Ignazio Dimino

Safety and Reliability Aspects of an Adaptive Trailing Edge Device (ATED)

In morphing structures, actuation is a key system for general aircraft-level functions. Similarly to the demonstration of safety compliance applied to aircraft control surfaces, novel functions resulting from the integration of a morphing device (ATED), imposes a detailed examination of the associated risks. Because of the concept novelty, literature references for a safe design of a morphing trailing edge device are hard to be found. The safety-driven design of ATED requires a thorough examination of the potential hazards resulting from operational faults involving either the actuation chain, such as jamming, or the external interfaces, such as loss of power supplies and control lanes. In this work, a study of ATED functions is qualitatively performed at both subsystem and aircraft levels to identify potential design faults, maintenance and crew faults, as well as external environment risks. The severity of the hazard effects is determined and placed in specific classes, indicative of the maximum tolerable probability of occurrence for a specific event, resulting in safety design objectives. A fault tree is finally produced to evaluate the impact of actuation kinematics on specific aspects of ATED morphing operation and reliability.

KRISTINA: Kinematic rib-based structural system for innovative adaptive trailing edge

Nature teaches that the flight of the birds succeeds perfectly since they are able to change the shape of their wings in a continuous manner. The careful observation of this phenomenon has re-introduced in the recent research topics the study of “metamorphic” wing structures; these innovative architectures allow for the controlled wing shape adaptation to different flight conditions with the ultimate goal of getting desirable improvements such as the increase of aerodynamic efficiency or load control effectiveness. In this framework, the European research project SARISTU aimed at combining morphing and smart ideas to the leading edge, the trailing edge and the winglet of a large commercial airplane (EASA CS25 category) while assessing integrated technologies validation through high-speed wind tunnel test on a true scale outer wing segment. The design process of the adaptive trailing edge (ATED) addressed by SARISTU is here outlined, from the conceptual definition of the camber-morphing architecture up to the assessment of the device executive layout. Rational design criteria were implemented in order to preliminarily define ATED structural layout and the general configuration of the embedded mechanisms enabling morphing under the action of aerodynamic loads. Advanced FE analyses were then carried out and the robustness of adopted structural arrangements was proven in compliance with applicable airworthiness requirements.

An adaptive control system for wing TE shape control

A key technology to enable morphing aircraft for enhanced aerodynamic performance is the design of an adaptive control system able to emulate target structural shapes. This paper presents an approach to control the shape of a morphing wing by employing internal, integrated actuators acting on the trailing edge. The adaptive-wing concept employs active ribs, driven by servo actuators, controlled in turn by a dedicated algorithm aimed at shaping the wing cross section, according to a pre-defined geometry. The morphing control platform is presented and a suitable control algorithm is implemented in a dedicated routine for real-time simulations. The work is organized as follows. A finite element model of the uncontrolled, non-actuated structure is used to obtain the plant model for actuator torque and displacement control. After having characterized and simulated pure rotary actuator behavior over the structure, selected target wing shapes corresponding to rigid trailing edge rotations are achieved through both open-loop and closed-loop control logics.

Real-time monitoring of a variable-camber aileron rib by original strain-angle transducer:

The object of this work is the conceptual design and modelling of a transducer based on fibre optic sensor and conceived to measure rotations of rigid components around a pivot. The device, namely, post-buckling-fibre Bragg grating, is constituted of a flexible metal plate hosting a fibre Bragg grating strain sensor; the edges of the plates are hinged onto the rotating rigid bodies, eccentrically with respect to the pivot. In this way, any increase in rotation produces a further bending of the plate corresponding to a fibre Bragg grating wavelength shift. Among the different applications, an aileron morphing architecture is considered. This architecture is composed of a rib made of three rigid parts, hinged each other and moved through a dedicated kinematic chain. Two post-buckling-fibre Bragg grating devices are installed between the adjacent rib blocks giving a measure of their current angular rotation. A peculiarity of the proposed device is its ability in working in post-buckling configuration, with two main advantages: (1) easy, plug-and-play, installation (the device supporting plate can be manually bent and plugged within the connection hinges) and (2) tuning of the sensitivity or range of measure, on the basis of the fibre Bragg grating location onto the plate and of the initial post-buckling level. At first, the conceptual design was dealt with a theoretical model describing the post-buckling behaviour of beams, highlighting the effect of the main design parameters; then, the plate displacement field was related to rotation angle of the rib; a dedicated numerical (finite element) model was thus realized to prove the concept feasibility and simulate in detail its functionality. Finally, experimental set-up was provided in order to validate the design.

Distributed Actuation and Control of a Morphing Wing Trailing Edge

In a morphing wing trailing edge device, the actuated system stiffness, load capacity, and integral volumetric requirements drive flutter, actuation strength, and aerodynamic performance. Design studies concerning aerodynamic loads, structural properties, and actuator response provide sensitivities to aeroelastic performance, actuation authority, and overall weight. Based on these considerations, actuation mechanism constitutes a very crucial aspect for morphing structure design because the main requirement is to accomplish variable shapes for a given trailing edge structural mechanism within the limits of the maximum actuation torque, consumed power, and allowable size and weight. In this work, a lightweight and compact lever driven by electromechanical actuators is investigated to actuate the morphing trailing edge device. An unshafted distributed servoelectromechanical actuation arrangement driven by a dedicated control system is deployed to realize the transition from the baseline configuration to a set of design target ones and, at the same time, to withstand the external loads. Numerical and experimental investigations are detailed to demonstrate system effectiveness and reliability using a feedback sensing data from integrated FBG sensors.

