Clean Sky's Morphing Wing project brings shape-shifting capabilities to European regional aircraft
In regional aviation, due to the brief period the aircraft is flying at a constant level cruising altitude, much of the flight is spent climbing and descending. This means that the wing is changing shape with the help of ailerons, flaps, spoilers and other control surfaces. Regional aircraft handle these ascent/descent cycles several times each day, so the wing has to be robust and operate with flawless dependability. In nature, birds do this effortlessly, but in the more mechanical world of aviation, technology is still catching up.
"The rationale behind Clean Sky's 'Morphing Wing for Regional Aircraft' project is to optimise the wing's aerodynamic capabilities — especially for these ascending and descending periods of the flight — by adapting the shape and camber of the wing to adapt to the required configuration for the corresponding phase of the journey" says Ruud Den Boer, Project Officer at Clean Sky. "This project, led by Leonardo, is looking at introducing advanced morphing devices for the leading edge, combined with a morphing trailing edge. With the morphing devices we are developing in Clean Sky we will have two or three hinges, making the wing more like that of a bird, allowing continuous rotation or shift in the camber of the wing, so you have more freedom to vary the wing's shape".
A morphing wing could bring significant energy-saving and therefore environmental benefits that align with the ACARE goals, and that's important in regional aviation (which represents 40% of total commercial flights) as regional air traffic is expected to triple at an average annual rate of 6% (versus 5% growth of total commercial aviation), generating a market demand of around 9000 new regional aircraft and adding to the global emissions burden.
"Every regional flight mission needs to be managed in order to have the absolute maximum level of flight performance in each flight phase — climb, cruise, descent, etc. — and, globally, to reach the minimum possible fuel consumption" says Giovanni Carossa, Head of Structural Loads in the Air Vehicle Technology Department at Leonardo S.p.A. Aircraft Division.
"The morphing wing project is a modern attempt to realize the age-old dream of a flying bird-like wing, since Leonardo da Vinci first started the science of flight by studying birds' configurations. Even the Wright brothers attempted to realize a morphing adaptive wing in order to control the Flyer while in flight at Kitty Hawk" says Carossa.
The morphing wing is designed to be 'adaptive', which means being able to seamlessly 'shape-shift' automatically during flight, without slots or steps on wing surfaces, to minimize the possible impacts on the aerodynamic drag, using a control system without any direct intervention by the pilot.
Currently, the work package coordinated by Carossa and the team at Leonardo is entering the advanced design phases of morphing concepts relevant to wing tips, wing leading edge and trailing edge. Aerodynamic performances have been evaluated and preliminarily assessed against requirements. Morphing elements, structural and final mechanical design have been completed, and the architecture design of the actuation and control systems is almost completed. The experimental technology demonstrators manufacturing phase will be shortly initiated.
"Full scale demonstrators of morphing devices shall be manufactured and tested on the ground, to check all the aspects relevant to the item manufacturing, structural elements assembly, morphing device functionality, internal items installations, accessibility and maintenance" says Carossa.
"These structural ground tests are underway and will be finalized by the end of 2019".
Regarding the morphing wing's aerodynamics aspects, high and low speed wind tunnel tests are planned and will be performed using large scale models of a flexible wing equipped with active morphing devices. The aim is to demonstrate aerodynamic performance improvements and morphing elements functionality under aerodynamic loads in ground tests that replicate flight conditions.
"These wind tunnel tests are organized in several phases and will be spread over two years, starting this year" explains Carossa. "The first phase will focus on low speed aircraft performance evaluation relevant to take off and landing conditions. A second phase will focus on the gust alleviation system. Dynamic gust conditions will be simulated in a wind tunnel and the gust loads alleviation capability will be demonstrated".
Clean Sky's Ruud Den Boer picks up on this point explicitly: "In addition to the morphing capability a key aspect of the morphing wing is load control and alleviation because in the design of the wing box the gust loads impose restrictions for designing the wings. When you have effective load alleviation you can lower the design constraints and have a weight reduction of the wing. So in this project there will be a new outer wing box design with a lower structural weight, which will result in lower recurrent and non-recurrent manufacturing costs".
A third phase will evaluate a high speed, flexible wing, using a 1:3 scale model, looking at aerodynamic performance and the loads alleviation capability of morphing devices. The large scale of the wing model will make it possible to partially reproduce the real internal mechanisms of morphing parts so as to contribute to the functionality demonstration of these movable devices under real aerodynamic loads, completing the previous full-scale mechanical test results.
"All these experimental steps are preparatory to the final demonstration step" says Leonardo's Carossa. "Active wing tip morphing devices linked with a structural active loads alleviation system will be installed on an existing aircraft, modified for this purpose. Flight tests will be carried out, bringing them in a real environment to demonstrate their functionality and their capability to reduce wing loads and to check the aircraft performance and handling qualities. This last experimental flight test will be facilitated by the results of the earlier structural and wind tunnel tests. This final step will make it possible to meet the technology maturation target (TRL 6) set at the outset of the project and planned to be completed in 2022".
Beyond the efficiency benefits of drag reduction and fuel consumption, morphing devices have been pointed out by the enhanced authority as a promising contender for alleviation purposes, with a consequent possibility of relaxing the structural weight. This of course contributes to a lighter aircraft, more compliant with the ACARE targets. Environmental protection aspects involving specific morphing concepts, such as on the leading edge, play a fundamental role within the project, where topics like the integration of the de-icing system, erosion protection, lighting strike protection and bird strike protection will be properly taken into consideration. The wing morphing trailing edge and the winglet also contribute to the overall robustness and to the flight safety.
Carossa concludes that the project has brought about a new integrated approach to design that will ultimately be conducive to Europe's leading position in aeronautics:
"A key aspect of the proposal is the deep and effective integration of different technologies and a strong interaction among different disciplines, with the objective of achieving a cutting-edge product. This changing of mind-set also involves a basic philosophy different from the current one. Until now the design of a component is the result of different separated tasks involving the sizing of the structure and the definition and sizing of another required subsystem. This approach leads to components not completely optimized, because the current level of integration generally does not provide a joined-up, combined and synergic design and does not consider a deep interaction of the needed tasks. On the contrary, Clean Sky's Morphing Wing Project points towards the direction of a deep integration of competences, promoting not only the modular, step by step maturing of the technologies, but also the gradual integration of the related tasks. In this way the final product will be highly optimized. All these considerations meet a clear and precise target: the preservation and the enhancement of the leadership of the European industry in respect of its main competitors".