If you had to design a flying creature for a sci-fi story, which had evolved two sets of wings, one large pair of bat/bird wings that could beat at a moderate frequency or simply extend like a soaring eagle/condor, and a smaller secondary pair of wings that would look like the wings of a fly and could beat at relatively high frequency.
In theory, would it be easier for such a creature to fly if the smaller/faster beating wings were located below or above the larger wings, and would it be better if they were slightly in front or behind the main wings? Im imagining the creature mostly gliding on the larger wings while the smaller wings help propel the creature forward.
(Im not sure if this question should go in physics, biology, engineering or science-fiction, but thanks in advance)