Publication grade concept drawings I am working on my Masters' thesis in aeronautical engineering and would like to make high-quality drawings (not technical drawings as in detail designs in CAD, but drawings of concepts and ideas, eg airplane with basic forces acting on it).

I am sure is this a common task in technical writings and would like to know if there is software available for such purposes?

Disclaimer: I am not a graphic designer and don't have the skill or time to make nice drawings from scratch. I am hoping there is software that has a library of a bunch of basic shapes and images that can be edited and freely used.
I think there is a TeX.SE question that deals with this. The details are not clear to me, but it appears that with a little work you can use TikZ with LaTeX to draw a plane:

This TeX.SE example used a variety of tools including Inkscape, Sketch, Blender, and Cinema4D (of which only Cinema4D is not FOSS) to produce:

From what I can piece together from this TeX.SE answer, details of how the above diagrams are made is available in Italian here. A Google Translate version of the abstract is:

This article shows how you can use the power of LATEX and PSTricks and TikZ packages in the production of advanced illustrations . The creation of designs that represent the three-dimensional scenes with directions of scientific content is made ​​possible with LATEX . The author shows how it is able to manipulate and arrange three-dimensional objects in a scene with the program Sketch of Eugene Ressler edil its intuitive scripting language , getting a ' output in the form of PSTricks or TikZ commands . The proposed working method allows to overcome the limitations that users of a package as PSTricks , which also has relatively advanced three-dimensional drawing capabilities , meet whenever are going to want to draw and manipulate three-dimensional scenes containing objects simple and primitive .
The teaching of a subject such as engineering Flight Dynamics is a field in which he operates, and which they refer to the specific examples given in the article

which suggests that Cinema4D may not be critical.