FBU 4EVER! From Norway, joined Jan 2001, 998 posts, RR: 7
Reply 1, posted (13 years 12 months 3 days 9 hours ago) and read 3300 times:
Very few planes are completely "straight",and most need to be trimmed slightly.
Usually cruise speed trim is used as a datum,and small trim changes will occur when speed is changed.Also flaps and slats extension might change the trim.Most larger planes have aileron trim tabs that can be controlled manually or electrically from the cockpit,while smaller planes have a tab that can be set (or bent) while on the ground.