THE HOME BUILT GYROCOPTER WAS BEING FLOWN BY THE OWNER/BUILDER/DESIGNER WHO HAD AN AIRPLANE, SINGLE-ENG, LAND RATING. SHORTLY AFTER THE GYROCOPTER TOOK OFF, THE ENG WAS OPERATING AT A HIGH RPM WHEN A WITNESS HEARD A POP/NOISE. SUBSEQUENTLY, THE GYROCOPTER CRASHED IN A CORN FIELD ABOUT 1-1/2 MI FROM THE DEPARTURE POINT. THE MAIN WRECKAGE WAS FOUND INVERTED. ONE ROTOR BLADE, THE OIL COOLER & THE LEFT VERTICAL STABILIZER & RUDDER WERE FOUND 60 TO 150 FT FROM THE MAIN WRECKAGE. BOTH OF THE WOODEN PROP BLADES HAD SHATTERED. THE OIL COOLER HAD BEEN INSTALLED BELOW THE ENG & JUST FORWARD OF THE PROP. ITS UPPER SIDE HAD BEEN ATTACHED WITH A SINGLE SOLID MOUNT USING AN 'L' SHAPED ALUMINUM STRAP. ITS LOWER SIDE WAS FASTENED WITH A SEMIFLEXIBLE MOUNTING. THERE WAS EVIDENCE THAT THE UPPER MOUNT HAD FAILED & ALLOWED THE OIL COOLER TO MOVE AFT INTO THE PLANE OF ROTATION OF THE PROP BLADES. EXCEPT FOR THE OIL COOLER BRACKET, NO PRE- ACCIDENT MECHANICAL PROBLEMS WERE FOUND.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

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