Commercial aircraft today require efficient high-lift and control systems on the wings to reduce the drag in flight or decrease the take-off and landing speeds. Morphing mechanisms are one approach for improved high-lift systems. In most cases the objective function is an increased lift to drag ratio or the noise reduction. On closer examination control systems as well as morphing mechanisms are located in a certain wing segment. The transition between a moving wing part and the fixed wing is a step, which creates additional vortices. This segments the wing in span-wise direction and reduces the efficiency. A flexible skin between a moving and a fixed wing parts smooths the contour and minimize the efficiency reduction of the wing. A full scale demonstrator of a wing segment was manufactured with two flexible skin designs. The first subcomponent connects a morphing leading edge with a rib of the wing over a span of one meter. The skin is a material mix of ethylene-propylene-diene monomer (EPDM) rubber and fiberglass-reinforced plastic. The rubber is the basis of the skin and the glass-fiber is added as local skin stiffeners in the form of strips in chord-wise direction. The second subcomponent blends the aileron with a rib of the wing in a triangular design. The connection of three different hinges realizes a morphing triangle, which is loaded in an in-plane shear only state of stress in each aileron position. The core of the triangle is a 3D printed structure, which is free in shear. The covering skin is a combination of EPDM with carbon fibers oriented in +/−30° direction to obtain shear compliance and to resist the loads on the triangle. The deformation of each concept is identified at the demonstrator. Therefore, an optical measurement system scans the surface in the initial and deflected state. The required deformation precision of the concepts differs due to their design. The contour at the leading edge requires a certain shape over the span. The analysis of the skin buckling is one requirement at the transition triangle during the aileron motion. The experimental results show a smooth transition contour at the leading edge and no buckling effects at the triangle. The results can be used for the validation of simulation models. Furthermore, both skin concepts cover the gap between a moving wing segment and a fixed wing part. The elimination of steps in span-wise direction can improve the aero-acoustic behavior along the wing for future aircraft.

Following significant effort over the past several years by AFRL and NASA, the X-56A flight vehicle has proven to be a useful platform for exploring controllers and distributed actuation on a flexible, swept flying-wing. The program sought to advance the state of the art in airworthiness for vehicles encountering flutter, leading to relaxed design constraints that could drastically decrease structural weight and improve aircraft performance. Specifically, the vehicle was designed to encounter different forms of flutter: body-freedom flutter, and wing-bending torsion flutter, making it an ideal candidate for identifying dynamic actuation challenges. Flight testing led to fundamental observations by controller designers about the actuation needs for such a vehicle. Namely, the small inherent actuator deadband led to significant constant-amplitude limit cycle oscillations of the system during post-flutter controlled flight. This work captures these observations by exploring theoretical changes in the actuators via a nonlinear simulation tuned with flight testing data and shows that a 60% reduction in actuator deadband can improve ride quality by nearly 50%. The results are combined into a set of actuation challenges for the adaptive structures community at large, including precise actuation for a large number of cycles over multiple timescales, with a relevant baseline described by original actuation system.

This work presents the design, optimization and testing of a novel lattice-structure based morphing wing. The lattice-structure concept spans a large design space, including the possibility to vary among others material, number, distribution and the orientation of the lattice rods. The used parametrization scheme considers both the positioning of the Carbon Fiber Reinforced Polymer (CFRP) rods and their orientation in spherical coordinates within the wing, thus allowing to appropriately cover the design space, while reducing the set of variables during the design optimization procedure. The morphing deformations are relying on electromechanical servomotors. Design objectives include weight minimization and structural requirements, while achieving sufficient roll control. The local deformation induced by the electromechanical actuators is distributed by an internal skeleton structure across the rear section of the wing. An extensible skin is ensuring a smooth cambering and minimizes the required actuation energy. The in-house developed and validated simulation environment couples the aerodynamic pressure and the structural deformations, to accurately predict the aeroelastic response of the wing to aerodynamic and actuation forces, considering large deformations. In addition to the lattice structure, the aeroelastic optimization also considers the actuation layout, and the layup-thickness of the wing skin. Planform and airfoil shape are fixed to a NACA0012 airfoil with 80 cm span, and 30 cm chord. The structural and morphing behavior was evaluated on a technology demonstrator. The demonstrator provides large continuous shape changes, improving the aerodynamic performance and achieving large deflections and high rolling moment coefficients. This is mainly achieved by exploiting the interaction of the tailored internal structure and the actuation system. Since the deformation is distributed over a large portion of the wing, local stress concentrations are minimized, and actuation forces are reduced. Wing-up bending tests have been carried out, confirming the simulation results, respectively the load-carrying capability of the presented concept. Furthermore, actuation tests resulted in peak-to-peak trailing edge deflections of 31mm, respectively a rolling moment coefficient of 0.062, which are consistent with the simulation results and guarantee sufficient roll control.

