Hi¡¡
This last week-end I made the maiden flight of my scrap build RCM Advance Trainer (BTW, kudos to Mr. Bridi and Mr. Dewey, the designers). It flew great, but with a significant tendency to pro verse roll couple when using rudder. In fact, it seems you can fly the model without the ailerons at all. Strangely, knife-edge were very good and somehow easy.
I thought the reason for the roll-couple was too much dihedral, but the most experienced guy in our field told me that the reason was the tail moment, specifically the rudder. For those who doesn't remember the model, it has the rudder behind the elevator, and I think it could "deflect" some differential airflow to the elevator, once rudder is applied, but honestly, I don't know. As an additional information, the plane was almost impossible to enter a spin, but it was a little nose heavy...

So, has roll coupling something to do with tail moments? Is there any guide to the consequences of using different moments on a given plane I can use to somehow forecast model's behaviors in advance?

Thanks