Development of a high-speed turbo electric propulsion system for remotely piloted aircraft systems

The turboelectric distribution propulsion system (TeDP) is considered a promising option to achieve the operational goal of an electric aircraft for the future. It allows for the combination of a turbine engine with an electric machine to optimally produce electricity and distribute electrical power to thrusters. This departs from traditional methods of aircraft propulsion, in which the potential energy from heavy fuels is converted into electrical energy which allows for various configurations, including those where distributed propulsion is advantageous. TeDP takes aerodynamic advantage of distributed electric propulsion (DEP) by distributing the thrust through small electric motors across the wings. It also provides increases in propulsive efficiency and lift, which furnish the means to reduce drag and energy consumption, as the concept produces an aerodynamic phenomenon known as boundary layer ingestion (BLI). However, weight penalties and design capabilities associated with existing mechanical and electrical systems make it challenging to produce a feasible technological design for aircraft. This thesis explores the design and manufacture of a high-speed machine design allowing for reduced weight and relatively higher electrical efficiency, thus making it suitable for aircraft integration. This thesis furthers the knowledge and inclusion of high-speed machines in this context. The high-speed machine can match current gas turbine engines operating at high rotational speeds (up to 600,000 RPM). This offers a good hybrid pairing due to the direct connection between a gas turbine and a high-speed electrical machine. Gas turbojet and turbofan technology is well-established for aircraft propulsion; thus, many off-the-shelf turbines at various scales can be retrofitted to include a high-speed machine. This thesis explores this concept to provide confidence in a novel aircraft propulsion concept. To validate the hybrid system, an experimental program is based around a scale gas turbine allowing for a hybrid system to be utilised on a remotely piloted aircraft system (RPAS). The technology can be applied and adapted at larger scale for mainstream aviation. Two matched micro-gas turbines are sourced, tested and weighed. Various electric machines are designed and manufactured based on speed, stack measurements, turns, voltage, weight performance factors and efficiency. A prototype is made and tested and the Brequet range and endurance equations are augmented to approximate aircraft performance when applied to a hybrid propulsion system. The findings of this thesis demonstrate that the new hybrid propulsion concept offers weight savings of up to 31% compared to existing turboprop engines and can increase range and endurance when DEP is additionally adopted. Furthermore, experimental tests are performed to validate the propulsive efficiency of placing the wing in a trailing-edge propulsion configuration when compared to that of a leading-edge configuration.