Airframe noise

Citation

Scarpa, F. (2001), "Airframe noise", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 3. https://doi.org/10.1108/aeat.2001.12773cag.001

Airframe noise

Airframe noise

Keywords: Internet, Noise levels, Aircraft

During the last Community Aeronautical Days in Hamburg (http://europa.eu.int/comm/growth/aeronautics-days/), the issues related to airframe noise and its impact on social and technological prospective of growth in Europe and North America have been extensively discussed. With a forecasted annual growth in civil traffic around the 5 per cent (and the consequent doubling of the current traffic volumes in 20 years), the issue of noise coming from planes in approach phases and flying over urban communities implies technological and political measures which could affect the industrialised societies for the next years.

The Web site of the European Commission (http://europa.eu.int/comm/research/growth/gcc/in-action-aircraft-noise.html) gives an overview of the problem, and explains how the different international institutions (ICAO and NASA) have tackled the issue. At the same time the Web site gives a general view on the European projects (like RANNTAC and SOURDINE, to name only two) devised during the last years to investigate aircraft external noise problems. A .PDF file showing the technology roadmaps for power plants and airframe noise reduction devised during the projects can be downloaded from the same site.

The framed ICAO Environmental Protection Web site (http://www.icao.int/cgi/goto_atb.pl?icao/en/env/overview.htm) gives a description of the ICAO's milestones in aircraft noise reduction, from Chapter 2 Annex 16 until the current discussions on future issues held by the Committee on Aviation Environmental Protection (CAEP), whose activities are described following the correspondent URL. The topic is really "hot", especially for urban communities: just have a look at Web sites like the HACAN one (Heathrow Association for the Control of Aircraft Noise: http://www.hacan.org.uk), to have a taste about the implications that not sufficiently addressed noise issues could have.

To understand the airframe noise technicalities, a primer in acoustics (and aeroacoustics in particular) is needed. A good start is represented by the Acoustics & Vibration WWW Virtual Library (http://www.ecgcorp.com/velav/). More than an online textbook, the Web sites provide good sources of links, like the ones to the Fast Noise and Information in the UK (http://www.noisenet.org). This Web site is really well structured, with well-explained introductory concepts on sound, noise physics, sound levels and powers. Other information on basic acoustics and vibration are given in the Acoustics FAQ (http://www.faqs.org/faqs/physics-faq/acoustics/), without graphics involved. Another interesting source of information (and definitely one of the best of the category) is the Active Noise Control FAQ (http://users.erols.com/ruckman/ancfaq.htm). Note that you can download the entire FAQ in a text file (useful for later printing).

Information on aeroacoustics impact on aircraft design are contained in the Aeronautical Technologies for the Twenty-First Century book, which can be freely browsed at http://www.nap.edu/books/0309047323/html/109.html. An introduction to airframe noise concepts is given in the Advanced Topics in Aerodynamics Web site (http://aerodyn.org/), created and maintained by Dr Antonio Filippone from UMIST. The site is well structured and easy to browse, and hosts a page on aerodynamic noise and aeroacoustics with the proper literature references.

Examples of computational aeroacoustics simulations on high-speed unsteady flow over airfoils are given in the NASA's Aeronautics Enterprise home page (http://larcpubs.larc.nasa.gov/randt/1994/7-SectionB5.www7.html). A consistent number of online documentation on aeroacoustics research activities can be found at departmental Web pages like the one of the University of Eindhoven (http://www.win.tue.nl/~sjoerdr/ceas-asc/HIGHLIGHTS1999_2.pdf).

An AIAA paper on investigations of airframe noise can be found at http://techreports.larc.nasa.gov/ltrs/PDF/1998/aiaa/NASA-aiaa-98-2224.pdf. The paper describes the numerical and experimental activities on airframe noise mechanism associated with high lift devices at NASA Langley Research Centre (LaRC).

General information on noise and hearing loss issues can be found at the National Library of Medicine (http://text.nlm.nih.gov/nih/cdc/www/76txt.html), with the complete statement of the National Institutes of Health Consensus Development Conference, January 22-24 1990. The document is in text form. More information on Aerospace Medicine could be found in http://www.faa.gov/avr/AAM/BIB.HTM, where a comprehensive list of publications is given. A most important source of information is the Aviation Noise Effect Paper of the Federal Aviation Administration (March 1985), which can be found at http://www.nonoise.org/library/ane/ane.htm. The document gives the definition of noise metrics and levels, human response, hearing loss, protection and technicalities in aircraft operations – definitely an essential source of information for airframe noise issues. The document is in html form and is completely printable.

Another source of accessible and general information on social and technical aircraft noise issues (and how to communicate them in plain language to non-technical people) is the one provided by the Australian Department of Transport and Regional Services in the discussion paper: "Expanding ways to describe and assess aircraft noise" (http://www.dotrs.gov.au/airports/discussionpapers.pdf). The paper describes the evolution of the ANEF (Australian Noise Exposure Forecast) map concept, the creation of merit figures to quantify the aircraft movements and noise levels, and provides an index assessing the total noise level on airports, and further studies for the future.

