The aerodynamic interactions in a quadcopter during forward flight reduce the efficiency of the back rotor(s) and increase generated noise levels. To alleviate interactions without compromising the vehicle’s compactness, a vertical offset between the front and back rotor(s) can be introduced as an alternative solution to increased hub spacing. The efficiency of a quadcopter in square and diamond configuration with a vertical spacing up to 0.38 rotor diameter is analysed experimentally and numerically using free-wake solvers. Forward flight conditions are considered, including high interaction cases with a nose-up tilt and close rotor hub spacing with overlapping blades. The results show that for the square configuration, a thrust comparable to four isolated rotors is achieved by the elevation of both back rotors. In contrast, introducing a vertical separation to the already underperforming back rotor in the diamond configuration further reduces its efficiency.

This paper presents a comparison of acoustic flyover measurements conducted using DLR’s Advanced Technology Research Aircraft for different aircraft configurations with simulations performed in the Parametric Aircraft Noise Analysis Module. The focus of the comparison is on quantifying the simulation uncertainty arising from the source models used to describe the individual noise components (model uncertainty). Combining the comparison of measurements and simulations with the model uncertainty analysis allows for the identification of systematic deviations and modelling insufficiencies in the simulation. Based on eight different aircraft flyover configurations, the study demonstrates that the simulations match the measurements very well in six cases. The deviations observed in the remaining two cases can be attributed to the selected source model for the slat.