Talk:Airfoil/Archive 1

Glauert Integral
Is it just the first term (1+cos(z))/sin(z)) or the whole Fourier series solution??? Bob aka Linuxlad 22:07, 21 January 2007 (UTC)

Merger of Lift (force) into Airfoil
On Lift (force) it is suggested to merge this sub-section into this article. I already gave my opinion on Talk:Lift (force), but repeat it here since the "merge tag" directs here:

In my opinion, "Flowfield formation" (formerly "Stages of lift production"), with its description closely linked to "Lift in an established flow", is more appropriate in this article ( i.e. Lift (force) ) than it is in the airfoil article. -- Crowsnest (talk) 23:41, 24 February 2009 (UTC)

Merger of Foil (fluid mechanics) into Airfoil
A copy from Talk:Lift (force): ( Crowsnest (talk) 07:14, 25 February 2009 (UTC) )

Just when I thought it was safe to go back in the water, because we have eliminated from Lift (force) most of the pseudoscience, original research and whacky alternative explanations, I discovered the existence of Foil (fluid mechanics)! It contains a section called Physics of foils, and it is just about all pseudoscience. I have flagged this section with a Dispute tag, and dissected its contents on the Talk page. I would appreciate other Lifters having a look at it. The best thing might be to merge Foil (fluid mechanics) and Airfoil. &mdash; Dolphin51 (talk) 02:48, 25 February 2009 (UTC)


 * Just the same subject as this article (Airfoil), so I support a merge. -- Crowsnest (talk) 07:20, 25 February 2009 (UTC)


 * Do it. I don't think forking was the correct decision in the first place. it looks like an editor above didn't get the article moved and decided to start a competing article instead. That doesn't make any sense. Most of the stuff about NACA airfoils is probably already in NACA airfoil, although it looks like it's be useful to save some things like the 4-digit series equation. Michael Belisle (talk) 18:55, 25 February 2009 (UTC)


 * Merge. This article has a lot of problems not found in other articles, so I almost just want to say delete and redirect rather than merge.  The only issue is that foil refers to both hydrofoils and airfoils. moink (talk) 11:42, 26 February 2009 (UTC)


 * So what to do with foil after the merge: make it a redirect to here, or a disambiguation page for "airfoil" and "hydrofoil". My preference would be a redirect to here, since this article ("airfoil") has the foil itself as its main topic, while "hydrofoil" is more on the ship as a whole (also called hydrofoil). -- Crowsnest (talk) 12:32, 26 February 2009 (UTC)


 * I also made note of the discussion here on Talk:Hydrofoil. -- Crowsnest (talk) 12:38, 26 February 2009 (UTC)

Merger of aerofoil into airfoil
I propose to merge the aerofoil article into here (i.e. airfoil), since both articles are to large extend the same, the fundamental difference being the American spelling "airfoil" and the British variant "aerofoil". Although the WP policy is to retain the variants of English spelling, see WP:ENGVAR, I do not think it is manageable to have two identical versions of the same article, one in each spelling. That is also apparent from the five-year history of the "airfoil" and "aerofoil" articles, where most changes are being made to the "airfoil" article, and hardly any to the "aerofoil" article. Because all the changes are here (in "airfoil"), I propose to keep this article, and convert the "aerofoil" page into a redirect, and to make due reference to differences in spelling in the merged article. -- Crowsnest (talk) 10:28, 30 May 2008 (UTC)


 * Done. This is non-controversial: WP:ENGVAR actually specifies to retain the first variant of the English spelling that is used; i.e. in this case airfoil. It seems that "airfoil" is a lot more common online, as well, than "aerofoil" is, which is a shame because the latter is what I've always used. Anyhow, I've merged the articles. BigBlueFish (talk) 21:48, 9 June 2008 (UTC)
 * I think you have it the wrong way round. Airfoil is the American variant of Aerofoil and since Wikipedia is supposed to be written in the Queen's English the article should revert to Aerofoil forthwith.Petebutt (talk) 03:28, 23 September 2009 (UTC)

Changing "aerofoil" to "airfoil" in article
I propose we change "aerofoil" to "airfoil" here since the name of the article (and file) is "airfoil". It is also the more common spelling. Personally, I like British spellings, but in this case I think we should err on the side of what's more common. It's different when we are discussing a distinctly British subject. This subject is not particularly British (or any other nationality for that matter). So, In this case, we should err on what is more common. Rapparee71 (talk) 19:18, 29 March 2009 (UTC)


 * The "aerofoils" were introduced in this edit, which I have reverted. -- Crowsnest (talk) 20:02, 29 March 2009 (UTC)
 * Wikipedia is supposed to be written in ENGLISH not AMERICAN, so I am sorry but this article should be titled Aerofoil.Petebutt (talk) 03:31, 23 September 2009 (UTC)


 * I think, one wouldn't contend that "American" is as English as "British," no less so at least, unless, of course, for someone who is clinging to the erstwhile British Empire that is no more. Epaulard (talk) 15:22, 13 January 2010 (UTC)

Angle of attack
The statement that any object with an angle of attack generates lift has an element of truth to it, and the author's idea should be captured. However, the sentence should probably be made more technically precise, for a Wikipedia article. First, the "angle of attack" of an arbitrary shape is a meaningless concept. More seriously, the statement as written is simply false, and would tend to mislead the reader into thinking that air flowing over a foil "knows" what the "angle of attack" is, a common misconception which the article should not propagate. A flag pole or a sailboat mast, for example, would not necessarily create lift even if it were logically possible to define its "angle of attack". Comments? Mark.camp (talk) 21:19, 31 July 2008 (UTC)


 * True--and then you have the oddball cases like a spinning cylinder, which has an undefinable angle of attack, yet still generates lift. How about noting that any object which displaces the fluid flow perpendicular to the direction of flow generates lift, including a flat plate set at an angle of attack?  I think that's the salient point, that it's all about fluid displacement, and while shape matters, but exactly 'what' shape is not that important, as many shapes will work, albeit at varying levels of efficiency.  scot (talk) 21:27, 31 July 2008 (UTC)


 * But then why can planes fly upside down? —Preceding unsigned comment added by 12.230.251.250 (talk) 23:41, 8 October 2010 (UTC)
 * Planes have no difficulty flying upside down. A wing (or airfoil) that is capable of generating lift in one direction (when the oncoming air flow approaches with an angle of attack) is equally capable of generating lift in the opposite direction.  All it requires is an angle of attack on the other side of the chord line of the wing (airfoil).  Dolphin  ( t ) 02:59, 14 October 2010 (UTC)

Translation required

 * For intermediate Reynolds numbers already before maximum thickness boundary layer separation occurs for a circular shape, thus the curvature is reduced going from front to back and the typical wing shape is retrieved.

