AN RV-6A EXPERIMENTAL AT 9500 FT DECLARED AN EMER AND DIVERTED DUE TO PROPELLER FAILURE. HALF OF ONE BLADE DEPARTED ACFT.

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FLT DEPARTED AND CLBED TO 9500 FT. APPROX 40 MINS INTO FLT WE HEARD A LOUD NOISE WITH IMMEDIATE SEVERE VIBRATION FROM ENG. I PULLED THROTTLE AND MIXTURE; BUT PROP WAS STILL TURNING ABOUT 600 RPM. I BELIEVE I ALSO TURNED OFF THE IGNITION SWITCH; BUT I AM NOT SURE. I CALLED AN EMER ON 121.5. 'GUARD' RESPONDED AS WELL AS SOMEONE ELSE; I CHOSE TO FOLLOW 'GUARD' INSTRUCTIONS. AFTER GIVING THEM THE DETAILS AND LOCATION; THEY GAVE ME XYZ APCH FREQ. XYZ APCH GAVE ME A CHOICE OF ARPTS TO LAND AT. I CHOSE ZZZ. I LANDED ON RWY 24 AND TURNED ONTO TXWY LIMA. THE PROP STOPPED AND THEN WE SAW THAT THE PROP WAS BROKEN AND ABOUT HALF OF THE BLADE WAS MISSING. FURTHER INSPECTION OF ENG REVEALED MINOR DAMAGE; ABRASION OF COWL FROM BAFFLES; EXHAUST PIPE SUPPORT BRACKETS CRACKED; AND COWL AIRSEAL FABRIC ABRASION. STILL NOT SURE IF BREAK WAS CAUSED BY BIRD STRIKE OR FATIGUE. PROP HAD 649 HRS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE PROPELLER WAS MADE OF WOOD AND IT WAS MANUFACTURED BY AYMAC-DEMUTH. RPTEDLY WHEN THE MANUFACTURER WAS CONTACTED AND INFORMED ME OF THE FAILURE; IT WAS ACKNOWLEDGED THAT 'THEY HAD A FEW FAILURES.' THE RPTR ADVISED THE MANUFACTURER THE ENG POWER HAD BEEN INCREASED BUT ONLY SLIGHTLY BY THE INSTALLATION OF NEW PISTONS. THE MANUFACTURER STATED THIS WAS THE CAUSE OF THE PROPELLER FAILURE; IE; THE INCREASE IN ENG POWER. THE RPTR STATED HE KNOWS OF TWO OTHER PROPELLER FAILURES ON THE RV-6A ACFT USING THIS MANUFACTURER'S PROPELLER. THE PROPELLER HAD A NORMAL PREFLT INSPECTION AND APPEARED NORMAL WITH NO DISCREPANCIES NOTED.