Sizing Method and Sensitivity Analysis for Distributed Electric Propulsion Aircraft

Abstract

Compared with conventional unmanned aerial vehicles (UAVs), the propulsion systems of vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) UAVs with distributed electric propulsion (DEP) are more complex. This paper analyzes the impact of VTOL and STOL requirements and of the DEP system on the takeoff mass and flight performance of UAVs. Analytical models are developed to investigate these properties of DEP VTOL and STOL UAVs. The results of the initial sizing were compared with the parameters of a DEP STOL demonstrator that was actually built. A sensitivity analysis of the design parameters of the DEP STOL UAV was carried out based on the analytical models, and the impact of key design parameters on the takeoff mass and endurance was calculated and discussed. The results show that the propulsion system mass and cable mass of the demonstrator account for 27 and 7% of the takeoff mass, respectively, which are significantly higher than those of conventional UAVs. The key design parameters are the battery energy density, mass-specific power of the motor, lift-to-drag ratio, endurance, and electric-ducted fan efficiency, of which battery energy density has reached a technological limit. The sensitivity of takeoff mass and endurance to the key design parameters varies with the level of technology available, indicating that some currently impractical configurations may perform well at the next level of technology.