Rudder Ratio
MechEngr’s comments stirred my memory. Boeing pedals did move 100% but the rudder movement decreased due to the rudder ratio mechanism. However, many years ago, in the early days of the 757, a slow L HYD leak required the system to be switched off until required for the approach (if stack pipe reserve was intact). For some reason all our aircraft required a great deal of rudder trim in the cruise (later corrected). Having such a leak and following the QRH, the result was an immediate 30 to 40 degree wing down. The aircraft, though, maintained straight and level (altitude but not wings!) flight with us hanging in our straps until the L HYD was quickly switched back on again. This was later shown to have been due to a full and immediate rudder deflection (at M.8). Mr B informed us later that the ratio of rudder deflection reduces with speed by 15 times, from slow to high speed. RUDDER RATIO though, of course, was switched off by selecting L HYD OFF. I believe the QRH was amended to include zeroing the rudder trim before switching off the L HYD. I remember at the time, being surprised that this had escaped being mentioned in the QRH because the excessive trim required on our aircraft was caused, I was told, by a design change requested by our company. Little finger and thumb sometimes do not speak and these things get lost in the fog of history and I have long been out of the game.
Prober