Aeroacoustics of Lift + Cruise eVTOL Configurations During Transition

During the transition of a lift + cruise aircraft from hover to forward flight, the thrust generated by the vertical lifting propellers compensates for the deficit in wing lift at low forward velocities. Predicting the noise generated during this transition phase remains one of the key challenges in the aeroacoustic analysis of these configurations. This study aims to characterize part of the aeroacoustic performance of a lift + cruise aircraft during transition. Anechoic wind tunnel testing was conducted on a wing with vertical lift propellers arranged in a lift + cruise layout, simulating the transition from hover to forward flight. Replicating realistic transition behaviour in an open-jet wind tunnel proved challenging, likely due to jet deflection effects altering the effective angle of attack on the wing. However, by maintaining zero net pitching moment and zero excess vertical thrust across increasing freestream velocities, the study investigated the acoustic contributions of the fore and aft vertical lifting propellers. Results indicate that the rear propeller increasingly dominates the acoustic signature at higher flow velocities, with a corresponding rise in broadband noise. The study further concludes that while rear propeller overlap with the wing benefits aerodynamic performance, it is detrimental to acoustic characteristics.