Originally Posted by
FCeng84
Mana - When Boeing developed the C*U control law that is the augmented pitch axis of the 777 a very deliberate design decision was made to provide positive speed stability that would require pilot action to "trim" column forces that build up when airspeed changes. C*U speed stability is implemented by managing within the control law a reference speed and requiring steady column force to fly at speeds away from that reference. Pitch trim on the 777 works to slew the reference speed up and down. The 777 does not drive the stabilizer directly to create speed stability, but it does augment the response characteristics in such a way that column force builds up that must be trimmed off. Without trim, the 777 seeks to return to the reference speed. 777 pilots must trim against the speed stability provided by C*U whenever they change speed regardless of the unaugmented speed stability characteristics of the bare airplane itself. In this way, the pilot task with regard to speed changes is not that different between 777 and 737.
Thanks! So there is a difference between US and European certification in this area? I don’t fly Airbus but I believe Airbus aircraft are kept in trim (pitch).
If I understand the 777 system correctly, you do not need at lot of trim if a short trim activation resets the speed reference?
I know what I would prefer my aircraft to do.