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From an article on kiting:

Leading edge inflatable kites, known also as inflatables, LEI kites or C-kites, are typically made from ripstop polyester with an inflatable plastic bladder that spans the front edge of the kite with separate smaller bladders that are perpendicular to the main bladder to form the chord or foil of the kite.

Earlier today I asked a question on what is it exactly that forms the chord or foil (according to the sentence): the bladder configuration as a whole or the smaller bladders only.

Now I want to confirm or refute my gut feeling that "chord" and "foil" are used synonymously here. I beleive they are, since the coordinating conjunction or is placed between them, meaning the sentence could be rephrased as:

The configuration of bladders forms the characteristic of the kite called "chord" or "foil".

In what other way could the use of OR be interpreted? That the bladder configuration sometimes forms the cord and in other instances forms the foil of the kite? That's illogical.

Moreover, citing from the Wikipedia article on Airfoil:

The chord line is the straight line connecting leading and trailing edges. The chord length, or simply chord, c, is the length of the chord line. That is the reference dimension of the airfoil section.

It feels like chord could be used synonymously with (air)foil.

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Now I want to confirm or refute my gut feeling that "chord" and "foil" are used synonymously here.

You are correct.

In what other way could the use of OR be interpreted? That the bladder configuration sometimes forms the cord and in other instances forms the foil of the kite? That's illogical.

While "X or Y" can be used to express that the subject can be in one of different, valid statuses (e.g. John came home and he is hungry or tired) it's also used to express that the subject can be called one of various valid names - in what I would say is an "educational context."

So ...

Leading edge inflatable kites, known also as inflatables, LEI kites or C-kites

sounds like a dictionary or schoolbook definition, so that is what cues me in to understand "forms the chord or foil" is two names for the same concept.

I know nothing of kites so without that cue I might be as confused as you until I researched. :)

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    But they are different. The chord is the line between the leading edge and the trailing edge of an airfoil. foil is short for airfoil and refers to the a wing's cross-sectional shape and sometimes to the whole wing. I think here each separate smaller bladder, when inflated turns the flat cloth into an airfoil by giving it shape in the direction of the chord. (Thus forming the chord). Inflating all the bladders forms the whole airfoil shape (or foil). I would make the analogy: offshoots from the trunk form the branches or canopy of the tree. – Jim Oct 29 '14 at 22:13
  • @Jim: I agree that the words denote different concepts. But the use of or seems to be illogical if we imagine the sentence treating them as different concepts. The sentence should then use and: "the bladder configuration forms the chord and foil of the kite". – CowperKettle Oct 30 '14 at 4:22
  • I read it as, "bladders [...] to form the chord, or [in other words, the] foil of the kite." – Jim Oct 30 '14 at 4:25

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