I'm opening a discussion on the figure of merit on the following configurations:
1. Ducted counter-rotating coaxial propellers;
2. Ducted single propeller and counter torque stator vanes;
As far as I know a single propeller is more efficient than coaxial propellers ( in textbooks coaxial props are comparable with 4 bladed prop) The coaxial helicopters are more efficient as the lower propeller "sucks" clean air because of top propeller stream contraction. In a duct that will not be the case and the downstream propeller will see the full speed of the air as it exits the first propeller. For me, that means the single propeller will be more efficient especially if some energy can be recovered from the swirl by stator vanes.
1. Ducted counter-rotating coaxial propellers;
2. Ducted single propeller and counter torque stator vanes;
As far as I know a single propeller is more efficient than coaxial propellers ( in textbooks coaxial props are comparable with 4 bladed prop) The coaxial helicopters are more efficient as the lower propeller "sucks" clean air because of top propeller stream contraction. In a duct that will not be the case and the downstream propeller will see the full speed of the air as it exits the first propeller. For me, that means the single propeller will be more efficient especially if some energy can be recovered from the swirl by stator vanes.