Hey this is a good start! My advice to make it more steam punk would be to expose the rear engines a little like the old WWI bi-planes. Throw in some guide wires and a few extra cogs and bits and you'll have a top notch concept.
An interesting cartoon you might want to look at would be Last Exile. They do an interesting steam-punk type feel that might help for a little inspiration towards adding the finer details to your work.
Keep it up!
~To create a new world through the imagination