Acoustic Mitigation

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.
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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.

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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)

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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.

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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.

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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

• Its 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.

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Questions?
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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/aeab4e3e783d2b608
  6256e3700762a57/FILE/AC36-3H.pdf
• http//www.nasa.gov/vision/earth/improvingflight/c
  17noise.html
• http//www.flychicago.com/cnrc/cnrc.shtm
• http//www.ueet.nasa.gov/overview.php