RE: Are verticals necessary on a Delta?
BD, Look for examples of successful single fin deltas and take it from there. It is easier to start out with an oversized fin and work your way back instead of working in the other direction. The further the prop is from the CG, the more fin you'll need.....most .40 size designs have the engine as far back as it can go, anyway. I do believe that the further back you can get the fin[s], the smaller they can be. If the plane just seems aimless on launch, like it just wants to spin, the vertical area behind the CG is lacking.
I've been thinking it would be fun to try a stunt delta with a rudder, myself.