# Talk:Chord (aeronautics)

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## Chord length

Hi. According to the article "chord refers to the distance between the leading edge and trailing edge of a wing measured in the direction of the normal airflow", so the first figure is wrong since the chord lenght should be horizontal. If I'm wrong, please explain me why.

Cross section of an airfoil showing chord

79.136.90.131 (talk) 17:50, 10 March 2009 (UTC)

This is a good observation. I have amended Chord (aircraft) to clarify the distinction between chord and chord length, as shown on the first diagram (which shows an airfoil.) I have also introduced the distinction between the chord of an airfoil and the chord of the planform of a wing of finite span. Dolphin51 (talk) 01:49, 11 March 2009 (UTC)
Just curious, but do any wings have infinite span? 70.250.198.35 (talk) 06:53, 6 September 2010 (UTC)
No. But there is an idealized flow situation called two-dimensional flow which is the flow that would exist around a wing that had no wing tips (a wing of infinite span.) Two-dimensional flow can be demonstrated in practice using a wind tunnel. If a wing is tested in a wind tunnel, and the span of the wing is the same as the width of the tunnel then the wing effectively has no wing tips. Therefore it is reasonable to say the airflow around the wing in the wind tunnel is the same as if the wing had infinite span. Dolphin (t) 07:11, 6 September 2010 (UTC)
Thanks, glad I asked.  :) 70.250.198.35 (talk) 10:50, 6 September 2010 (UTC)
Image the discussion is referring to below

— Preceding unsigned comment added by Ariadacapo (talkcontribs) 22:01, 21 May 2012 (UTC)

The chord line in the diagram is still wrong. The dashed red line should not simply follow the bottom of the outline of the wing. It should terminate at the center of curvature on the left side of the diagram. If you Google search "chord line," you will see how it is supposed to look. — Preceding unsigned comment added by 153.26.178.60 (talk) 05:49, 21 May 2012 (UTC)

I did as you suggested and Googled for chord line. I found THIS SITE which gives several different definitions, all saying the chord line is an imaginary line drawn from the leading edge of an airfoil to the trailing edge. If you have found a website with a significantly different definition please give us the URL. Thanks. Dolphin (t) 06:22, 21 May 2012 (UTC)
Hello 153.26.178.60, I am the author of the file you are referring to. The point you are making was brought up (in English) on the discussion page for the Dutch article "profile chord": https://nl.wikipedia.org/wiki/Overleg:Vleugelkoorde . Is the leading edge defined by the point that is furthest from the trailing edge, or by the point of minimum radius (which was what I wanted to show)?
I have found a reference that explicitly defines the leading edge as point of minimum radius, Houghton, E. L.; Carpenter, P.W. (2003). Butterworth Heinmann, ed. Aerodynamics for Engineering Students (5th ed.). ISBN 0750651113. p.18. I am going to add this to the file description and also look for other sources.
I would be glad to create a drawing similar to File:Airfoil_thickness_definition.svg showing clearly the difference in definitions, if anyone can provide me with a reliable source for an alternative definition. Thanks, Ariadacapo (talk) 21:59, 21 May 2012 (UTC)
That definition does not make sense. An airfoil could easily have no such point (eg: pointy nose), or two of those (eg. rounded corners), but it only ever has one "point that is furthest from the trailing edge" (except in minor extreme cases where that too sounds ambiguous, but simple observation will show that, when drawn, there will be just 1 point that matches it still) 120.151.160.158 (talk) 12:50, 7 January 2013 (UTC)

## Dubious definition

The "center of curvature" definition does not agree with all the formulas on the rest of the page (because the "wing area" is not measured to include parts of the under surface of the wing!). I added "Dubious" to the main page until an expert can properly sort this out. See also my comment above. 120.151.160.158 (talk) 13:07, 7 January 2013 (UTC)

I just tried to clarify the disagreement. I wholeheartedly agree that the definition I wrote and illustrated is incompatible with many existing drawings in printed books and in Wikimedia Commons — but it’s the only one for which I have a quote. Please, please give me a reference for the alternative definition and I will illustrate the difference just as I did for the differing definitions of "thickness". Thanks. Ariadacapo (talk) 17:45, 7 January 2013 (UTC)

## Idiomatic formula

The formula for MAC is listed as:

${\displaystyle {\mbox{MAC}}={\frac {2}{S}}}$${\displaystyle \int _{0}^{\frac {b}{2}}c^{2}(y)dy}$

This formula is rather unusual, and unnecessarily so, as it expresses the square of a function c(y) as c^2(y). This could easily be re-expressed as:

${\displaystyle {\mbox{MAC}}={\frac {2}{S}}}$${\displaystyle \int _{0}^{\frac {b}{2}}[c(y)]^{2}dy}$

with increased clarity (especially for someone unfamiliar with the subject matter). While I can't vouch for the formula itself, I can vouch for the fact that this would make it more accessible. As the idiom in the formula isn't introduced to the reader, I believe this is the correct approach (assuming the formula is valid). 70.250.198.35 (talk) 06:48, 6 September 2010 (UTC)

Thanks for spotting that. I have rationalised the formula and added in-line citation of Abbott and Von Doenhoff's Theory of Wing Sections.Dolphin (t) 07:45, 6 September 2010 (UTC)
Hey, that's cool, that will help, but that's not what I was getting at. My point was that c^2(y) is more clear as [c(y)]^2. 70.250.198.35 (talk) 10:10, 6 September 2010 (UTC)
I agree that [c(y)]^2 is clearer than c^2(y). However, the cited source uses c^2. Also I have a personal preference to use () brackets to indicate multiplication rather than clarifying that c is a function of y. Throughout Wikipedia brackets () are used in equations to indicate multiplication rather than showing a functional relationship. Dolphin (t) 03:37, 7 September 2010 (UTC)

## Suggestion for better illustration

The very interesting discussion above lead me to draw Image:Chord length definition (en).svg. It displays a turbine blade airfoil so that the distinction between "max length of airfoil" and "chord length" can be made visually.

My hope is to replace the rather mis-leading top-page illustration (Image:Airfoil.svg), please let me know if you’d rather not see it replaced. Ariadacapo (talk) 08:35, 27 November 2011 (UTC)

Done, please ping me if inappropriate Ariadacapo (talk) 09:02, 4 December 2011 (UTC)