What is a key requirement for the design of aircraft trim systems?

A key requirement for the design of aircraft trim systems is that it must allow the pilot to determine the trim position. This is essential because trim systems are designed to assist pilots in maintaining a desired flight attitude and to alleviate control forces experienced during flight. By allowing the pilot to set the trim position, the system provides flexibility and control, enabling the pilot to make adjustments based on varying flight conditions, weight distribution, and aerodynamic changes.

This capability ensures that the aircraft can be operated comfortably and efficiently, minimizing pilot workload and enhancing safety. Manual control is essential, as it allows pilots to respond dynamically to their environment and adjust the trim as necessary for optimal performance and control of the aircraft.

In contrast, options that suggest automation without pilot input or exclusively manual adjustments limit the adaptability and responsiveness of the aircraft's handling characteristics, which do not align with the fundamental purpose of trim systems.