Which type of tab is usually operated by a control rod connected to the main control surface?

The balance trim tab is designed to alleviate control forces on the main control surface by changing the aerodynamic characteristics of the surface. When this tab is operated by a control rod connected to the main control surface, it moves in conjunction with the control surface to create a more balanced aerodynamic load. This setup allows the pilot to make fine adjustments to the aircraft's flight attitude or stability without needing to exert as much physical effort on the control surfaces.

In contrast, other tabs perform different functions. The spring tab, for example, utilizes a spring mechanism to assist in controlling surfaces but does not typically connect to a main control surface in the same manner. An aileron trim tab is specifically intended for trimming the aileron to maintain a desired wing position, focusing more on lateral control rather than balance. The anti-servo tab, primarily used on control surfaces like rudders or elevators, enhances stability and control feedback but operates differently than a balance trim tab. Each of these tabs has its unique operational characteristics, but the balance trim tab's design is particularly focused on ease of control and maintaining equilibrium without a significant increase in pilot workload.