THE OWNER/BUILDER HAD PREPARED THE ACFT FOR ITS 1ST FLT. THIS PREPARATION INCLUDED HIGH SPEED TAXI TESTS, A BRAKE LINE REPAIR & ENG ADJUSTMENTS. TWO 17.6 LB BARBELL WEIGHTS WERE TIED TO THE WING LIFT BULKHEAD WITH 5/16 INCH HEMP ROPE FOR PURPOSES OF WEIGHT & BALANCE. A DECISION WAS MADE FOR THE OWNER'S FATHER, AN EXPERIENCED PLT, TO FLY THE INITIAL TEST FLT. THE PLT MADE A HIGH SPEED RUN WITH AN OPTION TO TAKEOFF & ABORTED WHEN THE ENG DEVELOPED A MISS. HE THEN PERFORMED A SATISFACTORY RUN-UP & TOOK OFF ON THE NEXT ATTEMPT. AFTER TAKING OFF, THE PLT REMAINED IN THE TRAFFIC PATTERN & TURNED ONTO A DOWNWIND FOR RWY 23. THE ACFT THEN NOSED OVER & CRASHED IN A NEAR VERTICAL DESCENT. AN EXAM OF THE FLT CONTROL SYS REVEALED NO EVIDENCE OF A PREIMPACT MALFUNCTION. ALL FRACTURES SHOWED EVIDENCE OF OVERLOAD FAILURE. THE BALLAST WEIGHTS WERE NOT SECURED IN ACCORDANCE WITH NORMAL AERONAUTICAL PRACTICES. THERE WAS EVIDENCE THAT THEY COULD HAVE COME LOOSE & JAMMED THE FLT CONTROLS OR SHIFTED THE CG.