Fundamentals in Coanda Flap Design

Using the Coanda-effect in active high lift flaps opens the way to achieve large lift coefficients, needed for the design of aircraft with short takeoff and landing capabilities. In transport aircraft applications overall aircraft design requirements also call for low power consumption of the active high-lift system. Moreover, these aircraft need a reasonable stall angle for their operations. The present contribution describes recent research that aims at high-lift augmentation to be achieved with low rates of active blowing and with suited angle-of-attack ranges. The characteristics of well designed internally blown flaps are addressed. Of similar importance is the design of the leading edge where droop noses and slats may be introduced to avoid locally large boundary layer losses. Moreover, blowing of a Coanda wall jet over a flap can be combined with boundary layer suction in order to yield even higher efficiencies of the overall high-lift system.