the FOIL in the fluid -- forest for the trees here again))). Pressure exerts an equal force in all directions, not just parallel to the flow. (((ibid)))
 * and the related Coanda Effect, which states that a fluid stream will follow a surface that curves away. The relevance of Coanda effect to explaining lift on a foil is disputed and controversial.  It is essential that claims of this kind are supported by in-line citations because they will inevitably be challenged. (((It IS a widely held view, and should be mentioned, albeit with a simple caveat you could have added here. The existence of the Coanda Effect and Newton would seem to synchronize here but that could have been an aside.)))
 * The traditional cambered wing is designed to accelerate airflow over the curved top surface, and deflect it downwards at the rear. This is true of all wings, airfoils and foils, not just cambered wings, and not even traditional cambered wings. (((Wings are not the only foils acting in fluids -- this is where your aerodynamic bias and blinders come in -- FINS on animals and surfboards, and other under-surface seacraft are FOILS doing foil work  in directing fluids, as are keels, and sails, and propellers.)))
 * This downwards deflection of air is balanced (according to Newton's Third Law) by a matching upwards force on the foil, which is the lift. Correct, in my view. (((THIS is a highly controversial subject and NASA and most feel that BOTH Newton and Bernoulli come into play here with regard to AIRfoils -- this one point - your editorial comment - AND the total absence of other fluids and types of foils shows you have a clear bias toward AERO, and an exclusively Newtonian view of lift, and together with the macro deletion of the parent subject Foils (Fluid Mechanics), all show that you have exercised much too much influence on this subject at hand.)))
 * It is a common misconception that the pressure differential (caused by the Bernoulli principle) is the only cause of lift, but the Bernoulli principle is only the means for generating the deflection. Who said this is a common misconception?  (((The Bernoullian pressure-delta-only explanation IS common. You know it is. You even agree with the thrust of the poster's statement, according to your comment above about Newton. Nobody DID challenge this. You merely assure us they "will.")))  This looks like original research.  It is essential that claims of this kind are supported by in-line citations because they will inevitably be challenged.
 * Examination of foils in operation shows a significant deflection of the fluid flow downstream of the foil. Yes, the deflection of the flow downstream of the foil is part of the foil's trailing vortices.  There is no reason to use this phenomenon to suggest that B's principle is somehow a misconception. (((Fair enough -- although you bring vortices into it unnecessarily and it SEEMS again, possily at odds with your Newtonian comment above, but you dont make clear that youre talking about both upper and lower surfaces of a foil and overall deflection of flow in your Newtonian comment -- hmm... you need editing too... It would be nice if the editor following YOU around didnt delete the entire subject willy-nilly though, wouldnt it?))
 * The three mechanisms all work closely together to generate the greatest amount of lift. This looks like original research.  An in-line citation is required. (((This looks like a synthesis of 3 well-known mechanisms into a synergistic process, and what SHOULD be required, and which could be endlessly editable, as per the design and intent of Wikipedia, is a comment that "it seems to be the case that all 3 mechanisms work together to produce lift.")))
 * The faster the fluid flows over the foil's surface, the more suction is generated, resulting in a stronger Coanda Effect This looks like original research.  An in-line citation is required. (((This might require a citation, but it does NOT look like original research to me. Unless you dont own any spoons or running water, or round surfaces of any kind. Then I could see how you might characterize this as looking like original research. It is not.)))
 * When the forces are right to keep the fluid flow attached to the surface of the foil, it is called laminar flow. This looks like original research.  An in-line citation is required. (((This looks like common knowledge, + a dictionary definition + a bit of bad grammar -- SOME source could perhaps be cited, but even unattributed, it should be left in -- or YOU should provide a cite.)))
 * If there is insufficient suction to keep the fluid flow attached to the foil's surface, then the flow will detach or separate and become turbulent.  This looks like original research.  An in-line citation is required. (((Bad usage of "suction" would be a fair critique and a pretty unclear second clause, but I would have simply re-phrased it and left it in -- your goal is clear by this point -- you want the parent subject killed and merged into your pet subject, AIRfoils, at the expense of: the public's understanding of foils- both natural and man-made, operating in different fluids- common sense with regard to parent and child subject headings and articles, and the Wiki project as a whole.)))
 * This turbulent flow often results in less deflection, loss of lift, and increased drag. It is true that when the angle of attack for maximum lift coefficient is reached, a further increase in angle of attack results in reducing lift coefficient and increasing drag coefficient.  However, this is more accurately described as being due to flow separation than turbulent flow. (((''This turbulent flow often results in less deflection, loss of lift, and increased drag."(((I would argue that both your comment AND the original should have been there, yours first + "turbulence" as a byproduct low pressure system.)))

