I have an OS 50SX in mine and had to add about .75 oz in the tail to get the correct balance. However, at about 1/2 throttle I have to put in about 5 degrees of elevator up trim to maintain level flight - this makes inverted flight a little sporty as it performs like it's real nose heavy. Anyone out there have a similar experience? beginning to think I have incidence problem with either wing or stab.