Can someone translate this into English please? -- 77.103.71.10 (talk) 08:49, 8 October 2010 (UTC)


 * I agree this sentence needs to be re-worked so that it is meaningful. It has been present in this article for a long time but it means very little to me.  If we can't promptly find someone who knows the background to this sentence and can edit it so we can understand it, it should be deleted. I will ask Crowsnest.   Dolphin  ( t ) 03:11, 30 December 2010 (UTC)
 * I attempted a rewrite.see image 47 from An album of fluid motion showing flow separation upstream of the maximum thickness of a cylinder at R=2000. Hence the need to increase the radius of curvature before the maximum thickness and the consequent elongation of the airfoil.--Nowa (talk) 18:03, 1 January 2011 (UTC)
 * Thanks Nowa. -- Crowsnest (talk) 10:44, 2 January 2011 (UTC)
 * Thanks Nowa and Crowsnest for your improvements to the offending sentence. Dolphin  ( t ) 21:50, 2 January 2011 (UTC)

Sorry guys it said translate into English and it was so I deleted but I didn't know it was to technical 77.103.71.10 should have told me that. I will try to simplify it but I don't understand it that well ether. Jamison Lofthouse (talk) 01:26, 4 January 2011 (UTC)

Aer(o)foil semantics
While I acknowledge the practicalities of the situation, I am with a small group dedicated to preserving the use of "good", ie. correct use of, English on the Internet. Certainly, "airfoil" is more widely used - but only because Americans outnumber English. This does not make it correct. The correct etymological term is "aerofoil". To permit policy determination by simple majority would not only lead to the hegemony of populism (and look what happemed there in the past) but to the eventual downfall of representative democracy. The majority of children are in the main reluctant to spend their evenings doing homework - should homework therefore be abandoned as a teaching reinforcement method? Most people are reluctant to pay taxes in one form or another - should this be permitted, to deny governments the means to carry out their programs? If a word is acknowledged as being "correct" in form and usage, then it should be adhered to regardless of numbers of users. Witness the confusion and endless variety of spellings and pronunciation before standard dictionaries were available. I feel passionately that to do otherwise can only lead to the deterioration of not only the English language, as distinct from the American language, but of all languages in general and eventually communication between humans.FoxIsCute (talk) 10:51, 17 July 2009 (UTC)


 * History wasn't kind to "aero". Airfoil and airplane are both here to stay, like them or not. I imagine that "aeroplane" and "aerofoil" will linger for a century or two as "British English", but I can say that to American ears at least, they already sound rather quaint, though in a pleasantly British, fussy way.
 * Mark.camp (talk) 23:12, 19 July 2009 (UTC)


 * The Manual of Style successfully grapples with the problem of different forms of English spelling. It does not specify that the English Wikipedia will adhere to either British or American spelling. It endorses the principle of retaining the existing variety, including retaining the first substantive variety of English spelling. See National varieties of English. In particular, the Manual of Style does not advocate exclusive use of American English spelling. See Retaining the existing variety. Dolphin51 (talk) 02:45, 20 July 2009 (UTC)


 * Surprisingly, the problem of different forms of English spelling predates one's own birth. It has existed since the 13th century.  Believe it or not, the Yanks joined the battle only very recently, in the early 19th century, when there was a movement to follow up the military victory at Yorktown with a new, supposedly (but incorrectly) more rational orthography of the new "American" language.  "Colour" became "color" back then, as Wikipedia may confirm, assuming that it would increase the self-esteem of its authors ;-)
 * !Mark.camp (talk) 01:51, 22 July 2009 (UTC)


 * While we are at it mentioning "aero" words that are getting swamped out of usage, let me add another clunker: "aerodrome". 98.67.107.6 (talk) 23:51, 27 July 2010 (UTC)


 * Yeh, lets all have airdynamics then (sic) - yeuch! The spellings only got changed because large parts of the (immigrant) US population couldn't spell, so some spellings were changed to make them 'simpler', see. BTW, these parts of the world all spell everything the 'proper' way. And I think India probably has a substantial population who speak and write 'proper' English.


 * ... personally though, I rather like seeing the US spellings on Wikipedia, as it rather brings to mind not-quite fully literate ten year-olds. —Preceding unsigned comment added by 86.112.83.135 (talk) 21:04, 22 March 2011 (UTC)

Foil (fluid mechanics)
The people doing this merger have inadvertently "broken" this. Foil is a nautical concept, yet the new post-merger article is entirely an aviation thing.

Worse still, it says see also: Foil (fluid mechanics) and that just redirects back here.

It would seem to me that a rudder would provide sideways forces while a wing would provide upwards forces. Perhaps it would be possible to address both in a single article, but it does not seem logical to me.

I do not have enough knowledge to fix this myself, and with the former article apparantly being riddled with pseudoscience, I wouldn't want to see a bad article brought back. But I do think that the merger was a mistake when a nautical article explaining how a rudder moves through fluid would clearly be in the interest of of the reader.

However, if you really do need to merge, airfoils and foils into a single article, I would have thought that the fact that sailing technology pre-dates flying technology would suggest that the merger should have gone the other way. If wings and centreboards really are the same thing then the wing is an evolution of the centreboard.