This topic about lift, how it is generated, and how it is best explained is controversial. The controversy has raged for several years on the Talk pages associated with Lift (force) and Bernoulli's principle. (((http://www.grc.nasa.gov/WWW/k-12/airplane/bernnew.html))) On these Talk pages we appear to have reached consensus and successfully narrowed the debate to what can be cited in reliable scientific sources. (((It's also a matter of controversy outside of Wiki, and you know it. As for HERE, you, by definition, are saying that the Wiki-users who differed with you (have given up) and do not continue to exercise themselves against you and those who agree with your primarily Newtonian view, which again, leaves aside the Bernoulli principle as an inherent factor in lift, thus a factor in foil design, Coanda in Bernoulli/lift, and you would and did set aside any mention of the low pressure engendered by turbulence... AIRfoils are your pet subject and you had this merger accomplished at the expense of the parent subject, the reader's understanding, and the integrity and completeness of Wiki.)))

It may be that the best course of action will be to merge this article with Airfoil. Dolphin51 (talk) 02:37, 25 February 2009 (UTC)(((CLEARLY, given the light weight of your quibbles and argument here and absent any supporting views here, which I have "dissected" to use your word, this deletion of the PARENT SUBJECT should not have been done. It is editorial overreaching, and wrong in so many ways it boggles the mind.)))


 * NOTE: The above unsigned comments in () were added by Juanguzman1967 some two years after the original comments by Dolphin. Is this how the talk page is supposed to work? I found it very hard to read and understand, and had to go back to the history to figure out what had been said by whom.  Should we fix this so that it's readable? (BTW, I understand that it's not normal ettiquitte to insert my comments between Dolphin's post and Crowsnest's reply, but I felt it was the best place to make the above Fisking make sense.)


 * My $.02 for what it's worth is that the merge made sense in 2009 and still makes sense today. I'd support reverting to the last edit by Crowsnest (simply a redirect to airfoil).  Mr swordfish (talk) 21:08, 5 July 2011 (UTC)


 * I fully agree with your critique and analysis. I added merge tags to both articles involved. The discussion on the proposed merge is at Talk:Airfoil. -- Crowsnest (talk) 07:39, 25 February 2009 (UTC)

THIS looks like all of TWO editors Deleted/Merged a PARENT subject into a constituent subject. Unbelievable. Juanguzman1967 (talk) 18:58, 25 June 2011 (UTC)

I've resurrected this parent subject and provided as many background and sub-subjects as I could think of -- it is hoped that the material here is NOT controversial, and that someone more versed in the nuances and intricacies of Wiki-citation can assist by going to the sub-pages and using citation of sources already deemed legitimate by the powers that be, as the material as herein stated is supposed and intended to be straightforward, non-argumentative and non-biased and should be supported in all cases by the legitimate sources cited elsewhere for the subject(s) at hand. 98.200.236.234 (talk) 03:06, 4 July 2011 (UTC)


 * @98.200.236.234: You have resurrected this subject? I thought User talk:Juanguzman1967 had resurrected it.  How many of them are you?
 * At WP:SOCK it states Wikipedia editors are generally expected to edit using only one (preferably registered) account. Please edit using only one identity.  It makes life easier for all concerned.  Thanks.  Dolphin  ( t ) 04:35, 5 July 2011 (UTC)


 * It states: "Do not use multiple accounts to mislead, deceive, or disrupt; to create the illusion of greater support for a position; to stir up controversy; or to circumvent a block." I (juan) am not doing any of that -- thanks for more of your energetic monitoring and effort to contain the ignorant masses but I think your energy is being spent according to your irritation at having an ill-considered and biased editorial decision to delete/merge an obvious parent subject noticed, questioned loudly, and reversed by a member of the concerned, passionate wiki-lay-public, after which criticism, in multiple locations, you would not discuss or simply reverse it in deference to the  obvious oversight/overreach.98.200.236.234 (talk) 02:27, 6 July 2011 (UTC)

@Juanguzman1967: How can you suggest I am opposed to restoration of the article on Foil (fluid mechanics)? I am the one who wrote to you ''If someone is willing to develop the former article, add references and in-line citations, add new information appropriate to the general topic of foils, there is no reason why the article can't be resurrected. Let me know if I can help you with any of the above. Happy editing.'' See my diff.

