Hi Harvey, There usually is no need to include flapping hinges in a coaxial system. You do not want flapping here. The blades should be built lightly, so they do not cause unwanted buildup of forces which could shatter them. The Super Libelle coaxial gyro had lead-lag hinges, but no flappers. Many users of this system don't have any hinging whatsoever, simply rigid rotors. I still might go this route, as it is simple and effective. I could fly a wingless gyro with rudder, elevator, and throttle. Thanx !!! Charlie