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Aircraft noise pollution refers to noise produced by aircraft in flight that has been associated with several negative stress-mediated health effects, from sleep disorders to cardiovascular disorders. [1] [2] [3] Governments have enacted extensive controls that apply to aircraft designers, manufacturers, and operators, resulting in improved procedures and cuts in pollution.
Sound production is divided into three categories:
Aircraft noise is noise pollution produced by an aircraft or its components, whether on the ground while parked such as auxiliary power units, while taxiing, on run-up from propeller and jet exhaust, during takeoff, underneath and lateral to departure and arrival paths, over-flying while en route, or during landing. 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:
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 modelling 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, such as the buzzsaw noise generated when the tips of the fan blades reach supersonic speeds. However, with advances in noise reduction technologies—the airframe is typically more noisy during landing.[ citation needed ]
The majority of engine noise heard 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 later breaks down into turbulence. The SPL associated with engine noise is proportional to the jet speed (to a high power). Therefore, even modest reductions in exhaust velocity will produce a large reduction in jet noise.[ citation needed ]
Engines are the main source of aircraft noise. [4] The geared Pratt & Whitney PW1000G helped reduce the noise levels of the Bombardier CSeries, Mitsubishi MRJ and Embraer E-Jet E2 crossover narrowbody aircraft: the gearbox allows the fan to spin at an optimal speed, which is one third the speed of the LP turbine, for slower fan tip speeds. It has a 75% smaller noise footprint than current equivalents. [4] The PowerJet SaM146 in the Sukhoi Superjet 100 features 3D aerodynamic fan blades and a nacelle with a long mixed duct flow nozzle to reduce noise. [4]
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 aerodynamics. Low-flying, high-speed military aircraft produce especially loud aerodynamic noise.
The shape of the nose, windshield or 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:
Cockpit and cabin pressurization 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 (APU), 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 specialized electronic equipment in some military aircraft.
Aircraft engines are the major source of noise and can exceed 140 decibels (dB) during takeoff. While airborne, the main sources of noise are the engines and the high speed turbulence over the fuselage. [6]
There are health consequences of elevated sound levels. Elevated workplace or other noise can cause hearing impairment, hypertension, ischemic heart disease, annoyance, sleep disturbance, and decreased school performance. [7] Although some hearing loss occurs naturally with age, [8] in many developed nations the impact of noise is sufficient to impair hearing over the course of a lifetime. [9] [10] Elevated noise levels can create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors. [11] Airport noise has been linked to high blood pressure. [12] Aircraft noise increases risks of heart attacks. [13]
A large-scale statistical analysis of the health effects of aircraft noise was undertaken in the late 2000s by Bernhard Greiser for the Umweltbundesamt, Germany's central environmental office. The health data of over one million residents around the Cologne airport were analysed for health effects correlating with aircraft noise. The results were then corrected for other noise influences in the residential areas, and for socioeconomic factors, to reduce possible skewing of the data. [14]
The German study concluded that aircraft noise clearly and significantly impairs health. [14] For example, a day-time average sound pressure level of 60 decibels increased coronary heart disease by 61% in men and 80% in women. As another indicator, a night-time average sound pressure level of 55 decibels increased the risk of heart attacks by 66% in men and 139% in women. Statistically significant health effects did however start as early as from an average sound pressure level of 40 decibels. [14]
The Federal Aviation Administration (FAA) regulates the maximum noise level that individual civil aircraft can emit through requiring aircraft to meet certain noise certification standards. These standards designate changes in maximum noise level requirements by "stage" designation. The U.S. noise standards are defined in the Code of Federal Regulations (CFR) Title 14 Part 36 – Noise Standards: Aircraft Type and Airworthiness Certification (14 CFR Part 36). The FAA says that a maximum day-night average sound level of 65 dB is incompatible with residential communities. [15] Communities in affected areas may be eligible for mitigation such as soundproofing.
Aircraft noise also affects people within the aircraft: crew and passengers. Cabin noise can be studied to address the occupational exposure and the health and safety of pilots and flight attendants. In 1998, 64 commercial airline pilots were surveyed regarding hearing loss and tinnitus. [16] In 1999, the NIOSH conducted several noise surveys and health hazard evaluations, and found noise levels exceeding its recommended exposure limit of 85 A-weighted decibels as an 8-hr TWA. [17] In 2006, the noise levels inside an Airbus A321 during cruise have been reported as approximately 78 dB(A) and during taxi when the aircraft engines are producing minimal thrust, noise levels in the cabin have been recorded at 65 dB(A). [18] In 2008, a study of Swedish airlines cabin crews found average sound levels between 78 and 84 dB(A) with maximum A-weighted exposure of 114 dB but found no major hearing threshold shifts. [19] In 2018, a study of sound levels measured on 200 flights representing six aircraft groups found media noise level of 83.5 db(A) with levels reaching 110 dB(A) on certain flights, but only 4.5% exceeded the NIOSH recommended 8-hr TWA of 85 dB(A). [20]
Simulated aircraft noise at 65 dB(A) has been shown to negatively affect individuals’ memory and recall of auditory information. [21] In one study comparing the effect of aircraft noise to the effect of alcohol on cognitive performance, it was found that simulated aircraft noise at 65 dB(A) had the same effect on individuals’ ability to recall auditory information as being intoxicated with a Blood Alcohol Concentration (BAC) level of at 0.10. [22] A BAC of 0.10 is double the legal limit required to operate a motor vehicle in many developed countries such as Australia.