I have been monitoring extensive discussion here, and on Crowsnest’s Talk page, by various people who advocate restoring this article. I thought there were six different people contributing to this debate. Look at all the following evidence of multiple Users participating in the debate:


 * Juanguzman1967


 * 98.200.236.234, 98.200.236.234


 * 99.88.232.255


 * 99.101.212.165, 99.101.212.165


 * 99.119.87.252


 * 206.16.109.32

Now I suspect there is only one – Juanguzman1967 – and all the other contributions are you masquerading as a number of different people who all support the one view. That is close to misleading, either deliberately or through negligence in not declaring your identity. Why would a registered User make so many contributions without logging on? Have another look at WP:SOCK. Dolphin ( t ) 03:17, 6 July 2011 (UTC)


 * The material is the material and supports itself - if you see dubious material and/or nefarious motives, please question it in the discussion page before editing - in the face of the good faith encyclopedic work I've done here and on related pages, major edits on your part and accusations of bad motives or behavior should be supported with evidence. Juanguzman1967 (talk) 14:21, 6 July 2011 (UTC)


 * I would also suggest a look at Discussion Guidelines and Verifiability.


 * As for the article in it's current state, it has many of the same problems that Dolphin outlined in 2009 before the re-direct to airfoil was in place: Bernoull's law is mis-represented (See Misinterpretations of Bernoulli's Law http://user.uni-frankfurt.de/~weltner/Mis6/mis6.html)Coanda effect is cited when this is in disputeThe Bernoulli Effect and the Coanda Effect are referred to as "forces"It states that the lifting force "gives a work value" when in the common example of an airplane wing the lift force (usually) does no work since it is perpendicular to the motion of the wing. And this is just the first three sentences.


 * I have no objection to the existence of a "parent" article to airfoil and hydrofoil that discusses foils in general, but the current article does not meet Wiki standards. Mr swordfish (talk) 16:07, 6 July 2011 (UTC)

“stick” to the curved surface)." - http://fun3d.larc.nasa.gov/papers/cc-paper-6.pdf
 * Re: Bernoulli, you'll have to be more specific than that for me to fix it -- or did you want to fix it -- I can probably manage it using this: http://www.grc.nasa.gov/WWW/K-12/airplane/presar.html. I didn't write it.
 * Re: Coanda effect, it does exist and you'd have to prove that it DOESNT happen on whatever foils youre arguing theoretically about in order to invalidate the fluid-turning effect (lift), wouldnt you? http://gltrs.grc.nasa.gov/reports/2010/CP-2010-216112/07%20Session%207/02%20Seume.pdf ; http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070005008_2007004956.pdf ; "Circulation control can dramatically enhance the lift of airfoils and wings. By blowing a jet of air along an airfoil surface near its curved trailing edge, separation can be delayed because of the Coanda effect (which causes the jet to
 * Fair point. Not "work." Vector is wrong. A simple edit for you, isnt it? Again, I didnt write everything here, but I did assemble it and try to make it all valid, verifiable, and usable. Simply doing away with the parent subject, subsuming it under the dubious/not-universal term of AIRfoil, and almost completely obliterating all natural and hydro- foils were one huge, obvious, terrible mistake. I havent gotten started on "Airfoil" yet, but it's extreme in its manmade/engineered bias (for some reason, haha) and is therefore inaccurate representation of the thing on Earth. Also the AIRfoil terminology is held out to be universal. It verifiably is not.  NASA, for one, does not hold that every  foil is an AIRfoil. ref: http://www.grc.nasa.gov/WWW/K-12/airplane/factors.html .  And by extension, every HYDROfoil is not a boat designed to be lifted out of the water by its ahem, AIRfoils.  I dont know how you can call the kind of foil occurring or designed for a fluid 800 times denser than air "aerodynamic" in front of a general audience with a straight face. It's like people who willfully mispronounce foreign names because "that's how we say it here."  Okay but thats not how it's pronounced. I also thought a full list of related articles and examples of different foils was important. There are foils. Some of these are airfoils. Some are hydrofoils. They do different things. Let's go on.Juanguzman1967 (talk) 02:03, 7 July 2011 (UTC)


 * Juan, Per your invitations, I will attempt to bring the article up to standard. Mr swordfish (talk) 15:41, 7 July 2011 (UTC)

Many thanks for the good faith effort.

I guess this is where I would suggest a second look at these things?


 * "A foil is a solid object with a shape such that when placed in a moving fluid at a suitable angle of attack the lift (force generated perpendicular to the fluid flow) is substantially larger than the drag (force generated parallel the fluid flow)." --- Grammar quibble: It's still a foil when it's stalled. I guess it's a matter of maybe adding emphasis.


 * Relatedly: "When oriented at a suitable angle, the foil deflects the oncoming fluid." --- Honest question re physics semantics: It deflects oncoming fluid when it's not "at a suitable angle," too, doesnt it?


 * Owing to the fact of Coanda Effect's existence, the fluid/foil surface interaction, and the NASA pages I provided you with, I think the Coanda Effect should be mentioned. If you want to qualify the verbiage as it relates to the final fluid turning that constitutes lift, you can do so, but please describe on the page how its *fluid-turning* does *not* contribute to the fluid-turning that defines lift, OR the specifics around controversy. I think the controversy is confused. I have NASA describing the effect's existence in the papers linked and we have the oncoming fluid / foil surface interaction covered on the page here. Where is the counter-evidence such that you have omitted Coanda altogether?

