A fairing is a cover over something that is exposed to the wind on a moving vehicle. Aircraft have fairings around the wheels sometimes, and where you have an antenna or engine part that bumps out into the airstream. To stiffen our elevator control system, we had to bump down below the tail boom, and that meant we had to make a fairing to cover that area.

 

This image shows the mold (technically a plug) for the fairing. It was 3D printed in sections, then joined and sanded smooth. The surface is metal tape with a wax coating to help remove the part once it has been made.