The basic handling problem with the DR-1 is excess aileron yaw caused by insufficient vertical tail area, along with its use of only two ailerons. The same problem afflicts many WW1 designs; the Tripe more than most. An enlarged rudder of the same shape would not be all that noticeable, and should give a big boost to handling. I have fixed several evil-handling model bipes by simply enlarging their fins and rudders, but haven't as yet tried this trick on a triplane.