- Mark-9 -
Offset Propeller Reduction Gearbox
The EPI Mark-9 PSRU is the gearbox used in the EngineAir Power Systems 440 HP liquid-cooled V8 powerplant. That engine system was installed in the Lancair 4P which won the Kittyhawk-to-Oshkosh race in 1999 (and which would have won in 2000 and 2001 if the pilot hadn't gotten lost), as well as in the Lancair-4P which won Grand Champion at Sun n' Fun 2001, in Doug Pohl's Lancair 4P, which made it's first flight on July 9, 2001, in Tom Hakes' Lancair 4P which made it's first flight in late 2001, in Gary Wolf's Lancair-4P and Steve Ramsey's Lancair 4P, both of which made their first flights in Mid-2002.
As of April, 2003, there are reported to be more than 20 of these PSRU's installed in various aircraft, ranging from Lancair 4P's to a modified Beech Duke. Many of those installations have flown, and several have accumulated significant time in flight. (For anyone interested, CLICK HERE for The Long Story behind the development of the Mark-9 PSRU.)
(For some higher-quality pictures of the Mark-9 and some of the aircraft on which it has flown, CLICK HERE )
The prototype of this design has reportedly accumulated over 800 hours of in-flight time in Lancair-4P aircraft, including several races, countless full-power demonstration flights, and extended instances of being flown in hard-IFR (by a very brave pilot).
As of late 2005, several production versions have accumulated over 500 hours of problem-free flight time.
The version of the Mark-9 PSRU currently used by EngineAIR Power Systems has a reduction ratio of 2.19, an input torque capacity of 600 lb-ft., a thrust capacity of 2000 lbs. and weighs 73 lbs. The propshaft uses the high capacity ARP-880 8-bolt, 2-dowel flange (the same one used on the PT-6 and TPE-331 turbine engines). The vertical distance between the crankshaft and propshaft centerlines is 6.125 inches. The ratios available range from roughly 1.75 to 2.45, in steps of about 0.05.
The EPI Mark-9 PSRU is a two-mesh (idler-type) reduction gearbox which allows the engine to turn in it's "natural" direction (the same direction as the standard US propeller). The gearbox includes a gear-drive (AND-20010) for a standard Woodward-Hartzell prop governor, fully internal plumbing for the prop control hydraulics and for lubrication, and an integrated dual-crank-trigger for the engine management computer. It uses pressure-fed engine oil for lubrication and cooling, and has an integrated scavenge pump to return oil to the engine sump.
The gears are straight-cut (spur) gears made from a specially heat-treated high-grade manganese-nickel-chrome-molybdenum alloy (E-9310), and finished to AGMA Quality 10 minimum. They have a face width of only 1.5 inches (in the model suitable for 600 LB-FT of engine torque). The gears have special design features which greatly improve their resistance to both hertzian and bending fatigue, as well as to prevent the edge-loadings which are so destructive to highly-loaded gears.
(For an expanded discussion of the advantages of Spur Gears, CLICK HERE)
EPI's proprietary system for coupling the engine to the PSRU attenuates over 99% of all engine torsional excitation and provides nearly turbine-smooth input to the PSRU. That provides an environment for the propeller which is free from torsional excitation.
Other versions of this PSRU can accommodate up to 850 lb-ft. of input torque and can have ratios from 1.60 to 2.58. The weight varies with the torque capacity and the reduction ratio. The prototype weighed 71 pounds and had a ratio of 1.86, but has a lower torque capacity of 500 lb-ft.
CLICK HERE for the complete story of the Mark 9 development, usage, and current status
.