Unsteady aerodynamics of free-to-roll nonslender delta wings

An experimental investigation on free-to-roll delta wings with A=50° has been conducted. Roll time histories showed that multiple trim positions are possible. Only nonzero roll angles, or a combination of zero and nonzero roll angles, are possible, depending on the angle of attack. It was found that the free-to-roll dynamics is closely correlated with the static lift characteristics at zero roll angle. In a small range of incidences, self-excited roll oscillations are observed. The effects of leading-edge shape and wing thickness on the self-excited roll oscillations were investigated. The self-excited roll oscillations are also observed for the wing with sharp leading-edge (for which the separation point is fixed), but are much smaller in amplitude. As the amplitude of the motion is amplified for a round leading-edge, characteristics of flow separation at the leading-edge are a contributing factor. It is suggested that the interaction of the reattachment lines play an important role in the self-excited roll oscillations.