The flapping illusion is caused by rotor disc tilt relative to the flight path; noseup in a gyro because its rotor must act in part as a windmill and extract its energy from the airstream whereas the rotor of a helicopter provides forward propulsion and flies nosedown.
The rotor of a compound helicopter where forward propulsion is supplied by a propeller and the rotor only provides lift can fly perfectly flat relative to the airstream. Cyclic pitch in such cases still does its job of equalizing lift between advancing and retreating blades but without the flapping illusion.
The rotor of a compound helicopter where forward propulsion is supplied by a propeller and the rotor only provides lift can fly perfectly flat relative to the airstream. Cyclic pitch in such cases still does its job of equalizing lift between advancing and retreating blades but without the flapping illusion.