Originally Posted by
vilas
Can you explain how does it compensate for thrust changes. In speed stable system if thrust is increased and if the flight path is maintained i.e. if the nose doesn't come up speed will increase. Similarly if the thrust is decreased if the nose doesn't drop speed will decrease. That's what happens in Airbus. What happens in 777?
It's FBW. On the 737, if the thrust changes, the pitch/thrust couple is affected and a pitch input is required to maintain the flightpath. Any sustained pitch force will need to be trimmed out. The FBW on the 777 compensates for the pitch/thrust couple when the thrust changes. A trim change isn't needed because the FBW deals with the control force that would otherwise be required. When climbing, flying level or descending at a constant speed, assuming the aircraft is trimmed to the reference speed, there will be no control force to hold irrespective of thrust. If the reference speed changes, it will produce a control load which will need to be trimmed out. It is easier to use in practice than a paper explanation would suggest.