Other information on noise footprints around airport areas could be found in the DETR home page (see http://www.aviation.detr.gov.uk/nec99/index.htm for noise maps around Heathrow, Gatwick and Stansted in 1999). The same Web site hosts the final report of the ANMAC workgroup on Noise from Arrival Aircraft, published 13 March 2000 (http://www.aviation.detr.gov.uk/anmac/index.htm). The report identifies the causes of variability of noise in initial approach, the parameters involving noise in final approach phase, and good practice and recommendations (descent clearance and ATC improved practices). Another important source of information related to airframe and airport noise is the Web site of the FICAN (Federal Interagency Committee on Aviation Noise: http://www.fican.org/). The Web page hosts a significant resource of reports, e.g. "Effects on aviation noise on awakenings from sleep", http://www.fican.org/pages/sleepdst.html, where dose-response curves are proposed to predict the percent of the exposed population expected to be awakened by single event noises around airports). Other information of national and federal policies on noise abatement and environmental compatibility could be found at the home page of the Volpe Centre (http://www.volpe.dot.gov/infosrc/strtplns/nstc/aviatrd/chap7.html), an American fee-for-service organisation within the US Department of Transportation. The FAA provides a milestone document on noise abatement policies at the Web page http://aee.hq.faa.gov/Noise/Index1.html. In this important document the wealth of technical and jurisdictional information on noise abatement issues is extensively developed. Complex governmental actions, at federal and local levels, with the co-operation of airport authorities and air carriers, are suggested and described. The document has naturally a special American flavour, but the suggested policies have a large echo in other white papers from other institutions. The Web page is in text format with URLs for different chapters.

A mixture of device applications, flight and ATC operations, together with local and international environmental policies, gives solutions of airframe noise problems. Muffling aeroengines is one of the solutions especially prospected to Stage 2 aircraft carriers. The explanation of the hushkit (muffler) concept can be found at http://www.abshushkit.com/hushkit.htm and http://www.wenet.net/~hpb/hushkit.html. Actually, the insertion of a mixer allows the cool exhaust fan air with the hot core exhaust, with a consequent reduction of the jet noise. The quarrel between EU and US governments about the effectiveness (and legal grounds) of the solution is well-described by different sites, like http://cgi.ttd.org/foxweb.exe/ttddview?487I, http://www.american.edu/projects/mandala/TED/eunoise.htm and http://ufcna.com/hushkit.html. This last site gives a general recapitulation of the American and (especially) European positions, but it requires a good brush up of French to browse the page. In any case, at Transport Canada homepage (http://www.tc.gc.ca/aviation/AERODRME/noise/listhk.htm) you can find a list of immatriculation numbers related to large aircraft equipped with hushkits. The design of novel concepts of high lift devices and undercarriage fairing is a significant step towards noise reduction in the approach phase. European BRITE/EURAM projects (like the RAIN in http://dbs.cordis.lu/cordis-cgi/srchidadb?ACTION=D&SESSION= 51372000-7-4&DOC=2&TBL=EN_PROJ &RCN=EP_RCN:39781&CALLER= PROJADVANCEDSRCH) have been setup to investigate engineering solutions in classical civil airliner configurations. A new engineering solution proposed consists also of the tip fence concept (http://ctoserver.arc.nasa.gov/techopps/tipfence.html), and improved designs of fan tips in aeroengines (http://larcpubs.larc.nasa.gov/randt/1995/SectionB1.fm531.html). Future aircraft layouts are being studied, like over-the-wing mounted engines (http://www-psao.grc.nasa.gov/Library/Abstracts/ISABE.html), showing that consistent noise shielding effects on the ground could be achieved with these solutions, although more structural considerations should be made for a complete assessment. The acoustics and noise reduction capabilities of high-bypass ratio turbofans are well illustrated in the ONERA Web site (http://www.onera.fr/dsna-en/brutur/gdtxdilu.html) and in the Japanese National Aerospace Laboratory (http://www.nal.go.jp/ndivision/propul/english/ap-anc/anc/anc.html). The latter Web page gives a good overview of potential active noise control techniques applied to turbofans, with good quality pictures. Another way to alleviate airframe noise in take-off and landing phases is the modification of extisting flight procedures. In http://www.daz-technology.demon.co.uk/steep/steep.html you can find an interesting paper from R.E. Caves and D.P. Rhodes from Loughborough University titled: "Steeper approaches: a contribution to alleviating airport environmental and physical capacity constraints". The paper also investigates the influence of steeper approach angles in aircraft design, such as fuselage diameters, wings and weight characteristics, engine layouts and economics. Several drawings are provided, together with a reference list – a highly recommended Web page to browse. The steeper approach phase is also described in the aircraft operating procedures paragraph of the FAA Aviation Noise Abatement Policy (http://www.netvista.net/~hpb/faanap-6.html). Other information on operational noise measurement and flight policy procedures can be found in the EU Consultation Paper on the Limitation of Impact of Noise from Air Transport (http://www.xs4all.nl/~rigolett/ENGELS/consult.htm). The Web page is in a very plain graphical format, but contains the text of the entire white paper.

Finally, if you are the owner of a light aircraft or ULM, you can find some advice (and material) on fuselage soundproofing methods in http://www.soundproofing.org/infopages/soundprf.html. The Web page is the online version of the booklet "Soundproofing light aircraft" by Bill Nash, a very useful and comprehensive source of information for the technician and the air enthusiast.

Fabrizio Scarpa