Here are the latest additions I made to the Onas with the Contra Drive installed. They are an added dorsal and some triangular pieces on the TE of the rudder. The net affect is increased yaw stability that the pair of props up front reduce. And a much softer rudder response. The Contra Drive removes the spiral slipstream affect and greatly increases the fuselage lift. Probably somewhat similar to the canalizer. I had reduced my normal mode rudder throw and increased the expo, but I was getting into expo values of 85 to 90% and I just didn't like that feel. The triangles allowed me to increase the throw and reduce the expo. They did change how the model stall turns and it took some changes in settings to get happy with them again. The positive affect was that it just about eliminated any yaw wobble after the stall turn.

BTW, the dorsal is 3/32" balsa cobered in Carbon Ultracote and the triangles are 1/2" x 1/8" balsa covered with the same Ultracote. They are then both taped on.

It sure would be fun to design a new model from the ground up for the Contra Drive!