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Lightening the load: Clean Sky's ReLOAD successfully concludes

CFD simulation of FTB2 aircraft with spoiler deflected

Clean Sky's ReLOAD (Regional turboprop loads control through active and passive technologies) project, which successfully concluded in March 2019, focused on innovative solutions around the topic of load alleviation on the wing of a regional turboprop aircraft. The project contributes to the Regional Aircraft domain within Clean Sky 2 and was also a precursor to the ongoing Clean Sky PERTURB (Power effects aerodynamics for a regional turboprop) project. Both are led by the Aircraft Research Association (ARA), an independent research and development organisation based in Bedford, UK.

Load alleviation is a concept where devices such as spoilers and ailerons are used to redistribute the forces on the wing during gust events or when turning in a manoeuvre. By alleviating loads, it is possible to design wings in a way that makes them lighter, which has the multiple benefits of reducing fuel burn, cutting emissions, and also reducing turbulence for passengers — all in alignment with Europe's Horizon 2020 ambitions.

‘The reduction of loads on an aircraft wing during gust events and manoeuvres is an active research topic on the global scene,’ says Andrew Peace, chief scientist at ARA and ReLOAD coordinator. ‘As well as the environmental benefits, successful use of load alleviation will lead to reduced operating costs and hence a competitive advantage for those who are first to market and/or who have a technological advantage.’

‘The ReLOAD project, in which Technical University Delft (TUD) was also a partner, looked at the use of spoilers and ailerons for manipulating the load on the wing. The focus was on the Clean Sky Flight Test Bench 2 (FTB2) aircraft, based on an Airbus C295W turboprop, and one aim of the project was to obtain aerodynamic data to inform planned demonstrator flight tests in 2021 and 2023. A second aim was to examine novel spoiler concepts and develop rapid tools, which can be used in future design studies involving spoilers and ailerons, in particular their dynamic effect during gust events and manoeuvres,’ says Peace.

The project analysed both active and passive load control, based on aileron and spoiler deployment. In terms of active control, the aerodynamic characterisation of fixed deflection of each of the control surfaces was assessed at various phases of flight — cruise, take-off, landing with flap deflection. Characterisation was obtained through a combination of computational fluid dynamics (CFD) and wind-tunnel testing (WTT) at the RUAG Large Wind Tunnel facility in Emmen, Switzerland, using a wind-tunnel model that was designed and manufactured within the Clean Sky 2 POLITE project. 

Gust impact on FTB2 aircraft with aileron and spoiler deflected

‘Work in ReLOAD focused on the power-off analysis. Through the use of novel data fusion techniques to combine the CFD and WTT datasets and extrapolate to full scale, the control effectiveness of aileron and spoiler was obtained as a direct input to the permit-to-fly activities of the project's topic manager, Airbus Defence and Space (ADS), on the FTB2,’ says Peace. ‘This combined data gave Airbus a view as to how they could use spoilers and ailerons as load control or load alleviation devices over and above normal use. In addition, dynamic, reduced-order methods were developed to evaluate the performance of ailerons and spoilers as gust load alleviation (GLA) devices. The methodology was shown to be effective by rapid aeroelastic analysis of control surfaces for GLA. For passive load alleviation, a methodology for designing aeroelastically tailored winglets to reduce wing bending loads during gust encounters was developed using unbalanced laminates, with the constraint that the new winglet must also lead to an overall weight reduction. Both these new procedures are capable of being embedded in a framework for future design studies.’

POLITE model with aileron and spoiler deflected in the RUAG wind-tunnel

The implications of the findings of ReLOAD, and the potential implementation of load control and alleviation in future aircraft designs, mean that excessive gust and manoeuvre loads can be avoided. This enables wings with enhanced structural designs that translate into weight savings and reduced fuel burn and emissions. 

An important benefit of the ReLOAD project is to pave the way for Clean Sky's PERTURB (Power effects aerodynamics for a regional turboprop) project, also led by ARA, which started recently and is focused on the aerodynamic characterisation of the FTB2 aircraft, again through a combination of CFD and wind-tunnel testing in real conditions.

‘The benefits to ARA in terms of knowledge gained and the development of technologies and capabilities are clear, but the relationships built with partners and also the topic manager have also been of equal benefit. The partner relationships have greatly assisted the continuity of ARA’s activity in Clean Sky through consortium building, and the relationships with topic managers have given commercial benefit to ARA outside Clean Sky. Also, ARA’s profile within Europe as a research establishment has vastly increased as a result of Clean Sky,’ says Peace.

‘The idea is to use the ReLOAD results in PERTURB because we will have the wind tunnel test and then also some calculations to understand how the aircraft is behaving based on real data coming from the wind tunnel tests,’ says Costin-Ciprian Miglan, project officer for Clean Sky. ‘ReLOAD was useful for European aviation because it is the first project in a series of projects which will contribute to the permit to fly of an important demonstrator. It was not a big project but it's the first project to close within the regional platform.’

Streamlines showing flow over the FTB2 aircraft deflected spoiler