Originally Posted by Dave Jackson
OK forget the gyro ~ for a moment.
Still worth considering, Dave. Flapback provides static stability, but a gyro is perfect for dynamic (ie transient input) stability.
One concept i have often wondered about is designing a 4-blade hingeless rotor with hiller bars. Basically two 2-blade designs at 90 degrees. Again complexity of this concept tells me that Lockheed got it right with final system (perfected after cancellation
).
Originally Posted by Dave Jackson
It therefore appears that the vibration may be lessened if the blade-crossing azimuths can be actively varied so that they always have a constant relationship with the ever-changing cyclical input azimuth.
My concern here is that you are introducing complexity for an otherwise simple to solve problem (extra blades). Ignoring the control complexity problems, the real headache is that every time you move the cyclic around the box you will perform an unrequested turn! The solution would simply be to provide additional drive to a smaller yaw control rotor, fitted aft of the main rotor.
Vibration is best cured from source, which to my mind means designing a main rotor assy which does not respond to frequencies to which it might be exposed. Continuously trimmable RPM rotors are feasible, but may increase the problem of rotor resonances (active or internal damping clearly helps - more complexity). Combine this with possible problems associated with high speed and it looks more daunting.
Mart