One would have naturally thought that a "3rd Generation" PSRU would be the "cat's meow"; but that evidently isn't the case, and it almost cost a pilot and pax in an RV-9A their lives!  The below report (see link) also states that there have been quite a few failures of this PSRU, and one came after only 160 hrs of usage! Amazing the "snake oil" that is out there and ready to hurt people...

http://www.ntsb.gov/aviationquery/brief2.aspx?ev_id=20140224X15602&ntsbno=ERA14LA130&akey=1

       Marc Wiese

       AIRPLANE INFORMATION

       According to Federal Aviation Administration (FAA) records, the RV-9A, a two-seat, all-metal, low-wing airplane with tricycle configured landing gear was issued an airworthiness certificate, in the experimental category, on July 18, 2011. It was built from a series of kits provided by Vans Aircraft and Eggenfellner Aircraft, Inc. The airplane was equipped with an Eggenfellner Subaru H4 modified automobile engine which included a Gen 3 V4 propeller speed reduction unit (PSRU) gearbox that was used to drive the propeller at a speed slower than the engine speed. The engine was equipped with an IVO propeller assembly that consisted of three electrically-controlled wooden propeller blades.

       The engine kit was based on an EJ-25, 2.5L Subaru water cooled 4-cylinder engine and was rated at 160 HP at 5400 rpm.

       The pilot/builder stated that he purchased the kit for the airplane in 2001 and began construction shortly after. He purchased the engine, which at the time, was equipped with a Gen 1 PSRU and solid flywheel, direct from Eggenfellner Aircraft, Inc. in 2002 and installed the engine about January 2008. In 2011, prior to receiving the airworthiness certificate, the pilot employed Eggenfellner Aircraft, Inc. to remove the original PSRU and replace it with a Gen 3 V4 PSRU.

       During a telephone interview a representative of Eggenfellner Aircraft, Inc., now defunct, stated that the Eggenfellner Subaru H4 engine transfers power to the PSRU through a spline shaft. One end of the spline shaft is inserted into a splined drive disk adapter at the engine. The splined drive disk is bolted to the engine crankshaft through the flywheel. The other end is inserted into the PSRU input spline.

       The spline shaft and PSRU input spline were taken from the transfer cases of Nissan Pathfinders. The machining of the drive disk adapter that affixes to the solid flywheel and crankshaft were outsourced to a separate facility and made from non-heat treated 4140 steel.

       The engine information system (EIS) installed in the cockpit showed that the total time for the airframe and engine at the time of the accident was 324.5 hours

       The last recorded annual inspection took place on September 13, 2013, at which time 278 hours were reported. A review of the maintenance records revealed no record that the PSRU had been removed or that the spline components had been inspected or lubricated since installation. In addition, the pilot/builder of the airplane stated that he had not inspected or lubricated the PSRU, the spline shaft, or drive disk adapter during the airplane's total time in service.

       Removal of the PSRU revealed that the spline shaft rotated freely within the drive disk adapter, which was attached to the engine solid flywheel. The PSRU input spline contained approximately one teaspoon of red dust (consistent with ferrous fretting-wear debris). The drive disk adapter and spline shaft were then removed from the flywheel and separated. The teeth of the spline shaft exhibited mechanical damage consistent with the wear on the drive disk adapter teeth.

       Further examination at the NTSB Material's Laboratory revealed that the PSRU input spline, spline shaft, and drive disk adapter exhibited severe wear and were void of lubrication. Examination of the spline shaft and drive disk adapter using a 5X to 50X stereo zoom microscope revealed the flanks of the spline shaft teeth that mate with the drive disk adapter were worn by about 75%, with the tips of the teeth forming sharp cusps that had been bent over consistent with rotation of the spline shaft within the drive disk adapter. Wear surface features on the spline shaft teeth were consistent with fretting wear that had progressed to adhesive wear. [Additional information can be found in the Materials Laboratory Factual report located in the public docket.]



   I thought everyone long since knew to not use an Eggenfailure PSRU. Strange that he would have used one without even doing any inspections given their propensity to fail. (even the 3rd generations)

   Does anyone know if this is the usual failure mode for these drives.  Tracys PSRU also includes a spline mated with the flywheel.  I never noticed any wear before, but its been a couple hundred hours since last inspection.  It does seem that Tracy's input shaft/spline is hardened.  I assume that could make all the difference in the world.

   Dave Leonard

   Tracy box's. The torque on that end is limited to 200 foot pounds and the
   spline is right out of the C6 A4OD tranny. I think he cuts the drum off.

   Paul Lamar


The spline fretting failure is a well known failure mode.  When I worked in transmission design for a major US auto manufacturer our design guides for splined connections had requirements to ensure that there was not a hardness mismatch between the male and female spline.  If there is you will eventually have a failure if there is ANY movement at all between the two parts.

Michael Robertson


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