# Acoustic Impact of Hybrid-Electric DEP Aircraft Configuration at Airport Level
## 5 Conclusions  
Acoustic impact assessments that include new propulsion technologies and new configurations of a regional aircraft (ATR42 pax) in a reference airport area were analysed and are here described. Two configurations, based on the ATR42 regional aircraft, were investigated:  
1. Configuration A: the baseline configuration consists of a simplified version of the ATR42 regional aircraft equipped with two thermal engines, located in the proximity to the fuselage;
2. Motorization 2: the hybrid-electric configuration consists of a modified version of the ATR42 regional aircraft with a new wing of equal length and higher aspect ratio, two tip propellers powered by thermal engines, aiming at reducing the induced drag, and a DEP system comprised of four propellers per side, powered by electric motors. An evaluation of the noise impact from tonal components was made by characterizing the aircraft as a noise source and then assessing the impacts of its operation. To this end, a procedure was set up at CIRA consisting of the following main steps:  
1. The evaluation of the aerodynamic pressures on the full configuration via a medium-fidelity aerodynamic solver;
2. The evaluation of aeroacoustic performance and a hemispheric noise field, using the FW-H approach;
3. The generation of noise-power-distance (NPD) databases by a ray-tracing approach;
4. The evaluation of the acoustic impacts at the airport level by AEDT procedure. The aerodynamic results highlighted the strong interactional process between the propellers, their wakes, and the aircraft, which was considerably higher in the DEP configuration because of the many propellers installed. In particular, a stronger impact was observed at the leading edge of the wing where an increased pressure expansion was generated in the region impinged by the propellers' wakes. This effect was especially significant for the DEP configuration, wherein pressure expansion was observed throughout the wing span, and in between the two innermost propellers, where the expansion extended to more than half the wing chord. The aeroacoustics analyses show the differences in the tonal noise fields generated by the two configurations. The baseline Configuration A showed a lower noise impact in the longitudinal direction than the hybrid-electric Motorization 2 aircraft, while in the lateral direction, an opposite behavior was observed. This effect is due to the different thrust distributions among the tip and DEP propellers in the hybrid configuration, as compared with the two main propellers of the baseline configuration. Comparing the two configurations in term of averaged overall noise, Configuration A had, still, greater noise levels than source levels on the SPL scale, while in term of the A-weighted scale, where the contribution of higher frequencies is more relevant, the hybrid configuration, Motorization 2, was noisier due to the higher BPFs of the distributed propellers. To model the aircraft noise impact analysis, airports from Naples and Turin as references, the above mentioned two configurations based on the ATR42 regional aircraft, the FAA AEDT software and noise-power-distance (NPD) as generated by RALPH code were used. Notably, standard take-off and landing profiles have been considered. For both configurations, single and cumulative operations were analyzed, and their impacts on the population were assessed. By comparing the results relatively between the two configurations under examination, it appears clear that the tonal contribution of the hybrid configuration had a much greater impact than that of the baseline, both in terms of the areas touched and the populations involved at both airports under study. L.D.V.--acoustic impact assessment, F.P.--noise results and writing, A.S.--NPD, M.B.--conceptualization, A.V.--aerodynamic results. All authors have read and agreed to the published version of the manuscript.