------------------- I was thinking about youre posts and was wondering.If i fly the plane inverted and move the rudder I should see some normal yaw in the plane due to the cg being below the wing anding more stability. thiswould prove the need for dihedral in the wing.If it does the same thing stall and drop the nose it needs more tail volume.
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Well you are asking if the airplane needs dihedral? Are you trying to find out
1. why the airplane doesn't roll with rudder input?
2. why the airplane pitches nose down with rudder input??
3. both???

The low wing design you have should be mostly uncoupled in all axes in normal upright flight. The rudder should make only yaw, elevator pitch and ailerons roll. If it is doing that it is working correctly for a full house aerobatic airplane.

When you put the zero dihedral airplane inverted, trim level, put in rudder and observe the airplane roll a little then this is normal. But that has nothing to do with the original question ....... does it.??????