Morphing Winglet: Clean Sky innovation waiting in the wings
Clean Sky's Morphing Winglet project not only promises operational performance improvements and emissions reductions, it's also aiming to reduce manufacturing costs and production lead times.
Winglets have become an increasingly ubiquitous feature of civil airliners over the past couple of decades due to their aerodynamic benefits, such as reducing the wingtip vortices, which lead to energy loss. Winglets also reduce drag, help boost aircraft performance and cut fuel consumption. Clean Sky’s Morphing Winglet project aims to enhance the aero-efficiency of more durable, affordable and lighter-weight wing structures through the design, build and ground testing of winglet structures with innovative curved contours made from lightweight composite materials that have integrated micro electromechanical actuators (EMA).
In terms of defined aerodynamic and environmental targets, the project aims to reduce weight at component level by around 15% relative to current state-of-the-art winglets, leading to drag reduction at aircraft level of around 5% and an expected 10% improvement in load alleviation. The cumulative anticipated benefit of these targets is intended to precipitate a corresponding reduction in fuel consumption that will be confirmed in forthcoming flight tests.
Another key target of the project is to also reduce the manufacturing costs of the winglets, helping curb impact on the environment in line with the goals of the European Green Deal. The manufacturing approach to achieve this is to employ a low-cost jigless one-shot composite material process. The ultimate objective is to reach TRL6 in respect of all the technologies integrated into the morphing winglet concept, which will be installed and flown in the Regional IADP Flight Test Bed Demonstrator, a C295-based aircraft, with a first flight test scheduled for 2021. A further flight demonstration regime is slated for 2023.
‘We wanted to incorporate a micro electro-mechanical actuator (EMA) in the winglet tab with independent actuation, in order to have benefits in terms of drag, especially in terms of aerodynamic optimisation, in respect of aerodynamic efficiency, in terms of lift, in terms of performance, and additionally as well to address load alleviation,’ says Antonio Hernández, airframe ITD coordinator and Airbus DS Clean Sky 2 manager at Airbus.
‘With this new winglet we are able to reduce the bending moment of the aerodynamic forces of the wing because we can deflect at a negative angle the tab of the winglet — we can move the centre of the pressure of lift to the inner part of the wing, converging to the wing root. This brings benefits in terms of load alleviation and can help us to reduce the weight of the structure of the wing, because the loads we need to apply for the design of the structure are less.’
The second stream of the project is that the winglet is designed in a highly integrated way so that fasteners and bondings are replaced by producing the winglet in a simplified and unified manner.
‘We are trying to progress towards a jigless process to manufacture the winglet in one shot, by integrating the different elements of the winglets and therefore reducing the number of part numbers and to eliminate as many of the joints as we can,’ says Hernández. ‘In conventional manufacturing, you have to combine the different elements — ribs, spars, skins — which are all connected with fasteners, rivets and screws. This creates a lot of weight in the structure, and what we want to do instead is to avoid that, so we wanted to manufacture for example the torsion box of the winglet in one shot.’
The process of manufacturing is focused around low cost tooling. Traditionally, tooling is made from hard-wearing metals that are expensive and slow to produce, but are required in order to ensure the correct tolerances in the geometry of the components. Instead, Hernández explains, the team decided ‘to use tooling manufactured from composite materials, and using a liquid resin infusion process which allows us to be more flexible in terms of geometry and reduce the non-recurring tooling costs, and therefore reduce the overall costs of manufacturing.’
This process also reduces the lead time. However, one of the challenges of soft tooling is faster degradation of the tool, which means that the number of cycles for making the winglet is less. Hernández says that this ‘is another challenge we need to face, but we are working on it.’
The target that the project has set itself is to reduce manufacturing costs and lead times by 5%, relative to current manufacturing methods, minimising the environmental impact during the manufacturing cycles.
The project's core partner, Aernnova, has developed the morphing winglet composite structure, with Airbus having provided the external loft, the loads and the high level technical requirements.
‘Aernnova has been engineering an innovative composite solution, including new design concepts and manufacturing processes that reduce the structural weight while enhancing competitiveness through technology innovation,’ says Dr. Miguel Ángel Castillo, VP Technology Development, at the Spain-headquartered aerostructures company Aernnova.
Aernnova's main activities include the winglet design, from early concepts formed together with Airbus to detailed design, drawings, and reports, as well as the development of new design principles associated with the new manufacturing processes, validated by tests.