Please could someone who knows how to do it, put in a proposal for this article to be demerged and for a good article to replace the old Foil (fluid mechanics) article. Big Mac (talk) 15:16, 9 January 2010 (UTC)


 * "Foil is a nautical concept"?? Very questionable. The most common meaning of the word "foil" is that of an quite thin sheet of rolled metal, such as aluminum foil, tinfoil, or copper foil. Then, there are other meaning of the word "foil" that come from other sources, such as airfoil and hydrofoil, and the kind of weapon used in fencing that is called a "foil". As for airfoils, you need someone who is very knowledgeable in one of the following areas to write about them: aerodynamics, aeronautical engineering, fluid mechanics, piloting airplanes, or just about any graduate of the U.S. Air Force Academy.
 * As for amateurs who wish to argue with experts in the above fields, my response is, "Get the manure out of your ears, as well as from your mouth." 98.67.107.6 (talk) 00:38, 28 July 2010 (UTC)

This may seem to be an esoteric point, but in my view the merge of Foil (Fluid Mechanics) and Airfoil shouldnt have taken place. Specifically, there are foils operating in fluids that do not conform at all to the model of a "hydrofoil" as the term is commonly used and as represented on the page of the same name. Surfboard fins are one, but I would argue that their natural analogue (and original model), the fins of sea animals and mammals are *certainly* also "hydrofoils," according to the lifting physics of their operation. Surfboard fins of certain design and configuration most definitely are. In the vast majority of cases, they are not designed to lift the hull clear of the water surface in any way, in fact the opposite is true, and they work much the same way as wings do in applying lift to the water surface and near-surface, albeit with very different effects on the hull theyre attached to (than wings). They are a unique type of foil, a merge of air- and hydro- foil, and the existence of this (and animal fins) necessitates a fluid foil page. As to "verifiability," the content and edits to a restored page on Foil (Fluid Mechanics) should be as verifiable as possible with regard to the most well-understood general characteristics of foils seen operating in all media. The air-, hydro-, and fin areas should be represented, as well as, I would argue, the spoilers of cars and race cars and other applications I am sure I'm forgetting or not aware of. The problem of coherence is simply one that Wikipedia works through with constant flux. The best it can be is the best it can be. Please consider restoring this page to cover the overarching thing and let the fluid understanding process. — Preceding unsigned comment added by 99.88.232.255 (talk) 15:15, 5 June 2011 (UTC) EDIT: I would add that keels are shaped to effectively deflect fluid and provide lift too (from "Sailboat keels" : In sailboats, keels use the forward motion of the boat to generate lift to counteract the leeward force of the wind. The rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion." These are obviously doing the work of LIFT: deflecting flow, in this case water, and yet are obviously not "hydrofoils," as given on the page of that name, nor "airfoils," as per that page. The broader page on the subject "Foils (Fluid Mechanics)" should be restored. — Preceding unsigned comment added by 99.88.232.255 (talk) 22:20, 5 June 2011 (UTC) I would also add Propellors to the list of foils acting underwater without lifting a hull clear of the surface as represented on the "hydro" foil page. http://en.wikipedia.org/wiki/Propeller. Why this didnt occur to me before as a clear example of a hydrofoil I dont know. The US Navy has used the term "hydrofoil" for submerged foiled control surfaces here: http://www.navysbir.com/n09_2/N092-143.htm. And consider the laughable confusion of terms here: http://www.docstoc.com/docs/68702716/CONTROL-SURFACE-AND-ACTUATOR-DESIGN-FOR-A-LOW-DRAG--LAMINAR-FLOW-AUV. Clearly the "Hydrofoil" page is totally incomplete, at a minimum. EDIT: After studying the pages on Aerodynamics (ref: "Aerodynamics is a branch of dynamics concerned with studying the motion of AIR" - emphasis added to highlight the relatively uniform viscosity of the subject medium vs the highly variable viscosity of ALL fluids, plasma, gases, liquids, air, etc), vs Fluid Dynamics, and Fluid Mechanics, it is impossible to not feel, yes, aggrieved that the subject of Foils (Fluid Mechanics) was evaporated willy-nilly into "AIRfoil."12.25.96.34 (talk) 01:09, 10 June 2011 (UTC)

Objections against the merger of Foil (fluid mechanics) into Airfoil
On request, I copy the following material from my talkpage to here, for discussion, Crowsnest (talk) 06:07, 10 June 2011 (UTC) :


 * This may seem to be an esoteric point, but in my view the merge of Foil (Fluid Mechanics) and Airfoil shouldnt have taken place. Specifically, there are foils operating in fluids that do not conform at all to the model of a "hydrofoil" as the term is commonly used and as represented on the page of the same name. Surfboard fins are one, but I would argue that their natural analogue (and original model), the fins of sea animals and mammals are *certainly* also "hydrofoils," according to the lifting physics of their operation. Surfboard fins of certain design and configuration most definitely are. In the vast majority of cases, they are not designed to lift the hull clear of the water surface in any way, in fact the opposite is true, and they work much the same way as wings do in applying lift to the water surface and near-surface, albeit with very different effects on the hull theyre attached to (than wings). They are a unique type of foil, a merge of air- and hydro- foil, and the existence of this (and animal fins) necessitates a fluid foil page. As to "verifiability," the content and edits to a restored page on Foil (Fluid Mechanics) should be as verifiable as possible with regard to the most well-understood general characteristics of foils seen operating in all media. The air-, hydro-, and fin areas should be represented, as well as, I would argue, the spoilers of cars and race cars and other applications I am sure I'm forgetting or not aware of. The problem of coherence is simply one that Wikipedia works through with constant flux. The best it can be is the best it can be. Please consider restoring this page to cover the overarching thing and let the fluid understanding process. — Preceding unsigned comment added by 99.88.232.255 (talk) 15:15, 5 June 2011 (UTC) EDIT: I would add that keels are shaped to effectively deflect fluid and provide lift too (from "Sailboat keels" : In sailboats, keels use the forward motion of the boat to generate lift to counteract the leeward force of the wind. The rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion." These are obviously doing the work of LIFT: deflecting flow, in this case water, and yet are obviously not "hydrofoils," as given on the page of that name, nor "airfoils," as per that page. The broader page on the subject "Foils (Fluid Mechanics)" should be restored. — Preceding unsigned comment added by 99.88.232.255 (talk) 22:20, 5 June 2011 (UTC) I would also add Propellors to the list of foils acting underwater without lifting a hull clear of the surface as represented on the "hydro" foil page. http://en.wikipedia.org/wiki/Propeller. Why this didnt occur to me before as a clear example of a hydrofoil I dont know. The US Navy has used the term "hydrofoil" for submerged foiled control surfaces here: http://www.navysbir.com/n09_2/N092-143.htm . And consider the laughable confusion of terms here: http://www.docstoc.com/docs/68702716/CONTROL-SURFACE-AND-ACTUATOR-DESIGN-FOR-A-LOW-DRAG--LAMINAR-FLOW-AUV . Clearly the "Hydrofoil" page is totally incomplete, at a minimum. EDIT: After studying the pages on Aerodynamics (ref: "Aerodynamics is a branch of dynamics concerned with studying the motion of AIR" - emphasis added to highlight the relatively uniform viscosity of the subject medium vs the highly variable viscosity of ALL fluids, plasma, gases, liquids, air, etc), vs Fluid Dynamics, and Fluid Mechanics, it is impossible to not feel, yes, aggrieved that the subject of Foils (Fluid Mechanics) was evaporated willy-nilly into "AIRfoil."
 * 99.101.212.165 (talk) 04:08, 9 June 2011 (UTC)


