Design and Analysis of Tandem Wing Aircraft at Ultra-Low Reynolds Numbers in Cruise Condition

This paper numerically investigates the aerodynamic performance and efficiency of a tandem-wing aircraft utilizing a Deflected Slipstream (DS) CoFlow Jet (CFJ) airfoil configuration designed specifically for cruise flight on Mars, where achieving high lift and efficiency is critical due to the extremely low air density environment. The tandem-wing system consists of front and rear DS-CFJ wings, each equipped with propellers positioned in front of the wings. Computational analyses employ a 3D Reynolds-Averaged Navier-Stokes (RANS) solver with the Spalart–Allmaras turbulence model, featuring a third-order Weighted Essentially Non-Oscillatory (WENO) scheme for inviscid fluxes and second-order central differencing for viscous fluxes. The simulations are conducted at a Mach number of 0.17 and a Reynolds number of 39,410. The tandem configuration comprises a small front wing (17.5% area of the rear wing) and a larger rear wing, both sharing identical chord lengths. The front and rear wings have aspect ratios of 3.5 and 20, respectively, yielding an area-averaged aspect ratio of 17.54. Both wings use the DS-CFJ-NACA6421 airfoil but feature distinct optimized flap angles (front: β = 15◦, rear: β = 35◦) specifically selected for Martian flight conditions. Leveraging a Wing-Wing Interaction mechanism, previously described in [1], this configuration enhances aerodynamic efficiency while ensuring a compact design, essential due to the limited fuselage dimensions feasible on Mars. The optimal aerodynamic efficiency for the complete aircraft is achieved at specific flap angles, resulting in a lift-to-drag ratio (CL/CD) of 10.35 and a corrected aerodynamic efficiency (CL/(CD)c) of 5.37. These conditions yield an exceptionally high cruise lift coefficient (CL) of 3.26, significantly surpassing conventional subsonic aircraft, which typically exhibit cruise lift coefficients below 0.6. This excellent aerodynamic performance, facilitated by CFJ active flow control, enables sustained flight beyond the limits of conventional aerodynamic technologies. The efficiency enhancement arises from favorable aerodynamic interactions between the tandem wings: the front wing’s tip vortex positively augments lift on the rear wing, while the rear wing’s high lift generation and increased circulation produce beneficial upwash that further boosts the front wing’s efficiency. This innovative tandem wing configuration enabled by CFJ renders fixed wing VTOL aircraft feasible on Mars, although further studies are necessary for continued optimization. To compare with conventional technology, the same aircraft is redesigned by replacing the DS-CFJ wing with a wing using NACA 6410 airfoil with the same aspect ratios, chords, and spans. The comparison indicates that conventional technology is not feasible to generate required cruise lift to support the weight of the structure.