‘There have been testing activities in close collaboration with the Spanish Foundation for the research development and application of composite materials (FIDAMC) for materials coupon testing and manufacturing trials for the new curved spars concepts,’ adds Dr. Castillo. Indeed, collaboration has been key throughout many aspects of the project, including, he notes: ‘the co-development with Airbus of the interfaces with the rest of the wing, the actuators and systems, and the winglet Digital Mock Up (DMU) development with very strong collaboration with the Airbus team including configuration control.’
Aernnova, with support from the other partners, has also been responsible for the development and manufacturing of the composite manufacturing tools for the inboard and outboard leading edges, the torsion boxes, and the tab; the assembly tools for the winglets and tabs, left and right; as well as the production of elementary parts prototypes, assembly of the winglets, quality assurance of the demonstrators and inspections prior to delivery to the Airbus assembly line for integration onto the Flight Test Bed Platform.
As for timelines and progress thus far, the Preliminary Design Review took place in 2017 with the first Critical Design Review in 2018. ‘We started the manufacturing for the elementary parts and the tooling in mid-2018, and ground tests were performed during the second semester of 2019. For 2020 the challenge is to produce all the technical documentation for the winglet to obtain a permit to fly for the winglet and also for the full flight demonstrator,’ says Airbus's Hernández.
In terms of deliverables, at the end of 2019 Aernnova provided Airbus with left and right airworthy morphing winglets for experimental flight testing.
‘The new production concepts can provide more competitive products in their life cycle,’ says Aernnova's Dr. Castillo. ‘The most relevant achievements include reduction of the winglet structure, due to the fact that the actuators, fittings and hardware for morphing are integrated within the structure, yet they have the same overall weight as the current metallic benchmarked winglets. The tests that validate the design have been completed, from coupon test level to the design detail and component testing performed in Aernnova for lightning strike test, curved spar strength and subcomponent load paths tests.’
Aernnova has also completed the manufacturing trials for curved spars to validate the new press forming process and the asymmetric stacking sequences, as well as the validation through testing of the new Tab RTM manufacturing process feasibility that includes copper mesh integration.
‘The manufacturing processes reduce the amount of fasteners required for assembly. This means recurring cost reduction during production and operation,’ says Dr. Castillo, whose company also, for this project, created ‘new manufacturing processes and design principles for the Torsion Box Elbow enabled by curved spars, highly integrated multi-spar torsion boxes, morphing winglet leading edge and tab, removable panels and hinge line fittings.’
‘One of the things we need to do is to measure what we have achieved with all these different elements that have been manufactured in terms of weight, in terms of drag reduction, in terms of loads alleviation, and performance enhancement. We have some targets and we have performed a wind tunnel test for the full mock-up, but we won't know the full results until the flight testing, in 2021 and in 2023, is complete,’ says Hernández.
As for the broader value of the Morphing Winglet project, Hernández says: ‘Clean Sky 2 allows us to establish collaborations with other organisations, other actors, universities, and other companies at industrial level. All the research and academia allows newcomers to enter the arena with new ideas that can contribute a lot to increased performance and competitiveness of the European aircraft industry. This collaborative research and this concept of approach enables us to see what's going on in new technologies in critical areas of the aircraft and what's going on in different organisations, and then work together to promote the aircraft as a product, address societal needs, and promote the aircraft industry at European level.’
In terms of industrial achievement for European aircraft manufacturing he adds: ‘this project helps ensure that we have enough maturity to enable highly integrated structures to be manufactured in one shot using composite materials, reducing the cost of manufacturing processes as well as the lead time. This way of integrating functionality and using composite materials allows us to significantly reduce the weight of the winglet. Additionally, the winglet’s morphing capability allows us to improve aerodynamic efficiency at aircraft level, reducing drag and increasing the performance of the aircraft with a positive impact on the fuel burn rate.’
Commenting on these benefits, Aernnova's Dr. Castillo refers to the fact that the EU's strategy of going climate-neutral by 2050 ‘is a challenge that requires extra research and technology efforts and collaboration of the European aeronautics value chain. Clean Sky is very important for this purpose. The opportunity to integrate and mature technologies, all the way from low TRL studies to ground and flight demonstrators, is a high added value for all the partners. Clean Sky is part of a coherent roadmap of technological and operational solutions needed to achieve this long term EU strategy. Clean Sky provides a long term basis that can balance the required flexibility with the timely delivery of key enabling demonstrators. Furthermore, different aircraft platforms require different solutions and this is enabled by the Clean Sky formula and by collaboration across the value chain.’