High-lift devices are designed to increase the maximum coefficient of lift. A first classification differences active and passive devices. Active high-lift devices require energy to be applied directly to the air (typically provided by the engine). Their use has been limited to experimental applications. The passive high-lift devices are, on the other hand, extensively used. Passive high-lift devices are normally hinged surfaces mounted on trailing edges and leading edges of the wing. By their deployment, they increase the aerodynamic chord and the camber of the airfoil, modifying thus the geometry of the airfoil so that the stall speed during specific phases of flight such as landing or take-off is reduced significantly, allowing to fly slower than in cruise. There also exist other types of high-lift devices that are not explicitly flaps, but devices to control the boundary layer. Readers are referred to $$F_{\text{RANCHINI}}$$ et al. [4].