The development of more efficient propulsion systems for aerospace vehicles is essential to achieve key objectives. These objectives are to increase efficiency while reducing the amount of carbon-based emissions. Hybrid electric propulsion (HEP) is an ideal means to maintain the energy density of hydrocarbon-based fuels and utilize energy-efficient electric machines. A system that integrates different propulsion systems into a single system, with one being electric, is termed an HEP system. HEP systems have been studied previously and introduced into Land, Water, and Aerial Vehicles. This work presents research into the use of HEP systems in Remotely Piloted Aircraft Systems (RPAS). The systems discussed in this paper are Internal Combustion Engine (ICE)-Electric Hybrid systems, ICE-Photovoltaic (PV) Hybrid systems, and Fuel-Cell Hybrid systems. The improved performance characteristics in terms of fuel consumption and endurance are discussed.
Turbo-electric Distributed Propulsion (TeDP) is a promising concept to achieve the operational goals of more electric aircraft. The application of TeDP architecture can achieve the desired weight reduction of an aircraft power system. The use of a superconducting machine is expected to provide the workaround for the weight issue, but its current state of technology has not yet been extensively tested for aircraft applications. Another more practical option is to directly couple the aircraft's propeller system to a high-speed permanent magnet (PM) electrical machine, eliminating the gear part that also contributes to the total weight. A critical part of the design for a high-speed PM machine is choosing the optimum magnet configurations. This study used finite element modelling to analyze the impact of scaling the PM’s critical parameters on the weight and machine speed. A prototype testing of a 2-KW high-speed machine, suitable for a Remotely Piloted Aircraft System (RPAS), was developed and tested. The results confirmed the following critical parameters that should be carefully designed to achieve the optimum output, such as the (a) number of winding turns, (b) stack length, (c) sleeve thickness, and (d) terminal voltage.
In pusher-type aircraft, the impact of putting the propeller on the trailing edge and impact of propeller on the tip of the wing has been carefully researched. The results reveal an increase in propelling efficiency and a reduction in drag. In addition, there is a lot of study being done right now on distributed propulsion and the advantages it has in terms of aerodynamic effects and propelling advantages. This paves the way for the possibility of positioning the propeller on the trailing edge of the wing and using the increased propulsive efficiency afforded by boundary layer ingestion (BLI). This research studies the effect of positioning the propeller on the trailing edge of the wing instead of the leading edge on power savings and advances in propulsive efficiency. A scaled Remotely Piloted Aircraft Systems (RPAS) wing is tested in a wind tunnel utilising a Brushless Direct Current (BLDC) engine with several propeller configurations. A new term, Ingestion Ratio (IR), is introduced to describe the effect of the change in propeller size on power savings. The investigation revealed that positioning the propeller on the trailing edge of the wing increases the propelling efficiency by up to 5.8% and saves up to 24.7% of electricity.
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