Hangar 9 P-51 Mustang ARF Assembly Manual page 44

Section 16: Checking the Control Surface Directions
Elevator
With the radio system still on, pull back on the elevator
control stick to give an up elevator input. The elevator
should move up from center. If not, check the radio
instructions on how to reverse the direction electronically
at the transmitter.
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Rudder
The final control surface direction to check is the rudder.
With the radio system on, move the rudder stick to the
right, this will make the plane turn right. The rudder
should deflect to the right as well. If not, check the radio
instructions on how to reverse the direction electronically
at the transmitter.
Note: Operating the functions at the
transmitter opposite as described will result in
the control surfaces moving opposite as well.