Baseline Design of Propeller for an eVTOL Aircraft to Achieve Urban Air Mobility

Abstract

Urban Air Mobility (UAM) has gained traction in the aviation industry. With the ever-increasing rate of urbanization, congested roads have become a common phenomenon in megacities across the world. Urban Air Mobility in the form of Electric Vertical Take-off and Landing (eVTOL) aircrafts presents an opportunity to revolutionize the transportation sector by providing sustainable intercity and intracity travel for the urban dwellers. Amongst the different eVTOL configurations, the tilt-rotor and hybrid lift + cruise configuration aim to combine the advantages of fixed wing and rotary wing aircrafts. The presented work aims to develop a detailed design procedure for the propellers of a tilt-rotor eVTOL aircraft to maintain low noise emission and to have high efficiency to utilize the capacity of current battery technology to the maximum extent. Multiple configurations such as coaxial tilt-rotor and hybrid lift + cruise were considered for the aircraft, and preliminary design calculations were carried out for all of these configurations to decide the number of rotors, diameter of the rotor, number of blades and the power required for take-off, hover and cruise performance of the aircraft. These calculations were performed based on the concepts of actuator disc theory/momentum theory. A propulsion configuration was selected based on the results of the above-said calculations provides such as tip Mach number, efficiency and rotor diameter to facilitate low noise and compactness. After selecting the configuration, the propeller blades were designed based on blade element theory. Since tilt-rotors are used for both hover and cruise conditions, it becomes necessary to analyze them for both conditions. Since the operating conditions such as airspeed and rpm are very different in hover and cruise conditions, the tilt-rotors were designed as controllable-pitch propellers to ensure all the sections of the blade operate at the desired angle of attack for both hover and cruise conditions. Computational Fluid Dynamics (CFD) simulations were carried out for the same to verify the results. The outcome of the current work is the theoretical dimensions and geometry of the propellers which provide the required thrust, efficiency and low noise emission for the considered eVTOL aircraft.