J-3 PLT WITH PAX HAD THE ACFT NOSE OVER AND BROKE THE WOODEN PROP. THE R BRAKE APPEARED TO DRAG OR LOCK UP.

Narrative

NOTED WINDSOCK INDICATIONS WERE JUDGED TO BE 3-4 MPH CLOSE TO DOWN THE RWY AND GOOD VFR CONDITIONS. THE CUB FROM RWY CTR WAS ROLLING OUT STRAIGHT AND DOWN TO ABOUT 15 MPH WHEN IT STARTED A MODERATE R TURN WITHOUT BRAKE OR RUDDER INPUT. I IMMEDIATELY APPLIED FULL L RUDDER; L BRAKE WITH STICK STILL FULL AFT (NO R BRAKE BEING APPLIED). THE CUB CONTINUED TURNING R WITH R WHEEL DRAGGING AND DECELERATING. THE CUB NOW AT ABOUT A 50 DEG ANGLE FORWARD TO THE RWY; AND AT THE EDGE; THE CUB TIPPED DOWN ON ITS NOSE DESTROYING THE WOOD PROP. THE CUB REMAINED ON ITS NOSE AND WE EXITED. THE NOSE-OVER WAS FAIRLY GENTLE WITH NO INJURIES. NO AIRFRAME OR FABRIC DAMAGE WAS DETECTED. MY LONG TIME TAILDRAGGER EXPERIENCE INDICATES THIS R TURN FORCE WOULD HAVE EASILY BEEN CORRECTED BY THE ACTION I TOOK IF EVERYTHING WAS FUNCTIONING NORMALLY. CAUSE OF UNPROVOKED R TURN IS YET TO BE DETERMINED. THE THROTTLE REMAINED CLOSED FROM FLARE TO STOP. WHEN THE TAIL LIFTED; I STOPPED USING L BRAKE AND R WHEEL SEEMED TO STILL BE BRAKING. THE TAIL WHEEL LEAVING THE GND TO NOSE ON THE GND WAS ABOUT 2 1/2 SECONDS. SUPPLEMENTAL INFO FROM ACN 604543: DETERMINING THE CAUSE FOR THIS SO FAR MIGHT HAVE BEEN WHEEL; BRAKE ICE; OR BRAKE MALFUNCTION.