My RC instructor always taught me to trim the rudder when pulling straight up away from you, in essence you would remove any pull to one side during proper rudder trim. The idea being when going straight up, the only effect gravity has on the plane is pulling directly down, not affecting the trim, making it "true". So I have to ask, if you notice pull in any direction going upline, isn't this an indication the rudder isn't trimmed properly? I can't see how the pull to the left wouldn't be seen flying straight and level as well...

Jack