In this study, the design and development of an autonomous morphing wing concept were investigated. This morphing wing was developed in the scope of, the Smart-X project, aiming to demonstrate in-flight performance optimisation. This study proposed a novel distributed morphing concept, with six Translation Induced Camber (TRIC) morphing trailing edge modules, inter-connected triangular skin segments joined by an elastomer material to allow seamless variation of local lift distribution along the wingspan. An FSI structural optimisation tool was developed, to achieve this optimised design, and to produce an optimal laminate design of fibre Glass weave material, capable of reaching target shapes and minimise actuation loads. Analysis of the kinematic model of the embedded actuator was performed, and a conventional actuator design was selected to continuously operate at the required load and fulfil both static and dynamic requirements in terms of bandwidth, actuation force and stroke. Preparations were made in this study for the next stage of the Smart-X design, to refine the morphing mechanism design and build a functional demonstrator for wind tunnel testing.

A slotted natural-laminar-flow airfoil design is a two-element airfoil design that employs a slot between the fore and aft elements. This slot alters the pressure recovery condition on the suction surface of the fore element, minimizing skin-friction and inhibiting the laminar to turbulent transition. These benefits reduce overall aircraft drag and increase wing lift. This allows smaller planforms, in turn, reducing fuel burn. This paper investigates the proposal that by help of piezocomposite surface actuation the aft element can be moved, rotated, and morphed to be used as a high-lift effector for take-off and landing conditions. A theoretical analysis is performed using a coupled fluid-structure interaction method assuming static aero-elastic behavior. During analysis the fore-element of the multi-element airfoil is assumed rigid. Thus, shape optimization is limited exclusively to the aft element. Airfoil morphing is achieved by way of piezocomposite actuating elements applied to the pressure and suction sides of the aft element. A genetic algorithm is used to independently optimize substrate thicknesses for each piezocomposite actuator as well as voltage, chord position and piezocomposite length. The nominal and leading edge substrate thicknesses of the airfoil are also varied. The optimized geometry for the high lift configuration is presented.

The future of technology lies in the diverse characteristics and capabilities of autonomous machines and devices and their application in many technical challenge. Rapid technology development, market globalization and availability of affordable electronics and controllers, have recently resulted in increased scientific and technical interest in drones as autonomous solutions for professional, as well as, amateur applications. On the other hand, researchers have been improving how manmade machines move through air by attempting to replicate animals motion by mimicking their aerial abilities. In this paper, we propose a development of a bio-inspired modular drone concept motivated by the bats agility, wingspan and wings folding into various shapes. The drone can be tailored for different applications, from sea port mapping, surveying, tank inspection and port traffic control to pollution monitoring and detection of illegal activities. The aerial performances of the drone allow it to be able to conduct windmills monitoring by connecting to their local monitoring units and send alerts to officials in real-time. This small bat-inspired drone is proposed to have an ability of performing flights with precisely defined trajectories. The accent will be put on the interchangeable wings, analysis of their dynamic attributes and transformation possibilities as a crucial segment of the overall drone performance. The design and fabrication process and the flight characteristics of the various wing configurations of the drone are discussed in details. Limitations of the drone, proposed solutions for further development and recommendations are also presented.

The so-called solid-state ornithopter concept seeks to employ piezoelectric materials to generate flapping motion instead of relying on conventional mechanisms and multi-component actuation systems. The motion can be induced on a wing-like partially-clamped composite substrate with a piezocomposite device (i.e. the Macro-Fiber Composite actuator.) In this research, a design for a flapping wing is proposed based on the analysis of critical system parameters such as geometric properties and boundary conditions. A series of finite element simulations are conducted based on the variation of those parameters. Consequently, the effects of parameters on the structural response is studied. Also, modal analysis is done to examine the effects of geometric parameters on the resonant frequencies of the system. Heaving and pitching responses are examined.

