Aerodynamics of a double-element wing in ground effect

An investigation of a cambered, double-element, high-lift wing operating in ground effect was performed. The effect of ground proximity and flap setting was quantified in terms of aerodynamic performance and off-surface flowfield characteristics. From that, it was found that the flow is three-dimensional toward the wing tip with the main element generating most of the downforce but retains quasi-two-dimensional features near the center of the wing. However, at large heights the downforce increases asymptotically with a reduction in height. Then there is either a plateau, in the case of a low flap angle, or a reduction in downforce, in the case of a large flap angle. The downforce then increases again until it reaches a maximum and then reduces with decreasing height above the ground. The maximum downforce is dictated by gains in downforce from lower surface suction increases and losses in downforce caused by upper surface pressure and lower surface suction losses, with a reduction in height. For the high flap angle there is a sharp reduction just beyond the maximum, mainly because of the boundary layer separating, and a resultant loss of circulation on the main element.