I always trim my models at 3/4 throttle setting. Anything above or below this throttle setting is you flying the plane. If down trim is required at this throttle setting I would check the CG location according to the manufacture placement. If your CG falls withing the reccommended range listed then I would do your own math and verify this location. Balance your plane at 27% CG as a reference point and enjoy. Unless your scratch bulding the designers of our model aircraft usually if not always have done the homework for you. Incidence angles and offsets of the powerplant have already been accomplished before they release the aircraft to the consumer. If your still having problems contact the vendor. H9 recently released an ARF Tiger Moth with the CG listed incorrectly.