This study examines the biomimicry of wave propagation, a mode of locomotion in aquatic life for the use-case of morphing aircraft surfaces for boundary layer control. Such motion is theorized to inject momentum into the flow on the upper surface of airfoils, and as a consequence, creates a forcible pressure gradient thereby increasing lift. It is thought that this method can be used to control flow separation and reduce likelihood of stall at high angles of attack. The motivation for such a mechanism is especially relevant for aircraft requiring abrupt maneuvers, and especially at high angles of attack as a safety measure against stalling. The actuation mechanism consists of lightweight piezoelectric ceramic transducers placed beneath the upper surface of an airfoil. An open-loop system controls surface morphing. A two-dimensional Fourier Transform technique is used to estimate traveling to standing wave ratio, which is verified analytically using Euler Bernoulli beam theory, and experimentally using a prototype wing. Propagating wave control is tuned and verified using a series of scanning laser vibrometry tests. A custom two-dimensional NACA 0018 airfoil tests the concept in a low-speed wind tunnel with approximate Reynolds Number of 50,000. Both traveling waves and the changes in lift and drag will be experimentally characterized.

A continuous-surface morphing airfoil is desirable for commercial aircraft in order to improve fuel efficiency, and due to the potential to morph the wing into a high-lift configuration for take-off and landing. Piezocomposite actuators have shown to be a feasible strategy for camber morphing in small unmanned fixed-wing aircraft with a Reynold’s number in the range of 50,000 to 250,000. As an extension, this paper presents a theoretical framework and results for morphing in single and multi-segment natural laminar flow airfoils with a maximum Reynold’s number of 825,000. The airfoils presented employ a continuous inextensible surface. To achieve morphing, piezocomposite actuating elements are applied on the suction and pressure surfaces of the airfoils. The geometric properties of the airfoils are determined using a genetic algorithm optimization method with a migration strategy in order to maintain population diversity. The algorithm optimizes independently the substrate thicknesses for the nominal airfoil, the leading edge, and the piezocomposite bonded surfaces. In addition, positions and voltages for each piezocomposite actuators are optimized. The genetic algorithm uses an objective function to maximize the change in coefficient of lift to morph the airfoil from its baseline (i.e. cruise) state to the high-lift state. Analysis is performed using a coupled fluid-structure interaction method assuming static aero-elastic behavior. Optimization is followed by a parametric analysis to examine lift, drag, and lift-to-drag ratio of the airfoils over their full operational range. The optimization is performed on a symmetric, asymmetric, and the aft element of a slotted multi-segment airfoil to examine the capabilities of induced-strain actuation at high dynamic pressures.

Morphing wings offer potential efficiency and performance benefits for aircraft fulfilling multiple mission requirements. However, the design of shape adaptable wings is limited by the inherent design trade-offs of weight, aerodynamic control authority, and load-carrying capacity. A potential solution to this trilemma is proposed by exploiting the stiffness adaptability of thin, curved structures which geometric instability results in two statically stable states. We design and manufacture a morphing wing section demonstrator composed of two compliant 3D printed ribs monolithically embedded with the proposed bi-stable elements. The demonstrator’s structural response is numerically modelled and compared with experimental results from a static loading test. A deflection field of the response under mechanical actuation is obtained through digital image correlation. Numerical and experimental results indicate the capability of the wing section to achieve four distinct stable configurations with varying global stiffness behavior.

Morphing wings and the adaptive systems they form have been developed significantly over recent decades. Increased efficiency and control performance can be achieved with their implementation, while advances in material technology, system integration and control, have allowed concepts to present a realistic alternative to fixed-wing and aft-tail aircraft. Set out in this paper is the preliminary design and development for a novel span-wise morphing concept which employs and heavily implements biomimetic design. Specifically, the skeletal structure of the bird wing by mimicking the humerus, ulna/radius, and carpometacarpus of birds of prey as they exhibit the most versatile wing shape enabling multiple manoeuvre and flight types. The concept comprises three sections corresponding to the skeletal structure, each consisting of a leading edge D-spar and an internal structural member onto which trailing edge plates are mounted. Pneumatic artificial muscle (PAM) actuators are presented as a drive for a biologically derived ‘drawing-parallels’ mechanism, through which a 75% semi-span length change and variable sweep angle, can be obtained. Analysis of initial CFD results is discussed in comparison with similar concepts in the field and a proposal for small scale wind tunnel verification put forward. While a rapid prototype is printed to confirm the viability of the concept.

