Matching fan and motor design parameters in electric ducted fans

Electric propulsion systems are gaining more research interest as a way to achieve zero-emission aviation. However, scaling up such systems for larger civil aircraft flying at higher flight speeds poses challenges. One major issue is aligning the performance of electric motors with the aerodynamic design of the fan. This paper discusses matching of the fan aerodynamic design parameters with two critical motor parameters, namely the power density of the motor per unit frontal area and the rotational speed. Based on these parameters, a simplified approach for motor assessment and preliminary fan design is proposed. It is shown that for conventional aerodynamic design of the fan the peak flight speeds can only reach 80 m/s due to limitations on the motor side. At higher speeds, most of the motors available on the market cannot deliver sufficient power and speed within required motor outer diameter. As a result, existing motor technologies often require fan design adjustments that lead to higher than optimal flow coefficient. The paper also gives an insight into motor development requirements suited for best practices in aerodynamic design.