Hangar 9 Sukhoi SU-31 Instruction Manual page 10

Note: A computer radio using flapperon mixing is recommended.
In this case, each wings servos plug into a Y-harness and
then the Y-harnesses are plugged directly into the receiver
using the aileron and appropriate auxiliary channel used for
flapperon mixing (see your radio's instructions).
Note: If a non-computer radio is used, three Y-harnesses
are required. Plug one Y-harness into the aileron port of
your receiver. Plug each wings servos into a Y-harness and
then plug those into the Y-harness connected to the receiver.
10
Step 5. With the servos in position, mark the four locations for
the mounting screws. Remove the servo and drill a 1/16" pilot
hole in the servo rails. Secure the servos to the wing using the
screws provided with the servos.