Experimental evaluation of transient and steady-state characteristics of a 180kW turboelectric-aircraft test rig

This thesis presents the experimental results of a turboelectric-aircraft power system operating under two electrical configurations. Hybrid turboelectric power systems enable increased versatility over their singularly hydrocarbon fuel or electrically based counterparts through the combination of their advantages: energy density in the case of combustion power systems, and power density in electrical systems. However, much of the research pertaining to such hybrid systems has been analytical, leaving a need for implementation and experimentation to characterize operating performance. The test rig assembled to undertake this work is comprised of a Cessna-172 airframe, a modified 180kW PBS-TP100 turboprop, and the components necessary to create two electrical configurations. The first of these configurations involved the use of a low system voltage, battery augmentation, and an inductive load in the form of electric motors; whereas the second configuration used a high system voltage, a variable-resistive load, and electrical power sourced exclusively from a turbine-driven generator. Custom electronics were fabricated to aid in the control of the variable-resistive load as well as for protection of the battery. The objective of the studies conducted on this system have been to evaluate the transient and steady-state performance of turboelectric aircraft under various engine and electrical load conditions. Configuration one was tested by varying electrical throttle at maximum engine throttle, whereas configuration two was tested through repeated variation in electrical load under four fixed engine throttle points. Engine operation data was acquired from every test including output shaft torque, speed of the free and gas turbines, and combustion gas temperature; while voltage, current, and power data was recorded at different locations within the electrical systems. Tests conducted on the first configuration showed 17kW of peak electrical power: 4kW from the generator and 13kW from the battery; while 142kW of mechanical power was transferred from the turboprop. Test two demonstrated consistent waveforms across all four turbine throttle points, with peak power output reaching 11.5kW from the generator, and 93.5kW from the engine. Observations from these tests highlight the importance of capacitance to hybrid powertrains, the forces induced on turbine engines by electric load, and functional safety considerations in the design and operation of hybrid systems. This thesis provides insight into practical implementation of turboelectric power systems for future electrified aircraft.