REPORTEDLY, THE PLT HAD PREVIOUSLY FLOWN IN A ROTEC RALLEY III ULTRALIGHT, BUT HANDLED THE CONTROLS FOR ONLY A FEW MINUTES. AFTER ASSEMBLING THIS ULTRALIGHT, N148RE, FROM A KIT, HE MADE THE NECESSARY GROUND CHECKS & PREFLT INSPECTION, THEN TOOK OFF ON THE 1ST TEST FLT. AFTER TAKEOFF, HE STARTED A LEFT TURN. WHILE IN THE TURN, HE ALLOWED THE AIRSPEED TO DECREASE & THE LEFT WING BEGAN TO STALL. HOWEVER, AT THIS POINT, HE BECAME CONFUSED ABOUT THE OPERATION OF THE FLIGHT CONTROLS & PULLED BACK ON THE STICK INSTEAD OF PUSHING IT FORWARD. THIS RESULTED IN A FULL STALL. BEFORE HE COULD RECOVER FROM THE STALL, THE ULTRALIGHT CRASHED IN A NOSE LOW, LEFT WING DOWN ATTITUDE. THE ROTEC RALLY III WAS EQUIPPED WITH AN OVERHEAD CONTROL STICK. THE PLT WAS ACCUSTOMED TO FLYING CONVENTIONAL ACFT WITH A STICK ON THE FLOOR. HE STATED THERE WAS NO MECHANICAL FAILURE OF THE ACFT & THAT IT PERFORMED WELL.