balance tab and trim tab
 

hi everyone!

I have a little bit confuse about balance tab and trim tab.

balance tab : assist in moving the main control surface
trim tab:after moving the main control surface zero the loads on pilots controls output?

and what's the relationship between (mass balance ,aerodynamic balance) and balance tab?

Tabs have little or nothing to do with mass balancing - they're all to do with changing the relationship between various aerodynamic forces on a control surface.

A balance or spring tab is designed to deflect in the opposite direction to the desired surface movement. Because it's further back from the hingeline, a small force on the tab has a proportionally larger moment, which changes the "float" angle of the surface - where it would be if no force were applied to the surface itself.

The surface may be controlled ONLY through the tabs - pilot applies force to tab, tab moves, control surface moves in response to tab movement - or the tabs may be used to unload the control surface hinge memonts, making it easier for a manual control to be used.

Trim tabs work aerodynamically exactly the same way; the only difference is that a pilot will have direct control over a trim tab, through whatever the trim control is (wheel or switch) whereas the balance/spring tab isn't necessarily directly controlled.

There's also a "fixed" tab, which is like a trim tab (used to rebalance the aero forces) but it's only adjustable as a maintenance item, and it used to take out any trim offsets due to aircraft asymmetry at the build stage.