Effect of Leading-Edge Cranks on Stability and Control of Active-Flow-Control-Enabled Tailless Aircraft

The Swept Wing Flow Test (SWIFT) is a tailless unmanned combat aerial vehicle (UCAV) model to be tested at high Reynolds numbers in NASA's National Transonic Facility. The model is designed around a ?-shaped wing with a single, large crank at its leading edge (LE). It suffers from an unstable nose-up pitch departure resulting from flow separation augmented by the LE crank. A small-scale, modular wind tunnel model (Re approximate to 10(6)) was built that allowed for changes in the crank angle by increasing the outboard wing sweep. Eliminating the crank entirely increased the C-L,C-max and changed the sign of pitch departure, thus exposing the significance of the LE crank. The model was equipped with sweeping jet actuators that could be individually enabled by valves located at the actuator inlets, allowing one to explore the role of active flow control (AFC) in expanding the model's longitudinal stability margins and controlling its yaw while being cognizant of the coupling between changes in the model's planform and their effect on AFC. Test results indicated that selective actuation depending on the model's attitude modified the flow and dramatically increased the trimmed C-L, while further suggesting that the actuation should dynamically change with incidence to improve AFC efficacy.