Abstract: Winglets can inhibit the formation of wingtip vortices and reduce the induced drag. The height of a winglet is one of the most critical parameters in drag reduction efficiency. Current winglet designs are typically optimized for cruise conditions. But they are inefficient in off-design conditions, such as takeoff, climb and landing. Morphing winglets can optimize the drag reduction efficiency through changing their geometric dimensions during flight. This paper investigates a retractable grid for morphing winglets which are actuated by a stepper motor to change the winglet heights at various flight conditions. According to the dynamic analysis based on automatic dynamic analysis of mechanical systems (ADAMS), the change rate of the winglet height reaches up to 13.9% and the cycle is less than 4.4 s when the motor torque is 970.9 N·mm. The simulation has been verified by model test. Subsequently, the effects of a morphing winglet on wingtip vortices and aerodynamic performance are estimated through computational fluid dynamics (CFD) and wind tunnel test. The test results show that increasing the winglet height is beneficial to inhibiting the wingtip vortices. The maximum decrease of wingtip vortices can be as high as 47.7%. With the increase of winglet height, the lift coefficient is also improved by 3.5% and the drag coefficient is reduced by 4.8% during the takeoff phase (Mach number Ma=0.1, angle of attack α=6°). Therefore, morphing winglet with retractable grid has the potential of improving aircraft takeoff performance.

Key words: morphing winglet, retractable grid, the height of the winglet, computational fluid dynamics, wind tunnel test, lift improvement, drag reduction