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 notably more quiet than the turbojets and low-bypass turbofans of the 1960s. 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. [23]
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 airports where the technology was first 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 glazing improvement, fireplace baffling, caulking construction seams can be evaluated. [24]
Stages are defined in the US Code of Federal Regulations (CFR) Title 14 Part 36. [25] For civil jet aircraft, the US FAA Stage 1 is the loudest and Stage 4 is quieter. [26] Stage 3 was required for all large jet and turboprop aircraft at US civilian airports from the year 2000, [25] and at least Stage 2 for under 75,000 lb (34 t) MTOW jets until December 31, 2015. [26] The previous was Stage 4 for large airplanes, equivalent to the ICAO Annex 16, Volume 1 Chapter 4 standards, while the more stringent Chapter 14 became effective July 14, 2014, and was adopted by the FAA as Stage 5 from January 14, 2016, effective for new type certificates from December 31, 2017, or December 31, 2020 depending on weight. [25]
The US allows both the louder Stage 1 and quiet Stage 2 helicopters. [26] The quietest Stage 3 helicopter noise standard became effective on May 5, 2014, and are consistent with ICAO Chapter 8 and Chapter 11. [25]
Chapter | Year | Ch. 3 Margin | Types [28] |
---|---|---|---|
none | before | none | Boeing 707, Douglas DC-8 |
2 | 1972 | ~+16 dB | Boeing 727, McDonnell Douglas DC-9 |
3 | 1978 | baseline | Boeing 737 Classic, MD-80 |
4 (stage 4) | 2006 | −10 dB | Airbus A320, Boeing 737NG, Boeing 767, Boeing 747-400 |
14 (stage 5) | 2017–2020 | −17 dB | Airbus A320, Airbus A320neo, Airbus A330, Airbus A350, Airbus A380, Boeing 737 MAX, Boeing 757, Boeing 777, Boeing 787 |
At Heathrow, Gatwick and Stansted airports in London, UK and Frankfurt Airport in Germany, night flying restrictions apply to reduce noise exposure at night. [29] [30]
Usage of satellite-based navigation systems can contribute to noise relief, trials in 2013-14 found, though results were not always beneficial due to concentrating flight paths. Changing flight angles and flight paths brought some changes in noise relief for some local people. [31] [32] [ better source needed ]
Modern High bypass turbofans are not only more fuel efficient, but also much quieter than older turbojet and low-bypass turbofan engines. On newer engines noise-reducing chevrons further reduce the engine's noise, [33] while on older engines hush kits are used to help mitigate their excessive noise.
The ability to reduce noise may be limited if engines remain below aircraft's wings. NASA expects a cumulative 20–30 dB below Stage 4 limits by 2026–2031, but keeping aircraft noise within airport boundaries requires at least a 40–50 dB reduction. [34] Landing gear, wing slats and wing flaps also produce noise and may have to be shielded from the ground with new configurations. [34] NASA found that over-wing and mid-fuselage nacelles could reduce noise by 30–40 dB to even 40–50 dB for hybrid wing bodies, which may be essential for open rotors. [34]
By 2020, helicopter technologies in development plus new procedures could reduce noise levels by 10 dB and noise footprints by 50%, but more advances are needed to preserve or expand heliports. [34] Package delivery UAS will need to characterize their noise, establish limits and reduce their impact. [34]
General:
A jet engine is a type of reaction engine, discharging a fast-moving jet of heated gas that generates thrust by jet propulsion. While this broad definition may include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet, turbofan, ramjet, pulse jet, or scramjet. In general, jet engines are internal combustion engines.
A turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a combination of the preceding generation engine technology of the turbojet, and a reference to the additional fan stage added. It consists of a gas turbine engine which achieves mechanical energy from combustion, and a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.
A supersonic transport (SST) or a supersonic airliner is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound. To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144. The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA. Concorde's last commercial flight was in October 2003, with a November 26, 2003 ferry flight being its last airborne operation. Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service. Several companies have each proposed a supersonic business jet, which may bring supersonic transport back again.
Environmental noise is an accumulation of noise pollution that occurs outside. This noise can be caused by transport, industrial, and recreational activities.
The Lockheed L-2000 was Lockheed Corporation's entry in a government-funded competition to build the United States' first supersonic airliner in the 1960s. The L-2000 lost the contract to the Boeing 2707, but that competing design was ultimately canceled for political, environmental and economic reasons.
