Ground Effect on the Dynamic Characteristics of a Wing-rock Delta Wing

Abstract

Aerodynamic forces and moments of a delta wing in unsteady motion were experimentally studied in a low-speed wind tunnel. Its flight attitude was altered smoothly and periodically in the wind flow by means of a manipulator equipped with six stepping motors, which were controlled by a microcomputer. Since it had six degrees of freedom, the delta wing could move arbitrarily in pitching, yawing, rolling, translation motions, and their combinations. The objective of the research is to analyze dynamic characteristics of the wing-rock delta wing with regard to the altitude under the ground effect. The lateral translation motion as well as the roll and yaw angles of the delta wing were changed with the frequency of 0.5Hz in the research. A developed compact force balance with the weight of 5.6 grams was used to measure lift, drag, rolling and pitching moments. Lift and drag were largely and monotonously increased with the delta wing approaching the ground, and the rolling moment was also effected, especially in the case of a high angle of attack. These forces and moments had a large hysteresis with the wing-rock motion, especially in the case of a high attack angle accompanied by the leading edge vortex breakdown. From the previous study on a rolling delta wing at a high angle of attack under the ground effects, the rolling moment coefficient, Crm, drew a hysteresis loop with a roll angle in the anticlockwise direction and had a tendency to be lateral static unstable. On the opposite to the results, Crm of the wing-rock delta wing in the study made a clockwise and lateral static stable hysteresis loop with a roll/yaw angle. Flow visualization for the leading edge vortices and pressure measurements at the ground just below the wing-rock delta wing were also carried out to analyze the dynamic characteristics. It was found for the reason that the leading edge vortex on the moving-down side of the delta wing was changed from the broken to the reconstructed one, which was opposite to the result of the rolling delta wing.