Aircraft noise 247935 225376828 2008-07-13T10:39:07Z Ahunt 253891 image added {{Citations|date=May 2008}} [[Image:Qantas b747 over houses arp.jpg|thumb|right|[[Qantas]] [[Boeing 747-400]] passes close to houses on the boundary of [[London Heathrow Airport]], [[England]]]] [[Image:GrummanAA-5BTigerInFlight01.jpg|thumb|right|Small [[general aviation]] aircraft produce localized aircraft noise]] [[Image:RotorwayExec01.JPG|thumb|right|[[Helicopter]] main and tail rotors produce aerodynamic noise]] '''Aircraft noise''' is defined as [[sound]] produced by any aircraft on run-up, taxiing, take off, over-flying or landing. Aircraft noise is a significant concern for approximately 100 square kilometers (65 square miles) surrounding most major airports. Aircraft noise is the second largest (after [[roadway noise]]) source of [[environmental noise]]. While [[commercial aviation]] produces the preponderance of total aircraft noise, [[private aviation]] and [[military]] operations also play a role. It is usually measured in ''[[Decibels]]''. Take-off of aircraft may lead to a sound level of more than 100 [[dBA|decibels]] at the ground, with approach and landing creating lower levels. Since aircraft landing in inner-city [[airport]]s are often lower than 60 meters (200 ft) above roof level, a sound level above 100 dBA can be realized. ==Mechanisms of sound production== A moving aircraft including the [[jet engine]] or [[propeller]] causes compression and rarefaction of the air, producing motion of air molecules. This movement propagates through the air as pressure waves. If these pressure waves are strong enough and within the audible [[frequency]] spectrum, a sensation of hearing is produced. Different aircraft types have different noise levels and frequencies. The noise originates from three main sources: *Aerodynamic noise *Engine and other mechanical noise *Noise from aircraft systems ===Aerodynamic noise=== Aerodynamic noise arises from the airflow around the aircraft [[fuselage]] and control surfaces. This type of noise increases with aircraft speed and also at low altitudes due to the density of the air. Jet-powered aircraft create intense noise from [[aerodynamic]]s, which is typically [[broadband]]. Low flying, high speed military aircraft produce especially loud aerodynamic noise. The shape of the nose, windshield or [[canopy (aircraft)|canopy]] of an aircraft affects the sound produced. Much of the noise of a propeller aircraft is of aerodynamic origin due to the flow of air around the blades. The [[helicopter]] main and tail rotors also give rise to aerodynamic noise. This type of aerodynamic noise is mostly low frequency determined by the rotor speed. Typically noise is generated when flow passes an object on the aircraft, for example the wings or landing gear. There are broadly two main types of airframe noise: *Bluff Body Noise - the alternating vortex shedding from either side of a bluff body, creates low pressure regions (at the core of the shed vortices) which manifest themselves as pressure waves (or sound). The separated flow around the bluff body is quite unstable, and the flow "rolls up" into ring vortices - which later break down into turbulence.<ref name="bluff"> {{cite web |url = http://www2.eng.cam.ac.uk/~acf40/research_ov.htm |title =Aircraft Airframe Noise - Research Overview |accessdate = 2008-07-13 }}</ref> *Edge Noise - when turbulent flow passes the end of an object, or gaps in a structure (high lift device clearance gaps) the associated fluctuations in pressure are heard as the sound propagates from the edge of the object (radially downwards).<ref name="bluff"/> ===Engine and other mechanical noise=== Much of the noise in propeller aircraft comes equally from the propellers and aerodynamics. Helicopter noise is aerodynamically induced noise from the main and tail rotors and mechanically induced noise from the main gearbox and various transmission chains. The mechanical sources produce narrow band high intensity peaks relating to the rotational speed and movement of the moving parts. In [[computer model]]ling terms noise from a moving aircraft can be treated as a [[line source]]. Aircraft Gas Turbine engines (Jet Engines) are responsible for much of the aircraft noise during takeoff and climb. However, with advances in noise reduction technologies - the airframe is typically more noisy during landing.{{Fact|date=May 2008}} The majority of engine noise is due to Jet Noise - although high bypass-ratio turbofans do have considerable Fan Noise. The high velocity jet leaving the back of the engine has an inherent shear layer instability (if not thick enough) and rolls up into ring vortices. This of course later breaks down into turbulence. The SPL associated with engine noise is proportional to the jet speed (to a high power) therefore, even modest reduction s in exhaust velocity will see a large reduction in Jet Noise.{{Fact|date=May 2008}} ===Noise from aircraft systems=== Cockpit and cabin [[pressurisation]] and conditioning systems are often a major contributor within cabins of both civilian and military aircraft. However, one of the most significant sources of cabin noise from commercial jet aircraft other than the engines is the Auxiliary Power Unit (or APU). An Auxiliary Power Unit is an on-board generator used in aircraft to start the main engines, usually with compressed air, and to provide electrical power while the aircraft is on the ground. Other internal aircraft systems can also contribute, such as specialised electronic equipment in some military aircraft. ==Annoyance effects== Lesser intensities of noise are produced for cruising velocities, mainly due to the altitudes of operation. This noise is more clearly heard in countryside settings where this noise can be intrusive even if much less in amplitude (say approximately 45 decibels). Landing aircraft descend on a three degree glide path towards an aiming point approximately 300 meters from the runway threshold. This places them at 60 meters (200 ft) above the ground at about 1200 meters (4,000 ft) from the aiming point or 900 meters (3,000 ft) from the start of the runway. This distance is usually outside the airport fence. Departing aircraft normally are over 150 