THE NON-RATED PLT HAD PURCHASED THE ULTRALIGHT VEHICLE ABOUT 1 MONTH PRIOR TO THE ACCIDENT. HE HAD COMPLETED APRX 8 HRS OF TAXI & LOW FLTS ALONG A GRASS RWY. EARLIER ON THE DAY OF THE ACCIDENT, HE HAD MADE 2 FLTS & REPORTEDLY HAD ACCUMULATED 1 HR OF FLT TIME IN THE ULTRALIGHT. ON THE 3RD FLT, HE TOOK OFF FROM THE MANSFIELD MUNI ARPT TO REPOSITION THE ULTRALIGHT TO A GOLF COURSE, ABOUT 3 MI AWAY. A WITNESS OBSERVED THE ULTRALIGHT APPROACHING A FAIRWAY & REPORTED IT APPEARED LOW AS IT APPROACHED TREES. HE REPORTED THAT THE NOSE PITCHED UP SHARPLY, THE LEFT WING LOWERED & THE ULTRALIGHT BEGAN TO LOSE ALTITUDE AS THE NOSE LOWERED IN THE VICINITY OF A HOUSE. HE REPORTED THAT THE NOSE PITCHED UP AGAIN, THEN THE ULTRALIGHT LOST ALTITUDE RAPIDLY & DISAPPEARED BEHIND TREES AND CRASHED. NO PREIMPACT FAILURE OF THE ULTRALIGHT OR ITS ENG WAS FOUND. THE PLT HAD HAD APRX 7 HRS DUAL FLT INSTRUCTION IN A CONVENTIONAL ACFT, BUT HIS 1ST SOLO FLT WAS IN THE ULTRALIGHT.