Remote controlled aircraft require light 3-dimensional wing surfaces, which can be made out of foam. Cutting such material generally means getting out a hot wire and passing it through said foam, which is quite different than normal* machining processes used on harder materials like wood, plastic, or metal. As such, a traditional CNC router isn’t generally the proper choice for wing creation.
However, if you were to hold two ends of a hot wire on independent CNC gantry assemblies, you could then create intricate sweeping shapes for your airframe or other foam creation. To get started with this pursuit, WindyHillHobbies is offering a Hotwire CNC Machine Kit that includes most of the mechanical parts that you’ll need to start precision-cutting foam on a 40″ x 40″ work surface.
The cutting process looks quite impressive in the video below, and the machine itself can reportedly be built in about 2 hours. In addition to the kit, you’ll need to supply four NEMA 17 stepper motors, an Arduino CNC control setup, and a few other bits and pieces. More on the setup process can be found on this FliteTest forum post.
*One might compare this process to that of a wire EDM machine, though cutting through foam is much faster.