I designed a model for the first time myself. It has a span op 190 cm and a length of 170 cm, 4 kg weight. Symmetrical airfoil, shoulder-wing configuration, wing and elevator angle 0 degrees to the center-line.
Loops, rolling, downlines etc. that is all perfect like a F3A plane. But when I apply rudder it acts horrible.
In the Hammerhead it kicks the tail back, wen I roll to knife -edge and apply rudder it makes a turn and with a lot of rudder in the knife edge it will snap. It is like a lot of up is applied all the time.

I searched this forum and got the idea that this is called rudder pitch coupling.

OK but what did I do wrong in the tail configuration?
Is the stab placed to low in relation to the wing.
Is it the shape of the rudder with the lage part in front of the hinge-line.
Or has it to do with the angle of the rudder with the fuselage that is 90 degrees.