# How is the chord length defined if the wing (whale flipper) is tapering like a wing and has a twist throughout the span? [duplicate]

Let me be more specific:

1. I have a 3D scan of a whale tubercle.
2. The tubercle is tapering and twisting along its half span.
3. I want to find the mean chord length. Now let us say that my airfoil section is at 10 degrees. So how is the chord length defined?

a) is it a line that directly joins the LE and the TE (chord length has a slant) b) is it the line joining the projection of the LE and TE on a flat plane ( slope of chord line =0)

• Which f̶l̶a̶t̶ (every plane is flat) plane would you want to use? The aircraft reference datum is rather arbitrary and the relative wind changes with speed and wing loading. Commented Dec 20, 2016 at 21:21
• Just added a picture in the question... so up here in the picture, the chord length is defined as 'a straight line joining the LE to TE' but book claim it to be 'the chord is simply the size of the wing in streamwise direction' Commented Dec 20, 2016 at 21:55
• I don't think it is a duplicate because the referenced question doesn't answer how to deal with variable twist when calculating the mean chord ("3. I want to find the mean chord length"). The question "Is $S=\int c(y) dx$ or is it the projected surface on a certain plane ($S=\int c(y)\cdot cos(\alpha_i(y)) dx$, with $\alpha_i$ the incidence angle)?" isn't answered there. @AdityaKulkarni You'll probably have to pick a definition yourself. I'd choose a plane which minimizes incidence angles along the span and calculate the projected surface on it. For the mean chord $MC=\frac{S}{Span}$. Commented Dec 21, 2016 at 8:17