If you flly the plane in primer for a time period, test the plane for cruise
flight and then fill the sides of the stab or rudder and shape it for
perfect trail; you can eliminate the need for a trim tab.  Looks prettier as
well.
Using templates from one side the other side was matched with 1/4 inch foam,
one bid and lots of work to true it up.  The rudder was concave on one side.
Many hours of work and it was trued.

Results?  I can fly in cruise speeds no feet on pedals and the ball is
centered.  Also the plane can bank up to 60 degree banked turns and it flies
center ball with feet flat on the floor. I was amazed at how true this 360
flies. Not so with any spam can or witchita wagon.  No trim tab, springs or
anything.  After a period of time the rudder cables and tubes will loosen up
and the rudder will follow in trail.

If you want a true  flying bird take the time, eliminate after thoughts and
fixups (ie tabs) and have a clean airplane.

Bob Smiley
N94RJ