Thanks again Juanguzman1967 (talk) 16:37, 7 July 2011 (UTC)


 *  Grammar quibble: It's still a foil when it's stalled. I agreee. Hence the use of the word "when".  


 *  A foil will deflect fluid at most (but not all) angles of attack. The word "suitable" was chosen to be sufficiently vague that we don't have to get into which AOA generate zero lift, and also to imply that some AOA will produce more lift than drag. It's a bit of shorthand and elision, but it's technically correct when parsed carefully and implies the correct things (i.e. to work well as a foil, the AOA must be suitable.) We could make things more explicit, but at the (probable) expense of readability.  I tend to favor readability in these tradeoffs.</li></ul>


 * <ul><li>There is a pretty good treatment of the Coanda effect and how it relates to lift at http://en.wikipedia.org/wiki/Lift_force#Coand.C4.83_effect .  One of the things we try to avoid as editors is repeating the same information over and over, so I'm hesitant to add it here.   As it is, the basic summary of lift is repeated here, in airfoil, wing, hydrofoil, sail, plus some others, and I think it best to have one detailed treatment and have the other articles give a cursory summary and point to the detailed treatment.  Whether the Coanda effect is a good explanation for why the fluid attaches to the upper (outside) surface of the foil depends on how one defines it, and the science of aerodynamics defines it more narrowly than "lay" persons, making it incorrect (according to the narrow definition) as an explanation - this causes confusion and is best avoided. See http://www.av8n.com/how/htm/spins.html#sec-coanda for one side of the controversy.</li></ul>


 * Mr swordfish (talk) 18:30, 7 July 2011 (UTC)

Re Coanda, if it's true that a fluid (flow - as with a body traveling through a static airmass - the Coanda page uses "jet") will attach to and flow along a curved surface, and given "fluid-turning" as the definition and result of Lift, it seems related, very closely, to Lift, and should be included, with the controversy or uncertainty noted, but only if the controversy's existence meets the standard of "verifiability." As the WP guideline states it, this article doesnt have to be perfect, and I think the onus is actually on the Coanda-deniers here, given flow attachment along a curved surface constituting "turning."

Also, I tend to think sub-subjects should agree with their counterpart articles or sub-articles. I dont understand the opposing view. Juanguzman1967 (talk) 20:32, 7 July 2011 (UTC)

Just to clarify - here's the quote from jet "A jet is an efflux of fluid that is projected into a surrounding medium, usually from some kind of a nozzle, aperture or orifice."

A jet is not necessary to achieve the Coanda Effect. Clearly, by definition, airfoils and hydrofoils exhibit flow attachment to the foil surface while being moved through fluid or being exposed to a fluid flow. As attached flow along a curving surface is "fluid-turning," Coanda should at least be mentioned in a discussion of Lift.Juanguzman1967 (talk) 20:54, 7 July 2011 (UTC) Through a fair amount of non-WP research I am given to understand that the effect was named BY Coanda specific to attachment after exit from an orifice. I stand corrected and apologize on that point. Displacement of the fluid accounts for the low pressure leading to the foil-side attachment then?Juanguzman1967 (talk) 21:11, 7 July 2011 (UTC)

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Who uses the word "foil" ?
I've not found a source which uses this word. The article seems to have made the best of it by talking about airfoils and hydrofoils. Is it a personal colloquialism or jargon? ThanksPieter1963 (talk) 16:18, 12 December 2023 (UTC)


 * Airfoils and hydrofoils share many physical characteristics, so when talking about them in toto, the word foil is used, i.e. hydrofoils and airfoils are particular kinds of foils. In particular, sailors understand that their sails are airfoils and the rudder and centerboard are hydrofoils and simply say "foil" when referring to both. Mr. Swordfish (talk) 17:08, 12 December 2023 (UTC)


 * If it's sailor's jargon for sails and rudders do you know of equivalent use by flyers?Pieter1963 (talk) 17:40, 12 December 2023 (UTC)
 * Aircraft rarely use hydrofoils and their airfoils are usually referred to as "wings" so probably not.
 * Sailboats have always had hydrofoils, but recently there's been a lot of attention to hydrofoils that lift the boat out of the water instead of just steering it. Those boats are usually referred to as "foiling sailboats" or "foilers". See for instance  Mr. Swordfish (talk) 20:38, 12 December 2023 (UTC)


 * Thanks for that. The only use of the term foil in air I can find is wing foiling.Pieter1963 (talk) 21:50, 12 December 2023 (UTC)