DCS units come with Trim function on FFB axis and if it works then everything is OK.
However, on some units (ww2 planes, some jets) if you use the trim on FFB axis it also moves the FFB center which messes everything up. For these cases it's better to use a "HW trim + override" in VPforce app (instead of in-game trim), that way FFB center stays where its supposed to be.