Full Scale Servo-Actuated Morphing Aileron for Wind Tunnel Tests

Typically, aircraft roll control is accomplished by simultaneously moving ailerons together and in opposite angular direction. Nevertheless, throughout the flying range, more particularly in cruise conditions, it is highly desirable to increase aircraft aerodynamic performance by a differential control of the lift distribution over the wing span. Recent European design studies concerning morphing devices, such as the Clean Sky multifunctional flap or the SARISTU trailing edge device, have largely proved the potential of novel aircraft structural systems, aiming at adaptively modify the wing structural shape to reduce the induced drag penalty associated with off-design flight conditions. In particular, wing camber variation was achieved through adaptive wing trailing edges because of the highly associated L/D ratio enhancements. Such projects proved also the aileron region to be the one where higher cruise benefits could be achieved by local camber variations. Following the enthusiastic results, achieved with the Adaptive trailing edge device, a new challenge has been faced up. The former configuration did in fact refer to the standard position of the flap, leaving apart the aileron region. There are several reasons to leave that part unchanged. The most relevant may be associated to the fact that the aileron has a critical function in the aircraft flight and its collapse could lead to dramatic failures. The investigated configuration would have lied over an extended region of the aileron instead than a limited part, as in the case of a flap, characterised by a large chord. As a direct consequence, the available volumes are reduced and the installation of integrated actuators could have been a problem. Finally, the aeroelastic response of the device is critical as well and its strong modification should have been deeply studied. On the other hand, the studies on the ATED showed as the region, farer from the root, gave a more significant contribution to the aerodynamic behaviour. So, it was really interesting to investigate the possibility to extend the adaptive trailing edge technology to the aileron region. The occasion was given by a joint Italian/Canadian research activity fostered by the Consortium de Recherche et d’Innovation en Aerospatiale au Quebec (CRIAQ). The activity aimed at realising a full-scale demonstrator of a wing section in the tip region for investigating the capability of wing box and trailing edge morphing device, to ensure a certain level of flow control and aerodynamic performance variations, respectively. The first issue was in charge of the Canadian team (ETS, NRC, Thales Aerospace, Bombardier AS), while the Italian group (University of Naples and CIRA) aimed at realising a device for the aileron camber control. The enlisted problems were all evident at the very first approach. Volume limitation forced the designers to follow a different strategy. Instead of having a couple of actuators acting on each rib, the architectural layout was specialised per each single bay. At the aileron root this possibility was maintained, while the more external two bays were commanded by a single actuator. In other words, the last two segments were made of two slave and a master ribs, driven by a single actuator. Calculation showed as this configuration was able to maintain the specified loads. Aeroelastic studies confirmed the reliability of the device, in sense that the selected architecture was demonstrated to be safe in the design flight conditions. The adaptive aileron finally maintained the original capability while ensuring morphing characteristic. This target was accomplished by realising a device with two separate motor system. The first, acting on the main aileron shaft, to preserve its characteristic dynamic response for flight control. The second, acting on the rib, implemented the searched camber variations to follow the aerodynamic necessities related to fuel consumption. Another relevant point concerns the skin. In order to check the possibility of skipping the need of implementing a compliant solution, a heavy and sophisticated element, the single hinged blocks were properly shaped to slide one into the other like a meniscus. This solution was however strongly correlated to manufacture tolerances and the assembly precision, because small deviation could have had a significant impact on the kinematic performance. As usual, vantages and disadvantages try to compensate each other. The innovative device can be considered as a system with augmented capabilities aimed at working in cruise, by means of symmetric deflection, to obtain a near optimum wing geometry enabling optimal aerodynamic performance. The approach, including underlying concepts and analytical formulations, combines design methodologies and tools required to develop such an innovative control surface. A major difficulty in the development of morphing devices is to reach an adequate compromise between high load-carrying capacity to withstand aerodynamic loads and sufficient flexibility to achieve the target shapes. These targets necessitate the use of innovative structural and actuation solutions. When dealing with adaptive structures for lifting surfaces, the level of complexity naturally increases as a consequence of the augmented functionality of the designed system. In specific, an adaptive structure ensures a controlled and fully reversible transition from a baseline shape to a set of different configurations, each one capable of withstanding the associated external loads. To this aim, a dedicated actuation system shall be designed. In addition, the adopted morphing structural kinematics shall demonstrate complete functionality under operative loads. Such a morphing device wants to augment the former device by adapting local wing camber shape and lift distribution through a quasi-static deflection, its excursion ranging into few unit of degrees, positive and negative. In a morphing aircraft design concept, the actuated system stiffness, load capacity and integral volumetric requirements drive flutter, strength and aerodynamic performance. Design studies concerning aircraft flight speed, manoeuvre load factor and actuator response provide sensitivities in structural weight, aeroelastic performance and actuator flight load distributions. Based on these considerations, actuation mechanism constitutes a very fundamental aspect for adaptive structures design because the main prerequisite is to accomplish variable shapes within the physical constraints established by the appropriate actuation arrangement. This thesis addresses the design of a morphing aileron with a specific focus on the structural actuation system sizing and integration while the structural sizing was under Unina responsibility. Particular focus is given to the numerical validation of the entire aileron integrated with the actuation leverage by means of FE model and experimental tests campaign. The aileron actuation system is driven by load bearing servo-electromechanic rotary actuator in a distributed and un-shafted arrangement which combine load carrying and actuation capacities. The use of electro-mechanical actuators is coherent with a “more electric approach” for next-generation aircraft design. Such an actuation architecture allows the control of the morphing structure by using a reduced mass, volume, force and consumed power with respect to conventional solutions. Benefits are obvious. No hydraulic supply buses (easier to maintain and store without hydraulics leaks), improved torque control, more efficiency without fluid losses and elimination of flammable fluids. In addition, it is potentially possible to move individual ribs either synchronously or independently to different angles (twist) in order to enhance aerodynamic benefits during flight. On the other side, actuators susceptibility to jamming may represent the most important drawback that can be tested and prevented by means of an iron bird facility. Finally, the realised system was assembled onto a wing model and tested in a wind tunnel at the National Research Council (NRC) facilities in Ottawa (CAN). On the same model, the adaptive wing box was also installed. The adaptive aileron device proved its functionality in real flow conditions and the main aerodynamic results are herein presented and widely described. The developed device has a lot of further potentialities, that will be object of further works and publications and that are currently explored by the authors: for instance, by giving it a large bandwidth, it could be used as an additional load alleviation device for the outer wing in order to reduce peak loads for gusts. Moreover it can be tailored for active load control distribution in order to modify spanwise lift distribution obtaining a reduced wing root bending moment; in such a manner a lightweight design can be assessed.