Aviation has delivered immense social and economic benefits to mankind. In Europe, turnover in the aeronautics sector exceeded €65 billion in 1999 and 400,000 people are directly employed in the industry. In response to our environmental responsibilities, the Advisory Council for Aeronautics Research in Europe (ACARE) has set strict objectives regarding noise reduction, fuel efficiency and emissions reduction. In parallel, EU directives have been put in place to control these parameters. If the EU aeronautics sector cannot meet these challenges, market share will be lost to US manufacturers. The outputs of ALLEGRA will result in pragmatic, validated solutions which will reduce noise, emissions and improve fuel consumption. These solutions will be developed in conjunction with an EU aircraft manufacturer (Alenia) to ensure feasibility and to reduce time to implementation.
During landing approach, when engines are operating at low thrust, the noise of the airframe contributes strongly to the overall noise signature of modern aircraft. Airframe noise is generated by airflow around components of the aircraft. The main sources of airframe noise are therefore the high drag elements such as landing gears and also the high lift devices on the wings. For larger aircraft, it is the landing gear noise that dominates.
This project will therefore focus on the design and test of Main and Nose Landing Gear noise reduction concepts. ALLEGRA has put together a consortium which comprises of a well known aero-acoustic wind tunnel company and some SME’s from around Europe with specific competence on landing gear design, manufacturing and structural analysis. In addition two of the EU’s most distinguished universities will take the lead in computational aeroacoustics, noise measurements and data analysis. All partners have participated and delivered in EU projects, in some cases extensively including coordination.
The ALLEGRA project has been developed in response to the requirements of the European Clean Sky Joint Technology Initiative to assess low noise technologies applied to both nose and main landing gear architectures. ALLEGRA consisted of a consortium of well recognized universities (Trinity College Dublin, KTH Sweden), a well-known aeroacoustic wind tunnel company (Pininfarina SPA) and SME partners (Eurotech, Teknosud) from around Europe supported by a leading landing gear manufacturer (Magnaghi Aeronautica). This group has well demonstrated competencies in landing gear design and manufacturing, computational aeroacoustics, noise measurements and data analysis. The negative impact of aircraft noise includes effects on population’s health, land use planning and economic issues such as building restrictions and operating restrictions for airports. Thus, the reduction of noise generated by aircraft at take-off and approach is an essential consideration in the development of new commercial aircraft.
The key issues associated with the landing gear noise problem are:
- Landing gear contributes to approximately 30% of the overall noise emission of the aircraft during approach phase
- The noise signature is broadband in nature covering frequencies from approximately 90Hz to 4KHz. The annoyance level associated with noise within this frequency range is high for exposed communities
- Landing gear consists of numerous structures, surfaces and components which are generally not optimised from an aeroacoustic point of view. Turbulence from these non-optimised components of the landing gear is a direct noise source
- The wake of the landing gear structures can interact with other airframe components and generate an indirect noise source.
In the past full-scale models of landing gear have rarely been tested due to the large test facilities required. Most experimental airframe noise research has been performed using small-scale models. This leads to great difficulty when using model-scale results for full-scale noise predictions due to the lack of details in the geometrical modelling. One of the significant contributions of ALLEGRA is that a full representation of the landing gear detail and associated structures (e.g. bay cavity, bay doors, belly fuselage etc.) have been included and addressed at a realistic scale. The nose landing gear is designed at full scale and the main landing gear at half scale.
All technical and scientific objectives of the project have been met. The results of the two wind tunnel test campaigns have been analysed and the best performing low noise technologies ranked and identified.