How to section meshes?

I almost never work in meshes. However, I have project were I we have to replicate a section of a plane that will be made by sculpting block of foam. Usually, I would section through the model (fuselage) at 18" centers, then print the section outline full-scale for the builder. I’ve no idea how to make these cuts in a mesh. I’m open to suggestions.

Hello - use the Section, or in this case the Contour command for this.