Steady and unsteady aerodynamic flow studies over a 1303 UCAV configuration

Abstract

This study generated new information through qualitative documentation of the main flow features and direct measurements of the aerodynamic performance of a tailless, unmanned combat air vehicle (UCAV) 1303 configuration under both steady and unsteady maneuvering conditions. Photographic evidence of flow features, measurements of large-scale flow effects, and that of forces and aerodynamic coefficients during static and dynamic pitch, roll and yaw maneuvers were obtained. Flow visualization images and force measurements were taken at various Reynolds numbers, model attitudes and pitch rates for comparison. A 1/72nd-scale model with a 47-degree leading edge sweep and a cranked trailing edge delta wing with a fuselage was investigated in the NPS water tunnel. Phase locked, high-resolution flow images were obtained using a five color dye injection system over the maneuvering model. Both static and dynamic pitch-up, roll and yaw maneuvers were considered. Additionally, a five-component strain gage and flow monitoring software were employed to record, in real time, yawing, pitching and rolling moment information and derive the aerodynamic force and moment coefficients for selected maneuver conditions. Flow visualization revealed the presence of a strong spanwise flow at low angles of attack and strong vortical flow structures at larger angles of attack, as can be expected, but not clearly established earlier, for such low sweep angle wings. It also indicated that the vortical structures and reverse flow were highly Reynolds-number dependent. Normal force and pitching moment load data correlated well with trends observed for low sweep angle delta wings, but unexpected side force, yawing moment and rolling moment variations were observed, which were attributable to asymmetrical vortical flow behavior on the tailless UCAV geometry.