I think the underlying premise here is that what is allowable are "devices that could work in real science if you could shrink down power generators enough." So you can have heavier than air ships held up by big propellers, and ray guns. But no paranormal stuff.

On the other hand, there are a few things that are plausible within the world framework but will not be allowable in this story. There will be no time travel or space travel (aliens, etc.). The focus of this story should be Wonder Machines, Fiendish Devices and the Romance of the Skies...

Giant robots kidnapping women will be allowable, however.