Hey Mike, The characters are reading really well; I can feel the personalities. For the gunner, the way the rifle is held feels strange to me, unless it is like held by the arm and not the hand. Also, for the driver, the tail catches my eye. I hope that helps. Rock on!
I think the "dora style" works pretty well for you. Good thing we have her for inspiration! I think the next step would be to add some more depth to the characters. In the same flat matter, just differentiate the light side from the shadow side. A SLIGHTLY lighter shade of gray (or dark blue) would be a nice way to block in some feathers getting hit by the light, especially on the driver's neck. I would like to see a shadow under the gunner's chin. You could just use the polygonal lasso tool to select the big shapes and fill them in with value.
I like these a lot Mike. This is subjective, but the driver's two arms/wings are kind of twinning, I'm not sure if you want that evenness in the pose. If you have time maybe you finesses the edges a little more. Otherwise, good stuffs!
Hey Mike, was gonna say the same as Vu, I'd tighten up the edges, but try not getting rid of the kinda frenetic/jittery style: which is working really well. Second, this is kinda minor, I think the bottom of the tail on the gunner could be designed more interestingly... its just kinda bland compared to the way the rest of him is designed.