Numerical and experimental investigation of aero-structural characteristics and performance of distributed compliance morphing wings

Abstract

Morphing wings have the potential to achieve higher aerodynamic efficiency owing to the optimal deformed shapes they can obtain, a characteristic not attainable by wings employing conventional discrete control surfaces. This paper assesses both the aerodynamic and the structural performance of a morphing wing concept based on fully compliant morphing structures. In this investigation we show that sufficient control authority in roll can be achieved using the proposed design. The elements of the proposed morphing wing, in particular, the spatially distributed compliant structure, the geometry, and the smart material-based actuation mechanisms, were determined through a concurrent aero-structural optimization which considered both static and dynamic aeroelastic effects. As the entire wing structure is taken into account during the optimization, all components -- including the distributed actuators -- are exploited as load carrying elements, thereby increasing the structural efficiency of the final design. A pair of compliant wings was optimized and manufactured for a 1.6 m wingspan model airplane, with the goal of achieving sufficient control authority in roll by means of active morphing. The actual aeroelastic response of the manufactured wings was experimentally assessed during wind tunnel tests, which were performed at different speeds, angles of attack, and actuation levels. The ability of achieving variation in lift and in rolling moment, while maintaining a high aerodynamic efficiency, is investigated experimentally during the wind tunnel test campaign, and compared to the numerical predictions. The results show that the proposed concept is able to achieve rolling moments comparable to conventional solutions, and sufficient to guarantee the controllability of the flight. Furthermore, the efficiency of the airfoil is not penalized when actively deformed, and in some conditions the lift-to-drag ratio is even improved. This leads to the possibility of using the presented morphing technique to efficiently vary the lift produced by the wings, without the need of changing the aircraft pitch and thus allowing minimization of total drag.