Is this the "inboard aileron"? And why is that thing really "nervous" when on short final, with...............

Question

...... the flaps deployed? It goes like when there is little wind like crazy. Always up and down.

http://i29.tinypic.com/2zhfbe1.jpg

Answer 1

Most of those movements that you see are caused by "George"

The automatic pilot input to correct lift, speed, drift, etc.

Answer 2

That is a flaperon if it is on a 777.  And it would be moving for trim (roll/bank).

Answer 3

That's a flaperon.  It combines the function of a flap and an aileron.  It will move down like a flap to increase lift, but its displacement is variable to help with roll control.

Its movement is more noticeable than the movement of an aileron because it moves with larger deflections.  Since it is on the inboard section of the wing instead of the outboard, it is acting on a shorter arm and needs more deflection to be effective.  The other reason that it moves a lot on short final is because that is when the airplane is flying the slowest.  Without as much air moving over the wings, control deflections have to be greater to have the desired effect.