One of the means of flight is via flapping and there were many attempts to mimic the wing motion of a bird for centuries. One interesting concept for achieving flight via flapping is the so-called solid-state ornithopter concept which works by using induced strain actuators such as piezoelectric materials for flapping. In this research, we seek to gain a better understanding of the feasibility and performance of the solid-state ornithopter concept. In this paper, the purpose is to analyze a solid state ornithopter wing concept and to study the effect of different geometric parameters. A two-way fluid-structure interaction analysis method is utilized since the geometry of the wing is changing throughout the flapping cycle, and the fluid and the solid domains interact significantly. A parameterized model is utilized in both solid and fluid domains, and the two domains are coupled. Different geometric parameters are defined in the model so that the system-level performance metrics as a function of each parameter can be examined.

The paper at hand focuses on the modeling and design of an experimental demonstrator of a blade segment, twisted through Shape Memory Alloy technology. The demonstrator will be used for the wind tunnel tests planned within the Project of SABRE (H2020 Eu Program), aimed at investigating the effects produced by blade oriented morphing technologies, both in fixed and rotary wing configurations. The design approach adopted for a SMA twist concept is herein described in its different phases, moving from the definition of the preliminary layout, its fitting to the reference blade mechanical features, the preliminary structural analysis to confine its operational envelope, up to the simulation of the SMA actuation through a SMA torque element. The results are presented in terms of operational envelope limits and transmitted twist.

Aircraft wing design optimization typically requires the consideration of many competing factors accounting for both aerodynamics and structures. To address this, research on morphing aircraft has shown its potential by providing large benefits on aircraft performance. In particular, by adapting wing lift distribution, morphing winglets are capable to improve aircraft aerodynamic efficiency in off-design conditions and reduce wing loads at critical flight points. For those reasons, it is expected that these devices will be applied to the aircraft of the very next generation. In the study herein presented, a preliminary failure analysis and structural design of a morphing winglet are presented. The research is collocated within the Clean Sky 2 Regional Aircraft IADP, a large European programme targeting the development of novel technologies for the next generation regional aircraft. The safety-driven design of the proposed kinematic system includes a thorough examination of the potential hazards associated with the system faults, by taking into account the overall operating environment and functions. The mechanical system is characterized by movable surfaces sustained by a winglet skeleton and completely integrated with a devoted actuation system. Such a load control device requires sufficient operational reliability to operate on the applicable flight load envelope in order to match the needs of the structural design. One of the most critical failure modes is assessed to get key requirements for the system architecture consistency. Possible impacts of the defined morphing outline on the FHA analysis are investigated. The structural design process is then addressed in compliance with the demanding requirements posed by the implementation on regional airplanes. The layout static robustness is verified by means of linear stress analyses at the most critical conditions, including possible failure scenarios. Results focus on the assessment of the device static and dynamic structural response and the preliminary definition of the morphing system kinematics, including the integrated actuator system.

This paper summarizes the results obtained in the framework of Clean Sky 2 REG-IADP, AIRGREEN on the development of a dedicated morphing device, i.e. a Leading Edge morphing. This device, designed so to be installed on a advanced, twin prop, regional aircraft, is conceived to guarantee high lift conditions together with a smoothed and continuous skin surface, especially important due to the presence of a laminar wing. The design of a such as complex devices required a multi-disciplinary approach, able to combine the aerodynamic performances and the structural ones related to the compliant structures concept adopted for the internal structure. The paper includes an overview of all the design challenges, the adopted solutions and finally the obtained numerical assessments.

Bistable structures have several applications in different areas, such as aircraft morphing wings, morphing wind turbine blades, and vibration energy harvesting, due to their unique properties. Bistable structures can be used in morphing wings and wind turbine blades since they are able to alleviate large loads by snapping from one stable position to the other one. A piezoelectric actuator can be used to bring the bistable structure back to its original position after the load is alleviated. In this paper, the transient response of a piezoelectrically actuated bistable beam is investigated experimentally for different force inputs. The goal of these experiments is to explore the ability of a commercial piezoelectric actuator to induce snap-through motion in a bistable structure. The feasibility of performing snap-through motion, and the required energy are found for different excitation force amplitudes and frequencies.

