That is easy, all you have to do is to ask
Open your fsx.cfg file with a notepad, find the section that says [DynamicHeadMovement] and replace it with this:
[DynamicHeadMovement]
LonAccelOnHeadLon=-0.000000
LonAccelOnHeadPitch=-0.000000
RollAccelOnHeadLat=0.000000
YawAccelOnHeadLat=-0.000000
RollAccelOnHeadRoll=0.000000
MaxHeadAngle=5.000000
MaxHeadOffset=0.300000
HeadMoveTimeConstant=0.000000