Rudder question
I have observed on many occasions that on idle aircraft the rudder moves about.Sometimes it's the wind but at other times there is no wind and no pilot in the front so why and how does the rudder move on it's own.Also I have notized that the 777 or A380 flap their rudder alot more than a 767 or E-195.The E-Jets never seem move their rudder when idle.The A320 and 737 does it alot,wonder why some jets do it more than others.