Make sure that when the servo is centered that the position of the two servo arms are in the same position. The easy/correct way to remedy this situation is to take off one of the servo arms, and reposition it the same as the other servo arm. Then unscrew the control horn from the flap where the control horn was moved. Adjust the clevis so the flap is level. The other flap position may also need adjustment. This situation is a problem that is caused by improper assembly. M recommendation is to center all the control surfaces by adjusting the clevis position, before doing any electronic adjustments with the transmitter. Making adjustments this way will ensure that the airplane will turn the same going both directions.
