Aerodynamic Analysis of Tandem Tilt-Wing eVTOL Aircraft in Cruise and Transition Flight

Tandem tilt-wing eVTOL (electric Vertical Take-off and Landing) aircraft is considered as one of the solutions for Advanced Air Mobility (AAM) and planetary exploration aircraft. However, the aerodynamics of these aircraft, particularly in cruise and transition flight, are not fully understood, due to the complex interference between multiple propeller slipstreams and the airframe. To design these aircraft effectively, it is essential to have Computational Fluid Dynamics (CFD) method capable of capturing these complex phenomena, along with a thorough understanding of the slipstream effects. In this study, both wind tunnel experiments and unsteady Reynolds-Averaged Navier-Stokes (URANS) analysis are conducted, and the validity of URANS analysis in evaluating the aerodynamic characteristics of a tandem tilt-wing aircraft in cruise and transition flight is confirmed. In addition, this study clarified that multiple propeller slipstreams increase lift by increasing the dynamic pressure around the forward and aft wings in cruise flight. It is also revealed that during transition flight, longitudinal stability in tandem tilt-wing aircraft is lost due to the propeller slipstream suppressing flow separation over the forward wing, leading to an earlier reduction of lift on the aft wing compared to the forward wing.