Originally Posted by
RVGuy71
I was closely associated with the S92FBW and CH148 flight control development and would like to weigh in on a couple of speculations....,
While the controllers are indeed passive unique trim design, the CH148 incorporates an envelope cueing system, which provides both aural and visual cues to control margin encroachment. The most common reason for activating these cues would be if the aircraft was being operated outside of the operational CG envelope.....
A couple other tidbits:
The controller configuration is 2 axis center mounted unique trim cyclic, floor mounted unique trim pedals, and conventional, trimmable, displacement collective.
FCC architecture is "dual-dual-triplex". There are 3 FCCs, each FCC has two lanes (either one can operate the servos). Each lane has dual processors, and they incorporate dissimilar software to address common mode failures.
RVGuy, please take this response as a desire for an open discussion of different system architectures, not an attempt to tie unique trim cyclic to the cause of this accident.
The S92FBW development preceded the Bell 525 by over two years. So when developing the 525 FBW architecture, Bell studied it in depth. A unique trim cyclic is obviously the lightest and least expensive configuration. But is it optimal for pilot cues?
During informal discussions with the FAA, Bell was advised that the FAA would not certify a unique trim cyclic configuration for a helicopter. Primarily due to the lack of tactile cuing between pilot and copilot. But also due to the lack of auto pilot tactile cuing. This is why the 525 while being a FBW side stick, still mimics the function of a conventional mechanical cyclic.
The USMC also had their reservations regarding unique trim cyclics. This is why they demanded installation of active BAE cyclics sticks that could mimic the function of mechanical mechanical controls in the CH53K.