It's hard to answer this question because it will look harsh. But don't take it bad, it's only for giving you the chance to realize what 3D is so you can improve your knowledge and skill.
You can't start learning to drive and go directly to a formula 1 competition. It's the same in 3D.
You want to bake and use Unity but you haven't learn the basics (how to model something, how to unwrap...)
- Your mesh is really bad, you have inverted faces, self intersected mesh, edge over faces, ngons,... try to learn what topology is about (quads, tris, ngons... why and when to use or not), even if it's just a hobby and you don't want to model like a pro you really need the basics.
- The same for your unwrap, there are overlaping parts, in fact quite all is overlaping, so no chance at all to even have an acceptable bake. And I don't speak about using it in Unity.
3D is hard at the begining but if you like it learn step by step, I swear, it'll really be easier than moving forward with a collection of crappy things at each level.
One more time, sorry if it looks harsh but I opened your Blend, and there is a lot to learn before going to the baking part.
If we really want something there is nothing we can't learn.
- Regarding the first point of my answer, the flaps (wings parts) have inverted normals, the small parts on the hood are self intersected, the wing is mostly a big really not suitable ngon.
- The unwrapping part need to have different places in UV space (not overlapping), otherwise you'll end up with bake parts covering other piece of the mesh.
- You have more marging parts than the bake itself, learn about resolution of baking image, if you have an image really too small like yours the marging take most of the picture and covers baked parts.
One more time, the question isn't about having a simple answer but about learning a bit more. Hope it can help peoples who start to learn 3D to not rush to "advanced" topics and make baby steps.