ORIGINAL: HighPlains
A more interesting question might be why did it crash at the end of the first flight? I believe it was due to vertical stabilizer being mounted inverted under the fuselage to protect the propeller (it was a pusher design). At some angles of attack, I believe that the rudder action would reverse, so when the pilot pushed left, the airplane would respond to the right. The end of the first flight ended with the plane snapping over and crashing inverted killing the pilot.
I was talking to a testpilot and he said the underside rudder is good but if you come in a tailslide the effect indeed is reversed in that kinda rudder. I immediately increased the upper side component of the rudder stab area on my design and made the underside rudder lower and thicker + longer ( wider ).