Body-axis rolling motion critical states of a 65-degree delta wing

Dynamic wind-tunnel test results of a 65-deg swept delta wing are reviewed. These tests involved bodyaxis rolling motions at moderate (15- to 35-deg) angles of attack in both the Institute for Aerospace Research 2 X 3 m low-speed wind tunnel and the 7 X 10 ft Subsonic Aerodynamic Research Laboratory facility at Wright-Patter son Air Force Base. They included static, forced oscillation, and free-to-roll experiments with flow visualization. Multiple trim points (attractors) for body-axis rolling motions and other unusual dynamic behavior were observed. These data are examined in light of the nonlinear indicial response theory. The analysis confirms the existence of critical states with respect to roll angle. When these singularities are encountered in a dynamic situation, large and persistent transients are induced. Conventional means of representing the nonlinear forces and moments hi the aircraft equations of motion, notably the locally linear model, are shown to be inadequate for these cases. Finally, the impact of these findings on dynamic testing techniques is discussed.