Lift on an airfoil at a given angle of attack may be assumed to depend on the camber alone, and could be modelled by the numerical techniques of the period. Drag depends on the thickness of the airfoil and requires an understanding of viscous flow, which was beyond contemporary capabilities.
The lift on an airfoil at a specific angle of attack can be approximated as being solely influenced by the cambered surface, and could be simulated using numerical methods prevalent during that era. Drag, however, is dependent on the airfoil's thickness and requires comprehension of viscous flow phenomena, which were beyond the reach of contemporary scientific understanding.