An Engineering Framework for Adaptive Winglet Design: Identification of the Optimal Morphing Mode and Envelope

Adaptive winglets improve aerodynamic efficiency by enabling geometry adjustments tailored to flight conditions. In this study, an engineering-oriented optimization framework is developed and applied to numerical aerodynamic evaluations based on the wing–winglet configuration of a KC-135 aircraft, under representative takeoff, climb, and cruise conditions. A Plackett–Burman design is employed to screen the 10 kinds of winglet geometric parameters, from which the dominant variables affecting drag are identified. Subsequently, response surface methodology is used to construct surrogate models and determine optimal parameter combinations for each flight phase, thereby defining a feasible morphing envelope for adaptive winglet operation. The results indicate that a coupled morphing of winglet height and cant angle constitutes the most effective morphing mode. Across the takeoff, climb, and cruise phases, the optimal morphing envelope involves a continuous transition from Height = 0.20b/2 and Cant angle = 86.3° at takeoff, to Height = 0.192b/2 and Cant angle = 8.2° during climb, and finally approaching the baseline configuration (Height = 0.135b/2, Cant angle = 20°) at cruise, while achieving a maximum drag reduction efficiency improvement of up to 8.8% at the climb phase.