Any specific comment on the use of a 'Counterpropeller'?: fixed vanes after the propeller blades, as vanes in turbines, changing the shape of helicoidal air flow from propeller into somethig more close to a linear, laminar flow.
There was a German inventor, R Wagner, proposing this, patent US1609978.
For sure the pass of propeller blades next to a fixed vane may induce vibrations, it's the engineers' expertise calculating this, but the results may not be clear.
I'd like having this type of arrangement in a Custer Channel Wing machine, and about this, I'm also not sure if the propeller placement in trailing side of Channel, the original Custer way, would yield same results as if put on leading edge, as in Antonov 'Izdelie 181', or over the thickest part of airfoil, or elsewhere. Blessings +