Date: 201509
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: RV-4
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Descent
Aircraft component: Propeller
Component problem: Failed
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Commercial
Human factors: Confusion; Situational Awareness; Time Pressure; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Diverted; Flight Crew Landed in Emergency Condition; Flight Crew Took Evasive Action; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: While descending from altitude for a landing I experienced catastrophic propeller failure. I lost a blade 8' out from the hub on a fixed pitch Sensenich propeller.This propeller has a rare 2600 rpm limitation in this application on fast homebuilts; for a harmonic issue. I had only owned it for 6 weeks and maybe flown it a total of 9 hours. It failed while I was cruising at 2450 rpm.It is normal in these fast homebuilts to pitch the prop for takeoff and climb; then just turn them up fast for cruise. This is not the way you run this prop. My learning experience is that I would have no way to know how this prop was operated prior to my purchase. This prop should have been replaced with a wood or composite prop more suited for this operation. I will be a huge advocate for getting these propellers off of fast homebuilts.After a quick shut down of the engine I positioned myself for an uneventful landing in an alfalfa field. No further damage occurred from the landing. Smooth landing on a good surface. Wings were pulled to get the airplane home. Upon further inspection once home took notice of damage to firewall.1. Engine mount broken clean through in 11 places.2. Alternator was busted up and loose inside cowling.3. Exhaust was broken at every flange and was laying loose inside cowling.4. Engine Crankshaft was severely bent.5. Starter ring gear was broken in several places.6. Cowling was cracked and damaged in several spots; but was structurally intact and aided in keeping engine attached to airplane.From the time of failure to prop stopped was best estimated at 8 seconds. I pulled mixture and turned magnetos off; after which I pulled the nose up to a point where the airplane slowed enough to stop the prop from Windmilling. My best guess by looking at the damage is that I had just a few seconds left before the engine would have come free from the airplane; leaving the airplane uncontrollable.I am concerned that this prop limitation is not widely known and it could take a life. I am an A&P/IA with lots of experience with these airplanes and it was this experience that help with quick recognition of the problem.

Callback: Reporter stated the propeller was aluminum; appeared to be in excellent condition with no nicks or damage of any kind. No indication in log book of when the propeller was installed.



Synopsis: An RV-4 pilot described his experience and aircraft damage sustained when his fixed pitch Sensenich propeller lost a blade 8' out from the hub in a descent. Engine damage was substantial even though secured within seconds of the failure.