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Acoustic Mitigation

Acoustic Mitigation. Thursday, November 02, 2006 AIAA Team 4 Mike Mangan Dzejna Mujezinovic. Aircraft noise abatement. Surprisingly little progress has been made in source quieting of aircraft noise, other than elimination of gratuitously loud engine designs from the 1960s and earlier.

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Acoustic Mitigation

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  1. Acoustic Mitigation Thursday, November 02, 2006 AIAA Team 4 Mike Mangan Dzejna Mujezinovic

  2. Aircraft noise abatement • Surprisingly little progress has been made in source quieting of aircraft noise, other than elimination of gratuitously loud engine designs from the 1960s and earlier. • Because of its velocity and volume, jet turbine engine exhaust defies any simple means of quieting. • The most promising forms of aircraft noise abatement is through land planning, flight operations restrictions and residential soundproofing. • These tactics are sometimes controversial since they can impact aircraft safety, flying convenience and airline economics. • In 1979 the U.S. Congress authorized the FAA to devise technology and programs to attempt to insulate homes near airports. • Some of the first airports at which the technology was applied were San Francisco International Airport, Seattle-Tacoma International Airport, John Wayne International Airport and San Jose International Airport in California. • Variations in aircraft types, flight patterns and local meteorology can be analyzed along with benefits of alternative building retrofit strategies such as roof upgrading, window glazing improvement, fireplace baffling, caulking construction seams and other measures.

  3. British Airways Airbus A321 flies over Myrtle Avenue on its landing path to Heathrow runway 27L. Myrtle Avenue is on the south east edge of London (Heathrow) Airport.

  4. Mechanisms of sound production • 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. • Low flying, high speed military aircraft produce especially loud aerodynamic noise. • The shape of the nose, windshield or canopy of an aircraft can greatly affect the sound produced. • Much of the noise of a propeller aircraft is of aerodynamic origin due to the flow of air around the blades. • Engine and other mechanical noise • Much of the noise in propeller aircraft comes equally from the propellers and aerodynamics. • Helicopter noise has a unique spectral content, essentially being aerodynamically induced noise from the main and tail rotors and mechanically induced noise from the main gearbox and various transmission chains. • 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). • The typical noise output of an APU is 113 decibels. This is about 27 decibels lower than that of a jet engine. • Other internal aircraft systems can also contribute, such as specialized electronic equipment in some military aircraft.

  5. Aircraft Noise Exposure • Generally, older jet aircraft are louder than newer ones. • Departing aircraft are louder than arriving aircraft • Aircraft departing for distant destinations are louder than those traveling to closer destinations (aircraft with greater fuel load cannot climb as rapidly) • An aircraft arriving or departing at night is generally perceived to be louder than the same aircraft arriving or departing during the day (a person's sensitivity to noise is greater during sleeping hours) • Low cloud cover may increase the noise level by reflecting back to the ground • List of aircraft noise levels can be found on the FAA website (see Sources for the link)

  6. Annoyance effects • Lesser intensities of noise are produced for cruising velocities, mainly due to the altitudes of operation. • However, this noise often is heard in country settings which are by nature very peaceful. • Thus the intrusion of this type of noise can be very 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 above the ground at about 1200 meters from the aiming point or 900 meters from the start of the runway. • This distance is usually outside the airport fence.

  7. Health effects of aircraft noise • 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. • High levels of aircraft noise that commonly exist near major commercial airports are known to increase blood pressure and contribute to hearing loss. • Some research indicates that it contributes to heart diseases, immune deficiencies, neurodermatitis, asthma and other stress related diseases. • Prior research indicates clearly that hearing loss is less a product of aging than a result of exposure to transportation related noise.

  8. Noise Mitigation Programs • In the United States, since aviation noise became a major public issue in the late 1960s, governments have enacted legislative controls. • Aircraft designers, manufacturers, and operators have developed quieter aircraft and more careful operating procedures. • Modern high-bypass turbofan engines, for example, are quieter than the turbojets and low-bypass turbofans of the 1960s; however, due to expanded numbers of flights, there is no clear trend of aircraft noise reduction for land uses near airports.

  9. Cal Poly Students Help NASA Reduce Aircraft Noise • The students were participating in the C-17 flight noise mitigation study, a NASA experiment that may one day make the world a quieter place. • Working to reduce the 'noise footprint' produced by aircraft. A key component of this plan is the development of extreme short-take-off and landing (ESTOL) aircraft and procedures.

  10. Summary • It’s hard to quiet aircrafts, therefore containment of the noise to airports is the main concern. • Noise comes from aerodynamic noise, mechanical noise, and aircraft systems noise. • Even at higher altitudes sounds from the aircraft can be annoying at the ground. • Noise can cause health problems, such as hearing loss, and higher blood pressure • Much research is being done to solve acoustic mitigation problems.

  11. Questions?

  12. Sources • http://www.parliament.uk/post/pn197.pdf • http://www.orlandoairports.net/goaa/noise/Overview.htm • http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/aeab4e3e783d2b6086256e3700762a57/$FILE/AC36-3H.pdf • http://www.nasa.gov/vision/earth/improvingflight/c17noise.html • http://www.flychicago.com/cnrc/cnrc.shtm • http://www.ueet.nasa.gov/overview.php

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