Total authority of the control surface is modulated in relation to aircraft IAS using “blowdown”, ie a constant pressure is applied to the surface by the actuator, and the movement of the panel reduces accordingly as the dynamic pressure on it increases. For this reason maximum rudder pedal movement is reduced with increasing airspeed. Maximum rudder panel deflection is approximately +/-15 degrees on the ground, reducing to around +/-8 degrees at a typical cruise altitude.
The rudder bars operate the rudder PCU via cables, through the Rudder Feel and Centering Unit, which uses a set of inner and outer springs to produce feel in the rudder pedals. The tension on the springs is adjusted by aircraft speed, so the rudder pedals are thus harder to push at speed, with the stiffness increasing with the amount of deflection.
Originally Posted by Jonty
I would imagine the 737 is like most other jets ... The internal computers then limit...
No computers on a 737 rudder flight control system! It's all springs, cables, cams and hydraulics
Good ol' engineering! (There is an elevator feel computer.)
Other jets are different - on the BAe146 for instance (from old memory), the rudder circuit had a "q pot" with a stepped plunger. As speed increased the plunger would move out of the q pot, and each step would block the movement of the rudder by an increasing amount. The rudder pedal movement would thus feel the same in effort, but be blocked by the q pot to progressively smaller deflections.
The airbus series use software to limit rudder movement in flight.