The elevator tabs are in the “balance mode” when the TE flaps are up where 2 solenoid control hydraulic valves de-energize and the tabs move opposite of elevator movement by tab mechanism design. With flaps extended they move in the same elevator direction also known as the “anti-balance mode”. Balance tabs look like trim tabs, but they have one major difference: balance tabs are attached to the control surface linkage, so when the control surface is moved in one direction, the balance tab moves in the opposite direction. the difference between a balance tab and a servo tab is , balance tabs, they move in the opposite direction of the control surfaces on which they are attached.
Servo tabs work by deflecting airflow so that the control surface is exposed to a greater force. Servo tabs are commonly found on elevators and ailerons. B-737 is a direct control a/c, meaning a physical cable going to power control unit you need assistance to mauver those. The Aileron Balance panels and tabs decrease the force to move the aileron in flight. It counters goes opposite directions of the movement of the Aileron vary much mechanical feature.
When the Aileron is commanded to move there is an incremental differential pressure between the upper and lower surface of the Aileron. The pressures are vented into the balance base to provide force on the balance panels to assist Aileron motion, balance tab moves it creates a differential force at the balance tab. This system have Found on the Elevator too and same concept as Aileron.
Author – WONDESON GETACHEW HAILE
