From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Physics / Fluid Dynamics  (Rated Start-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Physics, a collaborative effort to improve the coverage of Physics on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
This article is supported by Fluid Dynamics Taskforce.
WikiProject Aviation / Aircraft (Rated C-class)
WikiProject icon This article is within the scope of the Aviation WikiProject. If you would like to participate, please visit the project page, where you can join the project and see lists of open tasks and task forces. To use this banner, please see the full instructions.
C-Class article C  This article has been rated as C-Class on the project's quality scale.
Checklist icon
Taskforce icon
This article is supported by the aircraft project.


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 {{mergeto}} and {{mergefrom}} 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 (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)

Airfoil Physics: Expert Help Needed[edit]

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:

See this Yahoo answers article with some informative links to sources:

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 (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#Understanding Flight
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: [1] [2] — Preceding unsigned comment added by (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)
[3]. 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)

Suction surface: "... higher velocity and thus lower static pressure"?[edit]

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)

Opening sentence of second paragraph[edit]

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#Determining_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,,, or 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)

auto archive?[edit]

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[edit]

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)

External links modified[edit]

Hello fellow Wikipedians,

I have just modified one external link on Airfoil. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:

When you have finished reviewing my changes, please set the checked parameter below to true or failed to let others know (documentation at {{Sourcecheck}}).

You may set the |checked=, on this template, to true or failed to let other editors know you reviewed the change. If you find any errors, please use the tools below to fix them or call an editor by setting |needhelp= to your help request.

  • If you have discovered URLs which were erroneously considered dead by the bot, you can report them with this tool.
  • If you found an error with any archives or the URLs themselves, you can fix them with this tool.

If you are unable to use these tools, you may set |needhelp=<your help request> on this template to request help from an experienced user. Please include details about your problem, to help other editors.

Cheers.—InternetArchiveBot (Report bug) 10:11, 6 October 2016 (UTC)