Your insistence in ducted fans or in ducted propellers is both practical and welcome. Is a much welcomed efficient invention for a given airspeed. I love it very much! Another variation: do you know that in the 30's both Russia and Germany were developing efficient steam turbines for aviation applications, and both stopped all this investments in favor of gas turbines for a speed factor (coupled evidently with the war necessities)? Much different aircraft technology will result today in the full application of steam to aircraft propulsion, including nuclear furnaces as a steam source!