On this model here I was able to get the effect I wanted on the ax, armor, and the wings. Overall I consider the airbrushing a success so far, though there is still a long way to go until I recognize the limitations of the tool.
Still, I don't consider even the failures to be without their merits. On the image below I can see where my hand slipped between the wing areas, getting some grey on the red. Also on the chains I went too wide with my stroke. Both times were due to becoming impatient.
When we try new things it is easy to become discouraged when the results aren't what we would like. To grow in this hobby, though, risks need to be taken and mistakes learned from. Note your successes, improve on your failures, and keep trying. Your experience will improve and will show on your creations much quicker than you would expect.