A BE400 First Officer reported that on takeoff the aileron trim malfunctioned requiring a great deal of left yoke input to maintain aircraft control. The aircraft was returned to land but an emergency was not declared.

Narrative

On departure; I was Pilot Flying. During takeoff; after rotation; I needed to input excessive yoke pressure to the left to prevent the airplane from rolling to the right. Between establishing positive rate of climb and reaching 400 feet AGL; I continued the excessive control pressure and attempted to relieve the pressure with roll trim. Actuation of the roll trim provided no relief. Above 400 AGL; I informed the Pilot Monitoring that the airplane was severely out of trim and I was unable to correct the problem with the roll trim. While the Pilot Monitoring was communicating with departure; I visually checked the roll trim indicator and saw a large disagreement between the left and right indications. In an attempt to keep the airplane under control; I selected the left roll trim motor and actuated the trim again. This action improved but did not correct controllability and relieved some but not all of the excessive pressure. Above 1;500 feet AGL; the Pilot Monitoring and I discussed the problem. He verified what I was seeing. We discussed returning and both agreed to return. The PM made our request to ATC and we did not declare an emergency and did not request any assistance. The airplane remained out of trim; but under control. During the time we were receiving vectors to return; we executed the Emergency Checklist for Roll Trim Runaway or Failure. While this checklist did not address our specific problem; it provided guidance; and in compliance with the checklist; we landed as soon as practical. We landed with no further emergencies or abnormalities.