Planes burn their oil and spit it out on the bottom, so the bellies get greased up something terrible. ONR probably won't cut it, you'll likely need a solvent degreaser (we used to use Tarminator) and a pressure washer to get it clean in any reasonable amount of time.
Aircraft paint is pretty tough to get swirl-free, it's *much* harder than auto paint. We used
M66 on an orange pad @1400rpms, it did no correction but it got things perfectly clean and didn't introduce any holograms of its own.