- Mark-12 -
In-Line Planetary Propeller Reduction Gearbox (Discontinued)
In late 2002, EPI did a preliminary design of an in-line (non-offset), planetary PSRU for engines producing 350 HP or less. This PSRU had two available ratios and configurations: 2.474 with engine rotation opposite the prop, and 3.474 with engine rotation the same as the prop. It incorporated the proven load-capacity, vibration-attenuation, and prop-control technology implemented in our other PSRU products.
This preliminary design was initially conducted at the request of a customer who was interested in using the Subaru 3.3-liter flat-6 SVX engine, in a 260 HP implementation.
Soon after that, we became interested in the 3-liter Subaru H6 engine (model EZ-30D) as the basis for a liquid-cooled flat-6 high-output aircraft engine (245 HP in normally aspirated form, 325 HP turbocharged) as a potential replacement for some models of the IO-540 Lycoming and IO-520/550 Continental engines. (That project was ultimately dropped due to inherent problems with the EZ-30D, including a poor head design and the oppressive weight for the power it could produce in an aircraft application.)
The Mark-12 PSRU (part of this new powerplant) was a lightweight, high-reliability, modest-cost gearbox, having size, cost and capacity features which made it attractive to aircraft builders seeking to use Subaru or other similar configuration engines.
It would have weighed less than 50 pounds (including integrated, gear-driven prop governor). The distance from the engine bellhousing flange to the prop flange was about 14 inches, and the prop flange was the SAE ARP-502 (two 1/2" dowels, six 1/2" bolts) which has suitable strength for a 375 HP application. The prop centerline is coincident with the crankshaft centerline.
The housing is CNC'd from a high strength, heat treated aluminum alloy. Gears and shafts are high strength aircraft-quality alloys of nickel-chrome-moly and manganese-nickel-chrome-moly steels. The governor drive is standard AND-20010, integral with the housing, and torsionally isolated from the prop drive by proprietary technology. Torsional attenuation between engine and driving gear accomplished with the proprietary methodology described elsewhere on this website.
Design TBO is targeted at 2000 hours. (The highest time on one of our Mark-9 gearboxes is reported to be around 1000 hours, and the gears and bearings still look like new).