I guess when you have invented technologies that can compensate for a lack of aerodynamic forms or limitations only previously dedicated designs can overcome, you can start making machines in whatever way you like.
We already had robots completely made of clockwork parts in an earlier episode.
This episode is next week, Its about the British army making a new secret weapon in WW2, who really are the Daleks. At one plart in the trailer you can see the spitfires flying with some sort of sheild surrounding them, that probably explains it, and it looks like they are fighting the Daleks from what I can piece together from the trailer. Yes thats right. Spitfires, with sheilds, fighting Daleks in space. Invention of Awesome I think.