NOTES LEFT BY PLT INDICATE HE HAD BEEN TESTING THE FLIGHT ENVELOPE OF THIS EXPERIMENTAL RACING ACFT, INCLUDING OPERATION OF THE ENGINE BEYOND PROP LIMIT OF 4000 RPM. WITNESSES HEARD ENGINE SOUND SUDDENLY SPEED UP TO HIGH RPM THEN CEASE ALTOGETHER. SOME WITNESSES REPORTED HEARING AN EXPLOSIVE SOUND. ACFT WRECKAGE WAS SCATTERED OVER 1-1/2 MILES. HORIZONTAL AIRFRAME SURFACES WERE DISINTEGRATED; LARGEST PIECE WEIGHED LESS THAN 10 LBS. 3 PROP BLADES (WOOD CORE) HAD SEPARATED 8' OUTBOARD OF HUB; FOURTH BLADE SEPARATED INSIDE SPINNER. ONLY ONE BLADE WAS RECOVERED. EXAMINATION OF AIRFRAME FRACTURES REVEALED SEPARATIONS OCCURRED ALONG MULTIPLE AXES; SIGNATURES IN CONVENTIONAL MATERIALS SHOWED CHARACTERISTICS OF GROSS OVERLOAD. COMPOSITE MATERIAL SEPARATIONS PARALLELED WARP OF 'CLOTH' EXCEPT IN AREAS OF HIGH PEEL STRESS. ALL COMPOSITE STRUCTURES EXHIBITED UNIFORM SATURATION OF RESIN; NO AIR BUBBLES FOUND IN LAYUP.