- Mark-10 -
Offset Propeller Reduction Gearbox (Superceded)
The EPI Mark-10 PSRU was specifically designed for the EPI Aircraft Engine System which had under development for FAA certification. This gearbox was a single-mesh spur-gear reduction with a vertical distance between the crankshaft and propshaft centerlines of 7.917 inches. It contained the proven reliable technology (gear design, load-carrying, lubrication, cooling and vibration, integrated governor-drive) as the Mark-9, but had these advantages:
- It weighed approximately 57 pounds (16 pounds lighter than the Mark-9);
- It had an input torque capacity of 800 lb-ft. and a propeller-thrust capacity of 3000 lbs;
- It had the following (easily changeable) ratios available: 2.958, 2.800, 2.654, 2.519, 2.393, 2.276, 2.167, 2.065, 1.969, 1.879, 1.794;
- It included provision for a reversing prop and the beta-feedback mechanism for reversing control;
- It was a single-mesh gearbox, and therefore accommodated an engine section which turns in the opposite direction from the prop. That feature tends to cancel a large percentage of the prop's gyroscopic moment, allowing for lighter weight engine mount structures and better aircraft flying qualities; (see Engine and Prop Rotation issues)
- It had a lower parts-count, would have been simpler to manufacture, and easier to maintain than the Mark-9.
A prototype Mark-10 was never manufactured, since the Mark-15 was beginning to take shape in that time frame, and fitted all the Mark-10 applications, plus a host of other applications as well.