The research focuses on a delta wing built around the NACA 0012 airfoil profile, a symmetric section that has been a workhorse of aeronautical testing for nearly a century. What distinguishes the configuration is its sweep angle of fifty degrees, which places it firmly in the non-slender category. Unlike the dramatic, needle-nosed slender deltas of supersonic fighter fame, non-slender delta wings sweep at shallower angles and generate lift through a combination of conventional attached flow and leading-edge vortex systems. That hybrid behavior makes them attractive for small unmanned air vehicles, where compact planforms, structural simplicity, and forgiving stall characteristics are prized, but it also makes their ground-effect behavior genuinely complicated to predict.

The experimental campaign was structured around the full range of angles of attack that a small UAV might encounter between a ground run and a stalled climb-out. Force measurements were taken from zero degrees up to forty-two degrees of angle of attack in three-degree increments, a resolution fine enough to capture the gradual evolution of lift and drag as the wing’s vortex system matured and eventually broke down. To simulate the changing clearance of a vehicle during takeoff and landing, the researchers varied the ratio of the wing’s height above the ground plane to its chord length, testing values of 0.1, 0.2, 0.5, and 1. At the lowest ratio, the wing sits a tenth of a chord above the surface, deep inside the ground cushion; at a ratio of one, it is at the edge of where ground influence is typically considered significant.

Ground effect is not a single phenomenon but a bundle of interacting mechanisms. For a conventional wing, proximity to the surface suppresses the downwash behind the wing and reduces induced drag, which is why racing sailplanes and hovering birds seem to glide effortlessly over water. For a delta wing, the picture is richer. The dominant feature of delta-wing aerodynamics is the pair of primary vortices that roll up along the highly swept leading edges, spinning off the edge and coiling above the wing’s upper surface. These vortices generate additional suction on the upper surface, contributing what aerodynamicists call vortex lift, a mechanism famously formalized by Edward Polhamus in the 1960s through his leading-edge suction analogy. How those vortices behave when the ground is close by is the central question of the study.

Force coefficients alone, however, tell only half the story. To understand why lift and drag changed the way they did, Bay and Kara turned to surface oil flow visualization, a classic experimental technique that reveals the topology of flow on a wing’s surface. A mixture incorporating titanium dioxide pigment is painted onto the wing; as air flows over the surface, shear stresses in the boundary layer drag the oil into streaks, and the resulting patterns record where flow attaches, separates, and reattaches. The researchers conducted these visualization experiments from zero to forty degrees of angle of attack in five-degree steps, building a photographic atlas of the surface flow at each ground clearance.

The oil-flow experiments revealed the key flow phenomena governing the wing’s performance. The team identified the onset and progression of vortex breakdown, the dramatic event in which the coherent leading-edge vortex suddenly expands into a turbulent, disorganized mass, causing the suction peak over the wing to collapse and lift to plateau. They also mapped the reattachment region where the swirling vortex flow impinges back onto the wing surface, the footprint of the inner primary vortex, and the delicate surface signatures of the secondary reattachment line and secondary separation line, features that mark the smaller counter-rotating vortices nested beneath the primary system near the leading edge. Flow traces across the surface connected these features into a coherent topological picture at every angle of attack and ground height tested.

This combination of force measurement and flow visualization is what gives the study its practical value. A designer of a small delta-wing UAV can read the force curves to know how much lift and drag to expect during a ground run at a given clearance, and then consult the flow topology to understand the underlying mechanism, whether it is a strengthened vortex, a delayed breakdown, or a shift in the reattachment line. Because the tested height-to-chord ratios of 0.1 through 1 span the realistic range of wheel heights during takeoff rotation and landing flare, the dataset maps directly onto the flight phases the authors set out to investigate: takeoff, landing, and cruise out of ground influence.

What makes the work particularly compelling for the UAV community is that it did not stop at the wind tunnel. The authors also present the results of real flight tests of an unmanned aerial vehicle incorporating this wing, beginning with a real-time ground takeoff and continuing into flight out of ground effect. Flight test data of this kind is rare in academic ground-effect studies, which often remain confined to wind tunnels and computational models. By anchoring the laboratory measurements to the behavior of an actual aircraft leaving the runway, the study provides a bridge between controlled experimentation and the messy, gusty reality of a small vehicle climbing away from the ground.

The broader context of the research is a growing body of literature on wings in ground effect, a field that stretches from the wing-in-ground-effect vehicles studied extensively by Kirill Rozhdestvensky to recent experimental work on non-slender delta wings by groups including Tumse and colleagues, and Koçak and Yavuz, who examined both static and dynamic ground boundary conditions. Much of the earlier delta-wing ground-effect work used flat-plate or thin airfoil sections; building the wing from a full NACA 0012 profile with realistic thickness adds a layer of fidelity relevant to actual vehicle design. Prior studies have also shown that thickness-to-chord ratio itself alters non-slender delta wing aerodynamics, which makes the choice of a standard airfoil section a meaningful one rather than a mere convenience.

For the emerging fleet of small drones, eVTOL demonstrators, and micro air vehicles that spend much of their operating lives near surfaces, the message of this research is that ground effect is not simply a bonus of extra lift. It reshapes the vortex system that defines delta-wing flight, moves the boundaries of stall and breakdown, and alters the drag budget in ways that depend intimately on height, angle of attack, and planform geometry. By pairing precise force measurements across a dense grid of angles of attack and ground clearances with titanium dioxide surface visualization that exposes the underlying flow structures, and by closing the loop with real flight tests, Bay and Kara have delivered a reference dataset and a physical explanation that should help engineers design delta-wing unmanned aircraft that behave predictably in the most demanding moments of flight: the seconds spent leaving the ground, and the seconds spent returning to it.

Subject of Research: Ground effect aerodynamics of a NACA 0012-based non-slender delta wing for unmanned air vehicles

Article Title: An Experimental Investigation of Aerodynamic Performance of an NACA 0012-Based Non-slender Delta Wing Under Ground Effect

Article References: Bay, A. E., & Kara, T. (2026). An Experimental Investigation of Aerodynamic Performance of an NACA 0012-Based Non-slender Delta Wing Under Ground Effect. International Journal of Aeronautical and Space Sciences. https://doi.org/10.1007/s42405-026-01197-5

Image Credits: AI Generated

DOI: 10.1007/s42405-026-01197-5

Keywords: delta wing, ground effect, NACA 0012, unmanned aerial vehicles, vortex breakdown, aerodynamic performance, surface oil visualization, titanium dioxide, wind tunnel testing, leading-edge vortices, takeoff and landing, flight tests