ANALYSIS OF NONPLANAR WING-TIP MOUNTED LIFTING SURFACES ON LOW-SPEED AIRPLANES.

摘要

Nonplanar wing-tip-mounted lifting surfaces have shown to reduce lift-induced drag substantially. Winglets, which are small, nearly vertical, winglike surfaces, are an example of these devices. To achieve reduction in lift-induced drag, winglets produce significant side forces. Consequently, these surfaces can also seriously affect airplane lateral-directional aerodynamic characteristics. In this study, the effects of winglets on the lateral-directional stability and control of low-speed general aviation and agricultural airplanes are researched. In addition, winglet aerodynamic loading is investigated.;A lifting surface method is used to conduct a parametric study of the effects of various winglet parameters on lateral-directional stability derivatives of general aviation type wings. The results indicate that sideslip stability derivatives, in particular, are affectd by the installation of winglets. Winglet chordwise location, sweep angle, and cant angle appear to provide design freedom to trade small reductions in induced drag for larger reductions in the stability of side force and rolling moment due to sideslip.;An in-flight investigation of winglets mounted on an agricultural airplane has been conducted. Winglet aerodynamic loading appears to be largely dependent on airplane angle of attack and angle of sideslip. Comparison of flight test data and theoretically predicted results show reasonable agreement. Estimated stability and control parameters show that airplane sideslip stability derivatives are significantly influenced by winglets. For large sideslip angles, flow separation over upwind wing tip and aileron, which is induced by the stalled winglet, causes aileron stick force reversal. Winglets produce only small changes in Dutch roll and roll mode characteristics. Conversely, a significant increment can be observed in the level of Dutch roll excitation following an aileron control step input.;A discussion is presented of the considerations involved in the design of winglets for low-speed general aviation airplanes.