The General Electric GE90 is a family of high-bypass turbofan aircraft engines built by GE Aerospace for the Boeing 777, with thrust ratings from 81,000 to 115,000 pounds-force. It entered service with British Airways in November 1995. It is one of three options for the 777-200, -200ER, and -300 versions, and the exclusive engine of the -200LR, -300ER, and 777F. It was the largest jet engine, until being surpassed in January 2020 by its successor, the 110,000 lbf (490 kN) GE9X, which has a larger fan diameter by 6 inches (15 cm). However, the GE90-115B, the most recent variant of the GE90, is rated for a higher thrust than the GE9X.
The CFM International CFM56 series is a Franco-American family of high-bypass turbofan aircraft engines made by CFM International (CFMI), with a thrust range of 18,500 to 34,000 lbf. CFMI is a 50–50 joint-owned company of Safran Aircraft Engines of France, and GE Aerospace (GE) of the United States. GE produces the high-pressure compressor, combustor, and high-pressure turbine, Safran manufactures the fan, gearbox, exhaust and the low-pressure turbine, and some components are made by Avio of Italy and Honeywell from the US. Both companies have their own final assembly line, GE in Evendale, Ohio, and Safran in Villaroche, France. The engine initially had extremely slow sales but has gone on to become the most used turbofan aircraft engine in the world.
The Gulfstream IV and derivatives are a family of twinjet aircraft, mainly for private or business use. They were designed and built by Gulfstream Aerospace, a General Dynamics company based in Savannah, Georgia, United States, from 1985 until 2018. Aircraft power is provided by two Rolls-Royce RB.183 Tay turbofans.
A propfan, also called an open rotor engine, open fan engine or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan".
A hush kit is an aerodynamic device used to help reduce the noise produced by older aircraft jet engines. These devices are typically installed on older turbojet and low-bypass turbofan engines, as they are much louder than later high-bypass turbofan engines.
Noise control or noise mitigation is a set of strategies to reduce noise pollution or to reduce the impact of that noise, whether outdoors or indoors.
The Learjet 24 is an American six-to-eight-seat twin-engine, high-speed business jet, which was manufactured by Learjet as the successor to the Learjet 23.
The geared turbofan is a type of turbofan aircraft engine with a planetary gearbox between the low pressure compressor / turbine and the fan, enabling each to spin at its optimum speed. The benefit of the design is lower fuel consumption and much quieter operation. The drawback is that it increases weight and adds complexity.
The Pratt & Whitney PW1000G family, also known as the GTF, is a family of high-bypass geared turbofan produced by Pratt & Whitney. Following years of development and testing on various demonstrators, the program officially launched in 2008 with the PW1200G destined for the Mitsubishi SpaceJet. The first successful flight test occurred later that year. The PW1500G variant, designed for the Airbus A220, became the first certified engine in 2013. The program cost is estimated at $10 billion.
The Gulfstream G650 is a large business jet produced by Gulfstream Aerospace. The model is designated Gulfstream GVI in its type certificate. The aircraft can be configured to carry from 11 to 18 passengers over a range of 7,000 nautical miles [nmi] at a top speed of Mach 0.925. The aircraft is powered by two Rolls-Royce BR725 turbofans, mounted on the rear fuselage. Gulfstream began the G650 program in 2005 and revealed it to the public in 2008. The G650ER is an extended-range version of the G650, adding about 500 nmi by modifying the fuel system, an upgrade offered for existing G650 aircraft.
An airbreathing jet engine is a jet engine in which the exhaust gas which supplies jet propulsion is atmospheric air, which is taken in, compressed, heated, and expanded back to atmospheric pressure through a propelling nozzle. Compression may be provided by a gas turbine, as in the original turbojet and newer turbofan, or arise solely from the ram pressure of the vehicle's velocity, as with the ramjet and pulsejet.
The General Electric Passport is a turbofan developed by GE Aerospace for large business jets. It was selected in 2010 to power the Bombardier Global 7500 and 8000, first run on June 24, 2013, and first flown in 2015. It was certified in April 2016 and powered the Global 7500 first flight on November 4, 2016, before its 2018 introduction. It produces 14,000 to 20,000 lbf of thrust, a range previously covered by the General Electric CF34. A smaller scaled CFM LEAP, it is a twin-spool axial engine with a 5.6:1 bypass ratio and a 45:1 overall pressure ratio and is noted for its large one-piece 52 in (130 cm) fan 18-blade titanium blisk.
The Hawker Siddeley HS.141 was a 1970s design study and submission for a British V/STOL airliner requirement. Designed by Hawker Siddeley Aviation and tested in wind tunnels neither prototypes nor production aircraft were produced.
James David Raisbeck was an American aeronautical engineer, known for his entrepreneurship in developing products which enhance the performance of production aircraft.
The General Electric Affinity was a turbofan developed by GE Aviation for supersonic transports. Conceived in May 2017 to power the Aerion AS2 supersonic business jet, initial design was completed in 2018 and detailed design in 2020 for the first prototype production. GE Aviation discontinued development of the engine in May 2021. Its high-pressure core is derived from the CFM56, matched to a new twin fan low-pressure section for a reduced bypass ratio better suited to supersonic flight.
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