Just a word on the 747 rudder ratio system - as IAS increases the rudder ratio system reduces the travel on upper and lower rudder.Both systems are independently operated and monitored by a comparator which will give a warning in the cockpit if the two rudders are not synchronised. At speeds greater than 428 kts rudder movement is restricted to 5deg in each direction. As far as blow back valves are concerned I have never heard of them being fitted to 747 rudder hydraulics - there are hydraulic fuses in each hydraulic supply line which will close in event of a leak downstream to prevent loss of system fluid.
Last edited by bcgallacher; 7th May 2015 at 07:59.
Reason: Additional info