Originally Posted by
The Sultan
Real flight tests of a higher harmonic control was conducted by Hughes on a OH-6 in the early 80”s. Lot of pre-flight press and zero coverage post test flights. Those in the know indicated that the mechanical components between actuators and blade beat themselves to death in a very short period of operational time. Concept shelved as impractical.
Even with moving the entire thing to the rotating system, who thinks individual independent blade control is a good idea? There are so many failure modes the system safety assessment would be a nightmare (except for Boeing who doesn’t bother with such trivia). Any failure due to mechanical, wiring, electronic, or environmental (lighting) which results in the loss of pitch control to one blade is a catastrophic event which requires 1 in a billion level of reliability. So everything has to be independently triple redundant and impervious to common mode failure (lighting again). Concept impractical at the the most casual analysis.
The OH-6 wasn't the only HHC testbed, either. Several manufacturers tried this vibration or L/De improving approach 40 years ago and there are exactly zero fielded aircraft with HHC rotor control today. I think the primary reason it (and all of the downsides Sultan mentioned) are being investigated again is that HHC is seen as a solution to the even larger problems with rigid rotors.