Experimental Investigation Of The Aerodynamics Of A Reverse Delta Wing In Ground Effect Using Passive Control

"Wing-in-ground effect craft utilize the lift augmentation and drag reduction experienced by aircraft flying in close proximity to the ground. Several designs use a reverse delta wing with anhedral tips due to improved stability in ground effect, despite the inferior lift generation of this planform limiting its widespread adoption. Also, archived research into reverse delta wings is limited, especially in ground effect. The aerodynamic forces generated by a slender and non-slender reverse delta wing in ground effect was experimentally investigated using force balance measurements in an open return wind tunnel. The impact of anhedral, rear planform cropping and passive control via Gurney flaplike strips was investigated.The results demonstrate that the impact of ground effect on the reverse delta wing was greatest at low angles of attack and ground clearances. Increased lift is in part a result of increased static pressure on the lower surface. Anhedral further increased lift, suggesting the stagnation of high momentum flow beneath the wing resulting in an "air tunnel" like effect and resulting in significant lift increases at low ground clearances and high anhedral angles. The relation between the lift and drag increments in ground effect was found to be approximately linear, with marginal improvement in the lift-to-drag ratio. In the freestream, employment of side-edge strips shifted the lift-curve leftward (induced camber-like effect), resulting from reduced crossflow leakage and increased windward surface pressure. Equipping these strips in ground effect significantly augmented lift with increasing strip height. An increasingly adverse pressure gradient and extension of the side-edge strip beyond the boundary layer led to increased drag with strip height. Rear planform cropping in freestream conditions had a benign impact on aerodynamic forces, while in ground effect increased lift and drag from greater ground proximity, with increased drag suggesting an enhanced disruption of the spanwise vortex filaments. The optimum configuration was found to be a 30% cropped reverse delta wing with 15-degree anhedral, equipped with side-edge strips with height of 4% of the root chord, resulting in significant lift and aerodynamic efficiency improvements alongside weight loss from the cropping. The above findings generally agreed with the results for the non-slender models, with greater force magnitudes observed for the non-slender case. A non-zero lift coefficient was observed at zero incidence for the non-slender wing in ground effect. Further study is required to elucidate the flow mechanisms.The results presented here are first of a kind for a reverse delta wing in ground effect, demonstrating that lift augmentation may be achieved on reverse delta wings operating in ground effect through the utilization of passive control. These results provide benchmark data for further studies on reverse delta wings in and out of ground effect." --