A correction regarding the DHC-8-400:
(From the Q400 FCOM)
"Hydraulic pressure supplied to both rudder PCUs is regulated by the FCECU (Flight Control Electronic Control Unit) in response to airspeed inputs it receives. Rudder authority is limited as a function of airspeed to reduce excessive yaw rate. As airspeed increases, the FCECU reduces hydraulic pressure to the PCU's. This results in a reduction of rudder deflection in response to rudder pedal inputs. As airspeed decreases, the FCECU increases hydraulic pressure to the PCU's. This results in an increase of rudder deflection in response to rudder pedal inputs."
The earlier models (-100, -200, never flew the -300 so can't say about that one) had a similar system whereby the Rudder Pressure Regulator steped rudder actuator pressure up and down in response to TAS signals from the DADC passing through 140 KIAS.
These airspeed-based rudder limits are in addition to the previously-mentioned rudder input restrictor mechanism which limits rudder pedal travel mechanically based on flap lever position.
Last edited by hikoushi; 30th June 2009 at 07:09.