Aircraft, systems, and methods for trim control in fly-by-wire aircraft systems

A fly-by-wire system for a fixed wing aircraft, the fly-by-wire system comprising:

• an autopilot disconnect input device configured to receive a re-trim input from a user, wherein the autopilot disconnect input device is a pushbutton;
• a manual trim control switch, and
• a controller communicatively coupled with the autopilot disconnect input device and configured to:
• control a trim control system that is configured for controlling surfaces of the aircraft,
• obtain the re-trim input as a discrete depression of the pushbutton,
• set a position of the surfaces of the aircraft that achieves positive speed stability about a trimmed condition at a current airspeed of the aircraft in response to the re-trim input, wherein positive speed stability is a tendency of the aircraft to return to the trimmed condition after a disturbance of the aircraft from the trimmed condition,
• permit continuous manual flight and retain positive speed stability in response to receiving the re-trim input,
• command the trim control system to adjust towards the position in response to obtaining the re-trim input from the autopilot disconnect input device when an autopilot is disengaged, and
• disengage the autopilot in response to an autopilot disconnect input from the autopilot disconnect input device when the autopilot is engaged.

A controller for use with a fly-by-wire system of a fixed wing aircraft, the controller comprising:

• a processor;
• and
• a memory unit coupled with the processor, the memory unit storing instructions for the processor, wherein the instructions are configured to cooperate with the processor to:
• control a trim control system that is configured to control surfaces of the aircraft,
• set a pitch trim of the aircraft based on a manual trim input from a manual trim control switch when an autopilot is disengaged,
• obtain a re-trim input from a user of an input device as a discrete depression of a pushbutton,
• set a position of the surfaces of the aircraft that achieves positive speed stability about a trimmed condition at a current airspeed of the aircraft in response to the re-trim input, wherein positive speed stability is a tendency of the aircraft to return to the trimmed condition after a disturbance of the aircraft from the trimmed condition,
• permit continuous manual flight and retain positive speed stability in response to receiving the re-trim input,
• command the trim control system to adjust towards the position in response to the re-trim input when an autopilot is disengaged, and
• disengage the autopilot in response to an autopilot disconnect input from the autopilot disconnect input device when the autopilot is engaged.