It is amazing how efficient those counter-rotating props must be. One would think that the trailing blades would be quite inefficient “living” in the wake, but apparently this is not so.
So much for theory.
Turns out that the trailing props use the otherwise wasted rotational energy of the leading props, giving an overall 15% or so efficiency improvement. In other words, the lead props send air outward radially and this energy is wasted, were it not for the trailing props coming along and redirecting that energy to the back.