In fact, a start had already been made with FANPAC, a relatively modest project initiated by Rolls Royce in the UK in 1993 and designed to provide greater understanding of fan noise generation mechanisms in advanced aero-engines. FANPAC (Aeroacoustics Methods for Fan-Noise Prediction and Control) identified the possibility to achieve a reduction of up to 5 dB under certain conditions, through source control, the use of acoustic liners and the adoption of active noise control technologies.

Armed with these results, the FANPAC consortium members, together with a number of new potential partners, compiled a far more broadly based follow-up proposal involving some 40 participants. Presented in 1995, this envisaged a single seven-year programme, the Environmental Noise Reduction Initiative, dealing mainly with engine/nacelle design improvements. In its original form, however, this was deemed to be too cumbersome and unmanageable, and was therefore not accepted for funding by the EU.

The group's response was to assemble a taskforce, chaired by propulsion equipment specialist SNECMA of France, to analyse the reasons for the rejection, examine other noise and emission projects then underway, and identify the optimal method to manage such a large workload. Its report formed the basis for a new set of proposals designed to match the ICAO's three-point recommendations for action. The number of partners was reduced and the planned tasks divided into a series of discrete but communicating projects. This revised concept was generally agreed to offer a more focused and flexible means of tackling the inter-related questions of noise reduction, and EU approval duly followed.

The X-noise technology cluster was launched at the beginning of 1998, with overall co-ordination by SNECMA and the participation of leading industry players, research institutes and universities. The initial three-year phase, due to be completed by December 2000, is supported by funding of 27 million, 60% of which is provided by the EU and 40% by the European airframe and aero-engine industry. This will be followed by a four-year integration phase, known as SILENCER, worth around 100 million.

The overall initiative currently comprises three industry-led projects: RESOUND (Reduction of Engine Source noise through Understanding and Novel Design), RANNTAC (Reduction of Aircraft Noise by Nacelle Treatment and Active Control) and RAIN (Reduction of Airframe and Installation Noise), together with the purely research-oriented DUCAT investigation of duct acoustics and radiation. Close links are established with SOURDINE (Study of Optimisation procedures for Decreasing the Impact of Noise around airports), an examination of take-off and landing procedures supported by the European Commission's DG Transport.

Regular contact is also maintained with two other DG Research-supported networks: EEFAE (Efficient and Environmentally Friendly Aeroengines) and TRA3 (Aerospace Aerodynamics), as well as with a number of other national consortia.
RESOUND, led by Rolls Royce's Aerospace Group, is seeking new ways to limit noise at source, as a precursor to the design of derivative and new aero-engines that are 4 dB quieter than those currently entering service. Options being explored at model- and full-scale include novel technologies for the design of fans, combustors and turbomachinery, together with the use of auxiliary aeroacoustic control devices.

The goal of RANNTAC, under prime contractor Aerospatiale Matra, is to support this effort through the development of advanced engine nacelle concepts. This research will provide a foundation for future nacelle designs incorporating a wide range of new sound-absorbing liners, air intake shapes and in-duct active noise control systems.

RAIN, headed by British Aerospace, targets the influence of the airframe itself on the overall noise radiation from an aircraft. As well as modifying engine noise through diffraction, refraction and reflection, the airframe also acts as a strong source of additional noise radiation from components such as the undercarriage and high-lift wing devices. In fact, during a landing approach, airframe noise can equal that of the engines themselves.

Under RAIN, advanced analysis tools are being developed for accurate prediction of the noise contributions arising from individual airframe components and through installation effects on the main engine components. Work is also proceeding on the identification of practical approaches to reduce noise, to provide confidence that the tools will be of real value to designers in realising the full operational efficiency, and hence competitiveness, of tomorrow's aircraft.

The associated DUCAT project is a basic research study spearheaded by the Netherlands' National Aerospace Laboratory, with the aim of deriving computer models to describe acoustic behaviour and guide liner optimisation in complex nacelle geometries.

Although strictly part of a separate programme, SOURDINE is closely linked to X-noise. Airport procedures were a major topic at the first of three annual consortium workshops, and a successor project will probably be fully integrated into the next phase.

Annual conferences have disseminated the group's findings to a wide audience, helping to strengthen the initiative by attracting even more new candidate countries and organisations. With all efforts directed towards a common end, X-noise has already led to the framing of a technology platform supported by 14 EU countries as the basis of a proposal for the forthcoming SILENCER phase.

Co-ordinator Dominique Collin of SNECMA considers that the cluster approach brings multiple benefits beyond the prime objective of boosting European competitiveness. Underpinned by an agreed strategy, it offers an ideal means of bringing together science, industry and the regulatory authorities - opening the door to fruitful dialogue within the EU. Moreover, it will add weight to the European viewpoint in global deliberations such as the CAEP 5 meeting to be held in 2001, which must balance the needs of the environment with the continuing survival of a successful aeronautical industry.