Smart Morphing Concepts and Applications for Advanced Lifting Surfaces

In this research study, aeronautical "structural" morphing has been considered, focused on seamless structural wing shape adaptation, inspired by biologicallife. Available literature (Chapter 2) shows that international interest in the aeronautical field is focused in the morphing of specific wing parameters, such as leading or trailing edge curvature, wing torsion, wing span change, etc., each capable of generating aerodynamic advantages or better adaptability over a traditional design. Moreover, to overcame weight, mechanical complexity and costs penalties introduced by morphing architectures, many of these solutions adopt smart materials as actuators. Among them, Shape Memory Alloys have attracted a lot of attention and are present in many applications, due to their favourable force/volume or force/weight ratio: state of the art about SMAs features, numerical modelling and characterization is presented in Chapter 3. The chief objective of this dissertation is to propose plausible architectural solutions for changing different geometrical parameters of an airfoil; many of them integrate Shape Memory Alloys within the structure, having both actuation and load-bearing role. In particular, three airfoil parameters have been taken into account: airfoil (upper) bump; airfoil camber at trailing edge (morphing flap); airfoil chord. The formation of an airfoil upper bump is one of the first experiences in the morphing field done by the author and researchers at CIRA: it represents one of the less invasive possible morphing techniques, not affecting the wing primary load-bearing structure, and capable of introducing some benefits in transonic regime (Chapter 4). Then, activities moved towards a greater level of integration and interaction within the wing structure, trying to substitute a traditional hinged flap with a variable camber trailing edge, also known as morphing flap (Chapter 5). In parti cular , literature showed a dearth of real scale applications of morphing technologies with smart materials to civil transportation class aircrafts. Basing on the partnership with Alenia Aeronautica Spa industry (which founded part of these activities) , innovative concepts for a morphing flap have been conceived, suitable for real scale regional transportation aircrafts; expertise at CIRA in modeling and characterization of Shape Memory Alloys allowed for an high integration of these alloys both as actuators and structural load-bearingelements. Results of this collaboration brought to the design and manufacture of a SMA-based actuator (Chapter 6) and a morphing flap architecture highly integrating such an actuator devi ce (Chapter 7). Moreover, these research activities have raised great interest in the industriaI partner (Alenia): a patent is pending on both devices (Appendix) and further studies and collaborations are currently starting. Finally, new research activities started in the branch of variable chord are presented (Chapter 8). Chord morphing has the power to increase the airfoil surface and, so, its lifting capab il ity. Something similar already happens for high lift devices on transportation aircrafts, where the typical single/double slotted solution for trailing edge flaps allow not only to increase wing curvature, but also its chord (that is, wing area). The possibility to match the greater aerodynamic efficiency of a morphing flap with an airfoil chord (wing area) increase could lead to even better aerodynamic performance. In this work, an early concept has been studied and manufactured for a morphing rotorcraft bIade, basing on a three-month collaboration with the Department of Aerospace Engineering of the Pennsylvania State University (with particular reference to the Vertical Lift Research Centre of Excellence (VLRCOE)). The thesis, where possible, has been produced as a collection of publications (both on journals and to conferences). However, due to the patent pending on some of the presented activities and prototypes, great part of the research activities has not been published yet at the moment of writing: for this reason, some chapters will be offered as traditional reports. Therefore, the dissertation is organized as follows: Chapter 2 treats the worldwide state of the art in morphing technologies through a survey of aeronautical applications that can be found in literature, focused in the optimization of specific wing parameters, using traditional actuators or Shape Memory Alloys; Chapter 3 overviews the Shape Memory Alloys micromechanics and macroscopic behaviour, together with material modelling and characterization; then, current applications in various fields exploiting either the super-elastic or shape memory effect are presented, jointly with new discovered materials in the "shape memory" field; Chapter 4 introduces the first studied morphing application, focused on the bump formation on the upper wing skin for transonic drag reduction (paper): a device integrating Shape Memory AlIoys has been designed, manufactured and tested; Chapter 5 reviews some preliminary studi es carried out toldentify possible morphing solutions, actuated by SMAs elements, to produce a camber change Iocalized to the aft part of a wing airfoil, so to mimic a trailing edge flap: several architectures are presented and numerical results discussed (various papers); Chapter 6presents the conceived SMA-based smart actuator, expIaining in great detail its design features and alI the considerations, numerical simulations and optimizations which brought to the final prototype, experimentalIy tested and characterized; Chapter 7 shows in detail an application of the developed smart actuator to a real scale morphing architecture abIe to mimic a trailing flap: after numerical simulations, the solution has been built and prototype tested also in presence of static Ioads; Chapter 8 deals with the other morphing parameter taken into account in this research, that is airfoil chord, introducing an early concept for a morphing rotorcraft bIade, its design constraints and the realized prototype; Chapter 9 c10ses and comments on the work presented, discussing also future deveIopments. Finally, an Appendix is present, reproducing the patent communication from the European Patent Office with all the details.