 * Hello, the discussion on the content of Wikipedia articles takes place on the talk page of the concerning article. In this case that is on Talk:Airfoil, so that other editors can give their opinion, in order to reach consensus. It would be best if you bring up your concerns there, in a new section. If you wish so, I can copy this section to Talk:Airfoil. I myself am working on other subjects at the moment. Best regards, Crowsnest (talk) 10:49, 9 June 2011 (UTC)


 * Please do copy this to Airfoils Talk. My apologies.  The Foils page I'm referring to above is a matter of passionate interest to me (everybody's got something) but you won't see me elsewhere most likely--but I won't rest until the Foils (Fluid Mechanics) page is restored. Merging it with Airfoils was a huge mistake for all the above-cited reasons.  — Preceding unsigned comment added by 206.16.109.32 (talk) 15:35, 9 June 2011 (UTC)

My first thought is to further note and question this merger especially with regard to the stated academic background of Dolphin, the #1 editor (and here I thought Wiki was supposed to be an open democratic process) who studies AIRfoils pretty exclusively it seems--and quote the old saw: "When all you have is a hammer, everything looks like nails," and this version: "When you have a current foremost professional academic interest in AEROdynamics and there is plainly a gap in the English language around teh ubject of foils acting in all kinds of fluid from air to substances over a thousand times the density of air, all foils = AIRfoils, and the rest is just backwash," and #2 editor Crowsnest, whose background is in "several areas" but specifies only "water waves." Given the cited litany of gaps in the airfoil and hydrofoil pages and especially given a US Navy document (and several online dictionaries and thesauruses) referring to underwater control (lifting, per redirection, not upward per se) surfaces and animal fins as "hydrofoils," it's clear this merger was done out of a narrowness of vision and an excess of editorial enthusiasm in too few hands, not conducive to the mission or in accord with the the mission and democratic ethics of Wikipedia and state again (and again), that the macro subject page Foils (Fluid Dynamics) should have been left to stand. but on second thought, I think I'll just tell everyone I know that Wikipedia is completely unreliable inasmuch as with the limited numbers of academicians running the show behind the scenes, it ends up the case that Wikipedia refers to all seagoing animals' FINS as AIRfoils, though NASA apparently doesnt see the need to confuse the issue by mentioning fluids other than air anywhere I have found in its educational pages on the subject of AIRfoils. Discretion and a right understanding of "Wiki," gentlemen--seems vital 99.101.212.165 (talk) 17:34, 11 June 2011 (UTC)

From the editor commentary on this merger, with comments inline: Just the same subject as this article (Airfoil), so I support a merge. -- Crowsnest (talk) 07:20, 25 February 2009 (UTC)**Airfoils share characteristics which is a good reason to mention both on a Foils (Fluid MEchanics) page, but are NOT the same thing as underwater foils and ignoring the existence of underwater hydrofoils is a disservice to Wikipedia and its users, however casual, as well as to reality.** Do it. I don't think forking was the correct decision in the first place. it looks like an editor above didn't get the article moved and decided to start a competing article instead. That doesn't make any sense. Most of the stuff about NACA airfoils is probably already in NACA airfoil, although it looks like it's be useful to save some things like the 4-digit series equation. Michael Belisle (talk) 18:55, 25 February 2009 (UTC)**Almost totally insubstantial argument here, but the protocol about the prior editor is especially bad. The argument is solely about editor convenience, or workload, or something -- not the end user's benefit.** Merge. This article has a lot of problems not found in other articles, so I almost just want to say delete and redirect rather than merge. The only issue is that foil refers to both hydrofoils and airfoils. moink (talk) 11:42, 26 February 2009 (UTC)**Aha! The afterthought in this comment should have been a huge consideration on the front end, shouldnt it? But also, the provably incorrect material on the page should have simply been corrected. The macro Foils page didnt need to be deleted** So what to do with foil after the merge: make it a redirect to here, or a disambiguation page for "airfoil" and "hydrofoil". My preference would be a redirect to here, since this article ("airfoil") has the foil itself as its main topic, while "hydrofoil" is more on the ship as a whole (also called hydrofoil). -- Crowsnest (talk) 12:32, 26 February 2009 (UTC)**So you would delete the page on Airfoils because there is a powered machine called an Airplane and you only need to explain how that thing works, although there are other types and instances of foils operating in air. Definitely the choice should have been a disambiguation page. There shouldn't be an issue with a macro subject page (however long) which covers all types and natural occurrences of foils seen operating in all media, for the end user's best understanding of the subject, and a complete exploration of a thing which is definitely a viable subject as a whole. Foils (fluid Mechanics) page should also be extant if for NO other reason than to avoid the ridiculous spectacle of AIRfoil being argued to literally cover FINS, and AEROdynamics being argued to literally cover all foils in all fluids as the Airfoil page shows, in the face of the AEROdynamics page's own definition of Aerodynamics--as a subfield of fluid dynamics! This merger was a giving way to jargon at the expense of users' benefit and understanding. Just about any user trying to reach an understanding of this stuff as a new subject would have to go much too far to derive why a couple of academics (one most active in Airfoils and the other in Wave action) chose to delete the parent subject of Foil, omit the vast majority of hydrofoils in the world from Hydrofoils, and conflate them into Airfoils. Ref: http://www.google.com/search?rlz=1C1_____enUS424US424&sourceid=chrome&ie=UTF-8&q=aerodynamic and http://en.wikipedia.org/wiki/Aerodynamics 206.16.109.32 (talk) 18:37, 13 June 2011 (UTC) Also: http://en.wikipedia.org/wiki/Fins — Preceding unsigned comment added by 206.16.109.32 (talk) 18:45, 13 June 2011 (UTC)

Foil

From Wikipedia, the free encyclopedia

(Redirected from Foil (disambiguation))

Look up foil in Wiktionary, the free dictionary.