meters (500 ft) above the ground before crossing the end of the runway. ==Health effects of aircraft noise== {{main|Noise health effects}} The annoyance effects of aircraft noise are widely recognized; however, aircraft noise is also responsible for a significant amount of hearing loss as well as a contributor to a number of diseases. Only in the early 1970s did aircraft noise become a widespread topic of concern in the U.S. and federal regulations began to recognize the significance of abating these impacts in the vicinity of major commercial airports. High levels of aircraft noise that may exist near major commercial airports are known to increase [[blood pressure]] and contribute to [[hearing loss]]. Some research indicates that it contributes to [[heart disease]]s, [[immune]] deficiencies, [[neurodermatitis]], [[asthma]] and other stress related diseases. Further research is being carried out to better understand these effects. Research indicates that hearing loss is less a product of aging than a result of exposure to transportation related noise (Rosen, 1965). Any sound louder than normal conversation can damage the delicate hair cells in the [[cochlea]], the structure in the inner ear that converts sound waves into [[auditory nerve]] signals. Initially damage to the cochlea may be temporary, but with repeated exposure, the damage becomes permanent and [[tinnitus]] may develop. More recently the [[Centers for Disease Control]] and Prevention's (CDC) National Center for Environmental Health (NCEH) conducted an analysis to determine the prevalence of hearing loss among children using data collected from 1988-1994 in the Third National Health and Nutrition Examination Survey. The analysis indicates that 14.9% of U.S. children have low or high frequency hearing loss of at least 16 dB hearing level in one or both ears. From research of the [[National Institutes of Health]], roughly 65 million Americans are exposed to sound levels that can interfere with their function at work or disrupt sleep, and 25 million are exposed to [[health risk]] ([[cardiovascular]], [[immunological]], etc.) from environmental noise. ==Noise mitigation programs== {{main|Noise mitigation}} In the United States, since aviation noise became a public issue in the late 1960s, governments have enacted legislative controls. Aircraft designers, manufacturers, and operators have developed quieter aircraft and better operating procedures. Modern high-bypass [[turbofan]] engines, for example, are quieter than the [[turbojet]]s and low-bypass turbofans of the 1960s. First, FAA Aircraft Certification achieved noise reductions classified as 'Stage 3' aircraft; which has been upgraded to 'Stage 4' noise certification resulting in quieter aircraft. This has resulted in lower noise exposures in spite of increased traffic growth and popularity. In the 1980s the [[U.S. Congress]] authorized the [[FAA]] to devise programs to insulate homes near airports. While this does not address the external noise, the program has been effective for residential interiors. Some of the first airports at which the technology was applied were [[San Francisco International Airport]] and [[San Jose International Airport]] in California. A computer model is used which simulates the effects of aircraft noise upon building structures. Variations of aircraft type, flight patterns and local meteorology can be studied. Then the benefits of building retrofit strategies such as roof upgrading, window [[insulated glazing|glazing]] improvement, fireplace baffling, caulking construction seams can be evaluated.(Hogan, 1984). Another idea to reduce aircraft noise on communities is [[floating airport]]s which would be situated many miles out to sea. There are major drawbacks to this solution including expense, time and inconvenience to travelers in reaching such an airport. This includes the inability to integrate at-sea-airports with transport networks or proximity to business and cargo infrastructure. === Night flying restrictions === At [[Heathrow Airport|Heathrow]], [[Gatwick Airport|Gatwick]] and [[Stansted Airport]] in the UK, and [[Frankfurt Airport]] in Germany, [[night flying restrictions]] apply to reduce noise exposure at night.<ref name="DFT"> {{cite web|url = http://www.dft.gov.uk/press/speechesstatements/statements/nightflyingrestrictionsathea5940|title =Night flying restrictions at Heathrow, Gatwick and Stansted Airports|accessdate = 2008-07-12|last = Dept for Transport|authorlink = |year = 2006|month = June}}</ref><ref name="DFT2"> {{cite web|url = http://www.dft.gov.uk/consultations/archive/2005/nrheahtgatst/nightrestrictionsatheathrowg1775?page=19|title =Night restrictions at Heathrow, Gatwick and Stansted (second stage consultation)|accessdate = 2008-07-12|last = Dept for Transport|authorlink = |year = undated}}</ref> ==References== {{reflist}} *C. Michael Hogan and Jorgen Ravnkilde, ''Design of acoustical insulation for existing residences in the vicinity of San Jose Municipal Airport'', [[January 1]] [[1984]], FAA grant funded research, ISBN B0007B2OG0 *''U.S. Noise Control Act of 1972'' United States [[Code]] Citation: 42 U.S.C. 4901 to 4918 *S. Rosen and P. Olin, ''[[Hearing loss]] and [[coronary heart disease]], Archives of Otolaryngology'', 82:236 (1965) ==See also== *[[Aviation and the environment]] *[[Electric airplane]] *[[Hush kit]] *[[Hearing impairment]] *[[Helicopter noise reduction]] *[[Noise barrier]] *[[Noise pollution]] *[[Noise regulation]] *[[Tinnitus]] ==External links== *[http://www.fican.org/ Federal Interagency Committee on Aviation Noise (FICAN)] *[http://www.aef.org.uk/ Aviation Environment Federation (AEF)] *[http://www.soundinitiative.org/ Sound Initiative: A Coalition for Quieter Skies] *[http://airportnoisereport.com/ A weekly newsletter on litigation, regulations, and technological developments] *[http://www.aviation-noise.org/ National Organization to Insure a Sound-controlled Environment(NOISE)] *[http://www.dft.gov.uk/pgr/aviation/environmentalissues/Anase/ Attitudes to Noise from Aviation Sources in England (ANASE)] Study published by the United Kingdom [[Department for Transport]] [[Category:Aircraft|Noise]] [[Category:Noise pollution]] [[de:Fluglärm]] [[fi:Lentomelu]]