manufacturers and operators throughout the world are facing increasing
pressure to reduce levels of environmental noise pollution. This arises
both from public expectation of an improved quality of life and from the
need to compensate for the expected growth in air traffic. X-noise, a
cluster of research projects involving 32 organisations in nine European
countries, aims to deliver an aircraft noise abatement of 6 dB over eight
years. The size of ground areas affected by given noise levels will thus
be cut by more than half.
the International Civil Aviation Organisation (ICAO), the body responsible
for setting international standards, initiated a major review by its Committee
for Aviation Environmental Protection with the objective of progressively
imposing more stringent noise limits. CAEP recommended a three-pronged
strategy embracing the development of novel technology, a review of operational
procedures and an objective assessment of environmental impact.
USA, a $200 million government-funded research programme led by NASA
(National Aeronautics & Space Administration) has been exploring various
aspects of the problem since 1994.
a co-ordinated strategic approach is essential if European industry is
to match this effort and maintain its competitive position in the global
marketplace. Co-operative effort is necessary to address the issues in
a broader sense than would be affordable under separate proprietary or
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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.
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.
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.
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
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
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
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
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.
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.
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.
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.
project is a basic research study spearheaded by the Netherlands'
Laboratory, with the aim of deriving computer models to describe
acoustic behaviour and guide liner optimisation in complex nacelle
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.
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.
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.
on environmental noise pollution funded under the Growth Programme's
New perspectives for aeronautics key
action revolves around X-Noise, a thematic
network on external noise produced by aircraft. The network is
related projects, including:
- Reduction of Engine Source noise through Understanding and Novel
- Reduction of Aircraft Noise by Nacelle Treatment and Active
- Reduction of Airframe and Installation Noise (BRPR970528)
- An investigation of duct acoustics and radiation (BRPR970479)
- A study of optimisation procedures for decreasing the impact
of noise around airports (AI-98-SC.3043)