Foil may refer to:

...

Fluid dynamics (INCLUDING aerodynamics)(emphasis mine)

Airfoil, used on aircraft of all kinds

Foil bearing, a type of fluid bearing

Hydrofoil, an underwater foil used to lift a certain kind of rapidly moving motorboat. Or otherwise, a common term used for that entire motorboat, from bow to stern. (OTHERWISE, a foil used underwater to redirect flow and thereby provide LIFT, but not designed at all to lift the hull clear of the water)

Parafoil, a nonrigid airfoil, inflated during use (should this not be merged into airfoil too?

Shouldnt "HYDROFOIL" also be merged into AIRFOIL owing to its similarities? Shouldnt the whole kit and kaboodle be merged UNDER "Foils (Fluid Mechanics)" actually?? YES. Yes they should. The parent subject is the parent subject, people. How did the most logical hierarchy get overlooked here? Answer: an aviator who only knows wings exercised too much control over the decision. I continue to be amazed and frustrated by the eds inability to acknowledge this fact and reverse the merger. Juanguzman1967 (talk) 17:37, 29 June 2011 (UTC)

Introduction (or pre introduction)
Today I edited the third paragraph of the article to bring it in line with the treatment over at Lift(Force) and in accordance with WP:NPV. I also added some citations.

Please discuss here before reverting the edits. Thanks. Mr swordfish (talk) 15:39, 6 July 2011 (UTC)


 * Only one minor comment. Your new text applies the principle that an airfoil alters the speed and direction of the air, and the consequence is lift.  This principle is found in a number of places in Wikipedia and aviation-related literature.  I suggest a slightly different approach, saying the airfoil alters the speed and direction of the air, the consequence is the aerodynamic force on the airfoil; the component of this aerodynamic force perpendicular to the relative motion of airfoil and freestream is called lift ( and the component parallel to the relative motion is called drag.)  Dolphin  ( t ) 22:33, 6 July 2011 (UTC)

Proposal for better top-of-page illustration
I’ve been working on a diagram to replace image:Airfoil.svg with a cleaner, crisper diagram, it’s at image:Wing profile nomenclature.svg. Is it worth swapping the two images? Ariadacapo (talk) 19:11, 23 November 2011 (UTC)
 * I think your new diagram is a significant improvement over the one currently in use. I am in favour of the two images being swapped.
 * I can make a couple of suggestions for your diagram. You have labelled the top surface and the lower surface.  I suggest top surface should be changed to upper surface.  Your diagram, and the current one, show a line labelled chord.  The chord of an airfoil is a dimension, usually in feet and inches or metres.  The line on the  diagram is the chord line, similar to the camber line you have shown.
 * Congratulations on a great new diagram. Please go ahead and make the swap!  Dolphin  ( t ) 22:04, 23 November 2011 (UTC)
 * Thank you very much for the feedback! I incorporated your suggestions, and swapped the images. I intend to publish a French translation too, and gratefully take feedback. Ariadacapo (talk) 09:14, 24 November 2011 (UTC)
 * Thanks! It looks great.  Dolphin  ( t ) 10:32, 24 November 2011 (UTC)

Moving on, I’ve drawn a new one (image:Examples of Airfoils.svg) to illustrate the concept of airfoil (rather than just the vocabulary). It doesn’t fit too well in terms of graphical layout in the article, in my opinion. I’ll experiment; I welcome feedback. Ariadacapo (talk) 10:57, 4 December 2011 (UTC)

Definition of airfoil thickness
I seek help in defining the thickness of an airfoil, so as to make sure that File:Wing profile nomenclature.svg is correct. My struggle is detailed in the talk page of that file. Please participate if you can help. Ariadacapo (talk) 19:55, 8 December 2011 (UTC)
 * I hope that it is solved now, as by my edit of today (and with a new illustration). Ariadacapo (talk) 17:33, 11 December 2011 (UTC)

thin airfoil theory
The section on thin airfoil theory is pretty messy and convoluted. We need to separate the derivation of the theory from the actual theory itself. The theory itself isn't very well defined, and i have a source i can use to make it eaiser to understand. I'm gonna do that. Help would be great. Fresheneesz (talk) 19:08, 24 September 2008 (UTC)


 * And another note: the section refers to the article about lifting-line theory. If I recall correctly, lifting-line theory models the behaviour of a 3D wing with varying circulation. Thin airfoil theory on the other hand models the behaviour of a 2D wing/airfoil, and is therefore not related to lifting-line theory. In my opinion, the link is therefore not correct, but maybe I'm mistaken. Stefanlinden (talk) 17:19, 25 February 2012 (UTC)

Better airfoil schematic
I stumbled upon this image: http://www.boatdesign.net/forums/attachments/fiberglass-composite-boat-building/58709d1310445871-hydrofoil-parts-maker-sail-airfoil-shape.gif

This seems to explain the airfoil's shape better in relation to its features, and is more useful as the airfoils image now used on this page (this has airfoils of various animals, rotors, and wings). BTW: a dolphin has a hydrofoil, not airfoil

perhaps it can be recreated by the graphic lab and used in this article ? 91.182.226.124 (talk) 14:28, 19 February 2012 (UTC)


 * Hello 91.182.226.124, this is very interesting, definitely a good idea. Unfortunately I do not have the time to pursue this right now.
 * Note that a more advanced possibility is to draw the polar diagram for each profile, perhaps like on this draft file. I’ll definitely look into it in the future.
 * Thanks for the input, and apologies for the delay in answering, Ariadacapo (talk) 10:36, 17 March 2012 (UTC)

Airfoil categorization and there application
Hi,

I suggest that we need to add Airfoil categorization based on t/c ratios and list there applications. Like rounded Leading edge airfoil are used when flow is subsonic etc... --Raj 17:58, 21 June 2012 (UTC)

airvoil vs aerofoil redux
Someone has changed all the instances of airfoil to aerofoil. This has been discussed here several times before but I'm not sure that a consensus was reached, although the net effect seems to have been to use airfoil instead of aerofoil. I'm going to revert the latest changes pending some kind of consensus here.

