Trade Study of Tandem Wing at Hover With Deflected Slipstreme Enabled by CoFlow Jet at Low Reynolds Number

This paper conducts a trade study of a tandem wing configuration with deflected slipstream enabled by flapped coflow jet (FCFJ) airfoil at hover. The tandem wings are at low Reynolds number condition as a potential application for flight on Mars. The objective is to study the interaction effect of the propellers and the fore and hind wings in order to achieve the required hover lift coefficient with high efficiency. The in-house validated RANS CFD code is used with Spalart-Allmaras (SA) turbulence model, a third-order WENO scheme for inviscid fluxes, and second-order central differencing for viscous terms. The trade study investigates the effects of stagger distance (St) and vertical gap (G) on aerodynamic performance in 2D and 3D. Results indicate that the 2D configurations with large deflection angles on both the fore airfoil and the hind airfoil exhibit significant wake interference, leading to substantially reduced lift coefficients on the hind airfoil compared to the fore airfoil. It is observed that positioning the fore airfoil without deflection and directing its flow toward the hind airfoil achieves high hover lift coefficient and efficiency with reduced propeller power and CFJ momentum coefficients, substantially decreasing total power consumption. The 3D tandem wing simulation demonstrates the same features observed in 2D study. The 3D study also shows that a proper propeller disk loading distribution and coflow jet momentum coefficient between the fore and hind wings is crucial to keep the flow attached and achieve the required lift coefficient. The study indicates that a tandem wing configuration for VTOL aircraft at hover in Martian atmosphere is feasible.