There was an aircraft designed during, I think, the 1880s, I believe called the Henson steam carriage. It was never built because no one would invest money in it, yet it might possibly have flown, though structurally it looks a bit weak (it was a wire braced monoplane). The design was somewhat in the steampunk vernacular. So that steam plane might be considered steampunk.
I have long thought of trying to model that plane. Having my interest peaked in steampunk again, maybe I should look up all the drawings I have (none scale, all just perspective views, probably for stock promotion) and take a whack at building that.