This article introduces an origami-inspired passive morphing wing concept that is designed, analyzed and fabricated via a single analysis-oriented computational framework ensuring kinematic feasibility and path-uniqueness of a targeted motion. Supposing a notional in-plane wing morphing problem to provide perimeter boundary conditions, a fractal origami pattern that offers large in-plane strain while providing high out-of-plane stiffness is proposed as a supporting mechanism. To enable computational design and analysis of a complex origami pattern, a script-based multidisciplinary design and analysis computational tool, Computational Aircraft Prototype Synthesis (CAPS) is employed. A mathematical description of a fractal origami pattern is formulated to create the highly-symmetric, initial geometry. Then, a nonlinear structural analysis with a truss model is carried out to understand the evolving origami structure that promotes the desired wing shape change. CAPS is then employed to increase the geometric fidelity of the resultant shape by algorithmically converting the reconfigured origami structure from an infinitely-thin plate representation into a composite made of finitethickness plates and compliant hinges with multiple material assignments. A prototype of the final deformed design is fabricated in its maximally-compressed configuration using a multiple-material additive manufacturing technique, guaranteeing tensile loading over the operating domain, and thereby desired path uniqueness. The design, analysis and fabrication carried out in this work demonstrate the potential of using origami for morphing wings. More generally, the workflow developed for this study is demonstrated as a viable approach for multidisciplinary design and analysis of complex aircraft components.
Inspired by the wave-like camber variation in the trailing edge feathers of large birds, the aerodynamic impact of similar variations in the geometry of morphing wings is investigated. The scope of this problem is reduced by exploring parametrically generated geometries derived from an existing morphing wing design, namely the Spanwise Morphing Trailing Edge (SMTE), which is actuated via conformally integrated Macro Fiber Composites (MFCs). Utilizing this design, the deformation of the trailing edge of the SMTE is parameterized as a function of the spanwise location using a sinusoidal relationship. The aerodynamic responses are then obtained using Computational Fluid Dynamics (CFD) simulations, while the efficacy of the proposed approach is explored using a Pareto-like frontier approach.
Gust Load Alleviation (GLA) is an important aspect of flight dynamics and control that reduces structural loadings and enhances ride quality. In conventional GLA systems, the structural response to aerodynamic excitation informs the control scheme. A phase lag, imposed by inertia, between the excitation and the measurement inherently limits the effectiveness of these systems. Hence, direct measurement of the aerodynamic loading can eliminate this lag, providing valuable information for effective GLA system design. Distributed arrays of Artificial Hair Sensors (AHS) are ideal for surface flow measurements that can be used to predict other necessary parameters such as aerodynamic forces, moments, and turbulence. In previous work, the spatially distributed surface flow velocities obtained from an array of artificial hair sensors using a Single-State (or feedforward) Neural Network were found to be effective in estimating the steady aerodynamic parameters such as air speed, angle of attack, lift and moment coefficient. This paper extends the investigation of the same configuration to unsteady force and moment estimation, which is important for active GLA control design. Implementing a Recurrent Neural Network that includes previous-timestep sensor information, the hair sensor array is shown to be capable of capturing gust disturbances with a wide range of periods, reducing predictive error in lift and moment by 68% and 52% respectively. The L2 norms of the first layer of the weight matrices were compared showing a 23% emphasis on prior versus current information. The Recurrent architecture also improves robustness, exhibiting only a 30% increase in predictive error when undertrained as compared to a 170% increase by the Single-State NN. This diverse, localized information can thus be directly implemented into a control scheme that alleviates the gusts without waiting for a structural response or requiring user-intensive sensor calibration.
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 concept locally varies the trailing edge camber of a wing or control surface,
functioning as a modular replacement for conventional ailerons without altering the spar box. Utilizing alternating active
sections of Macro Fiber Composites (MFCs) driving internal compliant mechanisms and inactive sections of elastomeric
honeycombs, the SMTE concept eliminates geometric discontinuities associated with shape change, increasing
aerodynamic performance. Previous work investigated a representative section of the SMTE concept and investigated
the effect of various skin designs on actuation authority. The current work experimentally evaluates the aerodynamic
gains for the SMTE concept for a representative finite wing as compared with a conventional, articulated wing. The
comparative performance for both wings is evaluated by measuring the drag penalty associated with achieving a design
lift coefficient from an off-design angle of attack. To reduce experimental complexity, optimal control configurations are
predicted with lifting line theory and experimentally measured control derivatives. Evaluated over a range of off-design
flight conditions, this metric captures the comparative capability of both concepts to adapt or “morph” to changes in
flight conditions. Even with this simplistic model, the SMTE concept is shown to reduce the drag penalty due to
adaptation up to 20% at off-design conditions, justifying the increase in mass and complexity and motivating concepts
capable of larger displacement ranges, higher fidelity modelling, and condition-sensing control.
The flexure-box morphing aileron concept utilizes Macro-Fiber Composites (MFCs) and a compliant box to create a conformal morphing aileron. This work evaluates the impact of the number of MFCs on the performance, power and mass of the aileron by experimentally investigating two different actuator configurations: unimorph and bimorph. Implemented in a NACA 0012 airfoil with 304.8 mm chord, the unimorph and bimorph configurations are experimentally tested over a range of flow speeds from 5 to 20 m/s and angles of attack from -20 to 20 degrees under aerodynamic loads in a wind tunnel. An embedded flexible sensor is installed in the aileron to evaluate the effect of aerodynamic loading on tip position. For both design choices, the effect of actuation on lift, drag and pitching moment coefficients are measured. Finally, the impact on aileron mass and average power consumption due to the added MFCs is considered. The results showed the unimorph exhibiting superior ability to influence flow up to 15 m/s, with equivalent power consumption and lower overall mass. At 20 m/s, the bimorph exhibited superior control over aerodynamic forces and the unimorph experienced significant deformation due to aerodynamic loading.
Aircraft wings with smooth, hinge-less morphing ailerons exhibit increased chordwise aerodynamic efficiency over conventional hinged ailerons. Ideally, the wing would also use these morphing ailerons to smoothly vary its airfoil shape between spanwise stations to optimize the lift distribution and further increase aerodynamic efficiency. However, the mechanical complexity or added weight of achieving such a design has traditionally exceeded the potential aerodynamic gains. By expanding upon the previously developed cascading bimorph concept, this work uses embedded Macro-Fiber Composites and a flexure box mechanism, created using multi-material 3D printing, to achieve the Spanwise Morphing Trailing Edge (SMTE) concept. The morphing actuators are spaced spanwise along the wing with an elastomer spanning the gaps between them, which allows for optimization of the spanwise lift distribution while maintaining the continuity and efficiency of the morphing trailing edge. The concept is implemented in a representative section of a UAV wing with a 305 mm chord. A novel honeycomb skin is created from an elastomeric material using a 3D printer. The actuation capabilities of the concept are evaluated with and without spanning material on a test stand, free of aerodynamic loads. In addition, the actuation restrictions of the spanning elastomer, necessary in adapting the morphing concept from 2D to 3D, are characterized. Initial aerodynamic results from the 1’×1’ wind-tunnel also show the effects of aerodynamic loading on the actuation range of the SMTE concept for uniform morphing.