AIRFLOW over an aircraft wing gives lift — but also produces drag. For this reason the aerodynamicist always tries to improve the lift‐to‐drag ratio — a value which quantifies the aircraft's aerodynamic quality — in order to reduce fuel consumption. Drag reducing measures are on the one hand focused on the frictional drag occurring in the boundary layer of air immediately at the wing surface. On the other hand these measures are aimed at minimizing the effects of the shock wave, characteristic of transonic airflow, on aircraft operating in high speed regimes.