Thank you Bill. Your thought on the Batmissile engine is as good an explanation as any.
I don't know that I gave the obvious engine/wheel conflict much thought before I held the Batmissile model in my hands. As I when looking at how all the went together, it seemed obvious to me that there just wasn't enough space for both the wheel assemblies and engine. I even got the engine from the Batmobile that I have to make a comparison and thought, "Yep, there's just no way." and wrote the whole thing off to Heroic Fiction. Which means that it doesn't necessarily need to be believable, just imaginative and impressive. And both of those it certainly is.
Thanks for your comment,
David G.