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Does this web page really correctly depict the most common usage of the term "incidence" in the French language in the aviation context, in the context of speaking of an entire aircraft and not just an isolated part such as a wing section in a wind tunnel? Is the label "incidence" really attached to the correct angle?

I am referring specifically to the second airplane diagram, i.e. the first diagram that shows an airliner. Note that the text above the diagram uses the phrase "en croisière" which is a reference "cruising", presumably horizontal, flight. The line x-x' appears to represent the longitudinal axis of the aircraft, so it appears that the angle labeled "incidence" represents the angle between the flight path/ relative wind and the longitudinal axis of the fuselage, not the angle between the flight path/ relative wind and the chord line of the wing, which would clearly be a larger angle.

In fact the text above the diagram explicitly states "L'incidence est définie par rapport à l'axe de l'aéronef et non de la voilure.", which translates to something like "The incidence is defined relative to the axis of the aircraft and not of the wing."

Shouldn't the angle labeled "incidence" be the angle between the flight path/ relative wind and the chord line of the wing rather than the angle between the flight path/ relative wind and the fuselage?

Or is it just a matter of arbitrary convention, meaning that either usage would be equally appropriate?

(One way to concisely answer this question might be "The correct usage of 'angle d'incidence' in the French aviation context is exactly identical to the English-language usage of 'angle of attack' (or replace with other appropriate angle as needed) as noted in this ASE answer (give link)." Not all ASE answers have given the same perspective on the most correct usage of this term.)

Note that the angle labeled "angle de calage" is the angle that is called "incidence" in American aviation usage and some or most (but not all) British aviation usage-- the angle between the chord line of the wing and the longitudinal axis of the fuselage. This question is not about whether or not the diagram uses "angle de calage" correctly in the context of French aviation terminology-- it clearly does.

Bonus question-- in the French aviation context, is the term "angle d'attaque" used to mean something different than "angle d'incidence"?

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    $\begingroup$ A Belgian instructor (french-speaking) told me "angle d'incidence" must be translated as "angle of attack" and "angle d'attaque" should not be used in french because it is confusing. $\endgroup$
    – Manu H
    Commented May 4, 2020 at 15:18
  • $\begingroup$ @ManuH -- that seems as worthy of being an answer as anything else that is likely to be submitted re this question. $\endgroup$
    – quiet flyer
    Commented May 4, 2020 at 15:19
  • $\begingroup$ For me it is just an anecdote as I don't have written references to support the answer, and thus it does not meet quality standard required to be an answer. $\endgroup$
    – Manu H
    Commented May 4, 2020 at 15:21
  • $\begingroup$ @ManuH -- ok, thanks for the comment anyway, it is useful. $\endgroup$
    – quiet flyer
    Commented May 4, 2020 at 15:21

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Yeah it's right if we consider that the relative wind is parallel to the ground.

In French, the "angle d'incidence" is the angle between the chord line and the relative wind, contrary to the US and UK which it's the angle between the chord line and the longitudinal axis.(fr="angle de calage")

In french: In fluid mechanics, "l'angle d'incidence" is the angle formed by the chord of a profile and the relative wind speed vector. In English l'angle d'incidence" is called angle of attack (AOA). Attention, angle of incidence in English corresponds in French to the "angle de calage", the angle formed by the reference chord of a wing and the longitudinal axis of the aircraft. L'incidence (fr) notes : α angle d'incidence(fr)

angle between chord line and relative wind

"Croisière" is cruise flight .the picture of the website is not clear because it confusing chord line and longitudinal axis(perhaps to simplify)... other important notion: RELATIVE WIND is the relative movement of air relative to the plane; it is ALWAYS PARALLEL AND SENSE OPPOSITE to the TRAJECTORY OF THE AIRPLANE(path)

Source: (the second link is french because the same page is different in French and in English) https://fr.m.wikipedia.org/wiki/Incidence_(a%C3%A9rodynamique) https://www.lavionnaire.fr/AerodynCPFoyer.php

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  • $\begingroup$ I know we've talked about this before and thanks for the clarification again about how incidence is used in French but I think your answer should say the first airliner diagram is wrong because it specifically labels the incidence angle as something different than what you are saying here. Only in the second airliner diagram, not the first, are the chord line of the wing and the longitudinal axis of the fuselage shown as being the same thing for simplicity. $\endgroup$
    – quiet flyer
    Commented Apr 4, 2020 at 12:46
  • $\begingroup$ @quiet flyer (For me )to sum up:the picture is not clear...but this picture show more the "angle de calage" than "angle d'incidence" .the site show the "angle d'incidence" on first picture.so if the "incidence" in the picture is not correct,less important than the "angle de calage" which is correct $\endgroup$
    – L'aviateur
    Commented Apr 4, 2020 at 14:40
  • $\begingroup$ If you consider that it's not correct contact them and see with they. $\endgroup$
    – L'aviateur
    Commented Apr 4, 2020 at 14:44

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