Structural Design of an Adaptive Wing Trailing Edge for Large Aeroplanes

The structural design process of an adaptive wing trailing edge (ATED) was addressed in compliance with the demanding requirements posed by the implementation of the architecture on large aeroplanes. Fast and reliable elementary methods combined with rational design criteria were adopted in order to preliminarily define ATED box geometry, structural properties, and the general configuration of the embedded mechanisms enabling box morphing under the action of aerodynamic loads. Aeroelastic stability issues were duly taken in account in order to safely assess inertial and stiffness distributions of the primary structure as well as to provide requirements for the actuation system harmonics. Results and general guidelines coming from the preliminary design were then converted into detailed drawings of each box component. Implemented solutions were based on designer’s industrial experience and were mainly oriented to increase the structural robustness of the device, to minimize its manufacturing costs, and to simplify assembly and maintenance procedures. The static robustness of the executive layout was verified by means of linear and nonlinear stress analyses based on advanced FE models; dynamic aeroelastic behaviour of the stress-checked structure was finally investigated by means of rational analyses based on theoretical mode association.

Actuation System Design for a Morphing Aileron

In the field of European and International morphing structures projects, the CRIAQ MD0-505 enables collaboration among Italian and Canadian research centers and industries paying particular attention to the development of innovative design in the area of adaptive technologies. The main project goals involve the design of a wing trailing edge device capable to improve aerodynamic efficiency in all the flight envelope leading to fuel consumption reduction with positive impact on aircraft weight. This paper deals with the design and modeling of a novel actuation system of a full scale morphing aileron for a regional aircraft wing. The proposed aileron architecture is characterized by segmented adaptive ribs. Each rib is composed of two movable blocks connected by means of rotational hinges in which are housed bearings and bushing in a finger-like mechanism. Rib actuation is guaranteed by an actuation system composed of a dedicated kinematic chain derived from a quick-return mechanism. In order to achieve the aileron target shapes, the system is driven by a set of servo-rotary electro mechanical actuators that permit a highly integrated design which lay the groundwork for the technological transition from the torque shaft to the distributed actuation architecture.

Design and integration sensitivity of a morphing trailing edge on a reference airfoil: The effect on high-altitude long-endurance aircraft performance

Trailing edge modification is one of the most effective ways to achieve camber variations. Usual flaps and aileron implement this concept and allow facing the different needs related to take-off, landing, and maneuver operations. The extension of this idea to meet other necessities, less dramatic in terms of geometry change yet useful a lot to increase the aircraft performance, moves toward the so-called morphing architectures, a compact version of the formers and inserted within the frame of the smart structures’ design philosophy. Mechanic (whether compliant or kinematic), actuation and sensor systems, together with all the other devices necessary for its proper working, are embedded into the body envelope. After the successful experiences, gained inside the SARISTU (SmARt Intelligent Aircraft STrUctures) project where an adaptive trailing edge was developed with the aim of compensating the weight variations in a medium-size commercial aircraft (for instance, occurring during cruise), the team herein exploits the defined architecture in the wing of a typical airfoil, used on high-altitude long-endurance aircraft such as the Global Hawk. Among the peculiarities of this kind of aerial vehicle, there is the long endurance, in turn, associated with a massive fuel storage (approximately around 50% of the total weight). A segmented, finger-like, rib layout is considered to physically implement the transition from the baseline airfoil to the target configurations. This article deals with an extensive estimation of the possible benefits related to the implementation of this device on that class of planes. Parametric aerodynamic analyses are performed to evaluate the effects of different architectural layouts (in-plane geometry extension) and different shape envelopes (namely, the rotation boundaries). Finally, the expected improvements in the global high-altitude long-endurance aircraft performance are evaluated, following the implementation of the referred morphing device.

Manufacturing and Testing of Smart Morphing SARISTU Trailing Edge

Increasing environmental awareness and increasing fuel prices push aircraft industry to enhance aircraft efficiency. Morphing is considered a promising technology for future and next-generation aircrafts. Morphing aircraft changes its external geometry significantly during flight which moderates the design requirements. Adaptive Trailing Edge Device (ATED) is designed and manufactured under SARISTU (Smart Intelligent Aircraft Structures) project. The main challenge is to design and manufacture the smart ATED structure able to support the necessary loads, but it is also capable of changing its geometry. The structure design and actuation system are interrelated. Integration methodology drives multi-disciplinary thinking group from the preliminary design phase. In essence, this considerably amplifies the overall complexity of this work. After manufacturing the ATED, functionality tests have been performed successfully.

Distributed electromechanical actuation system design for a morphing trailing edge wing

Next-generation flight control actuation technology will be based on “more electric” concepts to ensure benefits in terms of efficiency, weight and maintenance. This paper is concerned with the design of an un-shafted distributed servo-electromechanical actuation system, suited for morphing trailing edge wings of large commercial aircraft. It aims at producing small wing camber variations in the range between -5° and +5° in cruise, to enable aerodynamic efficiency improvements. The deployment kinematics is based on multiple “direct-drive” actuation, each made of light-weight compact lever mechanisms, rigidly connected to compliant ribs and sustained by load-bearing motors. Navier-Stokes computations are performed to estimate the pressure distribution over the interested wing region and the resulting hinge moments. These transfer to the primary structure via the driving mechanism. An electro-mechanical Matlab/Simulink model of the distributed actuation architecture is developed and used as a design tool, to preliminary evaluate the complete system performance. Implementing a multi-shaft strategy, each actuator is sized for the torque acting on the respective adaptive rib, following the effect of both the aerodynamic pressure and the morphing skin stiffness. Elastic trailing edge rotations and power needs are evaluated in operative conditions. Focus is finally given to the key challenges of the proposed concept: targeting quantifiable performance improvements while being compliant to the demanding requirements in terms of reliability and safety.