What is the purpose of an elevator trim tab?

The primary purpose of an elevator trim tab is to modify the downward tail load for various airspeeds in flight. By adjusting the trim tab, pilots can alleviate the control forces required to maintain a certain pitch attitude, which helps in stabilizing the aircraft during flight.

When an aircraft is in motion, different airspeeds result in changes to the aerodynamic forces acting on the tailplane. The elevator trim tab allows for small adjustments to be made, which help to maintain balance without continuous control input from the pilot. This is especially important during long flights, where constant control pressure can lead to pilot fatigue.

Therefore, the trim tab acts to optimize the aircraft's flight characteristics for varying conditions, ensuring the proper aerodynamics are in place to maintain level flight or a desired climb or descent without requiring excessive force on the controls.