Thin Airfoils at Transonic Speeds
At transonic speeds linearized theory show that the wave drag associated to the wing thickness growth with the square of the thickness ratio.
Fig. 1 shows the effect of the thickness ratio as function of the Mach number. Thin airfoils yield a slow drag climb in the upper transonic regime. Unfortunately, thin wings of this sort are inadequate for producing lift and sufficient structural stiffness, to accommodate the necessary payload.