Can the ARRAY MODIFIER make a mesh multiply along a side of a round object? Instead of it duplicating vertically or horizontally?
In your modifier you can simply un-tick constant offset and relative offset, use object offset instead, and target an empty at your axis point and rotate the empty to set your increments. You will need to offset you blade from its origin in edit mode to create space for the motor but sure both objects share same origin location.
Another method I prefer is to use duplication.
Create a circle primitive the size of the motor, give it 7 vertices, under the duplication tab in its object properties select verts and tick rotation, parent your blade to the new object and make sure it has the same origin, align it to Y axis. Hit ctrl+shift+A to 'make duplicates real' and you can delete your original blade.