This article investigates a method of designing fractal origami tessellations through eigen analysis. Foldable structures with hierarchical geometric features could be beneficial in applications where a graded functionality is desired. A representative unit in an origami tessellation is modeled as networked truss elements with torsional springs at fold lines. Eigen analysis and nonlinear mechanics analysis of the representative unit with fractal boundary conditions reveal the foldability of a given fractal origami crease pattern out of its flat state. This configuration can be used to construct a folded fractal origami tessellation with a desired number of fractal levels, which can then be used to evaluate its functional merit. The design process is demonstrated for the design of a fractal origami tessellation with tailored boundary shape change (from rectangular to trapezoidal) through folding, that could be used as an enabling mechanism for an adaptive wing section.

In this work the aeroelastic behavior of locally resonating periodic structures is investigated. The plate-like wing behavior will be obtained from the Love-Kirchhoff plate model with a finite number of mechanical resonators periodically distributed along its surface and using assumed-modes expansion. The unsteady aerodynamic loads are obtained from the doublet lattice model. By combining the structural and aerodynamic models, the aeroelastic behavior of the wing over a range of airflow speeds is discussed. Frequency response functions due to simultaneous base and flow excitations are calculated from the absence of flow speed to the linear flutter speed of the system without resonators. The effects of bandgap presence on the flutter boundary of the wing are also discussed.

Early research on a new concept for a morphing system based on unit structures or cells containing pressurized fluid is presented in this article. The motivation stems from the desire to achieve 3D smooth variations with multiple degrees of freedom and variations in surface area. Such a cell is composed of a hybrid between elastomeric material and stiffening material, creating an orthotropic system. When connected in a network of cells, the morphing system is highly integrated in terms of the components of the skin, substructure and actuation means. Numerical predictions of small simple prismatic cells show a force and axial strain capability of above 200 N and 14% respectively for typical elastomeric and stiffening materials at 8 bar pressure. PolyJet™ additively-manufactured models of wings show how such actuators can be integrated into aircraft structures, including when 3D geometry is highly challenging. These additively-manufactured models were operated at low pressures in the order of 0.5 bar, and a number of open questions on the design, manufacture and operation of such structures are discussed along with intended future work towards higher grade materials and working pressures.

Regional aviation is an innovation driven sector of paramount importance for the European Union economy. Large resources and efforts are currently spent through the CleanSky program for the development of an efficient air transport system characterized by a lower environmental impact and unequalled capabilities of ensuring safe and seamless mobility while complying with very demanding technological requirements. The Green Regional Aircraft (GRA) panel, active from 2006, aims to mature, validate and demonstrate green aeronautical technologies best fitting the regional aircraft that will fly from 2020 onwards with reference to specific and challenging domains: from advanced low-weight and high performance structures up to all-electric systems and bleed-less engine architectures, from low noise/high efficiency aerodynamic up to environmentally optimized missions and trajectories management. The development of such technologies addresses two different aircraft concepts, identified by two seat classes, 90-pax with Turboprop (TP) engine and 130-pax, in combination with advanced propulsion solutions, namely, the Geared Turbofan (GTF), the Advanced Turbofan (ATF) and the Open Rotor (OR) configuration. Within the framework of the Clean Sky program, and along nearly 10 years of research, the design and technological demonstration of a novel wing flap architecture was addressed. Research activities aimed at demonstrating the industrial feasibility of a morphing architecture enabling flap camber variation in compliance with the demanding safety requirements applicable to the next generation GRA in both open rotor and turboprop configurations. The driving motivation was found in the opportunity to replace a conventional double slotted flap with a single slotted morphing flap assuring improved high lift performances — in terms of maximum attainable lift coefficient and stall angle — while lowering emitted noise, fuel-burnt and deployment system complexity. Additional functionalities for load control and alleviation were then considered and enabled by a smart architecture allowing for an independent shape-control of the flap tip region during cruise. The entire process moving from concept definition up to the experimental qualification of true scale prototypes, characterized by global and multi-zone differential morphing capabilities, is here described with specific emphasis on the adopted design philosophy and implemented technological solutions. Paths to improvements are finally outlined in perspective of a low-term item certification and series production.