Digital servos and heavy surfaces.

edit: Guess I should explain some more. You know how you can turn a motor even if it has no power to it? Well that's what a servo is, A small, powerful motor and a bunch of gears to give it more torque. When the motor is off, the surfaces have enough weight to move the control arm. For some reason (I don't know why cuz I can't afford digital servos) when digital servos are off, they have less resistance than normal ones.