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Integration and evaluation of a 180-kw turboprop engine with a turboelectric ground test rig

Melvin, Joshua
This paper presents the integration of a PBS Aerospace 180-kW turboprop engine with a Cessna 172, four seat, 1,090-kg (2,400-lbf) max takeoff weight aircraft for use as a turboelectric ground test rig. The quickly growing segment of hybrid propulsion aircraft, commonly used in the urban air mobility sector, are pressing regulatory bodies to develop new certification requirements for these unique aircraft. Small-scale turboelectric systems used in unmanned aerial systems are well documented, but large-scale manned systems are comparatively rare. Therefore, it is critical to develop a large-scale turboelectric ground test rig to study turboelectric system integration phenomena to inform new certification standards from regulatory bodies. To conduct large-scale turboelectric research designing an engine mount, generator mount, a power transfer system, and a propeller spacer are required. The goal of this study was to design, fabricate, install, and test an engine mount, generator mount, propeller spacer and power transfer system for a turboelectric aircraft ground test rig. The methodology included computer aided design, finite element analysis, static component tests and fully integrated tests to acquire data to validate analysis. Electric power demand of the electric propulsors were set as 20 to 30-kW using a 50-kW generator, this power rating drove the design of the belting system. Turboelectric architecture is a parallel partial hybrid system with power being delivered to a 1.8-m three blade propeller while a portion of the engine power is siphoned to the generator. The generator drives two electric motors with 1.3-m two blade propellers mounted to the wing leading edges while also maintaining battery charge. A static torque test of over 1,300-N∙m, peak engine torque is 800-N∙m, was conducted on the engine mount before engine integration to verify its integrity. Observations from testing the full turboelectric system installation, without generator load, indicate the engine successfully operated at all power levels with the engine mount delivering expected structural strength. Another observation from testing shows that the propeller spacer performed well within expected parameters without erratic propeller dynamics. Results from testing the full turboelectric system installation, without generator load, indicate the engine mount withstood all engine loads within expected torsional deflections from the static torque test of around 2 degrees of twisting.