STUDIES ON IMPROVEMENT OF NONLINEAR PITCHING MOMENT CHARACTERISTICS OF CRANKED-ARROW WING

摘要

A series of low speed wind-tunnel tests have been conducted to improve the non-linear pitching moment characteristics of a cranked-arrow wing configuration at high angle of attack. Aerodynamic forces were measured, and flow fields were visualized by the oil flow technique and smoke visualization. Results indicate that the non-linear phenomena obtained on the pitching moment occur at high angles of attack which are corresponded with the take-off and landing flight conditions. These non-linear pitching moment characteristics are caused by the outboard wing separation and the inboard vortex breakdown, respectively. Several aerodynamic devices have been equipped on the baseline configuration to improve the non-linear characteristics. The leading-edge flap deflection and pylon-shaped vortex generator could improve the non-linear characteristics effectively by the suppression of the outboard flow separation and enforcement of inboard leading-edge vortex. The improvements by these devices were also discussed with the low speed aerodynamic performance taken into account. Relationship between the rate of nonlinear characteristics and maximum lift to drag ratio (L/D) shows that the leading-edge flap could improve both non-linear problem and L/D, while the pylon-shaped vortex generator suffer drag penalty despite of its improvement effects.