Narrative:

The dual instructional flight departed from ZZZ; a private turf field. A thorough preflight inspection of the piper J-3/C65 was conducted; and instruction given on the proper preflight procedures. No anomalies or irregularities were discovered during the inspection or subsequent pre-takeoff run-up. After maneuvering in slow flight; the aircraft was returned to cruise confign at 2100 ft MSL (approximately 1850 ft AGL). With the engine turning approximately 2100 RPM; 14 inches of the outboard leading edge rock guard and 4 inches of the tip of the wood sensenich propeller separated. Immediate; severe vibration was observed as a result of the imbal. The PIC/CFI immediately secured the engine by simultaneously reducing the throttle to idle setting and switching off the magnetos. The aircraft was pitched up to slow airspeed and stop the propeller rotation. The pilot and student noted the condition of the propeller. The aircraft was trimmed for best rate glide speed; and turned in the direction of a nearby farm field. Upon reaching the field; the pilot noted tall grass; estimated at 30-40 inches in ht; presenting a pitch-over hazard. Altitude was noted at 1800 ft MSL. Adjusting pitch for least sink glide speed and establishing a downwind heading; the PIC elected to glide the aircraft approximately 3 mi to the east; returning to the departure airport. 3 alternate off-field landing sites were idented along the route; in case the primary field became unattainable. Examination of the propeller showed some apparent degradation of the wood inside the edge guard. This could not have been determined prior to flight. The pilot speculates that storage of the aircraft outdoors probably contributed to; or was the root cause of the condition.

Related reports:

Google
 

Original NASA ASRS Text

Title: A J-3 CUB DURING A DUAL INSTRUCTION FLT AT 2100 RPM 14 INCHES OF THE PROP ROCK GUARD AND 4 INCHES OF THE TIP SEPARATED.

Narrative: THE DUAL INSTRUCTIONAL FLT DEPARTED FROM ZZZ; A PVT TURF FIELD. A THOROUGH PREFLT INSPECTION OF THE PIPER J-3/C65 WAS CONDUCTED; AND INSTRUCTION GIVEN ON THE PROPER PREFLT PROCS. NO ANOMALIES OR IRREGULARITIES WERE DISCOVERED DURING THE INSPECTION OR SUBSEQUENT PRE-TKOF RUN-UP. AFTER MANEUVERING IN SLOW FLT; THE ACFT WAS RETURNED TO CRUISE CONFIGN AT 2100 FT MSL (APPROX 1850 FT AGL). WITH THE ENG TURNING APPROX 2100 RPM; 14 INCHES OF THE OUTBOARD LEADING EDGE ROCK GUARD AND 4 INCHES OF THE TIP OF THE WOOD SENSENICH PROP SEPARATED. IMMEDIATE; SEVERE VIBRATION WAS OBSERVED AS A RESULT OF THE IMBAL. THE PIC/CFI IMMEDIATELY SECURED THE ENG BY SIMULTANEOUSLY REDUCING THE THROTTLE TO IDLE SETTING AND SWITCHING OFF THE MAGNETOS. THE ACFT WAS PITCHED UP TO SLOW AIRSPD AND STOP THE PROP ROTATION. THE PLT AND STUDENT NOTED THE CONDITION OF THE PROP. THE ACFT WAS TRIMMED FOR BEST RATE GLIDE SPD; AND TURNED IN THE DIRECTION OF A NEARBY FARM FIELD. UPON REACHING THE FIELD; THE PLT NOTED TALL GRASS; ESTIMATED AT 30-40 INCHES IN HT; PRESENTING A PITCH-OVER HAZARD. ALT WAS NOTED AT 1800 FT MSL. ADJUSTING PITCH FOR LEAST SINK GLIDE SPD AND ESTABLISHING A DOWNWIND HDG; THE PIC ELECTED TO GLIDE THE ACFT APPROX 3 MI TO THE E; RETURNING TO THE DEP ARPT. 3 ALTERNATE OFF-FIELD LNDG SITES WERE IDENTED ALONG THE RTE; IN CASE THE PRIMARY FIELD BECAME UNATTAINABLE. EXAM OF THE PROP SHOWED SOME APPARENT DEGRADATION OF THE WOOD INSIDE THE EDGE GUARD. THIS COULD NOT HAVE BEEN DETERMINED PRIOR TO FLT. THE PLT SPECULATES THAT STORAGE OF THE ACFT OUTDOORS PROBABLY CONTRIBUTED TO; OR WAS THE ROOT CAUSE OF THE CONDITION.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.