Trim systems play a vital role in aircraft control, often seen as a “secondary” flight control system. Essentially, to “trim” an aircraft means adjusting the aerodynamic forces acting on the control surfaces. This adjustment allows the aircraft to maintain its set attitude without any pilot input. While aerodynamic forces impact all axes of rotation, not every aircraft can be trimmed across all three axes. Most aircraft designs include some form of pitch axis trim, and many also have mechanisms for yaw axis trimming. Roll axis trim is less common but is still present on several aircraft. There are various types of trim systems available, and it’s possible for multiple types to exist on the same aircraft. The trim tab is the most widely used system, which can be found in either fixed or flight-adjustable configurations. Other types of trim systems include adjustable springs, anti-servo tabs on stabilator-equipped aircraft, and trimmable horizontal stabilizers.
