The common conception of angels and demons is of humanoids with wings on their back. But in my story, angels and demons operate in 'nonmagical' ways; there are no 'spells' or any 'charms' in this story; just natural power.
So my question is how, realistically, angels and demons would take flight, if at all? With the idea of wings, I feel that they would need a ridiculous wingspan to lift their human forms off the ground. Would that still work? Would they not have human forms, like the glowing wisp angels and black smoke demons in Supernatural, or create bodies/possess humans on earth? Or maybe they don't fly at all.
Edit
I reviewed the other question, as suggested. It refers to making humans physically capable of having wings through altering their bodies. I refer to how, realistically, the 'biology' of a demon or angel would allow for flight.