How to cut out notches and holes in foam semi-precisely?
The &quot;aircraft&quot; you reference is made of expanded polystyrene foam, also known as Styrofoam™. It is sensitive to heat to the point that there are high-temperature-based tools to address your goal.
Rather than spend a bunch on specialized tools, you can use a soldering iron set just low enough to control the level of melt generated. If you have a single temperature tool, speed becomes the control.
Another approach that I've used is a bit more time consuming, but allows for much greater detail work. A butane lighter or steady heat source is used to bring a long sewing needle up to temperature. Obviously, pliers or similar must be used as a handle. You can drive the needle to the required depth at the corners of your recess, &quot;draw&quot; a cut-out outline and then use a soldering iron to eat away at the middle of the mass.
If you're handy with other tools, hammer the point of a nail to a flat blade and use that as your tool. You can hammer a spoon shape into the nail to get a smoothing tool.
The possibilities are limited only by your imagination and available resources in the tool department.