Jim,
did you spot BB's thread earlier about the B525 testing?
Link to the article here:
'Flight Testing' the Bell 525 Relentless | Vertical Magazine - The Pulse of the Helicopter Industry
An interesting extract here, with insights into the certification demands not keeping up (my bold):
The biggest change I noted was that the flight controls now have “tactical cues” when limits are reached. When Caudill had me pull the collective to a power limit, it increased the pull force — giving me adequate warning and time to correct. The cyclic will give a similar warning when Vne (never exceed speed) is approached.
The cyclic also has a trim follow-up feature in both fore and aft, as well as lateral modes. The trim follow-up feature is available throughout the entire envelope except when in Translational Rate Command (TRC). Here, the envelope is ˝ knot to 10 knots. At ˝ knot or below, position hold becomes active. Put the helicopter where you want it, and leave it alone. The pilot displaces the cyclic to get the desired speed, or he can beep for the change. Groundspeed from beeping is dependent on altitude: 10 feet and below you get 1 knot; 20 to 11 feet, 2 knots; and so on to 50 feet, which gives you 5 knots. You can’t beep out of TRC.
Since my first visit, Bell changed the trim follow up in longitudinal axis to return to trim. However, TRC is still available in the lateral axis. Therefore, any acceleration or deceleration if not re-trimmed will return to previously trimmed air/groundspeed. For example, if the helicopter is trimmed to 130 knots and decelerated to 50 knots without re-trimming, the helicopter will slowly accelerate back to 130 knots when the cyclic is returned to detent or the displacement is taken out. The same goes for an acceleration. “I wouldn’t say this was the only reason we made the change to longitudinal axis, but it cleans up the control laws and enables us to meet the FAR requirement of ‘Positive Longitudinal Static Stability,” said Caudill.
I'm curious about how many layers of redundency there will be and, therefore, how many levels of control law that may be 'available' - most FW FBW have Normal, Alternate and Direct laws plus mechanical back-up (for temporary control). If we have a cyclic that becomes a translational rate controller rather than an attitude controller, how readily can a pilot revert to primary effects of controls principles if he finds himself in Direct law on a dark night? The 'resilience' concept re-appears......