MD-80 aileron movement is controlled by aerodynamic tabs. This is also the case for the elevators in normal flight conditions. Rudder movement is hydraulically boosted in normal operation while during manual reversion, a tab system is unlocked and takes over.
General:
A control tab works by extending itself upon which aerodynamic forces cause the larger control surface to deflect in the opposite direction. For example, in commanding an aileron up movement, the tab is driven downwards forcing the aileron to deflect upwards.
Tabs, tabs, and more tabs:
Each aileron has an additional smaller tab located outboard of the control tabs for lateral trim. The elevators have two additional tabs located outboard of the control tabs for surface deflection assist and float control respectively. Longitudinal trim is accomplished via a conventional moving stabilizer. The rudder has a single tab used solely for control during manual (no boost) operation.
Feel and performance:
MD-80 control column forces are not extreme but they can be higher than the artificial forces generated on the 737 depending on the flight regime. It has been suggested by some that the DC-9 series is a bit mushy in the lateral axis thanks to the tab arrangement and down-wing spoiler linkage but I have never personally found nor heard it to be a problem even during gusty, crosswind landing conditions.
Let me know if you are interested in more information regarding the cable layout, control column and surface interconnections, or tab arrangements VL.
Last edited by vapilot2004; 6th Nov 2011 at 05:40.