Conceptual design and sizing optimization based on minimum energy consumption of lift-cruise type eVTOL aircraft powered by battery and fuel cell for urban air mobility

In conceptual studies and prototypes of aerial vehicles for Urban Air Mobility, batteries are generally adopted as only energy sources. However, batteries have a long charging time that is not suitable for consecutive flights, and a low energy density that limits the range and flight time of the aircraft. For this reason, the hybrid propulsion solution consisting of a battery and a fuel cell has attracted attention in aviation in recent years. This study proposes the conceptual design of a VTOL (Vertical Take-Off and Landing) aircraft for passenger transportation in metropolitan areas by the synergic optimization of the aircraft configuration and the sizing of the propulsion system aimed at minimizing the power request in cruise. In the proposed conceptual design method, VTOL type aircraft is powered by either the battery or the fuel cell according to the flight phase. A multivariate nonlinear optimization problem using as goal the minimization of the fuel cell size is solved. The optimal values of battery size, wing loading, aspect ratio, endurance speed, aircraft weight, maximum lift coefficient, disk loading, rotor solidity, and zero-lift drag coefficient are determined from the solution of the optimization problem.