Preliminary noise assessment of aircraft with distributed electric propulsion

Electric and hybrid-electric propulsion technologies are an increasingly attractive option for aviation stakeholders, providing more reliable and efficient power plants than traditional internal combustion engines, while reducing the dependency on fossil fuels, such as oil, whose value is volatile and availability uncertain. Combined with distributed electric propulsion (DEP), these propulsion technologies have shown significant potential in reducing civil aircraft noise emissions and are therefore viable candidates for delivering the strict mid-to-longterm environmental goals set by aviation organisations worldwide, such as ACARE and NASA. This paper examines the noise emission of a concept tube and wing aircraft that falls in the A320 category and features DEP systems using two different power supply units (turboshaft engines or batteries) and a varying number of propulsors. The transition of conventional propulsory systems to electric and hybrid systems is discussed, with Noise-Power-Distance (NPD) curves and noise exposure contour maps computed for several DEP systems and propulsor number configurations. Noise benefits of DEP especially at takeoff are demonstrated, whereas it is shown that based on predicted year 2035 entry into service technology, All Electric aircraft exhibit a larger noise footprint than aircraft using hybrid electric propulsion systems. Finally, our analysis indicates that the number of propulsors is a key parameter that may be used to optimise the environmental performance and noise benefits of DEP aircraft.