Rockstar

Sorry, I didn't explain that very well, if I input right rudder the plane yaws to the right and drops its nose, begining the first part of a bunt which i then correct with up elevator. And in knife edge with just rudder input will fly a wide circle.

I recently bought an ARTF acrowot. Its C of G is spot on and flys well. But in straight and level flight the plane bunts with a rudder input. This is also noticable in knife edge, with rudder input only the plane will bunt. Dihedral is fine. On talking to some other guys at the club, everyone who has a kit built acrowot says they have the same problem as does someone else who has the ARTF. I know this can be overcome with a rudder/elevator mix. Also it can be corrected by changing the angle of the vertical stabaliser back 15 degrees. But I was wondering if anyone has any thoughts about why aerodynamiclly this happens?