There is so many ways to weather a helo. first you have to ask yourself. Is is battle worn, everyday use or just plain lack of time to take care of the helo. I assume you are doing a all black helo (SOAR). I would start with outline of panels of dark blue first so that you have a base to work with before the black. How do you do shadows on black.....blue.
Nato black is a great color to work with. I would not cut too much with white or buff to make it worn out. you can do that with washes later. Nato black responds very well to Oil washes. You can finish the rest of your helo with Mig Pigments either apply by hand or airbrush (needs to be thin with tamiya thinner).
I have never seen blades with bare metal on the edge. you can accomplish the same effect of the worn look with an airbrush.
This is only my two cents, go luck and post photos when you can.
Oliver