Design of the Grand Touring sports car wing: geometric and aerodynamic twist

Abstract

Wing twist gives the Grand Touring sports car an eye-catching 'aerodynamic shape'. From the functional viewpoint, wing twist may improve downforce, provide stall control and enhance aerodynamic efficiency if the twist is optimised. This study aims, first, to explore the influence of linear geometric and aerodynamic twist upon spanwise upwash velocity, downforce and induced drag distributions and, second, to evaluate the use of optimum twist in achieving minimum induced drag while preserving high downforce, in wings with linear taper for the Grand Touring car. Baseline wing prototypes were designed and fitted, subsequently, with a Gurney flap and endplates to obtain complete wings. Aerodynamics for straight wings and wings with geometric, aerodynamic and optimised twist were computed using modified versions of the Prandtl's Lifting-line Theory. Straight and geometrically-twisted wings with constituent NACA 65 1 -412 airfoils present superior aerodynamic efficiency at angles of attack 4 1°and may be used as stabilisers on high-speed circuits. Geometric twisting elicits a partial, rather than complete, wing stall that contributes to safety in motor racing. A geometrically-twisted wing constructed with a NASA LS(1)-0413 airfoil yields high downforce at the expense of large induced drag via a double-peaked induced drag distribution, and it is suitable for high-downforce racing circuits. Nonetheless, the analysis suggests that a twist-optimised wing for the Grand Touring car very nearly duplicates the ideal aerodynamic performance of an elliptic wing and yields high downforce and minimum possible induced drag. The findings support the implementation of optimum wing twist at the conceptual stages of Grand Touring sports car design.