ORIGINAL: gaRCfield
ORIGINAL: Charlie P.
Full scale flight doesn't help with R/C much. When was the last time you flew a full-scale airplane while it was heading AT you?
If it's a nose-wheel trike have you ground-checked it so it rolls straight with the rudder centered? Common error is to have the nose wheel out of line with the rudder so they fight each other. The nose wheel has a lot more authority while in contact with the ground, but the instant you rotate if it is not set to the rudder the model suddenly turns when the rudder gets the airflow to be in command.
There is also a natural tendency to wander to port from the prop torque. Taildraggers, and in particular narrow carriaged biplanes need a bit of right rudder to compensate. Feed in throttle smoothly and gradually. Flooring it gives a lot of torque before the windspeed over the control surfaces gives you any control authority.
I thought I was having some similar problems - what turned out is that my nose wheel was keeping the plane straight on the ground, but when it left the ground I got the 'wind (something) effect (can't remember the name of the stupid thing) where the wind pushed my vertical stabilizer so the nose pointed towards the wind. Rudder to correct this.
Did you use trim to straighten out the roll on the ground?
If you did, then you've essentially trimmed in some yaw in the rudder in order to get the nosewheel straight. Rather than using trim to adjust the nosewheel for a straight takeoff run or roll out on landing you should use the nose wheel linkage to adjust for straight roll. This leaves the rudder trimmed properly so you don't see a sudden yaw as the rudder gains effectiveness either while still on the ground or just at take off.
My rudder/nose gear servo has a "slide through" type linkage at the servo for the nose gear pushrod. That allows me to loosen the set screw and move the pushrod forward or backward to straighten the nose wheel, while not affecting the rudder at all.
Bob