Clean Sky’s T-WING: In conversation with CIRA
The design, manufacture and qualification of an innovative wing for the Next Generation of Civil Tilt-Rotor (NGCTR) is the remit of Clean Sky’s T-WING project which kicked off in February 2018. Coordinated by CIRA, the Italian Aerospace Research Centre, it is currently tackling a complex set of technical and environmental challenges with stringent targets. Just one year into its six year timeline, Luigi Di Palma, Coordinator of T-WING, and Marika Belardo, T-WING’s Chief Engineer, discuss the magnitude of the project and the path ahead.
Design, manufacture and qualification of an innovative wing for the NGCTR are just the start of T-WING’s ambitions. The project also aims to study the scalability potential of the proposed solutions for the exploitation of technologies developed within the project, while the design and analysis activities focus on reducing weight and maximising safety and manufacturing efficiency in compliance with a flight condition approval plan (based on CS-25, CS-29, plus other airworthiness requirements). The project will also provide technical support in activities related to attaining the ’Permit to Fly’, and provide support during the assembly and installation phases of the NGCTR prototype.
Needless to say, this formidable project checklist has necessitated pulling together a diverse mix of specialist aeronautical resources and entities to address the project’s many challenges.
”CIRA is the main coordinator of the T-WING project but of course it’s not alone in this venture because we, as a research centre, don’t manufacture anything apart from some specific demonstrators of enabling technologies. So the T-WING proposal is based on a strong consortium of mainly Italian companies” says Luigi Di Palma, Coordinator of T-WING at CIRA.
These include Magnaghi Aeronautica (a longestablished company specialising in landing gear developments); Salver SpA, which worked on the development of the flaps and spoilers of the Bombardier C Series (now rebranded as the Airbus A220); Università di Napoli di Federico II, which has specialist knowledge of regional aircraft development; Step Sud Mare Srl, focused on design and crashworthiness; and Officine Meccaniche Irpine Srl which is responsible for manufacturing the titanium parts and the tools and jigs for the assembly of the control surfaces on the wing of the NGCTR. Hamburg-based IBK Innovation GmbH’s role centers around their research specialism in aeroelastic studies, because the Tilt-Rotor is a machine in which aeroelastic phenomena play a crucial role, especially with respect to the wing design.
”The concept of the wing is conceived directly from aeroelastic considerations” explains Marika Belardo, T-WING’s Chief Engineer at CIRA. ”In T-WING we’ve inverted the design approach, because this class of vehicle is very sensitive to aeroelasticity, so the approach is to start with aeroelasticity and to derive from it the minimum requirements as regards the stiffness of the structure. This is an innovative design methodology, but there are also many other innovations in the project – the wing has an innovative architecture and innovative manufacturing technologies and materials will be considered for the wing, where we’ll be looking at using additive manufacturing”.
This level of innovation required in T-WING is spurred by the societal need to enhance mobility options within Europe as well as to improve Europe’s industrial competitiveness in aeronautics. The wing will be an integral component of Leonardo’s Tilt-Rotor, which, Belardo says ”will be a potential candidate to be used in areas where big landing sites are not present. It has vertical takeoff and landing capabilities so it behaves like a helicopter in the landing and takeoff phases, but after conversion it behaves like an aircraft in the horizontal regime so you have the performance of both machines in one machine, and can reach places where aeroplanes cannot go. At the same time you will have the capability to cover a greater distance than you can with a helicopter, and with better performance”.
Di Palma adds that ”in the US, Uber and Amazon are investing in the development of electric unmanned Tilt-Rotors to improve mobility, and it is time for Europe to investigate this sector.
The NGCTR could reduce some disadvantages of current aeronautical mobility because there are some regions in Europe – for example in Norway or Sweden – where there isn’t space for airport infrastructure, so vertical takeoff and landing vehicles are one of the best candidates to do that”.
One of the many ambitions of the T-WING project is to investigate the possibility of manufacturing flight control surfaces using recyclable thermoplastics. But Di Palma points out that although in principle thermoplastics are recyclable, reused plastics have structural limitations: ”There is no standard way to qualify them for flight. Our intention is to develop full control surfaces – like ailerons – using thermoplastics, and this will be a first in aviation, but at this stage we don’t know whether we’ll reach TRL6 with a flight demonstration using thermoplastic control surfaces. But certainly, the manufacturing, the process qualification and full scale structural qualification will be carried out” he says.
Another environmental challenge is noise. ”In T-WING we have a number of activities focused on the noise and the prediction methodologies which have an environmental implication, because to be able to predict the noise with high fidelity level will enable us to have less impact on the environment as regards noise emissions” says Belardo.
But she adds that of no less complexity is the wing’s structural requirements when the unthinkable happens: ”We’re also committed to analysing the crashworthiness of this wing and we have some requirements related to the safety of passengers in case of a survivable crash. It’s quite standard for helicopters but not for aircraft, so in fact this class of vehicle has a specification certification plan which is not a mere mix between that of an aircraft and that of a helicopter, but it’s tailored for the specific machine. There’s been a big effort from Leonardo’s side to put together a specific certification plan. Some requirements are completely new and are a tailored mix of CS 25 and CS 29”.
And some of those requirements take the project into unchartered territory. For example, part of the issue at hand is that conventional helicopters don’t normally have fixed wings (the rotor behaves like a wing instead), but the Tilt- Rotor does have a fixed wing which incorporates fuel storage. Therefore a part of the vehicle’s fuel supply is located over the fuselage on top of where the passengers sit. ”So we have to guarantee that in case of a survivable crash – which is demonstrated typically by a drop test from a height of 50 feet – that there is no risk of crushing of the fuselage under the inertial forces of the wing mass nor fire due to puncture of the fuel tanks inside the wings” says Belardo. ”This is an additional requirement which is not present in aircraft but it is required for helicopters”.
T-WING started its Preliminary Design Review in November and is currently beginning some demonstrations, at manufacturing level, of the capability to produce the non-conventional architecture of the wing which, from a structural aeronautics point of view, has to incorporate much more than a conventional aircraft wing. Beyond its aerodynamic performance and fuel storage capability it has to hold all the systems among them the interconnecting drive shaft – ”inside the wing is a big shaft which is very long and this shaft also has some peculiar characteristics, so we have to cover all these aspects from a technical point of view. The wing will host a lot of things, so it’s quite a challenge” says Belardo.
Within the broader European context, CIRA’s Di Palma points out that all these many technical challenges all bode well for the fortunes of Europe’s aviation: ”This is the opportunity given by Clean Sky to work on something that’s not only an innovative demonstrator for flight but also it’s one of the ways to improve the competitiveness of the European aeronautics sector. Usually in aviation, development of new aircraft is based on pre-existing knowhow because OEMs have to minimise development costs. There is of course some innovation in every new aircraft but not as much breakthrough innovation as is made possible by project funding from Clean Sky. And although T-WING will result in a prototype, not a final product, for Europe this and other clean demonstrators in Clean sky represent a breakthrough in innovation as regards new product development, so for European aviation it’s a great opportunity” says Di Palma.