My own opinion is that I don't have strong feelings about it, but if we're going to title the article "airfoil" that's the term we should use throughout. I'd also observe that almost all of the references I have at hand use "airfoil". Mr. Swordfish (talk) 00:24, 25 June 2012 (UTC)


 * I've now read the relevant sections in the wikipedia Manual of style and it's pretty clear that "airfoil" is in accordance with the manual and changing it to "aerofoil" is not. Mr. Swordfish (talk) 01:40, 25 June 2012 (UTC)

Suction surface: "... higher velocity and thus lower static pressure"?
In the "Airfoil terminology" section, one definition is:

The suction surface (a.k.a. upper surface) is generally associated with higher velocity and thus lower static pressure

Is the "thus" necessary? Or is it perhaps even misleading, given the Bernoulli/airfoil confusion/controversy? (I'd delete it myself, but I'm in no way an authority on the topic...) -- Dan Griscom (talk) 00:43, 13 January 2013 (UTC)


 * I completely agree, the "thus" is misleading, and in any case, entirely unneeded in this terminology section. I have just removed it. Well spotted... Ariadacapo (talk) 08:11, 13 January 2013 (UTC)


 * Thanks, and thanks for fixing it. -- Dan Griscom (talk) 03:54, 14 January 2013 (UTC)

Airfoil Physics: Expert Help Needed
People, this article needs attention from an expert: airfoils generate lift primary by accelerating air downward (Newton's Law), not due to Bernoulli's Principle.

A good explanation can be found here: http://www.eskimo.com/~billb/wing/airfoil.html

See this Yahoo answers article with some informative links to sources: http://answers.yahoo.com/question/index?qid=20081101172100AALf6HT

It is common knowledge that stunt aircraft with symmetrical airfoils can fly inverted, and I have personally flown a radio-controlled aircraft with a "normal" (flat-on-the-bottom) airfoil inverted, in seeming violation of Bernoulli's Principle.

I respect your work, but this article is misleading. —Preceding unsigned comment added by 173.45.208.242 (talk) 03:15, 25 November 2009 (UTC)


 * This is particularly true for any wing -- accelerated air on top side of wing involves additional masses of air with it, and resulting air moves slightly down. Still, effect of Newtonian deflection of air looks much smaller, than the force generated by Bernoulli. ~ ☭Acodered (talk) 12:55, 25 November 2009 (UTC)


 * Wikipedia articles including Airfoil, Bernoulli's principle and Lift (force) have been regularly vandalised by anonymous persons, and the occasional registered User, who want to erase any suggestion that Bernoulli's principle is relevant in explaining the lift on a wing or airfoil. These people want to erase all reference to Bernoulli and replace it with the notion that lift on a wing or airfoil can only be explained by Newton's Third Law of Motion. These Users occasionally cite as their reference a Web site for enthusiastic amateurs, or the book Understanding Flight by David F. Anderson and Scott Eberhardt, but never has a legitimate, serious reference been cited. Fortunately, a number of registered users have been diligent in reversing all these well-intentioned but ill-informed attempts to erase Bernoulli from all articles related to lift and airfoils. I de-bunked the efforts of Anderson and Eberhardt at Talk:Bernoulli's principle/Archive 2


 * Newton's Third Law of Motion is universal. It applies in EVERY situation where a pair of forces exist, so it is never an explanation as to why a particular force exists. For example, when an electrical conductor is placed close to a magnetic compass, and an electric current is caused to flow through the conductor, the needle of the magnetic compass deflects. An amateur might attempt to explain why the compass needle deflects by saying, "Newton's Third Law of Motion. The compass needle exerts a force on the electrical conductor, and therefore the conductor exerts a force on the compass needle and this is why the needle deflects." However, most people would find this a highly unsatisfactory explanation of why the compass needle deflects because it asks for the follow-up question, "Well why does the compass needle exert a force on the electrical conductor?" For the same reason, saying an airfoil generates lift because of Newton's Third Law of Motion is highly unsatisfactory to many people, especially as it asks for the follow-up question "Well why does the airfoil exert a force on the air to accelerate it downwards?"


 * All readers who think that Bernoulli's principle has no place in explaining lift on an airfoil, and who think Newton's Third Law is the only legitimate answer, are invited to read David Ison's excellent summary of the situation at Bernoulli Or Newton: Who's Right About Lift?  Dolphin51 (talk) 22:18, 25 November 2009 (UTC)


 * I thought the application of Bernoulli's principle in relation to lift had long ago been disproved.  I'll cite: Arvel Gentry's work ::I thought the application of Bernoulli's principle in relation to lift had long ago been disproved.   I'll cite:    — Preceding unsigned comment added by 58.168.112.209 (talk) 10:46, 9 March 2013 (UTC)
 * You thought wrong. The phenomenon of airfoils generating lift is a perfect illustration of Bernoulli's principle. There are some authors who argue persuasively that Bernoulli's principle is too complex for many student pilots and newcomers to the field of aviation. Bernoulli's principle is only half the explanation of lift because it doesn't explain why air flows faster across one side of the airfoil than across the other - to understand the two different airspeeds it is necessary to be familiar with the Kutta condition. For readers not conversant with Kutta and Bernoulli, Newton's Third Law of Motion provides an explanation of lift that is more easily comprehended. None of these authors has stated that Bernoulli's principle applied to lift is incorrect, or that it has been disproved. These are authors who are writing for a readership that comprehends Newton's Laws of Motion but is not yet conversant with Bernoulli's principle and the Kutta condition. Dolphin  ( t ) 12:16, 9 March 2013 (UTC)


 * Samples with cites of "a common misconceptions" is awesome. ~ ☭Acodered (talk) 00:41, 26 November 2009 (UTC)


 * What are Samples with cites of "a common misconceptions" ?? Dolphin51 (talk) 01:55, 26 November 2009 (UTC)


 * . It's a good idea to collect all typical misconceptions in one article. Sorry for my English, I'm newbie there ~ ☭Acodered (talk) 02:59, 26 November 2009 (UTC)

Opening sentence of second paragraph
It currently reads:


 * The lift on an airfoil is primarily the result of its angle of attack and shape.

