Flat sides should face the build plate. Some support will still be needed.
You will need to mirror the sliced rear gear parts, rear thruster parts and the wing parts to get the both sides of them. Most 3d printer slicers can do that.
Original 3d model made by basbr123, check him out! https://www.thingiverse.com/basbr123/about
Link to my print of this sliced model and my settings: https://www.thingiverse.com/make:686374