In a Cessna 172, how does trim function?

Trim in an aircraft like the Cessna 172 primarily serves to relieve the pilot's workload by minimizing control pressures needed to maintain straight and level flight. When the trim is correctly set, it adjusts the position of the aircraft's control surfaces in a way that allows the aircraft to fly hands-free at a desired attitude. This means that the pilot can make small adjustments to trim to counteract any persistent aerodynamic forces acting on the aircraft, such as the tendency to pitch up or down or roll one way or the other.

Setting the trim appropriately means that the pilot does not have to continually apply pressure to the yoke or stick to keep the aircraft in a desired flight condition, thus reducing fatigue during longer flights and making control more precise. The function of trim is not to increase lift, enhance fuel efficiency, or adjust the center of gravity; rather, its main purpose is to maintain the aircraft in a stable flight attitude with minimal control pressure.