Recent proposals have been suggested and reverted:


 * The lift on an airfoil is primarily determined by its angle of attack and shape.
 * The lift on an airfoil is primarily the result of its shape and angle of attack.

As per Consensus,


 * "In discussions of proposals to add, modify or remove material in articles, a lack of consensus commonly results in retaining the version of the article as it was prior to the proposal or bold edit."

the current version should be kept until consensus is reached here on the talk page.

So, please justify the change. Mr. Swordfish (talk) 15:20, 30 July 2013 (UTC)

"Result of" says that lift is created by the mere presence of an airfoil. Obviously not true. And you still haven't explained why you don't like this phrasing. --Isaac Rabinovitch (talk) 15:32, 30 July 2013 (UTC)


 * I don't like it because it's passive. "Result of" is a more active phrase - tilt the airfoil or change it's shape and the lift changes. Pilot does X and the result is Y.  "Determined by" is less active and more equivocal.    It's not worth going to go to the mat on this one, but I'd like to keep the article more readable, and equivocal passive constructions inhibit readability.  Mr. Swordfish (talk) 18:27, 30 July 2013 (UTC)
 * OK, let's avoid passive voice. But my objection to "result of" stands. How about "function of"? Isaac Rabinovitch (talk) 19:38, 30 July 2013 (UTC)


 * The phrase "function of" assumes that the reader knows what a function is. While I have no problem with using mathematical terminology further down in the article I think it's best to avoid what might be an unfamiliar term this early in the article.  I still don't understand your objection to "result of".  An airfoil encountering a flow at some angle of attack will experience lift - that's all you need: airflow & AOA results in lift.  Mr. Swordfish (talk) 13:28, 31 July 2013 (UTC)
 * But the word "airflow" doesn't appear in the sentence. I certainly don't have an issue with saying that lift is the result of airflow. "Result" implies a cause-and-effect relationship. "Booth shot Lincoln. As a result Lincoln died". Not "Lincoln's death was the result of the kind of gun Booth used." --Isaac Rabinovitch (talk) 21:36, 31 July 2013 (UTC)


 * Angle of Attack is defined as the angle between the foil and the airflow, so the presence of an AOA implies an airflow. I think the context makes it clear that we are talking about a foil in an airflow; see the first sentence of the previous paragraph and the sentence that follows. Mr. Swordfish (talk) 12:47, 1 August 2013 (UTC)
 * Let me confuse things a little more. The sentence in question implies that the magnitude of the lift on an airfoil varies as the angle of attack varies, and as the shape varies. When talking about an airfoil we are talking about an airfoil of a particular shape, so shape isn't a variable. We could say The lift on an airfoil is primarily the result of its angle of attack. However, I prefer The lift on an airfoil is primarily determined by the angle of attack, the relative speed of the flow past the airfoil, and the density of the fluid. Notice I didn't mention the planform area of the airfoil; that is because when talking about an airfoil, its area has already been fixed.  Dolphin  ( t ) 13:36, 1 August 2013 (UTC)


 * While I agree that within the field of aerodynamics the term 'airfoil' has the special meaning of "the shape as seen in cross-section", common English usage refers to the wing (or blade or sail or whatever) itself. For instance, see http://www.thefreedictionary.com/airfoil, https://www.vocabulary.com/dictionary/airfoil, http://dictionary.reference.com/browse/airfoil, or http://www.merriam-webster.com/dictionary/airfoil.  Who are we writing this article for?  Mr. Swordfish (talk) 19:24, 1 August 2013 (UTC)
 * In my paragraph above, I was using airfoil to mean a three-dimensional body such as a wing, propeller or sail with finite span, rather than the specialized meaning of a two-dimensional shape with infinite span. I agree that we are writing the article for the widest audience possible, and that includes young people and newcomers to the field of airfoils. Dolphin  ( t ) 23:04, 1 August 2013 (UTC)


 * In that case the shape is variable. Airplane wings have flaps and such, sailboats have all sorts of controls to affect sail shape.  Many real 3-D bodies that act as airfoils are capable of changing their "airfoil" shape. agree that density and flow speed are two important factors.  Not sure if the article would be improved by adding those in the sentence at hand.  Mr. Swordfish (talk) 21:47, 2 August 2013 (UTC)
 * I see that the sentence in question is followed by: When oriented at a suitable angle, the airfoil deflects the oncoming air, I agree that mention of density and flow speed would only serve to complicate this paragraph. Perhaps the best way to begin the paragraph is by stating The lift on an airfoil is primarily determined by the angle of attack.  Dolphin  ( t ) 06:33, 3 August 2013 (UTC)

Discussion
I like this topic. let's discuss it!


 * OK. I've done a number of things on sailboats and sailing, and I generally use the term "foil" since they have both air foils (the sails) and water foils (centerboard, keel, rudder, etc.).  I'm thinking of renaming the article "foil (aerodynamics)" or the like, and pointing the "airfoil" entry at that.  I might also create some sections on simple foil designs, such as the NACA foils (the 00xx, for example, are widely used in boats) and the Extra section foils (also used in boats).  scot 17:02, 12 July 2005 (UTC)


 * I don't want to sound like an aeroshauvinist but no one will look it up as anything but airfoil or aerofoil. There are dozens of links to here as it is. Calling it "foil (aerodynamics)" wouldn't help. Please don't move it. There are sail and centerboard articles that need work and linking. This one too will be a good long article when we get to expanding it from the stub that it now is. Meggar 20:38, 2005 July 12 (UTC)


 * The problem with calling it "airfoil" is that an airfoil is a specialized case, a foil designed to work in air. Yes, almost everyone will come looking for "airfoil", unless they came from a boat article, but having a redirect or stub from "airfoil" and "aerofoil" directing them to "foil" for the technical description would still get them what they need quickly.  With boating articles, the reader is directed to the "foil" disambiguation page, where they have to dig through and find that for information on lifting foils under water, they are directed to the "airfoil" page (unfortunately, what should be the correct term for a water based foil, "hydrofoil", has been hijacked in English to cover a couple of classes of powerboats).  A generic foil article could cover foils in general, and then point out the differences in Reynolds numbers that split foils into two fuzzy groups, air and water foils.  All appropriate terms such as, airfoil, aerofoil, hydrofoil, lifting foil, etc. could all direct to the common page (and maybe "lifting foil" would be a better name?).  Ideally the article for lifting foils would be just "foil", since all other foil entries have some obviously applicable modifier.


