Smart Material Wing Morphing for Unmanned Aerial Vehicles.

Abstract

Morphing, or geometric adaptation to off-design conditions, has been considered in aircraft design since the Wright Brothers’ first powered flight. Decades later, smooth, bio-mimetic shape variation for control over aerodynamic forces still remains elusive.

Unmanned Aerial Vehicles are prime targets for morphing implementation as they must adapt to large changes in flight conditions associated with locally varying wind or large changes in mass associated with payload delivery. The Spanwise Morphing Trailing Edge (SMTE) concept is developed to locally vary the trailing edge camber of a wing or control surface, functioning as a modular replacement for conventional ailerons without altering the wing’s spar box. The SMTE design was realized utilizing alternating active sections of Macro Fiber Composites (MFCs) driving internal elastomeric compliant mechanisms and passive sections of anisotropic, elastomeric skin with tailorable stiffness, produced by additive manufacturing. Experimental investigations of the modular design via a new scaling methodology for reduced-span test articles revealed that increased use of more MFCs within the active section did not increase aerodynamic performance due to asymmetric voltage constraints. The comparative mass and aerodynamic gains for the SMTE concept are evaluated for a representative finite wing as compared with a conventional, articulated flap wing. Informed by a simplistic system model and measured control derivatives, experimental investigations identified a reduction in the adaptive drag penalty up to 20% at off-design conditions.

To investigate the potential for augmented aeroelastic performance and actuation range, a hybrid multiple-smart material morphing concept, the Synergistic Smart Morphing Aileron (SSMA), is introduced. The SSMA leverages the properties of two different smart material actuators to achieve performance exceeding that of the constituent materials. Utilizing the relatively higher work density and phase transformation of Shape-Memory Alloys combined with the larger bandwidth and conformal bending of MFCs, the resultant design is demonstrated to achieve the desired goals while providing additional control authority at stall and for unsteady conditions through synergistic use of reflex actuation. These advances highlight and motivate new morphing structures for the growing field of UAVs in which adaptation involves advanced compliance tailoring of complex geometry with synergistic actuation of embedded, smart materials.