RE: BT Bf109E-4
before shaping the rudder's leading edge i needed to install the hinges so i tacked the rudder in place and marked the hinge locations. i had forgotten about the cutout for the elevator control linkage and added a middle hinge to the rudder but there isn't a place in the fin to accept the middle hinge.
pic 2 - hinge points added.
pic 3 - now i could shape the rudder. i re-tacked the fin and rudder together and again slowly shaped both together.
pic 4 - now all that is left is to shape the rudder's leading edge and fin's trailing edge to match.