 * Tabling the issue of names, what sort of stuff should go in a generic lifting foil article? I can put some stuff together about NACA sections, especially the 00xx symmetric foils, as those are often encountered in sailboats, both the underwater lifting surfaces and rigid wing sails.  I've also run across formulas for other NACA foil shapes (the 4xxx series in particular), and a section used for thin symmetric foils called the Extra section, that is an elliptical leading edge and a wedge trailing edge.  I even have a copy of XFoil handy that I could used to generate some screenshots of pressure distributions across different foils.  scot 21:25, 12 July 2005 (UTC)


 * Try to concider how it will work in the future when all the articles have grown much larger. Anyway, my vote is not to merge or rename. Now the and  notices should be placed in the articles to be effected to get other opinions. Meggar 07:01, 2005 July 14 (UTC)


 * Hi. Partly since I'm interested in biomechanics, I feel scot's "Re-related topics" or medium-dependent topics ought to be covered somewhere. Also, I think the situation is a bit similar to that of propeller, which also is wing-related matter, and has both aero- and hydro- usage. Cavitation might also have a relationship.
 * By the way, if a general name is needed, what about Wing section? This doesn't have ambiguity as foil, nor aero-PoV. However, I don't know at all how common is this term... (well, I have a book named "Theory of Wing Sections", but I'm not so sure... it's old-fashioned maybe?) Is lifting foil better? Hmm... I can't judge..
 * Anyway, I feel we should keep this article at least, and then creating "lifting foil" or "wing section" or like that for general explanation. Do I miss the point? - Marsian / talk 09:34, 14 July 2005 (UTC)


 * I think "wing section" is a bit less general, since it implies "wings" which implies "aircraft". In fact, not all airfiols are used for generating lift; a fat NACA 00xx foil is perfect for, say, a landing gear support on a fixed gear airplane.  The NACA foil provides far less drag than a cylinder of the same thickness, since its purpose is to prevent flow separation; the lift it generates is really a byproduct of being able to operate at high angles of attack because it doesn't stall easily.  Of course, that argument goes against the term "lifting foil" as well...
 * I definately agree that there needs to be an article for "airfoil" since that is the most common use of foils. Since the "how" discussion of foils is really a case of applied fluid mechanics, maybe the technical article could just be "foil (fluid mechanics)"?  That seems to be perfect for discussions of Reynolds numbers, boundary layers, turbulent and laminar flows, etc.  Sections within the article could cover symmetric foils, supersonic foils, lifting bodies, and anything else related to forms that decrease drag and/or increase lift.  scot 15:55, 14 July 2005 (UTC)


 * I see. And your solution seems good, except one thing. There remains the possibility of "foil (fluid dynamics)". I myself do not care whichever the name will be, but some could argue this point... It might be better to ask the members of WikiProject Fluid dynamics and/or drop a notice at Talk:Fluid mechanics... But well, I'm too anxious maybe. After all, the name can be changed in the future so you don't have to care much. - Marsian / talk 02:32, 15 July 2005 (UTC)


 * The Wikipedia "fluid dynamics" article redirects to "fluid mechanics"; I'd have used dynamics, too, but picked mechanics since that's what the relevant article was named. I'll create a "foil (fluid mechanics)" page so development can start.  scot 13:57, 15 July 2005 (UTC)


 * I thought the internationally accepted terms were aerofoil and hydrofoil? I've never heard anyone (American, British or otherwise) use this term before. Isn't this just a logical extension of 'Airplane', with no real usage? — Preceding unsigned comment added by 151.225.64.22 (talk) 02:02, 18 December 2013 (UTC)
 * The spelling "aerofoil" is not used by American authors; they use the spelling "airfoil". Dolphin  ( t ) 02:12, 18 December 2013 (UTC)

Auto Archive?
We just had someone reply to an 8-year old thread. I think the time has come to auto-archive this talk page. Discussion? Mr. Swordfish (talk) 16:44, 19 December 2013 (UTC)
 * I agree. I'm not conversant with auto-archiving on Wikipedia so I can't be of much assistance. Dolphin  ( t ) 01:01, 20 December 2013 (UTC)
 * What's wrong with replying to an 8 year old thread?  Wikipedia is not in a hurry! ;-) --Kim Bruning (talk) 11:07, 17 October 2014 (UTC) They said, answering a 10 month old thread

Coanda effect
This online article by Jef Raskin on the Coanda effect makes a rather strong case that the Coanda effect is not only important in airfoil design, but is actually the dominant factor (over Bernoulli, by a very wide margin). The author points out that a lot of entry level texts are wrong, but that better researched science texts do provide the correct answers (else I suppose we wouldn't be able to build actual aircraft ;-). No matter how useful WP:RS-wise the article itself is, I think it puts forward good arguments, and there are plentiful (hopefully RS) sources provided (to peruse sometime in my -or someone elses :-P- copious free time ;-).

Certainly, having no mention of the Coanda effect here at all strikes me as strange. --Kim Bruning (talk) 11:04, 17 October 2014 (UTC)
 * What value is there in an article that "explains airfoils" in terms of Coanda effect, bases much of it on extrapolation from model aircraft, but never mentions Reynolds number? Andy Dingley (talk) 11:09, 17 October 2014 (UTC)

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What is "y" in Fourier coefficient definition?
Hello,

I don't really understand what is "y". Is it "yc" the camber line or something else? Please could you explain?194.214.171.57 (talk) 13:44, 14 November 2018 (UTC)
 * It appears to me that x and y describe the mean-line of a thin airfoil. y is the vertical component, or coordinate on the y-axis, of each point on the mean-line of a thin airfoil.
 * The section is currently unreferenced and this makes it more difficult to interpret than it should. I have inserted the “Unreferenced section” banner. Dolphin ( t ) 22:29, 15 November 2018 (UTC)