THE PLT WAS ON A FAMILIARIZATION FLT IN PREPARATION TO FLY THE ULTRALIGHT VEHICLE ON A X-COUNTRY TO EVALUATE IT FOR A MAGAZINE ARTICLE. THE ENG QUIT ON THE 1ST FLT & A SUCCESSFUL FORCED LANDING WAS MADE. REPORTEDLY, THE VEHICLE REQUIRED ONLY MINOR REPAIRS & A TEST FLT BY A COMPANY PLT WAS DECLINED BY THE PLT PRIOR TO HIS 2ND & LAST FLT. AFTER THE 2ND TAKEOFF, THE VEHICLE WAS OBSERVED TO CLIMB IN A RIGHT TRAFFIC PATTERN. ON DOWNWIND AT APRX 500 FT AGL, THE VEHICLE NOSEDOVER INTO ABOUT A 20 DEG DIVE. IT THEN ACCELERATED & POWER WAS MAINTAINED WELL INTO THE DIVE, EVEN AFTER IF APPROACHED 40 DEG. THE VEHICLE THEN WENT INTO A SLOW LEFT BANK & IMPACTED. THE POWER WAS REDUCED BEFORE IMPACT. THE AIRSPEED WAS ESTIMATED WELL ABOVE THE 'NEVER EXCEED' SPEED. AN EXAM OF THE WRECKAGE REVEALED NO EVIDENCE OF A PREIMPACT STRUCTURAL ORCONTROL FAILURE. REPORTEDLY, THE VEHICLE WAS SOMEWHAT NOSE HEAVY, BUT NO WT & BALANCE DATA WAS AVAILABLE. ALSO IT WAS REPORTED THAT THE PLT WORE CONTACT LENSES & PREVIOUSLY HAD PROBLEMS WITH HIS GOGGLES COMING OFF & LANDING IN HIS LAP.